Sol-Gel Technology as a Seeding Agent for Portland Cement Systems: Compatibility Studies

Calcium silicate hydrates (C-S-H), an amorphous gel, is the principal product of hydration responsible for the properties of Portland cement and concrete. We propose the possible strategy of incorporating sol-gel technology using silicon alkoxide precursors as a seeding agent to ‘guide’ the formation of C-S-H networks, in Portland cement systems. It is well documented that particles of micro and nano silica serve as nucleation sites for enhanced precipitation of C-S-H leading to denser microstructures. More importantly, cement hydration may be regarded as a special case of inorganic polymerization, bearing similarities to the sol-gel processes. We hypothesize, by optimizing the synthesis parameters of the sol-gel process C-S-H may grow on the ‘sites’ and engage with the networks of silica created in this composite sol-gel-cement system. This could promote long-chain polymerization of C-S-H, refined micro and nano structures, and facilitate enhancements in mechanical performance and durability.
As an initial step to our endeavour, compatibility of the sol-gel process with Portland cement was investigated. Acid and base catalysed sols were synthesized. Samples of Ordinary Portland cement pastes were prepared at a predetermined water-to-cement ratio of 0.4. The sols were subsequently added to the pastes and mixed together at varying dosages of 0.5, 1.0, 2.0, 3.0 and 5.0 % by mass of dry cement. A small quantity of each resultant paste was analysed using isothermal calorimetry to follow the kinetics of cement hydration. A control sample was used for comparative evaluation. The remainder of the pastes were placed in sealed polyethylene vials at room temperature for qualitative assessment. Our efforts so far have revealed the base catalysed sol to be favourable in terms of compatibility. The acid catalysed sol on the other hand appeared to impede hydration. Subsequent studies aim to examine the effects on the resultant cement pastes by varying the range of synthesis parameters and compositional make-up of acid and base catalysed sols. Properties including mechanical, chemical and microstructural characteristics will also be investigated.