Characteristics of Cinder Gravel as Road Pavement Construction Material in Meru County, Kenya Science in Civil Engineering

Abstract

The availability of suitable road construction materials that meet the specification requirements are becoming scarce and therefore the use of marginal materials presents challenges during construction and performance when used in the construction of road projects. This study exploited the gap that exists by investigating the engineering properties of cinder gravel sourced from Meru County in Kenya to test the suitability of the material for road pavement construction of Low Volume Sealed Roads (LVSRs). The study established that neat cinder gravel in its natural state was non-plastic and poorly graded due to deficiency in fine particles <0.075mm (μm). Cinder gravel was blended with locally available fine material (red soil and weathered rock) to improve its engineering properties. The optimum blending ratio of 90% cinder + 10% weathered rock met the requirements for natural subbase and base materials for LVSRs. The strength and grading properties of cinder gravel for the optimum blending ratio were evaluated at different levels of compaction. The study showed that the Maximum Dry Density (MDD) of the blended material increased with the level of compaction indicating better interlocking of the particles of the material. Similarly, the strength (unsoaked CBR) of blended cinder gravel increased with the level of compaction showing that repeated scarification and compaction of the material improved the strength. There was a gradual increase in the Plasticity Index with the number of compaction cycles of the material due to the breakage of cinder gravels and blending material into finer particles with further compaction. For soaked specimen, the CBR decreased as the cycles of compaction increased because with the ingress of water the finer particles of cinder gravel dispersed and lost the interlocking properties observed with repeated cycle compaction for the unsoaked material. An evaluation of the shear strength of cinder gravel and particle size at different levels of compaction for the optimum blending ratio showed that the shear strength of cinder gravel decreased with compaction cycles due to the decrease in the angle of shearing resistance (φ). The study established that even though cohesive properties of the material improved with compaction cycles, it did not result to increased shear strength of cinder gravel due to the decrease in the angle of shearing resistance (φ). In conclusion cinder gravel sourced from Meru County was suitable for road pavement construction material for LVSRs with blending with locally available weathered rock. Repeated cycles of compaction of blended cinder gravel improved the mechanical properties of the material including the cohesiveness of the material as the particles became finer.