The influence of laboratory testing conditions in the prediction of performance in natural materials for road construction

Current design guidelines for roads are based on laboratory field tests in predicting the performance of materials to be used for the construction . This requires that the tests earned out should realistically predict the performance of such materials under field conditions. However. the induced boundary conditions in the current laboratory tests are thought to deviate from those operating in the field. In this research an attempt has been made to induce the field boundary conditions in the laboratory tests in order to evaluate their influence on the test results. These include the effect of prolonged degradation by traffic, degree of lateral confinement, compaction energy levels. Field moisture contents and seasonal variation of field moisture contents on the performance of various locally available road construction materials. The results of tests performed in modified laboratory testing procedures have been compared with those obtained from the standard laboratory testing procedures. The test results indicate that the performance of natural materials for road construction depend on various factors including material type, degree of lateral confinement, degradation and field moisture content, compaction energy employed and compaction moisture content. The performance of natural materials for road construction is revealed to be more sensitive to the degree of lateral confinement among the factors investigated. This suggests that pavements are more prone to failure at their edges where the lateral support is minimum. The material strength is observed to decrease with the degradation of the material suggesting that the most appropriate strength test for material selection would be that performed on the material subjected to degradation to depict the long-term traffic effect. The rate of degradation is observed to depend also on the operating field moisture content.