If you were to ask homeowners what problems they are having with the concrete driveways, sidewalks, and patios around their homes, the answer would probably be scaling and cracking. We know properly finished, air entrained, and cured will eliminate scaling. But what can we do about cracking? Concrete, like other materials used in construction, contracts and expands slightly with moisture and temperature variations. These minute changes in volume are normal in all concrete. Provisions must be made to control these changes or random cracks will be produced. Also, when subgrades move due to settlement, erosion, swelling or frost heave, flatwork slabs tend to crack. Ways to minimize volume changes are: limit the water content of concrete; avoid conditions that increase the water demand of concrete, such as high slumps and high concrete temperatures; use the largest total amount of aggregate in the mix that is practical; use the largest maximum size coarse aggregate to fit job conditions; use fine and coarse aggregates that exhibit low drying shrinkage characteristics in concrete; avoid aggregates that contain excessive amounts of clay; avoid aggregates with high thermal coefficients of expansion; and avoid admixtures that increase drying shrinkage. Tensile stresses are the primary cause of cracks during the early life of an unjointed concrete slab single concrete does not have a high resistance to tensile stress at early ages. Cracking will result when stresses from volume changes are greater than the concrete tensile strength. The amount of cracking formed at this stage will vary, depending on factors such as concrete properties, slab thickness, variations in the type of subgrade, and climatic conditions. Factors that contribute to low tensile strength are coarse aggregate containing a large number of low strength particles. Certain hard, dense, coarse aggregates with smooth surfaces; weak mortar which may result from poor strength producing properties of the fine aggregate, too high a water-cement ratio or a cement content that is too low.