Metakaolin additions in autoclaved cement-quartz pastes:: a 29Si and 27Al MAS NMR investigation

Cement-quartz pastes containing 0-30.5% metakaolin (MK) were prepared and autoclaved at 180 degrees C for 8 h. MK was introduced as either quartz or cement replacement. Si-29 nuclear magnetic resonance (NMR) spectroscopy employing magic angle spinning was used successfully to defect unreacted MK in situ, thus providing valuable information on the practical limits of MK addition in these autoclaved products. Results were in excellent agreement with evaluations of the acid-insoluble residue; however in situ detection of unreacted starting materials, particularly MK, using Si-29 NMR eliminates the use of reagents which partially or completely dissolve them. Si-29 NMR results indicated that MK affects the overall distribution and nature of silicate anions in the product, presumably a consequence of both silica and alumina species participating in the reactions.