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Recycled coarse aggregate has its own characteristics of large porosity, high water absorption and high crushing index, which adversely affects the mechanical strength and durability of recycled aggregate concrete. In this study, the mechanical properties, durability and microstructure of recycled aggregate concrete (RAC) modified with nano-SiO 2 (NS) and fibres were investigated to prepare road RAC, using NS polypropylene fibres (PPF) and basalt fibres (BF) as test variables. Compared with RAC only incorporating NS, NS and fibre synergism can significantly enhance the mechanical properties of recycled concrete, compressive strength increased by 27–51 %, flexural strength increased by 12 %, and abrasion resistance increased by 25–72 %. The synergistic effect of NS and PPF significantly improves the frost resistance of recycled concrete. NS has a volcanic ash effect which can react with calcium hydroxide to produce a large number of C-S-H in the secondary hydration reaction, making the internal structure of the cement matrix denser. Interfacial transition zone microstructure is more compact, thus interfacial transition zone porosity is effectively reduced. The hydration products are attached to the fibre surface, which enhances the bonding ability between the fibers and matrix. Therefore, the fibres effectively inhibit the generation and development of internal micro-cracks. NS optimises the internal pore structure of recycled aggregate concrete and enhances the interfacial transition zone, and NS synergistically with PPF can improve the strength and durability of various mechanical properties of recycled concrete. The research results provide the scientific basis for the application of road RAC. • The mechanical properties, durability and microstructure of recycled aggregate concrete were investigated. • The synergistic effect of nano-SiO 2 and fibres significantly improves the frost resistance of recycled concrete. • Nano-SiO 2 and fibre synergism can significantly enhance the mechanical properties of recycled concrete. [ABSTRACT FROM AUTHOR]

The quality of the interface between new and existing concrete is a crucial factor that significantly affects the effectiveness of concrete patching and rehabilitation. This transitional zone between concrete layers exhibits inherent porosity and diminished structural integrity, which can potentially serve as the origin of cracks and fractures. The presented study was conducted to evaluate the quality of the new-to-old concrete interface when colloidal nano silica (CNS) is used. Apart from directly blending CNS with concrete materials, this study uniquely employed CNS as a surface agent to enhance the quality of the interface. The microstructure, mechanical bonding performance and chloride resistance property were evaluated on samples with new-to-old interface. By microstructural analysis, it was found that the porosity at the interface region was reduced from 24% to less than 16% when CNS was directly added into the concrete. Due to the improved hydration and the formation of a denser and uniform interface, a higher bonding strength was therefore achieved. Improvement in bonding strength was also found when CNS was used as an agent on the surface of the old layer, due to the precipitation and pozzolanic reaction of the nano silica particles. There were no apparent signs of increased porosity at the interface region as the precipitation of nano silica particles densified the cement matrix. Additionally, the solid precipitates generated frictional force, increasing the bonding strength under shearing loading. However, due to the lack of cohesion, the nano silica precipitates couldn't sustain the tension under flexural test. Durability evaluation showed that the chloride resistance of the double-layer sample was effectively enhanced as the quality of the interface was improved with the use of CNS, especially when the surface method was used. The outcome of this study provides insight into the use of low CNS dosage to improve the new-to-old concrete interface and sheds light on the use of CNS as an interface agent. • Colloidal nano silica (CNS) was used to enhance the quality of interface through both direct blending and surface coating methods. • A 3D X-Ray Microscope was used to visualize the interface between new and old layers. • The incorporation of CNS enhanced the bonding strength between two concrete layers, especially when employed through the direct blending method. • The surface coating method led to a compact interface with the lowest porosity, although a low tensile resistance was observed due to the intrinsic lack of cohesion of the nano silica precipitates. [ABSTRACT FROM AUTHOR]

Recycled Concrete Aggregate (RCA), derived from discarded concrete, substitutes or stabilizes Natural Concrete Aggregate (NCA) in constructing Recycled Aggregate Concrete (RAC). This study investigates Coconut Shell Biochar (CSB) as a potential mitigator of Alkali-Silica Reaction (ASR) in RAC, particularly in tropical regions like Sri Lanka. CSB, noted for its cost-effectiveness, undergoes assessment for its impact on concrete properties. Petrographic analyses, encompassing optical microscopy and SEM, conducted on CSB-modified RAC in Sri Lanka, reveal favorable mechanical outcomes. Grade 25 RAC, supplemented with CSB, demonstrates 28-day compressive, split-tensile, and flexural strengths of 25.4, 2.5, and 4.1 MPa, respectively. Results indicate CSB effectively alleviates ASR-induced alterations and chemical reactions in RAC, prompting further exploration of CSB's role in controlling specific precipitates and chemical reactions associated with ASR. • There is a demand for recycled aggregate concrete free from alkali Silica reactants. • A need for sustainable solution for alkali silica reaction in recycled aggregate concrete exist. • Petrographic studies show the fractured nature of recycled concrete aggregate. • Coconut shell biochar can reduce secondary alterations and chemical reactions by adsorption. • Finer-size particles of biochar have a high potential for adsorbing secondary materials. [ABSTRACT FROM AUTHOR]

Graphene oxide grafted carbon fiber (CF-GO) is prepared by "grafting to" chemical graft method. The elements and chemical bonds on the surface of CF-GO are characterized by XPS test, which confirms the successful preparation of CF-GO, and the monofilament tensile strength of CF-GO is tested. The dispersion effect of CF-GO under different dispersion methods is compared, and CF-GO modified concrete (CF-GOMC) is prepared. The strength and toughness of CF-GOMC are tested and compared with those of carbon fiber modified concrete. In addition, the modification mechanism of CF-GO on fiber/concrete matrix interface is analyzed by SEM-EDS test. The results show that the monofilament tensile strength of CF-GO increases by 22.22% compared with that of carbon fiber. When dispersing with high-efficiency water reducer combined with ultrasonic wave, the dispersion effect of CF-GO is the best, the resistivity of CF-GOMC is the minimum, and the strength is the maximum. CF-GO can improve the strength and toughness of concrete, and its improvement effect is better than carbon fiber. The optimal contents of CF-GO and carbon fiber are 0.3% and 0.2% respectively. Graphene oxide on the surface of CF-GO enhances the fiber/concrete matrix interface physically and chemically by improving the mechanical interlocking force between CF-GO and concrete matrix and promoting the formation of hydration products on the surface of CF-GO. Moreover, the content of C-S-H crystal at the CF-GO/concrete matrix interface increases. • Graphene oxide grafted carbon fiber (CF-GO) is prepared by "grafting to" chemical graft method. • The dispersion effect of CF-GO under different dispersion methods is compared, and the strength and toughness of CF-GO modified concrete (CF-GOMC) are compared with those of carbon fiber modified concrete. • Graphene oxide on the surface of CF-GO enhances the fiber/concrete matrix interface physically and chemically by improving the mechanical interlocking force between CF-GO and concrete matrix and promoting the formation of hydration products on the surface of CF-GO. [ABSTRACT FROM AUTHOR]

The use of Ground Granulated Blast-furnace Slag (GGBS) as an alternative cement replacement material in combination with conventional coarse aggregate have been successful in the production of near green concrete. Undoubtedly, GGBS has exhibited good cementitious attributes, however, there are concerns with slow strength development and workability owing to its non-pozzolanic activities as well as some degree of porosity notwithstanding the sustainability potential. Therefore, this study presents a lytag based geopolymer lightweight concrete with high strength development, improved mechanical properties and reduced embodied carbon. To further improve and enhance the potential production of green concrete, complete replacement of conventional coarse aggregate with a recycled lightweight aggregate from industrial waste was carried out. The geopolymer precursors consisted of sodium hydroxide, sodium silicate, GGBS and silica fume to optimize the performance of the concrete at 60–80% cement replacement for a target design mix of 20, 30, 40, and 50 MPa. The performance of lytag based geopolymer concrete was compared with that of non-geopolymer lytag based concrete (control samples). The results show a 42% increase in compressive strength for the geopolymer lightweight concrete and a 22% increase in ultimate compressive strain which is an indication of improved moment of resistance in structural design. The results also show a 46–61% reduction in embodied carbon for the use of non-geopolymer lytag based concrete and 69–77% reduction for lytag based geopolymer concrete. The geopolymer concrete between 7 and 63 days of loading increases by 0.55% in creep strain compared with increases of 2.81% for non-geopolymer lytag based concrete and reduction to 27.96% for the normal weight concrete. Modulus of Elasticity reduces with age of loading for the geopolymer concrete during creep at 0.39% compared to reduction of 1.93% for non-geopolymer lytag based concrete and increase of 12% for the normal weight concrete. • Design procedure for lightweight aggregate concrete was carried out. • 84% of compressive strength was developed by Lytag-GGBS based geopolymer concrete within 7 days. • Reduction in flexural strength to 15% with Lytag-GGBS based geopolymer concrete was established. • GGBS lytag based geopolymer concrete suggest reduction in creep strain and creep coefficient. • Good mechanical performance is observed with the addition of silica fume and superplasticizer in geopolymer concrete. [ABSTRACT FROM AUTHOR]

