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[Display omitted] • Mass ratio of CA-SA to MMT is 35:65 which can prevent the leakage of PCM. • CA-SA/MMT/GR has suitable phase change temperature and high latent heat. • CA-SA/MMT/GR can keep the thermal property after 300 thermal cycles. • The thermal conductivity of CA-SA/MMT/2 wt%GR increases by 156.4%. • CA-SA/MMT/GR significantly enhances the heat storage capacity of mortar. A novel composite phase change material (PCM) of capric-stearic acid/montmorillonite (CA-SA/MMT) with thermal conductivity enhanced by graphene (GR) was prepared. It was characterized by FT-IR, XRD, SEM, DSC and thermal conductivity tests. The temperature response of CA-SA/MMT/GR was evaluated by heating and freezing the composite PCMs in tinfoil cups. The phase change mortar containing CA-SA/MMT/2 wt%GR was also prepared, and its mechanical strength and thermal behavior were tested. The adsorption rate experiment results show that the mass ratio of CA-SA to MMT is 35:65, which can effectively prevent the leakage of PCM. The FT-IR, XRD and SEM results demonstrate that the prepared CA-SA/MMT/GR has good chemical compatibility and stability. The DSC results reveal that the CA-SA/MMT/GR has suitable phase change temperature and high latent heat, and it can retain the phase change behavior after 300 thermal cycles. The thermal conductivity of CA-SA/MMT/2 wt%GR increases by 156.4% compared with CA-SA/MMT. The heat transfer efficiency of CA-SA/MMT gradually increases with the increase of GR. The mechanical strength and thermal behavior results of phase change mortar demonstrate that the flexural strength and compressive strength decrease and the heat storage capacity increases with increasing the percentage of CA-SA/MMT/2 wt%GR. [ABSTRACT FROM AUTHOR]

Two-dimension MXene was applied in cement to fabricate MXene cement-based sensor used in structural health monitoring. The effect of MXene content on the piezoresistive performance of MXene cement-based composites (MCBC) was investigated. The fractional change in resistivity (FCR) under different loading rate, water content and failure load were also measured. Microanalysis results proves that MXene can construct electrical network in cement composites. The results demonstrated that the stress sensitivity has a maximum at 1.0 wt% MXene content. When loading rate increases, the sensitivities of composites decrease linearly, while the water content increases, the decrease of sensitivities is not completely linear. The relationship between compressive stress and fractional change in resistivity conforms to quadratic polynomial under failure load. [ABSTRACT FROM AUTHOR]

It is important to study the corrosion resistance of reinforcing steel in various chloride salt environment. In this study, the corrosion performance of reinforcing steel inside mortar mixed with a new deoxyribonucleic acid (DNA) primer inhibitor in various chloride salt solutions (NaCl, KCl, CaCl 2 , MgCl 2) was investigated. The results indicate that the chloride salt types have a significant effect on corrosion resistance of reinforcing steel in cement mortar mixed with DNA primer inhibitor, and the rule is NaCl ≈ KCl > CaCl 2 >MgCl 2. The new DNA primer inhibitor can maintain the good corrosion inhibition performance in cement mortar. NaCl and KCl can inhibit DNA primer inhibitor condensation and dissolution of calcium hydroxide, which can promote the formation of a better protective film compared with CaCl 2 and MgCl 2. MgCl 2 and CaCl 2 can lead to relatively high porosity and accelerate the diffusion of chloride ions to the steel surface than NaCl and KCl. • DNA primer inhibitor has good corrosion inhibition properties in cement mortar. • The corrosion resistance of steel follows the law NaCl ≈ KCl > CaCl 2 > MgCl 2. • NaCl and KCl can inhibit DNA primer inhibitor condensation. • The corrosion degree of steel immersed in NaCl and KCl solutions is relatively low. • Cement mortars exposed to MgCl 2 and CaCl 2 solutions tend to chloride ion diffusion. [ABSTRACT FROM AUTHOR]

