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• All measured values for dose were reported to be lower than the recommended values. • Fly ash as a concrete additive could increase the activity concentration in concrete. • External radiation doses were noted to be influenced by building properties. • Annual organ effective dose rates varied, with the minimum for ovaries and the maximum for testes. Environmental radioactivity in building materials can pose radiological risks to residents by exposure to the emitted gamma radiation and radon. In this study, we evaluated the radioactivity concentration of 53 raw building material samples (fly ash, cement, sand, and gravel) and estimated the dosimetric quantities in outdoor exposure scenarios for residents. The concentrations ranged from 40.1 to 77.4 Bq kg−1 for 226Ra, 27.4 to 91.7 Bq kg−1 for 232Th, and 253.5 to 956.2 Bq kg−1 for 40K. Annual effective dose and organ annual effective dose, were estimated for outdoor exposure scenarios for residents. Fly ash showed the highest values for these dosimetric quantities, while cement had the lowest. The annual organs effective dose rate was found to be minimum for ovaries and maximum for testes. However, all measured values were reported to be lower than the recommended values set by radiation safety organizations worldwide. External radiation doses were noted to be influenced by factors such as air exchange rate, room dimensions, wall thickness, and the type of concrete mixture used. Considering all the dosimetric quantities, the study concludes that the studied building materials might pose low radiological risks to public health. [ABSTRACT FROM AUTHOR]

Premature degradation of concrete, caused by frost damage, has been associated with inadequate transport properties and poor resistance to deicing salt. In this study, transport properties and deicing salt resistance of various kinds of ultrahigh-performance concrete (UHPC) containing Type V portland cement, fly ash, and microsilica were investigated. Seven combinations of cementitious materials (one reference, three binary, and three ternary) were used to batch UHPCs using a water-to-cementitious material ratio (w/cm) of 0.21. The aggregate-to-cementitious material ratio (Va/Vcm) of 1.20 was kept constant for all mixtures. The investigated transport properties included water absorption, volume of permeable voids, water penetration, rapid chloride penetration, and surface resistivity. The transport properties of the plain UHPCs were also compared to those of the corresponding steel fiber–reinforced UHPCs. The test results showed that the transport properties and deicing salt resistance of the studied binary and ternary UHPCs improved with the inclusion and increases in microsilica, replacing a portion of cement. The addition of steel fiber had a minor effect on strength and transport properties and a moderate increase in deicing salt resistance of the studied UHPCs. While rapid chloride penetration and surface resistivity tests were found appropriate to assess chloride transport through the studied plain UHPCs, both tests were deemed unsuitable for the companion steel fiber–reinforced UHPCs. [ABSTRACT FROM AUTHOR]

The extreme demand for aggregate leads to the exploitation of riverbeds for fine aggregates, affecting the environment adversely. Therefore, a suitable alternative to natural river sand is essentially required. This study focuses on preventing environmental impact by developing polycarboxylate ether (PCE) sand to replace natural river sand (NRS). Development of polycarboxylate ether (PCE) sand by mixing high-volume fly ash, bottom ash, cement, natural river sand, and locally purchased high-solid-content polycarboxylate ether–based superplasticizer (HSPCE). All the physical and chemical properties of PCE sand were observed and satisfied the requirement of current standards. PCE sand yields a good specific gravity of 2.31 and is classified as Zone I sand with a satisfactory friction angle (37°) compared with NRS and geopolymer fly ash sand (GFS). Although the water absorption (6.83%) and pH (12.18) are slightly more than those of GFS and NRS, the alkali silica reaction and soundness are well within the permissible limit as per Indian standards. The chemical analysis by X-ray fluorescence showed the presence of high amounts of SiO2 and Al2O3 with magnitudes of 58.879%, and 26.77%, respectively. Finally, the compressive strength of M25 grade concrete using PCE sand and GFS was observed to be 87.51% and 83.82% with respect to NRS after 28 days, respectively. The results of this study indicate that PCE sand can be a good alternative to NRS for construction work because it not only reduces the environmental effect due to sand mining but also focuses on utilizing fly ash and bottom ash. [ABSTRACT FROM AUTHOR]