The durability of concrete surfaces is frequently compromised by adverse external factors, such as freeze-thaw cycles and ionic corrosion among others. This study aims to investigate the comparative performance of three concrete coating techniques independently applied uniformly to concrete surfaces, namely the Graphene Oxide—Waterborne Epoxy Resin Coating (GO-WEP) coating and two commercially available WEP coatings (S1, S2). The corrosion resistances of the coatings were evaluated under various conditions: chloride drying-wetting cycles, chloride freeze-thaw cycles, and chloride immersion tests. In this study, the changes in color difference and adhesion of the coating after chloride erosion were studied. And after five drying-wetting cycles, the GO-WEP coating exhibited a color difference value approximately 56 % and 45 % lower compared to S1 and S2 coatings respectively. The S1 and S2 coatings demonstrated adhesive strength below 1.50 MPa after the 3rd and 4th cycles respectively, indicating a loss of protective capabilities. Conversely, the GO-WEP coating maintained adhesive strength greater than 1.50 MPa after five cycles, implying sustained protective capabilities. Following freeze-thaw cycles, the color difference value in GO-WEP was about 16 % and 7 % lower than S1 and S2 coatings respectively. S1 and S2 coatings lost their protective ability after the 4th and 5th cycles respectively, while GO-WEP maintained an adhesive strength greater than 1.50 MPa. Furthermore, following chloride immersion, the GO-WEP coating had a color difference value approximately 20 % and 17 % lower than S1 and S2 respectively. The adhesive strength reduced by 39.7 %, 46.4 %, and 43.1 % for the three coatings respectively, signaling the superior performance of GO-WEP in all tested properties. The surface morphology and compressive strength variations of the coated concrete were also studied. As the experimental cycles progressed, both S1 and S2 coatings suffered noticeable surface damage, while the GO-WEP coating demonstrated no significant changes until the end of the experimental cycles. During the chloride drying-wetting and chloride immersion tests, the concrete specimens showed an increase in strength. Initially, uncoated concrete showed a faster rate of strength increase than coated concrete. However, this rate slowed down and even reversed in later stages. Coated concrete on the other hand, exhibited a steady increase in strength over the experimental cycles, with GO-WEP coated concrete showing the slowest growth rate. In the chloride freeze-thaw cycle test, concrete strength decreased progressively. And by the fifth cycle, the compressive strengths of GO-WEP, S1, and S2 were 31.5 MPa, 30.8 MPa, and 30 MPa, respectively, a 9 %, 6 %, and 3 % improvement over the 29 MPa of uncoated concrete. These findings further reinforce the superior protective effect of the GO-WEP coating on concrete. ● The GO-WEP coating provides good protection for concrete under chloride erosion ● The GO-WEP coating plays a positive role in terms of contact angle, color difference, and adhesion to concrete. ● The GO-WEP coating can reduce the loss of strength in concrete after erosion and lead to a more stable change in mass. ● The GO-WEP coating provides the best protection for concrete compared to the other two commercially available coatings. [ABSTRACT FROM AUTHOR]

3D printing technology revolutionizes construction by creating custom building components with increased efficiency and reduced waste. This paper reviews advancements in the 3D printing of cementitious materials, focusing on integrating mineral additives (MAs) like metakaolin, micro-silica, slag, and fly ash to address environmental and economic challenges linked with high-Portland cement content in 3D concrete printing (3DCP). MAs enhance the pumpability, printability, and buildability of 3DCP while reducing its environmental impact. The review emphasizes optimizing cement mixtures, including alkali-activated materials, to enhance sustainability and performance. It discusses the mixture design's importance, balancing mechanical properties and environmental impacts, and examines MAs' influence on rheological properties, mechanical performance, and 3DCP durability, including layer bond strength. The paper also discusses global 3D printing technology adoption in construction and challenges in additive manufacturing implementation. By analyzing printing parameters, mixture proportions, and materials' effects on long-term performance, this review highlights 3D printing's potential for economically viable and eco-friendly structural elements. It aims to guide future advancements in 3D printable cementitious materials, meeting modern construction demands while addressing traditional concrete production's environmental challenges. • Using recycled mineral additives reduces 3D-concrete printing's environmental impact. • Optimizing printing parameters strengthens layer bonds in 3D-concrete printing. • Recycled materials promote sustainability and innovation in 3D-concrete printing. [ABSTRACT FROM AUTHOR]

This paper aims to examine the effect of coal gangue aggregate (CGA), fly ash (FA), and ground-granulated blast slag (GGBS) on the rheological, mechanical and microstructure properties of concrete. The rheological properties, compressive strength, splitting tensile strength, flexural strength, and uniaxial tensile behaviour of coal gangue concrete (CGC) were determined, and the microstructure of the concrete mixtures were investigated by use of XRD and SEM analyses. The results revealed the action mechanism of CGA and mineral admixtures on the microstructure and macroscopic properties of CGC. FA first increased and then decreased the yield stress and plastic viscosity, while GGBS considerably increased the yield stress and plastic viscosity. Furthermore, a constitutive model was established for CGC containing FA and GGBS under compression. The proposed stress–strain model for CGC is accurate and can be used for nonlinear analysis of structures made of this type of concrete. Moreover, the addition of FA and GGBS consumes calcium hydroxide, but increases products such as hydrated calcium silicate aluminate. These findings elucidate the understanding and optimisation of CGA use in concrete production, while contributing to lowering carbon emissions. • Concrete strength degrades with increasing coal gangue aggregate substitution rate. • Fly ash degrades coal gangue concrete mechanical properties, and slag enhances them. • Fly ash and slag combination provides a complementary superposition effect. • A precise coal gangue concrete uniaxial compression analysis model is proposed. [ABSTRACT FROM AUTHOR]

Forecasting the compressive strength (CS) of oil palm shell (OPS)-based lightweight aggregate concrete (LWAC) heavily relies on machine learning (ML) models. However, these models were primarily trained on limited data, and did not provide any uncertainties or explanations for CS predictions. To overcome these limitations, we compile a dataset of 813 experimental records with 9 input variables for OPS-based LWAC containing fly ash or silica fume. Natural Gradient Boosting (NGBoost), a notable probabilistic machine learning model, is utilized in this study to predict the CS value of OPS-based LWAC. The model is fine-tuned using the collected dataset, and normal distribution-based prediction intervals (PIs) are simultaneously determined to quantify the uncertainties of CS estimates. The results indicate that NGBoost has superb generalization capabilities within cross-validation (average R2/NLL: 0.943/6.111) and satisfactory probabilistic prediction performance on the testing dataset (R2/NLL: 0.969/6.790). To further enhance model transparency, both the mean estimate and its uncertainty are innovatively interpreted using Shapley additive explanation (SHAP). Analyses show that incorporating a reasonable amount of fly ash (<75 kg/m3) does not significantly affect the CS value. However, the addition of silica fume (<150 kg/m3) and superplasticizer (<7 kg/m3) can improve it. Despite its relatively low feature importance for mean predictions, OPS is the most influential factor positively correlated with PIs, primarily due to variations in its size, surface characteristic, and gradation. Additionally, an online graphical user interface based on NGBoost has been created to aid in the probabilistic estimation of CS value and mixture design for OPS-based LWAC. [Display omitted] • A total of 813 experimental records related to the mixtures and CS values of OPS-based LWAC are compiled from literature. • Normal distribution-based prediction interval is determined in BO-NGBoost as the uncertainty of the predicted CS value. • Both the mean CS value and its uncertainty for OPS-based LWAC are interpreted using SHAP method. • An online GUI is developed to streamline the probabilistic prediction process for the CS value of OPS-based LWAC. [ABSTRACT FROM AUTHOR]

Construction and demolition waste (CDW) has been recently identified as a potential aluminosilicate source for geopolymers. However, the available research has mainly focused on developing CDW-based geopolymer pastes and mortars, while studies on geopolymer concretes sourced from CDW have been very limited. Thus, the current study aimed at experimentally identifying different CDW materials suitable for producing geopolymer concretes. Additionally, the study analysed the mechanical, microstructural, and environmental properties of CDW- based geopolymer concrete produced. In this regard, the effect of relevant parameters on the compressive strength development of CDW-based geopolymer concretes was comprehensively investigated, including those related to precursor types/fineness, alkali activator solution, aggregate type/size and curing regimes. Microstructural analyses were also conducted on the selected samples (100% brick waste, 100% tile waste, 100% concrete waste and 75% brick waste + 25% GGBS). Finally, the environmental impact of geopolymer concrete was assessed and compared with similar traditional concrete. Results showed that employing CDWs alone is not suitable to achieve sufficient strengths under all curing regimes. However, the inclusion of 25% GGBS significantly improved the strength performance of CDW-based geopolymer concrete, in comparison to other supplementary cementitious materials (SCMs) such as Class-C fly ash and calcium hydroxide. The particle size of CDWs and concentration of alkaline activators highly affect the performance of CDW-based geopolymer concretes. Utilization of CDWs with particles finer than 75 μm and high concentrations of NaOH (12 M) is recommended to achieve good performance. The results also indicate that almost similar energy is needed for producing CDW-based geopolymer and OPC-based traditional concrete, whereas a huge reduction in CO 2 emission (∼40%) was estimated in the case of geopolymers. The outcomes of the current study are expected to contribute to the advancement of geopolymer concrete derived from CDW in addition to providing valuable insights into this type of concrete for practitioners and academics. • Comprehensive assessment of various CDW materials for producing geopolymer concrete was performed. • Mechanical and microstructural properties of CDW-based geopolymer concrete were discussed. • Effects of relevant parameters on the performance of CDW-based geopolymer concretes were comprehensively investigated. • Environmental impacts of the developed geopolymer concrete were assessed. [ABSTRACT FROM AUTHOR]

Utilizing nano-SiO 2 (NS) to reinforce the old mortar and the weak interfacial transition zone (ITZ) in recycled coarse aggregate (RCA) is a productive approach to enhance the quality of RCA. Throughout this paper, RCA was immersed in NS solutions with different concentrations (2, 5, 10 and 30 wt%). Subsequently, a systematic evaluation of the crushing index and water absorption of the treated NS modified recycled coarse aggregate (SRCA) was conducted. In addition, the calcium hydroxide (CH) content of RCA before and after modification was analyzed by Thermogravimetric and Differential Thermal Analysis (TG-DTA) curves. This study finds that the performance of SRCA modified with 2% concentration achieves comparable modification effects to other concentrations. Additionally, this paper delves into the impact of NS powder on the slump characteristics and compressive strength of concrete. Considering the above research and economic costs, this study adopts 2% concentration of NS for RCA modification and further investigates the stress-strain relationship of NS modified recycled aggregate concrete (SRAC) with various SRCA replacement ratios. Moreover, this paper establishes mesoscopic models of SRAC for various replacement rates and proposes constitutive models corresponding to these rates. The results indicate that when the SRCA replacement rate is within 60%, the stress-strain curve shape of SRAC closely resembles that of natural aggregate concrete (NAC); when the replacement rate exceeds 60%, the descending segment of the SRAC stress-strain curve becomes more precipitous, showing a higher tendency towards fragility in the concrete. ● Nano-SiO 2 can be used to improve the properties of recycled coarse aggregates. ● NS powder affects the slump and compressive strength of recycled concrete. ● As the concentration of NS solution increases, the compressive strength of concrete increases. ● Mesoscopic models of modified recycled concrete were established and constitutive models were proposed. [ABSTRACT FROM AUTHOR]

