【正文】 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。 工人所采用的修復(fù)工藝是另一個(gè)與修復(fù)有關(guān)的因素，有時(shí)它意味著水久性修復(fù)或者修復(fù)材料過(guò)早損壞。 外觀 修復(fù)材料與現(xiàn)有混凝土 的匹配程度取決于所修補(bǔ)的結(jié)構(gòu)和業(yè)主的要求。例如，粘性材料能促使混凝土堿性增加，其抑制作用能保護(hù)鋼筋免受更深的侵蝕，而環(huán)氧樹(shù)脂砂漿可防止氧氣、水分和其它有害物的侵人。然而，它的耐用性受很多因素的影響。這類高強(qiáng)度鋼筋通常是逐漸屈服的沒(méi)有屈服平臺(tái)。對(duì)這些變形的最低要求已經(jīng)通過(guò)實(shí)驗(yàn)研究予以確定。這種黏結(jié)力是由鋼筋 混凝土結(jié)合面上較強(qiáng)的化學(xué)粘合作用，熱軋鋼筋表面層的固有粗糙度，以及間距較小的肋形表面變形等所構(gòu)成的。 4 用于混凝土中的鋼筋 與混凝土相比，鋼是一種高強(qiáng)度材料。 當(dāng)混合料的溫度已知，一些專用圖可以用來(lái)計(jì)算混凝土的溫度。一加侖可以覆蓋 200~300ft2。 機(jī)械振搗可代替 3— 8個(gè)手持振搗棒。這種導(dǎo)管是由輕金屬制成的管子，具有可調(diào)節(jié)的長(zhǎng)度而且被連接到儲(chǔ)存的混凝土的罐的底部。 關(guān)鍵字： 混凝土；澆筑；養(yǎng)護(hù) 中國(guó)地質(zhì)大學(xué)長(zhǎng)城學(xué)院 2021 屆畢業(yè)論文 2 1 混凝土澆筑 若混凝土在地面上澆筑，地面應(yīng)該具有足夠的含水量以避免 它吸收混凝土中的水分。如果新混凝土將被澆筑在已經(jīng)凝固的混凝土上或其旁邊，已澆混凝土表面應(yīng)該徹底清除干凈，最好使用高壓空氣、高壓水流或鋼絲刷。當(dāng)模板被澆筑滿后，就可以抽出管節(jié)。 較低的含水量可提高混凝土的強(qiáng)度。 混凝土應(yīng)該在 40176。一條直線穿過(guò)所有三種比例，通過(guò)任意兩個(gè)已知溫度，就可以確定出第三個(gè)溫度。普通鋼筋在抗拉和抗壓時(shí)可以利用的強(qiáng)度，即屈 服強(qiáng)度，約為普通的結(jié)構(gòu)混凝土抗壓強(qiáng)度的 ，而且超過(guò)抗拉強(qiáng)度的 100倍。鋼筋的邊面并行為兩種材料間提供了很高的咬合作用。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。在這種情況下， ACI規(guī)范要 求在規(guī)定的最小屈服強(qiáng)度時(shí)的總應(yīng)變不應(yīng)超過(guò)。這包括那些設(shè)計(jì)和施工的失誤，使用劣質(zhì)材料和在侵蝕性環(huán)境下暴露。 基片粘結(jié) 使用基片粘結(jié)可進(jìn)行完整的修復(fù)，它可防止水分和大氣從界面進(jìn)人。當(dāng)外觀很重要或鋼筋的保護(hù)層很薄時(shí)，要求采用鑲面處理。 中國(guó)地質(zhì)大學(xué)長(zhǎng)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(shí)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。F for 3 days or 50176。 then the vibrator should be moved, or disintegration of the aggregate will occur. In general, the vibrator should not be permitted to perate concrete in the prior lift. The mainly advantage of vibrating is that it permits the use 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(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 poun