Effect of mixed basalt fiber and calcium sulfate whisker on chloride permeability of concrete

Abstract

Rapid chloride migration (RCM) test was used to determine the non-steady-state chloride migration coefficient (DRCM) of concrete mixed with calcium sulfate whisker (CSW) and basalt fiber (BF). Meanwhile, the microscopic morphology of CSW and BF in concrete was observed through scanning electron microscope (SEM), and the microstructural parameters were determined by the nuclear magnetic resonance (NMR) method. Results show that mixes with 3.0 kg/m3 CSW or BF alone outperformed in terms of chloride penetration reduction. However, by considering the strength factors comprehensively, the effect of enhancing concrete strength and chloride permeability resistance is better when 3.0 kg/m3 CSW and 4.5 kg/m3 BF are mixed. Binary problem optimal analysis results show that the optimal admixture dosage for improving the chloride impermeability and the optimum admixture dosage for enhancing the compressive strength (fc) of concrete are not consistent. According to SEM results, CSW is evenly distributed in the matrix and BF is wrapped by concrete matrix. The addition of BF and CSW to concrete reduced its porosity according to NMR tests. Increasing the content of BF would increase the contributive porosity (φ) of macro pores in concrete, while CSW could reduce the φ of macro pores. The DRCM has the strongest correlation with φ with a pore size of 100–1000 nm, followed by porosity.