Experimental And Field Monitoring Studies On Recycled Materials As Pavement Bases

Abstract

Natural aggregates derived from a variety of source rocks have been used as a road base material. But the extraction of natural aggregates resources is increasingly being constrained by urbanization, increased costs and environmental concerns. Thus, increased amounts of reclaimed materials are being used to supplement natural aggregates in road construction. Recycled Asphalt Pavement (RAP) material is one of the important recycled materials used in the present geotechnical applications. Many agencies are constantly seeking to reap the benefits of utilizing RAP. Main advantages of utilizing RAP include the preservation of the existing profile, conservation of asphalt and aggregate resources, conservation of energy, and reduction in life-cycle cost. Therefore, it is no surprise that state highway agencies have been moving toward increasing the percentages of RAP in their HMA pavements. The 1993 EPA report mentioned that approximately 73 million tons of asphalt pavement material was recycled annually, which amounts to about 80% of the asphalt removed from pavements each year. Quarry by-products are another important recycled materials showing good performance in many geotechnical applications. These are generally obtained from crushed natural stone. One of the fines obtained from limestone stone quarries are becoming popular. These fines when they are stabilized with some cementing materials can be used in any geotechnical applications. About 159 million metric tons (175 million ton) produced annually is thought to be used in many geotechnical applications. In a recent survey, three states (Arizona, Illinois, and Missouri) indicated that quarry by-products have been used as an embankment material and three other states (Florida, Georgia, and Vermont) indicated some use of quarry by-products in base or subbase for the pavement applications. These are also used as mineral filler in asphalt paving. In this present research, a comprehensive experimental program was performed on two recycled materials which include RAP and Cemented Quarry Fines (CQF) which were used as a pavement base material. All the tests provided repeatable and reliable results. Unconfined Compressive Strength (UCS) tests showed a peak stress of 1200 kPa for the CQF which was 12 times more than the untreated sample. UCS for the RAP material showed a strength of 340 kPa which was expected for the RAP materials. Peak values for the resilient modulus for RAP and CQF were 330 MPa and 370 MPa respectively. These samples required more number of cycles to know the actual resilient modulus. Untreated sample showed a peak value of 220 MPa. Values for the swell tests was zero for the CQF whereas for the untreated sample was around 6%. RAP showed a less strain of 0.7% which is negligible for these materials. Consolidation Indices for these recycled materials showed values less than 0.001. Field monitoring data showed that the settlements and pressures were in permissible limits. Results from the experimental program along with field monitoring data showed that these recycled materials are very best suited as a pavement base material. Based on these results these recycled materials can be used for future research projects.