Hydration Of Cement...PRC-I
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The document discusses cement hydration as a series of chemical reactions between cement and water, which leads to the hardening and strength development of concrete. It highlights the importance of understanding hydration for ensuring concrete's strength, durability, and minimizing thermal stresses. Additionally, the document covers the role of pozzolanic materials and admixtures in enhancing concrete properties.
Hydration Of Cement...PRC-I
- 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) 4
- 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 5
- 8. COMPOSITION OF CEMENT CLINKER 8
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- 15. 15 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
- 16. 16 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
- 17. 17 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.