Ensuring uniform dispersion of NS after being added to ultra-high performance concrete (UHPC) is a critical condition to further improve its material properties, and requires stabilization of the NS. In this research, hydrochloride acid (HCl) is used for the first time to support the stabilization of NS dispersion when mixed with UHPC based on the theory of proton protection at the NS surface. Four different types of NS sols with typical negative surface charge were used to investigate the effect of HCl stabilization on a comprehensive set of material properties. The material properties were compared to the UHPC without NS and to the nano-silica enhanced UHPC without HCl stabilization. It was found that well-dispersed negatively charged NS stabilized by HCl improves the UHPC workability, air void distribution, compressive strength, single fiber pullout resistance and microscopic pore size distribution compared to mixes comprising unstabilized NS. Furthermore, the stabilization effect of HCl was investigated on UHPC with added NS of positive surface charge. Based on the success of previous research, the results were also compared with using polyethylene glycol (PEG) as dispersion stabilizing agent. The results showed that using PEG significantly improves the single-fiber pull-out behavior, whereas using HCl leads to indifferent or reduced material properties. The research results showed that the effect of NS on UHPC material properties depends on the stability of NS dispersion after addition to the concrete mixture, and that using HCl and PEG are effective dispersion stabilization agents for negatively charged and positively charged NS sols, respectively. • Use of hydrochloride acid (HCl) to support the stabilization of NS dispersion when mixed with UHPC • Investigation of the effect of HCl stabilization on a comprehensive set of material properties • Comparing the effect of HCl and polyethylene glycol on UHPC properties with added NS of negative and positive surface charge [ABSTRACT FROM AUTHOR]

Tertiary alkanolamines play an essential role in the hydration of cement-based materials as one of the main components of cement grinding aids and concrete admixtures. Although the field has been well-studied, the significant effects of slight variations in alkanolamine type and dosage make it imperative for researchers to fully understand alkanolamines before using them. Therefore, it is necessary to understand in detail the mechanism of different alkanolamines affecting the hydration of cement-based materials and their effects on setting and hardening. Based on the synthesis and chemical characteristics of alkanolamines, the complexation between alkanolamine and metal ions is discussed in this paper. The influence of alkanolamines on hydration of cement-based materials and the role of complexation in hydration are studied. Various properties of cement-based materials in the presence of alkanolamines are rigorously reviewed. The synergistic effects of alkanolamine and other admixtures are also considered in this review. The research findings prove that the complexation of alkanolamines plays an essential role in hydration and further interferes the microstructure and properties of the cement-based materials. Variations in the molecular structure and dosage of alkanolamines can lead to significant differences in hydration. The modification of alkanolamines at the molecular level and their use in combination with other admixtures are the future research directions. The working mechanism of alkanolamines in the hydration process of cement-based materials still needs to be further explored. • Complexation of alkanolamines significantly affects cement hydration. • Different alkanolamines have different effects on mineral phase hydration. • Alkanolamines significantly affect the morphology of C-S-H gels and Ca(OH) 2. • The right dosage of alkanolamine could improve compressive strength. • TEA has a significant effect on setting time. [ABSTRACT FROM AUTHOR]

This study evaluates the effectiveness of improving the durability of recycled aggregate concrete (RAC) through the controlled deposition of biogenic silica (SiO 2). This process is optimised by growing diatoms in two artificial environments as a mean to produce a protective coating. Concrete samples with protective bio-coatings grown in two different environments were tested for durability against uncoated control samples and results suggest that the biocoating provides significant benefits. Increases of 30–50% in ultrasonic pulse velocity were demonstrated for bio-coated concrete samples suggesting that the diatom treatment produces surface densification thus increasing the mechanical strength of bio-coated concrete. Tests of chloride ion diffusion and resistance to freeze-thaw cycles showed reductions in permeability due to the biocoating of 29–34% and 34–45%, for each test respectively. Improvements in corrosion resistance were also shown in resistivity tests. In addition, SEM and BSEM microscopy provides evidence to support the conclusions of physical tests: diatoms migrate to fill surface pores and micro-cracks reducing the porosity of the concrete's surface matrix resulting in surface densification and decreased permeability. • The surface biodeposition of diatoms in hardened concrete is evaluated. • Biogenic silica acts as a biocoating which increases the durability of the concrete. • This biofilm increases the density of the surface matrix of recycled concrete. • Controlled environments in the laboratory favour diatom growth. • Biogenic silica is an eco-friendly option to other synthetic treatments. [ABSTRACT FROM AUTHOR]

There is a huge stock of industrial solid waste piles such as phosphogypsum (PG), desulfurization ash (DA), and waste soil (WS) in China, and their utilization rate is insufficient. These have potential risk for environmental safety due to pollutants contained in them. In this study, after proportioning design, raw material pretreatment, bubble regulation and multi-temperature section maintenance process, successfully prepared a high blending solid waste based functional prefabricated autoclaved aerated concrete slabs (FPAS) with excellent functional performance, and the optimal ratio of each raw material is PG: WS: DA: cement: lime = 8:50:20:10:12, and the dry mass ratio is up to 75%, the compressive strength of the slabs is up to 5.2 MPa, the standard dry density is 606 kg/m3, the dry shrinkage value is 0.36 mm/m, and the post-freezing strength is 4.0 MPa, which is in line with the basic requirements in the standard "Autoclaved aerated concrete slabs" (GB/T15762) , and at the same time, its fire-resistant integrity is qualified for 240 min, and the coefficient of thermal conductivity is 0.15w(m.k), airborne sound-weighted sound insulation is 46 dB, also can show different functional characteristics. In order to investigate the environmental safety of heavy metals (HMs) in the slabs, the simulation experiment of HMs leaching from outdoor stacking of slabs was carried out. The results show that the HMs in the slabs do not pose obvious risks to the natural environment and human body, but three of the characteristic HMs, Cr, Cd and Hg, have significant leaching patterns, which can be expressed by a second-order kinetic model. Finally, the life cycle assessment and cost analysis of the high blending PG-DA-WS based FPAS and the conventional aerated slabs were carried out. The main environmental damage category of the high blending PG-DA-WS based FPAS is land ecological risk, and it has obvious environmental and economic benefits compared with the conventional aerated slabs. • High blending phosphogypsumbased aerated concrete slabs were developed. • A ternary solid waste synergistic enhancement mechanism was studied. • A systematic study of heavy metals and life cycle assessment of FPAS were analyzed. [ABSTRACT FROM AUTHOR]

The study aims to understand the performance and durability of a sodium carbonate alkali-activated slag (AAS) based on a performance-approach. Equivalent performances were obtained between the AAS and CEM III/C-based concretes having a water/binder ratio of 0.4 regarding compressive strength, porosity, resistance to nitric acid, and sodium sulfate. AAS exhibited higher resistivity and better resistance to chloride, assessed by a chloride migration test. The AAS showed similar carbonation resistance to CEM III/C and CEM III/B concretes with w/b ratios of 0.47 and 0.53, respectively. A discussion of durability tests for their application to this type of binder is conducted. • AAS has good performance regarding nitric acid attack, equivalent to a CEM III/C. • Expansions lower than the limit are measured when AAS is subjected to Na 2 SO 4. • AAS has good resistance regarding chloride penetration, better than CEM III/C. • AAS (w/b 0.4) has similar carbonation rate to CEM III/C (0.47) & CEM III/B (0.53). [ABSTRACT FROM AUTHOR]

At the meso-level, the interface transition zone (ITZ) is an important part of concrete and is closely related to the macroscopic properties of concrete. In this paper, the influences of siliceous iron tailings powder on concrete ITZ have been researched, in order to better reveal the mechanism of the powder as an auxiliary cementitious material in concrete. Based on XRD, SEM, hardness test and numerical simulation, the Ca(OH) 2 (CH) crystal orientation, calcium-silicon ratio (Ca/Si), porosity, microhardness and elastic modulus of ITZ have been explored, and the results are as follows. When water-to-binder ratio (w/b) is 0.38 and 0.48, iron tailings powder increases the complexity of CH crystal orientation in the ITZ, but the effects of w/b and hydration age on the CH crystal orientation index with and without iron tailings powder are similar. The Ca/Si of ITZ blended with iron tailings powder is lower than that of benchmark group with the same w/b. The porosity in ITZ first decreases with the distance from aggregate surface, and stabilizes at about 40 μm, and the ITZ porosity in groups of iron tailings powder is less than that in the reference group at the same w/b and the same age. The microhardness and elastic modulus of ITZ decreases by mixing the iron tailings powder, and microhardness increases with the distance from aggregate surface, and at last stabilized at also about 40 μm, and elastic modulus increased with the decrease of w/b and the extension of hydration age. The findings show that incorporation of iron tailings powder has some degree of improvement on the microscopic structure of ITZ, but does not reduce its size, and the thickness of ITZ both with and without iron tailings powder are all 40μm. In particular, the variation law of pore in IZT needs to be studied more comprehensively and in-depth in the future. • Siliceous iron tailings powder is used as a mineral admixture for concrete. • The iron tailings powder complicates the CH crystal orientation in ITZ. • The iron tailings powder declines the Ca/Si and porosity in ITZ. • The iron tailings powder reduces the microhardness and elastic modulus in ITZ. • The iron tailings powder dose not change the thickness (40μm) of ITZ. [ABSTRACT FROM AUTHOR]

This study compares the effects of three techniques for reinforcing recycled concrete aggregate (RCA): chemical reinforcement, biological modification, and chemical-biological synergistic reinforcement. It evaluates their impact on both RCA and recycled aggregate concrete (RAC), analyzing their economic costs and environmental impacts through a life cycle assessment. The results indicate that composite reinforcement is more effective than individual methods, demonstrating the highest compressive strength and the best resistance to chloride ion penetration when RCA is replaced at a rate of 50%. Chemical reinforcement proves to be more economical, while biological modification shows less environmental impact. However, chemical-biological synergistic reinforcement requires further optimization to reduce both cost and environmental impact. This study offers valuable insights for the development of chemical-biological composite strengthening techniques and suggests avenues for cost reduction in practical applications. [Display omitted] • The chemical-biological synergistic strengthening method is studied. • The strengthening mechanism of the three strengthening techniques is revealed. • The improvement of the mechanical properties of RAC depend more on the mechanical properties and surface structure of RCA. • The cost analysis and environmental impact assessment of the three strengthening methods are carried out. [ABSTRACT FROM AUTHOR]

