Understanding Cracks in Concrete: Types and Prevention

Introduction

Concrete is one material that is quite common among all buildings, from short buildings to large ones, to provide strength and durability. However, it will require meticulous inspection from mixing to curing, or there is a chance that cracks can arise. Cracking of concrete could occur due to a lot of factors, including changes in temperature, growth of vegetation, excessive loads, and more. Cracks in concrete also consist of various types, which occur in different patterns. To understand more about the same, here’s a detailed blog about why concrete cracks and how to identify cracks in concrete.

Why concretes crack

When installed properly, concrete tends to be one of the most durable and long-lasting products that you can ever use in your home. However, the process of concrete placement must be done correctly. Here are a few reasons why concrete cracks.

Excess water was added to the mixture.

Concrete is one such substance that only requires a little water to settle quickly and gain strength; however, there are a lot of contractors who pour too much water into the mix. This leads to ease in the installation of concrete. This excess water, however, tends to reduce the strength of the concrete. Shrinkage is also one of the common reasons for cracking. As concrete hardens and dries, it undergoes shrinkage, which is due to the evaporation of excess mixing water. The more water present in the mix, the more the shrinkage will be.

Concrete drying quickly 

Quick drying of the concrete slab could increase the possibility of cracking. The chemical reaction that causes the concrete to convert from liquid to plastic state usually requires water. The hydration of this chemical reaction tends to continue even for days or weeks after you pour it.

Lack of control joints in concrete slab

In a concrete slab, the control joints tend to help in concrete cracks where you desire it to occur. The joints should be of the depth of the slab and should not exceed more than 2 to 3 times feet of the thickness of the concrete calculated in inches. So, if we take a 4-inch concrete, the joints should be 8 to 12 feet apart.

The foundation is poured in winter.

Foundations poured in the cold months or left unheated during the winter months could cause more cracks to occur. Foundations poured on ground that is not properly compacted can also lead to more cracks.

How to Identify Cracks in Concrete

Visual monitoring and inspection are the first steps in identifying cracks in concrete. There are multiple ways to identify cracks in concrete. One of the best ways is to check crack widths and depths.

Crack width

A crack width ruler can be used to check the severity of a crack on the surface of the concrete. Based on the opening of the cracks, they can be described as either tiny or quite severe.

Crack depth

Crack depth is also checked to determine the severity of cracks. Crack depth evaluation helps determine durability performance and structural integrity. The measurement can help the repair contractor decide on the cost of repair.

There are various ways through which this can be achieved:

• Visual examination of concrete cores—When checked, core samples can provide an idea of the extent, depth, and severity of the cracks. One method is to extract the core simply, and the other is to inject dye into the surface of the cracks, which is then later studied.
• Ultrasonic pulse velocity method—This is one of the non-destructive methods of quality control of concrete materials without damaging them. UPV is a way to check for uniformity, quality assessment, and crack depth estimation.
• Impact Echo method—In an Impact Echo method, a stress pulse is generated through the surface of the concrete. The pulse tends to flow from the test object and is reflected back by any areas with flaws, cracks, boundaries, and interfaces. The waves that are reflected are recorded with a transducer. This is then analyzed to check the depth of surface cracks.

Types of cracks

Over time, concrete is bound to form cracks, and this can be due to many reasons. Sometimes, these cracks are quite serious, and sometimes, they are not so serious. Here are a few different types of cracks in concrete that will help you evaluate how they differ from each other.

Shrinkage Cracks

Shrinkage cracks are one of the most common, especially in freshly poured concrete, and they are a result of the natural drying and curing process. As the water keeps on evaporating, the concrete shrinks, and there are small, often fine, lines present on the surface. While these cracks are usually superficial and do not affect the structural integrity, they may not look the best. Proper curing practices could be one of the ways through which the occurrence of cracks can be reduced.

