An ideal preservative for remedial treatment must primarily be characterized by two requirements. First, it must have an ability to diffuse and distribut evenly into the wood and secondly, it must be fixed properly so that it does not leach out too fast. However, these two characteristics conflict with each other, and the choice of preservative must of necessity be a compromise. Wood preservatives based on boric acid have excellent diffusibility but like the fluorides they are not appreciably fixed in the wood. It was therefore considered important to study the progress of the boric acid diffusion in creosoted sleepers in full scale tests. Impregnation equipment and technique were of course also of interest in the study. The tests started in September 1970, when approximately 100 creosoted sleepers, after being in service for 13 years, were treated with a boric acid paste and installed in a test track at the marshalling yard at Nässjö (the Nässjö test). To obtain an indication of the effect of the treatment for a track in use and to study the developed method and equipment, in April 1974, approximately 1000 seventeen years old creosoted sleepers on the main line south of Kungsbacka (the Kungsbacka test) were treated. Samples of timber have been extracted from the sleepers on the two sites and analysed after different times of exposure in order to follow the progress of diffusion of the boric acid. In total, more than 2000 chemical analyses have been carried out by Borax Holdings Ltd in England. In order to establish whether the boric acid treatment adversely affected the electrical resistance of a sleeper, a small scale trial was carried out with 11 sleepers from the Nässjö test. In May 1971 they were installed in a test track near the SJ Civil Engineering Laboratory in Stockholm. As the study progressed, a large amount of data from the chemical analyses was obtained, and to evaluate the fungicidal effect of the boric acid in the sleepers a series of biological tests was carried out at the Swedish University of Agricultural Sciences in Uppsala. The Swedish Wood Preservation Institute has been responsible for the final revision and editing of the results as well as compiling this report.

Download document (2.6 Mb)
free for the members of IRG. Available if purchased.

Purchase this document