Optimization of eco-friendly mixtures composed by granite-based crushed aggregates and inert fillers for structural applications

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Pressure is mounting in the civil construction industry to adopt more environmentally sustainable methods to reduce CO2 emissions. As the most commonly used construction material in the world, concrete has a particularly significant environmental impact, which continues to increase at a rapid rate. Global demand for concrete has increased by 400% between 1990 and 2002, and a 2.5-fold increase in global cement production is expected over the next 40 years. Portland cement often constitutes to more than two-thirds of the embodied energy of concrete, and its production generates 5% of global greenhouse gas emissions. A novel strategy to reduce Portland cement content in mixtures, without sacrificing performance, is the use of particle packing models and inert filler materials, which have lower or similar particle-size distribution than Portland cement. By reducing the volume to be filled by cement paste, Portland cement content can be significantly reduced by more than 50% in some cases. Moreover, the use of the bi index (i.e., the amount of binder required to produce 1 MPa of property, for example, compressive strength, has been used to quantify how environmentally friendly concrete mixtures may be, with typical values ranging from 10 to 15 [kg/m³.MPa] for standard conventional mixes. The embodied energy of concrete is also directly linked to extraction and transportation of aggregates and other raw materials that comprise concrete mixes. Furthermore, the use of river sand as a source of fine aggregates has led to the depletion of natural resources, lowering the water table, and posing other agricultural challenges. To address this concern, crushed stone waste, presenting particle-size distributions similar to sand (i.e. manufactured sand), or even lying between those of sand and Portland cement, has been proposed as an alternative to river sand. It has been shown that sources of good quality aggregates near construction sites can minimize transportation costs and energy use, while the fine residues generated during the crushing process (i.e. manufactured sand and inert fillers), may be used as a partial replacement for Portland cement. Hence, using coarse/fine aggregates (Particle Size>100 µm) and inert fillers (Particle Size<100 µm) from local quarries can be a novel strategy to produce eco-efficient concrete materials with a significantly reduced environmental footprint. Moreover, there is a lack of consistent and scientific mix-design procedures, especially addressing particle-packing model techniques, accounting for alternative fine residues in eco-friendly concrete. The proposed research project will focus on develop a new mix- design procedure including particle packing techniques to design low-cement concrete mixtures for structural applications, and evaluate the use of granite-based quarry processing materials and by-products, particularly crushed aggregates and inert fillers to produce eco-friendly low cement concrete with interesting short and long-term performance. The scientific benefit of this CRD include the development of a new performance-based design methodology for proportioning eco-friendly mixtures using locally available materials, which can significantly reduce the overall environmental impact of concrete suppliers and contractors across Canada. This result is expected to create new revenue streams for Fowler for fine granite-based aggregate production, which is not currently used for concrete applications, as well as a new opportunity for using quarry by-products.