Revista Română de Materiale / Romanian Journal of Materials 2019, 49 (2), 207 - 216 207 MULTIPLE LINEAR REGRESSION MODEL TO PREDICT MECHANICAL PROPERTIES AND IMPACT RESISTANCE OF HOOKED-END STEEL FIBRE-REINFORCED BLENDED CONCRETE S. JANANI, A.S. SANTHI  School of Civil Engineering, VIT, Vellore, Tamil Nadu, India. Concrete, being one of the most commonly used building materials in construction industries, has, cement as its principle component. Cement paste is responsible for bonding and strength gain in concrete. The production of cement releases an equal amount of CO2 to the atmosphere causing environmental pollution. This Study identifies the property enhancement of concrete due to the partial replacement of cement with pozzolanic materials such as fly ash and silica fume at 40% and 7% respectively. Tests were conducted to identify mechanical properties – compression, split tension, flexure; and Impact resistance. Steel fibres were also incorporated at 0.75%, 1.15% and 1.55% to the mix. Addition of steel fibre to blended concrete showed an increase of 33-77% on mechanical properties and 186% on impact resistance of concrete at 28 days. A Multiple linear regression model was formulated using SPSS, and consequently, equations were derived to predict the mechanical properties and impact resistance of concrete. The equations were found to be in a good agreement with the experimental results obtained by various other researches with significance level lesser than 0.05 in ANOVA. Keywords: fly ash; silica fume; steel fibres; mechanical properties; impact resistance; regression 1. Introduction Concrete production has developed rapidly and many researchers are trying to improve the physical and mechanical properties of concrete [1]. Cement is the principle component in the concrete production industry. The production of Portland cement approximately reaches four billion tonnes a year. The key role of Cement is to bind the aggregates and make the concrete components react chemically. Though cement has so many advantageous characteristics, it has become extremely costly and also poses a greater threat to the harmony of the environment [2]. This paved the way for the utilization of certain materials having cementitious properties (commonly called supplementary cementitious materials or SCMs) like fly ash, silica fume, metakaolin, ground granulated blast furnace slag and so on in concrete for sustainable development and improvement in durability aspects [3]. The utilization of these materials has also become extremely important because of their performance in safeguarding the environmental harmony in all aspects in terms of ecological, behavioural and economical methods of disposal of hazardous waste materials, providing a cleaner environment with reduced energy consumption and better strength characteristics [4]. The inclusion of these materials significantly improves the properties of concrete in both fresh and hardened states. These natural pozzolans improve the durability of the concrete by altering the microstructure and the interfacial transition zone between aggregate-paste or paste-reinforcement bonding [5]. Fly ash has been used as a mineral admixture to partially replace cement or sand [6]. Being smaller sized particle than cement, its major constituent of fly ash is silica (SiO2); however, the sum of silica (SiO2), alumina (Al2O3) and Iron oxide (Fe2O3) contributed to the typical value equal to that in cement. When fly ash is mixed with cement, it makes the cement paste smoother and allows better bonding between aggregate and cement particles, which, in turn, makes the concrete more durable and impervious in nature. Chemically, fly ash undergoes pozzolanic activity where it reacts with CH (calcium hydroxide) and produces secondary C-S-H (Calcium-silicate-hydrate) gel which is similar to that produced in the cement but at a different rate. In concrete, fly ash boosts up the workability without adding extra water by their hard and round shaped particle size. Fly ash reduces pores in concrete during hydration and subsequently makes the concrete a hard and durable one. Fly ash negatively affects the setting time of cement by delaying it. Concrete with fly ash as a replacement to cement (partially) showed a delay in the development of early strength and a better later strength [7,8]. Silica fume is also a by-product obtained in the manufacture of silicon or different forms of silicon alloys. Its major composition is SiO2 (80- 85%); this enabled its use in construction  Autor corespondent/Corresponding author, E-mail: as_santhi@vit.ac.in