5混凝土的过去和现在5.1商品产品与特殊产品很久以前,混凝土工业和工程师已经生产和明确了一种世界性通用混凝土,质量优异,可在任何环境下使用,其抗压强度通常为15～25MPa。后来在一些国家,混凝土抗压强度稍微有所增大,以致一些发展中国家混凝土的抗压强度达到 5 Past and Present of Concrete 5.1 Commercial Products and Special Products A long time ago, the concrete industry and engineers have produced and clarified a worldwide universal concrete with excellent quality and can be used in any environment. Its compressive strength is usually 15 to 25 MPa. . Later, in some countries, the compressive strength of concrete has slightly increased, so that the compressive strength of concrete in some developing countries has reached