Experimental Investigation of Superpave and Cement Treated Aggregate Base Mixtures for Long Life Asphalt Pavements

Abstract

Early deterioration of flexible pavements, due to increased traffic volume, environmental conditions, poor maintenance, and construction quality causes difficulties to road users, all around the world. The structural failures such as fatigue and rutting demand the reconstruction of the pavements which further leads to significant construction cost. One potentially sustainable solution to this problem is to adopt Long Life Asphalt Pavement (LLAP) technology. The fatigue and rutting distresses in the pavements can be minimized to some extent by utilizing Superpave and cement treated aggregate base mixtures with LLAP concept. The LLAPs are designed in such a manner that the response of the pavements to loads (particularly strains) is kept below certain threshold levels. In the current study two types of Superpave mixtures were prepared, one with Optimum Binder Content (OBC) designed at 4% air voids (Optimum mixtures) and the other with extra binder content of +0.5% over the OBC (Rich mixtures), for asphalt intermediate and base layers of LLAP respectively. The optimum mixtures were prepared with two aggregate gradations having two Nominal Maximum Aggregate Sizes (NMAS), 25mm and 19mm named as SP1 and SP2 respectively, for intermediate layers to enhance the rutting resistance. Rich mixtures were prepared with the same aggregate gradations for asphalt base layer to improve the fatigue resistance. Viscosity Graded (VG) 30 asphalt, Crumb Rubber Modified Binder (CRMB) of grade 60 and Polymer Modified Binder (PMB) of grade 40 were used as binders. The specimens were prepared as per Superpave mix design and were compacted in Superpave Gyratory Compactor (SGC). The performance of these mixtures was assessed in the laboratory through volumetric properties, Indirect Tensile (IDT) strength, rutting resistance, fatigue behavior, resilient modulus, and moisture susceptibility characteristics. In general, mixes with PMB 40, showed better properties. In case of IDT strength, rutting resistance, resilient modulus and ITS tests, optimum mixtures performed better compared to rich binder mixtures. However, in case of fatigue behaviour and moisture susceptibility tests, rich binder mixtures performed better compared to optimum mixtures. For all mixture types, SP1 gradationshowed better results than SP2, except for moisture susceptibility, in which both gradations performed almost the same. Cement Treated Aggregate (CTA) mixtures were also prepared with two aggregate gradations having two NMAS, 37.5mm and 45mm named as CTA1 and CTA2 respectively, for base course of LLAP to enhance the structural capacity with increased stiffness. Cement contents of 3, 5 and 7 % were used in the mixtures, and the modified compaction test was carried out to prepare specimens at their respective Optimum Moisture Content (OMC) and Maximum Dry Density (MDD). The performance of these mixtures was evaluated in laboratory through compressive strength, flexural strength, split tensile strength, modulus of elasticity and flexural fatigue behavior. The experimental investigations indicate that all the mixtures satisfied the 7-day compressive strength and 28-day flexural strength requirements as specified by Indian Roads Congress (IRC) for flexible pavement design. For all mixture types, CTA1 gradation showed better results than CTA2. The fatigue and rutting criteria of pavement sections proposed in the study were evaluated using KENPAVE software. In the analysis mainly eight pavement sections (denoted as S1, S2, S3, S4, S5, S6, S7, and S8) with different combinations of layers and materials were considered. The thickness of the layers in these sections was decided to obtain critical strains within permissible limits (tensile strain < 70 micro strain and compressive strain < 200 micro strain) and were chosen using trial and error method. The sections were divided on the basis of the mixtures used in asphalt intermediate and base layer and base course. From the results it was observed that, in case of SASW load, the critical strains were found to be within limits for pavement sections S2, S3, S7 and S8. The experimental results and analysis on pavement sections with proposed mixtures for intermediate and base asphalt layers and base course show that they can be considered as a better alternative for conventional pavements.