There are certain steps that need to be considered in order to decide whether defected concrete needs repair or not, and specify proper repair technique and material if repairing is needed.

These repair steps would ensure successful repairing process that is carried out efficiently and effectively without waste of time and money. Repair of concrete is needed from time to time as the structure gets old due to several reasons.

The steps of concrete repair include- investigating the cause behind the defect in concrete, assessing the extent and severity of the damage, evaluating the need for repair work, selecting suitable repair technique and materials, reparation process preparation, application of the repair technique, and, finally, curing the repaired area.

Steps for Concrete Damage Repair in Reinforced Concrete Structures

1. Determine Causes of Concrete Defects

The determination of causes that led to the defect should be done properly in order to tackle the problem. If the cause of damage is eliminated or declined to a great extent, the repaired structural member would be more durable and have a longer service life without the need for maintenance.

However, if the responsible factor of concrete damage is not tackled, then the same concrete defect can repeat itself in the future and may result in the waste of money and efforts.

It should be known that more than one or several factors may contribute to the concrete defect under consideration. In this case, all the factors need to be dealt with otherwise the repair work would not meet its goals.

Factors that may have an adverse effect on the durability and integrity of the concrete structures are bad weather, cavitation, abrasion, reinforcement corrosion, chemicals attacks, carbonation, cracks, design and construction defects, and aging of the structure.

If the cause of damage is repetitive in nature then the structural repair would have to consider the effect of the cause, but if the cause is a one-time event, then that can be neglected.

For more details about causes of defects in concrete structures, click here, please.

Some Common Causes of Defects in Concrete Structure
Fig. 1: Some Common Causes of Defects in Concrete Structure

2. Assess the Extent of Concrete Damage

Evaluation of the extent of damage to concrete helps to understand the severity of damage and its effect on the life and serviceability of the structure. If the degree of concrete damage is known, a proper decision can be made on whether the structural element needs replacement or repairing. It also helps to take precautionary measures to stop the damage in future for the known cause of the damage.

Extent of concrete damage assessment involves the determination of how much concrete has been deteriorated and how this deterioration affects the service life of the structure i.e. how much concrete has lost its strength or load-carrying capacity.

Deteriorated Reinforced Concrete Beam
Fig. 2: Deteriorated Reinforced Concrete Beam

2.1 Concrete soundness test

It is a usual method used to determine the extent of damage in concrete. If this method is combined with visual inspection and carried out by an experienced engineer, it would provide, in many circumstances, proper assessment of the damage.  

In this test, concrete surface is hit with a hammer; distinct ringing sound means concrete is sound whereas drummy, hollow, or dull sound is the sign of delaminated or disbonded concrete.

It should be remembered that deep delaminations or delaminations that contain only minute separation may not always sound drummy or hollow. The presence of such delaminations can be detected by placing a hand close to the location of hammer blows or by closely observing sand particles on the surface close to the hammer blows.

If the hand feels vibration in the concrete, or if the sand particles are seen to bounce however slightly due to the hammer blows, the concrete is delaminated.

Strength of concrete can also be determined while evaluation of the extent of damage by hammer blows. High strength of concrete gives a distinct ring from a hammer blow and hammer rebounds smartly. Low strength of concrete rebounds with a dull thud and little rebound of the hammer.

Assessment of the extent of damage of concrete may also be done with other Non-Destructive Testing of concrete. More details about NDT tests on concrete.

Concrete Sound Test
Fig. 3: Concrete Sound Test

3. Evaluate the Need for Concrete Repair

Repair of concrete structural members required cost and time that is the damage need to be evaluated to determine whether the structure needs the repair or not.

In case the damaged concrete effect the safety and serviceability of the structure, or the damage progress at a quick rate, then the repair process should start at once.

However, if concrete damage progresses at a slow rate and not severe (detected at early stages), then many alternatives can be used to slow damage progression.

Even if repair is required, early detection of damage would allow orderly budgeting of funds to pay the costs of repair.

4. Select Concrete Repair Method

After adequate information about the damaged area; size; and its severity, and repair construction time period is achieved, then proper economical and successful selections regarding repair materials and method of repairing can be selected.

This information would also determine when the standard repair materials cannot be expected to perform well and when nonstandard materials should be considered.

Repair materials and method of repair should be preferred in such a way that it would not accelerate the damage of existing concrete or reinforcement steel.

5. Prepare Damaged Concrete for Repair

Preparation of the old concrete for application of the repair material is of primary importance in the accomplishment of durable repairs. The very best of repair materials would give unsatisfactory performance if applied to weakened or deteriorated old concrete.

The repair material must be able to bond with sound concrete. It is essential that all of the unsound or deteriorated concrete be removed before new repair materials are applied.

Saw cutting of concrete perimeter in suitable shape, removal of loose concrete, steel cleaning and the coating of bonding agent on reinforcement steel, cleaning of the repair area, application of the bonding agent on the concrete surface (to make a proper bond between existing and new concrete) should be carried out before application of concrete repair.

Cut Perimeter of Deteriorated Area
Fig. 4: Cut Perimeter of Deteriorated Area
Cleaning and Coating of Bonding Agent on Reinforcement Steel
Fig. 5: Cleaning and Coating of Bonding Agent on Reinforcement Steel

6. Apply Suitable Repair Method

There are many different standard concrete repair methods and materials available based on the type of damage. Suitable methods and materials should be used based on types of concrete damage.

7. Cure Repaired Concrete

Suitable curing regime should be considered for the repaired concrete area in order for concrete damage to gain the required strength and durability. If concrete is not adequately cured, then repair works, cost, and time invested to repair the defected zone goes waste.

Various repair materials need different curing condition, for instance, some material may require extensive water curing whereas some materials may need less, and there are materials that need adequate protection with no water exposure till they achieve desired strength.