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Currently, soil stabilization is used in road construction in Sri Lanka, especially for soft road shoulders. The socioeconomic demand for sustainable development has raised the necessity of new environmentally friendly soil binders for construction engineering practices, including road construction. Industrial residues such as fly and bottom ashes are commonly used to reduce the amount of cement in concrete mixtures or soil stabilization practices, and new biological materials and methods have been introduced by a number of studies to improve the strength of soils without the use of chemical binders such as cement. Among others, microbial-induced biopolymers have been experimented with as a new binder material for soil treatment due to their high strengthening efficiency and low environmental impact. This study verified the feasibility of biopolymer application on local soil stabilization, specifically for road shoulder construction in Sri Lanka, by comparing the unconfined compressive strength (UCS) of local soil samples treated with cement-ash-based binders and xanthan gum biopolymer. The xanthan gum biopolymer-treated condition had significant UCS strengthening and high ductility compared with other treated conditions. Thus, xanthan gum biopolymer shows promising potential as an alternative material for road construction (particularly for shoulders and subbases) in Sri Lanka and in other nations with similar climates and socioeconomic conditions.

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This paper presents the statistical analysis results for correlating the stiffness characteristics of subgrade with subgrade soil properties using the long-term pavement performance database in the USA. The stiffness of subgrade soils was characterised by the falling weight deflectometer deflection basin parameters and subgrade modulus calculated using the backcalculation technique. For the statistical approach, both linear fixed-and mixed-effects models were applied to estimate the correlation between subgrade stiffness and soil properties. It is found from this study that the base curvature index and subgrade modulus are highly correlated with subgrade soil properties and variation of water content. The results also indicate that the mixed-effect model can accurately estimate the stiffness of subgrade soils using the soil properties and water content. Region-specific factors considered as the sources of random effects in the mixed-effects model can help to improve the degree of correlation.

A new temperature correction procedure was developed for multiload-level falling weight deflectometer (FWD) deflections for flexible pavements in North Carolina. In this procedure, temperature correction factors were dependent on the radial offset distance from the FWD load plate. Temperature and FWD multiload-level deflection data used in developing this procedure were collected from 11 pavements in three different climatic regions of North Carolina. The effect of the FWD load level on this temperature correction procedure was investigated. Research efforts focused on improving the accuracy of the current temperature correction procedure of the North Carolina Department of Transportation. The measured deflection and temperature data were also used to validate the long-term pavement performance (LTPP) temperature correction procedure. It was found that the effective pavement temperature prediction algorithm in the LTPP procedure is relatively accurate and that the temperature-deflection correction procedure undercorrects the deflections at higher temperatures in pavements with an asphalt concrete layer thicker than 242 mm. The main reason for this deficiency is that the LTPP procedure was developed from the national database and cannot fully consider the local variation in mixture characteristics.