The abundant natural volcanic ash (NVA) in East Africa is a prospective supplementary cementitious material that may be used to produce green and economical railway concrete. To mitigate the shrinkage of concrete with NVA, internal curing using a superabsorbent polymer (SAP) is employed in this study. The compressive strength, autogenous shrinkage, and drying shrinkage of internally cured concrete with NVA were measured. In addition, the water loss and internal relative humidity of internally cured concrete with NVA were analyzed. The results indicate that the compressive strength of concrete with NVA shows a linear decreasing trend with SAP. In addition, SAP significantly reduces the autogenous shrinkage but slightly increases the drying shrinkage of concrete with NVA. The internal curing using SAP increases the water loss of concrete, whereas the water released from SAP still significantly improves the internal relative humidity (IRH) of concrete. The positive influence of internal curing on the autogenous shrinkage overwhelms the unexpected influence on the drying shrinkage, resulting in the mitigated shrinkage of concrete with NVA. [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]

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]

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]

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]

In today's world, enhancing the performance of recycled aggregate concrete is an essential need, as it ensures the effective utilization of demolished construction waste. The advantages of fly ash and polypropylene fiber in conventional strength concrete are well known. However Further research is required to evaluate the impact of using fly ash, silica fume and polypropylene fiber in case of RA and its effect on the properties of recycled aggregate concrete (RAC). This study evaluates the effects of using 50%, 75%, and 100% recycled aggregate (RA) and 1%, 2%, and 3% polypropylene fiber with a fixed amount of fly ash and silica fume 87 kg/m3 and 21.75 kg/m3. The objective is to determine how these combinations affect concrete strength and durability properties (compression, tensile strength, acid resistance and water absorption). This study also investigates the reliability of non-destructive tests, ultrasonic pulse velocity and rebound number, in the presence of polypropylene (PP) fibers and fly ash with recycled aggregate. The experimental investigation showed that the combination of RA based concrete, fly ash (FA), and polypropylene fiber (PPF) improved concrete durability and strength. The concrete compressive strength made with 50% RA was 13% lesser than that of control concrete, but with the incorporation 3% PP fiber the same mix achieved 5% higher strength than control mix. On the other hand, the concrete compressive strength made with 75% RA and 100% RA was experimentally found 19% and 22% lower, respectively than control mix. The combinations containing constant fly ash and PPF, in addition to 50% recycled concrete aggregate (RCA), demonstrate greater resistance when exposed to sulfuric acid (H 2 SO 4) environments, in comparison to the control mixture. However, the worst performance is shown by mix (100% RA). [ABSTRACT FROM AUTHOR]

[Display omitted] • DFT calculations and experiments are combined to tunne cation types of LDHs. • CaAl-LDH has highest Cl- adsorption capacity, aligned with lowest binding energy. • CaAl-NO 3 -LDH transforms into Friedel's salt after reacted with Cl- • ZnAl-LDH retains the most Cl- after addition of SO 4 2- with crystallinity improved. • Divalent cations dominate LDHs' interlayer spacing and binding energy in some cases. Layered double hydroxides (LDHs) are new concrete additives that improve Cl- sorption capacity by varying their chemical composition. In this work, first-principles calculations were used to design the chemical compositions of LDHs with various cations. Accordingly, four cation types of LDHs (CaAl, MgAl, MgFe and ZnAl) were selected to be synthesized, their Cl- sorption kinetics were further measured. The objective was to establish a high-throughput screening approach to identifying the most promising cations for enhancing the sorption capacity of LDHs towards Cl-. Results revealed that the absolute value of Cl- binding energy increased as the interplanar spacing of different LDHs decreased from first-principles calculations. Particularly, CaAl exhibited the highest adsorption capacity for Cl- (3.25 mmol/g) from experiments, validating the simulation results that it has the highest absolute value of Cl- binding energy. MgFe-Cl-LDH has the smallest absolute value of Cl- binding energy with the lowest adsorption capacity for Cl- as well as the crystallinity. Moreover, multiple factors influencing the Cl- sorption ability of LDHs, such as chemical composition, crystallinity, microstructures and their synergistic effects, are discussed thoroughly based on the experimental results. This study established a connection between the simulation and experimental approaches in understanding the mechanism of Cl- adsorption. [ABSTRACT FROM AUTHOR]

