【正文】 f Portland cement, plus any latex additives for a Portland cementbased repair system. Precautions should also be taken to remove all loose and friable materials from the surfaces to be bonded. Stability Shrinkage of materials during curing should be kept to a minimum. Subsequent dimensional change should be very close in the substrate inorder to prevent failure. Resistance to Environmentally Induced Damage Some initial exposure conditions may lead to premature damage lo repairs. For example, partially cured Portland cement repairs can deteriorate from hot weather preventing full hydration of the cement. To prevent this from happening extra protection during curing time may be necessary. of Application Materials should be easily mixed and applied so that they can be worked readily into small crevices and voids. Ideally, the material should not stick to tools, and should not shear while being trowel led nor slump after placement. The degree to which the repair material should match the existing concrete will depend on the use of the structure and the client39。 Curing 中國地質(zhì)大學(xué)長城學(xué)院 2021 屆畢業(yè)論文 8 1Placing Concrete If concrete is placed in the surface, the surface should be filled with water sufficiently to prevent it from absorbing the concrete of its water. If fresh concrete is to be placed on or nearby to concrete that has solidified, the surface of the placed concrete should be cleaned absolutely, preferably with a highpressure air or water jetor steelwire brushes. The surface should be wet, but there should be no much water. A little quantity of cement grout should be brushed over the whole area, and then followed immediately with the application of a 1/2in Layer of mortar. The fresh concrete should be placed on or against the mortar. In order to decrease the disintegration resulting from carriage after it is placed. The concrete should be placed as nearly as probably in its final point. It should be placed in layers to permit uniform paction. The time interval between the placing of layers should be limited to assure perfect bond between the fresh and previously placed concrete. In placing concrete in deeper patters, a vessel should be used limit the free fall to not over 3 or 4 ft, in order to prevent concrete disintegration. The vessel is a pipe made of lightweight metal, having adjustable lengths and attached to the bottom of a hopper into which the concrete is deposited. As the patters are filled, sections of the pipe may be removed. Immediately after the concrete is placed, it should be pacted by hand pudding or a mechanical vibrator to eliminate voids. The vibrator should be left in one position only long enough to reduce the concrete around it to a plastic mass。 如果裂縫里有水氣、水和雜物時，要先補(bǔ)好漏洞。例如，熱天會阻礙水泥的水合作用從而使局部修復(fù)的普通水泥發(fā)生變質(zhì)，為了防止發(fā)生這種情況，養(yǎng)護(hù)期間應(yīng)對其作特別的保護(hù)。 修復(fù)工作所用的材料最起碼也要像基 層混凝土那樣耐用。 在惡劣的環(huán)境田間下，例如受除冰化學(xué)劑侵蝕的蕎麥內(nèi)，要求使用鍍鋅或環(huán)氧樹脂涂層的鋼筋，以便使鋼筋的腐蝕和隨之發(fā)生的 混凝土的剝落減至最小。因為后者更為經(jīng)濟(jì)，而且使用他們可以減少模板內(nèi)鋼筋的擁擠狀況?，F(xiàn)在可以使用的鋼筋的直徑范圍很大，在一般的應(yīng)用中從 10到 35毫米，兩種大型鋼筋的尺寸為 44和 57毫米。即使不存在這種必要性，所有受壓構(gòu)件也要配置最少數(shù)量的鋼筋，以保證這些構(gòu)件在偶然出現(xiàn)的小彎矩作用下的安全性 ，在這情況下，不加鋼筋的混凝土構(gòu)件可能會開裂，甚至破壞。F。對水進(jìn)行預(yù)熱是提供必要的溫度最中國地質(zhì)大學(xué)長城學(xué)院 2021 屆畢業(yè)論文 3 有效的方法。這可以用多種方法來實現(xiàn)，例如把模板留在混凝土中，保持表面潮濕，或在混凝土表面覆蓋 一層液體養(yǎng)生化合物，它可以形成一種不透水的隔膜來阻止混凝土中的水分遺失。 較低 的含水量可減少收縮和空隙。每層澆筑間隔的時間應(yīng)該限制在能夠保證新澆筑的混凝土與前面澆筑的有良好的結(jié)合。 當(dāng) 2021年 10月 8日 發(fā)生在巴基斯坦北部的一個 級地震的時候，這些施工技術(shù)上的缺點(diǎn)袒露無遺了 ， 破壞了數(shù)以千計建筑物、橋梁 ， 而且造成估計 79000人的死亡 。新混凝土應(yīng)鋪筑在砂漿上或其旁邊。一般來說，振搗器不應(yīng)該集中在先前提起的混凝土上。 2 混凝土的養(yǎng)護(hù) 若混凝土想要獲得最高強(qiáng)度或其它必要特性，則應(yīng)該對其用足夠的水分和適當(dāng)?shù)臏囟冗M(jìn)行養(yǎng)護(hù)。F以下進(jìn)行澆筑。然而，如果砂含有 3%的水分，則應(yīng)使用虛線。所以，兩種材料最好的結(jié)合使用是混凝土用于抵抗壓應(yīng)力。普通鋼筋在澆筑混凝土之前先置于模板內(nèi)。 ASTM中的 A706的條款是專門使用于焊接的?，F(xiàn)行的設(shè)計方法是按鋼材突然屈服，而且有屈服平臺的情況而制定的。如果某項工程不只需要作裝飾性處理，好的工作技巧很重要。所要采用的預(yù)防措施是：對即將被粘結(jié)的表面，必須先清理其上 面的疏松和易碎的物質(zhì)。認(rèn)真考慮選擇正確的方法和某一特定操作所用的材料，弄清到底是要滿足強(qiáng)度、耐用性的特定要求還是滿足其它的長期或短期的性能要求。在這種情 況下，修復(fù)工 作系統(tǒng)就要包括對整個表面進(jìn)行某種處理。 s requirements. A surface coating may be required when appear