The reaction between cement and water is exothermic, meaning that it gives off heat. Due to low thermal conductivity of concrete, the inner part of the concrete element (especially for thick structural elements) might reach high temperature and cracking might occur. The heat production during hydration can be limited by mean of a correct choice of the type of cement (blast-furnace slag cement or pozzolanic cement) and/or by the use of suitable admixtures slowing down the reactions (retarders, see below).