Nano-silicon dioxide (nano-SiO 2) can strengthen recycled aggregates and interface transition zones (ITZs), thereby improving the properties of recycled concrete structures. This study adopted nano-SiO 2 modifications to improve the seismic behavior of recycled concrete shear walls. Quasi-static tests of one natural aggregate concrete shear wall and four concrete shear walls with different replacement ratios (30%, 50%, 70%, and 100%) of nano-SiO 2 modified recycled aggregate (NSMRA) were conducted. The ductility factor, energy dissipation, lateral displacement components, stiffness, and strength degradation of NSMRA concrete (NSMRAC) shear walls were evaluated. The replacement ratio effects of NSMRA on the seismic behavior of shear walls were analyzed. It was determined that the NSMRAC shear walls exhibited higher ductility factor compared to recycled aggregate concrete (RAC) shear walls with similar conditions. The seismic behavior of the shear walls degraded as the replacement ratio of NSMRA increased. Based on the comprehensive evaluation of failure patterns and seismic performance indexes, the replacement ratio of NSMRA is suggested to be taken as 50% in the concrete shear walls. Finally, based on the summary of experiments and studies on the seismic behavior of RAC shear walls with shear failure, the applicability of existing formulae was evaluated by calculating the shear capacity of RAC shear walls, and the effect of nano-SiO 2 modifications on the shear capacity of recycled concrete shear walls was analyzed. • Five concrete shear walls with different modified recycled aggregate replacement ratios were experimentally investigated. • The cumulative energy consumption of the shear walls decreased as the replacement ratio of NSMRA increased. • When NSMRA replacement ratio didn't exceed 50%, NSMRA had limited influence on bearing capacity and ductility of the wall. [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]

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]

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]

Polycarboxylate superplasticizers have been synthesized as copolymers of acrylamide with polyethylene glycol metallyl ether (HPEG), acrylic acid, and 2-hydroxyethylacrylate, with a molecular weight of 25–33 kDa. The copolymers were characterized using GPC and NMR, revealing that during copolymerization, the copolymer includes up to 10 mol.% HPEG 3500 Da. Copolymers at a dosage of 0.12 wt% provide significant retention time of the concrete mix. When considering the same mole ratios of HPEG/(other monomers) in the initial mixture, copolymers containing the carboxylate and hydroxyethyl acrylate group are the most effective. In terms of concrete strength, the use of quaternary copolymers (AA/AM/HPEG/2-HEA) results in a slowdown in strength gain at the ages of 1–3 days, while the strength at the age of 28 days exceeds that of double (AM/HPEG) and triple (AA/AM/HPEG) copolymers. [Display omitted] • Copolymers based on methallyl esters were synthesized for use as plasticizers for concrete. • Quadruple acrylamide copolymers containing 2-hydroxyethyl acrylate units and 6.9 mol.% metallyl ether of polyethylene glycol have the best plasticizing ability and ensure longer workability retention of concrete. • Copolymers ensure the workability retention of concrete for 4 h and can be used as individual admixtures or as slump retention agents for concrete. [ABSTRACT FROM AUTHOR]

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Rheology of Self-Compacting Concrete (SCC) containing selected silica fume dosages (0% (control mix), 5%, 10% and 15%) in a binary binder has been investigated using the flow-curve test protocol implemented on a co-axial cylinder rheometer. At each silica fume dosage, coarse recycled concrete aggregate volumetric replacement levels were 0%, 50% and 100%. Calibration of selected flow models with the measured flow data showed that rheology transitioned from shear thickening to shear thinning as the silica fume dosage increased from 0% to 15%, other mix constituents remaining unchanged. Similar flow behaviour was noted in the SCCs made with the recycled concrete aggregates (SCRACs) across all replacement levels though for a given silica fume dosage, degree of shear thinning decreased with increasing contents of the coarse recycled aggregates. The experimental results have been used to propose a workability box containing bounds for acceptable rheology of the SCCs and the SCRACs. [ABSTRACT FROM AUTHOR]

Polycarboxylate (PCE) superplasticizers are the most important additive in concrete, which can effectively improve the workability of cement slurry. Different from the traditional regarding of PCEs as dispersants, here, we understand the PCEs as nano‐lubricants. By employing the molecular dynamics simulation, a sophisticated model was used to evaluate the interfacial friction between the C–S–H particles. The results reveal that the PCEs can reduce the interfacial friction between the C–S–H particles, and thus increase the fluidity of cement slurry. Further analyses infer the role of PCE segments in lubrication. The carboxylates on PCEs ensure the anchoring and hinder the separation of Ca ions. The side chains are used to lubricate the C–S–H surface, due to the weak adsorption between the side chains and the C–S–H surface. Predictably, this study not only provides a method to directly evaluate the performance of PCEs but also suggests new insights into the colloid dispersion of the low‐water content system. [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]

