Overcoming the Rehabilitation Challenge of Thin Existing Pavements using Basegrade Stabilisation by Scott Young

Abstract

Flexible pavement structures typically consist of a wearing surface, a base layer and a subbase layer to protect the subgrade from damage caused by traffic loads. Local government urban roads in Australia often only have a base layer sitting directly on the subgrade. When the thickness of the existing granular base layer is deemed too thin to satisfy rehabilitation design requirements, the base and subgrade layers can be insitu stabilised simultaneously with an appropriate binding agent. This is termed Basegrade Stabilisation (Young, 2020). Basegrade stabilisation not only provides an economical solution to local government asset owners, but offers another sustainable asset management approach that fits within the circular economy framework. National and international literature supports the use of basegrade stabilisation since the 1980’s in Australia, however no mix design procedure previously existed. Experimental research completed in 2020 developed a mix design procedure to allow practitioners to confidently evaluate an existing pavement structure and select a trial mix design for laboratory testing. Nine pavement types were examined in the research. They comprised three subgrade materials of varying plasticity and subgrade proportions of 20%, 35% and 50%. Three binders were added to the nine pavement types at various application rates. They were lime/cement/flyash triple blends, slag/lime blends and cement/flyash blends after lime pre-treatment. Unconfined compressive strength (UCS) testing was the principal test. The target strength was 1-2MPa which was based on the success of lightly bound materials used in local government in Australia for more than 50 years. 86% of the research UCS results exceeded 1MPa. The lowest result was 0.3MPa and the highest result was 3.3MPa. The mix design procedure developed consists of ten mix design trials for selection, based on preliminary assessment of the untreated basegrade structure. Elements for evaluation in the procedure include percent fines, linear shrinkage, plasticity index and proportion of subgrade proposed to be incorporated into the rehabilitated pavement. This paper explores the background of basegrade stabilisation and the subsequent development of a new mix design procedure and how it can apply to a local council asset management plan. References: Young, S. (2020). Masters Thesis. Development of a Mix Design Procedure for Basegrade Stabilisation. Centre for Pavement Engineering Education.