Experimental Investigations on Alkali Activated Concrete Developed By Incorporating Marginal Materials for Rigid Pavement

Abstract

Road infrastructure projects are very much important in the progress of any country and involves large budget. Concrete roads are being considered over bituminous pavements due to its longer design life and lesser maintenance costs. The higher demand for concrete roads and other infrastructure developments 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 to 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 (AAB) such as Alkali Activated Slag (AAS), Alkali Activated Slag Fly Ash (AASF), Geopolymers, etc. can be considered as potential alternatives to OPC. Also, there is a huge scarcity of natural aggregates to be used in road projects. Industrial marginal materials can be taken as fine aggregates in pavement quality concrete for sustainable growth. In the present study, Processed Iron Slag (PIS), an industrial by-product obtained from iron and steel industry is identified as an alternative to natural aggregates for concrete production, since there is an acute shortage of natural aggregates for concrete production. The present study is mainly focussed on evaluating the performance of PIS as fine aggregate in Alkali Activated Slag Concrete (AASC) and Alkali Activated Slag Fly Ash Concrete (AASFC) by replacing river sand. AASC and AASFC mixes are designed to attain a minimum strength of M40 grade and compared with conventional Ordinary Portland Cement Concrete (OPCC) mix of similar grade. AASC mixes were prepared with 100% Ground Granulated Blast furnace Slag (GGBS) as sole binder, while AASFC mixes were prepared by mixing GGBS and Fly Ash (FA) in different proportions, i.e., 75:25, 50:50 and 25:75. Along with slag and fly ash, Aluminium dross – a by-product from aluminium refinery industry was considered as a partial replacement for binder in this study. However, it could not be a suitable binder in AAS and AASF based concrete because of the swelling observed at 5 % replacement itself. It was not considered in further stages of development of AASC and AASFC. ii Preliminary tests were carried out to identify the optimal activator modulus and dosage of alkaline activators for each of the AASC and AASFC mixes. PIS as fine aggregates were incorporated in the AASC and AASFC mixes by replacing the river sand by weight 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 concrete mixes were evaluated as per the standard test procedures. The durability of concrete mixes in terms of resistance to sulphuric acid attack, magnesium sulphate attack, water absorption and Volume of Permeable Voids (VPV) were investigated. Flexural fatigue behaviour of various concrete mixes was determined by carrying out repeated load tests on beam specimens. The fatigue life data obtained were analyzed using S-N curves to establish fatigue equations. Probabilistic analysis of fatigue data was carried out using two parameter Weibull distribution method. Further, goodness-of-fit test was 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 was carried out. The economic benefits of AASC and AASFC mixes in comparison with conventional OPC concrete were analyzed. The results indicated that incorporation of PIS in AASC and AASFC mixes resulted in slight reduction in mechanical strength. The inclusion of PIS aggregates slightly reduced the durability performance of AASC and AAFC mixes. Water absorption and subsequent VPV were increased with inclusion of PIS in both AASC and AASFC mixes which may be attributed to higher water absorption of PIS as compared to normal aggregates. Alkali Activated Concrete (AAC) 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 AAC mixes slightly decreased with replacement of natural aggregates with PIS aggregates. Reduction in number of cycles for fatigue failure was observed in AASC and AASFC mixes containing PIS as compared to river sand. 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. iii Cost comparison was done to compare the costs of all the materials per cubic meter of concrete with respect to OPCC, AASC and AASFC mixes. AASC and AASFC mixes showed a slight reduction in cost when compared to conventional OPCC. Incorporation of PIS aggregates in AAC mixes led to further reduction in cost as compared to OPCC. Overall, PIS aggregates reported acceptable performance in AASC and AASFC mixes for its use in pavement quality concrete. AASC and AASFC mixes satisfying the requirements of M30 and M40 grades of concrete are recommended for low and high-volume concrete pavement construction.