The structural foundations in southern Iran face a formidable challenge due to extensive corrosion. To enhance concrete strength and durability, the construction industry in this region typically incorporates micro silica at a rate of 8% by weight of cement. Nonetheless, given that a significant amount, around 70%, of the concrete expenses in these projects can be attributed to micro silica, and the cost of natural pozzolan in proximity to project sites amounts to only 10% of the price of micro silica, the primary goal of this study is to investigate the durability of concrete incorporating both micro silica and natural pozzolan. The aim is to potentially replace a portion of the micro silica with natural pozzolan while maintaining the required durability and strength of the concrete as specified in the project requirements. To achieve this, eight different concrete mix designs were proposed and subjected them to assessments of compressive strength and various durability standard tests, including water absorption, resistance to rapid freezing and thawing, water permeability, chloride migration coefficient, electrical resistivity, and electron microscopy (Scanning Electron Microscopy (SEM)/Energy Dispersive X-ray Spectroscopy (EDS)/MAPPING). The obtained results indicated that the concrete sample containing 4% micro silica and 12.5% natural pozzolan exhibited similar characteristics to the project's mix design with 8% micro silica in terms of the durability and distribution of permeable spaces within the material. In addition, concerning the pozzolanic reaction, one kilogram of micro silica is nearly comparable to three kilograms of natural pozzolan. Moreover, despite the non-uniform nature of the concrete environment, the EDS and MAPPING results, obtained through random sampling of study points, closely mirrored trends observed in other controlled experiments. • Raising the proportion of natural pozzolan in the concrete up to 25% enhances the durability of reinforced concrete. • The mixture with 30% natural pozzolan displays the most significant reduction in compressive strength. • 4% micro silica + 12.5% pozzolan blend excels in durability and compressive strength compared other mixtures. [ABSTRACT FROM AUTHOR]

Cement concrete plays a crucial role in modern construction, but its production process results in significant CO 2 emissions, posing a substantial threat to the environment. To achieve green production, the use of industrial waste slag as a raw material for concrete has been widely accepted. This study focuses on the potential utilization of Bayer Process Red Mud (RM), a by-product of the alumina refining process, characterized by high alkalinity and low pozzolanic activity, limiting its application in cement concrete. The reactive activity of RM after calcination treatment was investigated to overcome this challenge and enhance the reactivity of RM. Fourier Transform Infrared Spectroscopy (FTIR) was employed to determine the degree of polymerization of RM at different calcination temperatures, and thus evaluate its pozzolanic activity. Integrating physical tests, chemical experiments, and microscopic analysis, this study thoroughly analyzes the relationships between different evaluation methods and finds a negative correlation between the degree of polymerization and the pozzolanic activity index, boasting a correlation coefficient of 0.904. The results indicate that RM exhibits the highest pozzolanic activity at a calcination temperature of 700 °C. Therefore, this method has been proven effective and can serve as a quick and convenient means of evaluating the pozzolanic activity of RM. The findings of this study are expected to promote the green development of the cement industry, better utilize waste slag resources, reduce CO 2 emissions, and enhance the performance of building materials. • Activity of red mud was analyzed from chemical, physical, and microstructural testing. • Polymerization degree was introduced for rapid pozzolanic activity assessment. • The degree of polymerization of RM was characterized through FTIR analysis. • A strong correlation between polymerization degree and strength activity index was found. [ABSTRACT FROM AUTHOR]

Use of recycled fine aggregates from clay bricks (RFCB) in the preparation of eco-friendly concrete was proposed to tackle the river sand (RS) shortage and satisfy the construction demand. This study explored the surface activity of RFCB influenced by additional water and particle size distribution (PSD) on the hydration, microstructure and chloride transport of concrete. Compared to the RS, more silica and alumina released from RFCB depending on its PSD under alkaline environment was noted, which verified its appreciable surface activity. Overall, the presence of RFCB could hinder early hydration process because of the higher additional water, while the surface activity and nucleation effect supplied from finer RFCB were beneficial for the improvement of the hydration kinetics. Furthermore, inclusion of RFCB increased the total pore volume and porosity but performed better in refining the pore size distribution, thus decreased the average pore diameter. The surface activity of RFCB decreased CH content while increased chemical bond water and additional hydrates, thereby leading to enhancement of the compactness of interface, cement matrix and surface rim. More importantly, RFCB helped to decrease the chloride migration coefficient and electric flux. Though the surface activity of RFCB was beneficial in the strength development, it could not offset a deteriorated influence of porous RFCB with a higher replacement. • RFCB possesses an appreciable surface activity depending on its PSD. • Inclusion of RFCB performs better in improving the compactness of interface and surface rim. • Surface activity of RFCB improves the hydration kinetics and mitigate chloride transport. • Surface activity of RFCB cannot compensate its porous structure at a high replacement. [ABSTRACT FROM AUTHOR]

Additive manufacturing using concrete for large-scale construction purposes has demonstrated economic, social, and environmental benefits compared to conventional building procedures. These advantages stem from the capabilities of concrete 3D printing, which facilitates a rapid, accurate, and low-waste construction process with substantially less labor and energy requirements compared to traditional casting procedures such as formwork fabrication and stripping, concrete pouring, and concrete consolidation. This technology can pave the way for sustainable and cost-effective housing solutions when coupled with low-carbon concrete formulations and optimized structural designs. However, scientific and industrial experiences have shown that formulating printable concrete requires extensive testing and costly equipment to reach appropriate fresh and hardened-state properties. Therefore, accessible and practical mix-design protocols for the evaluation of printable concrete formulation are needed to enable in-situ control and broader adoption of 3D printing. Once a printable material is developed, innovative design methods, such as topology optimization, that exploit robot-controlled construction to fabricate efficient, safe, and free-form elements can be explored. In this context, this article presents a methodology based on a set of low-cost and accessible experimental tests to develop cement-based matrices with low binder content suitable for layer-by-layer deposition. Furthermore, a framework to design and fabricate efficient structural elements based on numerical-based topological optimization and concrete additive manufacturing is proposed and validated. The systematic experimental campaign carried out indicates that the yield strength obtained from shear vane tests, initially designed for geotechnical field tests, is a reliable reference value for proportioning extrudable, pumpable, and buildable concretes. Employing the proposed framework, four formulations with excellent printing capabilities are presented. These formulations are successfully utilized for additive manufacturing of a topologically optimized deep beam, achieving a remarkable 52% mass reduction compared to a solid element. This showcases the possibility of 3D printing structurally efficient elements with intricate geometries while minimizing material usage, all without the need for formworks.Principio del formulario. • A set of low-cost experimental tests to develop printable cement-based matrices was proposed. • Special attention must be given to the binder/fine-aggregate weight ratio. • A framework to design efficient structural elements based on numerical-based topological optimization was validated. • A deep beam with a 52% mass reduction was fabricated through concrete 3D printing. [ABSTRACT FROM AUTHOR]

Rebar corrosion induced by chloride erosion and concrete deterioration caused by sulfate attack are two critical factors that affect bond properties between rebar and concrete in marine environment. However, current studies about above two influencing factors on bond properties either consider rebar corrosion or sulfate attack. The bond properties between rebar and concrete considering the coupled effects of rebar corrosion and concrete deterioration caused by sulfate attack are required to further explored. In this paper, through the accelerate corrosion test, pull-out test and microscopic analysis (including scanning electron microscopy and X-ray diffraction measurements), the bond properties considering rebar corrosion and concrete deterioration caused by sulfate attack were investigated. A total of 88 RC specimens were designed to study the influences of rebar corrosion level, sulfate attack degree, sulfate ions associated cation types (sodium and magnesium ions) and concrete materials types (ordinary concrete and concrete incorporating fly ash and silica fume) on bond properties. The bond strength, bond-slip curve and failure mode were measured, and the effects of cracking width on bond properties were considered. Results show that the rebar corrosion level corresponding to the peak bond strength decreases with the increase of sulfate concentration. The bond strength decreases and the slip increases with the rise of sulfate concentration. Sodium sulfate attack causes the splitting failure, and severer magnesium sulfate attack leads to the transition from splitting failure to pull-out failure. The rebar corrosion level causing the concrete to crack decreases with the increase of sodium sulfate concentration. The higher the magnesium sulfate concentration, the less prone to produce rust-expansion cracks, but the worse cementing properties of RC bonding interface. Magnesium sulfate attack results in the severer attenuation of bond strength than sodium sulfate attack. The bond properties can be significantly improved by incorporating 20% fly ash and 5% silica fume. A prediction model of bond strength variation coefficient considering rebar corrosion level, sulfate ions concentration, sulfate ions associated cation types, and concrete materials types was established and verified. • Reveal bond properties of RC considering rebar corrosion and sulfate attack. • Analyze relationship between rust-expansion cracks and bond properties under sulfate attack. • Compare bond properties under sodium sulfate and magnesium sulfate attack. • Establish bond strength prediction model considering rebar corrosion level and sulfate attack. [ABSTRACT FROM AUTHOR]

Permanent deformation, fatigue and thermal cracking are the three typical distresses of flexible pavement. Using hydrated lime (HL) into the conventional limestone mineral additive has been widely practiced, including in Europe, to improve the mechanical properties of hot mix asphalt (HMA) concrete and as the result the durability of the constructed pavement. Large number of experimental studies have been reported to find the optimum addition of HL for the improvement on HMA concrete mechanical properties, moisture susceptibility and fatigue resistance. Pavement in service is under complex thermomechanical stress-strain conditions due to coupled atmospheric and surrounding environment temperature variation and the traffic loading. To predict and analyse the performance of pavement structures the data only from uniaxial compressive test for the resilient modulus and permanent deformation would be not enough. However, so far, the data of HL modified HMA concrete under complex loading conditions are still not well informatively complete. To contribute new knowledge, this paper reports an experimental study of both uni- and tri-axial tests for the asphalt concrete using HL into mineral additive for the mixes designed for the applications of wearing, levelling, and base layers, respectively. All the tests were conducted under three controlled temperatures and four stress deviations. The test results have showed that, for all three types of mixes, the permanent deformation of the HL mixes is less than the ones of no HL addition. The degree of the improvement on permanent deformation resistance using HL is much pronounced at high stress deviation states. The results have also showed that the resilient modulus strongly depends on the temperature and stress deviation while the mixes of HL addition demonstrate higher rigidity. At last, mathematical characterization models have been proposed for the measured material properties. A numerical simulation case study has been performed to test and demonstrate the application of the proposed unified property model. • Experimental work on uni- and tri-axial tests for asphalt concrete mixes using and without using the hydrated lime filler modification. • Novel mathematical characterization modelling on the experimental results for the resilient modules and permanent deformation. • Numerical case study simulation to demonstrate the application of the mathematical model proposed and developed in this work. [ABSTRACT FROM AUTHOR]

