Abstract:
This study considered a 2.05 km section of the JPCP component of the Kagere –Ndunyu -Munyange–Njigari-Gitugi (E571) road in Othaya, Kenya. The road developed surface cracks within the first 2 years of construction. The study was carried to determine possible causes of the said cracking. The strength of the sub-base and subgrade layers were assessed in terms of California Bearing Ratio (CBR) by using the dynamic cone penetrometer (DCP). The Falling Weight Deflectometer (FWD) was used to assess the stiffness of the pavement through pavement deflection measurements. Concrete core samples from un-cracked slab sections were used to measure concrete strength, determine slab thickness and establish the constituent material proportions of the concrete. Other cores were cut at the saw-cut joints, to enable measurement of saw-cut joint depth. With a CBR of 10-17%, the subgrade layer met the basic strength requirement and was ruled out as a possible cause of cracking. However, half of the tested subbase layer samples did not meet the minimum CBR of 60%, and 24% of the pavement did not attain the recommended minimum layer modulus value of 345 MPa for neat gravel construction. The average strength of the slabs was less than the design crushing strength of 30N/mm2. Only 5% of the slabs met the design slab thickness of 185mm and none of the saw-cut joints met the recommended depth of at least 25% of slab thickness. Inadequate slab thickness, inadequate depth of cut joints, and inadequate strength of concrete slabs and subbase layer could have been responsible for the development of surface cracks. To avoid these shortcomings, there is need for deliberate efforts to enhance capacity in concrete pavement design and construction in Kenya.
