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Mining wastewater (MWw) in tailing ponds is one of the major obstacles in reusing tailings in practice and should be disposed preferentially. This paper investigated the feasibility of exploring MWw from copper mining as a source of mixing water to prepare activators for alkali-activated slag materials (AASM). Four MWws with different concentrations were prepared by using MWw to replace all, 1/2, 1/3, and 1/4 of tap water. The influences of different MWws on the setting time, hydration kinetics, hydration products, compressive strength, nano-mechanical properties, pore structure of AASM were investigated. Experimental results confirmed that MWw can be upcycled as the partial or total mixing water for alkali-activated slag materials. The influence of MWw on the properties of AASM was related to its concentration. MWw with low concentrations accelerated the hydration of slag at early ages, nevertheless raw MWw without dilution slightly impeded the hydration process. Although no new hydration product is induced by adding MWw, both NMR pore analysis and nanoindentation testing suggested that the addition of MWw densified the hydration products, which is beneficial for mechanical properties of AASM. As a result, the 28d compressive strengths of AASM increased with increased concentrations of MWw by − 0.8 to 19.9%. Through this paper, a low-cost, green and practical method was developed as an option for the disposal and recycle of MWw. [Display omitted] [ABSTRACT FROM AUTHOR]

The high-value utilization of sulfate-rich tailings (SRCTs) can accelerate their mass consumption, so the many problems caused by the massive accumulation of SRCTs can be alleviated, such as environmental pollution, land occupation, security risk, etc. This study proposes using SRCTs to replace fine natural aggregates in MgO-activated slag materials (MASMs) and investigate the influence of the sulfur content in SRCTs on the properties of MASMs. The experimental results showed that the 28 d compressive strength of MASM mortars was increased by up to 83% using SRCT composites. Two major mechanisms were discovered: additional hydration product formation and pore structure refinement. The results of XRD suggested that incorporating SRCT composite into MASMs increased the production of expansive sulfate-containing hydration products, such as ettringite, gypsum, and hydroxyl-Afm. The results of element mapping showed that the oxidation of pyrite in SRCTs could release sulfates into the surrounding area and participate in the hydration of MASM, indicating that SRCTs can work as an auxiliary activator for MASMs. Furthermore, the addition of SRCT significantly refined the pore structure of MASMs, leading to the reduction in porosity by up to 37.77%. These findings confirm a synergistic effect on activating the slag between SRCTs and MgO, promoting the mass utilization of SRCTs. As a result, the additional expansive hydration products contribute to the enhanced compressive strength and refined pore structure. [ABSTRACT FROM AUTHOR]

Based on the controllability of the pore structure of perforated cenospheres (PCs), this study utilized PCs with different etching concentrations for the internal curing of alkali-activated slag (AAS), aiming to achieve the optimal etching parameters for efficient internal curing. Three etching concentrations (0.3 M, 0.7 M, 1.0 M) were set to investigate the effects of water-filled PCs on the performance of internal curing of AAS mortars. The results indicated that the water released from the PCs delayed the hydration of AAS and maintained high internal relative humidity. The chemical shrinkage of AAS could be reduced. Water-filled PCs internal curing promoted the generation of hydration products around the PCs and increased their packing density, leading to a reduction in mesopores and a 12.7—27.7% increase in elastic modulus at 28 d. With the optimal etching concentration of 0.7 M, water-filled PCs significantly mitigate the autogenous shrinkage by 75.8% while enhancing the compressive strength of AAS mortars. • Three etching concentrations of perforated cenospheres (PCs) were investigated for the internal curing efficiency of AAS. • PCs internal curing increased the internal relative humidity and reduced the chemical shrinkage. • PCs internal curing enhanced the packing density and elastic modulus of hydration products. • The optimal 0.7 M etching concentration reduced autogenous shrinkage by 75.8% and enhanced compressive strength. [ABSTRACT FROM AUTHOR]

