Improving clay soil for Road Construction by adding mechanical additives
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Date
2025
Authors
رغد قاروط
دانا زبيده
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Abstract
This study investigated the improvement of clayey soil for road subgrade construction by incorporating four mechanical additives: recycled asphalt pavement (RAP), sand, glass powder, and rubber. Laboratory tests evaluated the effects of these additives on the soil's engineering properties, including the California bearing ratio (CBR), swelling potential, maximum dry density (MDD), and plasticity index (PI).
The results showed that using recycled asphalt pavement (RAP) at the optimum ratio, which was 60%, improved the California bearing ratio (CBR) to 6.29% (from 2.08% in pure clay), reduce swelling to 6 %( from 21% in pure clay).
For sand, the optimum ratio is 60% sand, which increases the CBR to 5% and reduces swelling to 7%. Its advantages include local availability, lower cost, and improved drainage, with limited improvement in CBR (min 20%) compared to other additives.
Glass Powder
The optimal ratio was 60% crushed glass, achieving the highest CBR value (11.6%) and reducing swelling to 3.44%. This product utilizes crushed glass waste, significantly improving its durability and reducing its environmental impact, but requires processing (crushed) and is more expensive than rubber-based synthetic resin (RAP) or sand.
For rubber, the optimal ratio was 25% rubber, which reduces swelling to 6.03% but showed inconsistent improvement in CBR value (peaking at 3.44%). It recycles tire waste, enhances its flexibility, and reduces soil plasticity, but has low stiffness and poor bearing capacity at high ratios compared to other additives.
From an economical and environmental perspective, sand and glass are both economical, but also offers moderate engineering improvements. Crushed Glass offers superior engineering performance and environmental benefits (waste reuse), but processing costs are higher.