Kaolin, fly-ash and ceramic waste based alkali-activated materials production by the “one-part” method

Abstract

Portland cement production is related to the release of a large amount of carbon dioxide during its production and application in the construction industry. One way to minimize this environmental degradation is to search for new binders that can be used as possible substitutes for Portland cement. The Alkali Activated Materials (AAM) are a class of materials that are produced by activating aluminosilicate sources with alkaline solutions. Activation by the “one-part” method has demonstrated good results in the production of materials with good application in situ. In this work, kaolin, ceramic residue and fly ash were used to produce a binder material using the “one-part” method. The insertion of the activator into the dry mixture was carried out by calcination at 800 °C. The dry samples were produced by replacing 10, 20 and 30% by weight of fly ash with calcined material (molar ratio Na2O/SiO2 = 2.0). The samples produced (after mixing with water) were thermally treated at 75 °C and subsequently cured for 7, 14 and 28 days at room temperature until characterization. The AAM showed mechanical strengths close to 28 MPa when materials containing 30% activated ceramic residue were produced. The increase in the curing time promoted an increase in the resistances that were associated with the greater formation of the N-A-S-H gel, responsible for the increasing resistance of the matrices. Physical analyzes showed that the use of calcined kaolin significantly increased the water absorption of the hardened matrices at all curing times. The SEM analysis showed some unreacted fly ash particles, which had a decrease with the increase of the concentration of Na2O and SiO2 in the dry mixes.