The development of a rotational shear device for evaluating erodibility of stabilised subbases

Abstract

Paper presented at the 23rd Annual Southern African Transport Conference 12 - 15 July 2004 "Getting recognition for the importance of transport", CSIR International Convention Centre, Pretoria, South Africa. Soil properties and climatic effects all contribute to erosion of subbase material, which leads to rigid pavement failure. The erosion takes the form of pumping of material and water, subsequently creating voids. The formation of voids can lead to a rapid decline in the durability and serviceability of the pavement. At present there is not a single laboratory test, which could identify materials resistant to pumping. Thus there is a need to develop a laboratory test, which could predict erosion of material in a pavement. The aim of this paper is to present the initial results of a Rotational Shear Device (RSD) constructed to simulate erosion of subbase layers under a concrete slab. A review is given of existing tests, which are used to test for erosion. Motivation for the adoption of the RSD is given. Details of the device as well as pilot laboratory tests are also presented. Pilot laboratory tests were preformed on a G2 material stabilised with 2% and 4% Cem I 42.5 cement. Duplicate samples were tested at the CSIR with the mechanical wet-dry brushing test. As expected, the 4% stabilised samples eroded less than the 2% stabilised samples under the conditions in the RSD and thus was confirmed by results from the mechanical wet-dry brushing tests.