Effect of Bottom Ash as Fine Aggregate on Shrinkage Cracking of Mortars

Abstract

The effect of the nonground bottom ash (BA), as fine aggregate in mortar or concrete, on shrinkage cracking is observed on mortar specimens in this study. The replacement was made by weight; the replacement ratios for BA as fine aggregate were 0, 10, 20, 30, 40, 50, 60, 70, 80, 90, and 100%. After that, unit weights, ultrasonic pulse velocity, flexural and compressive strengths, and length changes due to free shrinkage were determined by producing 1.58 x 1.58 x 6.3 and 0.984 x 0.984 x 11.22 in. (40 x 40 x 160 and 25 x 25 x 285 mm) prismatic mortar specimens for each series. Furthermore, the modulus of elasticity was also determined by producing 5.91 x 5.91 x 5.91 in. (150 x 150 x 150 mm) cubic mortar specimens. Finally, a ring test was conducted to determine the effect of BA on shrinkage cracking. The widths of the cracks during the ring test were measured using an optical crack microscope. Consequently, it was seen that BA usage up to 100% replacement ratio decreases shrinkage cracking because of the porous structure of mortar specimens related to the coarser structure of BA compared to reference sand. Free shrinkage, however, occurred irregularly. Moreover, the strength and modulus of elasticity also decreased with the increase in BA content due to the same increased porous structure of the mortars containing higher replacement ratios of BA.