Performance predictive model for sisal-plastic modified asphalt concrete for road pavement

Abstract

Preserving road network requires a coordinated approach for good performance and efficient movement of goods and services. The road construction materials and design have great influence on future road conditions and maintenance scenarios. Weather changes and increase in traffic loads have exposed pavements to major distresses such as rutting, potholes, fatigue cracking, and temperature cracking. These forms of pavement failure cause traffic congestion, loss of man hour, increase in wear and tear of the vehicle and increase in road accidents. There is loss of money in frequent road repairs, vehicle repairs and treatment to the injured persons. Therefore, there is need to increase the load-bearing capacities of road pavements. The aim of this study was to investigate the performance of sisal-plastic modified asphalt concrete for road pavements. The properties of modified gap graded asphalt concrete was evaluated through characterization of asphalt concrete mixes modified using sisal fibre and waste plastics. Sisal fibre and plastic wastes were used as asphalt concrete stabilizers and modifiers respectively to enhance stability against bitumen drain down, bleeding and cracking. Clean waste plastics were cut into small sizes so as to pass through 2-3 mm sieve using shredding machine. The aggregate used in preparation of gap graded asphalt (GGA) were sizes 20-6mm for stone matrix asphalt (SMA) concrete and 12-6mm for open graded asphalt (OGA) concrete. The respective aggregate mix was heated and the waste plastics effectively coated over the aggregate. Sisal fibre was cut into 5 mm long threads, treated using sodium hydroxide solution and mixed with hot bitumen. The waste plastic coated aggregate was mixed with the mixture of treated sisal fibre and bitumen. Sisal fibre treated in 0.5N solution of sodium hydroxide makes sisal fibre become less porous with high density thus making more rigid asphalt concrete mix. The treatment improves the adhesion due to increase in surface tension and surface roughness. The asphalt concrete mix samples were analyzed for various engineering properties to assess their suitability for road pavement construction. The samples were subjected to different performance tests, namely, Marshall Test, drain down test and indirect tensile strength test. Using the Marshall procedure, the optimum additive contents were determined as 0.3% for sisal fibre and 5% for waste plastics in asphalt concrete mixes respectively. The Optimum Binder Content (OBC) values determined were 5.5% and 6.5% for open graded asphalt (OGA) and stone matrix asphalt (SMA) respectively. The stability test result values for both gap graded asphalt (GGA) concrete were 11.8kN and 12.8kN when modified with sisal fibre and waste plastics respectively. However, when sisal and plastics were both used, the stability values recorded were 13.6kN and 12.9kN for sisal-plastic modified OGA and sisal-plastic modified SMA respectively. The tensile strength test value determined was 1.23MPa for both sisal-plastic modified gap graded asphalt concrete. The tensile strength ratio was 99.9% while bitumen drain down value determined was 0% for both sisal-plastic modified gap graded asphalt concrete. A mathematical model was developed to predict the tensile strength of sisal-plastic modified asphalt concrete. The model was found to be adequate with 97.5% confidence level. A model road pavement consisting of control section and sisal-plastic modified were constructed. There was no bleeding, rutting, cracking or aggregate loss observed on modified section. However, the control section had 2mm settlement and loss of aggregate was observed. In conclusion, the use of this innovative technology in the usage of sisal and waste plastics will strengthen the road pavements by 99%, reduce loss of bitumen by 100%, increase the roads’ service life by 99% and help in the improvement of the environment through utilization of waste plastics. Hence, sisal-plastic modified OGA and SMA mixture provide better resistance against permanent deformations due to their high stability and high MQ. This technology contributes to recirculation of plastic wastes to protect the environment. The effective utilization of the sisal fibre and waste plastics will result in substantial increase in the scrap value for sisal and waste plastics. This will also lead to an ecofriendly sustainable construction method. It is recommended that sisal-plastic modified road section can be constructed on a busy road and monitored for longer period exceeding five years so as to evaluate its performance characteristics under prolonged heavy traffic loads.