Dust from chlorine bypass installation as cementitious materials replacement in concrete making

Abstract

The utilization of waste as an alternative source of energy in a cement kiln contributes to generation byproducts rich in chloride potassium, i.e. cement bypass dust (CBPD). This study aimed to investigate the feasibility of using this type of dust as an ingredient of concrete. In this paper, concrete mixtures were prepared with the substitution of CEM I 42.5R cement with an “untreated” raw bypass dust at the ratios of 10, 20, and 30% along with a control specimen without additives. Prior to tests, the characteristics of CBPD using various analysis techniques such as XRD, FT-IR, SEM, TG/QMS and calorimetric method were performed. A high value of free lime obtained in CBPD, as much as 19%, affected a high content of calcium hydroxide in phase composition. It was calculated an equivalent alkali (Na2Oäq) in CBPD was up to19% that may increase the alkali-silica reaction (ASR) damage in concrete when an aggregate rich in reactive silica is used. The compressive strengths of the modified samples ranged from 65 to 51 MPa after 90 days and were lower compared with the base sample, which can be attributed to the increased porosity and water demand. The progress of the hydration process after 2, 28 and 90 days of curing was analyzed using XRD, FT-IR and SEM. The results confirmed the expected hydration products, including portlandite, ettringite, C–S–H and unreacted clinker phases in all the specimens. The calorimetric measurements showed that in the presence of 30% CBPD, the induction period is extended by about 3 h, while the released heat is reduced by 19%. The use of bypass dust in the controlled amounts as cement substitute meets the principles of circular economy.