Enhancing Flexible Pavement Performance Through Stabilising the Sub-base Layer and Adding Crumb Rubber to the Wearing Course / Tang Eng Hie

Thesis submitted for the degree of Master of Science by Research in Civil Engineering Universiti Teknologi Brunei

Abstract
Roads constructed on weak-bearing natural subgrade soil having fluctuating groundwater level and experiencing rainfall-induced flooding and traffic overloading are susceptible to pavement deteriorations that drastically reduce pavement durability, serviceability, lifespan and safety. While an appealing option that reduces construction cost and time, accelerates strength development over a short curing period is to chemically stabilise native sandstone aggregate with polymer, cement or polymer-cement blend when used in the sub-base, a sustainable option that offers improved wearing course is the partial replacement of imported mineral aggregate with crumb rubber while treating the asphalt mixture with hydrated lime. To achieve the aims to optimise the use of local sandstone aggregate in the sub-base and to introduce the use crumb rubber in the wearing course, the research evaluates experimentally and compares the (quantitative) engineering strengths of sandstone aggregate before and after chemical stabilisation and evaluates the (quantitative) engineering performance of crumb rubber modified dense-graded hot mix asphalt when compared to conventional dense-graded hot mix asphalt. Outcomes from the soil stabilisation laboratory investigations had shown that the (1) gradations, (2) cement contents, (3) polymer contents, (4) polymer-cement blend contents at which the gravel:sand ratios, unconfined compressive strengths, indirect tensile strengths and California bearing ratio met the design requirements were (1) 1.2–2.1, (2) 3%–5%, (3) 0.5%–1% and (4) 0.75%–3%–0.75%–5%. The minimum dry curing periods for the cement-stabilised, polymer-stabilised and polymer-cement-stabilised samples were 3, 7 and 7 days respectively. Outcomes from the asphalt modification laboratory investigations had shown that the optimum bitumen content and optimum rubber content, at which the percentage voids of asphalt, percentage voids in mineral aggregate, percentage voids filled with bitumen, percentage of absorbed bitumen and Marshall stability and flow for diorite-based samples using 0.71mm and 2mm rubber sizes and granite-based samples using 2.36mm rubber size were within the permissible ranges, were 5.5%–6.0% and 1%–2% respectively.

Thesis (Master) - Universiti Teknologi Brunei, 2022

Includes bibliographical references from page 138-153