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]

A circular economy based on symbiotic relationships among sectors, where the waste from one is resource to another, holds promise for cost-effective and sustainable production. This research explores such a model for the agriculture, energy, and construction sectors in California. Here, we develop new an understanding for the synergistic utilization mechanisms for rice hull, a byproduct from rice production, as a feedstock for electricity generation and rice hull ash (RHA) used as a supplementary cementitious material in concrete. A suite of methods including experimental analysis, techno-economic analysis (TEA), and life-cycle assessment (LCA) were applied to estimate the cost and environmental performance of the system. TEA results showed that the electricity price required for break even on expenses without selling RHA is $0.07/kWh, lower than the market price. As such, RHA may be available at little to no cost to concrete producers. Our experimental results showed the viability of RHA to be used as a supplementary cementitious material, meaning it can replace a portion of the cement used in concrete. LCA results showed that replacing 15% of cement with RHA in concrete can reduce carbon dioxide equivalent (CO2e) emissions by 15% while still meeting material performance targets. While the substitution rate of RHA for cement may be modest, RHA generated from California alone could mitigate 0.2% of total CO2e from the entire cement production sector in the United States and 1% in California. [ABSTRACT FROM AUTHOR]

Using ordinary Portland cement (OPC) in concrete has significant environmental and sustainability concerns. Notably, in the production of OPC, large volumes of greenhouse gases are produced, which contribute to global warming, and large amounts of natural raw materials are used, which can lead to the depletion of nonrenewable resources with time. In addition, OPC production is highly energy-intensive. To mitigate these concerns, it has become common practice to reduce the amount of OPC used in concrete production by partially replacing OPC with a supplementary cementitious material (SCM). Most of the SCMs used have pozzolanic properties and react with free lime in OPC to provide more cementitious material, which increases the long-term strength of concrete and also densifies the pore structure, resulting in improved durability in harsh environments. This study explored the effect of OPC on the resistance to sulfuric acid attack and drying shrinkage when OPC is partially replaced by processed bagasse ash (PBA) at dosages of up to 50%, together with 5% silica fume. Both materials are pozzolanic and are expected to react with free lime in OPC concrete to increase the strength and densify the concrete; however, with increased PBA dosage, the cement is diluted, and a reduction in strength can be expected. This study explores the benefits that can be realized, focusing primarily on sulfuric acid resistance and the reduction of drying shrinkage. [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]

This study investigated the suitability of recycled asphalt pavement and polyethylene wastes as coarse aggregate in asphaltic concrete by evaluating the impact of the use of polyethylene polymer wastes and recycled asphalt pavement composite as aggregates on the physical and mechanical properties of the asphaltic concrete. The physical characteristics of the aggregate and bitumen were determined using relevant parametric tests. Recycled asphalt pavement was used to make asphaltic concrete samples using LDPE at 5%, 10%, 15%, RAP at 5% and HDPE at 5%, 10%, 15%, and a mixture of LDPE + HDPE at 5+5%, 7.5+7.5% and 10+10% RAP at 5% as additives. Marshall Stability test was conducted to assess the mechanical strength of the asphaltic concrete, and the results included information on the aggregate's stability, flow, density, voids filled with bitumen, voids filled with air, and voids in mineral aggregate. In addition, the surface and crystal structure of the aggregates was studied by carrying out a microscopic examination with a Scanning Electron Microscope (SEM) and X-Ray diffraction (XRD). The results obtained from this study demonstrated that RAP, HDPE & LDPE are viable conventional aggregate substitute for asphalt concrete production. [ABSTRACT FROM AUTHOR]

Aiming for an all-solid waste concrete, a quaternary solid waste binder (SWBs) system comprising blast furnace slag, fly ash, desulfurization gypsum, and Bayer red mud was developed and utilized for both binders and preparation of cold bonded artificial aggregates. The first section investigated and discussed the hydration properties and strength gain mechanism of SWBs, revealing that ettringite formation and growth contribute to early age strength development of SWBs, while C-A-S-H formation contributes significantly to the later strength gain. The second section systematically studied the concrete performances, including mechanical properties, shrinkage, chlorides, and seawater resistance. An all-solid waste-based concrete strategy was presented by gradually substituting cement and natural aggregates. It was observed that SWBs-based concrete exhibited significantly lower shrinkage and excellent chloride ion resistance, although slightly lower mechanical properties were observed. The solid waste-based artificial aggregates proved viable alternatives to natural rock aggregates in low-strength concrete classes. Incorporating artificial aggregates endowed the concrete with self-curing properties and reduced its shrinkage and chloride migration, with only a minor effect on its mechanical strength. Lastly, an all-solid waste concrete combining the characteristics of SWBs and cold-bonded artificial aggregates was achieved. The resulting concrete exhibited lower shrinkage and excellent chloride and seawater resistance. This study provides a reference for designing and developing solid waste-based binders and concrete. [Display omitted] [ABSTRACT FROM AUTHOR]

