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1) It is early: Build concrete is it is it over basically to send out heat to cement to begin, generally one day by oneself. Two characteristics at this stage, first, the cement emits a large amount of heat of hydration, second, mix and congeal the changing sharply of elastic model quantity. Because of the change of elastic model quantity, form the remaining stress in the concrete in this period.
2) Middle period: Up till the concrete is cooled until stability temperature from cement send out heat function basically when expiring, in this period, the temperature stress is mainly because the cooling of the concrete and external temperature change cause, these stresses and remnants stresses that is formed in early days are superposed, mix and congeal the elastic mould amount that goes to and does not change much during this period.
3) Later period: Operation period after the complete cooling of concrete. Temperature stress whether external temperature change cause mainly, these stresses and first two kinds of remnants stresses are changed and added.
Can be pided into two kinds according to the reason why the temperature stress causes:
1) Spontaneous stress: There are not any restraint or totally static structure at the border, if inside temperature is non-linear distribution, temperature stress appearing because structure restrains from each other. For example, the body of mound of the bridge, the physical dimension is relatively large, surface temperature is low when the concrete is cooled, inside temperature is high, present the stress of drawing on the surface, present the stress of pressing in the middle.
2) Restrain the stress: All of the structure ones or it restrain external one some border, can't out of shape and stress not cause not free. Such as case roof beam roof concrete and guardrail concrete.
These two kinds of temperature stresses draw back stresses caused to act on with the doing of concrete together frequently.
It is a more complicated job to want to analyze the distribution, size of the temperature stress accurately according to known temperature. In case of great majority, need to rely on the model test or the number value to calculate. To is it make temperature stress have sizable limp to creep concrete, at the stress accounting temperature, must consider the influence that creep , calculate concretely that no longer states thinly here.
1.3 Control and preventing the measure of the crack of temperature
For prevent crack , lighten temperature stress can from control temperature and is it is it set about to restrain terms from two to improve.
The measure of controlling temperature is as follows:
1) Is it improve aggregate grade mix , is it do rigid concrete to spend , mix mixture to adopt, is it guide angry pharmaceutical or plasticization pharmaceutical ,etc. measure in order to reduce cement consumption of concrete to add;
2) Add water or the water to cool the broken stone in order to reduce the temperature of building of the concrete while mixing and shutting the concrete;
3) Reduce the thickness of building while building the concrete on hot day, utilize and build the aspect to dispel the heat;
4) Bury the water pipe underground in the concrete, enter the cold water to lower the temperature openly;
5) Stipulate rational form removal time, the temperature keeps warm the surface while lowering suddenly, in case that the rapid temperature gradient takes place in the concrete surface;
6) The concrete with medium and long-term and exposed construction builds a piece of surface or thin wall structure, take the measure of keeping warm in cold season;
The measure of improving condition of restraining is:
1) Divide and sew and pide one rationally ;
2) Prevent the foundation from rising and falling too big;
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