MECHANICAL AND FRACTURE PROPERTIES OF REINFORCED CONCRETE USING STEEL INDUSTRIAL SLAG AND GGBS AS PARTIAL REPLACEMENT OF CEMENT

Abstract

Concrete is an essential building material that is always being improved to satisfy the needs of modern infrastructure while increasing environmental sustainability. This study evaluates the mechanical and fracture properties of concrete using the addition of fiber and the partial replacement of cement with industrial by-products such slag and Ground Granulated Blast Furnace Slag (GGBS). Five concrete mix combinations were used according to the mix design by replacing cement content with the ladle slag, GGBS and fiber at various percentages in the concrete mix. The control mix namely Mix-1 was 100% cement content, whereas 10% ladle slag and 30% GGBS has been replaced with cement in the Mix-2 and Mix-3 respectively. Fiber was used in the Mix-4 and Mix-5 with the same ingredients of Mix-3 by 0.05% and 0.10% of concrete volume respectively. It was observed Mix-1 achieved maximum compressive strength whereas a decrease of 4% and 16% in Mix- 2 and 18% and 22% in Mix-3 at 7 and 28 days. The results showed that the GGBS improved the compressive strength compensating for the decrease in cement content to some extent. The results also indicate that the compressive strength of Mix-4 increased by 4% with the addition of 0.05% fiber but decreased by 6% in the Mix-5 when 0.10% fiber was used comparing to the Mix-3. Thereafter the only difference between Mix-3 to Mix-5 is the amount of fiber content used in the mix, which implies that, the addition of fiber improved the strength but for the uses of excessive amount of fiber does not improve strength rather decreases the strength. Ladle slag, GGBS, and fiber improved flexural strength (MOR), and MOR increases by as high as 48% for Mix-5 over the control Mix-1. The fracture energy Gf which represents the amount of energy needed for the formation of cracks in the concrete surface. In addition of 0.05% and 0.10% fiber in the Mix-4 and Mix-5 enhancing the Gf values by 6% and 45% respectively but reduction of cement content by 40% in the Mix vi 3, it’s Gf value decreases by 54%. Which implies that fibers significantly improved the Gf capacity and on the other hand, reduction of cement content decreased the fracture energy values. The fracture energy Gf values has been obtained in the range of 80-175 N/m from the all mix combination where control sample Mix-1 has achieved the highest value. The measure of material’s ability to prevent an unstable fracture or crack is called stress intensity factor Kic. In this study highest Kic is obtained at control Mix-1 indicating above mix has maximum ability to resist the growth of the cracks. The Kic values are gradually decreases by 8% and 54% for the reduction of 10% and 40% of cement in the Mix-2 and Mix-3. Addition of fiber in the concrete mix significantly enhanced the fracture toughness Kic value by 39% and 33% in the mix combination Mix-4 and Mix-5. The range of Kic values has been evaluated 0.82-1.78 MPa m0.5 in this study.