If you’re considering concrete for your parking area, you’re on the right path! When designed and properly constructed, concrete parking lots are the strongest and longest-lasting parking pavement surfaces available. They also enhance curb appeal.

We’ll provide the details you need about concrete parking lots, installation and how to keep them looking great. But first, let’s talk about why choosing concrete is a great decision for your property.

A SMART FINANCIAL INVESTMENT

Concrete parking lots can last 25-30 years at the least—that’s roughly 10 years longer than asphalt lots. In addition to their long life, the required maintenance is minimal. This translates to low annual costs and few business interruptions.

Asphalt parking lots, on the other hand, require more frequent maintenance throughout their shorter service life, from sealcoating every couple of years to adding new layers of asphalt every five to 10 years. As a result, total maintenance costs of asphalt pavement can be as much as 80% of the initial construction cost. In some cases, asphalt can cost twice as much as concrete over its life span. 

Competitive initial costs. While prices have fluctuated over the years, the cost of concrete pavement has become more comparable to asphalt. In fact, when looking at total project costs, concrete parking lots are very cost competitive. When comparing the products inch for inch (in depth), concrete is less expensive. In addition, a considerable amount of subgrade work is required to install asphalt parking lots, as well as separate curb-and-gutter installations. Concrete requires less subgrade preparation, and curbs and gutters can be placed along with the parking lot in one pass.

Depending on project specifications and scope, a concrete parking lot can range between $4 and $7 per square foot (material and labor). A less expensive option is to apply a concrete overlay to an existing lot. Concrete overlays can be used on both concrete and asphalt surfaces.

Low energy costs. Due to their lighter color and smooth surface, concrete parking lots reflect more light than other materials. Fewer light poles and/or wattage are needed to illuminate the parking area. This significantly lowers utility bills—by roughly 30-35 percent per year as compared with asphalt lots.

Enhanced safety/comfort. Concrete’s brighter, more reflective surface makes pedestrians and obstacles more visible to drivers both day and night. Safety does not stop at visibility. A light broom concrete finish provides a slip-resistant surface, and on hot summer days, it is better to walk on concrete than on hot asphalt. (Your pets’ paws will agree!)

Curb appeal. With its clean look and lighter color, concrete is an aesthetically pleasing contrast to the blacktop lots owned by most businesses and multifamily property owners… which brings us to the next benefit, customization.

Custom options. For such a hard and durable material, concrete is extremely versatile. It can be colored, textured, patterned and even shaped to complement your building or simulate other materials (wood, brick, stone, etc.). Plus, there’s no need to install new pavement to update the parking area’s look. Simply apply chemical stains to create beautiful color tones or engrave the surface to add a logo or a bit of pizazz.

CHOOSE SUSTAINABILITY
In today’s market, it is advantageous for any business to show they are choosing long-lasting, environmentally friendly options. Concrete has always been considered a sustainable building material due to its long life, durability and resource efficiency. And now, the global cement industry—which produces a key ingredient of concrete—is committed to achieving zero carbon emissions by 2050. Below are ways concrete parking lots are eco-friendly: 

• Less energy used on repairs. Because a concrete parking lot is low maintenance, repair efforts require minimal equipment and energy usage. 
• Reduction in urban heat island effect.Concrete’s ability to reflect light and reduce ambient temperatures helps fight against spiking temperatures in urban and commercial areas. 
• Recycled materials.Concrete pavement mixtures often incorporate industrial byproducts, (i.e., fly ash, slag cement, silica fume) and can even include old wash water and old concrete (crushed into aggregate), all of which help to lower disposal needs, reduce demand for virgin materials and conserve natural resources.   
• Manufactured locally.Transport time and distance is minimized, reducing air pollution.  
• No material is wasted. No need for pallets, boxes, tape and other items to dispose of or burn. Concrete can be produced in the quantities needed for each project and comes mixed and ready to pour from trucks. 

PREPARING FOR INSTALLATION: WHAT TO EXPECT

Concrete pavements can be placed in service within a couple of days, but contractors must first address what’s underneath. The subgrade and subbase will determine how well your parking area holds up over time. An uneven, poorly drained base will lead to excessive cracks in the pavement and significantly impact its service life.

Subgrade is the natural ground, graded and compacted, on which the parking lot is constructed. Because concrete slabs are rigid, they do not necessarily require strong support from the subgrade. However, the subgrade must be reasonably uniform without abrupt horizontal changes from hard to soft, and the upper portion of the subgrade must be of uniform composition and density. Soft spots, frost-susceptible soils and hard/soft spots lead to lack of support in the subgrade.

