Prepared by madam rafia firdous. She is a lecturer and instructor in subject of Plain and Reinforcement concrete at University of South Asia LAHORE,PAKISTAN.

1. CEMENT HYDRATION
AND ADMIXTURES
Engr. RAFIA FIRDOUS
PRC-I

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4. HYDRATION
 Series of irreversible exothermic chemical reactions
between cement and water
 Cement-water paste sets and hardens, “gluing” the
aggregate together in a solid mass
Formation of hydration products over time leads to:
 Stiffening (loss of workability)
 Setting (Solidification)
 Hardening (Strength gain)
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5. WHY IS IT IMPORTANT?
Understanding the basics of hydration is
important to
• Ensure the strength and durability of concrete
• Recognize and mitigate the thermal stresses
to prevent cracking
• Appreciate the importance of good curing
and construction practices
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CEMENT-Hydration

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CEMENT-Hydration

8. COMPOSITION OF CEMENT CLINKER
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CEMENT-Hydration

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CEMENT-Hydration

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CEMENT-Hydration

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CEMENT-Hydration

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CEMENT-Hydration

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Pozzolanic Materials
 Pozzolanic cements are those cements in which we add artificially some
pozzolans (ASTM C-618)
 Pozzolans are natural or artificial material containing silica in a reactive
form.
 Pozzolans are usually added to improve certain characteristics of concrete
resulting in improved durability.
 Commonly used pozzolan in the world are:
 Fly Ash
 Metakaoalin
 Silica Fume
 Rice husk Ash
 Blast furnace slag etc

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ADMIXTURES
 Admixtures are chemicals added to concrete, mortar or grout at he time of
mixing to modify the properties either in the wet state immediately after
mixing or after the mix has hardened.
 The dosage may be expressed as liters or “kg” per 100 kg of cement
 Important types of Admixtures are:
 Normal Plasticizing/ water reducing (WRA)
 Super plasticizing/ high range water reducing (HRWRA)
 Retarders
 Accelerators
 Air entraining
 Water retaining
 etc

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ADMIXTURES
 Admixtures act in the following ways
 Chemical interaction with the cement hydration process
 Adsorption onto cement surfaces, typically causing better particle
dispersion
 Affecting the surface tension of the water, typically resulting in
increased air entrainment.
 Affecting the rheology of the water usually resulting in an increased
plastic viscosity or mix cohesion.
 The benefits obtained from the using the admixture are often in the
hardened properties. The properties affected by affecting the following:
 Affect water demand
 Change the stiffening rate
 Change the air content and plastic viscosity.