At an early age, the temperature rise in mass concrete is attributable primarily to the propagation of heat due to an exothermic reaction of cementitious materials and water. The temperature variation in the mass concrete between the core and its surfaces results in the development of thermal stresses. It might occur cracking if these stresses surpass the gained tensile strength of concrete. The paper compares experimental and numerical outcomes of heat generation in concrete mould 0.15 m × 0.15 m × 0.15 m in size. Four concrete mixtures with ground granulated blast-furnace slag (GGBS) replacement to cement 0%, 10%, 30%, and 50% were used in the study. Virtual Cement and Concrete Testing Laboratory (VCCTL) software was used for obtaining the degree of hydration and adiabatic temperature of the four mixtures. Finite element modeling of these mixtures observed good agreement with experimental testing captured by the thermometer. Following that, numerical simulation was utilized to study the effect of the block size (cubic models with edge length 0.5 m, 1.0 m, 2.0 m, and 3.0 m) on temperature rise and the associated risk of cracking in mass concrete blocks.