Development and Evaluation of Bituminous Paving Mixtures Containing Treated and Untreated Recycled Concrete Aggregates

Abstract

With the rapid depletion of resources for natural aggregates, recycling has become very essential for the construction industries. Recycling and resource protection is being encouraged in construction industries, but its application is limited due to several constraints. In the bituminous paving industry, some innovative materials and technologies have been explored to determine their suitability for the design, construction and maintenance of the pavements. Demolition of concrete structures creates a large amount of debris and waste, which is generally called construction and demolition (C&D) waste. The debris that remains after demolition needs to be appropriately reused and not disposed of in landfills. When these C&D wastes are recycled and turned into aggregates for new construction works, these are known as recycled concrete aggregates (RCA).
Use of recycled concrete aggregate in bituminous paving mixtures is limited mainly because of its high water absorption. Therefore, in this study, an attempt has been made to pre-treat the RCA using bituminous emulsion to reduce its water absorption characteristics, which is referred to in this study as pre-treated recycled concrete aggregates (PRCA). Similarly polyethylene is widely used as a packaging material for many items in day-to-day life which after use are converted into waste. One good use of polyethylene is found mainly in packaging of milk. Due to inadequate alternatives for recycling, a large percentage of polyethylene wastes are sent to landfills, which adversely impact the environment because they are not readily biodegradable. Considering the above, an attempt has been made to explore the use of recycled concrete aggregates and waste polyethylene collected from milk packaging (WPMP) in bituminous paving mixtures. In this study, the dense bituminous macadam (DBM) mixtures were prepared using PRCA, RCA and natural aggregate (NA) as coarse aggregates, with two different types of filler, i.e. cement (CM) and stone dust (SD), and with WPMP. The mixtures thus developed were evaluated in terms of various engineering properties such as Marshall test parameters, indirect tensile strength, moisture susceptibility, dynamic modulus, flow number and rutting effects using wheel tracking test. It was observed that the PRCA and RCA mixtures, in general, satisfy the requirements in terms of Marshall test parameters and moisture susceptibility. From the dynamic modulus tests conducted and master curves developed at reference temperature of 21ºC, mixtures with PRCA and WPMP (PRCAP) show higher stiffness values compared to samples prepared with NA and RCA. Also in resilient modulus test, the maximum modulus value has been observed for mixtures prepared with PRCA and cement, modified by WPMP at all three test temperatures. This is followed by mixtures with RCA and cement, modified by WPMP. Cement as filler is found to result in somewhat better engineering properties compared to stone dust. In the present study, after observing various engineering properties of different mixtures, it is concluded that the mixtures with pre-treated recycled concrete aggregates and cement as filler produce comparable results as that with natural aggregates. Further, mixtures prepared with PRCA and cement or stone dust as filler can be used for paving applications considering the superior engineering properties observed through this study. Based on the Indian Roads Congress (IRC) method of flexible pavement design, it is observed that there has been reduction in thickness of bituminous layer made with RCA and/or waste polyethylene. As a result, it is observed that there is a cost saving of 8-10% by using RCA/PRCA and/or waste plastic modification, in respect of a pavement designed on the basis of assumed design inputs for a period of 30 years. Maximum saving is achieved when the DBM mixtures with PRCA are modified by waste polyethylene.