In order to address the limitations of recycled aggregate concrete prepared from recycled fine aggregates (RFA), the utilization of nanomaterials has been demonstrated as an innovative and effective approach. This study aimed to enhance the performance of ultra-high performance concrete (UHPC) reinforced with recycled fine aggregates (RFA) by incorporating industrial-grade graphene oxide (GO). The effects of GO on various aspects of UHPC, including workability, mechanical properties, autogenous shrinkage, permeability, interfacial transition zone (ITZ), and microstructure, were thoroughly investigated. The results demonstrated that the addition of RFA significantly reduced the early compressive strength of UHPC and increased water permeability and chloride ion penetration. However, it effectively mitigated autogenous shrinkage, and the 7-day autogenous shrinkage was reduced by 61.07%. Moreover, increasing the GO content improved the compressive strength and transport performance of RFA-reinforced GO-UHPC. The incorporation of GO led to a substantial enhancement in the tensile strength of UHPC due to its bridging effect and changes in pore structure, thereby improving the interface bonding between steel fibers and the matrix. At a critical GO content of 0.06%, the autogenous shrinkage was further reduced by 54,85%, and the compressive and tensile strengths were improved by 8.24% and 28.39%, respectively, with an increase in the matrix density. The addition of GO promoted the formation of more calcium silicate hydrate, resulting in a more homogeneous microstructure and an increased proportion of small pores in the ITZ. Overall, this study highlights the synergistic effect of GO and RFA in UHPC as a promising approach for developing low-cost, environmentally friendly, and sustainable building materials. • A method of preparing low-cost, environmentally friendly, and sustainable UHPC using industrial-grade graphene oxide and recycled fine aggregate are proposed. • The synergistic influence mechanisms of industrial-grade graphene oxide and recycled fine aggregate on the early autogenous shrinkage of UHPC are investigated. • The addition of industrial-grade graphene oxide enhances the mechanical properties and chloride penetration resistance of UHPC containing recycled fine aggregate. • The improvement of industrial graphene oxide on the pore structure of matrix and the interfacial transition zone of recycled fine aggregate interface are revealed. [ABSTRACT FROM AUTHOR]

Nanomaterial integration in building materials has become a pivotal approach to provide cementitious composites with dual functionality, namely photocatalytic and antimicrobial attributes, conferring self-cleaning and anti-polluting characteristics to these materials. We conducted a systematic literature review on the photocatalytic and antimicrobial properties of ZnO-NP in construction materials, selecting all articles from the last 5 years. We performed a search on the Web of Science and 25 articles were selected consistent with the study purpose, after the filtration process aligned with PRISMA guidelines. This is the first article on this topic using a methodological review, covering all recent literature and the most cited articles from recent decades. Although the volume of articles is still limited, it was possible to identify the most efficient percentages of ZnO-NP in different construction materials (paint, mortar, concrete, wood, others). The main applications, challenges, and themes for future research are discussed to produce safer and more sustainable materials and with potential to be used in the civil construction industry. [Display omitted] • Application of ZnO-NP in building materials is reviewed. • Antimicrobial and photocatalytic potential was summarized. • ZnO-NP helps to creation of building materials that provide safer environments. • This paper aims to encourage and promote the use of ZnO-NP in building materials. [ABSTRACT FROM AUTHOR]

Coal gangue (CG) and fly ash (FA) buildup and storage pose significant environmental and human health issues. Thus, enhancing their use in several applications has gained widespread attention. In the same context, this study aims to evaluate the properties, and structural characteristics of a Lightweight Alkali-Activated Material (LAAM) combining CG and FA as aluminosilicate sources, in the presence of other activating additives such as lime and gypsum and metallic zinc powder as an expansion additive. The research explores various mix proportions and activator concentrations to optimize the LAAM performance. The results reveal that the addition of CG significantly affects the compressive strength of LAAM, an optimal CG content of 25% was identified as the optimal formulation in terms of mechanical properties. Increasing the concentration of sodium hydroxide (NaOH) results in higher compressive strength, with 12 M NaOH achieving a compressive strength of 4.58 MPa, meeting industry standards for autoclaved aerated concrete. The microstructural investigations, which included XRD, FT-IR, TG-DTA, and SEM-EDS, revealed that the activated products of the optimal LAAM ratio elaborated in this study are mainly hydrated alkali-aluminosilicate gel (N-A-S-H/C-A-S-H) with less unreacted Portlandite compounds. [Display omitted] • New lightweight aerated concrete: Moroccan wastes (CG and FA), lime, gypsum, metallic powder zinc. • Coal gangue and fly ash as sustainable binders address environmental issues in construction. • 25% CG optimally boosts compressive strength. • Higher NaOH concentrations enhance strength, reaching 4.58 MPa at 12 M NaOH. [ABSTRACT FROM AUTHOR]

Fiber-reinforced geopolymer concrete offers a sustainable alternative to conventional concrete; however, its application to repair and strengthen existing concrete structures is inadequately understood. The effectiveness of repairing and strengthening system depends upon the bond characteristics of existing and overlay concrete. Therefore, the present study aims to assess the bond performance of normal (old) concrete and fiber-reinforced geopolymer (new) concrete (FRGC) using different bond tests such as split tensile, bi-surface shear, and slant shear tests. The performance of four interface preparation techniques has been compared: wire brushing, epoxy, carbon fiber reinforced polymer (CFRP), and glass fiber-reinforced polymer (GFRP). Moreover, the effect of various sizes of groove width on the bond characteristics of old and new concrete interfaces is also investigated. CFRP and GFRP, as surface preparation techniques over plain old concrete surfaces, showed the highest split tensile, bi-surface shear, and slant shear strength. Additionally, the interface prepared with grooves of 40 mm width and 10 mm depth with epoxy represented a 113.5% enhancement in slant shear strength compared to the ungrooved one because of the additional mechanical interlocking provided by the defined shape of the grooves. The composite prepared with FRGC as new concrete performed equivalently and even better in some cases than new normal concrete due to the increased interfacial adhesion and dense transition zone created by PVA fiber. Thus, FRGC, being sustainable, has the tendency to replace conventional concrete as an effective and efficient repairing and strengthening concrete. Finally, the obtained experimental results have been compared with the predicted interfacial shear capacity using different design code models, and amongst them, Eurocode 2 predictions are closest to the experimental results. • FESEM image analysis of FRGC confirmed strong bond between amorphous gels in concrete and PVA fiber. • Grooved composite with 40 mm groove width and epoxy at the interface displays superior slant shear strength. • Ungrooved composite samples with CFRP/GFRP as a surface preparation technique showed the best bond performance. • FRGC, as new concrete, showed equivalent and even better bond performance than conventional concrete. [ABSTRACT FROM AUTHOR]

In this work, novel calibration curves and calibration surfaces of Electromagnetic (EM) characteristics are modeled as a function of the water and chloride contents of concrete. An experimental campaign was carried out on cores extracted from two types of concretes: C1 (Ordinary Portland Concrete) and C3 (62% slag + 38% clinker). The cores were initially saturated at three sodium chloride (NaCl) concentrations and then oven-dried to attain different degrees of saturation. They were tested with the electromagnetic and electrical cell to determine the dielectric permittivity and electrical resistivity, respectively, at the targeted hydric and chloride ion contents. The calibration curves and calibration surfaces, which represent the resistivity and permittivity as a function of chloride content and/or degree of saturation, were adjusted and presented for both concretes. The calibration surfaces developed herein serve as an essential tool to study complex phenomena, such as the coupled water-chloride ingress. • Developing novel calibration curves and calibration surfaces that correlate the permittivity and resistivity of concrete to its chloride and water content. • Investigating the impact of slag on the permittivity and resistivity of concrete. • Proposing a non-destructive methodology to monitor chloride and water content for reinforced concrete structures exposed to a tidal zone. [ABSTRACT FROM AUTHOR]

Sulfuric acid in sewage systems causes great damage to concrete elements every year. Also, the excessive release of carbon dioxide develops global warming and climate change. A lot of studies have been separately carried out to solve mentioned problems and some solutions have been provided. But, research that simultaneously mitigates the harmful effects of both problems has rarely been conducted. Therefore, sulfuric acid resistance of carbonated concretes with replacement levels of 10 %, 20 %, and 30 % of hydrated lime was investigated in this study. 28 days of moist curing and up to 24 h of CO 2 curing were considered for the specimens. Then the samples were immersed in sulfuric acid solution (pH=0.6) up to 90 days. Parameters such as compressive strength, water absorption, and CO 2 absorption of concrete samples were measured before immersion in sulfuric acid solution. Also, compressive strength loss, mass reduction, 3D scanning, and FT-IR analysis of concrete samples after immersion in sulfuric acid solution were performed. The results showed that the CO 2 curing method can increase the durability of concrete mixtures in the sulfuric acid environment. It was also observed that replacing hydrated lime with cement increases the durability of concrete mixtures against sulfuric acid attacks in both moist and CO 2 curing methods. In general, replacing hydrated lime up to 30 % of cement increased CO 2 absorption up to 36 % and increased sulfuric acid resistance up to 38 % in terms of mass loss. • CO 2 uptake of the mixtures increased with increasing the hydrated lime replacement. • CO 2 curing of concretes increases the durability under sulfuric acid attack. • CO 2 curing period has no significant effect on the durability against sulfuric acid. • Hydrated lime replacement increased the durability of concretes against sulfuric acid. [ABSTRACT FROM AUTHOR]

Sulfur dioxide (SO 2) is the primary pollutant in industrial atmospheres, leading to significant damage to industrial buildings. The corrosion caused by SO 2 in concrete, including neutralization and solid phase volume expansion, poses particular concerns. However, there is a lack of research on the electrochemical behaviour and corrosion mechanisms of reinforcing bars embedded in concrete. This study conducted indoor simulations of reinforced concrete specimens exposed to industrial SO 2 corrosion utilizing an SO 2 testing chamber. The corrosion behavior of the reinforcing bars was monitored through half-cell potential, weak polarization, and electrochemical impedance spectroscopy (EIS). Additionally, the corrosion mechanisms of the reinforcing bars under SO 2 exposure were investigated using scanning electron microscopy with energy dispersive spectroscopy (SEM/EDS), X-ray diffraction (XRD), and Raman spectra. The results demonstrated a consistent correlation between variations in corrosion potential (E corr) and corrosion current density (i corr) of steel rebars in different types of concrete. The corrosion rates of the reinforcing steel in C1 (w/b=0.57), C2 (w/b=0.47), and C3 (w/b=0.37) concrete exceeds 0.1 μA/cm2 after 42, 72, and 90 days of SO 2 corrosion, respectively. At this time, the ratio of the depth of neutralization to the thickness of the protective layer is 0.51–0.65. The rust exhibits a layered structure with a presence of S elements adsorbed and deposited on the surface of the rust layer. Moreover, the research has identified the accumulation of S elements within corrosion pits, which can be attributed to localized acidification reactions. The rust products identified include iron hydroxide (FeOOH), and iron oxide (Fe 2 O 3), rozenite (FeSO 4 ·4 H 2 O). The formation of FeSO 4 ·4 H 2 O in corrosion pits suggests that significant localized corrosion on the surface of reinforcing bars in concrete under the impact of SO 2. ● Simulate typical industrial SO 2 corrosion environments. ● Surface analysis reveals the corrosion mechanism of steel rebars in concrete. ● Corrosion products contain ferrous sulphate hydrates. [ABSTRACT FROM AUTHOR]

