The phenomenon of concrete mixing plant working in hot weather?

2017-10-11

There are some special problems with pouring concrete in concrete mixing plant in hot weather, which is due to the higher temperature of concrete. As well as in many cases the increase in the rate of fresh concrete evaporation. These problems relate to the mixing, pouring and curing of concrete. It is necessary to develop reasonable processes and procedures for each project (the existence of one or more of the above conditions) and to strictly abide by it; keeping consistency is essential and the trouble from the easy-to-establish specification.
The higher ambient temperature of the concrete mixing plant increases the water consumption of the concrete, increases the temperature of the fresh concrete and causes the slump loss to be accelerated, the hydration reaction is faster, the latter causes the concrete to accelerate the condensation, but the long term strength decreases. In addition, rapid evaporation may cause plastic shrinkage and cracking, followed by cooling of the hardened concrete will produce tensile stress. It is generally believed that plastic shrinkage cracks occur when the rate of water evaporation is greater than the rate at which the bleeding rises to the surface, but it has also been observed that cracks are also generated under a layer of water and become apparent in dry conditions. When the evaporation rate per hour is greater than 1.0kg / ©O plastic cracks prone to concrete mixing station plastic shrinkage cracks may be very deep, ranging from 0.1 ~ 3mm range, sometimes very short, sometimes even up to 1m. Once produced, it is difficult to permanently closed.
The decline in environmental relative humidity will promote the generation of such cracks, so the reasons for the emergence of cracks seem quite complicated. According to ACI305R-91, pouring concrete at concrete mixing plant at the following temperatures and relatively hot weathers presents some more complex conditions such as bleed air, although this can be done by using more air entraining agents. A related problem is that if the relatively cold concrete is swelled at a higher temperature, the air will also expand so that the strength is reduced, for example, where the concrete mixing station pours the horizontal plate, Pouring vertical plate will not. Because the steel form can prevent expansion. A wind speed of more than 4.5mls will worsen the situation; windshields and sun visors are beneficial.
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