Ettringite morphology

Fig. 7a-c show images of the products of hydration in the cement paste. Ettringite, hydrated calcium silicates and Ca(OH)2 were detected due to their typical morphologies. 

The morphology of cement hydration products is very little affected by plasticizers [349]. In some works the reduction of ettringite crystal size [367] and of calcium hydroxide [368] in the presence of lignosulphonates is reported. This effect can be attributed to frequently long lasting adsorption of plasticizer particles on the sirrface of crystals [367]. 

In concrete mixes the microstracture of the interfacial zone differs markedly from that of the plain bulk paste (Lu et al., 19%). Here, ettringite is the main hydrate present, but its morphology varies, depending on the amormt of gypsum in the original cement and the conditions of hydration. Three-dimensional restraint of the hydrating mix may improve the interfacial microstracture the thickness of the interfacial zone decreases and the size of the formed crystalline hydration prodncts becomes smaller. 

In the presence of limestone, the needles have a fibrillar morphology, but they are thinner and are straight, perpendicular to the surface of the grains. The alite paste is similar to the C3S paste. In clinker samples, especially on STEM cross sections, it is more difficult to distinguish between C-S-H needles and ettringite needles. 

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