1. REPAIR OF SPALL CONCRETE
NOORLI ISMAIL

2. INTRODUCTION
Definition of spalling is concrete which breaks up, flakes, or becomes pitted. Flaking and scaling are also used to describe different types of spalled concrete.

3. In the repair of a structure showing spalling, it is usual to find that there have been substantial losses of section and/or pronounced corrosion of the reinforcement
Both are matters of concern from a structural viewpoint, and repair generally involves some urgency and some requirement for restoration of lost strength

4. CAUSES OF SPALLING Temperature Water content
Corrosion of reinforcement
Poor workmanship

5. TEMPERATURE
Due to freeze-thaw and hot condition.
In 4 season country, concrete is not air-entrained, or prepared to this condition. When it contains tiny air bubbles, it can spall when it freezes.
In hot country such as Asean country, exposure of the concrete to high temperatures can make the condition worst.
WATER CONTENT
Too high a proportion of water will weaken concrete.
This is a mistake that can occur when the concrete is mixed, when it's poured under wet conditions or when it's being spread and leveled.
When an overly wet mix cures, the concrete will be weaker than normal and prone to spalling.

6. CORROSION OF REINFORCEMENT
In poured concrete walls, slabs and other structural elements, steel reinforcing bars (rebar) and/or steel mesh are usually embedded in the concrete to add strength.
If the steel begins to corrode for some reason, the surrounding concrete can break away
Once steel is more directly exposed to moisture, the corrosion and spalling cycle will accelerate.

7. POOR WORKMANSHIP
As concrete is placed in forms, it often requires vibration using special tools.
This step helps the mix flow into all areas of the form, eliminating voids (empty spaces) that can be a cause of spalling.
Other installation errors that can cause spalling include introducing impurities (like dirt, leaves or construction debris) into the mix.

8. EXAMPLE

9. EXAMPLE

10. METHOD OF REPAIRING The repair process generally includes:
Standard practice for the repair of concrete spalls varies depending on the type of concrete element being repaired, cause and extent of damage, location of the spall and repair material selected.
The repair process generally includes:
1. an inspection to document the extent and details of damage,
2. an evaluation to determine the cause of distress and the as-constructed details for the damaged element,
3. the selection of a repair material, and
4. the application of the repair material in accordance with standard concrete practice for portland cement based concretes or in accordance with the manufacturer's instructions for commercial products.

11. JACKETING
Primarily applicable to the repair of deteriorated columns, piers and piles
Jacketing consists of restoring or increasing the section of an existing member, principally a compression member, by encasement in new concrete
The form for the jacket should be provided with spacers to assure clearance between it and the existing concrete surface
The form may be temporary or permanent and may consist of timber, wrought iron, precast concrete or gauge metal, depending on the purpose and exposure
Timber, Wrought iron Gauge metal and other temporary forms can be used under certain conditions

12. Filling up the forms can be done by pumping the grout, by using prepacked concrete, by using a tremie, or, for subaqueous works, by dewatering the form and placing the concrete in the dry
The use of a grout having a cement-sand ratio by volume, between 1:2 and 1:3 , is recommended
The richer grout is preferred for thinner sections and the leaner mixture for heavier sections
The forms should be filled to overflowing, the grout allowed to settle for about 20 minutes, and the forms refilled to overflowing
The outside of the forms should be vibrated during placing of the grout

13. CONCRETE JACKETING OF CONCRETE PILE
Problem: Precast concrete piles have major deterioration due to sulphate attack. Deterioration extends to the mud line.
Description of Repairs: See Figure 1.
In this example, the original pile section was 40 cm (15 ¾ inches) square. The concrete jacket, as shown, is 76 cm (30 inches) in diameter. A timber encasement, with galvanized steel bands, is used in the tidal zone. A corrugated sheet metal form is used down below the mudline. See FIGURE 3 for the pumped concrete method of injecting the new concrete. Figure 1 shows the top portion of the pile encased with either a pneumatically placed or hand-placed grout (FIGURE 2).

