摘要
One of the chief materials used in the construction of buildings and roads is eement(水泥),a powder made mainly from limestone(石灰石) and clay(粘土 ). Even the ancient Egyptians and Romans(罗马人) used a kind of cement,but it was not until 1824 that an English bricklayer(泥瓦匠) developed a cement strong enough for modem roads and building.
