Procedure for Concrete Repair-CIVIL

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Procedure for Concrete Repair

This Procedure describes the step by step procedure for all affected concrete structures noticed (after the removal of form works).

General Procedure for Concrete Repair

1) Defects on structural concrete can be due to the use of excessive water, poor cement, poor construction practices, improper mixture proportioning, dirty or low quality aggregate and inadequate curing.
2) A deficiency must be differentiated from the actual cause and it is imperative that causes and not symptoms are dealt with wherever possible or practical. For example, cracking is a symptom of distress that may have a variety of causes.
3) Hollow spaces and cavities left in concrete mass on surface or inside the concrete mass where concrete could not reach. These look like honey bees nest, honeycombs which are on sides are visible to naked eyes and can be detected easily as soon shuttering is removed.

4) Due to non-reaching of concrete to all places in which cavities and hallow to hallow pockets are created. Main reasons are improper vibration during concrete, less cover to reinforcement bars and use of very stiff concrete (this can be avoided by controlling water as per slump test).
5) Selection of the correct repair technique for cracking depends on knowing whether the cracking is due to repeated thermal cycling, accidental overloading, drying shrinkage, inadequate design or construction, or some other cause. Only after the cause or causes are known can rational decisions be made concerning the selection of a proper repair system.

Work Procedure

1) Preparation & Repair Methods

a. As per manufactures recommendation approved repair materials shall be applied by skilled mason assuring that this material pushed to fill all surface voids.
b. All identified surfaces to be repaired shall be chipped out carefully and clean the surface surroundings to expose dense and sound concrete and ensure no feathered edges at the area perimeter of the chipped surface any exposed steel reinforcement shall be thoroughly cleaned and treated as required according to the manufacturer recommendations as per the selected material to be used for the repair.
c. Chipping along the cracks to enlarge and clean the enlarged cracks blowing out by oil free compressed air washes the chipped and allows drying.
d. Brushes apply of suitable repair material on the exposed steel reinforcement
rods and chipped surface. Mix components of the approved repair materials shall be applied according to the manufacturers’ instructions.

2) Concrete Defects

a. Shrinkage Cracks – Repair of concrete after the plastic shrinkage cracks have formed usually consists of sealing them against ingress of water by brushing in cement or low viscosity polymers.
b. Settlement Crack – Remedial measures after the concrete has hardened consist of sealing the cracks in order to protect the reinforcement. However, consolidation of concrete immediately after the cracks start to form is by far the best course of action.
c. Dormant or Dead Cracks – Cracks wider than about 1.0 mm on the horizontal surfaces can usually be sealed by filling them with cement grout. This is commonly done by brushing in dry cement followed, if necessary, by light spraying with water.
d. Live Cracks – The sealant must then be adhered to the sides of the chase but debonded from the bottom so that the movement is spread over the full width of the chase.

e. Thermal Crack – These types of cracks should be sealed to protect the reinforcement by brushing in cement or low viscosity polymers.
f. The mortar should be applied over the whole area of the concrete with a rubber faced float, and finally it can be rubbed down with a smooth stone or mortar block for a smooth finish.
i. Repair Inadequate Cover
• If the face of the concrete is weak, it should be scabbed or grit-blasted to provide a sound, roughened surface. If it is sound but smooth, it will usually be cheaper to apply a coat of polymer-modified cement and sand, in proportions of about one part of cement to two parts of sand, before applying the first coat of rendering.
• If it is not possible to increase the dimensions of the structure, a surface coating can be applied. Such a coating should be of a type having low permeability to carbon dioxide and moisture, but it should preferably allow water vapor to escape from within the concrete.

3) Identification and Evaluation Concrete Defect

a. The QC inspector & Client Representative upon finding any defects in the cast concrete structure (precasted) shall issue a Report.
b. According to the type of defect identified shall be reviewed to determine the most suitable method of repairs to be applied. The full information, identification of the defects and the recommended methods or repair shall be issued to Client Representative to carry out inspection of Contractor before proceeding on the repair works.
c. Inspection and Evaluation of the deteriorated concrete structures is conducted to identity the nature & Extent of the existing problem and its cause to enable effective & long lasting repair/remedial work to Avoid recurrence of surface defects on concrete.

4) Removal of Unsound Concrete

a. All unsound or loose concrete shall be removed by lightweight chipping hammer.
b. The boundaries of all unsound concrete to be removed shall be delineated with saw cuts to provide a neat edge and the remainder of the cut out may be done with appropriate tools.
c. All concrete shall be removed around the corroded re-bar to a minimum depth behind it.

5) Submittal

a. Repair material to be used shall comply with ARAMCO Specification.
6) Material Handling and Storage Protection
a. All repair material shall be delivered to the jobsite in original containers and packaging bearing the manufacturer’s tags and labels.
b. Tags and labels shall indicate the type, brand, content by volume, color and other important related information.
c. Material shall not be removed from the storage until immediately prior to mixing or use.
Please read also:  Procedure for REINFORCED MASS CONCRETE -CIVIL

Tools & Equipment

1) All tools and equipment shall be inspected by  HSE dept. in accordance with  Specification and Requirements.
2) All of tools and equipment e.g. hand and power tools etc. require special attention and protection for their use and guidelines.
3) All damaged, unsafe or defective tools will be marked, tagged as Unsafe or with a Red Paint and taken away from operation to assure that no one will use such tools on the job.
4) Electrical tool and equipment shall be used in accordance with GFCI requirement.
a. Wire brush
b. Hammer & Chisel
c. Application Trowels
d. Smoothing Floats
f. Mixing Container
g. Drill and Mixing Paddle Small Quantities
h. Double Mixing Paddle Medium Quantities
i. Forced Action Pan Mixer Large Quantities

References

1. Project Specification
2. Project IFC Drawings
3. Saudi ARAMCO Standard
a) SAES – Q – 001- Criteria for design and construction of concrete structures
b) SAER – 5803 – Concrete Repair manual chapter 4
c) SAER – 5803 – Concrete Repair manual chapter 5
4. Manufactures Technical Data Sheet

4. Approved Project Safety Plan

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