Overloading Cracks

Another type of crack is overloading cracks, which occur when heavy weight is added to the concrete slab. While concrete is a heavy and durable material, too much weight could eventually crush it. In residential concrete slabs, the presence of heavyweight directly on the slab itself is rare.

Instead, there is a higher chance of excess overload on the ground beneath the slab. When the ground below a slab becomes wet and soft due to excessive rain or snow, it could be pressed down by heavy objects and eventually lead to cracks.

Hairline Cracks

Hairline cracks usually form due to the concrete settling while the curing process is ongoing. They are usually quite thin cracks, but they can also run deep into the slab. Because these cracks run deep, unlike their appearance, they tend to pose a great risk once the concrete has hardened.

As moisture and water make their way deep into the cracks, the water tends to expand. This expansion causes the cracks to widen even further and tends to get worse after every freeze-thaw cycle.

Settling Slab Cracks

The soil under the slab hardly settles well before the new concrete is poured upon it. This means that over time, soil could be settled continuously while the top slab is being brought down. This soil movement causes unsupported weak spots in the slab to occur, which makes it easy to form cracks in them.

Foundation Settlement Cracks

Foundation settlement cracks are also one type of crack in concrete found around the perimeter or corners of the building in the form of a stair-step pattern inside the wall. They usually occur when the ground or soil underneath a concrete foundation tends to compress or sink over time, and the foundation settles unevenly with it. Settlement cracks could happen for multiple reasons, such as soil issues or improper site preparation when the foundation was initially poured in.

Plastic Shrinkage Cracks

When the surface of the freshly poured concrete tends to dry out too quickly, it can lead to plastic shrinkage cracks. This happens especially if the top layer dries out way too soon compared to the concrete present beneath, which causes the surface to pull apart and leads to the formation of shallow cracks. These cracks are significant indicators of how insufficient moisture affects the initial stage of the concrete setting.

 Plastic settlement cracks

Plastic settlement cracks occur when the wet concrete settles unevenly due to inadequate formwork, especially during the early stages of concrete setting. These cracks do get deeper once the formwork is removed and the concrete undergoes a shift while losing control.

Crazing and Crusting of Concrete

Crazing is more like a web of fine shallow cracks present on the surface of the concrete. It is mainly caused by the rapid evaporation of moisture from the surface of the concrete during the early stages of curing. However, it could also be caused by a number of factors, such as low humidity, high temperatures, and exposure to direct sunlight or wind.

Concrete crusting, on the other hand, is wider and deeper than crazing cracks, and it occurs during the later stages of the curing process. Crusting cracks form on the surface when the concrete dries out too quickly, forming a hard crust that traps moisture inside the concrete. This moisture then tries to escape, causing the concrete to crack.

Concrete Crack Prevention

Cracks in concrete can be nerve-wracking to deal with, and they can impact not only the aesthetics of the building but also damage its structural integrity. While there is no sure-shot way to eliminate cracks in concrete, certain concrete crack prevention methods can reduce them. To understand the same, here are a few ways to prevent them.

• Keeping an eye on the temperature
• Preventing the use of excess water
• Providing sufficient concrete cover
• Starting the curing process as soon as possible
• Paying particular attention to the timing of the concrete finishing process.

The Impact of Environmental Factors on Concrete Cracks

One of the significant impacts of environmental factors on concrete is the freeze-thaw cycle. Pitting or spalling occurs when water tends to penetrate unsealed concrete or porous stone surfaces and undergoes freezing. When water expands, it creates an internal pressure which causes cracks to appear. There are also other factors, such as environmental temperatures, relative humidity, the ratio of wetting time, and the chloride ion concentration, that affect the concrete cracks.

Conclusion:

Concrete is prone to cracking regardless of the factor, which could be structural or nonstructural. While some types of cracks may not seem like a primary concern, others could be dangerous and compromise the overall structural integrity of the buildings. Hence, it is important to prepare the site properly using the right mix design and following proper installation methods and best maintenance practices to prevent cracking from occurring.

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