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The hydration process of blended cementitious materials is primarily affected by the effect mechanism of supplementary cementitious materials. This study utilizes electrochemical impedance spectroscopy (EIS) method to investigate the hydration kinetics of cementitious materials incorporating metakaolin (MK), quartz (Q) and limestone powder (LS). The experimental results reveal the influence of MK+Q+LS on the hydration kinetics, phase assemblage, and microstructure of the blended systems. Besides, the electrochemical impedance response of blended cement materials exhibits variation based on the MK contents and the curing age. Furthermore, the resistance of the continuously connected micro-pores (R ccp) in the blended cementitious material progressively increases throughout the hydration process. The inclusion of MK reduces the R ccp values at early ages, while contributes to an increase in R ccp values from 7 days onward. Additionally, positive correlations are established between the R ccp value and compressive strength/heat release across different MK contents and curing ages. The combination of R ccp values and other characterization method can effectively reveal the microstructure evolution process. Therefore, as a nondestructive method, EIS can be effectively applied to predict the hydration of cementitious materials and the mechanical properties. • System with 40 % MK and 60 % quartz, simulated as low-grade calcined clay, exhibit comparable compressive strength to OPC. • The R ccp value, associated with the connected pores, exhibits a correlation with compressive strength and heat release. • R ccp values is related with the filler effect, carboaluminate formation effect and the pozzolanic reaction effect of MK. [ABSTRACT FROM AUTHOR]

Integration of phase change materials (PCMs) into buildings contributes to mitigating indoor temperature fluctuations, offering opportunities for alleviating energy crisis. However, prevalent PCM integration methods commonly suffer from shortcomings in mechanical properties, compatibility, and environmental sustainability, restricting their applications. This study developed a novel shape-stabilized PCM (SSPCM) using cenospheres from coal-fired power waste and bio-based PCMs from vegetable oil by-products, subsequently sealed with silica coatings to inhibit PCM leakage and improve thermal stability, termed as SCS@PCM, exhibiting melting enthalpy up to 103.9 J/g. SCS@PCM was then integrated into cement mortars by replacing fine sand to fabricate thermal storage cement-based materials (TSCM), followed by assessments of their microstructural, mechanical, and thermal properties. The results showed that the silica coating helps to lowrer adverse impact of SCS@PCM on the compressive strength and thermal conductivity of TSCM. TSCM containing 30.0 vol% SCS@PCM reached a 28-day compressive strength of 45.3 MPa, exhibiting only a 17.4 % reduction compared to the control group, notably less than reductions observed for other SSPCMs reported in literature. Moreover, integration of SCS@PCM improved thermal storage capacities and decreased thermal fluctuation rates of TSCM, evidenced by a 4.7 ℃ decrease in peak temperature at dosage of 30.0 vol%. This study endeavors to develop an eco-friendly TSCM with excellent thermal and mechanical properties, providing insights for applications in improving the thermal regulation and energy efficiency in building roofs. • An eco-friendly, compatible, and robust shape-stabilized PCM was developed using cenospheres and bio-based PCMs. • Effective inhibition of PCM leakage and improved thermal stability of SCS@PCM was achieved by the SiO 2 coating. • SCS@PCM replaced up to 30 % by volume of fine sand without noticeable reduction in the mechanical strength of cement mortar. • SCS@PCM significantly improved the heat storage and temperature regulation capabilities of cement mortar. [ABSTRACT FROM AUTHOR]

Concrete structures are prone to damage from various factors, particularly chloride ion penetration, which can lead to premature deterioration. Although self-repairing materials can mitigate damage and erosion, methods for evaluating their efficacy are lacking. This study explores concrete damage development, chloride and water transport in damaged concrete, and post-repair transport behavior. A comprehensive mechanical-transport-healing model for concrete was established to investigate the influence of damage and self-healing rates on chloride distribution. Results show that tensile loads under 5 μm have minimal impact on concrete transport, whereas larger displacements significantly accelerate water and chloride migration. This acceleration resulted in a 66 % increase in the chloride concentration at a depth of 15 mm with a displacement of 10 mm. Higher self-healing rates effectively reduced the chloride concentration within the 10–30 mm range. Increasing the healing rate from 70 % to 90 % led to 75 % and 35 % decreases in the chloride concentration at a depth of 30 mm after 100 years, respectively. These findings provide valuable insights into the relationship between the mechanical damage and chloride transport in concrete, which can inform the development of strategies for enhancing the durability of concrete structures exposed to chloride-rich environments. • A coupled mechanical-transport-healing numerical model is developed. • The relationship between damage on the acceleration of concrete erosion medium transport was quantified. • The effect of self-healing rate on the transport properties of damaged concrete was calculated, and the self-healing rate requirement for damaged concrete was proposed. [ABSTRACT FROM AUTHOR]

