The need to produce sustainable cements has driven research towards nanotechnology. The main cement hydration product, calcium silicate hydrate, is nanosized; hence, the addition of nanoparticles to blended Portland cement formulations can remarkably modify mechanical strength, porosity and durability. The present paper discusses the material aspects of two different nanoparticles, nanosilica and montmorillonite nanoclay, the complications that arise from their addition to cement pastes and ways to mitigate these limitations. It is deduced that nanosilica solids in blended cement pastes should be limited to 0.5, whereas nanoclay solids to almost 1 mass- binder. Competitive reactivity of nanoparticles with other constituents is expected, and the possible pozzolanic activity is critically addressed. Notwithstanding progress made, there are significant potentials related to inorganic nanoclays.

The compatibility of three nano-montmorillonite (NMt) dispersions in hydrating cement binders was investigated and a new theory linking the nanostructure of nanoclay dispersions to their effect on the macroscale performance of cement pastes is presented. Two aqueous organomodified NMt dispersions (one dispersed with non-ionic fatty alcohol and the other with anionic alkyl aryl sulfonate) and one aqueous inorganic NMt dispersion (dispersed with sodium tripolyphosphate) were characterized via transmission electron microscopy imaging and crystallography, X-ray diffraction, Scanning electron microscopy/X-ray energy dispersive spectroscopy, and thermogravimetric analysis/differential thermogravimetry. With this characterization protocol, the way carbon loading and surfactants interact with the nanostructure of the nanoclay dispersions in light of their addition in composite cements was clarified. The suggested methodology is suited for the characterization of nanoclay dispersions and the new theory developed will open up a new horizon for the understanding and exploitation of nano-montmorillonite as a supplementary cementitious material.

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