Kelio istorija. Kelių tiesimo medžiagos

Abstract

Competition from other binders increased later in the ninteenth century, the tar byproduct was distilled to produce more viscous and durable tars. These more marketable materials came to be known as road tars and led to a much improved product. Such tars shared in UK market equally with bitumen. However, bitumen possesses a number of technical and cost advantages over tar and is now by far more common binder. Newertheless, many citizens still believe that most roads are built of tar. One of the important lessons that the tar developments taught was that it was not essential to rely on unmodified, natural products. Paving materials could be manufactured. Clearly, the innovations with tar had taken the world a long way along the route to a successful road pavement. Cements are usually made from burnt limestones or dolomite. They have been used since 6000 B.C. and was extensively employed by the Egyptians, Cretans, Greeks, and Romans and then largely forgotten. The Romans used concrete extensively, it had had some use in Saxon England in about S.D. 700, and the Normans used it for a major building works. However, the art of burning lime, grinding it, and the adding of other materials to produce high-strength and water- resistant concretes and mortars was slowly lost, and was effectively nonexistent by the beginning of the eighteenth century. When th edesign of concrete mixtures came to be well understood in the late 1860s, concrete became a strong and reliable product. The process was aided by the development of the new construction equipment such as introduction of continuous concrete mixers in 1875.