Development of Eco-Friendly Concretes – A Step Towards Sustainable Construction

Abstract

Owing to the rapid advancements in industrialization and urbanization, the utilization of concrete has witnessed an exponential surge over the past few decades. This escalating demand for concrete necessitates a proportional increase in natural resources for both cement production and the procurement of coarse aggregates. Notably, the production of cement not only depletes limestone resources but also entails environmentally unfriendly processes. Furthermore, the surge in concrete demand is accompanied by a substantial increase in the generation of construction and demolition (C&D) waste, owing to evolving trends, economic development, and the heightened demolition of existing structures in the 21st century. This surge in C&D waste generation poses a significant environmental challenge. To render concrete production more sustainable, it is imperative to mitigate the reliance on conventional cement. This can be achieved through the incorporation of supplementary cementitious materials and the utilization of C&D waste as aggregates in concrete. Such measures not only diminish the demand for natural aggregates but also contribute to reducing landfill volumes, aligning with contemporary principles of environmental conservation and sustainable development. The present study focuses on the processing of C&D waste into the quality of Recycled Coarse Aggregates (RCA) and uses them in the production of cement-less concrete. This study proposes an alternative method for processing the demolition waste into high-quality recycled coarse aggregate using the ball mill. Taguchi’s design of experiments based on orthogonal array was used to minimize the number of trials for saving material and time. Experiments were carried out based on L25 orthogonal array with three processing parameters: charge, revolution duration, and aggregate weight with five levels. The revolution speed of the ball mill was set to 60 revolutions per minute. The Taguchi method was then combined with grey relational analysis to achieve the best combination of processing parameters for producing high-quality aggregate. Experimental studies on water absorption, specific gravity, impact value, and abrasion value were used to assess the quality of recycled coarse aggregates. The best combination for each performance characteristic was achieved by using the mean of Signal to Noise ratio graphs. The optimal combination of processing parameter levels i to generate superior quality recycled aggregates and the most significant processing parameter were identified based on the response table of means of grey relation grade. The processed RCA along with Ferrochrome Slag aggregates (FCSA) was used for the production of One-Part Alkali-Activated concrete (OPAAC) by replacing cement with Fly ash (FA), Micro silica (MS), and Ground granulated blast furnace slag (GGBS). The proportion of MS is maintained at 20% of FA, while the maximum replacement of FA with GGBS is set to 60%, varying in 20% intervals (i.e., 0%, 20%, 40%, and 60%). Moreover, the natural aggregates (NA) are substituted with RCAs, FCSAs, or a combination of both. Additionally, microstructural and mineralogical investigations are conducted to determine the formation of distinct hydration products, utilizing scanning electron microscopy (SEM) and X-ray diffractometry (XRD) techniques. In OPAAC containing FA, the primary hydration products identified are alkaline alumino silicate hydrates (CASH and NASH). As the GGBS content increases, calcium silicate hydrate (CSH) becomes the predominant hydration product. Furthermore, in order to assess the sustainability of OPAAC, an analysis of embodied CO2 emissions is performed, and the results are compared with CC and alkali-activated concrete. Notably, OPAAC comprising 40% FA replaced with GGBS, 50% RCAs, and 50% FCSAs demonstrates the most favourable mechanical properties and exhibits lower CO2 emissions. In this study, an examination of the performance of OPAAC mixes under elevated temperatures was also conducted. The mechanical properties results dictated a fixed combination of RCAs and FCSAs)at 50% each. The binder composition was identified as a critical factor influencing the performance of concrete at elevated temperatures. Consequently, OPAAC mixes were meticulously formulated using various combinations of FA, MS, and GGBS. These mixes underwent exposure to temperatures ranging from 200℃ to 800℃, with increments of 200℃. Notably, the mix comprising 60% FA and 40% GGBS exhibited superior performance compared to all other OPAAC mixes and conventional concrete under the specified elevated temperature conditions.