The hydrophobicity nature of the waste carbon fiber felt (WCF) surface results in the formation of a weak interface with the paste during the curing process of WCF concrete, which seriously affects the performance of WCF concrete and the reuse of WCF. To address this problem, this paper utilized polydopamine (PDA) for the functionalization of WCF to enhance bonding between WCF and paste. The wettability, Ca2+ complexation, and functional groups of PDA coating on WCF were analyzed by contact angle, ICP-OES, and XPS, respectively. Additionally, the effects of incorporating PDA-functionalized WCF on the flowability, compressive strength, hydration kinetics, pore structure, water absorption capillary, and SEM of mortars were tested. Experimental results showed that the PDA coating improved the wettability of WCF and enhanced the flowability of WCF mortar. What's more, the PDA coating could chelate Ca2+ and promote the formation and deposition of hydration products on the WCF surface, resulting in a denser interfacial transition zone (ITZ). Compared with ordinary WCF mortar, the compressive strength of the PDA-modified WCF mortar was increased by 18% at 28d. Furthermore, the capillary water absorption of the modified group mortar was also decreased by up to 13%, significantly enhancing the durability of mortars. This paper presents a green and simple bio-inspired method to strengthen the ITZ between WCF and paste, which is fundamentally different from the traditional modification methods, and also offers a theoretical basis and technical foundation for the sustainable utilization of WCF. • Introducing hydroxyl and amino groups on WCF using PDA. • The contact angle of WCF was maximum decreased to 40.49°. • The interface gap of WCF/paste was enhanced owing to the chelation of PDA with Ca2+. • The compressive strength of WCF mortars modified by PDA was improved from 39.43 MPa to 46.52 MPa at 28d. [ABSTRACT FROM AUTHOR]

• Simulated cement pore solution was proposed as the pre-wetting agent for lightweight aggregates. • The compressive strength of lightweight concrete can be obviously increased through the proposed technology. • The ITZ of lightweight aggregates was enhanced by the release of simulated cement pore solution. • Saturated cement solution can be the optimal pre-wetting agent. Lightweight aggregates (LWAs) are typically pre-wetted to prepare lightweight concrete. However, the incorporation of pre-wetted LWAs by water, may dilute the pore solutions of the cement matrix surrounding the LWAs during the process of internal curing. To this end, this paper proposes an alternative pre-wetting method for LWAs using simulated cement pore solutions (saturated Ca(OH) 2 or real cement solution) instead of water. The effects of LWAs pre-wetted by various agents on the performance of lightweight high-performance concrete (LW-HPC) were investigated and compared. Experimental results confirmed that water released from LWAs diluted the pore solutions of cement in LW-HPCs. By using cement solution and Ca(OH) 2 solution, the compressive strengths of LW-HPCs were respectively increased by 41.7% and 28.2% at 3d, and 11.6% and 3.2% at 28d compared with LWAs pre-wetted by water only. Among the three pre-wetting agents, the saturated cement solution was found to be the optimal one for promoting the hydration of cement, elastic modulus of the interfacial transition zone, and compressive strength. [ABSTRACT FROM AUTHOR]

• Fluoroacid etching wastewater for producing perforated cenospheres can be used for preparing alkali-activated slag. • The wastewater's elevated alkalinity and substantial Ca2+ content facilitated the activation of slag. • The addition of the wastewater increased the 28d compressive strength of mortars by 6.0–24.6%. • Significant economic and environmental benefits can be generated by recycling the wastewater. The fluoroacid etching process to produce perforated cenospheres generates a considerable volume of waste etching water, yet no effective strategy has been proposed for the treatment or reutilization of this environmentally harmful wastewater. In light of this, the present study explores the feasibility of utilizing lime-treated etching wastewater (LTEW) as a potential source of mixing water for alkali-activated slag (AAS). LTEW exhibits a high concentration of Ca2+ and possesses strong alkalinity, making it potentially suitable for activating slag. The experimental findings revealed that the addition of LTEW enables a reduction in the concentration of the activator, NaOH solution, due to the presence of Ca2+ and NH 4 + within LTEW. Consequently, the setting and hydration processes of AAS were retarded in correlation with the incorporation of LTEW. However, the reaction between Ca2+ in LTEW and NaOH resulted in the formation of Ca(OH) 2 , which could act as an auxiliary activator for AAS. Furthermore, the presence of expansive Ca(OH) 2 crystals, possessing a higher elastic modulus compared to C-S-H gel, refined the pore structure of the mortars. The addition of increasing amounts of LTEW exhibited a gradual improvement in the compressive strengths of the mortars at all ages, ranging from 2.2% to 23.5% at 3 days, 2.4% to 21.6% at 7 days, and 6.0% to 24.6% at 28 days. The utilization of LTEW in AAS preparation offers significant economic and environmental benefits. [ABSTRACT FROM AUTHOR]

