The concrete used for large-scale construction projects needs constant supervision of temperature fluctuation, and efficient heat control. This aspect is critical because of the huge amount of building material required in large-scale concrete projects.
This form of construction is usually required to build extensive infrastructure, such as power plants, bridges, dams, highways, skyscrapers, etc.
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These immense construction projects are easier to develop if the raw materials are easily available. Besides, the ease of construction, durability, cost-efficiency and mechanical factors of the building also play a considerable role.
However, many construction professionals and engineers still struggle with issues related to temperature control, as large-sized projects have significant concrete components to control. Lack of proper control over the temperature of concrete during construction can cause deficiency in the structure’s integrity. This can lead to visible cracks developing on the concrete surfaces.
In this article, we have described in detail the reasons for cracking and the essential tips to preventing concrete cracks.
Why does Concrete Crack?
There are several factors that contribute to cracking of concrete in large-scale construction projects. It is important for professional builders to understand the critical nature of ample heat generation and efficient dissipation, to ensure optimal integrity of the concrete structure.
The concrete mixing process causes an exothermic reaction in which the cement produces significant heat. This heat can cause noticeable differences in temperature within the same concrete structure.
Some of the main factors that influence generation of heat during concrete mixing are the type of cement selected, grade of its grains, its composition and their specific proportions in the mix. Apart from these, other factors include the kind of cementitious materials used, insulation, framework, placement dimensions and environmental conditions.
The inherent thermal properties of concrete components can cause challenges with sufficient heat dissipation in mass concrete structures, by preventing faster heat loss. Large-sized structures can also undergo extreme internal temperatures and more hydration, especially in the core of the component, where heat is more likely to be trapped due to adiabatic conditions.
For example, the core of a concrete component may take days and even years to stabilize its internal temperature completely. An excellent example is of the world-famous Hoover Dam in the U.S.A. which reportedly took almost 200 years for its concrete core to cool entirely.
For normal construction projects, it is recommended to use top-grade concrete admixtures to successfully prevent concrete from cracking.
Here are some of the major elements that cause concrete to crack –
Thermal Difference
The difference in temperatures of the exterior and interior of the concrete component causes thermal gradients, leading to thermal stress. Cracks begin to form in concrete when the thermal gradient rises higher than the concrete’s tensile strength. Such cracks significantly affect the structural integrity of the concrete, and result in lower durability and shorter life of buildings.
Additionally, shrinkage from uncontrolled water evaporation during curing of concrete also causes the concrete to develop cracks. Hence, in order to achieve higher fluidity of the concrete, the modern construction industry is increasingly looking for concrete with higher water-to-cement ratio.
As the excess water in such construction evaporates in the hardening stage, the concrete inevitably contracts, leading to visible cracks developing on the surface.
It is possible to avoid cracks in concrete from various causes, by simply using top-quality admixtures.
Cement Hydration
Cement hydration has five distinct stages –
1. Pre-induction
This stage causes the temperature of concrete to rise rapidly as soon as the cement is mixed with water.
2. Dormant
The dormant stage of cement hydration slows down the hydration process significantly, as diffusion barriers are created.
3. Strength-Gain
The next two stages both involve the concrete getting harder over a period of several hours, or even days.
4. Steady Stage
The last stage of cement hydration experiences stable temperatures, depending on the environmental factors, and hydration continues in this stage.
However, one of the biggest challenges professional builders face today is preventing concrete cracks in large-scale projects.
Tips to Preventing Concrete Cracks
Let’s find out about the different types of cracks that can develop in constructed structures, their individual causes, and the most efficient ways of preventing concrete cracks –
1. Thermal Cracks
Thermal cracks form as a result of uneven shrinkage, or expansion of concrete components, which is usually caused by frequent fluctuation in internal and external temperature.
The best way of preventing thermal cracks in concrete is to use tried-and-tested temperature control methods, such as using the appropriate admixtures. This involves using techniques that allow gradual and proper cooling of concrete components, and using the perfect admixtures in the concrete mix.
2. Expansion Cracks
Expansion cracks in concrete are usually caused by either a chemical reaction, such as ASR, or from thermal expansion.
To prevent expansion cracks in concrete, you should integrate expansion joints in the components. Besides this, you should avoid using building materials that contain reactive aggregates, and ensure proper drainage of water from the concrete mix.
3. Shrinkage Cracks
Concrete develops cracks from shrinkage due to quick loss of moisture during the curing stage.
It is highly advised to use proper curing practices by using special cement curing compounds, and by controlling the overall water content of the concrete mix.
4. Plastic Cracks
Plastic cracks in concrete develop due to premature drying of the concrete when it is pliable or fluid.
For preventing plastic cracks in concrete, experts advise using covering sheets, creating wind-breaks and maintaining the surface moisture levels till the concrete component cures completely. Besides, construction experts also recommend adding the correct admixtures in the concrete mix to prevent plastic cracks.
5. Corrosion Cracks
Concrete components in construction projects also develop cracks when their underlying steel reinforcement gets corroded from exposure to moisture, or water seepage.
To prevent corrosion cracks in concrete, it is recommended by experts to use ample concrete cover, waterproofing materials, and to use corrosion-resistant reinforcement material.
6. Overloading Cracks
Concrete structures can sometimes develop visible cracks when excessive loads are frequently laid on the concrete, which are beyond its compressive capacity.
You can avoid overloading cracks in concrete structures by utilizing stronger reinforcement materials. In addition, you should design the component based on expected load the surface will bear when in use. In addition, using the best-suited admixtures is also an additional help in preventing cracks from overloading.
7. Settlement Cracks
Uneven settling of the substrate, and even the foundation, can cause noticeable cracking in concrete.
The best way to preventing settlement cracks in concrete is by ensuring the concrete is compacted uniformly, and the appropriate sub-grade cement is used.
8. Chemical Reaction Cracks
ASR (Alkali-Silica Reaction) is the most common cause for cracks resulting from chemical reaction. This reaction causes internal expansion in concrete, which results in visible cracking.
According to construction experts, the best way to preventing concrete cracks caused by chemical reactions is by using non-reactive cement aggregates, and ensuring optimal moisture control during the curing stage.
Conclusion
In short, preventing concrete cracks is easier and more efficient when you use the above-listed tips by construction experts. Any concrete component can develop cracks from one or more causes.
Hence, it is extremely crucial to follow the best building practices and employ the expert tips to preventing concrete cracks. In addition, it is highly recommended to use the best-quality construction chemicals and admixtures, such those provided by Sakshi Chem Sciences Pvt. Ltd, for best results.
FAQS
How can you prevent concrete from cracking?
To prevent concrete from cracking, it is advised to let the concrete mix cure properly, keep the water content low, add sufficient reinforcement, avoid excess fluctuation in temperature, and use high-quality admixtures from leading manufacturers.
How to permanently fix cracks in concrete?
Some of the most effective ways to permanently fix cracks in concrete include epoxy injections, using concrete caulk, applying concrete sealer, or with good-quality admixtures in the concrete mix.
How to make concrete that doesn’t crack?
The best way to make concrete that doesn’t crack is by using high-quality admixtures, keeping water content low in concrete mixes, controlling temperature, and letting the concrete cure properly.
What additive stops concrete from cracking?
The best additive to stop concrete from cracking is any admixtures that contain polypropylene fibers. These admixtures are considered one of the most widely available and cost-efficient additives to use to prevent concrete from cracking.