# Early-Age Cracking in Concrete: Causes, Consequences, Remedial Measures, and Recommendations
## 3 Causes of Early-Age Cracking  
Early-age cracking occurs in concrete structures because of temperature differences and stress development during hardening of concrete. At the early-age of concrete elements or structures, when the tensile strain created from restrained thermal contraction or temperature differential surpasses the tensile strain capacity of concrete, cracking is the outcome (refer to Figure 6); the tensile strain may also be aroused from early contraction caused by autogenous shrinkage [16]. High-strength concrete is more prone to early-age cracking due to autogenous shrinkage [17]. Drying shrinkage hardly plays a role to cause the early-age cracking in concrete. [PERSON] and [PERSON] [10] divided drying shrinkage into two types: external drying shrinkage and internal drying shrinkage, and this was supported by [PERSON] and [PERSON] [8]. [PERSON] and [PERSON] [12] divided shrinkage into three types, i.e., drying, thermal, and autogenous shrinkages. Concrete for repair purpose requires high early strength; therefore, accelerators are commonly used in the mixture to increase hydration rate. However, the increased hydration rate also causes high heat of hydration which can potentially increase autogenous deformation and subsequent cracking in concrete [18]. Hence, the proper choice of accelerator is very important regarding the use of high-early-strength concrete in repair or overlay work. [PERSON] et al. [19] studied the  
Figure 5: Early-age map cracks that occurred in a newly cast concrete floor slab; these cracks appeared within 14 days of concrete placement; the floor slab was cured by spraying of water. Figure 6: Restrained shrinkage cracking that occurred in a roadside concrete curb; this crack initiated within 56 days of concrete placement; the curb was cured with curing compound. effect of nitrate- and chloride-based accelerators on the cracking risk in concrete at the early-age. They reported similar cracking tendencies for both accelerator types at different concentrations. However, the concrete with the chloride-based accelerator experienced higher shrinkage compared to that with the nitrate-based accelerator. Thermal strains driven by high temperature gradients occur between the interior and surface of structural elements since concrete has poor thermal conductivity [8; 10]. The partial and fully restrained movement from the cooling or other temperature change induces tensile stress in concrete [20; 21]; because early-age concrete is generally not strong enough to resist this stress, it cracks. [PERSON] and [PERSON] [12] named this phenomenon as the thermal dilation effect. Some researchers [6] have different viewpoints on drying shrinkage cracking and defined drying shrinkage as a reduction in concrete volume due to moisture loss at constant temperature and relative humidity. The loss of water through evaporation results in plastic shrinkage and subsequent internal stresses [13; 22], leading to early-age map cracks on the concrete surface, as shown in Figure 5. [PERSON] et al. [23] deduced that the presence of microsilica and the rapid drying of the concrete surface are the main reasons for plastic shrinkage in concrete elements. [PERSON] [24] pointed out that the chemical shrinkage and autogenous shrinkage of concrete may contribute to its ultimate cracking risk. Chemical shrinkage is induced when the volume of hydration products becomes smaller than the original volume of reacting constituents: cement and water. It is defined as the internal volume reduction in the hydrated cement paste of concrete. In contrast, autogenous shrinkage is considered as the external volume reduction of hydrated cement paste. It happens when the hydration process consumes water and causes internal drying, resulting in a decrease in the material volume [8; 10].