Development of supplementary cementing materials from red mud

摘要

The aim of this work was convert red mud (RM) into supplementary cementing material SCM.The RM, alone or in composition with two kinds of clays, was calcinated and converted to powder, ＜74 μm sieve.RM content varied from 80 to 100％.Calcinations were carried out on a continuum rotary kiln and bath kiln.Temperatures varied from 1100 to 1200 ℃.Residence time varied from 2 to 60 min.The products (RM-SCM) were characterized by available alkalinity (AA) and pozzolanic activity index (PAI), replacing 35％ of Portland cement by RM.According to Brazillian standards this properties should have: PAI ＞ 75％ and AA ＜1.5％ for an SCM.The results were subject to statistical treatment in order to evaluate the effects of composition, temperature and time.Results for PAI were between 73 to 97％, and presented positive correlation respect to temperature.PAI represents relative compression strength of test pieces compared to reference mortar.PAI =100％ represents no changes on mortar strength.Results for AA were between 1.7 and 7.8％, and negative correlation respect to temperature and time.According to statistical model extrapolations, little increasing on clay content (+5％), temperature (+65 ℃) or time (+30 min) could match AA to standards.