A comparative evaluation of the single and combined effect of nanoparticles (NPs) on the static and impact properties of concrete is presented. Different NPs (silicon dioxide, aluminium oxide and ferric oxide) were used separately and in combination as partial replacements of cement at 0.5% and 1% by weight of cement. The effects of the NP additions on the unit weight, compressive strength, split tensile strength, flexural strength, toughness, fracture energy and impact performance of concrete were experimentally examined. The effects of the NPs on the microstructure of concrete was investigated using scanning electron microscopy (SEM). The cost effectiveness of the use of NPs in concrete was also assessed in order to evaluate the commercial production of NP-doped concretes. Desirability function analysis was also conducted to compare the overall performance of the concretes. The addition of NPs had a positive effect on improving the mechanical performance of the concrete, with the addition of NPs increasing the compressive strength, split tensile strength, flexural strength and energy absorption capacity. The NPs did not have any significant influence on the unit weight of the concrete. SEM analysis showed that the use of NPs improved the concrete microstructure, but the NPs did not have a good influence on the impact performance of the concrete. [ABSTRACT FROM AUTHOR]

This study investigates the synthesis and electrochemical performance of cobalt-BTC acid-based metal-organic frameworks (Co-MOFs) under different hydrothermal conditions. The crystal growth was controlled by varying the concentration of NaOH during synthesis, resulting in three Co-BTC MOF varieties (labeled as COMOFDW-0mM, COMOFDW-3mM, and COMOFDW-6mM). Exhaustive structural-microstructural characterizations, including X-ray diffraction (XRD), scanning electron microscopy (SEM), and N 2 adsorption-desorption isotherms, elucidate the structural and morphological variation among these Co-BTC MOF varieties. The crystal structures of COMOFDW-0mM and COMOFDW-3mM exhibit similar laminar configurations, while COMOFDW-6mM shows major variations, such as changes in the coordination modes between BTC and cobalt complexes and differences in BTC plane directions in MOF crystal faces. SEM images reveal distinctive needle-like morphologies, and the as-synthesized crystals exhibit varying aspect ratios. Nitrogen adsorption-desorption isotherms indicate variations in the presence of micropores and mesoporosities, revealing microstructural differences. Electrochemical evaluations in a three-electrode system reveal superior performance for COMOFDW-6mM, with a maximum specific capacitance of 261.27 F/g, an energy density of 7.34 Wh/kg, and a maximum power density of 1325.2 W/kg under 2 M KOH electrolyte. Two-electrode coin cell measurements further validate its potential, maintaining competitive capacitance values. This systematic exploration of Co-MOFs not only elucidates the impact of growth conditions on crystal structures but also underscores the potential for tailoring electrochemical properties. Moreover, the findings present opportunities for further enhancements through composite strategies, opening new avenues for advancing MOFs in energy storage applications. [Display omitted] • Controlled, large-scale, highly oriented, single crystals of Co- BTC MOFs are synthesized hydrothermally. • Deionized water was utilized as a solvent instead of any other organic solvent. • Addition of Different molar conc. of NaOH before putting in the furnace led to the different size crystals. • Higher conc. of NaOH exhibited smaller average-size Crystals. • Coin cell device demonstrated high energy and high-power density commercially acceptable. [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]

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]

