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. A 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 consumption pattern than the calcined clay and Portland cement. The 27Al MAS NMR showed that the calcined clay/palm kernel shell pozzolan produced stable mono-sulfate compounds in the octahedral environment. The 29Si MAS NMR results also proved that additional calcium silicate hydrates were formed in the cement containing pozzolan than in the Portland cement. The formation of stable mono sulfates combined with the formation of additional silicate hydrates are the reasons for the strength enhancement of the calcined materials than Portland cement