【正文】 of a drier concrete, which has a higher strength because of the reduced water content. Among the advantages of vibrating concrete are the following: 1. The decreased water permits a reduction in the cement and fine aggregate because less cement paste is needed. 2. The lower water content decreases shrinkage and voids. 3. The drier concrete decreases the cost of finishing the surface. 4. Mechanical vibration may replace three to eight hand puddles. 5. The lower water content increases the strength of the concrete. 6. The drier mixture permits the removal of some patters more quickly, which may reduce the cost of patters. 中國地質(zhì)大學(xué)長城學(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。 s requirements. A surface coating may be required when appearance is important or when cover to reinforcement is small. of Repair Methods A suitable repair counteracts all the deficiencies which are relevant to the use of the structure. The selection of tile correct method and material for a particular, application requires careful consideration, whether to meet special requirements for placing strength, durability or other shortor longterm properties. These considerations include: 1. Nature of the Distress 中國地質(zhì)大學(xué)長城學(xué)院 2021 屆畢業(yè)論文 13 If alive crack is filled with a rigid material, then either the repair material will eventually fail or some new cracking will occur adjacent to the original crack. Repairs to live cracks must either use flexible materials to acmodate movements or else steps must be taken prior to the repair to eliminate the movement. 2. Position of the Crack Techniques which rely on gravity to introduce the material into the crack are more successfully carried out on horizontal surfaces but are rarely effective on vertical ones. 3. Environment If moisture, water or contaminants are found in the crack, then it is necessary to rectify the leaks Repair to slop leaks may be further plicated by the need to make the repairs while the structure is in service and the environment is damp. 4. Workmanship The skill the operatives available to carry put the repairs is another relevant factors. Sometimes this can mean the difference between a permanent repair and premature failure of the repair material. 5. Cost The cost of repair materials is usually small pared with the costs of providing access, preparation and actual labor. 6. Appearance The repair surface may be unsightly, particularly when it appears on a prominent part of the building. In this case, the repair system will include some form of treatment over the entire surface. 。F for 3 days or 50176。 Placing。 中國地質(zhì)大學(xué)長城學(xué)院 2021 屆畢業(yè)論文 6 與為修復(fù)工作提供通路、做準(zhǔn)備工作和實際勞力的成本相比，所用的修復(fù)材料的成本是相當(dāng)小的。 依靠材料重力填充裂縫技術(shù)在水平面上裂縫修補中的成功率較高，但在豎直面上裂縫修補中效果很差。當(dāng)外觀很重要或鋼筋的保護層很薄時，要求采用鑲面處理。 對環(huán)境引起的損傷的早期防護 一些開始就暴露在外的情況會引起修復(fù)的過早損壞。 基片粘結(jié) 使用基片粘結(jié)可進行完整的修復(fù)，它可防止水分和大氣從界面進人。 耐久性 選擇有相當(dāng)耐久性的修復(fù)材料非常重要 。這包括那些設(shè)計和施工的失誤，使用劣質(zhì)材料和在侵蝕性環(huán)境下暴露。在特殊情況下，例如高層建筑的下部樓層的柱子，使用這一高強度范圍內(nèi)的鋼筋就非常適合。在這種情況下， ACI規(guī)范要 求在規(guī)定的最小屈服強度時的總應(yīng)變不應(yīng)超過。屈服強度為 40KSI的鋼筋，在 20年前幾乎是標(biāo)準(zhǔn)的盲目前大部分已由屈服強度為 60鋼筋所取代。不同的鋼筋制造廠家采用不同的變形花紋，他們?nèi)慷寄軌驖M足這些要求。 最常見的鋼筋