In this study, two-dimensional (2D) MXene cement-based material with high electrical conductivity was prepared. The conductive behavior of cement pastes was measured by electrochemical impedance spectroscopy (EIS) and four-probe method. Besides, the microstructures of cement pastes were examined by scanning electron microscope (SEM), X-ray diffraction (XRD), and mercury intrusion porosimetry (MIP). The results demonstrate that the variation of electrical conductivity corresponds to percolation theory, and curing age exerts a negligible influence on the percolation threshold. Increasing the MXene content leads to both an increase in the electrical conductivity and the compressive strength (at an MXene dosage below 0.5 wt%). SEM analysis reveals that MXene can form a conductive network in the percolation zone of the matrix. Moreover, the hydration degree is promoted with the addition of MXene within 1.0 wt%, reflected by XRD analysis. The MIP results demonstrate that the addition of MXene at 0.7 wt% significantly reduces the porosity. • MXene can effectively improve the electrical conductivity of cement pastes. • The cement pastes with 0.463 wt% MXene reach percolation threshold. • MXene clumps and chains provide channels in cement matrix for electron transfer. • The compressive strength of cement pastes reaches the maximum at 0.5 wt% MXene. • The cement pastes with 0.7 wt% MXene have the lowest proportions of harmful pores. [ABSTRACT FROM AUTHOR]

The suitable disposal and utilization of phosphogypsum (PG) remain a large challenge due to its huge accumulation and potential impacts on environment and human health. Magnesium chloride cement (MOC) was utilized as the carrier for PG, with the addition of KH 2 PO 4 to further improve its main properties. The feasibility and intrinsic mechanism were systematically analyzed through assessments of fluidity, setting time, strength, water resistance and microscopic properties. Results revealed that the proper substitution of PG for light-burned MgO powder could mitigate the strength reduction caused by the dilute effect. The addition of KH 2 PO 4 could reverse this reduction. Notably, the substitution of PG enhanced the water resistance of MOC samples and enlarged the fluidity and setting time, further bolstered with KH 2 PO 4. Microscopic analyses manifested the filled PG particles and formed gel-like phases contributed to a denser structure. Additionally, the phosphate ions hindered the transformation from phase 5 to brucite, promoting water resistance. Furthermore, the PG-MOC samples with KH 2 PO 4 exhibited lower cost and carbon emission, decreasing at most 35.2 % for C P and 44.6 % for CI. The study provides a potential approach for improving the water resistance of MOC and reducing the accumulation of PG. • Exploring the utilization of phosphogypsum holds promise to reduce the burdens on environment. • MOC samples with phosphogypsum and KH 2 PO 4 exhibit lower cost and carbon emissions than pure MOC samples. • The water resistance of MOC with phosphogypsum and KH 2 PO 4 gets greatly improved. • Incorporation of 1 % KH 2 PO 4 in PG-MOC relieves the appearance of scumming. [ABSTRACT FROM AUTHOR]

• Alkali-activated slag (AAS) mortar has better resistance to chloride ion corrosion. • Different cation types affect the D app of AAS mortar. • MIP and XRD was performed to show a decrease in porosity. • EIS was performed to show an inverse exponential relationship between R c,d and D app. This work focuses on evaluating the influence of four cationic chloride salts (NaCl, KCl, MgCl 2 and CaCl 2) on chloride ion diffusion characteristics of alkali-activated slag mortar. The chloride ion concentration profiles of alkali-activated slag mortar were tested in single cation and combined cation source solutions. The hydration products and mechanism of action were analyzed by XRD and MIP, and the chloride ion transmission characteristics of alkali-activated slag mortar were further analyzed in combination with EIS. The chloride ion apparent diffusion coefficient D app related to the chloride salt solutions with the four cation types decreases in the order of D app (KCl) > D app (NaCl) > D app (MgCl 2) > D app (CaCl 2). The combination of monovalent cations can promote the chloride ions diffusion of alkali-activated slag mortar, and the results of the combination of monovalent cations and divalent cations are different. The hydration products of slag are mainly C-S-H gels with low calcium to silicon ratio, which reacts with chloride salt to form Friedel's salt, which can fill the internal pores, optimize pore size distribution, and improve the resistance to chloride ion corrosion. [ABSTRACT FROM AUTHOR]

