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Techniques for Rehabilitation & Repair Of Structures

Introduction

The success of repair activity depends on the identification of the root cause of the deterioration of the concrete structures. If this cause is properly identified, satisfactory repairs can be done for the improvement of strength and durability, thus extending the life of the structure, is not difficult to achieve. General procedure in the repair of distressed concrete structure:

Support the structural members properly as required.
Remove all cracked, spalled and loose concrete.
Clean the exposed concrete surfaces and steel reinforcement.
Provide additional reinforcing bars, if the loss in reinforcement is more than 10%
Apply shortcreting/polymer concrete for patch repair work and grouting for porous/honeycombed concrete.
Apply protective coatings over the exposed/repaired surface.
Gunite & Shortcrete
Guniting is mechanically applied material consisting of cement, aggregates and water. The cement and sand are batched and mixed in the usual way and conveyed through a hose pipe with the help of compressed air. A separate pipe line brings water under pressure and the water and cement aggregate mix are passed through and intimately mixed in a special manifold and then projected at high velocity to the surface being repaired.

In good quality work, a density around 2100kg/m3 is achieved. For effective guniting, the nozzle should be kept at 60cm to 150cm from the work normal to the surface. Before guniting is applied, the old concrete surface is prepared properly, all the cracks treated and the new reinforcement fixed in position. Cracks wider than about 0.5 mm should be cut out and filled with hand-applied mortar or with gunite.

Shortcreting

Shortcrete is defined as “ mortar or concrete pneumatically projected at high speed onto a surface”.Types of shorcrete:

Dry mix: Dry cement, sand and coarse aggregate are premixed with only sufficient water to reduce dusting.
Wet mix: The cement, sand and coarse aggregate are mixed with water and the resulting concrete is then pumped to the nozzle where compressed air propels the wet mixture onto the surface.
Applications :
Shortcrete has been used to repair :

canal and spillway linings and walls Shotcreting in progress


the faces of dams, tunnel linings
highway bridges and tunnels
deteriorating natural rock walls and
earthen slopes
to thicken and strengthen existing concrete surfaces