3. Hardened concrete

3.1 Cement hydration

The various cement constituents react with the mixing water (figure 7 ). Thus, calcium silicates (SiO ₂ .3CaO and SiO ₂ .2CaO) give a hydrated calcium silicate (2SiO ₂ .3CaO.3H ₂ O), known as C-S-H, which is primarily responsible for cement hardening. These reactions are accompanied by the formation of calcium hydroxide [Ca(OH) ₂ ], known as "portlandite", which can react with other constituents, such as tricalcium aluminate (3CaO.Al _2...