Bond strength characteristics of high strength alkali activated slag concrete mixes

Abstract

Bond characteristics are influenced by several factors such as concrete compressive strength, type, diameter, and embedment length of the bar and confinement of concrete. Herein, an attempt has been made to evaluate the bond strength characteristics of a new class of high-strength, flowable, alkali activated slag concrete mixes made using the industrial by-products from iron and steel industries. Such evaluations are made using the results of direct pull out tests where again, the bond stress – slip behaviour of the trial mixes at different ages are also studied. GGBFS was used as the principal binder along with fine amorphous quartz powder in the development of the present class of high strength, flowable AASC mixes. While mixtures of steel slag sand and quartz sand were used as the fine aggregates, 12.5 mm down electric-arc furnace slag aggregates constituted the coarse aggregate fractions in all these mixes. The alkaline solutions used consisted of mixtures of specified amounts of sodium hydroxide flakes dissolved in the calculated quantity of water pre-mixed with the liquid sodium silicate solution. The experimental study was planned based on Taguchi’s design of experiments methodology. A set of AASC mixes were developed and evaluated for their workability characteristics along with compressive strengths at the ages of 3, 28, 56 and 90 days. Bond strength characteristics of a set of nine of such mixes were evaluated in an initial calibration phase. Strength prediction equations were then derived based on those initial results, the predictive capability of which were then assessed and ascertained with actual results of experiments on a set of six new mixes, in the prediction phase. Further better bond stress-slip behavior, with higher bond strength values, varying in the range of 12–14 MPa as compared to control OPC based reference concrete mix were obtained for the AASC mixes.