• Pre-carbonation can be a solution to the incompatibility of calcium carbide slag with cement. • The generation of CaCO 3 through the carbonation of calcium carbide slag refined the pore structure of mortars. • The carbonation process of calcium carbide slag was characterized. • Calcium carbide slag can be a good CO 2 absorbent. To promote the utilization of high-calcium and high-alkali calcium carbide slag (CCS) in the construction industry, a pre-carbonation method has been employed to convert Ca(OH) 2 in CCS to CaCO 3 to improve the compatibility of CCS with cement. The study investigated the effects of different carbonation durations (10 min, 20 min, and 30 min) on the performance of CCS mortars. Results showed that 30 min carbonation duration for CCS achieved a 24.83% CO 2 uptake and converted 92.2% of Ca(OH) 2 to CaCO 3 , thereby reducing the pH of the CCS suspension from 12.5 to 11.4. Moreover, the carbonation process generated CaCO 3 , which acted as seed and filling effects, accelerating, and promoting the hydration of the mortar. This led to an optimized pore distribution and a denser microstructure at 28d. The mortar with carbonated CCS for 20 min demonstrated the highest compressive strength, exhibiting an enhancement of 0.8% to 41.4% at 3d, 7d, and 28d compared to un-carbonated CCS mortar. These experimental findings provide a sustainable and efficient solution for the consumption of CCS in the construction industry. [ABSTRACT FROM AUTHOR]

[Display omitted] • The pore structure of perforated cenospheres can be fully controlled by adjusting the etching conditions. • Increasing the etching concentration can significantly increase the porosity of the perforated cenospheres. • The perforated cenospheres with a higher porosity exhibited better water release characteristics at high relative humidity. • The autogenous shrinkage of the mortars was drastically reduced by using highly porous perforated cenospheres as internal curing agents. • Oxalic acid can replace hydrochloric acid to prepare the etching solution. The pore structure of internal curing agents can significantly influence their effectiveness in reducing the autogenous shrinkage of cementitious materials with low w/b ratios. Optimization of their pore structures is meaningful, whereas it is rarely concerned. This study demonstrates that the pore structure of the perforated cenosphere can be adjusted to achieve a better internal curing performance. Increasing the etching duration can expose the own pores of cenospheres at an etching concentration of 0.7 M, gradually increasing the porosity of the perforated cenospheres. A higher etching solution concentration can significantly increase both size and number of the perforating holes. The results of the desorption properties test showed that more porous perforated cenospheres released up to about 90 % of the carried water to the surrounding environment at a higher rate, thereby achieving better effectiveness in reducing the autogenous shrinkage of low w/b cement mortars. An optimal etching condition that an etching duration of 15 min and a concentration of etching solution of 0.7 M were confirmed to prepare perforated cenospheres to almost eliminate the autogenous shrinkage of cement mortars. In addition, it is confirmed that a non-volatile acid, oxalic acid, can be used to replace hydrochloric acid to prepare the etching solution for cenospheres. [ABSTRACT FROM AUTHOR]

• Vitamin-C (VC) can be used as a retarder for calcium sulfoaluminate cement (CSA). • Addition of 0.5% or 1% VC prolonged the setting times of CSA over 200 min without compromising 28d compressive strength. • Pore structure of CSA mortars was refined by VC. • The size of ettringite crystal was reduced by VC. Vitamin-C (VC), also known as ascorbic acid, is a water solvable vitamin and can be found in various plants. Its function as an essential nutrient for human being is well known and has been extensively studied. This study explores a novel application of VC as a retarder for calcium sulfoaluminate cement (CSA). CSA has gained significant research interest for its potential as a low-carbon alternative of ordinary Portland cement (OPC). However, CSA sets very fast, leaving very limited processing time. Experimental studies carried out in this study show that the setting times of CSA can be extended over five times by adding VC at only 0.5% of the weight of the cementitious material. More importantly, this addition of VC doesn't reduce the compressive strength of the produced mortar samples at 28d because their pore structure is refined by the added VC. The retarding mechanisms of VC on CSA can be attributed to both the surface adsorption and complexation with Ca2+. [ABSTRACT FROM AUTHOR]

This study was conducted to investigate the influence of gallic acid (GA), the smallest molecular unit of tannic acid, on the performance of metakaolin (MK) mortars. GA was added directly as an admixture (Method I) or pre-mixed with MK (Method II) for bio-functionalization. Experimental results showed that GA improved the dispersion of MK by generating electrostatic repulsion and spatial site resistance between particles. The GA functionalization of MK by Method II displayed superior efficiencies in adjusting the fluidity of mortars owing to better dispersibility. The functionalization of MK by GA could enhance the pore filling effect resulting from the dispersed MK, and enable more products to be generated owing to the formation of GA ∼ Ca intermediates, contributing refined pore structure and increased compressive strength to mortars. The compressive strength of MK mortars has been optimally increased by 13.0—18.0% when using 0.1% GA. • Two bio-functionalization methods for MK were proposed. • GA promoted mortar hydration by dispersing MK and GA ∼ Ca seed. • GA functionalized MK reduce the porosity of mortars by filling the pores. • Method II achieved better fluidity and higher compressive strength than Method I. [ABSTRACT FROM AUTHOR]

