Calcined Marl as a Pozzolan for Sustainable Development of the Cement and Concrete Industry

摘要

Marl was calcined at temperatures between 600 and 1000 °C and compressive strength of mortars was tested after 28 days curing at 20 °C, when 20% of OPC was replaced by calcined marl at equal w/c-ratios. The clays were hold for 45 min. at the respective temperatures and the optimum calcination temperature with respect to reactivity as pozzolan seemed to be 800 °C. Higher replacement levels were tested for the most reactive temperature and even with a replacement level of 50% OPC the same strength as without cement replacement could be achieved. The 1-day strength for mortar with 50% calcined marl replacing cement was sufficient for demoulding concrete in field practice. Pozzola-nicity was tested on pastes of calcined marl and calcium hydroxide in different ratios with an alkaline solution by the use of thermal analysis, XRD and SEM. Ca(OH)2 consumption and formation of hydration products was analysed after curing for 28 days and 6 month at 20 & 38 °C.