An investigation into the cement content of stabilised pavement

Abstract

Motor vehicles dominate Australia's transport system, for both travel and freight; consequently the road network in Australia is of critical importance to the social and economic welfare of our nation and to national and regional growth. About 90% of this network is constructed of compacted unbound granular materials with thin bituminous seals. Many of these granular pavements were not designed to carry the current traffic volumes or increased axle mass loadings; and are therefore highly likely to require some form of remedial works in the near future.Stabilisation with cement is becoming increasingly important as a means to upgrade or recycle existing materials in deteriorated pavements due to the economic, social and environmental benefits. With limited road maintenance funding and increasing heavy vehicle axle loads reducing pavement life; cementitious stabilisation is an ideal low-cost pavement rehabilitation technique that can improve the strength and durability of the overlying pavement materials and thereby enhance traffic carrying capacity over a longer period of time.It is advantageous to know the cement content of the improved material to ensure an appropriate design and to predict the future performance of the pavement. Being able to determine the cement content of stabilised basecourse is also an important diagnostic tool which can be used to help ascertain the cause of failures. Various methods for determination of the cement content of basecourse material are currently specified in road construction projects to verify that the requisite levels of stabilisation are achieved. These methods however are limited by the variability of the pavement materials and the costs and delays associated with test procedures.An investigation into the determination of the cement content of stabilised road base was undertaken utilising a test method trialled in 2009 in order to develop and validate the method.A range of typical Western Australian basecourse materials were assessed when stabilised with General Purpose cement. They included limestone and crushed rock base from the Perth Metropolitan area; scree gravel from the Pilbara region; high plasticity index (PI) gravel from the Wheatbelt region; and lateritic gravel from the Midwest region.The main focus areas were to confirm the suitability of the method for testing of cement content in more extreme road base materials; and to establish the long term veracity of the test method by testing samples at increasing hydration periods.Following the laboratory testing of the limestone samples it was concluded that the test method is not considered suitable for testing on granular pavement material with either; a high calcium carbonate content or granular pavement material whereby the material reacts strongly with hydrochloric acid to the extent that more than 10 % of the original mass is consumed.Testing based on the results obtained for the Mid-West Lateritic Gravel and the Wheatbelt North High PI Gravel samples indicate that the test method is reliable for these materials at one month hydration. However the predicted cement content values achieved for the Pilbara Scree Gravel samples and the Crushed Rock Base samples at one month hydration and were not consistent with the actual cement addition.The predicted cement content values achieved for all tested basecourse types then showed a marked decrease over the 3, 6 and 12 month hydration periods and it was therefore concluded that the test method is not suitable for cement content determination where the hydration period is three months or longer.Further testing utilising the test method is recommended as continued research into stabilisation processes should be promoted as they can potentially improve the performance and the cost of maintaining and upgrading the road network, which is vital for the continued growth, prosperity and well-being of the Australian nation.