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Steelmaking involves the removal of iron's impurities and the addition of desirable alloying elements. Steel was first made by cementation, a process of heating bars of iron with charcoal so that the surface of the iron acquired a high carbon content. The bars were then fused together, yielding a metal harder and stronger than the individual bars but lacking uniformity in these properties. The crucible method, consisting of melting iron together with other substances in …

…fine particles, and, when used on roads and streets, limit scaling and provide room for the water in the concrete to expand harmlessly as freezing occurs. Block and brick building units molded of concrete are used in all types of construction. Masonry units are cored to reduce weight and to provide an insulating air space within the block. Basic block types are fairly well standardized today and are manufactured in virtually any color or texture.