Mechanical characteristics of Soil-RAP-Geopolymer mixtures for road base and subbase layers

ABSTRACT

Traditionally, soils have been stabilised using cement and lime for road base and subbase layers. However, due to some environmental concerns associated with such materials substitute materials for stabilisation are desirable. Geopolymer binder could be for soil stabilisation, as it produces fewer greenhouse gasses compared to cement. In this study, two types of soils were stabilised using fly ash-based geopolymer and reclaimed asphalt pavements (RAP). The soils were modified with various percentages of RAP and fly ash (FA). Optimum moisture content was substituted with alkali to produce Soil-RAP-Geopolymer at a maximum dry density. An experimental design matrix was established for determining mechanical characteristics of the mixtures. The results of tests facilitated in the development of regression models for the unconfined compressive strength (UCS). The models enabled in evaluating the sensitivity of mixture variables including FA, RAP, Sodium hydroxide, and Sodium Silicate contents and optimisation of the mixture design. Higher FA and RAP contents yielded mixtures with higher UCS. Optimum sodium silicate content, however, depended on the type of soil and the percentage of FA and RAP. Mchanical and durability properties of the optimum mixture were either better or similar than conventional soil-cement mixtures. The microstructure and morphology analysis ascertained that geopolymers were formed thus, supporting the improvements in the mechanical characteristics of the mixtures.

KEYWORDS:

• Geopolymer
• fly ash
• reclaimed asphalt pavement
• unconfined compressive strength
• soil-cement mixture
• RAP
• resilient modulus
• durability test