Explanation:

The setting and hardening of cement after the addition of water is due to the process of hydration of some of the constituent compounds of cement. Cement is composed of four main compounds: tricalcium silicate (C3S), dicalcium silicate (C2S), tricalcium aluminate (C3A), and tetracalcium aluminoferrite (C4AF). When water is added to cement, a chemical reaction called hydration takes place. During hydration, the compounds in cement react with water molecules and form new compounds, which bind the aggregates together and give the cement its strength.

The process of hydration can be divided into two stages: the initial setting and the final hardening. During the initial setting stage, the cement paste starts to stiffen and harden. This is caused by the formation of calcium silicate hydrate (C-S-H) and calcium hydroxide (Ca(OH)2) from the reaction of C3S and C2S with water. The setting time of cement is influenced by the composition of the cement, the fineness of the cement particles, and the temperature and humidity of the surrounding environment.

During the final hardening stage, the cement paste becomes even stronger as more C-S-H and Ca(OH)2 are formed. This process can continue for several years, and the strength of the cement can increase over time. The strength of cement is also influenced by several factors, including the water-cement ratio, the curing conditions, and the use of additives such as pozzolans and superplasticizers.

In conclusion, the setting and hardening of cement after the addition of water is due to the process of hydration of some of the constituent compounds of cement, primarily C3S and C2S. This process results in the formation of new compounds, which bind the aggregates together and give the cement its strength.

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