All about Maintenance of Concrete Structures
All you need to know about structural maintenance and repair!
Maintenance is preventive. Activities include inspection and works necessary to fulfill the intended function or to sustain the original standard of service. The maintenance of the structure is done to meet the following objective:
- Prevention of damages due to natural agencies and to keep them in good appearance and working condition.
- Repair of the defects occurred in the structure and strengthen them, if necessary
Types of Maintenance
Maintenance work is broadly classified as:
- Preventive Maintenance
a. The maintenance work is done before the defects occurred or damage developed in the structure is called preventive maintenance.
b. It includes a thorough inspection, planning the programs of maintenance and executing the work
c. It depends upon the specifications, condition, and use of structure. - Remedial Maintenance
a. It is the maintenance done after the defects or damage occurs in the structure. It involves the following basic steps:
— Finding the deterioration
— Determining the causes
— Evaluating the strength of the existing structure
— Evaluating the need for the structure
— Selecting and implementing the repair procedure - Routine Maintenance
a. It is the service maintenance attended to the structure periodically.
b. The nature of work done and interval of time at which it is done depends upon specifications and materials of structure, purpose, intensity, and condition of use.
c. It includes whitewashing, parch repair to plaster, replacement of fittings and fixtures, binding of the road surface. - Special Maintenance
a. It is the work done under the special conditions and requires sanction and performed to rectify heavy damage.
b. It may be done for strengthening and updating the structure to meet the new condition of usage or to increase its serviceability.
c. It may include particular or complete renewal occurring at long intervals, such as floors, roofs, etc.
The causes that necessitate the maintenance effects of the service and durability of the structure include Atmospheric agencies such as Rain, etc, Normal wear and tear, and Failure of structure.
Causes of Damage
Rain is an important source of water. Water drastically affects the structure if not handled with appropriate care. It causes both physical and chemical damage.
Physical:
- Dissolving and carrying away minerals as it is a universal solvent.
- Expansion and contraction — The materials are subjected to repetitive expansion and contraction while they become wet and dry and develop stresses.
- Expansion of water — The variation of temperature causes the expansion and contraction of absorbed water and affects the micro-structures of the materials.
- Erosion — Transportation, attrition, and abrasion of the materials is quite an evident effect of the water.
Chemical:
- The water available in nature contains acids and alkaline and other compounds in dissolved form act over the material to give rise, which is known as chemical weathering.
Wind: It is the agent, which transports the abrasive material and assists the physical weathering Its action is aggravated during rains and, When it is moving with high speed, it may contain acidic gases like CO2 fumes which may act over the material and penetrates quite deeply in materials and structure.
Temperature: The seasonal and annual variation of the temperature, the difference in temperature in two parts of the materials and the surface of material causes expansion and contraction, this movement of the material bond and adhesion between them is lost when it is repeated. This responsible for the development of cracks and the rocks may break away into small units. Exploitation or peeling off the shell takes place if the exterior layer is heated externally with respect to internal layers. The temperature variation may also cause a change in the structure and chemical composition of the material.
Repairing Strategy
Repair is the technical aspect of rehabilitation. It refers to the modification of a structure partly or wholly which is damaged in appearance or serviceability
Repair of a concrete structure is carried out in the following stages:
- Removal of damaged concrete:
a. Prior to the execution of any repair, one essential and common requirement is that the deteriorated or damaged concrete should be removed.
b. Removal of defective concrete can be carried out using tools and equipment the types of which depend on the damage.
c. Normally, removal of concrete can be accomplished by hand tools, or when that is impractical because of the extent of repair, it can be done with a light or medium weight air hammer fitted with a spade-shaped bit.
d. Care should be taken not to damage the unaffected concrete portions.
e. For cracks and other narrow defects, a saw-toothed bit will help achieve sharp edges and a suitable undercut. - Pre-treatment of surfaces and reinforcement
a. Complete removal of unsound material.
b. Undercutting along with the formation of smooth edges.
c. Removal of the cracks from the surface.
d. Formation of a well-defined cavity geometry with rounded inside corners.
e. Providing, rough but uniform surface for repair. The cleaning of all loose particles and oil and dirt out of the cavity should be carried out shortly before the repair. This cleaning can be achieved by blowing with compressed air, hosing with water, acid etching, wire brushing, scarifying or a combination. Brooms or brushes will also help to remove loose material. - Application of repair materials
a. After the concrete surface has been prepared, a bonding coat should be applied to the entire cleaned exposed surface.
b. It should be done with minimum delay.
c. The bonding coat may consist of bonding agents such as cement slurry, cement sand mortar, epoxy, epoxy mortar, resin materials, etc.
d. Adequate preparation of surface and good workmanship are the ingredients of efficient and economical repairs. - Repair procedure: The repair of the cracked or damaged structure is discussed under two distinct categories, namely, ordinary or conventional procedures; and special procedures using the latest techniques and newer materials such as polymers, epoxy resins, etc. A repair procedure may be selected to accomplish one or more of the following objectives:
1. To increase strength or restore load-carrying capacity.
2. To restore or increase stiffness.
3. To improve functional performance.
4. To provide water tightness.
5. To improve the appearance of the concrete surfaces.
6. To improve durability.
7. To prevent access of corrosive materials to reinforcement
Reference: CE 2031: Repair and Rehabilitation of Structures. http://fmcet.in/CIVIL/CE2071_uw.pdf
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Reference: CE 2031: Repair and Rehabilitation of Structures. http://fmcet.in/CIVIL/CE2071_uw.pdf
