Does concrete gain strength by drying out? In simple terms, no. Although water in concrete can cause a chemical reaction, it does not leave the material. As a result, water in concrete does not evaporate. It becomes a part of the concrete form and the chemical reactions between it and the water continue to strengthen the concrete. The water causes the cement to dry out and it gains strength as a result. However, this is not the case for all cases.
When you pour concrete, it dries out and begins to harden. The process can take as little as 24 hours or as long as 28 days. Once it dries out completely, it reaches its full strength. Depending on the type of concrete, this process can be prolonged for as long as necessary. The water content in concrete can vary significantly from batch to batch, so the amount of water is necessary to achieve the desired strength.
When the concrete dries out, its properties are fixed. It gains 90% of its strength in the first 28 days. If the conditions are dry, it can gain strength forever. This is not true for all mix designs, but in some cases it can be detrimental to the development of strength. The process can also be damaging to the integrity of the material. The addition of water to the concrete will cause the material to lose its quality.