Enhancing the Mechanical Properties and Microstructure of Basic Magnesium Sulfate Cement with Basalt and Carbon Fibers.

Basalt fiber (BF) and carbon fiber (CF) were added to the basic magnesium sulfate cement (BMSC) in this paper to enhance the cement's brittleness and mechanical properties. Then, by comparing the fluidity, flexural strength, and compressive strength of fiber basic magnesium sulfate cement and through the comparison of microstructures of BF and CF in the BMSC mortar, the mechanisms of action of the two fibers were analyzed. Different lengths of BF also demonstrate varying effects on the fluidity of the BMSC mortar. Careful consideration should be given to the dosage of the BF when it is applied. Conversely, as the dosage of CF increases, the fluidity of the BMSC mortar diminishes sharply, and an increase in fiber length further diminishes the fluidity of the BMSC mortar. When 6 mm and 12 mm BF are introduced in quantities ranging from 0 to 0.6%, the 28-day fracture strengths of the mortar are markedly improved. The flexural strength of the BMSC mortar is enhanced by the addition of CF at each age, and the flexural strength of the BMSC mortar increases progressively with the increasing amount of CF added. Furthermore, chopped fibers demonstrate a superior effect in improving the flexural strength of BMSC mortar. When BF with an appropriate length ratio and an additional amount is added into the BMSC mortar, the compressive strength can be improved. When 0.6% 6 mm fibers are added, the 28-day compressive strength of mortar increases by 6%, whereas when 0.3% 12 mm fibers are added, the 28-day compressive strength of mortar improves by 4%. The cross-linking mechanisms of these two kinds of fibers at the microcracks are obviously different. The cement mortar matrix and BF have a lower interface bonding strength than that of the cement mortar matrix. In the process of test specimen compression failure, the BMSC mortar is damaged first, before the removal of BFs from the matrix. For the addition of CF into the cement mortar system, when cracks appear inside the fiber set cement test specimen, the disorderly distributed CFs can form the bond force and mechanical interaction on the crack, thus restricting the propagation of local cracks.