Ultrasonic Pulse Velocity and Mechanical and Physical Properties of Structural Geopolymer Concrete Containing Lightweight Expanded Clay Aggregates: Experimental and Computational Study

In the present study, the influence of adding lightweight expanded clay aggregate (LECA) and natural zeolite (NZ) on the geopolymer concrete (GPC) based on ground-granulated blast furnace slag (GGBS) was investigated in terms of density, water absorption, compressive and splitting tensile strengths, and ultrasonic pulse velocity (UPV) at ambient temperature. Two sizes of LECA as the replacement of course and fine aggregates ranging from 0 to 100% were used in order to examine their suitability to produce lightweight GPC (LWGPC). NZ was utilized as a binder in the GPC with up to 15% replacement of GGBS. Test results indicated that the density of GPC decreased and water absorption value was increased with higher LECA percentage, and this behaviour is observed for NZ addition with less intensity. Compressive strength of the lightweight GPC is extremely decreased from 5 to 20% by incorporation of NZ in place of GGBS. Results indicated that LWGPC with 100% LECA compared with the specimens without LECA can effectively decrease the tensile strength by about 50% and the reduction for NZ addition is approximately 15%. The experimental results show that the variation in splitting tensile strength, compressive strength, and UPV of LWGPC is significantly influenced by binder content. A machine learning-based model was created for the mixtures produced within the scope of the experimental study and equations generated from M5p model tree that represents a strong correlation between the actual and predicted values for splitting tensile and compressive strengths with more than 99% of accuracy.