What Is Concrete Crack?
Cracking is a phenomenon of “ a complete or incomplete separation of either concrete or masonry into two or more parts produced by breaking or fracturing”. This definition is given by American Concrete Institute (ACI). In this article, we will discuss various concrete crack repair methods.
A structure is subjected to cracking or crack formation due to one or more factors like:-
- Temperature and plastic shrinkage.
- Thermal variations.
- Drying shrinkage.
- Chemical reactions.
- Weathering process.
- Construction overload, and
- Poor construction practices like improper curing, inadequate water content in concrete mixture, inadequate formwork support, etc.
The development of cracks in structures is an indication of structural distress or a lack of durability. Due to cracks, the structure may face problems like weakening of structure, water leakage through cracks, etc.
The development of cracks is a big deal if observed and examined from a structural perspective. Other than the structural aspects, it also aﬀects the interior as well as the exterior aesthetics of the structure.
Cracks aﬀects the structure in many ways. So it is important to examine and repair the cracks as soon as possible. Crack repairing can be done by various methods, which depend upon the nature of cracks and the type of structure. There are many other factors on which suitable crack repair methods are chosen.
Concrete Crack Repair Methods
Crack repair can be done using diﬀerent methods and techniques. They are as follows:-
- Epoxy injection grouting
- Routing and sealing
- Flexible sealing
- Providing additional reinforcement
- Drilling and plugging
- Prestressing steel
Let us learn each method of crack repair in detail below:
1. Epoxy Injection
Epoxy compounds possess properties like high compressive strength, tensile strength, and bond strength. They are widely used for making repair mortar.
Epoxy compounds are not suitable for concrete crack repairs, especially for external applications. It is because epoxy compounds are not compatible with various weather conditions and temperature changes.
Epoxies can also be used on wet surfaces. Wet surfaces require some special grade of epoxy. It is way too costly than the normal epoxy compounds.
Epoxy compounds can be used to seal the cracks as narrow as 0.002 inch which is approximately 0.05 mm. It is an eﬀective method for crack repair. The procedure for crack repair by epoxy injection grouting is as follows:-
- Clean the cracks.
- Seal the surfaces.
- Install the entry and venting points.
- Mix the epoxy compound.
- Inject the epoxy.
- Remove the surface seal.
2. Routing And Sealing
The crack sealers used for repair of cracks should ensure structural integrity and serviceability. Additionally, they should be able to protect from ingress of harmful substances.
This technique of crack repair is used in conditions where remedial repair is required and structural repair is not needed. In this method, the original crack formed on the surface is enlarged, which is known as routing, and then after the crack is sealed using a suitable joint sealant.
This method is commonly used as its procedure is relatively simple and requires no special training for repairing the cracks. It is mostly used for flat surfaces like floors and pavements, respectively. It can be used on vertical and curved surfaces.
This method is suitable for repairing both, fine cracks and large cracks as well. The sealants used for the treatment of concrete may be of several materials, including epoxies, silicones, and asphaltic materials.
Cement grouts are generally avoided as they are likely to crack. The sealant should be applied depending upon the use of the area on which is it applied.
In this method, a groove of 6 mm to 25 mm depth is prepared by the means of concrete saw a hand tool, or a pneumatic tool. Then the groove is cleaned by water blasting or air blasting.
The groove is allowed to dry. Once it is completely dried, the sealant is placed in the groove and is allowed to cure. After the surface is cured properly, it can again be used.
3. Flexible Sealing
In this method, a recess is cut along the line of the crack and it is filled up with a suitable flexible material. The breadth of recess and the sealant’s strength capacity determine the joint movement that can be accommodated.
So, the sealant bond must have a suitable width and shape for the expected movement. A bond breaker should be used to prevent the sealing material from bonding to the bottom of the recess.
In this technique, holes are drilled on both sides of the crack. The holes are cleaned up and the legs of stitching dogs are anchored in it using either a non-shrink grout or an epoxy-resin based bonding system. The stitching dogs should be variable in length and/ or in orientation.
It should be located in such a way that the tension transmitted across the crack is spread over an area and not applied to a single point. This method is preferred when the tensile strength is to be re-established across major cracks.
5. Providing Additional Reinforcement
a) By Conventional Reinforcement
This method of crack repair is used to repair the cracks of reinforced cement concrete. In this method, first of all, the crack is sealed using a sealant. Then, holes of approximately 20 mm diameter are drilled so that it intersects the crack plane at approximately 90 degrees.
The holes are then filled up with epoxy reinforcement bars of 12 mm or 16 mm diameter is placed into that, extending at least 500 mm on each side of the crack. The spacing of reinforcement bars is decided on the severity of cracks or as suggested by engineers.
b. By Prestressing Steel
When a major part of a member is to be strengthened, or a crack is to be treated, this method is often the preferred method. This method uses prestressing strands or reinforcement bars to apply a compressive force. Suﬃcient anchorage should be provided for the prestressing steel.
5. Drilling And Plugging
In this method, a hole of 50 mm to 75 mm diameter is drilled down the length of the crack. The hole is thoroughly cleaned and filled with grout.
The grout key is responsible for preventing the transverse movements of the concrete sections adjacent to the crack. The key also helps to reduce the heavy water leakage through the cracks and loss of soil from behind the leaking wall.
Based on grout material used, there are three methods for crack repair by grouting. They are as follows:-
- Portland cement grouting
- Chemical grouting
- Epoxy grouting
Portland Cement Grouting
Portland cement grout is used to repair wide cracks, especially in structures like gravity dams and thick concrete walls. Portland cement grout prevents water leakage, but it does not bond the cracks structurally.
The procedure for this method is as follows:
- Clean the cracks by air jetting or water jetting.
- Installation of grout nipples at suitable intervals and sealing the cracks with a suitable sealant.
- Grout the aﬀected area with Portland cement grout and let it dry.
The Portland cement grout generally contains cement and water or cement, water, and sand. Sometimes additives such as water reducers are added to the grout mixture to improve its properties.
For chemical grouting, chemicals such as sodium silicate, urethane, and acrylamide are used. Two or more chemicals are mixed to form a new chemical, which may be in the form of gel, a solid precipitate, or foam. The chemical grouts can be used in moist conditions also because of their properties to resist moisture.