Concrete is the most durable product you can use for the paving of parking lots, driveways, roadways, bridges and more. But, over time, even concrete can become distressed and experience cracks and scaling. Concrete maintenance is key to maximizing the life of your pavement and has many benefits, including preserving the structural integrity of your pavement and substantial cost savings over its life. According to a Pavement Coatings Technology Council (PCTC) article shared by ForConstructionPros, cost savings occur when pavement preventive maintenance is applied early in the pavement’s life. “It is much less expensive to keep pavement in good shape if treatments are applied early in its service life or to repair a pavement when distresses are just beginning to appear.”
Why Does Concrete Crack?
While concrete is known for its durability and long life, there are factors that can cause cracking. These include deformation, swelling and shrinkage. In winter months, snow and ice cause water to seep into the concrete. When the temperature drops, the water freezes, causing the concrete to expand. As temperatures rise, the concrete shrinks causing cracking.
To minimize large cracks, proper installation plays a huge part in the lifespan of your concrete driveway or parking area. Concrete must be installed on a uniform, compacted, well-drained base. If not, when excess water in the soil under the concrete freezes and thaws, it displaces the concrete above it, leaving it susceptible to large cracks when heavy vehicles drive on it. While concrete can be installed in any weather condition, if proper hot and cold weather protections are not employed, it may not cure properly and be susceptible to defects.
Concrete joints help control cracking and allow for normal contraction during extreme temperatures. The joint layout should be submitted to the architect or engineer for approval prior to construction. Joints do not need to be sealed and give the concrete a controlled way to move with expansion and time.
Taking care of your concrete will also help minimize cracks and extend its life. The first year is critical for protecting the life of your concrete drive or parking area. Basic tips include:
- Don't drive on your concrete until it has reached opening to traffic strength or at least two or three days.
- Don't allow water to be trapped beneath the slab. Check your home's downspouts to make sure excess water is being drained away from the pavement.
- Do not apply deicing chemicals for snow or ice removal the first winter. Use sand if extra traction is needed. After the first winter, use only sodium chloride (rock salt).
- Keep snow and ice cleared from the concrete, particularly during the first winter.
- Never use deicers that contain magnesium chloride, calcium chloride, ammonium sulfate, or ammonium nitrate. These products will cause concrete to deteriorate.
- Apply a penetrating sealer about 30 days after your concrete is installed when the surface is dry, and temperatures are above 55 degrees. Reapply as recommended by the manufacturer, usually every five to seven years.
To learn more about minimizing cracks, read our blog post here.
Crack Repair Options
Kim Basham, president of KB Engineering, LLC, provided a list of options for repairing cracks in a recent ForConstructionPros article. These include:
- Clean and fill, a simple technique that, because routing isn’t required, provides a repair width the same as the crack width, and is faster cleaning and more economical.
- Rout and seal/fill, the most common repair method for isolated, fine and large cracks, is ideal for horizontal surfaces but can also be used for vertical surfaces with non-sag repair materials.
- Epoxy injection can bond or weld extremely narrow cracks and restore the concrete’s integrity, strength and stiffness. This method is a rigid, full-depth repair where the injected crack will be stronger than the adjacent concrete which could lead to other cracks to form near or far from the repaired crack.
- Polyurethane injection is a permanent method that seals active or dormant cracks that are wet and leaking. This repair option is primarily used to stop water leaks in narrow cracks, is flexible and will tolerate future crack movements.
- Autogenous healing is a natural repair process that occurs in the presence of moisture due to the hydration of unhydrated cement particles that are exposed to moisture and the formation of insoluble calcium carbonate on the surface. Healing will not occur if cracks are subjected to fast-flowing water and movement.
- No repair. According to Basham, sometimes “no repair” is the best option. Not all cracks require repair (at least not immediately) and monitoring those may be the best approach.
The American Concrete Institute (ACI) Committee 116 defines scaling as the “local flaking or peeling away of the near-surface portion of hardened concrete or mortar.” Scaling is a physical action created by hydraulic pressures from repeated freeze and thaw cycles within the concrete. The expansive forces found in severe exposure climates like Michigan are caused by the formation of ice and exacerbated with deicing chemicals increase the concrete saturation and the number of freeze and thaw cycles. The most common causes of scaling are related to one or more of the following factors:
- Lack of, or inadequate, curing and protection. Do not let the concrete surface dry out after placement. Cement reacts with the water in the mix. Once the water is gone, the chemical reaction stops and the concrete stops gaining strength. A surface that dries out before it reaches strength will be weak. Curing compounds and/or secured plastic sheeting can be used to keep the surface from drying during the first few days, allowing it to gain full strength.
- Improper finishing operations that trap water at the surface, resulting in a high water-cementitious ratio and low strength. Delayed or extended finishing will also allow early drying of the exposed concrete surface, prior to curing application, which can result in a weak surface.
- The use of non-air-entrained concrete or too little entrained air, resulting in a non-durable concrete mix. A poor air-void system may also be created at the surface through over-manipulation of the plastic concrete during finishing operations.
- Using concrete with low strength or excessively high water-cementitious ratio will allow for deeper penetration of water and deicing chemicals.
- Exposure of new concrete to freeze and thaw cycles before it has been adequately cured (and not allowed to air dry) and to deicing chemicals (intentional or from vehicle traffic) greatly increases the likelihood of scaling.
- Exposure to aggressive/corrosive salts and fertilizers. While calcium or magnesium-based deicers should never be used on concrete, sodium chloride (table, rock or safe salt) may be used in moderation.
- Misunderstanding the use of supplemental cementitious materials (SCMs) may lead to scaling. Properly designed, finished and cured mixes containing SCMs improve strength, durability and water tightness. However, they also extend the concrete set time. Knowing set time and when to perform finishing operations is crucial to the overall durability of a mix containing SCMs.
Exterior concrete must be proportioned with durable ingredients designed for the climate with an entrained air-void system using proper placement, finishing, curing and protection to resist hydraulic pressures that can promote scaling. Read more about how to prevent, repair and treat scaling here.
What is Concrete Safe Salt?
Those living in a northerly climate like Michigan regularly deal with snow and ice accumulation. How to best remove snow and ice while protecting your concrete pavement requires more than simply throwing down some salt. MCA shares the dos and don'ts of concrete salt and winter care here. These include:
- Do keep your pavement clear of snow and ice.
- Do not use deicers of any type during first year. Instead, use sand for slip resistance and traction.
- Do use only light to moderate applications of deicing chemicals after your concrete’s first year in service.
- Do consider using common rock salt (sodium chloride) instead of other deicing salts like calcium chloride or magnesium chloride which are more harmful, physically and chemically, to concrete than rock salt. Sodium chloride also has a significant cost advantage, particularly in the Michigan market.
Which Salt am I Using?
A simple way to determine which deicer product you are using is to check the pavement for a damp or wet appearance on a mild winter day. If the concrete is damp or wet, it is very likely that calcium or magnesium chloride has been applied. Compounds containing sulfates and nitrates commonly used in fertilizing products should never be used as concrete deicers because of their very aggressive interactions with the concrete.
Ultimately, if you have a concrete lot or driveway in a cooler climate, you can help maintain its good condition by keeping it clear of snowfall and, if necessary, using sodium chloride as little as possible. If you keep your concrete driveway clean and clear, it can stay in top shape for decades.