TITLE:
Causes of Cracks on Recently Constructed Flexible Pavements: A Case Study on Kabati to Mareira Road in Kenya
AUTHORS:
Benjamin K. Chamia, Zachary Abiero Gariy, Stephen M. Mulei
KEYWORDS:
Design and Construction, Flexible Pavement, Material Parameters, Pavement Cracks, Traffic Axle Loading
JOURNAL NAME:
Open Journal of Civil Engineering,
Vol.7 No.2,
May
11,
2017
ABSTRACT: Increased surface roughness of road due to emergence of cracks makes travelling on the road uncomfortable to road users; reduces road safety; increases wear and tear of vehicles, which push up the operating costs of vehicles, and increases travel time leading to the loss of useful man-hours to the local economy. The main objective of the study was to establish the causes of cracks on recently constructed flexible pavements with focus to Kabati to Mareira Road. To realize the study objectives, a case study was done on Kabati to Mareira road. Primary data comprising traffic count surveys; field and laboratory data for coring for compressive strength tests, tests on bearing capacity of pavement structure, and pavement deflection measurements analysis tests on improved pavement materials were undertaken on the road under study. The Secondary data on traffic axle load survey along the road under study were obtained from Kenya Rural Roads Authority, Ministry of Roads. The traffic loading was found to be 1.1 million equivalent standard axles over a design period of 15 years at a growth rate of 5%, which is on the lower limit of T4 assumed during the design stage. The material characteristics recommended in design are sufficient for the designed traffic loading. The range of UCS values was 1.12 to 5.83 MPa for soaked cores and 4.76 to 6.94 MPa for un-soaked cores. The DCP results showed that subgrade has a mean CBR of 15% and a median of 14% (subgrade class S4); the sub-base has a mean CBR of 53%, a range of 16% to 93% and thickness of 186 mm and; the base has a mean CBR of 145% a range of 20% to 433% and thickness of 137 mm. The ratio of modulus achieved after construction for base to sub-base is 2.7:1 and 10.7:1 for the sub-base and subgrade. It is concluded that design has no aspect in development and propagation of cracks. Cracks were caused by combination of factors, namely: sub-grade does not provide sufficient support to the pavement due to high base and sub-base strengths; and the variation of strength for pavement layers and the collapse of some cores during soaking process point to cases of inadequate/non-uniform mixing and insufficient curing of the pavement layers. Recommendation is made that the stabilizer content for base and sub-base to be varied in accordance with the properties of natural material being used based on frequency set out in standard specifications; and use of fully flexible pavements where the fill material adopted is alluvial or expansive clays. Emphasis should be placed on adequate pavement support. In improved pavement construction, the stabilizer should be uniformly distributed, thoroughly mixed and pavement layers sufficiently cured.