Comparison of stearic acid and oleic acid for shrinkage-mitigating of alkali-activated slag composites

The large drying shrinkage is one of the most serious factors limiting the practical application of alkali-activated slag concrete (AASC). In this study, based on the successful shrinkage reduction of waste cooking oil for alkali-activated slag paste (AASP), the influence of stearic acid (saturated fatty acids) and oleic acid (unsaturated fatty acids) on fresh properties (setting time and fluidity), physical characteristics (density and water absorption), mechanical strengths (flexural strength and compressive strength), and durability (drying shrinkage, self-shrinkage, and carbonation resistance) are systematically compared. The experimental results reveal that admixing stearic acid and oleic acid can effectively inhibit the drying shrinkage and self-shrinkage of the AASP. Specifically, adding 1 wt% stearic acid (oleic acid) can reduce the drying shrinkage of the AASP by 20% (25%) and self-shrinkage by 32% (55%), respectively. Remarkably, the combined usage of the two additives can maximize the performance of the AASP, such as obtaining satisfactory mechanical strengths, extending the initial setting time, and improving the carbonation resistance. The developed AASP can be regarded as a low-cost and environmentally-friendly product, which can promote practical applications of AASC.