CO₂ ABSORPTION AND PRODUCTS IN CARBONATED PORTLAND CEMENTS

Abstract

This paper discusses CO₂ absorption and carbonation of hardened normal （N）, moderate （MPC） and low heat Portland （LHC） cements. Calcite, vaterite and gel phase are produced in carbonated all cements. Si rich gel phase is produced in carbonated samples and Ca/Si of carbonated products analyzed by SEM-EDS is varied. Ettringite （AFt） is decomposed in all carbonated cements, but AFt is reproduced by reaction of gel phase and SO₃ in carbonated MPC and LHC containing rich rate of SO₃/Al₂O₃ compared with N. The reaction of belite is accelerated but the reaction rate of alite is not changed in carbonated samples. Total CO₂ absorption measured by total carbon analyzer （TC） is larger than that of measured by thermal gravity （TG）. This is related to calcium carbonate. Absorption of CO₂ in hardened cements is range of 25 to 30mass％ measured by TC. Temperature of weight loss of TG is determined by DTG. About 10-20％ of CO₂ is fixed as compounds other than calcium carbonate.