01-02-2013, 02:18 PM
ADMIXTURES OF CONCRETE
ADMIXTURES.ppt (Size: 1.68 MB / Downloads: 549)
INTRODUCTION:
Admixtures is defined as a material, other than,
Cement
Water
Aggregate
That is used as an ingredient of concrete and is added to the batch immediately before or during mixing.
Admixtures are used to modify the properties of ordinary concrete so as to make it more suitable for any situation.
HISTORY:
History of admixtures is as old as the history of concrete. It embraces a very vast field, but a few type of admixtures called Water Reducers or High Range Water Reducers, generally referred as plasticizers and superplasticizers, are of recent interest.
Specially developed in Japan & Germany around 1970.
Why Are They Used?
To modify properties of fresh & hardened concrete
To ensure the quality of concrete during mixing, transporting, placing & curing
To overcome certain unexpected emergencies during concrete operations (ie, set retarders)
Why Are They Used?
Increase slump and workability
Retard or accelerate initial setting
Reduce or prevent shrinkage
Modify the rate or capacity for bleeding
Reduce segregation
Retard or reduce heat evolution during early hardening
Increase strength (compressive, tensile, or flexural)