Effect of High-Volume Fly Ash on Shear Strength of Concrete Beams

Every year concrete production exceeds 6.5 billion tons worldwide, nearly 1 ton for every man, woman, and child on the planet. In fact, concrete is used 10 times more than any other building material in the world, primarily because of its incredible versatility, availability, and relatively low cost. Unfortunately, the production of portland cement—the key ingredient in concrete—generates approximately a pound of carbon dioxide for every pound of cement produced. One method of reducing concrete's carbon footprint is to replace a significant amount of the cement with fly ash, a by-product of coal-burning thermal power stations. This paper presents the results of an investigation of the shear strength of full-scale reinforced concrete beams constructed with both high-volume fly ash concrete (concrete with at least 50% of the cement replaced with fly ash) and conventional concrete. A test matrix of 16 beams included 12 beams without shear reinforcing and four with shear reinforcing in the form of stirrups; eight beams were constructed from each concrete type. Evaluation of the test results included a comparison with U.S. and international design codes, an examination based on AASHTO load and resistance factor design provisions of the longitudinal strains and angle of the critical flexure-shear crack, a comparison with an extensive database of shear tests on conventional concrete, and a detailed statistical study. The results revealed that the high-volume fly ash concrete beams had higher shear strengths than the conventional concrete beams tested in this investigation.