Effect of High Doses of Chemical Admixtures on the Freeze-Thaw Durability of Portland Cement Concrete.

摘要

The usual approach to increasing concrete's resistance to freeze thaw damage is to modify its microstructure. Because concrete readily absorbs water, when it is in a wet environment and then cooled to below 0, any water that freezes inside the concrete will expand and, depending on the nature of the internal pore structure, could lead to internal micro-cracks. A single freezing event does not cause much harm, but repeated freezing and thawing cause the tiny cracks to grow and ultimately result in conspicuous cracks on the surface of the concrete, known as frost damage. This weakens the concrete and reduces its service life. There are several mechanisms responsible for this damage, so preventing it is complex. However, there are several practical methods used today to counteract problems caused by freezing water, including (1) incorporating entrained air into the concrete to relieve pressures caused by freezing water, (2) using low water-to-cement ratios to minimize the type of voids in which water typically freezes, and (3) using silica fume to refine the pore system so that water may not be able to freeze at normal ambient temperatures. This report reviews the frost damage mechanisms, considers the usefulness of current prevention techniques, and advances a new approach for making concrete resist the deleterious effects of freezing and thawing.