Triethanolamine (TEA) is a multifunctional organic additive, applied chiefly to a grinding aid and accelerator for cement. Its effect on cement paste in a sulfate-rich environment remains still unclear and elusive. In this paper, the expansion and mechanical performance of cement paste under external sulfate attack were measured. Thermodynamic model lent itself to estimate the correlation between triethanolamine and generated products content ahead of quantified phase analysis. The transformation of internal component was surveyed by multiple technologies of thermal gravimetric (TG), scanning electron microscope (SEM), X-ray diffraction (XRD), and nuclear magnetic resonance (NMR), while inductively coupled plasma (ICP) was applied to investigate the evolution of interstitial ion concentration. Furthermore, the changes of pore structure over immersion time were separately figured and tabulated by virtue of mercury intrusion porosimetry (MIP). The above analysis shows that when cement paste suffers sulfate attack, triethanolamine intensifies the formation of calcite and exacerbates the decalcification of C-S-H, promoting a large quantity of insoluble precipitation including mirabilite of abundant crystalline water which accounts essentially for severe damage. Determined after comprehensive evaluation, the addition of TEA is conducive to the emergence of physical sulfate attack and an increment of the total porosity and permeability, contributing to an extension of microcracks and a more fragile structure, ultimately makes cement paste appear as a reduction in strength and stiffness. • Triethanolamine correlates adversely with the resistance to sulfate attack of cement paste • The complex of sulfate and aluminum ions occupied by the TEA intensifies decalcification of C-S-H • Triethanolamine loosens internal structure and permeability paths inside cement paste within sulfate attack [ABSTRACT FROM AUTHOR]

As a part of by-product generated during the incineration, the municipal solid waste incineration fly ash (MFA) is a secondary pollutant. The ordinary Portland cement (OPC)-based stabilization/solidification (S/S) is a prevalent and robust technique for the treatment of MFA, which can not only effectively dispose the MFA, but also decrease the demand of OPC and reduce the greenhouse gas emissions. However, when MFA was directly utilized to partly replace the cement with a replacement ratio of 15%, the MFA-OPC based composites exhibited inferior mechanical properties. The nano silica (NS) was considered to be introduced to compensate for the strength loss caused by the MFA. In this research, the NS with varying dosages and particle sizes were integrated into the MFA-OPC composites and in total seven groups of the composites were prepared. The mechanical properties of the composites were examined and the results indicated that the composites containing 2 wt% 100 nm NS presented relatively superior mechanical properties. The incorporation of NS could increase the compressive strength of MFA-OPC composites by 37.5% at later age. Then, thermodynamic modelling and the micro-structural analysis including hydration heat, XRD, TG, MIP and SEM were coupling applied to probe into the NS modification mechanism. Experimental results indicated that the addition of NS enhanced the strength of OPC containing MFA at both early and later ages via pozzolanic reaction, hydration acceleration and micro filling effects. Overall considering the macro performance improvement and microstructure modification effect, the 2 wt% NS with particle size of 100 nm was recommended to be utilized. Therefore, this study expands the emerging application of NS and demonstrates that NS-augmented binders can ensure low-carbon and high-performance S/S of hazardous materials. • The nanoSiO 2 with varying particle sizes and dosages were utilized to compensate for the performance loss caused by the MFA. • The experimental analysis and thermodynamic modeling were coupling used to investigate the effect of nanoSiO 2 on the composites. • The optimal nanoSiO 2 particle size (100 nm) and dosage (2%) was recommended. [ABSTRACT FROM AUTHOR]

