Dry shrinkage is the contraction or shrinkage of hardened aging concrete due to the loss of capillary water mainly through evaporation. It depends on the amount of water used at the time of mixing and can cause serious loss of strength and major deflections and cracking.
The standard consistency or standard water content that the cement will completely use up for Ordinary Portland cement is 28%. But now, it has got two problems. Firstly, it so turns out that the cement in the concrete doesn’t hydrate completely at 28% moisture even though after pretty good mixing. To improve it, you’d need to hand mix 100g samples for 10 minutes each as we do for the standard consistency test. This isn’t feasible. Also, even then, there won’t be complete hydration. To ensure complete hydration, we must use around 45% to 55% water content for cement. Secondly, the concrete has very poor workability at 28% w/c and needs at least 45% water to be well workable. Now, the cement will use up around 28% water, and the rest will remain there as capillary water. This water, when evaporates with age, causes drying shrinkage.
The effects are cracking, deflection, and loss of strength before the service life of the concrete members.