Influences of fiber length and water film thickness on fresh properties of basalt fiber-reinforced mortar

In plain mortar, the water film thickness (WFT) has been found to play a key role in the fresh properties. However, in fiber-reinforced mortar, the role of WFT has not been investigated yet. In this research, basalt fibers of different lengths were added to the mortar, and the dynamic and static flowability, cohesiveness, adhesiveness, and packing density were tested to study the effects of fiber length on the packing density and WFT, and the combined effects of fiber length and WFT on the fresh properties. The results showed that in fiber-reinforced mortar, the WFT also plays a key role, whereas the fiber length exerts its influences through the indirect effects on the packing density and WFT and the direct effect on fiber-mortar interaction. Basically, an increase in fiber length decreases the packing density and WFT, decreases the dynamic and static flowability needed for placing, increases the cohesiveness needed for avoiding segregation, and, quite unexpectedly, decreases the adhesiveness needed for rendering and spraying applications. Regression analysis yielded good correlation of the fresh properties to fiber length and WFT, and best-fit formulas for the mix design for basalt fiber-reinforced mortar were obtained.