[Display omitted] • A new nano-modified superstable foam was designed to improve the mechanical properties and pore structure of carbon fixation foam concrete. • High performance additive technology and early carbonation curing were used to improve the mechanical properties of eco-porous carbon fixation concrete. • The influence mechanism of polyvinyl alcohol on carbonation behavior of carbon fixation foamed concrete and its performance improvement mechanism were found and clarified. The introduction of carbon fixation components (calcium hydroxide) can improve the carbon fixation performance of foam concrete, however, it will reduce its mechanical properties. In order to solve the adverse effects of carbon fixation components on the mechanical properties and optimize carbon absorption properties, a specific amount of polyvinyl alcohol (PVA) is incorporated. In this study, a serial of test was employed to study the production process of nano-modified foam, and some basic properties of the foam concrete of interest. Further, the micromorphology and pore structure of the samples were analyzed by scanning electron microscope and mercury injection test. The evolution of mineral phases was examined by X-ray diffraction and thermogravimetric analysis. The results show that the carbon sequestration efficiency of foam concrete increases significantly as the amount of calcium hydroxide is increased, however, the cementitious properties of materials deteriorate, resulting in a decrease in strength. When PVA is added as a water-soluble admixture, it can enhance the mechanical properties of test blocks. It can also strengthen the bubble film of nano stabilized foam, increase bubble stability, and refine the internal pore structure of carbon fixation foam concrete. In addition, PVA can modify the calcium hydroxide morphology from a laminar structure to a smaller volume edge corrosion structure, which improves the reaction activity of calcium hydroxide with CO 2 and boosts the efficiency of carbon sequestration. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel hybrid nanoSiO 2 containing fluorinated organic (NS@TOFS) was designed. • NS@TOFS can reduce the water absorption and carbonation of coated mortar. • NS@TOFS modified surface shows less degradation after exposure to UV-rays. • A triple layered structure of NS@TOFS modified surface was found and clarified. In surface treatment technics of cement-based materials, nanoSiO 2 (NS) is effective in refining pore structure while organic water-repelling agents are often used for producing a hydrophobic surface. Due to its advantages of pore refining effect and hydrophobicity, the organic-inorganic hybrid nanoSiO 2 has attracted increasing attention. However, the UV-irradiation can result in photodegradation of organic constituents, leading to deterioration of hydrophobicity. In this study, a novel UV-resistant fluorinated hybrid nanocomposite, NS@TOFS, was synthesized and used for surface treatment on hardened cement-based materials. The water and gas permeability of the treated samples before and after UV-aging were assessed by measuring the water absorption rate, water contact angle and carbonation degree. The experimental results showed that the NS@TOFS treated samples possess enhanced water and gas impermeability after 14 days of exposure to UV rays. A morphological observation of the treated surface revealed that a synergistic effect of organic film and refined pore structure was responsible for the improved surface properties. Findings from this study well demonstrate that the developed fluorinated hybrid nanoSiO 2 holds great promise for enhancing the durability of cement-based materials under UV-irradiations. [ABSTRACT FROM AUTHOR]

This work investigated the influence of polyacrylamide on carbonation behaviors of cement pastes by measuring carbonation depth and pH value. Electrochemical impedance spectroscopy, X-ray diffraction, thermogravimetric analysis, scanning electron microscopy, and mercury intrusion porosimetry were performed to monitor changes in hydrates and microstructure of cement pastes to dissect underlying mechanisms. The results show that polyacrylamide decreases the amount of portlandite (CH) and alters its morphology from a larger size with parallel-stacked lamellar structure to a smaller size with edge-corroded structure, thereby enhancing CH reactivity with CO 2 during carbonation. Higher Ca/Si ratios of C-S-H phases with a higher carbonation rate form in the presence of polyacrylamide. Polyacrylamide reduces porosity and improves pore refinement by transferring capillary pores to gel pores due to filling effect of CaCO 3 grains with a small crystal size during carbonation. Overall, polyacrylamide yields an accelerating effect on the carbonation of cement paste in a dosage dependent manner. [ABSTRACT FROM AUTHOR]

• Calcium formate correlates adversely with chloride-induced-corrosion resistance of cement mortar. • The content of calcium formate influences corrosion of steel bar. • Calcium formate loosens internal structure of cement mortar after soaked in NaCl solution. Calcium formate has been widely added in concrete as an accelerator to obtain a high early strength in civil engineering, such as shotcrete and concrete repairment. However, its effect on chloride ion erosion and steel bar corrosion under marine environments is elusive. In this study, rapid chloride migration and chloride ion titration methods were employed to investigate the effect of calcium formate on the chloride ion erosion in cement mortars. Electrochemical impedance spectroscopy and the loss weight ratio of rebar were measured to quantitatively characterize the corrosion extent of the steel bars. Furthermore, the relationship between chloride ion penetration and internal structures of the composite was established based on its pore structures characterized by means of mercury intrusion porosimetry. The crystalline phases and microstructures of the cement pastes were examined by XRD and SEM analyses, respectively. The results showed that calcium formate increased the formation of C 2 AH 8 resulting in a significant increase in porosity and reducing the amount of chemical bound chloride ions inside, increasing the diffusion coefficient and content of chloride ion. Moreover, the increase in the number of internal pores allowed chloride ions to migrate easier in mortar and readily trigger corrosion of steel bars. [ABSTRACT FROM AUTHOR]

