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Variations in the dynamic triaxial strength of hybrid basalt–polypropylene fibre-reinforced concrete (HBPRC) with strain rate and confining pressure were investigated, and a dynamic non-linear Mohr–Coulomb (M–C) strength criterion for HBPRC was established. The results showed that the dynamic strength of HBPRC increased non-linearly with the strain rate and confining pressure; however, the strain rate effect decreased with an increase in the confining pressure. The restraint effect of the basalt fibre and polypropylene fibre on the cracks enhanced the strain rate effect of the dynamic strength of concrete. The cohesion of HBPRC increased with the strain rate and confining pressure but decreased with an increase in the amount of fibre monofilaments. However, the internal friction angle showed a reverse trend. The established dynamic non-linear M–C strength criterion reflected the relationship of the dynamic strength of HBPRC with the confining pressure and strain rate, as well as the effect of fibre content on dynamic strength. The less average standard deviation and the tangential relationship between the strength envelope and the Mohr’s circle of stress demonstrated the applicability of the established dynamic non-linear M–C strength criterion.

This article presents the effects of basalt-polypropylene fibers on the compressive strength and chloride ion resistance of concrete with matrix strength grades C30, C40, and C50. Test results indi...

This study investigated the chloride transport performance of basalt-polypropylene fiber reinforced concrete (BPFRC) subjected to drying-wetting cycles. The effects of the strength grade, basalt fiber (BF), polypropylene fiber (PF), and hybrid BF-PF on the pore solution pH, chloride concentration distribution, chloride peak concentration (Cmax), and apparent chloride diffusion coefficient (Da) of the BPFRC were analyzed, and a multifactor model of Da was established. Moreover, the microstructures of BPFRC were studied to explore the effect of fibers on chloride transport performance of concrete in terms of theoretical pore volume, fiber-matrix interface, fiber bonding properties, and corrosion morphology. The results showed that the chloride concentration of the BPFRC increased and the pore solution pH of the BPFRC decreased with the increase in the exposure time. The chloride concentration and Da of the BPFRC decreased with the increase in the strength grade. At a fiber volume content of 0.1%, the addition of BF and PF reduced the chloride concentration and Da of the BPFRC; at a fiber volume content of 0.2%, the addition of hybrid BF-PF increased the chloride concentration and Da of the concrete. The chloride peak concentration appeared at the depth of 2 mm inside the concrete, and the change of the chloride peak concentration with exposure time followed the power function model. The theoretical pore volume of the BPFRC specimens decreased initially and then increased with the increase in the exposure time. FE-SEM observed that the bonding property between BF and matrix was better than that of PF, which could effectively control the development of microcracks.

In this study, the chloride diffusion behavior of coral aggregate concrete (CAC) in a salt-spray environment was investigated. Ten concrete groups were designed using different mix proportions, and the concrete samples were exposed to a salt-spray environment for 180 days. The effects of the aggregate type, CAC strength grade, fly ash (FA) content, and basalt fiber (BF) content on chloride ion diffusion were analyzed. The results showed that the chloride concentration of CAC was higher than that of ordinary aggregate concrete. The chloride corrosion resistance of CAC could be effectively improved by adding 30% FA or 0.1% BF to the concrete mix, and the peak chloride concentration decreases by 15.9% and 16.3%, respectively. The peak chloride concentration of concrete appeared at 3–5 mm in the concrete and exhibited a power function increase with the exposure time. In addition, a model for calculating the peak chloride concentration was established. The chloride diffusion coefficient decreased with an increase in exposure time. When the BF content was 0.1%, the chloride diffusion coefficient was the smallest. X-ray diffraction and thermogravimetric analysis were performed to analyze the erosion products, and the deterioration mechanism of the CAC in the salt-spray environment was determined.

The impact-resistance behaviour of basalt‒polypropylene fibre-reinforced concrete containing the mineral admixture (BPFRC) was experimentally investigated under impact loading using a ϕ75 mm split-Hopkinson pressure bar. The results showed that the dynamic compressive strength, dynamic elastic modulus and critical strain of BPFRC increased with increasing strain rate. The addition of basalt fibre (BF) and polypropylene fibre (PF) yielded significant increases in the strain rate effect of the dynamic compressive strength and dynamic elastic modulus of concrete and improved the deformation capacity of concrete. The influence of PF on the strain rate effect of dynamic compressive strength of concrete was greater than that of BF. However, there was no clear difference between the influences of BF and PF on the strain rate effect of the dynamic elastic modulus of concrete. There was a significant positive correlation between the hybrid volume of fibre and the strain rate effect of the dynamic compressive mechanical behaviour of BPFRC. The proposed viscoelastic damage constitutive model in this study can be used to accurately describe the dynamic mechanical behaviour of BPFRC.