Massive concrete structures are susceptible to thermal cracking due to the large surface-to-internal temperature gradients induced by the exothermic cement hydration, threatening their durability and safety. This study explored a novel thermal-tailored strategy to mitigate thermal cracking of cement-based materials by incorporating carbon fibers (CF) and liquid-metal-based microencapsulated phase change materials (MEPCM). Specifically, spherical MEPCM composed of In-Bi-Sn alloy cores coated by polyvinyl alcohol shells was prepared through a high-speed liquid-phase dispersion method, with average diameters of 36.26 μm and a high volumetric latent heat of 214 MJ/m3. The synergistic effect of CF and MEPCM on the microstructure, mechanical and thermal properties of cement mortars was further investigated. Upon adding 0.3 wt% of CF and 3.2 vol.% of MEPCM, the flexural strength of cement mortars exhibited a significant increase of 30.3 %. Microanalysis revealed that the molten MEPCM could flow to fill the pores and microcracks within its surrounding matrix and form a network skeleton with well-dispersed CF, imparting flexibility to the typically rigid cement hydrates. By this way, the thermal conductivity of cement mortars was increased by 21.7 % and internal temperature rise was decreased by 12 ℃ by adding 4.8 vol.% of MEPCM, contributing to the mitigation of risks associated with thermal cracking. The research outcomes will provide valuable insights into the development of thermal cracking-resistant cement-based materials in a highly efficient way. • Fabrication of microencapsulated phase change materials (MEPCM) based on In-Bi-Sn alloy was achieved. • The synergistic effects of carbon fiber (CF) and MEPCM on the performance of cement mortars was evaluated. • Incorporation of CF and MEPCM significantly enhanced the flexural strength and thermal conductivity of cement mortars. • Cement mortars containing 0.3 wt% CF and 4.8 vol.% of MEPCM exhibited a maximum internal temperature reduction of 12 ℃. [ABSTRACT FROM AUTHOR]

The transport of chloride in cement-based materials is influenced by various factors, and the chloride diffusion coefficient in numerical models should be the steady-state value under specific conditions, which is difficult to obtain through traditional experiments. In this article, based on an improved non-contact resistivity instrument, the steady-state chloride diffusion coefficient and porosity of cement-based materials are characterized. Considering the acceleration effect of moisture convection and electric field on chloride transport, a numerical model for moisture and chloride transport coupling diffusion, convection, and electromigration is established. Based on the measured steady-state chloride diffusion coefficient and porosity values, the influence of interface transition zone (ITZ), electric field type, chloride binding effect, initial conditions, and boundary conditions on moisture and chloride transport is numerically analyzed. It is found that the increase of ITZ thickness, electric field strength, boundary concentration, and initial concentration can accelerate chloride transport. The chloride concentration distribution curve exhibits a "shoulder peak" caused by chloride binding effect, and its peak height and width are positively correlated with the chloride binding coefficient. In conclusion, this study aims to better understand the ion transport behavior inside cement-based materials under coupling of convection, diffusion, and electromigration, and identify the key factors influencing this behavior, which provide a feasible scheme for durable design of concrete construction in environments rich in erosive media. [Display omitted] • The chloride diffusion coefficient and porosity of cement-based materials were measured using the improved NC-ERM method. • A numerical model was established for cement-based materials, incorporating convection, diffusion, and electromigration. • Accelerated chloride transport was observed with ITZ thickness, electric potential difference, and concentration. [ABSTRACT FROM AUTHOR]

