A concrete slab may dry in two directions if no vapor barrier is installed. If the concrete at the surface is shrinking faster than the underlying concrete, stresses develop in the concrete surface that are relieved by cracking. We call them "shrinkage cracks". Shrinkage cracks are often not continuous. For a more detailed look at forces that affect concrete, see my article Visual Inspection of Concrete. Skip to content Home inspectors will encounter cracks in almost every part of a home made of materials brittle enough to crack.
This can happen when a part of the structure is heated more than the other. During the hydration process, different compounds in cement hydrate at different rates and evolve different quantities of heat. This can result in differential changes in the volume of the concrete which may lead to thermal cracking.
In addition, during the hydration process, the concrete core gets heated more than its shell because the shell being exposed to the environment gets cooled quickly. This temperature gradient triggers the formation of cracks. Thermal cracks assail the tensile strength of the concrete and therefore, proper measures are to be taken timely. The internal temperature of concrete must be regulated.
In addition, the tensile strength of concrete should also be checked, and thermal insulation can also be provided. If the cracks appear, grouting or sealing is to be done. Craze cracking in concrete occurs when proper curing is not done. This happens when the concrete surface gets dried due to high temperature, wind action, or low humidity.
Moist curing the concrete for ample duration is possibly the best preventive measure. However, if such cracks attack the concrete, a thin overlay is usually the only option since the use of sealers or surface hardeners can make crazing more obvious. Concrete structures are vulnerable to expansion and contraction depending upon the atmospheric temperature and humidity. In hot weather, the expansion process triggers, and in cold weather, contraction takes place.
If not taken into account, these processes may produce cracks in the concrete. The best measure to prevent the onset of expansion and contraction cracking is by introducing an expansion and contraction joint in the respective cases. These joints act as grooves and help allocate space for the concrete to expand or contract without inducing stresses in it. When the bond between the steel reinforcement and concrete is inadequate, the steel is prone to corrosion. This is because improper bond at the interface invites moisture and air to penetrate and attack the steel.
If this happens so, the concrete gets vulnerable to cracking, preceded by spalling of the cover to reinforcement. As a preventive measure, corrosion-resistant bars can be used. However, a remedial measure involves removing the concrete and placing new rods followed by epoxy coating and packing with fresh concrete. Material Concrete. This study uses quantitative analysis methods, to the analysis of fracture patterns of rigid pavements with transverse reinforcement on expansive soils.
Rigid pavement is modeled into 2 types, namely rigid transverse reinforced pavement models due to swelling pressure forces on expansive soils and transverse reinforced rigid pavements without swelling pressure forces on expansive soils. The swelling test on the soil carried out in the laboratory was 37 kPa. The rigid pavement model is subjected to load testing. As the water content increases, the rate of shrinkage rises equivalently.
Drying shrinkage may be a full-length cracking. Usually contraction joints are placed to predetermine the drying shrinkage. This cracking will be in the form of transverse, pattern or map cracking. The designer should control the shrinkage effects by providing adequate rebar and predetermined contraction joints.
During the time of construction provide good curing to allow the concrete to gain sufficient tensile strength before significant shrinking forces develop. Use of shrinkage compensating concrete and admixtures prevent shrinkage cracks. Concrete will contract and expands with changes in moisture and temperature. As long as these contraction movement is free to take place tensile stress will not develop in concrete members.
But in reality, movement of this contraction will be restrained due to internal or external restraints, which causes development of tensile stress, leading to cracking.
Thermal cracking occurs during the hardening state. When cement reacts with water, heat of hydration is released from the cement, as a result thermal expansion occurs in the concrete member.
Thermal crack possibly will be a full depth crack.
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