Assessment of basalt fiber and gelling enhancement effects on mixed mode I/III fracture performance of the mortar composites

Abstract

The study of the crack resistance of modified cement-based materials can provide a valuable guidance for pavement structural design. In this work, the plain mortars with 3 different water/cement ratios (0.35, 0.45 and 0.55) and the basalt fiber (BF) reinforced mortars with 3 different amounts of basalt fibers (0 %, 0.3 % and 0.8 % by mass) were prepared to investigate mixed mode I/III fracture performance. In the BF reinforced groups, we take the water/cement ratio of 0.45 as a reference. Then, the fracture experiments were conducted using the Edge Notch Disc Bend (ENDB) testing, and the pore structure measurements of each sample were performed using the nuclear magnetic resonance (NMR) testing system. The results show that an appropriate reduction in water/cement ratio and an increase proportion of basalt fibers are both beneficial to improving the fracture performance of the cement mixtures. However, a superior fracture performance was achieved for BF reinforced mortar composites over the mortar with gelling enhancement. For instance, the enhancement rate of applied load, fracture energy, and effective fracture toughness for BF reinforced mortar under mode III are 3.27, 2.35, and 1.34 times the values of those for gelling-enhanced mortar under mode III, respectively. We also find that the three dimensional maximum tangential strain (3D-MTSN) criterion is applicable for predicting mixed mode I/III stress intensity factor (SIFs) of mortar composites. The reduction in water/cement ratio significantly increases the amount of micropores inside the mortar specimen. By contrast, the addition of basalt fibers to the cement mixture deteriorates its pore structure by raising the proportion of macropores to total pores from 3 % to 10 %. However, the basalt fiber crack-bridging effect on improving the fracture toughness of the cement mixtures is also revealed.