Workability, Mechanical Properties, and Microstructure Analysis of Bottom Ash Mortar Reinforced with Recycled Tire Steel Fiber

Recycled tire steel fiber (RTSF) is added to mortar with pre-wetted bottom ash (BA) to enhance the mechanical properties of the mortar, in addition to providing an internal curing effect. This work investigated the mechanical properties of BA mortar, such as the compressive strength, splitting tensile strength, and flexural strength, including the heat of reactions and the total shrinkage, considering different contents of BA (i.e., 10%, 20%, and 30% replacements by volume of fine aggregate) and recycled steel fiber (RSF, i.e., 0.5% and 1.0% by volume). The results showed that BA reduced all mechanical properties; however, it increased the degree of hydration by raising the heat peak of hydration in the first 7 days, increasing the amount of calcium hydroxide at 28 days, and significantly refining the pore structure during the curing period. Regarding the effects of RTSF, the bridging effect positively affected the compressive strength, splitting tensile strength, and flexural strength of the mortar with 30% BA when 1% RTSF was added, increasing them by 25%, 46%, and 40%, respectively. Moreover, adding 1% RTSF reduced the total porosity of the mortar with 30% BA from 17.2% to 14.8%.