5 WAYS TO REDUCE OR CONTROL CONCRETE CRACKING

Concrete is the most used material for construction. If installed properly, the structure stays strong and looks the same for years while minor discrepancies during installation or careless maintenance can cause structural issues like concrete cracking. Our professionals at W.F. Botkin Construction Ltd. are devoted to providing you with quality concrete supply services.

Concrete cracking can happen due to several reasons. In some structures, it is the result of a weak foundation, but it’s mostly related to poor quality installation procedures. However, you cannot have a concrete structure without any cracks as some cracks occur naturally. Some of the possible reasons for concrete cracking are:

• Rapid expansion and contraction due to extreme temperature
• Settlement of the structure
• Heavy loads
• Too much water in concrete
• Insufficient vibration while placing
• Improper protection
• High water-cement ratio
• Corrosion of reinforcement steel

You should take care of the concrete for up to 28 days, until it sets completely. Here are a few of the preventive measures you can take to avoid cracks:

Reduce the Water Content in the Concrete Mixture

The ratio of the weight of the water to the weight of the cement should not exceed 0.5. Lower ratios yield stronger structures and fewer cracks. You can add plasticizer or superplasticizer to increase the workability of concrete. When the concrete dries and hardens, the water evaporates and causes shrinkage. Less water leads to less shrinkage; too much shrinkage means more cracks on the surface.

Use of Quality Materials

Your concrete should be of good quality and the mixture should be in adequate proportions. A standard mixture will have one part cement, three parts sand and 3 parts aggregate. The water and cement mixture acts as a binder which holds the gravel aggregate together. When much less cement is present, cracks are to be expected. The use of appropriately sized and good quality aggregates reduces shrinkage.

Finishing of Concrete Surface

Skilled professionals use proper finishing and timing techniques. They use flat floating and flat troweling. Do not overwork the concrete with vibrating screeds. This may cause the aggregate to settle and bleed water. Finishing the concrete at this point may cause cracks in the future.

Proper Placement and Vibration While Pouring the Mixture

You should take care while placing and vibrating the structure when the concrete mixture is being placed. It helps to avoid any entrapped air bubbles, which could weaken the concrete.

Proper Compaction of Soil

Before you start laying the concrete mixture, you need to compact the subgrade and granular base layers properly. If they are loose or poorly compacted, it could settle causing cracks in the concrete.

Add Control Joints

Even if you use quality materials and cure concrete properly, the concrete can crack due to the natural movements of the soil or normal drying shrinkage. This happens when the seasons or temperatures change and the ground heaves or contracts. Control joints are crucial and the places where these joints are introduced are estimated to be prone to cracking. You can introduce joints by cutting the slab to about a quarter of its depth at the specified spots. You can do it in any of the following ways:

• Make them in pliable wet concrete using a grooving tool
• Insert joint strips during the pouring process
• Cut the slab using a circular saw fitted with a concrete blade after a day of pouring

You can consider perpendicular and closely placed joints for better protection against cracks.

Consider the Temperatures

Cracks can form when there are temperature extremes. The ground surface temperature should not be less than 10 degrees Celsius, the concrete mix temperature should be between 15 degrees Celsius and 22 degrees Celsius and the air temperature between 10 and 28 degrees Celsius. Suitable temperatures allow gradual curing and drying of concrete which creates stronger structures.

Proper Curing

After 24 hours of placement, it is recommended to cure the slab continuously for 7 to 14 days. Rapid drying will lead to rapid loss of water from the surface resulting in shrinkage and cracking. It is a good practice to pond water on the concrete slab. You can also keep the slab covered with mats or burlap soaked in water or continually spray it with water to keep it moist. Don’t overload your concrete slab during the curing period or the structure may become weak. If it is exterior flatwork it is recommended that an acrylic concrete sealer be applied after 28 days and annually thereafter. This will mitigate any absorption of moisture and de-icing salts into the concrete surface.

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