[Display omitted] • Sediment had weak pozzolanic activity and led to a reduction in strength. • Combined use of GGBS and calcium carbide slag offset sediment-induced strength loss. • Developed mortar is eco-sustainable and holds promise for practical application. The generation of dredged sediments (DS) exerts a heavy burden on the surrounding environment. Traditional landfills of DS not only contaminate the environment, but also waste precious resources. In this study, DS from Taihu Lake, together with calcium carbide slag (CCS) and ground granulated blast-furnace slag (GGBS), was used as supplementary cementitious materials (SCM) to replace cement to develop a novel cementitious binder for the production of mortar. The effects of varying contents of DS, CCS, and GGBS on the properties of the specimens were systematically investigated. The results showed that the incorporation of DS in cement mortar led to a reduction in the flexural and compressive strength at all curing ages in a dosage dependent manner due to a rather weak pozzolanic activity. The addition of GGBS in the specimen significantly increased the 28-d flexural and compressive strength, which was even higher than that of the samples with the same amount of cement. More importantly, this beneficial effect was more obvious in the co-existence of GGBS and CCS because of the formation of more C-S-H gel (with a simultaneously high pH) revealed by XRD, SEM and TG analysis. The optimum mechanical properties were obtained by a combination of 60% OPC, 20% DS, 10% GGBS, and 10% CCS. Whereas, the mix with a higher content of DS (20% OPC, 60%DS, 10% GGBS and 10% CCS) can be potentially used for controlled low-strength materials. The application of the developed product in eco-friendly construction materials can sustainably alleviate the burden of DS, CCS, and GGBS on the environment. [ABSTRACT FROM AUTHOR]

[Display omitted] • Combined use of waste glass and RHA greatly alleviates wastes disposal at landfills. • Use of RHA improved mechanical and durability of cement mortar. • Addition of RHA suppressed RG-induced ASR expansion. • RHA holds great promise as eco-friendly pozzolanic materials. Using recycled glass (RG) to replace river sand in the production of cement-based materials saves the increasingly depleting natural sand resources. Previous studies have shown that the smooth surface and reactive silica of RG adversely affected its bonding with the cement paste and thereby caused a potential alkali-silica-reaction (ASR). This study used rice husk ash (RHA) as an eco-friendly mineral admixture to ameliorate the properties of the RG incorporated mortar. A fixed replacement of 50% RG was used to replace sand, while varying proportions (10%, 20% and 30%) of RHA were adopted to replace cement. For comparison, a mixture containing only sand and cement was used as the reference sample. The flexural and compressive strength, water absorption, ASR expansion, and rapid chloride mitigation (RCM) of the hardened samples were evaluated. In addition, SEM, XRD, and TG analysis were employed to analyze the microstructures and chemical compositions of different samples. The results showed that incorporating RG as a river sand replacement in cement mortar reduced flexural and compressive strength and increased water absorption and chloride ion penetration. Moreover, the ASR expansion value (0.34%) was beyond the permissible limit (0.1) indicated by the ASTM C1260. The addition of RHA improved the mechanical properties and durability of the cement mortar at a later curing age as a result of the RHA-induced pozzolanic reaction and micro-filler effect. By converting portlandite (CH) derived from cement hydration into secondary C-S-H, the use of RHA greatly reduced the porosity (augmenting the compressive and flexural strength) and concurrently suppressed the RG-induced ASR expansion. The results of XRD, SEM and TG analysis corresponded well with the macro-property analysis and helped to elucidate the underlying mechanisms of the RHA-induced beneficial effects. Findings from this study provide new insights into the potential use of eco-friendly RHA in addressing the mechanical and durability problems associated with the use of RG as aggregate in cementitious materials. [ABSTRACT FROM AUTHOR]

