【正文】 itoring, and to take timely cooling or insulation measures, reducing the temperature difference between inside and outside of the concrete. 7 is to strengthen the concrete curing, pouring concrete, timely cover with wet straw mat, linen piece, and note the sprinkler maintenance, appropriate to extend the curing time. Eight is to configure a small amount of the small size reinforced concrete or mixed fiber material to control the temperature cracks of the concrete within a certain range. Chemical reaction caused by cracks and Prevention Alkali aggregate reaction cracks and steel corrosion cracks in two kinds of cracks caused by the chemical reaction is generally divided into the reinforced concrete structure. Construction works is limited to the position of the concrete, after mixing some alkaline ions, these ions react chemically with some of the reactive aggregate expansion and to absorb the moisture in the surrounding environment, resulting in shortening of concrete, Splitting. Such cracks generally appear in the concrete structure during the event difficult to remedy, and should therefore take effective measures to prevent construction. The main preventive measures are: First, the choice of the alkali reactivity of small gravel aggregate. Second, the selection of lowalkali cement and alkalifree admixture. The third is optional and can inhibit the admixture of alkali aggregate reaction. Adverse phenomenon due to the reinforced protection of reinforced concrete structures during construction caused by bad thin, exposed tendons, cellular, pockmarked face, making the hazardous substances and exposed reinforcement through the concrete and internal reinforcement to react to rust, corrosion of reinforced volume expansion, resulting in concrete spalling, cracks of this type generally along the reinforced positions. The usual precautionary measures。 rigid sealing material of polymer cement mortar. 5. Crack control measures Contraction (shrinkage) cracks in the control Contraction (shrinkage) cracks in the control is to control the humidity changes, the structure of the ponent has a relatively stable humidity. To strengthen the early curing of concrete, concrete pouring after the exposed surface with straw mats, straw bags or plastic mulch, and watering moist conservation. Should try to cover in the hightemperature, low humidity, wind speed, weather, spray mist conservation, and appropriate to extend the curing time. To strengthen the concrete surface of the wiping pressure, but it should be taken to avoid excessive wiping pressure. Seal water sprayed on the concrete surface curing agent or covering of plastic film, so that water can not evaporate, or to use other way to feed air flow (such as set up a wind wall, cover), slow down the evaporation of surface moisture. Prestressed ponent, to avoid piling up longterm tension. Proper mixing ratio, to avoid watercement ratio, the amount of cement, sand ratio is too large, and strictly control the sand, stone, clay content, avoid the use of silt, in order to improve the tensile strength of concrete. Component of longterm openair pile up should continue to be the proper watering or covering conservation, to longer moisture conservation, especially thinwalled structures, should be a cool place to cover stacked. Temperature control of the cracks Prevent the surface temperature cracks in the concrete caused by internal constraints, the general control of the concrete surface with the outside world or the internal temperature difference, it is less than 25 ℃ . Commonly used control measures are: the ponents of the heat conservation, the slow heating and cooling, lift a temperature not greater than 10 176。 use late (90d, 180d) strength to reduce the cement consumption and temperature rise。 backfill concrete form removal, timely, and to avoid the structural side of the longterm exposure. 4, the large volume basis to take the stratified subblock placement, a reasonable set of construction joints, pouring seam in the appropriate location, to speed up the heat。 the seam area, and increase reinforcement ratio, and concealed beam, in order to reduce edge effects and to improve the tensile strength。 lower vibration can be reinforced when gently on the upper steel vibration to minimize the upper steel stick with a water slurry。 support node with microconnection, such as the use of bolted connections, and set aside hole equipped with rubber gaskets, flexible connections to reduce restraint stress。 the die must be straight prestressed ponent holes for pouring concrete after the timer (15min) rotating steel pipe , handpumped tube pressure concrete surface is not significant imprint is appropriate, smoke pipe should be smooth slow。 roof trusses, columns, such as lifting, should be required to set the hanging point。s lives and property safety, according to the different parts, shape and extent of concrete cracks, careful analysis, using a reasonable method for processing, to take effective preventive measures to prevent the emergence and development of cracks in the construction, to ensure that construction material and ponents safe, stable job.