Concrete is everywhere – from the roads we drive on to the homes we live in. It’s strong, durable, and built to last. But if you’ve worked with concrete long enough, you know that it’s not perfect.
One of the most common and frustrating issues that engineers, contractors, and homeowners deal with is cracks in the concrete.
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Cracks can occur for many reasons. Sometimes they are minor, cosmetic issues. Other times, they can be indicators of bigger problems, indicating potential issues for the structural integrity of the whole structure.
Regardless of the severity, understanding the science of why concrete cracks and how to avoid it can save you time, money, and stress in the future.
So, let’s take a look at the steps.
Why Concrete Cracks?
Before we can determine the reasons why concrete cracks, let’s start by defining concrete. Simply put, concrete is a combination of cement, with sand, aggregates, and water. Once water is present, a chemical process known as hydration begins.
Hydration continues over a period of time in which the concrete hardens and binds the other materials together forming the solid structure that we rely on.
However, the trick is that as the concrete cures and dries, the concrete shrinks. This shrinkage is a natural part of the hydration process, but this shrinkage is also coupled with internal stress.
This internal stress comes into play when the compression exceeds the tensile strength of the concrete and cracks begin to form.
In other words, Concrete wants to move as it dries, but if it invests internal energy and doesn’t move, it cracks.
Other Reasons Concrete Might Crack
While shrinkage is the most common way concrete cracks, it is not the only way. Here are other causes of cracks in concrete.
1. Improper Mix Design
If the mix has a high water-to-cement ratio, you will lose the strength of the concrete. If the mix has too much water, the concrete will have weaker areas and will crack more easily. The paste will become more porous and dilute the concrete if there is too much water.
2. Poor Workmanship
Really, the important aspect of mixing, placing, compacting, and curing is simply that it must be done properly. Most cracking problems usually start with haste. If the contractor is rushed, they may not pay as close attention to the details that make a solid, successful slab. Skipping steps or cutting corners during finishing can create weak spots that may then crack.
3. Drying Too Quickly
Moisture is lost from the surface of the concrete too quickly during the curing or drying phase. Rapid evaporation from the concrete surface, usually caused by hot conditions, low humidity, wind, or other hotspots, causes the concrete to shrink based on the now dry surface.
In an ideal environment for curing, you are losing moisture from the surface of the slab slowly. If conditions dictate otherwise, the surface moisture will evaporate, and you will probably develop shrinkage cracks at the surface called plastic shrinkage cracks.”
4. Absence of Control Joints
Concrete will expand and contract, and, if not controlled by jointing, will expand and contract by finding weak points to crack along.
5. Structural Load
Concrete is strong in compression and weak in tension. If an element is under too much load without proper reinforcement, it can crack due to the excessive load.
6. Temperature Changes
Concrete will expand in heat and contract in cool. If the concrete goes through repeated temperature cycles without proper allowances for temperature changes (i.e., through expansion joints,) then it may crack due to thermal expansion or contraction.
Types of cracks in concrete
There is not just one type of crack. Here are the most common types of cracks and what they mean.
1. Plastic shrinkage cracks
Plastic shrinkage cracks show early in the age of concrete while it is still plastic. They are generally shallow, random, and caused by the evaporation of moisture too fast from the surface of the concrete.
2. Drying shrinkage cracks
Drying shrinkage cracks are the next step after plastic shrinkage cracks. They start appearing once enough drying has occurred and concrete is now able to actively continue drying and shrinking. These cracks can be quite prominent and tend to widen over time.
3. Settlement cracks
Settlement cracks are cracks that are caused due to the ground underneath the concrete settling or shifting. They are strongly correlated with poor subgrade preparation.
4. Structural Cracks
These cracks are serious. They can appear anywhere on a load-bearing element, whether it is a beam, column or foundation, and may appear as diagonal cracks or horizontal cracks. Structural cracks can indicate failure or excessive stresses.
5. Crazing
A pattern of fine cracks within the surface, generally regarded as cosmetic, is typically caused by rapid drying or excessive troweling.
Acceptable Crack Width
We get this question often: “Are any cracks acceptable?”
The answer: It depends.
In terms of non-structural concrete (pavements, sidewalks, for example), small surface cracks under 0.3 mm wide are generally acceptable, and will not adversely affect the function, or durability, of the slab.
In terms of structural concrete (beams, columns, etc.), the acceptable crack width is even smaller (<0.2 mm ,depending upon exposure conditions and reinforcement considerations).
Wide, deep, or actively growing cracks should always be investigated. When water begins to infiltrate or a risk of corrosion of reinforcement becomes evident, it is time to take action.
How Admixtures Work to Reduce Cracks?
Using chemical admixtures is one of the most effective ways to decrease the probability of cracks in cement powder and water composite materials. Based upon the use of specific type of admixture, modification of a concrete mix may change the properties of the composite material itself.
Here are some uses for admixtures:
1. Shrinkage-Reducing Admixtures (SRAs)
These minimize shrinkage as concrete dries, minimizing internal stress and of cracking.
2. Water-reducing admixtures:
These reduce the amount of water needed in the mix to provide the same level of workability at less water resulting in stronger, less porous concrete, with a lower likelihood of cracking.
3. Plasticizers and Superplasticizers:
These improve the workability of the concrete but do not contribute to the water content, also resulting in a better placement and less segregation and therefore improves overall strength.
4. Curing Compounds:
These improve moisture retention in the new concrete during the early stages of hydration and minimize the chances of plastic shrinkage cracks.
5. Fiber Reinforcement:
While technically not a chemical admixture, adding fibers, such as polypropylene or steel, to the concrete mix can help control micro-cracking by providing a more even distribution of internal stresses.
Why Use Sakshi Chem Sciences Admixtures?
At Sakshi Chem Sciences, we know that concrete cracks are much more than inconveniences; they are liabilities. That’s why we offer high-performance admixtures designed to solve the root cause of cracking.
So, what is our difference?
Tailored Solution: Our admixtures and formulations can be tailored to meet the requirements of your project, whether residential foundations or high-performance infrastructure.
Research-Driven Formulas: Our products are carefully developed through extensive R&D to ensure consistency, durability, and compatibility with local raw materials.
Expert Support: We do not just provide materials; we partner with you. Our technical team will work closely with engineers and contractors to ensure that the right amount is dosed, the correct mix is designed, and the right placement techniques are used.
Sustainable: Our admixtures of resources need to be less cement, and water – helping the industry to adopt more sustainable construction methods.
Therefore, whether you need to reduce shrinkage, improve workability or simply extend the life of your concrete, Sakshi Chem Sciences has a product that will work for you.
Conclusion: Prevention is Always Better Than Repair
There are cracks in the concrete internals, but it doesn’t mean that there is damage. If you understand the science behind the reason that cracks can occur and ensure that you have the correct preventions in place, this will give you the opportunity to deliver a concrete definition of stronger and more durable.
Every step can count: water content, correct admixture, ensure curing in accordance with the placement. Choosing the right partner in Sakshi Chem Sciences means that you are not just purchasing a product, you are purchasing peace of mind, knowing that you have given yourself a great opportunity to succeed.