[Display omitted] • The heat welding method can be used as a green, easily available, and economical way to modify the polypropylene (PP) surface. • The fly ash fixed on the surface of PP by heat welding can effectively improve its wettability and pozzolanic activity. • With the addition of F@PP, the microscopic pore structure of the mortar is more compact, and the mechanical properties are greatly enhanced. • The hydration products of the F@PP interface play the role of "micro-pile" in connecting the paste and PP. The weak bonding of plastic/paste caused by the hydrophobicity of plastic surface is a significant bottleneck for the large-scale application of plastics in concrete, which seriously affects the macro and micro structure of plastic concrete. To address this issue, a heat welding modification method was proposed in this paper, which utilized the thermoplastic of the plastic, fly ash was welded to the polypropylene (PP) surface to form a composite aggregate with fly ash properties (F@PP). Experimental results revealed that F@PP exhibited better wettability (contact angle = 75°) and pozzolanic activity compared to unmodified PP. Moreover, compared to PP mortar or F/PP mortar (simply add fly ash to PP mortar), the microscopic interface of F@PP/paste was more compact and its Ca/Si was mostly reduced to less than 2.0. The porosity of F@PP mortar was significantly reduced by 50–57% at 28d and the compressive strength was increased by 11–28% at 3d, 7d, and 28d. These findings highlight the effectiveness of the proposed heat weld method in enhancing the plastic/paste interface and the performance of plastic mortars. [ABSTRACT FROM AUTHOR]

• Tannic acid (TA) is exploited as an eco-friendly admixture to disperse MK. • TA dispersion densifies the hydration products. • Low-density calcium hydrate silicate was converted to high density by the TA dispersion. • Compressive strength of cement mortar at 28d was enhanced up to 97% by TA dispersed MK. Partially replacing ordinary Portland cement (OPC) with metakaolin (MK) can refine the pore structure, improve mechanical properties, and enhance the durability of concretes. However, MK tends to agglomerate due to its high surface area and high concentration of hydroxyl groups. To overcome this problem, this study exploits a plant-derived polyphenol, tannic acid (TA), as an eco-friendly admixture to disperse MK. Due to its similar chemical functional groups as the adhesive protein in the mussel byssus, TA can adhere to various surfaces like the mussel's adhesive protein. An experimental program was carried out to characterize the TA treated MK and investigate the effects of the proposed method on the properties of the cement paste and mortar. After mixing with the MK, TA can be adsorbed on the surface of MK particles, achieving deflocculation and dispersion of mineral grains by electrostatic repulsion forces and steric effect, significantly improving the workability of the mortar. Pore structure analysis suggests that TA dispersion densifies the hydration products, as revealed by the much-reduced gel and interhydrate pores. The nanoindentation results indicated that all low-density calcium hydrate silicate (C S H) was converted to high density by the TA dispersion, leading to a drastic improvement in the compressive strength of the produced mortars. As a result, the 28 days compressive strength of cement mortar prepared with TA dispersed MK was enhanced by up to 97 % compared with the one prepared without MK substitution, which exhibits great potential in reducing the carbon footprint of cement-based construction materials. [ABSTRACT FROM AUTHOR]

• Naturally occurring compound, Tannic acid is used to treat fine recycled concrete aggregate (RCA). • Microstructure and quality of fine RCA are significantly improved by the treatment. • Over 50% reduction on the total porosity of the mortar can be achieved by the treatment. • Up to 25% increase in compressive strength can be achieved by the proposed treatment. A massive fraction of recycled concrete aggregates (RCAs) is fine RCA. Once recycled in new concrete, fine RCA can significantly reduce the mechanical strength and durability of the concrete since fine RCA has high water absorption and high porosity. To address this issue, this study proposes to treat the fine RCA using a tea-stain inspired compound, tannic acid (TA). To this end, fine RCA is first immersed in dilute solution of TA. In this process, TA can react with calcium hydroxide (CH) and calcite of RCA to produce nanoparticles on the surface of the RCA particles. These nanoparticles can fill the capillary nanopores in the mortar, significantly reduce the porosity of the produced mortar. This can be confirmed by the scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) analysis. Experimental studies have been carried out to examine the effect of this treatment on the hydration and mechanical behavior of the mortars made with the treated fine RCA. Testing results confirm that the strength and durability of the mortar can be significant enhanced by the proposed method, which can be mainly attributed to two reasons. First, TA coated on the surface of the fine RCA can capture calcium ions to induce local mineralization and facilitate the hydration of cement in the interface transition zone (ITZ), densifying the ITZ according to nanoindentation test. Second, the cohesion of hardened cementitious material can be enhanced by the unique binding capacity of TA through covalent and non-covalent interactions. [ABSTRACT FROM AUTHOR]