Coating is the process by which a section of an existing structural member is restored to the original dimensions or enlarged by casing using suitable materials. A steel reinforcement cage or a composite sheath may be constructed around the damaged section on which the cast concrete or cast concrete is placed.
Necklaces are jackets that surround only for a part of a column or dock. These are generally used to provide greater support to the slab or beam at the top of the column. The shape of the jacket consists of wood, corrugated metal, prefabricated concrete, rubber, fiberglass, or special fabric; and may be permanent in some cases. The form must be provided with spacers to ensure an equal play between the form and the existing member. Materials such as conventional cement and mortar, epoxy mortar, grout and mortar modified with latex and concrete, are used as encasado materials. For the liner, the gap between the shape and the existing member is filled using pre-set pumping, tremie or aggregate concrete.
The coating is especially used for the repair of damaged columns, springs and piles and can be easily used in underwater applications. The method is applicable to protect concrete, steel and wood sections against further deterioration and for strengthening. Permanent forms are preferred when protection against weathering, abrasion and chemical contamination is desired. The collar provides greater cutting capacity for the slab, and decreases the effective length of the column. The necklaces are considered architecturally better than the coating but they perform the same structural function.
Before applying jackets or collars, remove all deteriorated concrete, repair cracks, clean existing reinforcement, and prepare surfaces. Surface preparation improves the bonding of the newly placed materials with the existing structure, which is difficult for underwater repairs. For underwater conditions, a plastic cover may be applied to the splash area to help minimize abrasion. One drawback of jackets and necklaces is that they take up space that was previously available for other uses.
The shapes of wood, cardboard and corrugated steel can be used as temporary or permanent forms. Permanent forms of fiberglass, rubber and cloth have gained considerable popularity because they provide resistance to chemical attack after the repair is completed.
Coatings used for purposes other than deteriorated concrete coating and lateral confinement, for example to support longitudinal loads, require special considerations. The existing column may have undergone a total shrinkage and most of the creep and also has elastic deformations due to supported loads, whereas the shrinkage and creep of the new material must occur. The transfer of charge to the coating is also a big problem. It is better to use the lift to release the load on the member prior to coating, to use non-shrinkable materials for the coating and to hammer steel wedges at the transfer points of the coating after curing.
If the material used for the coating is cement mortar or concrete, the cement content should be exactly in accordance with the requirements; both excessive contents and less than cement can be dangerous. Use clean, stable, and larger aggregates. In order to reduce shrinkage, check the temperature of the materials and the immediate environment during placement and curing. The use of additives such as plasticizers, air entraining agents, retarders, accelerators and impermeable additives is more beneficial in repair than even ordinary construction. Expansive mortars / concretes can be made by adding aluminum powder to the matrix to overcome the shrinkage contraction and part of the shrinkage by drying. The use of iron or powder fillings can also perform this function if moisture and air are available.
If grout is used to fill the forms, leave it to stand for about 20 minutes after full filling and then refill to the overflow state. The top of the jacket must be finished with pneumatically designed or hand-laid concrete.