Rapid urbanisation leads to increased construction activities, resulting in significant amount of Construction and Demolition (C&D) Waste. India alone generates approximately 150 million tons of C&D waste annually, with concrete waste comprising 23%. Only 1% of this waste is recycled and reused in construction. Recycled concrete aggregate (RCA) production generates waste concrete fines (WCF). They comprise 20–30% of the volume, while RCA accounts for 70–80%.
The primary goal of the proposed work is to maximize the utilisation of WCF. This presentation delves into a comprehensive review of existing literature on using WCF as recycled cement (RC), the beneficiation of WCF through CO2 mineralisation using different techniques, and the challenges and opportunities associated with utilising WCF in 3D printed concrete.
RC can be obtained by thermally activating WCF at high temperatures. This process yields a porous and reactive material with a high surface area and significant free lime content. RC has drawbacks such as high-water demand, rapid setting time, and low long-term strength, although it can be used as a binder in concrete. These challenges highlight the need to explore alternative options for utilising WCF effectively.
Mineralisation enhances the strength and density of WCF. Moreover, it can increase the cementitious activity of WCF by increasing the content of reactive silica and alumina gel in the WCF. Various carbonation techniques have been proposed to increase the WCF carbonation capacity and reactivity. Many studies have focused on the WCF generated from laboratory-cast cement paste or mortar, which consists largely of hydrated cement paste, making it suitable as a supplementary cementitious material (SCM) after carbonation. However, in real scenarios, WCF obtained from various production mechanisms of the RCA would have different compositions. It contains a high proportion of aggregate fines derived from the coarse and fine aggregate of the waste concrete during RCA production. The presence of these fines reduces the reactivity and CO2 uptake capacity of the WCF. This also makes it challenging to use WCF as an SCM. So, there is a need to find the actual CO2 sequestration capacity of the WCF obtained from the different production mechanisms of RCA and to find an alternative option for utilising it.
Another promising method for valorising WCF is its application in 3D printed concrete. 3D printing is an emerging technology that enables the creation of complex shapes and structures with reduced material waste and labour costs compared to conventional methods. However, 3D printing poses challenges in terms of concrete mix design, including flowability, buildability, extrudability, and open time. WCF can improve these properties by modifying the rheology, hydration, and microstructure of the concrete mix.
The presentation comprehensively covers the identified research gaps and objectives derived from the literature review. It outlines the methodology, scope, limitations, expected outcomes, and work plan of the study. Furthermore, it discusses the physical, chemical, and mineralogical properties of WCF obtained from different sources as part of the first objective.