Use of crushed cobblestone as a replacement for aggregates in wearing course construction.

Abstract

Bituminous mixtures are currently being used for the wearing course of pavements in Uganda, with aggregates as one of the main components. Unfortunately, the roads tend to fail due to moisture entering the voids of the pavement, leading to a cascade of problems that involves stripping, rutting, potholes. In response to the aforementioned problem, the task to establish feasibility of crushed cobblestones as a replacement for aggregates in wearing course construction was taken on. The crushed cobblestones were characterised according the following parameters: aggregate crushing value, aggregate impact value, flakiness index, ten percent fines value (soaked and unsoaked), specific gravity and water absorption. Additionally, the moisture susceptibility of the crushed cobblestone-bitumen mixture was established and an economic evaluation of crushed cobblestones in relation to conventional aggregates undertaken. All laboratory testing was conducted using the laboratory testing manual (2000). The results obtained were analyzed, and the effects of the various tested aggregate parameters (ACV, AIV, Flakiness index, Ten Percent Fines Value, Specific Gravity, Water absorption, among others) on the longevity of the pavement were discussed. The results were later compared to the specifications (BS 882, ASTM C33, EN 1744, EN 12620 and EN 206) to establish whether the cobblestones were feasible for use. An economic analysis was then carried out to assess the economic feasibility of the endeavor. The aforementioned obtained results were then compared to the often-used aggregates from Mobuku Quarry and it was established that the crushed cobblestones are feasible as replacements for the aggregates in wearing course construction. However, more parameters need to be tested in order to fully establish whether the conclusion made was sound. Therefore, a wider range of tests should be carried out to ascertain the full range of properties that crushed cobblestones possess as a paving material. Government or non-government organisations should encourage the implementation of crushed cobblestones on a few of the feeder roads, so that the performance of these pavements out of the laboratory can be established. The actual field conditions play a vital role in cementing the data collected.