CONCRETE CHEMICALS & APPLICATIONS Admixtures & construction chemicals are the chemicals added along with the ingredients of concrete or afterwards to get the required mix or strength & durability.

CONCRETE CHEMICALS & APPLICATIONS Added along with the ingredients of concrete. Added at the time of grinding cement in the cement factories.

CONCRETE CHEMICALS & APPLICATIONS The effect of admixture depends on the  Brand of cement.  Grading of aggregates.  Mix proportion. Some important admixtures are discussed below:

PLASTICIZERS& SUPER PLASTICIZERS :  In order to attain the high degree of workability these admixtures are used.  Super plasticizers permit the water reduction up to 30% without reduction in workability.  Used for production of flowing, self leveling , self compacting & production of high strength & high performance concrete.  The quantity used are 0.1 to 0.4 % percentage weight of cement.  The most common used plasticizers are calcium, Sodium & Ammonium lingnosulphates.

COMMONLY USED PLASTICIZERS

RETARDERS:  Slows the process of hydration because of the concrete remains Plastic & Workable.  If the concreting is done in hot weather, these retarders overcome the effect of high temperatures.  Calcium sulphates, lignosulphonic acids & their salts.hydroxylates & their salts are most common retarders. These admixtures which increase the compressive strength by 10 to 20 %

COMMONLY USED RETARDERS

ACCELERATORS:  Added to gain the earlier strength.  Such situation may occur when º Early removal of farm work is needed. º Reduction in the period of curing time. º Put the structure early to use. º Accelerating setting time in cold weather.  Calcium chlorides, Soluble carbonates, Silicates& some organic compounds are used as accelerators. Very much used in underwater concreting.

COMMONLY USED ACCELERATORS

AIR-ENTRAINING ADMIXTURES:  Concrete is made by using air entrained cement or addition of air-entraining agent.  Produce large quantity of air bubbles and modify the concrete properties regarding workability, segregation, bleeding & finishing quality of concrete.  Gains Resistance to frost action & permeability Natural Wood resins, animal and vegetable fats, Water soluble soaps of resin acids etc.,

Commonly used air entraining admixtures

POZZOLANIC ADMIXTURES:  Application of pozzolanic admixtures to the cement improves the quality of concrete such as Lower the heat of hydration . Increase the water tightness. Reduce the alkali-aggregate reaction. Resist the sulphate attack & improve the workability.  Naturally available pozzolanic materials are clay, volcanic tuffs.  Artificial pozzolanic materials are fly ash, steel slag, rice husk ash, marble powder, quartz & granite powder.

Commonly used air entraining admixtures

DAMP-PROOFING ADMIXTURES: Advantages in reducing the permeability.  These admixtures are available in powder or liquid form.  It has the property of pore filling inside the concrete  Silicates of soda,Aluminium & zinc sulphates, Aluminum & calcium chlorides are most common damp-proofing admixtures.

Commonly used air entraining damp-proof admixtures

CONSTRUCTION CHEMICALS Chemicals which are used to enhance the performance. Some common construction chemicals are, Concrete curing compounds. Polymer bonding agents. Water proofing chemicals.

CONCRETE CURING COMPOUNDS: In order to prevent the loss of water from the surface these curing compounds are used. Synthetic resin,wax,chlorinated rubber are used as curing compounds Resin and wax based compounds effectively seal the concrete from the surface evaporation. Chlorinated rubber curing compounds forms a thin film on the surface of the concrete which protects drying and at the same time they fill the pores on the surface of the concrete.

POLYMER BONDING AGENTS: By providing a bond coat between old concrete and new concrete. Mixing of bonding agents with new concrete helps to provide a better bond. Also increase the workability and reduce the shrinkage. Roof bond ERB , Nit bond PVA are most common type of bonding agents used for Concrete repair work such as ceiling of concrete roof, hydraulic structures, prefabricated members, pipes etc.,