The use of superabsorbent polymers to reduce cracking of bonded mortar overlays

The use of superabsorbent polymers (SAP) was found to significantly improve cracking characteristics of normal strength bonded mortar overlays containing silica fume. Mortars were designed with two water/binder ratios and three different SAP contents and tested for relevant material properties such as tensile strength, tensile relaxation, elastic modulus and drying shrinkage. With respect to overlay cracking, SAP addition generally resulted in an improvement in all tested properties, especially with respect to increasing relaxation and reduced elastic modulus. To observe cracking in real bonded overlays, mortars were cast on a rigid substrate and their cracking behavior observed for a period of approximately 7 weeks. The results indicate that SAP additions of 0.4% and 0.6% are very effective in reducing cracking in bonded mortar overlays with water/binder ratios of 0.45 and 0.55, respectively.