In this research study, medium and high plastic soils were utilised in evaluating the physical, microstructural, mechanical and durability characteristics of fly ash-based soil-geopolymer mixtures. Class F fly ash was used with a mixture of sodium silicate and sodium hydroxide to prepare fly ash-based soil-geopolymer mixtures. An experimental design was developed incorporating various combinations of fly ash content, sodium silicate to sodium hydroxide ratio, and sodium hydroxide concentration. Several mixtures were cured at different conditions, and tested for unconfined compressive strength. Based on developed regression model and sensitivity analysis various mixtures from each soil type were selected for further evaluation. The resilient modulus, dynamic modulus, durability, FTIR, XRD, and scanning electron microscopy (SEM) tests were also conducted for the selected mixtures. The results indicated that soil-geopolymer demonstrated satisfactory performance under static and dynamic loadings, and passed the wet and dry durability test criteria. SEM analysis revealed that microstructure and morphology of the mixtures displayed formation and stable growth of geopolymerisation during the progression of curing period. XRD and FTIR results also indicated the formation of geopolymer products in soil-geopolymer mixtures. The mechanical, durability, and microstructural characteristics revealed that the soil-geopolymer mixtures have an immense potential to be used as pavement subbase and base layers.

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.

Timely rehabilitation and preservation of pavement systems are imperative to minimising agency's costs and maximising benefits. Reasonable estimates of treatment life and pavement life extension can be made possible by developing reliable treatment performance models. Louisiana Department of Transportation and Development initiated a three-phased study to develop pavement treatment performance models in support of cost-effective selection of pavement treatment type and the time of treatment. As a result of the study, international roughness index (IRI) models for overlay treatment of composite and flexible pavements were developed. Various factors affecting the IRI of overlay treatment were identified. Climatic indices pertaining to Louisiana were developed which exhibited strong statistical significance along with the other variables as used in the IRI models. The developed IRI models provided good agreement between the measured and predicted IRI values with the majority of data within 5% of prediction error. The models could be used as a good pavement management tool for pavement maintenance and rehabilitation actions.