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By crushing the prepared cement paste, the recycled powder (RP) was prepared by grinding. The study systematically investigated the effects of microwave power and activation time on the activity of RP. The results showed that the maximum enhancement in the activity of RP occurs when the microwave power is set to 490 W and the activation time is 10 minutes, with the activity increased by 14 %, 15 %, and 22 % at 3, 7, and 28 days, respectively. After microwave activation of RP, the decomposition of C-(A)-S-H and ettringite in the RP provides calcium, silicon, and aluminum phases, and the evaporation of bound water promotes the secondary hydration of RP. After microwave activation, the content of calcium oxide (CaO) in the RP increases, while the contents of silicon dioxide (SiO 2) and alumina oxide (Al 2 O 3) decrease; Adding activated RP to prepare mortar generates more hydration products to fill the pores, making the structure more compact. Compared with the control group, the porosity of the MRP-5 group decreased by 2.38 %. • Studied the effect of microwave excitation on the activity of recycled powder. • The mechanism of microwave-induced recycled powder has been revealed. [ABSTRACT FROM AUTHOR]

By considering the current global challenges such as greenhouse gas emission and waste disposal management, the exploration of geopolymer concrete is highly focused now-a-days. On the other hand, the use of costlier commercial activators acted as the major drawback for the practical existence. Although the recent geopolymer researchers suggested the use of alternative activators from various resources such as palm oil ash, olive ash etc, the application of which are not appreciably promoted due to the complex derivation process. To overcome these effects, in this paper, first time, an attempt is initiated to develop a cost-effective geopolymer concrete by using textile mercerizing water as an alternate activator system. The viability of using mercerizing water instead of commercial sodium hydroxide activator was studied initially. By conducting the pH electrode test and Infrared Analysis, the alkalinity and the presence of sodium metal cations responsible for the reaction kinematics were confirmed. Also, the molar concentration of sodium cations in the mercerizing water was quantified using chemical titration analysis. The feasibility of using mercerizing water in the preparation of geopolymer was assessed using workability, mechanical strength and sustainability. From the results, it was inferred that the developed geopolymer concrete with 100 % textile mercerizing water exhibited the maximum strength of 46.9 MPa, 5.16 MPa and 5.81 MPa respectively under compression, tension and flexure which are almost equivalent and slightly better than the control geopolymer concrete. Also, the developed geopolymer concrete using 100 % textile mercerizing water and the combined flyash-GGBS binder system showcases the highest post-fire residual strength and 48 % reduced water absorption. The cost of construction of geopolymer concrete was significantly reduced by 58.43 % and showed 10.28 % reduced carbon footprint due to the complete replacement of sodium hydroxide solution using textile mercerizing water. The findings of this research work will lead to the development of equivalent molar sustainable activator from the textile mercerizing water and the exploration of eco-friendly and durable geopolymer concrete in an affordable price. [Display omitted] • TMW waste as a 100 % alternative to commercial hydroxide activator. • Alkalinity and reactive metal ions of TMW induced the maximum strength of 46.9 MPa. • GF-TM100 % offered 48 % reduced rate of water absorption and better fire resistance. • Consumption of TMW showed 10.28 % lower carbon footprint than commercial activator. • 58.43 % reduced construction cost in GF-TM100 % geopolymer. [ABSTRACT FROM AUTHOR]

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]