Effects of In-situ Moisture Content on Pavement Performance of Low Volume Sealed Roads

Abstract

The introduction and appreciation of the low volume sealed road technique in Kenya has heralded a new era in construction of efficient and effective rural road network. The performance of such roads are affected by various environmental parameters including changes in the in-situ moisture. The objective of the research was to investigate the effects of in-situ moisture and density on the pavement performance of Low Volume Sealed Roads (LVSRs) before, during and after improvement by modification of the cross-section profile, side drains and surface sealing. This was done by conducting field Dynamic Cone Penetrometer (DCP) test and laboratory California Bearing Ratio (CBR) test and establishing the DCP-CBR correlation. Appropriate testing with the simple DCP device was used to assess the in-situ conditions including material quality and moisture regimes along the road alignment. This information was used to identify uniform sections; the in-situ layer strength diagrams of each of these sections were analyzed to determine the layer quality and thicknesses. The method of data analysis of pavement entailed assessment of the in-situ moisture, pavement strength and correlation of CBR-DCP results and moisture changes. Sampling was conducted on the alignment before construction, pavement and subgrade during construction and after allowing traffic flow were tested and analyzed as per the ASHTOO and BS standards. The research shows that, alignment soils before improvement the MDD and OMC for Wamumu - Karaba were 1090 kg/m³ and 46.5% respectively while the Maximum Dry Density (MDD) and the Optimum Moisture Content (OMC) for Kyeni - Karurumu were 1125 kg/m³ and 45.1% respectively and were predominantly borderline granular materials were susceptible to effects of moisture. As such they exhibited inferior characteristics but were improved by processing the subgrade and compacting heavily to improve the strength and reduce permeability. During construction, by adding sub-base and base layers, since the pavement had not fully consolidated it required 3 mm/blow to penetrate to 150 mm thickness and at a higher CBR of 102, hence reduction of moisture and increased pavement strength. A DCP –CBR correlation of 3.0 for Kyeni Karurumu and 2.7 for Wamumu Karaba was established hence along the road sections works could continue based on the DCP and CBR only used for confirmation on both sections. After construction and opening to traffic, the CBR achieved was 152% for the 0-150 mm layer and 106% for the 151-300 mm layer. This showed improved pavement strength due further consolidation and reduction in moisture content. In conclusion, the existing alignment materials can be used as the subgrade by processing and compacting at or near optimum moisture content (OMC). During construction, by adding sub-base and base layers, improving drains and sealing surface the resulting pavement becomes stronger. Further consolidation is achieved when the pavement is opened to traffic. It is recommended that the effects of in-situ moisture be assessed before, during and after traffic flow when upgrading or constructing new LVSRs as this will inform the use of existing alignment soils, required pavement strength and proper drainage.