Nanotechnologically modified cements

: Effects on hydration, microstructure and physical properties

Abstract

Cement science and industry aim at the design of cement formulations with minimum Portland cement content. At the same time, nanotechnology is offering a combination of solutions towards stronger, less permeable and more durable cement.In this research two different types of nanoparticles; nanosilica, nS, (aqueous and carboxylic nanosilica suspension) or nanoclay, nC, (inorganic and organomodified nanoclay dispersions and undispersed nanoclay powder) were implemented. Both, nS and nC were characterised with different techniques. Particularly the nC particles, were developed exclusively for the FIBCEM project and, as an effect, their properties were investigated with XRD, TEM crystallography, TGA and SEM/EDX. The differences between the three fundamentally dissimilar types were identified and discussed. Furthermore, their nanostructure and characteristics were associated with expected performance in terms of mechanical strength and pozzolanic activity in cement pastes. Three different formulations constituted the reference pastes [containing Portland cement (PC), limestone (LS), fly ash (FA) (and microsilica only in combination with nS)]; (i) 60%PC/40%LS, (ii) 60%PC/20%LS/20%FA and (iii) 43%PC/20%LS/37%FA by mass of binder. The w/b ratio was generally kept constant at 0.3. The nS and nC particles were added to the reference pastes, creating ternary, quaternary or quinary (i) cement pastes, (ii) fibre cement pastes and (iii) mortar formulations.The combined effect that the addition of the nanoparticles had on the strength was studied with a series of compressive or flexural strength tests at different ages. The effect that nS or nC had on the hydration products and microstructure of the nanomodified pastes was investigated with the help of XRD, TGA, SEM or FESEM, MIP, relative density measurements and impermeability tests at various ages.The limits to the usage of the nanoparticles were drawn and the most advantageous combinations were discussed. In specific, it was found that the nS addition to blended or composite cement pastes should not exceed 0.5% of solids by mass of binder, especially in the presence of high quantities of FA. With the addition of up to 0.5% nS, both strength gain and microstructure of pastes can be enhanced. The nC particles showed significant diversity amongst them due to their high structural and chemical complexity. In most pastes, 1% nC solids by mass of binder addition was identified as the upper limit. The nCs were found to be partially pozzolanic, consuming Ca(OH)2 to produce additional C–S–H. The OMMTs contained an excess of organomodifier, weakening their beneficial effects in Portland cement formulations. However, inorganic nC dispersions, although neglected for long, could offer new possibilities to cement science. In fact, the shape of the nC particles can even alter traditional characteristics of cement, by providing ductility to the pastes and can offer significant enhancements particularly in flexural strength. With the advancement of nanostructural investigation techniques, more conclusive and innovative results are to be expected by the nanomodification of Portland cement blends.

Date of Award	7 Apr 2015
Original language	English
Awarding Institution	University of Bath
Supervisor	Kevin Paine (Supervisor) & Pete Walker (Supervisor)