SUITABILITY OF CALCRETE AS A ROAD CONSTRUCTION MATERIAL FOR LOW VOLUME ROADS IN THE ARID AND SEMI-ARID REGIONS: CASE STUDY NORTH-EASTERN KENYA

Abstract

Gravel materials have to meet the minimum Kenya Road Design Manual (KRDM) Part III specification of grading, plasticity and soaked California Bearing Ratio (CBR) requirements for them to be used for road works in Kenya. Calcrete, which is a gravel material that forms exclusively under arid regions and has different material properties due to its different formation process from the temperate climate soils for which the materials specifications were developed, does not meet these specifications mainly due to high plasticity and low soaked CBR. The main objective of this study was to establish the properties of calcrete materials that relate to their suitability as road construction material. Materials from six sites were subjected to carbonate content test so as to establish if they were actually calcrete and the two material samples (from two of the six sites) with the highest carbonate content selected for further testing. The materials from the two sites were subjected to soil index tests, heavy proctor and CBR tests at different moisture contents under-soaked and unsoaked condition so as to establish the properties of the materials and effect of moisture on their strength. The results obtained indicated that plasticity index results were erratic, while linear shrinkage results were consistent. The CBR value increased by between 100% and 200%, between optimum moisture content (OMC) and dry end moisture content. The study concludes that in the case of calcrete materials, the properties that relate to their suitability as road construction material in the arid regions are linear shrinkage and CBR at the likely in-service moisture content and that a higher degree of compaction be specified in the field and CBR test.