01-02-2013, 02:18 PM
CHEMICAL CONCRETE
CHEMICAL CONCRETE.ppt (Size: 818 KB / Downloads: 146)
ADMIXTURES - 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.
WHY ARE THEY USED?
To modify properties of fresh & hardened concrete
To ensure the quality of concrete during mixing, transporting, placing & curing
To 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
MINERAL ADMIXTURES:
Cementitious
Pozzolanic
Ground Granulated Blast Furnace Slag (GGBS)
Fly ash
Silica Fume
Rice Husk
TYPES OF CHEMICAL ADMIXTURES:
According to characteristics effects produced by them chemical admixtures used are as follows.
Plasticizers
Super Plasticizers
Retarders
Accelerators and Accelerating Plasticizers
Air-entraining admixtures
PLASTICIZERS (WATER REDUCING):
These admixtures are used for following purposes:
To achieve a higher strength by decreasing the water cement ratio at the same workability as an admixture free mix.
To achieve the same workability by decreasing the cement content so as to reduce the heat of hydration in mass concrete.
ACCELERATING PLASTICIZERS:
Certain Ingredients are added to accelerate the strength development of concrete called plasticizers or super plasticizers. Such accelerating super plasticizers, when added to concrete result in faster development of strength
The accelerating materials added to plasticizer or superplasticizers are triethenolamine chlorides, calcium nutrite, nitrates and flousillcates etc.,
The accelerating plasticizers or accelerating super plasticizers manufactured by well known companies are chloride free