Concrete Beam Repairing – A Case Study

Concrete Beam Repairing – A Case Study
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Honeycomb Concrete Beam
Overview of the problem

Honeycomb is found at the bottom of the beam after shuttering (formwork removing). Reinforced bars are exposed. Aggregates are exposed without cement mortar.

Possible causes

The reason may be caused by one of or all of bellows:
a. Lack of vibration during concreting
b. The concrete is too dry to vibration

Repairs of damages:
The damages should be repaired with materials that:
> high strength
> non-shrink
> good bonding to the concrete of the structure.

Steps of repairing

The repairing work should follow strictly the steps of surface preparation and repairing application as follows:

A. SURFACE PREPARATION

Remove loose or honeycombed concrete mechanically. Area to be repaired must be clean, sound and free of contaminants. Where reinforcing steel (with or without active corrosion) is encountered, the following procedures will be used: sandblast or wire brush reinforcing steel to remove all contaminants and rust. If half of the diameter of the rebar is exposed, chip out behind the reinforcing steel for providing at least 10 mm clearance between steel and surrounding concrete if a hand applied mortar or grouting material (without aggregate) is used.

At edge locations, provide right angle cuts to the concrete surface to avoid feather edging of repair material, i.e. saw-cut to 10mm depth, impact breakers.
Repair configuration should be kept as simple as possible, preferably straight edges and corners. Check concrete surface is clean and insure that surface is free from additional loose aggregates and that additional honeycombing is not present.

B. REPAIRING SYSTEMS

There are 2 methods: one for thin repairing with thickness of 5-6 cm and one for thick repairing with thickness of 10-15cm as follows:

1. MANUALLY APPLIED REPAIR SYSTEM (FOR SMALL HONEYCOMBING)

 Mix Sika Monotop 732 with clean water as per instructions given in the technical data sheet. Apply the bonding slurry with a stiff paint brush on to the substrate and the exposed steel reinforcements.

 Mix Sika Monotop R repair mortars as per instructions given in the technical data sheet. Apply Sika MonoTop R onto the still wet bonding bridge by trowel in a layer thickness of not more than 30 m. Then apply the second layers after 12 hours and not later than 3 days. Cure for at least 3 days by covering with wet hessian or approved curing compound.

2. FORM AND CAST-IN-PLACE (FOR LARGER HONEYCOMBING)

Mix Sikadur 732 as per instructions given in the technical data sheets. Within its potlife, Sikadur 732 shall be applied by brush onto concrete and steel exposed surfaces.

Form-up the area to be repaired with suitable formwork properly fixed to the concrete substrate and sealed with sealant. Drill the concrete from the top of the beam for grouting. Vent holes could be provided for making sure that the formwork will be properly filled up with repair material. Mix SikaGrout 214-11 HS in accordance with the technical data sheet. Within the open time of Sikadur 732 bonding agent, pour the grouting material in place and tamp formwork slightly with a hammer. During pouring process, the vent holes are capped one after another when steady flow is evident. Leave the formwork in place for at least 3 days and cured properly repaired area with wet hessian or approved curing compound.



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