【文章內(nèi)容簡(jiǎn)介】 of some patters more quickly, which may reduce the cost of patters. 中國(guó)地質(zhì)大學(xué)長(zhǎng)城學(xué)院 2021 屆畢業(yè)論文 9 2Curing Concrete If concrete is to gain its maximum strength and other desirable properties, it should be cured with adequate moisture and at a favorable temperature. Failure to provide these conditions may result in an inferior concrete. The initial moisture in concrete is adequate to hydrate all the cement, provided it is not should replace the moisture that does evaporate. This may be acplished by many methods, such as leaving the patters in place, keeping the surface wet, or covering the surface with a liquid. curing pound, which es being to a watertight membrane that prevents the escape of the initial water. Curing pounds may be applied by brushes or pressure sprayers. A gallon will cover 200 to 300 sq ft. Concrete should be placed at a temperature not less than 40 or more than 80176。 lower temperature will decrease the rate of setting, while a higher temperature will decrease the ultimate strength. 3Placing Concrete in Cold Weather When the concrete is placed during cold weather, it is usually necessary to preheat the water, the aggregate, or both in order that the initial temperature will assure an initial set and gain in strength. Preheating the water is the most effective method of providing the necessary temperature. For this purpose a water reservoir should be equipped with pipe coils through which steam can be passed, or steam may be discharged directly into the water, several outlets being used to given better distribution of the heat. When the temperatures of the mixtures are known, some specific charts may be used to calculate the temperature of concrete. A straight line pass all three scales, passing through every two known temperatures, will assure the determination of the third temperature. If the surface of sand is dry, the fact lines of the scales giving the temperature of concrete should be used. However, if the sand contains about 3 percent moisture, the dotted lines should be used. Specifications usually demand that freshly placed concrete shall be kept at a temperature of not less than 70176。F for 3 days or 50176。F for 5 days after it is placed. Some proper method must be provided to keep the demanded temperature when the cold weather is estimated. 4Reinforcing steels for concrete Compared with concrete, steel is a high strength material. The useful strength of ordinary reinforcing steels in tension as well as pression, the yield strength, is about 15 times the pressive strength of mon structural concrete, and well over 100 times its tensile strength. On the other hand, steel is a highcost material pared with concrete. It follow that the two materials are the best used in bination if the. 中國(guó)地質(zhì)大學(xué)長(zhǎng)城學(xué)院 2021 屆畢業(yè)論文 10 Concrete is made to resist the pressive stresses and the pressive force, longitudinal steel reinforcing bars are located close to the tension face to resist the tension force. and usually additional steel bars are so disposed that they resist the inclined tension stresses that are caused by the shear force in the beams. However, reinforcement is also used for resisting pressive forces primarily where it is desired to reduce the crosssectional dimensions of pression members, as in the lowerfloor columns of multistory buildings. Even if no such necessity exits , a minimum amount of reinforcement is placed in all pression members to safeguard them against the effects of small accidental bending moments that might crack and even fail an unreinforced member. For most effective reinforcing action, it is essential that steel and concrete deform together, that there be a sufficiently strong bond between the two materials to ensure that no relative movements of the steel bars and the surrounding concrete occur. This bond is provided by the relatively large chemical a