Quality Of Construction Materials And Their Effects On The Sustainability Of Highway Pavements In Parts Of Anambra State, Southeastern Nigeria

Abstract

Construction of any sustainable road requires the determination of engineering properties of the materials to be used in the project. In this work, the impact of the construction materials used in some parts on Anambra State (southeastern Nigeria) with significant road pavement failure rate is investigated. Soil and aggregate samples were collected in situ on some failed spots on major roads in the state and were subjected to standard laboratory analyses. The results indicated that the roads were constructed on sandy subgrades with gravel-sized particles that ranged from 0 – 43 %, sand 25 – 77 %, and fines 14 – 63 %. The liquid limit of the subgrade materials ranged from 27 – 44 %, plasticity index 10 – 24 %, while the linear shrinkage ranges from 8 – 11 %. These Atterberg limit results denote low to moderate expandable soils. Maximum dry density ranged between 1.93 - 2.20 Mg/m³, while optimum moisture content ranged from 6.78 to 15.9%. The California bearing ratio (CBR), on the other hand, ranged between 60 – 161 %, for unsoaked condition, and 17.8 %, for soaked condition, indicating fairly stable materials. Based on the American Association of State Highway and Transportation Officials (AASHTO) classification system, the subgrade samples classify mainly as A-2-6 soil or as CL according to the Unified Soil Classification System (USCS). The particle density value ranges from 2.35 - 2.71 Mg/m³, while the field relative compaction density ranges between 89 – 108 %. Analysis on the sub base and base course aggregates indicated bulk density of fine aggregate (sand) that ranged from 0.16 - 1.68 Mg/m³. Comparison of the results with an engineering standard revealed that the materials did not meet standard limits(FMW&H), hence, the failure recorded on the paved roads. Water inflow would result in subgrade material expansion, hence, stability and bearing capacity reduction. ANOVA test result indicates significant variable from the data source while principal component and correlation analyses suggests that moisture content, liquid limit and plasticity index have direct statistical relationships. This research therefore advocates proper drainage design and stabilization of the subgrade materials in the area during road construction.