PERFORMANCE ASSESSMENT OF SAND–CLAY BLENDS: PRACTICAL APPLICATIONS IN SUSTAINABLE PAVEMENT DESIGN
Abstract
A vital role is played by Subgrade soils in the overall performance of low-volume pavements. In areas underlain by weak clays, this often leads to early pavement distress, and modification of the soil is often required to achieve economical and durable designs. Although lime is commonly used for chemical stabilization, these methods may not always be effective or sustainable. Alternatively Mechanical modification using granular inclusions serves as a simple and practical alternative. This research examines the influence of sand addition on the overall strength, compaction, and pavement design implications of clay subgrades. Clay–sand mixtures were prepared with sand contents varying between the ranges of 0% to 50% by dry weight. Standard and Modified Proctor compaction tests were performed to determine the effect of sand on optimum moisture content and maximum dry density. In other to evaluate strength and bearing capacity the unconfined compressive strength (UCS) and California Bearing Ratio (CBR) tests were carried out. These test results were incorporated into the analysis of pavement thickness design following AASHTO, USACE, CBR, and Caltrans methodologies. Compaction results shows that sand inclusion consistently increased maximum dry density and lowered optimum moisture content, leading to improved workability. However, strength parameters declined as sand content increased. The 50% sand blend exhibited revealed more than a 50% loss in strength compared with natural clay, requiring an increase of 37% to 47% in pavement thickness depending on the design method. An optimum range of 10% to 20% sand was identified, providing a balance between compaction benefits and acceptable strength (UCS values 752–516 kPa; CBR values 19%–18%). Beyond this value, the decrease in structural strength outweighed compaction advantages. For rural areas with low traffic, controlled sand–clay blending may be used as a modification technique to improve workability characteristics, provided adequate drainage and maintenance are ensured.
Keywords: Sand–clay optimisation: Soil modification; CBR-UCS characteristics; Subgrade performance: Low-volume roads
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