Lithium Slag (LS), also known as Delithiated Beta Spodumene (DBS), is a by-product of lithium extraction from spodumene ore that contains active silicon dioxide and aluminium oxide making it a potential supplementary cementitious material (SCM) for concrete. This study investigated the transport properties of concrete at 28, 90, and 180 days by incorporating LS as an SCM with cement replacement levels of 20%, 40%, and 60%. The findings reveal that 20% to 40% LS enhanced compressive strength, and reduced permeable voids, water penetration, sorptivity, and porosity, leading to improved transport properties. As LS reacts slowly, 40% LS resulted in 18.34% higher compressive strength at 180 days compared to that of the control mix. Therefore, VPV, water penetration depth, and sorptivity co-efficient of concrete with 40% LS were found 15.96%, 24.79% and 38.46%, respectively, lower than the control mix. In addition, porosity analysis confirmed that with the increase of LS in concrete, porosity decreased over time. Moreover, SEM analysis demonstrated the development of CaCO 3 crystals at 40% LS, further reducing porosity. However, beyond 60% cement replacement by LS, a decline in concrete properties was observed due to unreacted LS particles. Therefore, this research underscores the potential use of LS to enhance durability of concrete. ● High SiO 2 and Al 2 O 3 in LS promote C-S-H gel and improve durability at later ages. ● LS significantly improves porosity by forming CaCO 3 in 40% replacement. ● Higher replacement degrades durability due to unreacted LS particles. [ABSTRACT FROM AUTHOR]

Overlays are used in bridges atop of ultra high performance (UHPC) components despite the lack of data regarding overlay-UHPC bond performance. To address this knowledge gap, this study evaluated the adhesion of polyester polymer concrete (PPC), latex modified concrete (LMC) and modified concrete type D (MCD) overlays bonded to UHPC substrate via the bond pull-off test method. The test variables included coring depth into the UHPC, overlay age, and surface preparation method (grinding and sandblasting, surface retarder treatment, and hydrodemolition). PPC exhibited superior bond performance, followed by LMC and MCD. The overall better performance of PPC and LMC over MCD was accredited to enhanced chemical adhesion enabled by polyester and latex, respectively. Surfaces prepared via surface retarder and hydrodemolition exposed fibers in UHPC which resulted in fiber-bridging effect across the interface. • Surface profile gauge is the most appropriate for UHPC roughness characterization. • Coring depth impacts pull-off bond strength and failure mode. • PPC exhibits consistent high bond strength across roughened surfaces. • PPC and LMC exceed minimum recommended bond strength for all surface preparation methods. • MCD consistently showed lower pull-off bond strength compared to PPC and LMC. [ABSTRACT FROM AUTHOR]

This paper presents an investigation into the potential of recycling fly ash - based geopolymer concrete, to produce a recycled binder for circular re – use as starting material. The aforementioned would be a significant advantage over Portland cement which is non – recyclable, owing to its irreversible hydration. The experiment conducted involved crushing and sieving old parent fly ash – based geopolymer concrete, to separate out the paste from aggregate. The paste was then pulverized using a ball – mill to produce the recycled aluminosilicate starting material, herein referred to as recycled geopolymer cement (RGPC). Fly ash was blended with 0 to 100% RGPC, then used to prepare fresh geopolymer paste and mortar mixtures activated using a binary alkali activator consisting of sodium hydroxide and sodium silicate. Samples were cast then cured at 23 or 80 °C. The various tests done were workability, setting time, compressive strength, splitting tensile strength, drying shrinkage, water absorption, and volume of permeable pores. Analytical studies were done using X – ray diffraction, scanning electron microscopy and Fourier – transform infrared spectroscopy. Results showed that incorporation of RGPC into geopolymer mixtures generally led to reduction of workability and setting time, reduction of compressive and tensile strength, along with increase in drying shrinkage. It was, however, found that up to 60% RGPC can be incorporated into geopolymer mixtures while maintaining adequate performance suitable for structural applications. Unlike Portland cement, hardened geopolymer concrete is evidently recyclable to produce a circularly re – usable binder. [Display omitted] • FA–GPC is fly ash geopolymer cement, RGPC is recycled geopolymer cement. • FA-GPC concrete is recyclable to produce a circularly re - usable binder. • RGPC effectively underwent geopolymerisation to form the binder phase. • RGPC incorporation led to reduction of mortar strength and workability. • Mortars containing ≤ 60% RGPC gave strengths > 50 MPa suited for structural uses. [ABSTRACT FROM AUTHOR]

This study aims to develop a novel concrete that integrates a metal-organic frameworks (MOF) and accelerated carbonation curing to offset the emissions attributed to cement production. A MOF, NH 2 -MIL-125(Ti), was synthesized to sequester CO 2 in concrete through accelerated carbonation curing. Its impact on the concrete properties was assessed while examining various process parameters, including MOF content, initial curing duration, carbonation curing duration, and carbonation curing pressure. The parameters were evaluated through CO 2 uptake, phenolphthalein indicator solution, compressive strength, water absorption, and volume of permeable voids. The microstructure of carbonated MOF-incorporating concrete was characterized using powder X-ray diffraction analysis, scanning electron microscopy, and Fourier transform infrared spectroscopy. Experimental results showed that the addition of MOF promoted a higher degree of carbonation of cement, especially with a longer initial curing duration and higher pressure. Incorporating up to 6% MOF, by cement mass, in concrete cured for 20 h in open air, followed by 20 h of carbonation curing at a pressure of 1 bar, led to a CO 2 uptake of 19%, carbonation depth of 11 mm, and 28-day strength of 46 MPa, water absorption of 4%, and permeable pore voids volume of 11%. Exceeding 6% MOF addition did not improve the uptake or performance. Microstructure characterization highlighted the formation of calcite, aragonite, and calcium silicate hydrate and the consumption of calcium hydroxide. The MOF-incorporating concrete can be used in construction applications to mitigate CO 2 emissions while maintaining concrete performance. • Properties of carbonation-cured concrete featuring metal-organic frameworks (MOF) were assessed. • MOF incorporation in concrete improved the degree of carbonation of cement. • Adding 6% MOF by cement mass improved the concrete compressive strength. • Water absorption and permeable voids decreased upon adding 6% MOF to concrete. • Calcite, aragonite, and C-S-H formed while calcium hydroxide was consumed. [ABSTRACT FROM AUTHOR]

Metaconcrete, as a new type of composite material with vibration attenuation characteristics, is formed by replacing traditional coarse aggregates with a heavy metal core wrapped with an elastic soft coating and mixing with cement mortar. However, due to the high bandgap frequency and narrow bandgap width, it is greatly limited in the engineering application of low frequency vibration control. In order to broaden the range and number of elastic wave bandgap of metaconcrete materials and solve the problem of low frequency vibration, a novel three-component cement-based phononic-like crystal model is proposed based on local resonance theory, and phononic-like crystal metaconcrete vibration reduction material is developed accordingly. Secondly, the band structure, bandgap mechanism, and frequency response function of the phononic-like crystal metaconcrete are calculated and analyzed, and indoor tests of the phononic-like crystal metaconcrete are conducted. Finally, a phononic-like crystal metaconcrete subway track bed is prepared using the developed phononic-like crystal metaconcrete material, and applied to the practical subway engineerings to solve the low frequency vibration problem generated during subway operation. The results show that the phononic-like crystal metaconcrete opens 6 low frequency bandgaps in the frequency range of 200 Hz, and the attenuation values are mostly above 10 dB in the frequency range of the bandgap, and the attenuation effect is good. Meanwhile, the on-site monitoring results show that the phononic-like crystal metaconcrete subway track bed has good low frequency vibration reduction effect in the 200 Hz frequency range. The maximum value of the one-third octave insertion loss of the tunnel wall is 13.22 dB, the maximum vertical Z-vibration level difference of the tunnel wall is 5.052 dB, and the maximum vertical frequency division vibration level difference of the tunnel wall is 5.926 dB. The maximum value of the vertical frequency division vibration level difference in the frequency range of 4–200 Hz is 13.87 dB, and the average value is 5.74 dB. The relevant research results of this paper provide a new technical approach to solve the problem of low frequency vibration in subway engineering and other engineering construction, breaking through the traditional vibration reduction control technology of civil engineering structures, and providing new idea and method for long-term vibration reduction and application of engineering structures. • This paper develops phononic-like crystal metaconcrete vibration reduction material. • The material can open multiple low frequency vibration reduction bandgaps. • The material is used to prepare a new type of subway vibration reduction track bed. • The subway track bed has remarkable low frequency vibration reduction performance. [ABSTRACT FROM AUTHOR]

Cement production causes a threat to environmental sustainability owing to the enormous volume of greenhouse gas releases and high energy consumption. Similarly, agro-industrial waste contributed significantly to environmental pollution when disposed of in landfills. Waste from date palms is one of the main agro-waste generated in Saudi Arabia. This waste is normally disposed of without treatment or burnt for energy. The date palm ash (DPA) due to its pozzolanic properties could be suitable for use as supplementary cementitious material (SCM) in concrete. However, due to its weak or slower pozzolanic reactivity, the DPA negatively affects the performance of concrete. In this research, the DPA was used as a SCM in concrete. Eggshell powder (ESP) owing to its abundant calcium oxide content was used as an additive to the concrete containing other pozzolanic materials with high silica content. Cement was partially replaced with DPA at dosages between 10% to 40%, and ESP was added at different proportions between 1% to 4% by weight of the binder. The workability of the concrete was decreased with adding blends of DPA and ESP. The mechanical strengths (compressive, flexural, and tensile strengths), modulus of elasticity (MoE), water absorption, and porosity of the concrete were negatively affected by adding DPA. Blending up to 30% DPA with up to 3% ESP as cementitious materials help alleviate the adverse effects of the DPA on the strengths, MoE, and durability performance of the concrete. DPA increases pore volume and porosity by decelerating C-S-H production through its slower pozzolanic reaction at early ages. DPA reduced total embodied CO 2 emissions and enhanced the eco-strength efficiency of the concrete. Using DPA and ESP blends in concrete improves performance, minimizes environmental effects, and reduces CO 2 emissions during cement production. • Sustainable concrete was developed using ternary blends of DPA and ESP. • Blends of DPA and ESP enhanced the mechanical properties of concrete. • Blends of DPA and ESP densified the concrete's microstructure. • DPA as SCM reduced the embodied CO 2 emission in concrete. [ABSTRACT FROM AUTHOR]

