Abstract

Sustainability is a primary concern that needs to be addressed since infrastructure development requires significant natural resources. Using Recycled Concrete Aggregates (RCA) for road construction has numerous benefits in saving natural resources and the environment. In the present investigation, the demolition waste is being used for road construction, partially/fully replacing natural aggregates. The Cement Treated Recycled Concrete Aggregate (CTRCA) specimens were prepared at 3%, 5%, and 7% cement with various blends of RCA and Natural Coarse Aggregates (NCA) ranging from 0 to 100%. The strength characteristics in terms of Unconfined Compressive Strength (UCS), Flexural Strength (FS), Elastic Modulus, Indirect Tensile Strength (ITS) and durability tests were conducted on cured samples. Microstructural analysis using Scanning Electronic Microscope (SEM) revealed that the pores and cracks in the old mortar have a detrimental influence on the mechanical properties of CTRCA mixes. However, Energy Dispersive Spectroscopy (EDS) and durability tests have shown positive results. The Response Surface Method (RSM) was utilised to optimise the RCA and cement content in CTRCA mixes. The research resulted in the maximum possible RCA of up to 70% with a cement content of 5.8%, which met the Indian Road Congress (IRC) specifications for Cement Treated Bases (CTB).

Introduction

The demolition waste generated from old structures is inevitable due to economic development and technological advancement. More than half of global demolition waste comes from China, India, and the United States of America, with concrete waste accounting for up to 67% of total demolition waste (Chung and Lo 2003, Akhtar and Sarmah 2018). Every year, more than 6 billion tonnes of concrete is produced worldwide (Ä et al. 2012). This waste is disposed of in dumping yards, water bodies, drain trenches, and untilled grounds around human habitations.

Furthermore, accumulating demolition waste in landfills tends to inhabit vacant land that could have been used for other purposes. These waste materials have become vital resources increasingly in road construction due to the scarcity of natural resources. Recycling aggregates from construction and demolition waste is the sole solution to conserve traditional aggregates and safeguard the environment. The potential application of RCA in base and sub-base pavement courses will solve disposal problems and conserve natural resources (Leite et al. 2011, Arulrajah et al. 2014). It is necessary to characterise RCA before its use in pavements. A crucial factor influencing the performance of pavements is the particle size distribution. Different crushing techniques and the concrete’s strength are responsible for the variances in the particle size distribution of RCA (Aydilek.pdf n.d., Arulrajah et al. 2012, Gabr and Cameron 2012). The density of RCA is lower than NCA because of the attached mortar content on its surface (Tang et al. 2018).

Conclusions

In this study, the optimisation and characterisation of the CTRCA mixes were carried out. The RSM was employed to study the effect of individual and combined factors on CTRCA mixtures. Based on test results, RCA can be used in cement-treated base and sub-base courses in Pavements. The following conclusions are drawn based on the present investigation in the laboratory.

. The mix with NCA could get the required strength in UCS, FS, ITS and Elastic Modulus at 5 per cent Cement content after seven days of curing. It also passes the durability test.

. The CTRCA mix with 30 per cent NCA and 70 per cent RCA could get the required strength with 5.8 per cent cement after seven days of curing in terms of UCS, FS, ITS and Elastic Modulus. All the samples satisfy the durability test.