Recently, the usage of a cold-bonded method in the production of artificial green geopolymer coarse aggregates (GCA) has been crucial from an economic and environmental perspective because the sintering method consumes an enormous quantity of energy and generates a significant quantity of pollutants. This research investigated the manufacture of GCA via cold-bonded pelletization using two distinct industrial byproducts (GGBFS and FA) via a new and simpler pelletization technology. Three different binders were used to produce three distinct types of GCAs as partial replacements for natural coarse aggregate (NCA) at varying replacement rates (0%, 25%, 50%, and 75%). The first group used ground-granulated blast furnace slag, while the second used GGBFS with perlite, and the third used FA with perlite. An alkaline activator was commonly used with all three groups. The physical and mechanical properties of three distinct varieties of GCA were recorded. The results indicated that the mechanical and chemical properties of three different types of GCAs were nearly identical to those of natural aggregate, with the exception of their increased water absorption. According to the findings, the recommended mixtures were suitable for usage in the construction industry. The results indicated that the ratio of all investigated attributes declined as the number of GCAs increased. In contrast, lightweight concrete can be obtained at a ratio of GCA (FA with perlite) equal to 75%, where unit weight, compressive, splitting tensile, flexural, and water absorption strengths were 1.87 gm/cm3, 20.2 MPa, 1.8 MPa, 8 MPa, and 6.0%, respectively (FA with perlite). [ABSTRACT FROM AUTHOR]

Reinforced concrete (RC) is one of the most widely used building materials. However, RC, especially in coastal seaside or humid environments, can suffer reinforcement corrosion with the result that the reinforcement fails to perform its function over time. The effect of a retarder additive used to eliminate loss of consistency in hot, windy and humid weather on the corrosion of RC elements was investigated in this work. Four different concrete types were assessed, with 0%, 1%, 1.5% and 2% additions of the chemical additive. Along with accelerated corrosion and pressure tests, physical properties such as electrical resistivity, water absorption, porosity, unit weight and capillary water absorption were also determined. The results of this work indicate that the use of up to 2% of the setting retarder did not pose a problem in terms of the physical and mechanical properties of the concrete. However, in terms of the frequently encountered corrosion problem, the use of 1.5% is more appropriate. Many chemical additives are used for different purposes in concrete and it is suggested that, alongside physical and mechanical properties, durability characteristics should also be examined when determining the suitable ratios of these additives. [ABSTRACT FROM AUTHOR]

This study investigates the feasibility and effectiveness of employing waste ceramic (WC) in rigid pavement as a replacement for fine aggregate. WC was integrated into concrete; untreated and treated with a silane compound, where 30 wt.% and 50 wt.% sand was replaced with WC. The workability, compressive strength, water absorption, skid resistance, microstructural analysis, and surface chemistry of mixtures were evaluated. The results illustrated the positive impact of using treated WC on the water absorption of mixtures, where a maximum reduction of 19% was achieved in the mixture with 50% treated WC. Moreover, concrete with 30% treated WC attained a higher compressive strength of 43 MPa than its untreated counterpart, which achieved 29 MPa, when tested at 28 days. The integration of treated and untreated WC in concrete pavement reduced its skid resistance due to the presence of glaze in the untreated mixture and silane in the treated mixture. The morphological and surface chemistry analyses confirmed the development of C–S–H, CaCO3, and SiO2 in high contents in concrete with silane-treated WC. Also, a strong bonded interfacial transition zone was noticed in concrete with silane-treated WC, unlike concrete with untreated WC, which had a poor interfacial transition zone. [ABSTRACT FROM AUTHOR]

The advantages of using geopolymer materials instead of cement in concrete are not limited to high durability properties. geopolymer concrete was introduced to mitigate the environmental damages caused by CO2 emissions and the great level of fossil fuels consumption during cement manufacturing. In the present investigation, a number of experimental studies were conducted on slag-based geopolymer concrete. Accordingly, nano-silica particles were used to improve the geopolymer concrete structure's matrix. In the current study, slag-based geopolymer concrete was used with 0–2% polyolefin fibres and 0–8% nano-silica. They were subjected to water absorption and permeability tests to assess their durability. The addition of nano-silica enhanced the whole properties of the slag-based geopolymer concrete. By using the nano-silica, the concrete paste microstructure became denser and more homogeneous, and the pores decreased. The compressive strength and tensile strength of the concrete increased by up to 22% and 14% respectively. On the other hand, in terms of durability, the nano-silica lowered the water absorption and permeability coefficients by up to 24% and 44%, respectively, by filling the pores of the concrete. In the weight loss test, geopolymer concrete achieved superior results (up to 16%) compared to ordinary concrete. [ABSTRACT FROM AUTHOR]

