The Complete Guide for Concrete Repair in 2018
Table of Contents
- Concrete Repair Overview
- Why Does Concrete Crack?
- Concrete Cracking
- Random Cracks
- Hairline Cracks
- Crazing Cracks
- Settlement Cracks
- Heaving Cracks
- Concrete Repair: Bottom Line
Concrete Repair Overview
Concrete is one of the most widely used paving materials known to man and even though it is exceptionally strong and remarkably durable, it's not completely immune to natural deterioration or damage over time. To ensure maximum concrete lifespan, it is generally recommended to get your concrete pavement sealed every 5 years after installation.
Not only will this help protect exterior concrete that is exposed to ever-changing weather conditions, but it can also help protect against harsh chemical spills, oil stains, and moisture absorption. A high-quality sealer can even enhance the color of stained or stamped concrete.
Even with proper sealing, it is still very common for paving contractors to be called upon to perform some type of concrete repair, often as a result of structural issues that have been in the works for a long time.
To give you a clearer picture of what we're referring to, below is a list of some of the most common concrete repair problems and what can be done to fix them.
Why Does Concrete Crack?
You have to realize that when it comes to concrete pavement, cracking is pretty much inevitable no matter how well-installed the slab may be.
One of the most important things that your paving contractor will do during the finishing process is install "control joints", which are basically cracks or grooves that are intentionally saw-cut into the pavement at certain intervals.
Without these control joints put into place, it is highly likely that the slab will crack in some unexpected area due to factors such as shrinkage during the curing phase and/or temperature changes.
This is exactly why they're called control joints – they help the paving contractor "control" where the crack is going to end up!
The concrete has still cracked (which is perfectly normal) but does so within the control joint, allowing for an attractive and pristine appearance of the freshly paved concrete driveway.
When properly installed, concrete is one of the strongest and most durable building materials you'll find, but achieving this type of crack-resistant concrete is not always as easy as it looks.
Here are some of the most common reasons why concrete tends to crack:
* Rapid drying: It's obviously a good thing for your pavement installation to dry out, but it's not so great when it dries too fast as this can make the slab highly susceptible to cracking.
Concrete requires water in order to convert its composition from a semi-liquid state into a hard, solid state and it's up to your paving contractor to know how to properly cure the slab so that it dries effectively. An unskilled paving contractor can easily botch the curing process, allowing the slab to dry too quickly and subsequently making it more vulnerable to cracking.
* Too much water in the mix:
Achieving the maximum strength level for a concrete installation requires a good understanding of how much water should be added to the mix in each phase of the process. Many unskilled paving contractors add too much water to the concrete during the installation, mainly because it makes the concrete a little easier to work with.
Unfortunately, this excess water has a detrimental effect on the overall strength of the concrete. As mentioned earlier, concrete slightly decreases in volume as it dries. So if the mix has a relatively high water content (i.e. it's more "soupy" vs. a thick milkshake), it has a higher potential of experiencing notable shrinkage once this excess water begins to evaporate.
To sum it up, the lower the water-to-cement ratio, the stronger the concrete will be when it dries and vice-versa. Your paving contractor will need to ensure that the right mix ratio is used so that your pavement installation will achieve its maximum strength level.
* Not enough control joints: As mentioned earlier, control joints are put into place by your paving contractor to ensure that the concrete has a place to "stress out", so that it won't crack in unexpected places.
A general rule of thumb that experienced paving contractors abide by is that control joints should be spaced apart no more than 2 to 3 times (in feet) what the thickness of the concrete slab is (in inches). For example, a 4-inch thick slab should have control joints placed approximately 8 to 12 feet apart.
There is a common misconception that if steel-reinforced bars (aka rebar) are used in the installation, the pavement won't crack. While using rebar won't completely prevent cracking, it will definitely help hold the concrete together should cracking occur.
* Concrete is not the proper strength for the job: Ready-mix concrete is available in several different "compressive strength" ratings. These ratings can vary from 2500 psi for residential purposes, to 5000 psi and higher for commercial applications.
Your paving contractor should be well-versed in which compressive strength rating will be the most appropriate for the type of installation being performed.
* Poorly installed subbase: Cracking is often the result of poor installation practices and one of the most prevalent areas where subpar paving contractors miss the mark is during the installation of the subbase.
In order to provide optimal support for the pavement slab, it is a must for the subbase to be tightly compacted with high-quality aggregate before pouring the paving material over it. Unfortunately, some unprofessional contractors will install a subbase that is either too thin, or even use inappropriate subbase materials such as dirt or sand.
Once this looser material is exposed to moisture, it will inevitably fall victim to the expansion and contraction phases from natural freezing and thawing cycles, putting undue pressure on the slab and setting the perfect stage for cracking to occur.
A reputable paving contractor, on the other hand, will only use high-quality aggregate for the subbase so that it can provide the much-needed stability to support the heavy pavement slab.
