The various factors which affect the performance of concrete admixtures are: 1. Type of super-plasticizer: The admixture will be more effective if molecular weight of the super-plasticizer is high. 2. Dosage: The quantity of admixture should be optimum. Excess of admixture may cause segregation or bleeding. It may also cause excessive retardation. The optimum does(…)
Concrete Admixtures
STANDARD CODES FOR CONCRETE ADMIXTURES
Standard Codes for concrete admixtures: Admixtures used should conform to the following relevant standard codes. In reinforced concrete, the chloride ion of any admixture used should not exceed 2% by weight of the admixture as determined in accordance with IS:6925 and the total chloride ion in all admixtures used in concrete mi shall not exceed(…)
PROPERTIES AND USES OF CONCRETE ADMIXTURES
What are Concrete Admixtures? Ingredients other than cement, water, and aggregates that impart a specific quality to either plastic (fresh) mix or the hardened concrete (ASTM C496) is called concrete admixture. Why use Concrete Admixtures? 1. Reduce cost of concrete construction 2. Achieve specific concrete properties more effectively 3. Ensure quality of concrete during mixing,(…)
FUNCTIONS OF CONCRETE ADMIXTURES
Concrete admixtures are added to change the properties of concrete to make it function as required. Admixtures are used to modify properties of both fresh and hardened concrete as discussed below: Functions of admixtures to modify fresh concrete properties: a) To increase workability without increasing water content or to decrease the water content at the(…)
ACCELERATING WATER-REDUCING CONCRETE ADMIXTURES
Accelerators increase the initial rate of chemical reaction between the cement and the water so that the concrete stiffens, hardens, and develops strength more quickly. They have a negligible effect on consistence, and 28-day strengths are seldom affected. Accelerating admixtures have been used mainly during cold weather when the slowing down of the chemical reacting(…)
RETARDING WATER-REDUCING CONCRETE ADMIXTURE
Retarding water-reducing admixtures are chemicals that slow down the initial reaction between cement and water by reducing the rate of water penetration to the cement and slowing down the growth of the hydration products. The concrete therefore stays workable longer than it would otherwise. The length of time during which a concrete remains workable depends(…)
SHRINKAGE REDUCING CONCRETE ADMIXTURE
Shrinkage-reducing concrete admixture promote expansion of the concrete at about the same volume that normal drying shrinkage is contracting it. The net change in length of the hardened concrete is small enough to prevent shrinkage cracks. The typical materials used for shrinkage compensation in concrete are based on calcium sulfo-aluminate or calcium aluminate and calcium(…)
CORROSION INHIBITING ADMIXTURES
Corrosion-inhibiting admixtures are not currently covered by EN 934 but are effective after the concrete has hardened and give a long-term increase in the passivation state of steel reinforcement and other embedded steel in concrete structures. The three most common generic types of corrosion inhibiting admixture are: Calcium nitrite (normally contains a residual amount of(…)
1 2