Using cellulose nanomaterials (nano-crystalline [NC] and/or nano-fibrillated [NFC] cellulose) with a high content of supplementary cementitious materials and special class of basalt fiber/polymer (BFP) pellets could produce sustainable and resilient composites for a suite of infrastructure applications. Hence, this study investigated the development of cementitious composites comprising high content slag (50% as cement replacement), BFP (4.5% by volume), NFC ranging from 0 to 0.5% (addition to the mass of the binder) and NC (0 to 0.1% addition to the mass of the binder) to prepare multiple formulations without/with nano-silica (reference nanomaterial) for repair/overlay applications of concrete flatwork. An integrated experimental program including constructability, mechanical capacity, and durability properties as well as compatibility with substrate concrete was conducted. Findings of these tests were corroborated with thermal and microstructural tests to evaluate the hydration/pozzolanic development and pore structure features. The overall results indicated that the development of high-cementitious composites with cellulose nanomaterials is possible, as they achieved balanced behaviour in terms of workability, hardening rates, high early- and later-age compressive strengths, high ductility, improved durability, and superior thermal and elastic integrity/compatibility with the parent/normal concrete. Thus, they may present an attractive option for repair and overlay applications of concrete flatwork. • Cellulose nanomaterials (NC and/or NFC) were used for concrete repair applications. • The effect of cellulose nanomaterials on HPFRCC were comprehensively assessed. • The HPFRCC consisted of a high content slag, nanomaterials, and innovative basalt fibers pellets. • The results indicated that producing HPFRCC with high content slag and cellulose nanomaterials is possible. • mixes achieved balanced fresh, strength, durability, and compatibility required for repair/topping applications. [ABSTRACT FROM AUTHOR]

To study the deterioration law of aeolian sand concrete (ASC) under the coupling effect of sulfate freeze-thaw, this paper uses aeolian sand as a substitute for river sand to prepare ASC with different replacement rates (0%, 20%, and 100%). Freeze-thaw cycle (FTC) tests are conducted in different salt solution environments (5% Na 2 SO 4 , 10% Na 2 SO 4 , and 5% Na 2 SO 4 + 3.5% NaCl) to analyze the changes in physical and mechanical properties, and the mechanism of performance degradation of ASC is analyzed by SEM, XRD and NMR. The results show that incorporating aeolian sand significantly improves the salt-freeze erosion resistance of concrete, and when the content is 100%, the impact on salt-freeze erosion on macroscopic properties such as mass loss and compressive strength is minimized, signifying the salt-freeze erosion resistance is the best. During the FTCs, the relative dynamic elastic modulus of concrete initially increases and then decreases, while the trend in mass loss rate reverses. SO 4 2- and Cl- in the salt solutions react with the hydration products to form calcium vanadate, gypsum, and Friedel salts. During the initial stages of FTCs, erosion products fill the matrix pores, increasing the compactness of the concrete, which positively affects macroscopic properties. As the FTCs progresses, ice crystals and excessive erosion products accumulate, resulting in a further expansion of internal pores and cracks in concrete. Consequently, the ratio of harmful to beneficial pores continues to increase, resulting in freeze-thaw damage. After 200 FTCs, in the 5% Na 2 SO 4 + 3.5% NaCl erosion medium, the internal cracks in aeolian sand concrete get bigger and the holes get larger, causing the most damage and deterioration. Different degradation indices are used to predict the residual lifetime of ASC based on a Wiener random probability distribution. The Wiener stochastic process effectively predict the lifetime of ASC under the coupling effect of sulfate FTCs, with the compressive strength loss rate as the most sensitive degradation index. Among them, for ASC-0, ASC-20, and ASC-100 in the 5% Na 2 SO 4 + 3.5% NaCl environment, the maximum FTCs, based on the compressive strength loss rate, are 198, 206, and 213 times, respectively. This study could provide a theoretical foundation for the durability design of concrete structures in cold regions and other salt-frozen regions within Northwest China. • Effect of erosion solution and aeolian sand content on frost resistance of ASC. • The macroscopic properties and microstructure of ASC under FTC were analyzed. • The FTC damage is the most serious in 5% Na 2 SO 4 + 3.5% NaCl environment. • The Wiener random distribution can be applied to the life prediction of ASC. [ABSTRACT FROM AUTHOR]

The improved damping capacity of concrete materials is crucial for many applications, especially the ones exposed to dynamic external forces. This study explores the optimal circumstances of copolymer composite binder, ratio of fine to coarse aggregate, curing time, size and content of tyre crumb rubber on enhancing damping ratio of hybrid polymer concrete. Owing to the limitation of conventional models and experimental methods in effectively handling the multiple and complicated relationship between the input parameters of the hybrid polymer concrete and its damping capacity, two robust machine leaning models including extreme gradient boosting (XGB), and artificial neural network (ANN) algorithms were developed to predict the values of damping ratio from an experimental database of 196 samples. Multiple linear regression (MLR) was employed in this study as a benchmark for comparing with the ANN and XGB methods. The results indicate that the considered algorithms yield accurate models for predicting the damping ratio of HPC composites. However, ANN and XGB outperform MLR with an impressive R-square of 0.985 and 0.981, respectively versus 0.875. Analysing the importance of input features using the XGB algorithm also reveals that the curing time has the highest impact on predicting the damping ratio. The volume fractions of resin matrix and crumb rubber are the next most important features. The crumb rubber size, within the studied range, appears to be the least impactful one. • A large experimental dataset on damping capacity of the hybrid polymer concrete has been produced. • Dataset feature effects of optimised ratio of fine-to-coarse aggregate and curing behaviour of the novel copolymer binder used for the hybrid polymer concrete. • Damping ratio of the hybrid polymer concrete predicted using machine learning techniques. • The importance of the input variables analysed using the extreme gradient boosting algorithm. [ABSTRACT FROM AUTHOR]

The present study concerned the effect of electrochemical chloride extraction (ECE) to chloride-contaminated concrete on chloride removal with incremental depths after the ECE at 1000 mA/m2 for 2, 4 and 8 weeks. The steel reinforcement was taken as an anode, while the titanium mesh as cathode. The chloride was extracted by diluting concrete dust sample in acid solution and still water for total and free chlorides, respectively. As a result, most free chlorides were removed from concrete at the increased current density, while bound chlorides were quite removed, presumably due to a reduction of the alkalinity of concrete. • A removal of chlorides at electrochemical chloride extraction was studied. • Free chlorides were mostly removed under ECE except at near the surface. • Bound chlorides were quite removed under ECE at all depths. • The ECE lowered the alkalinity of inner concrete pore solution. [ABSTRACT FROM AUTHOR]

This study investigated the feasibility of applying defect-containing recycled aggregates (RA) in ultra-high-performance concrete (UHPC) and studied the effect of nanosilica (NS) and steel fiber (SF)) together on its modification. The effects of RA substitution rate, SF content and NS content on the flexural behavior and microstructure of RA-UHPC were analyzed by four-point bending test. The experimental results showed that the specimens without added SF exhibited a linear elastic growth on the load-deflection curve, with a sharp decrease in load after the peak without a significant falling segment. In contrast, the specimens with added SF showed a typical three-phase characteristic with a smoother and flatter descending phase. The cross-distributed SF improves the ductility of the specimens after the peak by bridging effect and changes the damage behavior from quasi-brittle to ductile. Increasing the SF content significantly improved the flexural strength and toughness of the specimens, while increasing the RA substitution rate and NS content slightly decreased the flexural strength. The trends of the residual strengths calculated by the two methods were basically the same, while the specimens with brittle failure had almost no residual strengths. In addition, crack locations could be predicted prior to peak loading using digital image correlation techniques, while SEM analysis revealed the pore space between the cement matrix, interfacial transition zones, and fibers, as well as the ameliorating effects of SF and NS on micro- and macro-scales. These findings are valuable for understanding the flexural mechanism of fiber-nanocomposite concrete. ● RA-UHPC was prepared by incorporating RA in UHPC and co-modified with NS and SF. ● SF improves the flexural strength and toughness of RA-UHPC and transforms its brittleness into ductile failure. ● DIC measurements captured the initiation and evolution patterns of cracks. ● NS filled material's pores and improved ITZ structure between SF and the matrix. [ABSTRACT FROM AUTHOR]

Concrete is a widely used material that presents vast opportunities for energy harvesting applications. Among these, thermoelectric concrete shows promising potential for harvesting waste heat generated in urban and industrial environments. However, the development of thermoelectric concrete poses several challenges that need to be addressed, such as the need to accurately account for the intrinsic voltage. This factor is frequently disregarded, but it has a significant impact on the measurement of thermoelectric properties in improving the intrinsically low electrical conductivity and Seebeck coefficient. In this context, this study evaluates the performance of industrially scalable geopolymer-based concrete that incorporates recycled aggregates as low-cost and environmentally friendly additives for thermoelectric energy harvesting applications. The concrete exhibited an intrinsic voltage of 15 mV, and a new test protocol was proposed to exclude its impact on thermoelectric measurements. The geopolymer concrete demonstrated a significantly high Seebeck coefficient of 570 µV/k, surpassing all previously reported values for geopolymer-based materials. Furthermore, it was discovered that the thermoelectric behavior of geopolymer-based concrete is of ionic origin, indicating that further improvements can be made by adjusting the pore solution chemistry. This finding suggests that there is ample opportunity for innovation and optimization in the development of thermoelectric concrete. [Display omitted] • Investigating geopolymer concrete for thermoelectric energy harvesting applications. • Addressing intrinsic voltage's impact on thermoelectric property measurements. • Proposing a new test protocol to exclude intrinsic voltage's effect. • Achieving a high Seebeck coefficient (570 µV/K) after accounting for intrinsic voltage. • Discovering the ionic origin of thermoelectric behavior in geopolymer concrete. [ABSTRACT FROM AUTHOR]