• NA can be used as reactive alumina resource in cement paste. • Influence of NA on the chloride binding capacity of blended cement pastes were investigated. • NA is beneficial for improving the chloride binding capacity of cement paste blended with SCMs. Chloride ingress is one of the main causes for the degradation of reinforced concrete structures. Increasing the chloride binding capacity of concrete is generally thought as a feasible way to restrain the chloride ingress. In our previous study, the γ-phase nano-Al 2 O 3 (NA) was found to be beneficial for improving the chloride binding of plain Portland cement paste as a result of the formation of additional Friedel's salt. Herewith, the cases of blended cement pastes were further investigated, into which supplementary cementitious materials (SCMs) were incorporated, including fly ash (FA), blast furnace slag (SL) and silica fume (SF). NA with a dosage of 1% and 2% was introduced to blended cement paste, and the chloride binding capacity of which were determined with the conventional equilibrium method. The results showed that the use of NA was even viable to improve the chloride binding capacity of blended cement pastes. X-ray diffraction (XRD)/Rietveld refinement method and thermogravimetric analysis (TGA) were performed to unravel the phase assemblages change upon exposure. It was revealed that besides the formation of more Friedel's salt, the addition of NA could allow the enhanced physical binding of chloride as a result of the formation of C-A-S-H, i.e., the substitution of Si by Al in C-S-H gel. [ABSTRACT FROM AUTHOR]

• PL additive had a diminishing retarding effect on cement hydration. • Appropriate dosage of PL had positive effects on the work performance of cement-based materials. • PL could increase the dispersion of cement system. The application of lignin dispersants in cementitious materials has been limited due to its strong retarding effect on cement hydration. In this study, polyaniline modified lignin (PL) was prepared to be as a new lignin additive to increase the dispersion of cement system and maintain good mechanical properties of cementitious materials. This investigation systematically revealed that different contents of PL (0%, 0.5%, 1.0%, 2.0%) had various effects on the early hydration, the work performance and the microstructure of cement paste and mortar. Appropriate dosage of PL was beneficial to achieve better dispersion and improve the fluidity of cement system. The retarding effect on cement hydration was significantly reduced by PL, compared to unmodified lignin. When the content of PL was 0.5% and 1.0%, the mechanical properties of the mortar was maintained as well as mortar without PL. However, excessive content of PL (2.0%) decreased the flexural strength and compressive strength significantly. XRD and TG tests exhibited that no new hydration products were generated and the formation of calcium hydroxide was inhibited after the addition of PL. Besides, SEM and MIP results showed that low dosage of PL could decrease the porosity due to the filling effect. When the dosage of PL in cement exceeds 2.0%, the structure was more loose and porous, attributed to the delayed hydration and air entertainment. The dispersion mechanism was also discussed and ascribed to electrostatic repulsion caused by PL adsorbed on the surface of cement particles and the steric effect due to the branched chains of PL. This study provides a new idea for high-value application of lignin and the promotion of low-carbon building materials by using renewable resources. [ABSTRACT FROM AUTHOR]

• Sulfate attack under three conditions. • Parts of bound chlorides will be released due to sulfate attack. • C b is more advantageous than R b for evaluating the chloride binding. • The influence of MgSO 4 attack on the stability of bound chlorides depends on the concentration of MgSO 4 solution. Chloride binding is an important factor for chloride transport in cementitious materials. The ions from the pore solution or the environment may affect the stability of the bound chlorides. In this study, the equilibrium method was used to investigate the stability of bound chlorides of well hydrated cement paste (HCP) with different concentrations of sodium sulfate (Na 2 SO 4) and magnesium sulfate (MgSO 4) attack under three conditions (including: I. HCP intermixed with chloride was submerged in sulfate solution; II. HCP was soaked in combined chloride-sulfate solution; III: HCP was exposed to chloride solution, followed by sulfate solution). Experimental techniques including X-ray diffraction (XRD) and thermogravimetric (TG) were combined to identify the phase assemblage of HCP before and after sulfate attack. The results show that the presence of sulfate decreases the amount of bound chlorides, which is mainly caused by the decomposition of Friedel's salt. Besides, the influence of MgSO 4 attack on the stability of bound chlorides depends on the concentration of MgSO 4 solution. As a result of the "blocking effect" of brucite, sample exposed to 1% MgSO 4 presented a higher chloride binding capacity than that exposed to 1% Na 2 SO 4 solution. However, extensive brucite and gypsum were formed with the increase of the concentration of MgSO 4 solution. This leads to the formation of microcracks in cement paste, which provides additional routes for the ingress of sulfate ions. [ABSTRACT FROM AUTHOR]