Are Hairline Cracks in Fresh Concrete Normal?

It's normal to see fine cracks in freshly laid concrete, and they are usually nothing to worry about. These cracks, which are caused by plastic shrinkage, are usually very small, about 0.003 inches (0.08 mm) wide and shallow. A well-made concrete structure should not develop structural cracks quickly, but fine cracks can be expected. Don't stress; these cracks are not a sign of poor quality and can be fixed without much effort. Concrete naturally cracks on its own, unless it is given a place to crack, such as a control joint or expansion joint.

As concrete cures, heats up and expands. In summer, I saw the slab crack before I could walk on it. The main cause of fine cracks in concrete is shrinkage. Concrete is poured wet and then dried. As concrete dries, it becomes hard and strong.

This process is called healing and can take a total of 28 days to complete. But it's the first day that's most important to prevent fine cracks. If concrete loses moisture too quickly, small cracks can form. To avoid this, reduce the speed of the drying process by keeping the concrete surface moist. There are two main ways to do this.

As the concrete cures, excess water evaporates and the volume of the concrete at the inlet is reduced. ACI 116R-90, Cement and Concrete Terminology, defines fine cracks as cracks in an exposed concrete surface that has widths so small that they can barely be perceived. The main cause behind the generation of fine cracks in concrete is plastic shrinkage, which is the rapid depletion of moisture from fresh concrete into its plastic state. The causes of these cracks can be due to variations in air temperature, concrete temperature, relative humidity and wind speed on the concrete surface. Repairing a fine crack in a concrete structure involves filling the space with a material that adheres well to the concrete, restores its original appearance, and prevents liquids from penetrating inside the structure and staining the concrete. Big D Ready Mix Concrete has been serving customers in the Dallas, TX area since 2002, with more than 400 utility mixes, heavy-duty wall mixes, exposed aggregate mixes, flexural strength mixes, stamped concrete mixes, fluid fill mixes, grout mixes and mixes for trailer pumps. If cracks appear right after pouring a concrete base, the concrete may have dried too quickly, mixed poorly, or overworked.