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This research investigated the freeze/thaw cycles (0 cycles, 150 cycles, 400 cycles, and 600 cycles) influence on the mechanical properties of mortar blended with steel-PVA hybrid fibers and CaCO3 whiskers. The freeze/thaw cycles influence was assessed through mass loss, relative dynamic elastic modulus, flexural performance, and compressive behavior. The mechanical parameters were residual flexural strength, toughness index, flexural toughness, equivalent flexural strength, post-crack strength, compressive strength increment, and compressive toughness increment. The experimental results represented that these mechanical parameters of mortar blended with CaCO3 whiskers were higher than those without CaCO3 whiskers under 150 cycles condition. The relative dynamic elastic modulus of mortar blended with and without CaCO3 whiskers decreased only 4.6% and 7.5%, respectively, after 600 freeze/thaw cycles. Furthermore, a damage constitutive model containing damage variable D of mortar blended with and without CaCO3 whiskers was established under freeze/thaw cycles conditions. [ABSTRACT FROM AUTHOR]

Calcium carbonate whiskers (CW) showed good cracking resistance at the microscale. In this research, four different CW volume fractions (1.0%, 1.5%, 2.0%, and 3.0%) were added into cement mortar. The purpose was to further investigate the fracture behavior by using a semi-circular bend test (SCB) of SCB-CW after different freezing and thawing cycles (0 cycles, 25 cycles, 50 cycles, 75 cycles, and 100 cycles). In addition, three analytical models of SCB-PM and SCB-CW were established to predict the stress-strain response after different freezing and thawing cycles. The experimental results showed that the lowest mass increment, electric flux, highest residual flexural strength, fracture toughness, and fracture energy after different freezing and thawing cycles were observed in SCB-CW3.0. It was observed from the experimental results that only model II completely satisfied its basic requirements and its parameter c was closely correlated with the number of freeze-thaw cycles and the CW volume fraction. Calcium carbonate whisker is added to enhance the fracture behavior of mortar. The different freezing and thawing cycles are considered. The results are obtained using semi-circular bend test and analytical models are established. The highest fracture parameters are observed in SCB-CW3.0 under different freezing and thawing cycles. The model II is suggested for predicting the experimental response of composites. [ABSTRACT FROM AUTHOR]

• CaCO 3 whisker is used in mortar to improve the abrasion resistance. • Enhancement mechanism of the abrasion resistance of MMCW is proposed. • A linear relationship is observed between the abrasion parameters and compressive strength. • The prediction model for abrasion resistance parameters is established. Abrasion resistance is a critical parameter in the durability of cement-based materials. Calcium carbonate (CaCO 3) whiskers are added into the mortar to enhance the abrasion resistance. Herein, two standards (GB/T 16925-1997 and JC/T 421-2004) were employed to evaluate the abrasion resistance of the mortar modified with CaCO 3 whiskers (MMCW). The mortar abrasion resistance was characterized using the abrasion parameters such as abrasion resistance depth (D), abrasion loss (G), mass loss (ML), and abrasion resistance indices (I α). These results indicate that the abrasion resistance of MMCW was markedly improved, and the abrasion resistance of MMCW increased with the rise in CaCO 3 whiskers content. By adding different content of CaCO 3 whiskers into mortar, the compressive strength (f cu) enhanced from 2.4% to 10.2%, as compared to that of the plain mortar. The bridging effect of CaCO 3 whiskers prevented the cracks development, while the filling effect of CaCO 3 whiskers refined the large pores. The calcium hydroxide (CH) orientation improvement effect and the dilution effect of CaCO 3 whiskers limited the growth of CH hydration product of mortar, enhanced the compactness of mortar, and ultimately, improved the abrasion resistance of MMCW. An excellent linear relationship was established between the abrasion resistance and compressive strength. By comparing the experimental data with the data from the literature, the prediction model of the relative abrasion resistance parameters was obtained, which can provide a reference for studying the abrasion resistance of different cementitious materials. [ABSTRACT FROM AUTHOR]

• FA can both improve high temperature resistance and restorability of cement blends. • CW is favorable to recover compressive strength after exposed to 400 °C. • FA and CW demonstrate a combined effect to facilitate the compressive strength and microstructure recovery. Building fire disasters may cause large economic loss and casualties. To improve the fire resistance ability of concrete and repair the fire-damaged concrete structures using an in-situ repairing technique (such as post-fire-curing) can greatly offset these adverse effects. Thus, the present study employed fly ash (FA) to form a CW-FA-cement system which was proved to enhance the high-temperature resistance of cement and CW blended cement and was also favorable for recovery of compressive strength and microstructure induced by water re-curing. In details, incorporation of FA was effective to reduce the deterioration of cement and CW blended cement and was favorable for recovery of compressive strength and microstructure after water re-curing. Incorporation of CW was favorable to increase the restorability of compressive strength re-cured after 400 °C and performed a combined effect with FA to improve the recovery of compressive strength re-cured after 800 °C. Through the microstructural tests, the deterioration of compressive strength was due to the decomposition of hydration products. The recovery of compressive strength was due to the rehydration of dehydrated cement, further hydration of unhydrated cement particles, pozzolanic effect of FA and combined effect of CW and FA. Furthermore, the cement blends containing CW and FA had a good high temperature resistance and restorability. [ABSTRACT FROM AUTHOR]