Dynamic compressive behaviour of basalt–polypropylene fibre-reinforced concrete (BPFRC) was experimentally investigated using a 75-mm-diameter split-Hopkinson pressure bar. The results showed that the addition of basalt fibre (BF) and polypropylene fibre (PF) is effective at improving the impact-resistance behaviour of concrete. The dynamic compressive strength, critical strain, and energy absorption capacity of BPFRC increased with increasing strain rate. At strain rates of 20–140 s−1, the addition of BF and PF significantly increased the dynamic compressive strength, critical strain, and energy absorption capacity of concrete. The dynamic increase factor of BPFRC increased linearly with the decimal logarithm of strain rate. The hybrid addition of BF and PF significantly improved the strain rate effect of the dynamic compressive strength. The strengthening and toughening mechanisms of BF and PF are discussed in detail. The proposed dynamic damage constitutive model can be used to accurately describe the dynamic stress–strain relationship of BPFRC.

This study investigated the chloride diffusion behavior of coral aggregate concrete (CAC) under drying-wetting cycles. The influences of the aggregate type, strength grade, fly ash (FA) content, and basalt fiber (BF) content on the free chloride concentration in the concrete were determined. The apparent chloride diffusion coefficient (Dapp) of the CAC was calculated, and then used to analyze the instantaneous chloride diffusion coefficient (Dins) of the CAC. The test results showed that the free chloride concentration of the CAC was higher than that of ordinary aggregate concrete (OAC), with a smaller free chloride concentration for a higher strength grade. The Dapp and Dins first increased and then decreased with increases in the FA content and BF content. The Dins was 65 ~ 87% smaller than the Dapp. The time attenuation coefficient of the chloride diffusion coefficient had good positive correlations with the strength grade and FA content, and a good quadratic functional relationship with the BF content. The peak chloride concentration appeared at approximately 4 mm inside the concrete, and increased with the erosion time, which conformed to the power function law. In addition, a calculation model for the apparent chloride diffusion coefficient was established. The porosity of CAC can be effectively reduced when the FA content is 30% or the BF content is 0.1%, in addition, the chloride diffusion coefficient is positively correlated with the porosity.

This study investigates the chloride transport performance of coral aggregate concrete (CAC) in a marine environment. The effects of the aggregate type, strength grade, and fly ash (FA) content on the chloride concentration distribution, surface chloride concentration (Cs), chloride diffusion coefficient (Da), and porosity are discussed. The results show that the higher the strength grade of CAC is, the lower the Cs and Da will be. The Cs and Da of CAC initially decrease and then increase with increasing FA content. The compressive strength of CAC has a negative correlation with the Da, whereas the porosity is positively correlated with Da. The Da of CAC is higher than that of ordinary aggregate concrete (OAC) at the same exposure time. The Cs of CAC increases exponentially with the erosion time. In addition, the attenuation law of Da with the exposure time can be expressed as a power function. The decay rate of CAC is relatively slow, and the age reduction factor (m) of OAC is 11.95% higher than that of CAC. Furthermore, the age reduction factor is positively correlated with the strength grade and FA content. The content of Friedel's salt decreases gradually with increasing CAC strength grade at the same exposure time; with increasing erosion time, the content of Friedel's salt also increases, but the magnitude of increase is reduced.

With the development of marine technology, the potential of coral aggregate concrete (CAC) for use in the construction of reefs has been identified. However, the shape, surface structure, high porosity, and chloride-ion-carrying properties of coral aggregates yield special microstructures and affect the mechanical properties and durability of CAC. This study investigates the effect of basalt fiber (BF) on the mechanical properties, chloride content carried in coral aggregates, and water absorption of CAC. The results indicate that with the increase in fiber content, the mechanical properties and water absorption resistance of basalt fiber reinforced coral aggregate concrete present an increasing trend then followed decreasing trend. Furthermore, 0.05% BF yields the highest improving effect on the mechanical properties and water absorption resistance at 28 days. Compared with the reference concrete, the compressive strength and splitting tensile strength of CAC with 0.05% BF increase by 9.87% and 1.36% at 28 days, respectively. When the fiber content continues to increase, the strengthening effect decreases, and cause adverse effects. The dissolution of chloride in coral aggregates was accelerated by 0.05% BF, while the chloride dissolution was inhibited by 0.1%–0.2% BF. Moreover, the microstructure of CAC is investigated to elucidate the enhancement mechanism of BF in terms of thermogravimetric analysis, theoretical total pore volume, fiber bonding performance, and fiber-matrix interfacial characteristics.