The experimental study has been done to get data of heat hydration. It important to know the temperature in the concrete during hydration reaction and forming a gel condition of silica reaction with water. Eighteen concrete specimens of cubes have been tested for many dimensions, those are cube 25cm, 50cm, 75cm for length all of side. They made from a fine and coarse aggregate of natural and recycled aggregate from burning building waste and ready-mix residual as a base concrete material. Base on the experimental study, the peak of heat hydration occurs at 10 to 21 hours. Then it will decrease that caused by hydration reaction will be complete and form to gel condition. The heat hydration in the concrete is not affected by site or room temperature, because it is caused by the hydration reaction process between silica and water until gel condition. The peak of heat hydration will increase along with higher concrete strength because it requires more cement that is reactor with water. It can affect to surface cracking for the mass concrete because it causes increasing adiabatic to fresh concrete in the early age. And it also affects a volumetric expansion in the core, so the surface of concrete gets excessive tensile stress beyond of capacity.