• The effect of calcium formate on the hydration of light burned magnesia was systematically studied. • The effect of calcium formate on the hydration and expansion property of light burned magnesia in cement-based materials was systematically studied. • Monte Carlo simulation was used to study the adsorption of formate ion and hydroxyl ion on the surface of magnesium oxide and cement. • A model was established to explain the different effects of calcium formate on light burned magnesia in different systems. Light-burned magnesia (LBM) cement is an advanced material to compensate for thermal shrinkage of concrete. Its deformation property is related to the hydration of MgO. The effect of additives on the hydration of LBM cement is worthy of exploration but always ignored. This paper systematically studied the effect of calcium formate (CF) on the hydration of LBM cement. Results showed that in LBM-H 2 O system, CF inhibited the hydration and setting of LBM; however, in Cement-LBM-H 2 O system, CF accelerated the hydration of LBM and increased its expansion efficiency. Combine with Monte Carlo simulation, this phenomenon can be explained as follows: CF is adsorbed on cement surface and accelerates hydration of cement phase at first; secondly, this reaction releases OH− to accelerate the hydration of MgO. Besides, SEM figures show that incorporation of CF leads to the formation of fibrous C-S-H gel and promotes the formation of hexagonal Mg(OH) 2. [ABSTRACT FROM AUTHOR]

• 1% EDTA-2Na improved the resistance of steam-cured slag mortar against Na 2 SO 4. • 0.5% and 1% EDTA-2Na improved the resistance of steam-cured slag mortar against MgSO 4. • 1% EDTA-2Na retarded the cement hydration distinctly. • EDTA-2Na retarded the formation of gypsum and ettringite during sulfate attack. This paper explored a novel method to inhibit sulfate attack in slag cement mortar under steam curing, by using ethylenediaminetetraacetic acid disodium (EDTA-2Na) to chelate calcium ions. 0.5 and 1% EDTA-2Na were used in slag cement mortars to evaluate the inhibition effect in sulfate solution (7.5% Na 2 SO 4 and MgSO 4 solution) for 360 days. The weight variation, compressive strength, along with FT-IR spectroscopy, XRD and DTG, were conducted to analyze the sulfate degradation. Additionally, the isothermal calorimetry was measured to study the effect of EDTA-2Na on the hydration of cement. Results indicated that 1% EDTA-2Na retarded the cement hydration distinctly. The EDTA-2Na enhanced the resistance of steam-cured slag mortar against sulfate attack. For the Na 2 SO 4 attack, the enhancing effect of 1% EDTA-2Na was higher than that of 0.5% EDTA-2Na. For the MgSO 4 attack, 0.5 and 1% EDTA-2Na was both beneficial. The EDTA-2Na decreased the amount of calcium hydroxide due to the chelation, retarding the formation of gypsum and secondary ettringite. [ABSTRACT FROM AUTHOR]

• The influence of four retarders on the hydration of light-burned magnesia were studied. • Retarder mainly affects the early hydration rate of lightly-burned magnesia. • The micro-morphology of the hydrated light-burned magnesia sample will be affected by retarders. • Sodium gluconate has very strong retarding effect on light burned magnesia. Light-burned magnesia (LBM) is a common expansive agent to compensate for the thermal shrinkage of mass concrete, and the expansive property of MgO mass concrete is affected by the hydration behavior of LBM. Besides, retarder is usually added to extend the setting time of mass concrete in hot climate construction. Retarder affects hydration of cement and LBM at the same time. However, little is known about the effect of retarder on the hydration of LBM expansive agent. This paper investigated the effects of four retarders (citric acid, sodium gluconate, tartaric acid and calcium sulfate) on the hydration behavior of LBM expansive agent. Setting time, hydration heat, hydration degree and compressive strength were employed to characterize the hydration process of LBM with various retarders. Moreover, the composition of the product was quantitatively and qualitatively analyzed by XRD and TG, and the morphology of the product was analyzed by SEM. The results showed that retarders mainly affected the hydration behavior in the early age of LBM. Citric acid inhibited the hydration of LBM, but improved the compressive strength by forming flower-like Mg(OH) 2 crystal. Tartaric acid inhibited the hydration of LBM, and produced products with poor crystallinity. Furthermore, sodium gluconate significantly prolonged the setting time of LBM and obtained complete brucite products. Besides, calcium sulfate accelerated the hydration of LBM at 1.0 water/LBM ratio, but inhibited the hydration at 0.45 water/LBM ratio. Finding from this study may provide new insights into the design and comparison of experimental studies on the expansive property of MgO mass concrete affected by retarders. [ABSTRACT FROM AUTHOR]