* Excessive weight: One of the first things that your paving contractor will find out when assessing your pavement project is how much weight the slab is intended to bear. As strong as concrete is, it's not invincible and there will come a point where its load tolerance reaches its limit.
In the same way that pressure from underneath the slab can cause it to crack, pressure from above the slab can produce cracking as well. Variables such as the type, thickness or depth of the concrete, quality of the subbase, and whether or not the material will contain reinforcements such as rebar or fiber mesh can all factor into a pavement's weight tolerance.
Generally speaking, extremely large vehicles such as semi-trucks and RV's that weigh well beyond the typical residential vehicle are most likely to crack a pavement slab due to their excessive weight.
This is especially true for concrete paving structures that are subject to regular load stresses such as driveways, parking lots, and interstate roads. Cracks will typically start on the surface of the pavement, and then work their way down to the bottom over several weeks or months.
If a crack reaches the subgrade of the slab, your paving contractor will more than likely have to completely replace that area of the structure in order to restore it back to its optimal strength. Some cracks can appear shortly after the concrete was poured, while others might take years to emerge.
Either way, the job of your paving contractor is to assess what type of damage has occurred (especially why it occurred), and then come up with an effective game plan to fix the situation. Below is roundup of some of the most common types of concrete cracks, followed by a list of the key reasons why these cracks develop in the first place.
As the name implies, random cracks do not follow any particular pattern but tend to spread out in several different directions. This stands in contrast to other common cracking patterns in pavement such as vertical, transverse, longitudinal, or diagonal cracks.
Random cracks are typically distributed across the surface of the pavement in an uneven fashion and although their depth can vary, they rarely extend below the mid-depth level of the slab.
If moisture happens to seep underneath the concrete, this can cause an expansion of the crack once the moisture freezes. You might also see flaking (i.e. small, thin chips or shards of concrete) in the areas immediately surrounding the crack.
More often than not, these types of cracks are caused by some type of concrete shrinkage (also known as "plastic shrinkage"), especially during the period of time when the slab is hardening or drying after installation. This is particularly true when the surface layer of the pavement is drying too fast in relation to the concrete below it.
Another common reason for random cracks is the settlement of the ground or subgrade upon which the concrete slab was poured.
These cracks are very thin and somewhat "unimpressive" in appearance, but they can run very deep. Hairline cracks often occur as a result of settlement of the concrete during the curing process. Because hairline cracks can run so deep, they can wreak even more havoc once the concrete mixture has fully hardened, often producing major cracks later down the line.
This type of cracking definitely lives up to its colorful name. Also known as "map cracking" or "checking", crazing refers to a network of small, fine, spiderweb-like cracks that primarily affect the surface layer of the pavement.
These cracks typically remain on a shallow level so they won't really have any impact on the structural stability of the pavement, but they can definitely diminish its overall appearance.
One of the most common culprits for crazing is the premature shrinkage of the surface layer, not too long after the pavement has been placed. Other common causes for crazing include insufficient curing or using an overly wet cement mix.
As you can see, poor installation practices can have a big effect on whether a condition like crazing develops in your pavement. This underscores the importance of working with a qualified paving contractor and is what Save On Paving is all about.
These are cone-shaped fragments of aggregate that break out on the surface of the pavement. Pop-outs are typically the result of particularly porous aggregate materials with high absorption rates taking in too much moisture, and then expanding to the point of "popping out" of the concrete slab.
Examples of common materials that are subject to pop-outs include shale, coal, ironstone, and fine-grain limestone. Most of the time, pop-outs will happen within one year of the initial placement and can sometimes be brought on by prolonged wet weather.
While they are unsightly, pop-outs don't really pose a threat to the structural stability of the pavement and other than being a potential eyesore, they generally do not hamper the service life of the slab.
Also known as "offset cracking", these are larger cracks that typically cause the concrete to become uneven on its surface. Settlement cracking is often a symptom of a deeper structural issue, such as the slab being laid over subgrade soil that was of a poor consistency, or lack of compaction of the subbase before the pavement was placed.
Another common cause for settlement cracking is installing the pavement over an uneven surface, or the shifting or settling of the underlying subgrade after the installation has taken place. In addition, it is not uncommon for settlement cracking to occur due to tree roots growing and expanding underneath the concrete.
To remedy this issue, your paving contractor may need to excavate the affected area and restore the subbase to prevent future cracking.
These types of cracks come from soil expansion beneath the pavement and they are the result of the regular freezing and thawing cycles of the soil. Heaving cracks are similar to settlement cracks in appearance and they are typically more prevalent in colder northern climates.
Once warmer weather arrives, the frost heave will obviously settle down a bit, but the main concern to look out for is moisture penetration into the cracks that have already occurred. This moisture could end up seeping into the underlying soil, possibly compounding the problem by the time the next wave of cold weather arrives.
