【正文】 ntries were investigating cementing agents made from gypsum, limestone 2 and other natural materials. One discovery was a method of making a cement by burning a naturally occurring mixture of lime and clay. properties of the natural cement were very erratic because of variations in the proportions in the natural material, although use of this natural cement continued for many years. In 1824 Joseph Aspdin , a brickmason of Leeds, England, took out a patent on a material he called Portland cement, so called because concrete made with it was supposed to resemble the limestone quarried near Portland, England. Aspdin is generally credited with inventing a method of proportioning limestone and clay, burning the mixture at high temperature to produce clinkers, then grinding the clinkers to produce a hydraulic cement. His small kiln, producing about 16 tons of clinker at a time, required several days/or each burn. Expansion and development of cement manufacturing was slow for a number of years. About 1850, however, the industry had bee well established not only in England, but also in Germany and Belgium. Shipments to the United States were started in 1868 and reached a peak about 1895, at which time production was well under way in the United States. Meanwhile the United States production of natural cement had been started early in the 19th century as a result of the demand for cement for construction of the Erie Canal and related works. Subsequent development of the rotary kiln led to large scale production of cement throughout the world. The use of concrete was expanded by the construction of railroads, bridges ,buildings and street pavements. Research in reinforcing concrete with steel rods had been started in France, and the year 1875 saw first use of reinforced concrete in the United States. Much39。在最初時(shí)期，建筑物是由土夯實(shí)而成，或者在沒(méi)有任何連接或粘接物的情況下，用石頭一塊一塊地壘砌而成。希臘人用的材料是一種取自圣多林島的火山灰，至今仍在世界的那個(gè)地區(qū)使用。該工程的設(shè)計(jì)師及工程師約翰之所以如此命名是因?yàn)橛眠@種水泥制成的混凝土被認(rèn)為很象是從英國(guó)波特蘭附近采集來(lái)的石灰石。 ?其后，水泥回轉(zhuǎn)窯的開(kāi)發(fā)致使大規(guī)模的水泥生產(chǎn)遍及全世界。亞布拉姆斯公布了他的研究及觀測(cè)結(jié)果。骨料通常占一塊特定混凝土體積的百分之七十五。 因此，常常將鋼筋埋人混凝土中。萬(wàn)一這種現(xiàn)象出現(xiàn)，混凝土 養(yǎng)護(hù)完后，濕氣會(huì)很容易地進(jìn)入其內(nèi)。其結(jié)果 是經(jīng)常調(diào)配出強(qiáng)度非常低的混凝土。這便是為什么在混凝土內(nèi)總存在一些孔隙的原因。 砂漿與其他膠凝材料，如混凝土、熟石膏和灰泥有著密切的關(guān)系，但是若把砂漿和這些材料混同起來(lái)，或是想用這些材料來(lái)替代砂漿是錯(cuò)誤的，因?yàn)槊恳环N材料均具有各自的特點(diǎn)，互不相同。 但為了論證，假定一面磚墻是用比磚的抗壓強(qiáng)度還高的砂漿砌成的，這面墻所承受的任何應(yīng)力一比如說(shuō)由墻下土的沉陷而導(dǎo)致的應(yīng)力，將導(dǎo)致磚塊沿最大應(yīng)力方向斷裂，這種斷裂將形成一條從墻頂?shù)綁δ_，貫穿墻體的鋸齒狀裂縫。砂漿具有粘性，當(dāng)把砂漿涂抹在磚的側(cè)面時(shí)，這一特性使砂漿能保持自身的形狀，并防止由于自身的重量而坍落。就像很難說(shuō)明煎薄餅用的面糊或者軟化了的奶油的稠度一樣，砂漿的和易性很難用 語(yǔ)言來(lái)描述，但不具備這一特點(diǎn)的新砂漿是不能將砌塊緊緊地粘結(jié)在尸起的。實(shí)際上，在不影響結(jié)構(gòu)整體強(qiáng)度的情況下，砂漿實(shí)質(zhì)上可以比磚的強(qiáng)度低很多。當(dāng)把水加入到這些成分中時(shí)，就形成了一種可塑性物質(zhì)，這種物質(zhì)可用來(lái)粘結(jié)磚、瓦、混凝土砌塊和其他種類的砌塊。 但是在水灰比中，水的比例越大，最終制成的 混凝土的強(qiáng)度越低。它表示從體積上一份波特蘭水泥、二份砂子和四份卵石拌合在一起，之后加人足夠的水來(lái)獲得和 易性良好的拌合物。一些濕氣會(huì)遷移到加工最好的混凝土 中。 混凝土的主要結(jié)構(gòu)缺點(diǎn)是它抗拉強(qiáng)度 低。砂 子和碎石或卵石共同構(gòu)成混凝土拌合物的骨料。然而，許多混凝土的使用者認(rèn)識(shí)到，使用濕混凝土是件蠢事。此時(shí)美國(guó)的水泥生產(chǎn)也已初具規(guī)模。 1824 年，一位英國(guó)里茲的瓦匠約瑟夫后來(lái)石灰的質(zhì)量開(kāi)始改進(jìn)，十四世紀(jì)或稍后，又開(kāi)始使用火山灰水泥。 后來(lái)，希臘人和羅馬人發(fā)現(xiàn)了用石灰石來(lái)燒制生石灰，然后把它熟化制作灰泥的方法。 the properties required of each are distinctive and differ from the others. By a mistaken analogy with a chain and its weakest link, it is a mon belief that for any 5 masonry construction to be strong, the mortar must be strong also. Very often, for example, a person who is familiar with concrete will infer that mortar, being a cementitious material like concrete, should have properties similar to those of concrete and be mixed and used in much the same way. w Since, for example, concrete has, or should have, a high pressive strength, mortar should have a high pressive strength also. But the primary function of mortar is to bind the masonry units together, not to resist pressive loads or add to the strength of the masonry units. A great many tests have been made of brick walls built with mortars h