Concrete, a composite material is used extensively for construction activities. Countries all over the world are on the surge of improving their infrastructure and heavily rely on concrete. This creates a huge demand of the raw materials used in concrete such as cement, crushed sand and natural aggregates (Soundara B et al 2015; Vasudevan Mangottiri et al 2020). Researchers are constantly investigating for alternative sustainable materials that can be made used off in concrete without compromising its quality (Cai G 2016; Wałach D 2019; Esparza LA 2020). Use of by products and waste materials could be a sustainable approach (Bhuvaneshwari S et al 2014; Pillai RJ 2019; Preethi V et al 2020). Widely studied material for replacement of cement includes ground granulated blast slag (GGBS) which is a by-product of iron and steel industry. In case of mass concreting, the amount of heat generated becomes a major issue and this could be reduced by using mineral admixtures GGBS, in addition to improvement in physical properties of concrete (Alawad et al 2015; Hawileh et al 2017). Literature indicates that though the initial rate of strength gain of concrete with GGBS is comparatively less, it matches with the strength of a conventional concrete mix with OPC grade cement after 28 days (Phul et al 2019). In a study it was found that GGBS can be used up to 40% replacement of cement which improves the concrete strength. The study also confirmed that the usage of GGBS in concrete improves its flow-ability in plastic stages (Mo et al 2015).
River sand, the commonly used fine aggregate is a non renewable resource but its demand is exponentially increasing and as a result causing serious environmental issues (Scrivener et al 2015). Many countries have limited the use of river sand in construction and therefore the construction industries are opting for alternative materials including crushed sand (Ananthkumar et al 2020; Lalith Prakash et al 2021) and dolomite rock sand (DRS). DRS is a finely powered crystalline silica and is a by-product from cement manufacturing industries through the beatification process of limestone using silica as raw material. From literature it was inferred that DRS can replace sand till 30%. When the % addition of DRS is greater than 30%, the amount of water available for hydration is reduced and results in shrinkage and reduction in strength (Chinnaraju et al 2013; Nandakumar et al 2017; Landu et al 2020).
Coarse aggregates have a major role on the strength property of concrete and take up a major part of the load that occurs on the concrete structures. Once the building is no longer serviceable, it is demolished and the wastes are disposed in landfills. According to a research work more than twenty thousand tons of C& D wastes (Construction and demolition) are piled up everyday (Al-Ansary 2013). Incorporating recycled coarse aggregate in concrete (RCA) helps in achieving closed loop system in the construction industry and reduces the demand on fresh coarse aggregates. Replacement of RCA up-to 30% does not affect the strength and durability of concrete. (Zheng et al 2018). Studies have shown that RCA is generally porous in nature and higher percentage replacement decreases the strength which can be attributed to the weak residual mortar layer, and also the characteristics of RCA obtained from the construction and demolition site. It was reported that concrete slump and strength decreased as more RCA was added for natural aggregates (Heidari A 2018; Tufail et al 2020). In studies conducted by Chakradhara Rao M (2018) found that the compressive strength reduces by 20% for complete RCA replacement. Hadavand (2019) in his studies have shown that on using RCA in a repeated fashion show that the strength parameters decrease over successive usage in concrete, though it makes the mix more economical. Further it was found that 20 to 40% replacement with RCA helped to achieve good workability, and at 60% replacement, the compressive strength was maximum and then decreased progressively.
Design of Experiments (DoE) using RSM (response surface methodology) is commonly used in the recent days to optimize the independent variables (factors) for improving the output (response) of any experimental setup by developing and analysing regression models (Hilal N 2021; Boukli et al 2015). It also reduces the cost of the project by reducing the number of experimental trials especially when there are a greater number of independent variables (factors) (Chinnaiyan et al 2019; Senthil Kumar et al 2014). RSM was commonly employed Concrete for instance is highly unpredictable as it’s a culmination of different materials having different properties. Developing a model helps in analyzing the relationship between various factors and the response. Studies on effects of fibres, cement and water on flexural and compressive strength of high strength concrete and concrete pavement were conducted using RSM and optimum quantities were evaluated(Mardani et al 2015; Rooholamini et al 2018).
In this study, sustainable materials like ground granulated blast slag (GGBS), dolomite rock sand (DRS) and recycled coarse aggregate (RCA) were chosen as replacement for cement, fine and coarse aggregate respectively. Regression models was developed involving the use of above materials in concrete and their impact on the strength parameters viz., compressive, flexure and split tensile was studied employing response surface methodology.