What is grouting in prestressed concrete pdf

 What is grouting in Civil Engineering?

The purpose of post tensioned tendions in prestressed concrete members is to provide permanant protection to the post tensioned steel and to develop bond between the prestressing steel and the surrounding concrete.

The grout is a mixture of cement water with or without admixtures. The recommended grout mix is 1 bag (50 kg) of portland of cement water 22 kg (5 Gallons) Of water, which works out to a water cement ratio is 0.50. Sand should not be added in grout mix. Research has that confirmed that for basically horizontal tendons in rigid ducts,satisfactory quality of grout may be achieved without any admixture. Admixture should be impart the properties of low water content, good flow ability and minimum bleed. Aluminium powder and proper fineness of quality which is well dispersed can be used to obtain a 5 to 10 percent unstrained expansion of the grout. The essential qualities of a good grout are :

1. It should be sufficiently fluid in the time of pumping.

2. It should be good consistency, without excessive water and it must shrink very little on setting.

3. It should have good mechanical strength necessary for necessary bonding, when it has set and hardened.

4. It should be resistant to frost.

5. It should not contain any ingredient which would corrode the steel.

Good grouting is obtained by pumping under pressure and by properly chossing the composition of the mix considering length of the sheath to be grouted, its profile, its material and the amount of steel within the sheath by adding an expanding agent like aluminium powder and by choosing proper water content ratio.

The grout shall be pumped with a pressure of about 0.4 to 0.8 N/mm2 . The cube strength of the grout mix may be  as high as 30 N/mm2.