According to ACI, mass concrete refers to any volume of concrete with dimensions that are large enough to require that measures be taken to cope with the generation of heat that comes from the hydration of cement to minimized cracking. Ambient temperature, concrete mix temperature and differential temperature all need to be monitored and adjusted appropriately to avoid thermal cracking.
Thermal cracking develops when the tensile stress of the concrete exceeds its tensile strength. When this happens, various types of cracking may occur such as random map cracks, series of vertical cracks in walls with the widest near the base of the wall, and uniformly spaced cracks in beams. In severe cases, these cracks can affect the entire structures integrity. There are a number of measures that one can put into place as a means of controlling temperature.
First, it is imperative that an optimal concrete mix design is used. Using low-heat cement, using aggregate substitutes such as fly ash, limestone or slag or using low water-to-cementitious materials are all such means. Another method is the use of insulation to control the temperature differential (core temperature vs. surface temperature).
Concrete cooling before placement is also helpful in maintaining control of temperature. Ways of doing so include the use of chilled water, chipped or shaved ice or liquid nitrogen. Similarly, cooling after placement is also effective. This can be done by installing cooling pipes; non-corrosive piping that is embedded prior to the concrete placement. This removed heat from the placed concrete by circulating cool water from a nearby source.
In order for the implementation of any of these measures to make any valuable difference, one must be able to monitor and report on the changing temperature levels. Currently there are a number of temperature monitors in the market for this purpose such as the Doka and the Intellirock and of course, the SmartRock2.
Like other temperature monitors currently in the market, the SmartRock2 provides real-time analysis of temperature and strength in all stages of the concrete placement. The sensors are embedded into the concrete where they measure the temperature development that takes place from the fresh to the hardened stage at regular intervals. It is in this way that one is able to monitor the changes that are taking place following the implementation of various temperature control measures previously discussed. Having this information ensures optimization of concrete formulation and optimal temperature curing conditions.