Concrete Repair Work – Part 4 - civildigest for Construction & Maintenance Building Material

This is the fourth article in a series of articles on concrete repair work. Here we are going to discuss in detail the recommended rectification method for structural cracks using SIKADUR®-52 and SIKADUR®-31 CF Normal. We will also discuss the repair method using SIKA® MicroCrete-2000 (25 mm–75 mm) in brief.

Table of Contents

Concrete Repair Work using SIKADUR®-52

Sikadur®-52 should be used to repair cracks in concrete in dry conditions.

Type 3 cracks, also known as structural cracks, with a crack diameter of more than 0.2mm and a depth of more than 25mm can be repaired.

It’s essentially an epoxy injection.

It is a two-part, solvent-free injection liquid with a low viscosity based on high-strength epoxy resin.

Sikadur®-52 fills and seals voids and cracks in structures such as bridges and other civil engineering buildings, industrial buildings, and residential buildings, including columns, beams, foundations, walls, and flooring.

A precisely performed crack injection will restore concrete strength and seal it against moisture, dirt, and chemicals.

Injection-repaired concrete cores frequently have a higher crushing strength than the parent concrete. This is due to the resin’s reinforcing effect.

Concrete Repair Work — **SIKADUR®-52: Source**

Area Preparation

The surface of the application should be structurally sound, clean, and free of standing water, oil, grease, and surface treatments, among other things.
High-pressure water jetting (compressed air plus water) or mechanical procedures such as grinding, chiselling, and so on should be used to completely prepare the concrete. To remove dust, cracks must be cleaned using compressed air.
Concrete fully contaminated with oil or grease must be removed to the depth of sound and uncontaminated concrete.

Mixing

Pre-batched packaging and bulk packaging have independent mixing techniques.
Add all of Part 8 to Part A for pre-batched packaging. Mix on low speed (max. 250 rpm) for at least 3 minutes using an electric mixer. Avoid the entrainment of air.

Add both parts in the exact proportions to a suitable clean, dry container for bulk packaging and mix in the same manner as for pre-batched units.

Rectification Procedure

As previously said, prep the surface.

Sikadur-31 or an equivalent epoxy resin-based bonding paste used in general construction should be used to secure the injection ports along the crack line at approximately 25cm intervals.
If the concrete surface at the crack is not flat enough to allow for a firm binding between the concrete and the ports, utilize injection nipples with 50 mm depth and 5 mm diameter drilled holes.
Crack mouths should be opened and sealed using Sikadur®-31 (or an epoxy resin-based bonding paste of equal quality).

With the same epoxy, seal the surface of the crack at the soffit.
Using an injection pump, mixed Sikadur®-52 can be injected under pressure through injection ports.
The initial injection port is sealed as soon as injection resin flows out of the next one, and the injection procedure is resumed from the next port.

For horizontal cracks, injection should begin at any of the ends and continue until the last port is used. Injection should begin at the lowest port and progress higher for vertical cracks.
After the injection process is completed, the injection ports and the sealing materials between the ports are removed.

Concrete Repair Work using SIKADUR®-31 CF Normal

Sikadur®-31 and Sikadur®-52 should be used together to repair cracks in concrete in dry conditions.

It is a moisture-tolerant, thixotropic structural two-part adhesive and repair mortar composed of epoxy resins and special fillers.

Area Preparation

The surface of the application should be structurally sound, clean, and free of standing water, oil, grease, and surface treatments, among other things. All lost particles must be cleaned up.

High-pressure water jetting (compressed air plus water) or mechanical procedures such as grinding, chiselling, and so on should be used to completely prepare the concrete. To remove dust, cracks must be cleaned using compressed air.
Concrete fully contaminated with oil or grease must be removed to the depth of sound and uncontaminated concrete.

Mixing

Considering pre batched units:

Part A: Part B = weight or volume ratio of 2:1
Mix parts A and B for at least 3 minutes with a mixing spindle attached to a slow-speed electric drill (max. 600 rpm) until the material is smooth and gray in color.

Aeration should be avoided during mixing. Then, pour the entire mixture into a clean container and stir for about 1 minute on low speed to keep air entrapment to a minimum.

Procedure for rectification

As previously said, prepare the surface.

When applying a thin layer of adhesive, use a spatula, trowel, or notched trowel (or gloves) to apply the mixed adhesive to the prepared surface.
The maximum layer thickness is 30mm. It is non-sagable on vertical surfaces up to 15mm.

Now that we are considering the minimum concrete cover to be 30 mm, when the crack depth is greater than 25 mm, the reinforcements will be exposed to the atmosphere and undergo corrosion and degradation of the structure. Even during the repair process, the moisture of fresh concrete and the degree of contamination of the concrete by chloride ions had a tendency to increase the corrosion potential.

Hence, it is advisable to apply a corrosion inhibitor like SIKATOP® ARMATECH®-110 EpoCem before the application of a bonding agent. Thereafter, apply the water-proofing and bonding agent (Barra Emulsion 57D) prior to the application of grouting owing to the reasons stated in Article 3. Please refer to Article 2 of this series for the recommended procedure for the application of bonding agents. Below is the correct method for the application of the corrosive protecting agent.

SIKATOP® ARMATECH®-110 EpoCem

It is a three-component cementitious, epoxy resin-compensated coating compound with corrosion inhibitors that is used as a bonding primer and reinforcement corrosion protection.

Area Preparation

Concrete:

Dust, loose debris, surface pollution, and items that impede bonding or inhibit suction or wetting by repair materials should be removed from the application surface. To reveal a sound surface, hack and remove the weak concrete.

Steel Reinforcement:

Rust, scale, mortar, concrete, dust, and other loose material that reduces bond or contributes to corrosion must be removed and reinforcement cleaned to SA 2 in accordance with ISO 8501-1 (i.e., thorough localized blast cleaning: the surface must be free of visible oil, grease, and dirt, loose paint coatings, and most of the mill scale, rust, and foreign matter when viewed without magnification).

Mixing

Shake components A and B thoroughly before opening.

Pour liquid components A and B into a suitable mixing vessel and mix for 30 seconds at low speed using an electric mixer (250 rpm).
While still mixing, slowly add powder component C. Mix the three components together for a minimum of 3 minutes, minimizing the addition of air.
Leave to stand for 5–10 minutes until the mixed coating material exhibits a brushable, weakly dripping consistency.

Do not add water.

Rectification Procedure

When applying as a reinforcement corrosion protection agent, apply the first layer, approx. 1mm thick, using a medium-hard brush or spray gun to the cleaned reinforcement. Apply the second layer when the first coat is hard to the fingernail (2–3 hours at +20 °C).

When to apply the mortar

At +30 °C, the mortar should be applied at least 6 hours after the application of the corrosion inhibitor.

At +20 °C, the mortar should be applied at least 5 hours after the application of the corrosion inhibitor.

SikaTop® Armatech®-110 EpoCem® must be protected from contamination and rain until the repair mortar is applied.

The application must be carried out at temperatures below 30°C.

Rectification of structural cracks using SIKA® MICROCRETE-2000

The procedure for the repair of structural cracks using SIKA® MICROCRETE-2000 is exactly similar to that for surface cracks; however, it should be accompanied by the application of a corrosion protective agent like SIKATOP® ARMATECH®-110 EpoCem and a bonding agent like EMACO® 157D PRIMER (BARRA EMULSION 57D).