1. Initial Mixing:
* When water is added to cement powder, a paste forms. This paste contains various cement compounds, primarily:
* Tricalcium silicate (C3S): The main component, responsible for the early strength development.
* Dicalcium silicate (C2S): Contributes to later strength development.
* Tricalcium aluminate (C3A): Reacts rapidly with water and contributes to initial setting.
* Tetracalcium aluminoferrite (C4AF): Reacts slower than C3A and contributes to strength development.
2. Hydration Reactions:
* Hydration of C3S and C2S: These compounds react with water to form calcium silicate hydrate (C-S-H) gel, which is the main constituent of hardened cement paste. The reaction is exothermic and releases heat.
* C3S + H2O → C-S-H + CH (calcium hydroxide)
* C2S + H2O → C-S-H + CH
* Hydration of C3A: C3A reacts rapidly with water to form calcium aluminate hydrates (C-A-H). This reaction is highly exothermic and can cause rapid setting if not controlled.
* C3A + H2O → C-A-H
* Hydration of C4AF: C4AF reacts with water to form calcium aluminoferrite hydrates (C-A-F-H), which contribute to strength development.
* C4AF + H2O → C-A-F-H
3. Setting and Hardening:
* Setting: As hydration progresses, the cement paste starts to solidify, forming a rigid structure. The initial setting is due to the rapid reaction of C3A.
* Hardening: Continued hydration leads to the formation of more C-S-H gel, which binds the particles together, resulting in increasing strength.
4. Strength Development:
* The strength of cement concrete increases over time as hydration continues. This is primarily due to the formation of C-S-H gel and the filling of pores within the paste.
Factors Affecting Reactions:
* Water-cement ratio: The amount of water used affects the rate of hydration and the strength of the concrete.
* Temperature: Higher temperatures accelerate hydration, while lower temperatures slow it down.
* Admixtures: Chemical additives can modify the hydration process, affecting setting time, strength, and other properties.
Note: This is a simplified explanation. The actual chemical reactions are much more complex and involve numerous phases and intermediate products.
If you're looking for more detailed information, you can refer to specialized textbooks on cement chemistry and concrete technology.
