Performance of Alkali Activated Concrete Mixes with Steel Slag as Coarse Aggregate for Rigid pavements

Abstract

Improved road connectivity is very essential for any countries progress. Well designed and constructed concrete pavements have been identified component for the development of a sustainable highway infrastructure. The higher demand for concrete roads and other construction purposes has resulted in the increased production of Ordinary Portland Cement (OPC), which is one of the basic constituents required for concrete production. However, the production of OPC is associated with emissions of large amounts of CO2, with the cement industry accounting for about 5-8% of worldwide CO2 emissions. In addition to CO2 emissions, the production of OPC requires considerable amounts of natural raw materials and energy. The present research community is focused on the development of alternative binders, with the aim of minimization of production of OPC. Alkali Activated Binders (AABs) such as Alkali Activated Slag (AAS), Alkali Activated Slag Fly Ash (AASF), Geopolymers, etc. can be considered as potential alternatives to OPC. Steel slag, an industrial by-product obtained from manufacture of steel can be identified as an alternative to natural aggregates for concrete production, since there is a possibility of acute shortage of natural aggregates for concrete in future. The present study is conducted to evaluate the performance of steel slag as coarse aggregates in Alkali Activated Slag Concrete (AASC) and Alkali Activated Slag Fly Ash Concrete (AASFC) by replacing natural granite aggregates. AASC and AASFC mixes are designed to attain a minimum strength of M40 grade and compared with conventional OPC concrete mix of similar grade. AASC mixes are prepared with 100% GGBFS as sole binder, while AASFC mixes are prepared by mixing GGBFS and FA in different proportions, i.e. 75:25, 50:50 and 25:75. Preliminary tests are carried out to identify the optimal activator modulus and dosage of alkaline activators for each of the AASC and AASFC mixes. Steel slag as coarse aggregates are incorporated in the AASC and AASFC mixes by replacing the natural coarse aggregates by volume replacement method at different levels of replacement, i.e. 0%, 25%, 50%, 75% and 100%. The fresh and hardened properties such as workability, compressive strength, split tensile strength,flexural strength, and modulus of elasticity of different concretes are evaluated as per standard test procedures. The durability of concrete mixes, in terms of resistance to sulphuric acid, magnesium sulphate, water absorption and Volume of Permeable Voids (VPV) are investigated. Flexural fatigue performance of various concrete mixes is evaluated by carrying out repeated load tests on beam specimens using repeated load testing equipment. The fatigue life data obtained are represented and analyzed using S-N curves to establish fatigue equations. Probabilistic analysis of fatigue data is carried out using two parameter Weibull distribution method. Further, the goodness-of-fit test is done to ascertain the statistical relevance of the fatigue data using Weibull distribution model. Survival probability analysis to predict the fatigue lives of concrete mixes with required probability of failure is carried out. The impact of the properties of AASC and AASFC mixes on the rigid concrete design is analyzed by carrying out standard pavement design. The ecological and economical benefits of AASC and AASFC mixes in comparison with conventional OPC concrete are analyzed and discussed. The results indicated that incorporation of steel slag in AASC and AASFC mixes resulted in slight reduction in mechanical strength. Reduction in number of cycles for fatigue failure was observed in AASC and AASFC mixes containing steel slag as compared to granite aggregates. Two parameter Weibull distribution was used for statistical analysis of fatigue data and it was observed that the fatigue data of concrete mixes can be approximately modelled using Weibull distribution. The inclusion of steel slag aggregates slightly reduced the durability performance of AASC and AAFC mixes. The higher water absorption and subsequent VPV increase, with inclusion of steel slag in both AASC and AASFC mixes, due to higher water absorption of steel slag as compared to normal aggregates. Alkali activated concrete mixes with natural aggregates exhibited better resistance to sulphuric acid and magnesium sulphate environments as compared to OPCC, which may be attributed to properties/structure of binders. The acid and sulphate resistance of alkali activated concrete mixes decreased with replacement of natural aggregates with steel slag. The Embodied Energy (EE), Embodied Carbon Dioxide Emission (ECO2e) and cost of alkali activated concrete with natural aggregates are foundto be quite lower as compared to OPCC. Incorporation of steel slag in alkali activated concrete mixes led to further reduction in EE, ECO2e and cost as compared to OPCC. Steel slag aggregates reported acceptable performance in AASC and AASFC mixes for its use in pavement quality concrete.