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• Variation law of wear amount with concrete strength grade, ice pressure, and environment temperature was obtained. • Morphology and pore characteristics of ice–wear natural pumice concrete were analyzed. • The degradation mechanism of natural pumice concrete worn by ice was revealed. • The prediction model of the wear amount of natural pumice concrete under ice wear was established. Wear amount of ice on pumice concrete was investigated to understand wear mechanism of natural pumice concrete (NPC) during ice flood season of the Yellow River in China. Sawn NPC is used as the research object in this study. Strength grades (LC20, LC30, and LC40), ice pressure (1–5 KPa), and environment temperature (0 °C to − 20 °C) on the wear amount of natural pumice concrete as well as changes of surface topography and pore structure characteristics of NPC were analyzed with a super–depth–of–field microscope through the anti–ice wear test. Results showed that apertures increase with the increase of the wear amount because pumice aggregate and cementitious material jointly resist liquid pressure and cutting and fatigue wear modes of the NPC are caused by ice. Detached free abrasive particles cause scratches and wear on the surface and gradually form inward cracks, which cause the pore wall to break and result in the increase of apertures. A wear model with concrete strength grade, ice pressure, and environment temperature as variables combined with test data and degradation mechanism is established. The results of this study can provide a theoretical basis for the application of NPC in the Yellow River during ice flood season. [ABSTRACT FROM AUTHOR]

• Effect of icing content on compressive strength was studied. • The law of pore icing was analyzed. • The variation law of pore structure was investigated. • A prediction model of compressive strength in Permafrost environment was established. This study aimed to investigate the influence of low temperature ranging from −20 °C to 0 °C on the compressive strength and pore structure of a certain pile foundation concrete in the permafrost regions in China. This study analyzed concrete microstructure by low-temperature SEM. To quantify the influence of freezing amount, the relationship model of the compressive strength of concrete in a low-temperature environment was established based on the theory of accumulative curve of liquid saturation. Compressive strength increased with decreasing temperature. This finding was due to the gradual decrease in the pore radius of the water–ice phase transformation of concrete, and the amount of ice increased. This condition forms a complete and compact ice body and concrete bond, which gradually reduces concrete porosity. The calculated value of concrete compressive strength model established under pore icing is consistent with the experimental value. [ABSTRACT FROM AUTHOR]

Cement with high toughness and early strength are widely utilized in the field of rapid repair. This study is focused on the development of PVA fibre reinforced magnesium phosphate cement (FRMPC) that possesses these properties. The compressive, flexural, and tensile strengths of the FRMPC were measured at various ages, including 1, 2, 3, 4, 5, 6 and 24 h. The relationships of the element contents, hydration products, hydration process, and the microscopic morphology with the mechanical properties were analyzed. Importantly, the mechanical formation process of the 6 h was analyzed in detail. Results show that the tensile strain of the FRMPC exceeded 3% at all ages, and the flexural strength was greater than 10 MPa at all ages. The compressive strength reached 15.53 and 25.63 and 32.48 MPa after 1 h, 6 h and 24 h, respectively. The ultimate tensile strength, flexural strength and compressive strength of 6 h reached 98%, 90% and 78% of the final strength of 24 h.The incorporation of fly ash and quartz sand mitigates the exothermic rate of hydration and optimizes the filler structure. Furthermore, the addition of fly ash engenders an amorphous phase gelling material and MgSiO 3 , characterized by effective filler properties.This results in an enhanced integration of PVA fibres with the cement matrix, thereby exhibiting improved toughness.The main hydration product was MgKPO 4 × 6 H 2 O, and its formation rate and amount affected the mechanical properties. The nature of the hydration products and the density of the specimen structure were determined to be key factors in the progression of uniaxial tensile properties. FRMPC's strength, toughness and shrinkage are in a relatively good state, and the potential for its early-stage mechanical properties still can be improved. • The mechanical properties and hydration process of MPC-ECC are studied at 1, 2, 3, 4, 5, 6, and 24 h. • The uniaxial tensile strain of MPC-ECC reaches more than 3% throughout the entire age. • The compressive strength of MPC-ECC reaches 32.48 MPa in 24 h. • MPC-ECC has early strength and high toughness properties and can be used for rapid repair within 24 h. [ABSTRACT FROM AUTHOR]