Additive manufacturing with concrete – guidance for planning and implementation of projects This guideline, created by the DAfStb Working Group "Digital Concrete Construction through Additive Manufacturing," serves as a comprehensive resource to support the planning and implementation of additive manufacturing projects in concrete construction. It is intended for architects, planners, applicants, material manufacturers, construction companies, and other parties involved in construction. After a brief introduction to the classification, terminology, and methods of additive manufacturing, legal aspects and approval procedures are highlighted to ensure seamless integration of this technology into construction practice. The guide addresses the integration of additive manufacturing methods with concrete into construction law, explains the approval process, and offers assistance for coordinating responsibilities in projects. It addresses technical rules for the design and construction of structures, particularly for walls produced by additive manufacturing, and covers constructive aspects of reinforcement. An important component is concrete and component testing, including methods for sample preparation and testing procedures for fresh and hardened concrete, making the guide a useful tool for professionals in the field of digital concrete construction. [ABSTRACT FROM AUTHOR]

Recycled concrete aggregate (RCA) is an important form for reusing of waste concrete. However, the presence of corrosive ions, specifically chloride ions, which are absorbed on the surface of RCA or infiltrated from the external environment, significantly affects the mechanical performance and durability of recycled aggregate concrete (RAC). This paper aims to suppress the erosion and diffusion of chloride ions in RAC by adding calcined layered double hydroxides (LDOs), utilizing the restructuring and anions exchange properties of LDOs. The dissolution ratio of chloride ions carried by RCA and the adsorption efficiency of LDOs on the leaching ions were analyzed using the silver nitrate titration method. The maximum chloride adsorption capacity of the LDOs is 31.052 mg/g. Additionally, the inhibitory effect and mechanism of LDOs on chloride ion attack were detailed evaluated by the techniques combining mercury intrusion porosimetry (MIP), scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM and EDS), rapid chloride migration coefficient method (RCM), and electrochemical impedance spectrum. The results indicate that LDOs exhibit a good adsorption effect on chloride ions leaching from RCA, and the adsorption efficiency is negative correlation with the pH value. Furthermore, the small size effect of LDOs plays a filling role in the pores of concrete, increasing the compactness and penetration resistance of chloride ions of RAC. This work provides a promising approach to enhance the mechanical and durability properties of RAC by incorporating with LDOs utilizing its chloride ion capture feature and nano-filling effect. And the findings of this research can also be extended to the use of LDOs for treatment of other corrosive anions, such as SO 4 2− and CO 3 2− in RAC, demonstrating its applicability in a broader context. [ABSTRACT FROM AUTHOR]

Concrete is an important material for the construction of buildings, and highways. However, natural resources are being depleted by using natural coarse or fine aggregates for the production of concrete. The substitution of natural coarse aggregate (NCA) with recycled coarse aggregate (RCA) efficiently manages construction waste and preserves natural resources. In the present study, 50 and 100% NCA have been replaced with RCA for the preparation of recycled aggregate concrete (RAC) with blended hydrated-brick powder (RAC-HBr). Additionally, cement was replaced by 10 and 20% of blended HBr in the preparation of RAC mixes. To investigate the strength and durability properties of RCA-HBr mixtures, compressive strength, water permeability, chloride penetration test, and ultrasonic pulse velocity (UPV) tests were conducted. The outcomes indicate that the optimum percentage of blended HBr enhances the compressive strength of RCA mixes. However, blended HBr positively influenced the RCPT, water permeability, and ultrasonic pulse velocity of the RCA concrete mixes. Further, the RCPT outcomes show that the chance of corrosion was reduced by 20%, while the UPV value confirms that the density of the RAC-HBr mixes was enhanced by 28.7% at the age of 56 days. Furthermore, based on the FESEM and EDS analysis, the pozzolanic materials have densified the concrete matrix by reducing the pores and voids of RAC-HBr mixes. Thus, practically, 100% RCA with blended hydrated lime and brick powder can be used to create M35-grade concrete. The current paper investigates the effect of blended HBr on the properties of RAC. 10% HBr was an optimum percentage which has significantly enhanced the strength and durability characteristics of RAC mixes. CSH gel CH crystals densify the concrete matrix. CSH gel and CH crystals were confirmed from the microstructure analysis through FESEM and EDS analysis. [ABSTRACT FROM AUTHOR]

