Thermal Cracking of Concrete and Prevention
Concrete structures are vulnerable to temperature differences that can arise from various causes. One such cause is the varying rates at which different parts of the structure lose heat of hydration. Additionally, weather conditions can also impact the temperature of different portions of the structure, leading to differential heating or cooling rates. The resulting temperature differences can cause differential volume change within the structure, ultimately leading to the formation of cracks. This phenomenon is typically observed in mass concrete structures such as columns, piers, beams, footings, and slabs that are larger than 500mm in size. However, it’s important to note that temperature differentials due to changes in ambient temperature can affect any type of structure.
Concrete structures may experience temperature gradient due to the liberation of heat during cement hydration or more rapid cooling of the exterior relative to the interior. Such gradient causes tensile stresses on the exterior that can lead to cracking if the tensile strength is exceeded. The amount of tensile stress is affected by the temperature differential, the coefficient of thermal expansion, the effective modulus of elasticity, and the degree of restraint. The potential for temperature differential and restraint increases with the massiveness of the structure.
The coefficient of thermal expansion of hardened concrete typically ranges from 4 to 9×10-6 per deg. F. When one portion of a structure undergoes temperature-induced volume change, the possibility of thermally induced cracking arises. Special attention must be paid to the design of structures in which some portions are exposed to temperature changes while other portions are partially or fully protected. A drop in temperature can lead to cracking in the exposed element, while an increase in temperature may cause cracking in the protected section of the structure.
Preventive Measures:
Concrete structures may experience temperature gradient due to the liberation of heat during cement hydration or more rapid cooling of the exterior relative to the interior. Such gradient causes tensile stresses on the exterior that can lead to cracking if the tensile strength is exceeded. The amount of tensile stress is affected by the temperature differential, the coefficient of thermal expansion, the effective modulus of elasticity, and the degree of restraint. The potential for temperature differential and restraint increases with the massiveness of the structure.
The coefficient of thermal expansion of hardened concrete typically ranges from 4 to 9×10-6 per deg. F. When one portion of a structure undergoes temperature-induced volume change, the possibility of thermally induced cracking arises. Special attention must be paid to the design of structures in which some portions are exposed to temperature changes while other portions are partially or fully protected. A drop in temperature can lead to cracking in the exposed element, while an increase in temperature may cause cracking in the protected section of the structure.