Archive for May, 2016

Winter and Concrete

There are two main methods of winter concrete work: with heating (including electrowarming) and with pro- supplements. Warming up is especially helpful when a sufficiently large arrays of monolithic concrete. For narrow joints this method can not be recommended because it is not enough to warm the actual concrete seam, it is necessary to ensure a positive temperature adjacent arrays of prefabricated elements, intensely consuming the heat from the concrete joint. In addition, warming (particularly elektroprogrev) narrow joints leads to rapid drying of concrete, quality of welds obtained in this unsatisfactory. The most useful when frosts, reaching -30 C, to zamonolichivanie seams with antifreeze additives.

This allows virtually year-round in most parts of the North. Antifreeze additives must meet the following basic requirements: have a wide temperature range of their possible use; provide enough intensive growth of concrete strength at low temperatures, to ensure workability (Adaptability) of concrete with additives, to improve, at least, not to reduce the frost resistance of concrete, be economical and affordable. The most affordable and accessible additives are a mixture of calcium chloride and sodium. However, they can not be recommended as it causes corrosion of reinforcement. Common antifreeze additives are potash and sodium nitrite, and mixtures thereof. These additives can cause alkaline corrosion of concrete, in addition, the use of sodium nitrite leads to some reduction in water resistance and fracture toughness of concrete. Potash is added to the concrete at temperatures up to -30 -35 C, sodium nitrite – -10 C in the following amounts (% by weight of cement).