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Cement

Cement. Portland Cement Production: Two basic raw ingredients: calcareous material (limestone, chalk, or oyster shells) + argillaceous material (silica and alumina from clay, shale and blast furnace slag). Cement. Chemical composition of Portland Cement:. Cement.

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Cement

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  1. Cement • Portland Cement Production: Two basic raw ingredients: calcareous material (limestone, chalk, or oyster shells) + argillaceous material (silica and alumina from clay, shale and blast furnace slag)

  2. Cement • Chemical composition of Portland Cement:

  3. Cement • Cement Properties and Characteristics • Oxides • Sources • SiO2 (silicon dioxide) - cap rock (Sandstone) • CaO (calcium oxide) - limestone • Oxides used to calculate theoretical cementitious compounds: • Al2O3 (aluminum oxide) - clay • C3S, C2S, C3A and C4AF • Fe2O3 (ferric oxide)

  4. Cement • Compounds • Tricalcium Silicate (C3S) hardens rapidly and is largely responsible for initial set and early strength. • In general, the early strength of portland cement concrete is higher with increased percentages of C3S. • Dicalcium Silicate (C2S) hardens slowly and contributes largely to strength increases at ages beyond 7 days. • Tricalcium Aluminate (C3A) liberates a large amount of heat during the first few days of hardening and, together with C3S • and C2S may somewhat increase the early strength of the hardening cement (this effect being due to the considerable heat of hydration that this compound evolves). It does affect set times.

  5. Cement • Tetracalcium Aluminoferrite (C4AF) contributes very slightly to strength gain. However, acts as a flux during manufacturing. Contributes to the color effects that makes cement grey.

  6. Hydration of cement Hydration of cement • When Portland cement is mixed with water its chemical compound constituents undergo a series of chemical reactions that cause it to harden. This chemical reaction with water is called "hydration". Each one of these reactions occurs at a different time and rate. Together, the results of these reactions determine how Portland cement hardens and gains strength.

  7. Hydration of cement • OPC hydration • Hydration starts as soon as the Hydration starts as soon as the cement and water are mixed. • The rate of hydration and the heat liberated by the reaction of each compound is different. • Each compound produces different products when it hydrates. •

  8. Tricalcium silicate (C3S). Hydrates and hardens rapidly and is largely responsible for initial set and early strength. Portland cements with higher percentages of C3S will exhibit higher early strength. • Tricalcium aluminate (C3A). Hydrates and hardens the quickest. Liberates a large amount of heat almost immediately and contributes somewhat to early strength. Gypsum is added to Portland cement to retard C3A hydration. Without gypsum, C3A hydration would cause Portland cement to set almost immediately after adding water. •

  9. Dicalcium silicate (C2S). Hydrates and hardens slowly and is largely responsible for strength increases beyond one week. • Tetracalciumaluminoferrite (C4AF). Hydrates rapidly but contributes very little to strength. Its use allows lower kiln temperatures in Portland cement manufacturing. Most Portland cement color effects are due to C4AF.

  10. Cement

  11. Cement • Main Types of Portland Cement:

  12. Cement Required chemical composition and fineness for Portland Cement (ASTM C150)

  13. Cement • Types of Portland Cement (cont’d): Air entrainers can be added to type I, II, III cement to get type IA, IIA, IIIA. Other types such as: white Portland cement, masonry cement, expansive cements,…etc Specifications of Standard Properties of Portland Cement (ASTM C150)

  14. Cement • Hydration of Portland Cement (cont’d): Primary Chemical reaction during Cement Hydration

  15. Cement • Fineness of Portland Cement: Fineness is important. Since hydration starts at the surface of cement particles. The larger the surface area the faster the hydration. i.e finer material results in faster strength development. Finesses is related to productivity cost and detrimental to concrete quality. Blaine air permeability Test (ASTM C204) or % passing the 0.045mm sieve (No.325) (ASTM C430) • Hydration of Portland Cement: Hydration is a chemical reaction between cement particles and water. The solidification of the cement paste relates to the time of setting.

  16. Cement • Properties of Hydrated Cement: Quality control issue • Setting: stiffening of the cement paste or change from plastic to solid state. • Setting = Final - Initial setting levels • Vicat Test (ASTM C191) or Gillmore (ASTM C206) • Soundness: ability of cement paste to retain its volume after setting. • Le Châtelier Test • Compressive Strength: measured by preparing 50 mm cubes and subject them to compression (ASTM C109). Minimum values of compressive strength in ASTM C150

  17. Cement • Water-Cement Ratio: (Abrams 1918) w/c affects the concrete quality (strength and other desirable properties). Hydration requires 0.22 – 0.25 kg water per 1 kg cement. Concrete require excess moisture, beyond hydration, for workability. As w/c increases. Concrete porosity and permeability increase, the strength decreases. Low w/c increases the resistance to weathering, provides good bond between concrete layers, and between concrete and steel reinforcement, and limits volume change due to wetting and drying.

  18. Cement MPa ksi MPa 40 40 6 6 28-day 5 5 30 30 28-day 4 4 7-day 20 20 3 3 7-day 3-day 2 2 3-day 10 10 1-day 1 1 1-day Cylinders 15x30 cms Type I, 21oC cured 0 w/c , non-air-entrained concrete w/c , air-entrained concrete 0.4 0.4 0.5 0.6 0.5 0.6 ksi • Water-Cement Ratio (cont’d):

  19. Cement Specifications of Standard Properties of Portland Cement (ASTM C150)- (cont’d)

  20. Cement • Admixtures for Concrete: • Air entrainers • Water reducers • High-range water reducers—Superplasticizers • Retarders • Accelerators • Fine minerals • Specialty admixtures

  21. Cement • Admixtures for Concrete (cont’d): • Air entrainers: produce tiny air bubbles in hardened concrete to provide space for water to expand upon freezing. ( salts of wood, synthetic…) • Water Reducers: minimize the amount of water required for workability. Increase the mobility of cement particles in the plastic mix. (no effect on slump, increase strength, decrease cost using less cement) • Superplasticizers: increase the flow of fresh concrete or reduce the amount of water required. • Retarders: delay the initial set of concrete ( offset the effect of hot weather, allow for long distances placement, provide time for special finishes)

  22. Cement • Admixtures for Concrete (cont’d): • Accelerators: develop early strength of concrete at a faster rate than that developed in normal concrete. The ultimate strength, however, is the same as in normal concrete. (reduce curing time, increase rate of strength, plug leaks under hydraulic pressure efficiently). • Fine minerals: (waste from a production process) improve the characteristics of both plastic and hardened concrete ( cementitious, pozzolanic, …) • Specialty Admixtures: workability agents, corrosion inhibitators, damp proofing agents, permeability reducing agents, pumping aids, bonding agents, coloring agents,…etc.

  23. Cement Tests

  24. Cement Table of Equivalence between different Norms

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