ACI 308R-01 Guide to Curing Concrete

ACI 308R-01 Guide to Curing Concrete. 3.1—Pavements and other slabs on ground 3.1.1 General—Slabs on ground include highway pave- ments, airfield pavements, canal linings, parking lots, driveways, walkways, and floors. Slabs have a high ratio of exposed surface area to volume of concrete. Without preventive measures, the early loss of moisture due to evaporation from the concrete surface could be so large and rapid as to result in plastic shrinkage cracking. Continued loss of moisture, and the accompanying decrease in the degree of hydration, would have a deleterious effect on strength, abrasion resis- tance, and durability. When moisture loss is predominantly at the top surface of the concrete, the gradient in moisture content leads to greater shrinkage at the top than at the bot- tom, which in turn leads to an upwards curling of the slab (Ytterberg 1987a,b,c). Alternatively, moisture can be lost from the bottom surface due to absorption into a dry sub- grade, causing the opposite moisture gradient if the top sur- face is kept moist. This also leads to distortion of the slab. To minimize the development of such gradients in moisture content, both the top and bottom of slabs on ground should be uniformly moist or uniformly dry. Uniformly moist con- ditions are usually required if the properties of the concrete surface are important for the performance or appearance of the slab. This is achieved by prewetting the subgrade, and minimizing moisture loss at the top surface through initial, intermediate, and final curing as described in Chapter 1. Similarly, when an impervious membrane or vapor barrier is installed below the slab, maintaining the top surface in a moist condition is imperative to minimize curling. 3.1.2 Curing procedures—To maintain a satisfactory moisture content and temperature, the entire surface of the newly placed concrete should be treated in accordance with one of the water-curing methods (Section 2.2), one of the curing material methods (Section 2.4.2), or a combination thereof, beginning as soon as possible after finishing operations, without marring the surface. To avoid plastic-shrinkage cracks, protective measures such as sun shields, wind breaks, evaporation reducers, or fog spraying should be initiated immediately to reduce evap- oration. Exposed surfaces of the slab should be entirely covered and kept wet until the required concrete properties have developed to the desired level. Mats used for curing can either be left in place and kept saturated for completion of the curing, or...