Co-fired Ghanaian clay-palm kernel shells pozzolan: Thermogravimetric, 29Si and 27Al MA NMR characteristics

Abstract

Pozzolanic materials are well known to improve the mechanical and durability properties of cement based products including concrete, mortar and paste. This has therefore made pozzolans widely accepted for construction. In this work pozzolans were produced from a mixture of clay and palm kernel shells. Thermal gravimetric analyzer (TGA) was used to determine the lime consumption pattern of the calcined clay pozzolan whereas the 29Si and 27Al solid state magic angle spinning nuclear magnetic resonance (MAS NMR) was used to determine the aluminate and the silicate phases of the hydrated product. The TGA results showed that the calcined pozzolan containing palm kernel shells had a higher lime consuming pattern than the calcined clay and Portland cement. The 27Al MAS NMR showed that the calcined clay/palm kernel shell pozzolan produced stable monosulphate compounds at the octahedral environment. The 29Si MAS NMR results also proved that additional calcium silicate hydrates were formed in the cement containing pozzolan than the Portland cement. The formation of stable monosulphates coupled with formation of additional silicate hydrates are the reasons for strength enhancement of the calcined materials than Portland cement.