SOME STUDIES ON THE ENGINEERING PROPERTIES OF LATERITES IN SRI LANKA

Laterite is a highly weathered rock material, which is rich in secondary iron and aluminum oxides but poor in silica. The chemical composition and mineralogy of laterites vary significantly and depend on their parent rocks, location, climate and depth. It can be seen especially in the western and southwestern part of Sri Lanka which is an island in the tropical region. Laterite is getting harder after the exposure to the atmosphere. Therefore it is widely used as a construction material like bricks from the past. Hence, the objective of this study is to determine some engineering properties of laterite and find out relationships between those properties for further experiments and use.

Laterite samples in fresh and hard (aged or exposed more than 25 years) were collected from different locations for the laboratory studies. The standard test methods ASTM D2958, ASTM D5607-02, ASTMD2216-98, ASTMC97-96 and BS1377-7 were used to determine the engineering properties for hardened and fresh laterites separately. Accordingly the results can be summarized as aged and fresh laterites.

Aged laterite: Porosity, water absorption and bulk density vary from 18% to 33%, from 12% to 20% and from 1500kg/m³ to 1700kg/m³ respectively. The maximum uniaxial compressive strength varies from 2.5Mpa to 5.90Mpa with moderate moisture content when it is in room temperature. Direct shear test results indicate that the friction angle and the cohesion as 16.55⁰ and 0.71Mpa respectively.

Fresh laterite: The moisture content in fresh laterites varies from 20%to 35% and it decreases at a rate 0.5%/day with the exposure to the environment. Fresh clayey laterites gained 359kpa unconfined compressive strength (UCS) after 5 days of the extraction and it was increased up to 733kpa in 36 days. UCS increases with the decrease of moisture content but no uniform relationship.

It can be recommended that hardened laterite is a good material for building constructions after two months exposure to the atmosphere. Fresh laterite areas are good to use for normal building construction sites. Cut slopes in laterite hilly areas can be made more effectively than normal soil due to relatively high shear strength parameters.