Modern concrete technology places a strong emphasis on incorporating diverse resources, particularly industrial byproducts, into the concrete production process. The utilization of fly ash, a notable industrial waste, has gained increasing importance due to its potential to enhance concrete properties and provide economic advantages. In this study, we conducted experimental investigations on concrete, varying the concentrations of graphene oxide (ranging from 0.1% to 0.5%) and coal ash (at levels of 5%, 10%, and 15%). We evaluated the mechanical characteristics of concrete, including compressive strength, tensile strength, and flexural strength, by creating a total of 45 different mix specimens across 15 distinct mix formulations. Remarkably, the combination known as 4GOCA (Graphene Oxide and Coal Ash at 5%, 10%, and 15%) exhibited the highest strength, demonstrating a remarkable 65% increase compared to the reference mix. Similarly, both 2GOCA and 3GOCA demonstrated strength gains exceeding 50%. The unique aspect of this research lies in its innovative utilization of graphene oxide and coal ash in the concrete mix, showcasing the potential for sustainable and high-performance construction materials. [ABSTRACT FROM AUTHOR]

The aim of this study is to promote the application of the excited zeolite powder (ZP)with aeolian sand powder (ASP) in the field of aeolian-sand concrete (ASC) production. This study utilises NaOH to treat composite cementitious materials containing aeolian sand and zeolite powders, which were used to replace 50% of the cement in aeolian-sand concrete (ASC). Production of alkali-inspired cement-based windswept concrete(AAZC).The mechanical properties of treated ASC considerably improved, especially when the NaOH dosage was 4% by mass. After curing this sample (denoted as AAZC-4) for 28 d, its compressive strength improved by 17.2%, and its split tensile increased by 16.3%. Potassium feldspar and montmorillonite in zeolite powder and SiO2 in the sand were decomposed by OH− and combined with other elements to generate various silicate gels and A-type potassium zeolite crystals inside the concrete. Microscopic examination showed that the gels and crystals intertwined to fill the pores, decreasing (increasing) the percentage of large (small) pores, thus optimising the pore structure. This substantially improved the mechanical properties of ASC. Freeze–thaw salt-intrusion tests showed that the extent of mass loss, degree of damage and loss of compressive strength of AAZC-4 were similar to those of ordinary concrete but were reduced by 36.8%, 19% and 52.1%, respectively, compared with those of ASC. Therefore, AAZC-4 has a sustainable working performance in chloride-ion permeable environments in cold and arid areas. [ABSTRACT FROM AUTHOR]

Externally bonded strengthening technique to the concrete has been widely used with epoxy adhesive. However, the adhesive is considerably weak against high temperatures, which has been regarded as the critical point in the loss of integrity of the strengthened system. Alternatively, geopolymer materials have shown an excellent performance at high temperatures, thus, their potential to be used as adhesive material has been investigated in this work. In experimentation, the composite specimens were developed using both types of adhesives, epoxy and geopolymer, and their performance was evaluated at three temperature levels (20, 60, and 120°C) by conducting pull‐off strength tests and classifying their failure modes. It was observed that the strength of concrete and epoxy was reduced with temperature. In contrast, the strength of geopolymer‐based adhesives strength was increased due to the reactivity of the precursor at high temperatures. Also, bond strength was reduced for both composite specimens at elevated temperatures. The highest bond strength was observed for the epoxy‐based adhesive system at 20°C, and about 70% loss in bond strength was observed when exposed to 120°C. The failure mode was also shifted from concrete to adhesive interface failure, that is, failure between the adhesive and the fiber fabric layer. The geopolymer‐based adhesive system has lower strength than its counterpart at all temperature levels, and the failure mode was adhesive interface failure. To enhance the bonding capacity at high temperatures, efforts are being made by adding different minerals has been employed. From the experimental results, it was found that there were some improvements, however, it was still less than that of epoxy‐based system. Further optimization of the geopolymer adhesive using minerals is required and then high‐thermal resistance geopolymer adhesive can be established. [ABSTRACT FROM AUTHOR]

Conduct alkali silica reaction (ASR) tests on concrete by using cement with different alkali contents and according to different test standards. The influence of cement alkali content on the alkali-silica reaction of concrete was explored, and the effects of different test methods on the results of alkali-silica reaction tests were compared. The results indicate that: the type of cement and the testing method used have no significant impact on the experimental results of the alkali silica reaction. The rate of alkali silica reaction accelerates with the increase of cement alkali content. When the alkali content of cement is greater than 2.0 %, there is no potential harm of alkali silica reaction in the aggregate, which will cause harm of alkali silica reaction. The research conclusion can provide reference for the control value of alkali content in engineering cement. [ABSTRACT FROM AUTHOR]