• The ultimate deflection of the reinforced PVA-FRCC beam can reach 39 mm-57 mm. • The force versus deformation model of the reinforced PVA-FRCC beam was proposed. • The deflection expression of the reinforced PVA-FRCC beam was established. PVA-FRCC (polyvinyl alcohol-fiber reinforced cement composite) materials have superior tensile strain hardening characteristics, which can significantly improve the bearing and deformation capacities of the structure. The load-deflection performance of the PVA-FRCC reinforced beam is investigated in this study. Four-point bending experiment and theoretical analysis are conducted on the PVA-FRCC beams with different PVA fiber volume mixing ratios and reinforcement ratios. The experimental results show that the PVA-FRCC beams conform to the assumption that plane sections remain plane and the steel bars have the deformation compatibility with the PVA-FRCC material. The load-deflection curves obtained by the experiment show that the PVA-FRCC beams exhibit obvious deflection hardening and high performance of ductility compared with the RC beams, and the ultimate deflections are about 2.4–3.1 times that of the RC beams. In the theoretical part, the force versus deformation model of the PVA-FRCC beam is proposed. Based on the geometry compatibility equations, the constitutive equations and the force equilibrium equations, the theoretical expressions of the load-deflection curve at the mid-span of a PVA-FRCC beam subjected to flexural loading at different working stages is developed and validated by the experimental results. [ABSTRACT FROM AUTHOR]

[Display omitted] • A high-value-added low-carbon cementitious material containing multiple solid wastes. • The hydration mechanism and microstructure of cementitious material were studied. • The cementitious material is cleaner. Coal gangue and carbide slag accumulate annually and cause significant pollution, due to the lack of practical and efficient uses for these waste materials. In this series of studies, coal gangue, calcium carbide slag, steel slag, dihydrate gypsum, and calcium carbonate were used synergistically to prepare low-carbon cementitious material (LCCM) clinker. This method increases the utilisation rate of carbide slag and coal gangue, which was able to reach 80%. The mechanical properties of the LCCM were tested. The compressive strength of LCCM after hydration for 3 days achieved the same compressive strength as 42.5 Portland cement (PC42.5) that had been hydrated for 28 days. In addition, the hydration characteristics of the LCCM were analysed by measuring heat of hydration and chemically bound water, X-ray diffraction, thermogravimetric analysis, infrared spectroscopy, and scanning electron microscopy. Results showed that the hydration rate of the LCCM was faster in the early stage and was mainly concentrated in the first 3 days, yet it maintained continuous hydration in the later stage. In addition, the life cycle assessment method was used to evaluate the advantages of LCCM in terms of CO 2 emissions and energy consumption. LCCM had greater advantages in the context of CO 2 emissions and energy consumption compared with traditional cement. Specifically, CO 2 emissions reduction could reach 55%. This study demonstrates the efficient resource utilisation of carbide slag and coal gangue, which can reduce their pollution to the natural environment. [ABSTRACT FROM AUTHOR]

• The maximum crack width of PVA-SHCC beam did not exceed 0.1 mm. • PVA-SHCC beam has the characteristic of multiple cracks under flexural load. • A calculation model for the stress of steel bars was established. • The change of neutral axis height was considered in calculation of crack spacing. • A calculation model for crack width of PVA-SHCC beam was proposed. A strain-hardening cementitious composite with polyvinyl alcohol (PVA-SHCC) has the characteristic of multiple cracks under tensile load. PVA-SHCC has been utilized to replace ordinary concrete material in this study with the PVA fiber volume as a variation. Five PVA-SHCC and two reinforced concrete (RC) beams were designed to investigate cracking performance under concentrated loads (including crack number, width, spacing, and height). Results of the serviceability limit state showed that cracks on PVA-SHCC beams with fiber volume ratio of 2% were densely distributed, and the maximum crack width did not exceed 0.1 mm. Compared with the RC beams, crack height was reduced by 21.6%−30.9%, and the average crack spacing was reduced by approximately 60%. After the PVA-SHCC beam cracked, the strain on the steel bars did not increase immediately, and the steel bars were considerably coordinated with the deformation of the PVA-SHCC. The reason for this phenomenon is that the addition of randomly distributed PVA fibers effectively limited the expansion of cracks. Given the tensile strain hardening characteristics of PVA-SHCC, the formula for calculating the average crack width of the PVA-SHCC beam is proposed, which can be used for analysis and verification of the crack width of PVA-SHCC beams. [ABSTRACT FROM AUTHOR]