A novel method for reusing construction waste and simultaneously sequestering CO 2 in the form of mineral carbon is presented in this study. The method involves the production of construction bricks using waste concrete fines treated with carbonation. Initially, waste concrete is crushed and ground into recycled concrete fines (RCF), which are then subjected to a carbonation process to obtain carbonated recycled concrete fines (CRCF). Comprehensive characterization using XRD, TGA, FTIR, and zeta potential measurements reveals that CRCF exhibits a microstructure featuring silica-coated calcium carbonate particles on its surface, imparting significant reactivity to CRCF. In this investigation, RCF and CRCF are separately mixed with Ca(OH) 2 , molded, and compressed into bricks, with performance testing conducted under various material ratios and manufacturing conditions. The results indicate that bricks made with CRCF exhibit mechanical properties exceeding those of RCF-based bricks by more than two-fold. This improvement can be attributed to the refined pore structure observed in CRCF bricks. The highly reactive silica gel present on the surface of CRCF reacts with Ca(OH) 2 to form C-S-H, providing a rationale for the superior strength displayed by CRCF bricks. • Novel method combines construction waste reuse with CO 2 sequestration in brick production. • Carbonated recycled concrete fines (CRCF) exhibit superior reactivity and microstructure. • CRCF bricks surpass RCF-based bricks by over two-fold in mechanical properties. • Optimal conditions for water-solid ratios, curing temperature, and forming pressure identified. • CRCF-bricks demonstrate higher strength and refined pore structure, offering sustainable construction. [ABSTRACT FROM AUTHOR]

Using of magnetized water (MW) in the manufacturing of Portland cement concrete has shown promising effects in recent decades. This research investigates the effect of using alkaline activator (AA) solution prepared with MW on producing fly ash (FA) and silica fume (SF) based geopolymer concrete. The MW was prepared by passing tap water (TW) through two permanent magnetic fields of 1.4 and 1.6 Tesla intensities. Sodium hydroxide (SH), potassium hydroxide (PH), and sodium silicate (SS) solutions were the AA used. In total, 28 geopolymer concrete mixes were produced and tested in this study. Half of the mixes was made with the proposed MW (activator and added water), and compared with the other half that made with TW (activator and added water). Variables like; water type (TW or MW), SF content (10%−100%), AA type (SH+SS or PH+SS), AA concentration, AA to cementitious materials (AA/C) ratio, and water to cementitious materials (W/C) ratio were applied in this study. Physical and chemical properties of the utilized water and AA were measured. Concrete fresh and hardened mechanical properties were measured including workability, compressive strength, tensile strength, flexural strength, bond strength, and water absorption. Ultrasonic pulse velocity non-destructive testing was also conducted on the produced concrete. Scanning electronic microscope (SEM), energy dispersive X-ray (EDX), and X-ray diffraction (XRD) analyses were carried out on selected mixes to closely investigate the microstructure of the introduced geopolymer concrete. The results showed that compared with TW, utilizing MW in preparing the AA of geopolymer concrete caused notable increase in the concrete slump with an average of 14%, compressive strength increase by up to 64%, tensile strength increase by up to 60%, flexural strength increase by up to 41%, bond strength increase by up to 40%, and water absorption decrease by up to 38%. • Geopolymer concrete alkaline activator (AA) was made with magnetized water (MW). • Sodium hydroxide, potassium hydroxide, sodium silicate solutions were the AA used. • Twenty-eight mixes were tested for fresh and hardened mechanical properties. • MW increased slump with average of 14%, increased compressive strength by up to 64%. • MW increased tensile strength by up to 60%, decreased water absorption by up to 38%. [ABSTRACT FROM AUTHOR]

Sulfide-bearing aggregates can cause significant damage when concrete has been produced without considering their potential deleterious oxidation reactivity. This study aims to find a reliable quantitative approach for assessing the impact of the harmful reaction of sulfide minerals (essentially pyrrhotite) in concrete specimens produced under laboratory conditions. To achieve this objective, different parameters such as an electrochemical treatment have been applied over 14, 28, 35 and 56-day periods on a series of concrete specimens made in the laboratory with a reactive sulfide-bearing aggregate (MSK 0.9) and non-reactive aggregate (PKA) After the treatment, the concrete specimens were tested with different tools such as non-destructive (Ultrasonic Pulse Velocity), semi destructive (expansion, modulus of elasticity and stiffness damage test) and destructive (concrete polished section and compression) methods to evaluate the impact of the deleterious reaction of the sulfide-bearing aggregates. The results show that concrete with the reactive aggregate can lose a significant amount of its mechanical performance exhibited principally by a significant reduction in modulus of elasticity (decreasing around 28% after 35 days of electrochemical treatment). Signs of damage associated with the use of the MSK aggregate were identified within concrete polished sections and under the SEM, which allowed to better describe the mechanisms of the oxidation reaction of the sulfide minerals. Ideal parameters/conditions can be achieved to evaluate the potential oxidation reaction of sulfide-bearing aggregates using the electrochemical treatment and the reduction of the modulus of elasticity of the concrete in a reasonable period of time. • Optimal 35-day electrochemical treatment assesses damage in sulfide-bearing concrete. • Chloride ions act as catalysts. • Relative elasticity modulus reliably gauges sulfide-bearing aggregates' deleterious reaction. • Oxidation by-products and sulfates confirm iron sulfide minerals' reaction. [ABSTRACT FROM AUTHOR]

This study investigates the effects of various mineral admixtures, such as fly ash, metakaolin, and limestone powder, on the mechanical, chloride, and sulfate resistance properties of alkali-activated slag (AAS). The resistance of alkali-activated concrete (AAC) to chloride and sulfate is evaluated using the rapid chloride migration (RCM), wetting-drying cycles, SEM and XRD, TG/DTG. The results reveal that introducing fly ash improves workability but degrades the strength and durability of AAS. The 15% slag substitution by metakaolin is recommended to improve durability. Incorporating 15% limestone powder increases the compressive strength and reduces porosity due to filling and nucleation effects. The replacement ratio of 30% for each mineral admixture induces a considerable Ca2+ dilution, resulting in reducing the strength and durability of AAC. Under short-term wetting-drying cycles, the continued hydration of raw materials under MgSO 4 erosion and the subsequent production of gypsum, hydrotalcite, and brucite from the matrix initially increase the AAC strength. However, the continued substitution of calcium in the C-(A)-S-H gel by magnesium and precipitation of gypsum under excessive cycles adversely deteriorates the compressive strength. The chloride migration degree in AAC is closely related to the porosity. Although the porous gel N-A-S-H facilitates chlorine migration in accelerated tests, it prevents further chlorine penetration by adsorbing chloride ions in large quantities, exhibiting the dominant effect on chloride immobilization. The formation of Friedel's salt, stemming from the chemical bonding of chloride, is present only in the high-calcium specimen G100 and the highly reactive aluminum specimen G85M15. Improvements in the gel chemistry and porosity are key factors in bolstering the durability of AAC. The findings of this study contribute to advancing the application of eco-friendly AAC in marine environments. • Alkali-activated slag-based concretes (AACs) with different mineral admixtures are developed and evaluated. • The mechanisms on sulfate erosion and binding, chloride migration and binding of the designed AACs are explored. • Optimized alkali-activated system for marine concrete is proposed considering strength, pore structure and durability. [ABSTRACT FROM AUTHOR]

This study aims to investigate the effect of combined alkali-activators and alkali contents on the engineering and sustainability performance of the alkali-activated slag recycled concretes (AASRCs). The optimal activator type and its alkali content were identified using a combined analytic hierarchy process and integrated performance degree (IPD) model from a decision-making perspective. Three activators were selected, i.e., water glass (WG), combined WG and sodium carbonate (WN), and combined calcium oxide and sodium carbonate (CN). The alkali contents of activators were determined as 4%, 5%, and 6% in terms of the mass ratio of Na 2 O to binder. The results showed that WG-activated concrete (WGC) obtained the highest slump and compressive strength, and followed by WN-activated concrete (WNC) and CN-activated concrete (CNC). The autogenous shrinkage of CNCs drastically reduced compared to those of WGCs and WNCs. Moreover, CNCs exhibited obvious advantages over WGCs and WNCs in energy consumption, environmental impacts, and life-cycle cost. The AASRCs with higher alkali content generated greater environmental and economic impacts. The CNC with an alkali content of 4% showed the highest IPD value of 0.727 and obtained the optimum overall performance. This study extends the knowledge of the effect of combined activators on AASRC performance, and proposes a framework incorporating engineering, environmental, and economic aspects to optimize the activator type and its alkali content. • The WGCs obtained the highest slump and compressive strength, while the CNCs had the lowest autogenous shrinkage. • The CNCs showed significant benefits in energy consumption and environmental impacts. • The CNCs contributed a lowest life-cycle cost compared to WGCs and WNC. • The CNC with an alkali content of 4% obtained the optimum overall performance. [ABSTRACT FROM AUTHOR]

The phenomenon of sustainable salt damage caused by soluble salt solutions in salt environments has raised concerns in asphalt pavement. However, the evaluation methods for salt erosion damage in asphalt concrete are limited, and there is a lack of comprehensive analysis of the composition of asphalt concrete. In this study, asphalt concrete specimens immersed in NaCl solution were subjected to dry-wet cycles and freeze-thaw cycles to analyze the erosion mechanisms of NaCl solution on their mechanical properties. The chemical stability and microstructure of asphalt after immersion in NaCl solution, as well as the microstructure and mechanical properties of aggregates after NaCl solution immersion and dry-wet cycles, were investigated. The results showed that NaCl solution has a softening effect on asphalt, promoting the intrusion of NaCl crystalline salt into the asphalt. The salt crystallization of NaCl solution altered the surface roughness of the aggregates, resulting in a decrease in skid resistance but an improvement in compressive strength. Specifically, limestone exhibited more stable mechanical properties than basalt. Meanwhile, the NaCl solution concentration has no significant impact on the mechanical performance of asphalt concrete initially, but its domination over mechanical performance gradually increases as the salt environment's cyclic effects intensify. The mechanisms of salt damage in asphalt concrete by NaCl solution mainly involve dry-wet cycles (crystal volume expansion), freeze-thaw cycles (ice volume expansion), and asphalt softening and viscosity reduction. The findings of this study provide a basis for the durability research of asphalt pavements in salt environments. • Chlorine salt-water-temperature action affects mechanical performance of asphalt concrete. • Chlorine salt solution has a softening effect on asphalt. • Salt crystallization alter the roughness of the aggregate. • Dry-wet cycles accelerates the chlorine salt erosion to asphalt concrete. [ABSTRACT FROM AUTHOR]