There are several causes of cracks in concrete. Cracks caused before hardening are due to constructional movement, settlement shrinkage, and setting shrinkage. Cracks caused after hardening are due to chemical reactions, physical movement, thermal changes, stress concentrations, structural design, and accidents. The concrete itself contains many elements that affect cracks. Water is a big one. It has been found the more water used, the greater the cracking tendency because water both increases shrinkage and reduces strength. The amount of cement is also important; in general the richer concretes crack more. The mineral composition, shape, surface texture, and grading of aggregate variously affect the required proportions, thermal coefficient, drying shrinkage, stiffness, creep, and strength of concrete. Some admixtures may also affects cracking because of their effects on such contributory factors as rate of hardening, shrinkage, and creep. There are ten ways to help keep down cracking. (1) Design the structure with a mind to the degree of restraint during drying or cooling of the concrete. (2) Prestress wherever feasible. (3) Provide competent inspection, and back it up. (4) Use materials known to have a good service record with regard to cracking, irrespective of shrinkage or other tests on single contribution causes. (5) Use the minimum cement content consistent with design requirements. (6) Use the minimum water content necessary for workability; do not permit overwet consistencies. (7) Place the concrete uniformly, and take account of early settlement in the forms, around reinforcement , on slopes, and elsewhere. (8) Cure the concrete moist or sealed, beginning very early. (9) Avoid extremes of temperature. And finally (10) protect the concrete in service from moisture and temperature changes wherever feasible, as by backfilling, shading, or coating.