Advancing sustainable gravel road construction through innovative nano-emulsion treatment of a micaceous gravel.

Abstract

Materials used for road construction play a critical role in the performance of the pavement structure. Winning and haulage of virgin materials have been highlighted as factors that contribute significantly to the increased construction cost and environmental degradation. In the quest to achieve sustainability, it has been recognised that functionalising locally available materials is one of the ways of tackling the challenge highlighted above. Such materials are enhanced through stabilisation traditionally using products such as cement and lime. However, these (cement and lime) have limitations and various products have been developed and marketed as viable alternatives for material enhancement. This study evaluated the efficacy of Nano-Modified Emulsion (NME), a relatively new product, for stabilisation of gravel materials, particularly for use as a gravel roadwearing course. NME comprises of Conventional Bitumen Emulsion (CBE) modified with an organofunctional nanosilane. Therefore, the product (NME) draws on the properties of nanotechnology to functionalise and improve properties of materials traditionally considered of marginal quality. Previous studies show that this product has great potential in this regard. However, it is recognised that current knowledge of the product is limited and further research is required on the fundamental properties and behavioural traits of NME stabilised materials (NMESMs) to streamline concepts, understanding, leading to the development of design guidelines of the materials. A marginal quality micaceous gravel material was chosen as a suitable candidate to demonstrate the efficacy of the NME. The material, stabilised with varying NME applications from 0.7% to 1.5%, was evaluated for various engineering properties, including mechanical strength, stiffness and deformation characteristics. Results of tests for mechanical strengths conducted through California Bearing Ratio (CBR), Unconfined Compressive Strength (UCS), Indirect Tensile Strength (ITS) and Static Triaxial Tests (STT) showed improved material properties by more than 70%. It was observed that minimal applications of NME are required to achieve specified strengths and that increasing the application dosage does not significantly improve material strength. The NME is also shown to impart hydrophobic properties on the gravel material such that increased applications of NME increase the gravel’s resistance to moisture damage as determined by the Moisture-Induced Damage Ratio (MDR). The STT results demonstrate that the NME improves the shear strength of materials by increasing the cohesion parameter by up to 54% while the angle of friction remains virtually unchanged. The resilient modulus of NMESMs exhibits a combination of stress-dependent and -independent behaviour and it was determined that the parabolic model suitably represents this behaviour. Results of plastic strain tests also show that NMESMs provide better performance with regard to resisting deformation. Modelling and pavement structure analysis was implemented using a Finite Element (FE) based software, ANSYS 2022 R2. This was done to simulate the performance of the material in an actual pavement structure. It was determined that incorporating a NMESM layer as a wearing course on a gravel road pavement structure improves pavement responses to loading i.e. strain and deflection by up to 14% and 28%, respectively. The use of NMESM also reduces the thickness of the layer, resulting in a saving on materials. Additional studies are recommended for Life-Cycle Cost Analysis (LCCA) to help in quantifying cost-benefit ratios of implementing NMEs in industry.