It is indeed disheartening that India recycles only 1% of the C&D wastes, rest is going to landfills! Thanks to IIT Madras and two universities from South Africa, the Research Monograph on recycled aggregate concrete published by them would be a good tool for the construction professionals who could use it in their day-to-day practice and increase the share of recycled aggregates in their concrete.

The Foreword to this Monograph is reproduced here with the permission from the publishers. The Monograph can be downloaded from https://ioasiitm-my.sharepoint.com/:b:/g/personal/manus_ic

Foreword

It gives me immense pleasure to provide a brief foreword to the Research Monograph on Recycled Concrete Aggregates (RCA) and their Influence on Concrete Properties. The Monograph is the outcome of a collaborative research work done jointly by Indian Institute of Technology, Madras, Chennai, and University of Cape Town and University of Witwatersrand from South Africa.

At the outset, the authors, and reviewers of this Monograph deserve to be applauded for the painstaking efforts they have taken in preparing it. They have critically reviewed selected 120-plus technical papers/articles/standards and presented the crux of the findings from the lab and field studies done on RCA in such a manner that the reader gets a good and up-to-date overview on the subject.

The Monograph is being published at a juncture when the organized sector of the concrete industry in India has achieved some tangible growth and it is slated to accelerate further. Penetration of ready-mixed concrete has been growing – both in numbers and volumes – in different parts of the country and the use of mechanized and semi mechanized techniques of construction is also receiving due acceptance.

Owing to rapid urbanization and the growth in infrastructure construction, existing sources of aggregates near the major consumption centres are nearly exhausted. The leads of fetching aggregates are continuously increasing, resulting in the increase in the transport cost. While the erstwhile hillocks near the urban centres that were supplying aggregates to the industry have now vanished, ugly mounds of construction and demolition (C&D) wastes are springing up on the outskirts of cities, creating environmental hazards. It therefore makes good sense to use RCA from the C&D waste in new construction – a circular economy practice that will enhance the sustainability of concrete construction.

Further, it is sad to witness the use of legally or illegally dredged river sand in certain locations of India. Excessive mining of sand from rivers lead to erosion of its bed and banks, forces the river to change its course, destroys the habitat of aquatic species and micro-organisms and adversely affects ground water recharge. Hence, construction professionals need to discourage its use for sustainability considerations.

The topic of using RCA is not new for the concrete industry in India. A number of workshops and conferences have been held on this topic in the the past. For example, the Indian Concrete Institute (ICI) came out with a publication on the subject more than a decade ago and the 2016 revision to the IS 363 specified the use of RCA in both plain and reinforced concrete for lower grades, with replacement of RCA limited to 20-25% of the natural aggregates. In the meantime, nearly a dozen facilities of C&D wastes have reportedly come up in the country. However, it is sad to know that India recycles only 1% of the C&D wastes! Further, excepting a few notable examples, the practice of using RCA from C&D facilities is yet to take off in a sizeable manner.

RCA has higher water absorption, lower density, lower stiffness and lower abrasion resistance, which has adverse effects on the fresh and hardened properties of concrete containing RCA. However, the Monograph highlights some of the beneficiation techniques of RCA (Chapter 2) which help in overcoming these adverse effects (Chapter 4). One of the beneficiation techniques involves the use of supplementary cementitious material (SCM) such as fly ash in concrete. Most of the ready mixed concrete plants in India today use at least one SCM in their concretes and this augurs well for the use of RCA. The Monograph points out that it is the lack of accepted design methods to optimise the quality of RCA and RAC that may have contributed to the apparent shortcomings in the properties of RAC. The Monograph therefore advocates the use of performance specifications to achieve the so-called “fit-for-purpose” mix design to produce desirable engineering properties using RCA.

The authors and the advisers of the Monograph are aware that there are a number of challenges in successful use of RCA. The critical challenges are mainly regulatory in nature. The present writer believes that unless the local regulatory authorities frame appropriate policies for collection, transport and separation of C&D waste, and make ways for the recyclers to get adequately compensated by the C&D ‘creators’, the cost of RCA may not become attractive for the concrete producer.

Another major challenge is to create awareness amongst the wider sections of the construction industry in the use of RCA in concrete. For this purpose, this Monograph needs to reach a large number of civil engineering fraternity in the country. Seminars/workshops or lectures of experts could be organized through professional bodies like ICI, ACCI, IAStructE, etc. One more suggestion is to conduct ‘fit-for-purpose’ mix design competitions using RCA, in which professional engineers and even students could be encouraged to participate.

Finally, I would like to once again congratulate the entire team of authors, and reviewers. Special thanks are due to both Prof Manu Santhanam and Prof Mark Alexander, who requested me to write this review.