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Unformatted text preview: Chemical Admixtures Types Air entrainment agents (AEA): ASTM C250 Water reducers (WR) High range water reducers (HRWR) ASTM C494 Accelerators (Acc) Retarders (Ret) Air Entrainment Agents Surface active agents Prime function: provide freezing and thawing protection for the cement paste (cement, water, mineral admixtures) Secondary function: improves workability, especially for low cement content mixtures (less than 500 lbs/cy of cementing materials) Factors affecting efficiency: temperature, reduced at higher temperatures Chemical Admixtures Water Reducers (WR) and High Range Water Reducers (HRWR) ASTM C494: WR: reduces the quantity of mixing water HRWR: for the same consistency, reduces the water by 12% or greater Surface active agents: reduce the surface tension of water produces a dispersed cement structure Without With flocculated dispersed Typical water reduction At given cement and air content WR: 5 to 10% Increases consistency HRWR: 15 to 30% Increases strength Chemical Admixtures...
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This note was uploaded on 04/01/2008 for the course CEE 3684 taught by Professor Wang during the Fall '08 term at Virginia Tech.
- Fall '08