Scaling is another common concrete repair issue. Also known as "pitting", scaling refers to a loss of surface material that almost looks like the top layer has been roughly shaved off, producing small pock marks that expose the aggregate directly beneath the surface layer.
Scaling generally starts as a small, localized patch but it can eventually merge with other small patches to create a larger patch that is hard to overlook. When light scaling is present, the coarse aggregate underneath generally remains hidden but with heavier scaling issues, the aggregate will be clearly exposed making it stick out like a sore thumb.
Scaling almost makes the pavement surface look like it has "scabs" and if light enough, causes little more than a cosmetic problem. However, if left too long it can cause significant structural damage.
When left unaddressed, scaling can lead to deterioration that includes large chunks of concrete separating from the slab itself. Scaling is very common in areas of the country where regular freezing and thawing cycles occur, and is often exacerbated by the use of de-icing salts on the pavement surface.
Sometimes scaling can occur due to delamination, which is basically where too much air or water remains within the concrete after it has been finished. Tiny little pockets of air and water begin to form just beneath the surface, forming "blisters" that sometimes break open to produce scaling.
Causes of Scaling
* Inexperienced contractors often use concrete that contains little to no entrained air. For the uninitiated, air-entrained concrete is a special mix that includes billions of microscopic air pockets that help to relieve pressure within the concrete by giving water a place to expand when it freezes.
* As briefly mentioned earlier, de-icing salts – particularly those that contain chemicals such as ammonium nitrate or ammonium sulfate – can introduce significant chemical trauma to the surface of the pavement which often will result in scaling.
* Subpar finishing procedures can sometimes result in scaling. For example, inexperienced paving contractors will sometimes work bleed water back into the top surface of the pavement slab, which boosts the water-to-cement ratio and thus reduces the strength of the surface layer.
In addition, overworking the surface layer during the finishing process will diminish its air content, making it more vulnerable to scaling during freezing conditions.
* Yet another example of how poor installation practices can reduce the durability of pavement can be seen in the effects of insufficient curing. Shortcutting the curing process will often result in a weak or substandard surface skin, which can be susceptible to scaling when exposed to regular freezing and thawing cycles.
One of the most common preventative measures that can defend against scaling is to refrain from using de-icers during the first winter after the concrete installation has taken place.
A more severe form of scaling is known as spalling, which are surface depressions that run a little deeper than those of scaling. Similar to scaling, spalling is also caused by pressure underneath the surface of the slab.
If steel rebar was used in the installation, it is not uncommon for spalling aberrations to follow a linear path that basically mimics the direction of the rebar. If the rebar begins to rust, this process of corrosion can create pressure as the rust starts to form underneath the surface.
This can push away portions of the pavement, exposing the corroded metal within the pavement slab. Spalling that exposes rusted rebar to air and moisture can accelerate the corrosion process, setting the stage for even faster deterioration of the pavement.
This can be any type of light or dark patch on the concrete and it often results from improper installation practices. Other common causes for discoloration include exposure to chemicals such as oil or other fluids from leaky vehicles.
Motor oil in particular, when not cleaned up quickly, can begin to eat away at the pavement surface which may eventually result in pitting or major chunks of the pavement becoming dislodged.
If you start to notice discoloration on your pavement installation, be sure to address it as soon as possible so that it won't begin spreading across other areas of the slab. It is highly recommended for you to consult with a professional paving contractor regarding this issue, because incorrectly applied cleaning solutions can do more harm than good to your pavement surface.
Dusting, as the name implies, is when a powdery, dust-like material is present on the surface of the slab after it has dried and hardened. Dusting is typically caused by – you guessed it – poor installation practices, where bleed water is worked back into the surface of the slab during the finishing operation.
Inadequate curing is another common cause of dusting. When the pavement slab is not given enough time to properly cure, the surface of the concrete can become soft and chalky. Cold weather installations in particular can become susceptible to dusting, as the concrete will set a little slower in low temperatures.
If relative humidity levels are high, the pavement slab will often be subject to water condensation which can cause dusting if this water is worked back into the surface of the slab via troweling.
This is when hollow bumps emerge on the surface of the pavement. The bumps are typically on the low-profile side and they usually measure about two to three inches in diameter.
As with practically all of the other common pavement problems discussed here, blistering can also be caused by poor installation practices. For example, it is often the result of troweling the surface of the pavement before the underlying mixture has firmed up enough.
Concrete Repair: Bottom Line
If you detected a running theme throughout all of the above concrete repair problems, it would be that improper concrete installation is a make-or-break factor in regards to the long-term quality and durability of your pavement slab.
Unfortunately, many people find this out too late after they've been left with a substandard paving job that was performed by an unskilled or inexperienced paving contractor.
If you're having any pavement repair problems, you've come to the right place. Save On Paving can connect you with highly skilled, experienced, and trusted paving contractors who know how to accomplish your concrete repair job with the proper technique and workmanship.
Contact us today to see how our paving contractors can help you get your concrete installation back in top shape again.
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