👉THE CHEMISTRY OF A CONCRETE MIX

💫When you combine Cement + Water + Aggregates + (Admixtures) a set of chemical reactions begin automatically.

🚧The most important chemical process is hydration — the reaction between cement and water.

🏷1. Chemistry of Cement

Cement is mainly made of four compounds:

*Tricalcium Silicate , C₃S for Early strength + heat
*Dicalcium Silicate, C₂S for Later strength
*Tricalcium Aluminate, C₃A to Controls setting (fast reaction)
*Tetracalcium Aluminoferrite,  C₄AF for Minor strength

Gypsum (CaSO₄·2H₂O) is added to control setting time.

🏷2. When water is added → Hydration begins

Water reacts with cement compounds to form new materials that make the concrete hard and strong.

🧬 A. Main Reaction: Formation of C–S–H Gel

C₃S + Water → C–S–H (Calcium Silicate Hydrate) + Ca(OH)₂

C–S–H gel is the glue that binds everything

Gives strength + durability

Forms 50–60% of the final hardened concrete

C₂S reacts slower:

C₂S + Water → C–S–H + Less Ca(OH)₂

This provides long-term strength.

🧬 B. Formation of Ettringite (Setting Control)

C₃A reacts extremely fast, so gypsum controls the reaction:

C₃A + Gypsum + Water → Ettringite

Ettringite crystals cause initial setting (stiffening).

If gypsum is finished, ettringite converts to monosulfate:

Ettringite → Monosulfate

🧬 C. Reaction of C₄AF

Produces ferrite hydrates that help setting but add little strength.

🏷3. Chemistry of Aggregates

Aggregates do not react much chemically.
Their main role is:

*Fill space
*Provide bulk
*Reduce cement content
*Improve strength by interlocking

But their surface bonds chemically with the C–S–H gel.

🏷4. Water–Cement Ratio (w/c) Chemistry

Lower water = denser hydration products.

Low w/c → more C–S–H, higher strength

High w/c → more pores, weaker concrete


🏷5. Chemistry of Admixtures
Admixtures modify hydration:

*Plasticizers / Superplasticizers

Disperse cement particles

Reduce water demand

Delay or accelerate hydration based on type

*Retarders
Slow down C₃A + C₃S reaction

*Accelerators
Speed up early hydration

🏷6. Chemistry Timeline of Concrete Hydration

*0–2 Hours: Initial setting

-C₃A + Gypsum → Ettringite
-Early C₃S reaction begins

*2–10 Hours: Final setting

-Needle-like crystals lock particles
-Concrete becomes solid

*1–7 Days: Early Strength

-Rapid C–S–H growth from C₃S

*7–28 Days: Major Strength Gain

-Slow hydration of C₂S
-Pore structure becomes tighter

*Months–Years: Long-term Hydration

-Continuous formation of C–S–H gel
-Increase in durability

📌 In simple words:

⏺Concrete gets hard because cement reacts with water and forms glue (C–S–H gel) and crystals that bind sand and stone together.

@etconp