Investigation of concrete incorporating ultra-high volumes of ash: a case study in India

Abstract

Coal-fired thermal power plant ash (CTPA) has been widely used in construction works not only as a partial replacement for conventional cementitious binders but also as a substitute for fine aggregates. However, higher volumes of CTPA in concrete typically lead to non-satisfactory performance of concrete in terms of strength and durability. This was remedied by incorporation of hyperplasticisers, which offset the negative effects of loss of workability, segregation, bleeding and strength reduction. This study describes three field studies undertaken with ultra-high volumes of CTPA in terms of class F fly ash and coarse bottom ash in M40 grade sustainable pavement-quality concrete at National Thermal Power Corporation (NTPC) Khargone, Khargone, India; NTPC Mouda, Nagpur, India; and Dhariwal Infrastructure Limited Tadali, Chandrapur, India. Core samples of 100 mm diameter and varying slenderness (H/D) ratios were drawn from cast segments at the sites after 28 days of curing, and the results in terms of compressive strength and durability characteristics were evaluated against the results of laboratory investigation. Statistical analysis was also conducted using Student’s t-test to analyse the variance in the results. The effects of the H/D ratio of core samples on the compressive strength of cores were also analysed. The results indicate a non-significant difference in the values of the means of the compressive strength of the batches for H/D = 1, indicating the field applicability of the developed mix designs for severe exposure conditions.