14. FIGURE 1
FIGURE 2

15. FIGURE 3

16. ANOTHER EXAMPLES OF COLUMN JACKETING

17. GUNITING/SHOTCRETE
Gunite is also known as shotcrete or pneumatically applied mortar
It can be used on vertical and overhead, as well as on horizontal surfaces and is particularly useful for restoring surfaces spalled due to corrosion of reinforcement
Gunite is a mixture of Portland cement, sand and water, shot into the place by compressed air
Sand and cement are mixed dry in a mixing chamber, and the dry mixture is then transferred by air pressure along a pipe or hose to a nozzle, where it is forcibly projected on to the surface to be coated

18. Water is added to the mixture by passing it through a spray injected at the nozzle
The flow of water at the nozzle can be controlled to give a mix of desired stiffness, which will adhere to the surface against which it is projected

19. SURFACE PREPARATION
Prior to preparation of concrete surfaces, exposed reinforcing should be inspected for proper exposure, clearance, cross-sectional area, and location.
Reinforcing bars must be further exposed if the remaining concrete is debonded from the reinforcing steel.
Removal must be continued to completely expose the bar if more than half of a reinforcing bar perimeter has been exposed.
The process involved in surface preparation are;

20. 3.1 CONCRETE REMOVAL
mark off the area to be repaired using straight lines between corners,
make a normal-to-the-surface cut along the marked boundary,
remove all concrete from within the cut perimeter to a near uniform depth,
sound the remaining concrete within the repair area for weaknesses and perform removal as needed, and
clean all surfaces within the repair area.

21. CONT’
Concrete should be removed to produce a near uniform depth for the
repair area.
Full-depth repairs require that a full-depth saw cut be made at the boundaries. Impact hammers are typically applicable for smaller and moderate areas of removal and for areas of limited access.
Removal should begin at the interior of the repair area and progress toward the boundaries.
Hydrodemolition (water jet blasting) is applicable for large areas of spall repair where the reinforcing steel is to be exposed and reused in the repair.

22. 3.3 FORMWORK
If repairs are to be made to vertical or overhead surfaces and a non-sag material is not to be used, formwork will be required.
Prior to installing forms, the concrete surface must be inspected for any surface contours that could result in air being trapped during concrete placement or pumping.
If found, concrete must be removed to change the contour, or vent tubes must be installed.
Formwork should be secured to the concrete with expansion anchors or standard form ties.

23. 3.4 REPAIR MATERIALS
Repair materials must be dimensionally compatible with the existing concrete substrate to minimize the potential for cracking and debonding as a result of restrained contraction.
Those material properties which influence dimensional compatibility include shrinkage, thermal coefficient of expansion, modulus of elasticity, bond, and creep.
The types of repair materials are;

24. 3.4.1 CONVENTIONAL CONCRETE
Conventional concretes are low-cost, general-purpose repair materials that are typically used where the depth of repair is greater than 50 mm (2 in.).
to increase strength gain and improve durability of the hardened concrete, and
to inhibit the corrosion of reinforcing steel.

25. 3.4.2 RAPID HARDENING CEMENTITIOUS REPAIR MATERIALS
to minimize out of-service time for repairing pavements and bridge decks.
Repair depth and volume are usually small due to the high cost and rapid heat generation of the rapid-hardening materials.
Concrete containing high alumina cements will have increases in porosity, permeability, and strength losses with time due to the conversion of hydrated aluminate compounds (Zia, Leming, and Ahmad 1991).

26. 3.4.3 DRYPACK MORTARS
Typically used to repair small confined areas and cavities in vertical and overhead surfaces.
To reduce shrinkage, the batched mortar should be allowed to stand for 30 min and remixed before placement.
For commercial drypack products, follow the manufacturer's recommendations.

27. 3.4.4 REPLACED AGGREGATE CONCRETE
Used for repairing large areas where low volume change is required.
For repairs to vertical and overhead surfaces, the surface must be formed and aggregate tightly packed within the form.
The preplaced aggregate is gap graded to exclude fines and typically has a 40- to 50-percent void ratio after the aggregate is packed (Emmons 1993).

28. 3.4.5 POLYMER CONCRETE
Used for making shallow repairs up to 50 mm (2 in.) deep in structural concretes where a less permeable, higher tensile strength material than conventional concretes is required.
For repairs of greater depth, the concrete mixture must be placed in lifts.
The properties and application of these concretes vary widely depending on the type polymer and dosage rate used in the mixture.

29. REMOVAL & SURFACEPREPARATION

30. REPAIRING

31. END