Kelio istorija. Kelių tankinimas praeityje

Abstract

This article, among others dealing with the history of roads, continue the history of road construction techniques. The earlier observations by road engineers led to the conclusion, that for better performance of road pavement and longer its life compaction plays the important role. Compaction, at first, was executed by traffic, which used the road itself, and later was discovered that good compaction is sometimes achieved by using the feet of herds of animals. By observing how well sheep compacted an unbound California pavement and thus engineers had developed the sheepsfoot roller, which kneaded rather than pressed the clay layer. The Romans achieved their desired compaction levels by rolling their roads with large and heavy cylindrical stones. Chinese had developed a novel and effective compaction technique using a large piece of stone jerked into the air by quickly tightening the ropes to which it was radially attached. Telford and MacAdam were amongst those who regarded compaction by traffic, as adequate, for their stone pavements. Rolling would produce smoother and less permeable surfaces, but could also break down the individual stones and hence reduce the life of the pavement. In the 1830s French engineer also added rolling as an integral part of the process. A major problem was that horses often could not pull rollers heavy enough to produce the high contact pressures needed to provide adequate compaction. Steam traction engines became available in 1842, and the British roller-making company of AVELINC realized that they could be used to replace the underpowered horse. In 1866-1867 the weight of roller increased from 20 tones to 30 tones by using steam powered roller. The heavier roller made roads better able to resist horse-drawn traffic, but caused premature damage to the base course. In the end, the steam roller won due to its work-place efficiency, rather than to the long-term effectiveness of its actions. Increased number of motor trucks after the First World War greatly increased the demand for road rolling, for now there was no doubt that pavement layers has to be compacted to maximum density to avoid premature failures. In addition, the new asphalt surfaces needed careful rolling to achieve their desired surface finish. The roller was now a key part of every major road job.