Concrete is one of the most durable materials available for construction. Concrete is commonly used in all sorts of buildings – from houses to sidewalks and driveways. The large choice of applications it provides, it’s behavior, strength, affordability, durability, flexibility etc play a vital role in making it the preferred building material for the majority of the industry experts. The cracks in concrete are extremely common and often misunderstood. Concrete contractors must follow well-established guidelines concerning concrete placement to ensure the efficiency and crack resistance of the mixture. The durability, strength and crack resistance of the concrete is not accidental. Concrete shrinks or expands with variations in moisture and temperature. Shrinking can induce cracking at an early age of the concrete. Irregular cracks are unsightly and challenging to maintain but usually, it won’t affect the integrity of the concrete. Here listed are valid reasons for the cracking of concrete and by going deeper into these grounds we can easily avoid the cracking and take effective measures for avoiding the same.
Composition of Basic Concrete Mix
There are mainly four standard ingredients within the concrete mix: binding materials, aggregates or inert materials, water and admixture. Although lime is also used, cement is the most common binding material used in the concrete mix. When water is blended with the cement, a paste is created that coats the aggregates within the mixture. The cement sets connects the aggregates and form a stone-like substance. Aggregates are further divided into coarse and fine aggregates. In most cases, sand is the fine mixture and gravel or crushed stone is the coarse mixture. Water helps the chemicals to react with the cement and provide workability to the concrete.
Why Concrete Cracks?
1. Excess water in the mix
Concrete does not need much water to obtain maximum strength, but concrete used in residential pours tends to have too much water added to the concrete on the job site since it makes it easier to install. This excess water will reduce the strength of the concrete and hence causes cracks after setting. As concrete dries its gets hardened and it shrinks. The shrinkage is due to the evaporation of excess mixing water. The wetter or humid the concrete mix is, the higher the shrinkage will be. Shrinkage is the most common factor responsible for cracking.
2. Improper curing
The prime intention of curing is to maintain the moisture content and temperature control which helps in concrete gaining its full strength and prevention of crack. If curing is not done properly, compressive strength and flexural strengths are lowered, permeability increases which result in decreased durability. This will also result in plastic and drying shrinkage which will cause cracks.
3. Rapid drying of the concrete
Quick-drying of the concrete enhances the chances of cracking. The chemical reaction which takes place while the concrete transform from semi-solid to solid-state requires water. This hydration continues to transpire for days and weeks after you pour the mixture.
4. Lack of control joints on the concrete slab
Concrete slabs determine where you want the concrete to crack. The control joints should be of the depth of the slab and no more than 2-3 times (in feet) of the thickness of the concrete (in inches).
5. Foundations poured in the winter
Foundations are not commonly poured during cold weather since it will result in more cracks than usual. Concrete can be porous. Water from rain or snow can leak below the exterior, freeze, expand, and then contract when the water thaws. This expansion on overall winter results in flakes and worst case, cracks.
Methods to repair concrete cracks
Although there are multiple crack repair methods are available, prevention is always better than cure. Prevention of concrete cracks gives efficient strength, saves money and gives more durability to the structure. Fixing cracked structures involves a lot of time and money. Choosing the right material to repair ease the trouble a little. Here are some of the best ways to repair cracked concrete:
- Epoxy Injections
This method is used to fill narrow cracks that are up to 0.05 mm. In this method, the cracks in the exterior of the structure are sealed by injecting epoxy under the concrete. Before the process, it always better to understand the underlying cause of the cracks or otherwise the cracks may appear again after the process. Epoxy injections require skillful execution so it is always better to make sure that the person executing the process actually knows what he does.
- Sealing and routing
This method is only suitable when structural repairing is not required. In this method, the cracks are enlarged further and filled and sealed afterward using a joint sealant. The executioner should be aware of the width to the depth aspect ratio of the crack to make sure that there is enough space available for the process.
Stitching is one of the most simple and reliable crack repair methods available. In this method, holes are dug to make entry and exit points over the cracked surface. Several U-shaped metallic staples are then passed into the holes and moored strongly in the holes with grout or an epoxy-based system.
- Plugging and drilling
This is cost-effective and time-saving method to repair vertical cracks that run in straight lines. Under this procedure, vertical holes are drilled in the cracks and grout is passed through to form a key. This grout key formed helps to prevent leakages and the consequent loss of soil from the walls. Depending on the nature and depth of the cracks, other filling methods such as gravity filling, dry packing, overlay and surface treatments are also practiced.
- Crack-resistant concrete mix
Crack-resistant concrete mix is a professional strength blend of cementitious materials, sands, stone, and fibers formulated to reduce the risk of surface shrinkage cracks. There are multiple providers available in the market for the mix and most of them will assure an average strength of about 4000 psi. Crack-resistant concrete is commonly used for constructing driveways, transportation construction, walkways, curbs, stairs, etc where cracking of the concrete is not at all tolerable. Most of the crack-Resistant concrete mixes available are air-entrained to improve its freeze-thaw durability and fiber-reinforced to decrease shrinkage cracks and enhance impact resistance.