Subbase is the layer of sand or gravel placed on top of a prepared subgrade. No special subbase material is required for most light-duty concrete parking areas.

Inspection checklist. Your concrete contractor should follow a checklist before installing a concrete parking lot to ensure suitable subgrade soils are in place and properly blended and compacted, organic matter (i.e., vegetation) has been removed that could push through the pavement and cause cracks, utility trenches are properly backfilled and compacted, there are no wet areas in the subgrade and a final grade has been properly prepared. A soil engineer may be consulted.

Once all items have been checked off, the contractor likely will perform a test roll over the subgrade, using a large vehicle to check for rutting in the base and overall grade. These final checks will ensure water will not pond on the parking area.

Curbs and gutters. Properly placed curbs help control access to the roadway—a key component of traffic control. Joint placement in curbs and gutters must line up with pavement joints so as not to cause uncontrolled cracking. If your parking lot incorporates sidewalks or building entrances, be sure your concrete contractor consults local and state codes to meet all accessibility standards.

Weather conditions. Hot and cold temperatures, humidity and wind conditions affect how concrete pavement should be constructed and treated. Discuss with your contractor how project work may be adjusted to account for any foreseen weather conditions.

Curing. Immediately after the concrete has been placed, struck off, smoothed and textured, the concrete contractor should cover the surface with a white pigmented curing compound or a white polyethylene or waterproof paper for seven days. Waterproof covers are typically used when temperatures are above 40 degrees Fahrenheit. Otherwise, a spray-on curing compound can be used. Sealers are applied after a 30-day air-drying period.

Opening to traffic. Pavement under construction should be partitioned off with barricades while the concrete is poured and during the subsequent curing period, which ranges from two to seven days. All vehicle traffic should remain off the newly placed concrete until it is fully cured and at the required strength.

TAKING CARE OF YOUR CONCRETE PARKING LOT

Once your concrete parking lot is installed, it’s easy to fall into the trap of thinking low maintenance means no maintenance. However, that is not the case. Follow these tips to keep your lot in the best shape possible. 

Periodically clean the surface. A clean parking lot is a safe parking lot. Markings are more visible and the concrete reflects light better, making the lot brighter at night. Keeping the pavement free of grease and oil will reduce the chances of slip and fall incidents, and removing buildup increases pavement durability.

Depending on climate, the parking lot’s use, types of vehicles that drive on it and other factors, the cleaning schedule may simply be an annual power sweeping to remove loose debris. Power washing is a great way to remove adhered materials, such as oil and grease. Do not overlook vacuuming debris from stormwater drainage structures within the parking lot. If necessary, stormwater lines should also be jetted out. A well-drained pavement that is not subject to pooling water lasts longer.

Restripe every two/three years. New pavement markings are much easier to see in low light, making wayfinding more apparent to drivers as they navigate the parking area. Waterborne pavement marking paint is generally more economical, while sprayable thermoplastic paint markings tend to be more durable and reflective.  

Seal the pavement. Sealers help the surface repel water. They reduce moisture intrusion, improve stain resistance, reduce freeze-thaw and deicer-related deterioration, and help to slow the growth of mold, mildew and the rate of efflorescence formation.

• Penetrating sealers are absorbed into the concrete and essentially become invisible once applied. While they do not wear away due to traffic, freeze-thaw cycles cause them to break down so they must be reapplied periodically. 
• Surface sealers sit on top of the concrete, becoming the wearing surface that traffic rides on. They are commonly used where colored, stamped or other decorative concrete has been placed to accentuate decorative effects. Care should be taken with these sealers to provide the necessary level of traction or grip when wet. Because they wear away with traffic use, they eventually need to be reapplied. 

Seal cracks. Cracks happen. It is generally recommended to leave tight, hairline cracks alone. Wider cracks that develop for structural and nonstructural reasons should be sealed to keep water out and reduce cracking from freeze-thaw cycles. These cracks may be filled as is, or they may need to be routed open prior to filling. Crack-filling materials need to fit the crack type. For instance, if there is some crack movement, a semi-rigid or flexible crack filler may be needed. A rigid crack filler, such as epoxy, can be used with a crack that is not moving. 

Reseal joints. It is important to keep joints sealed so that they can function as intended. Joint sealants typically have a design life of five to 10 years. Sealed joints should be observed regularly and replaced when they are no longer performing as designed. When this happens, the existing joint seal needs to be removed and the joints cleaned and prepared for the new seal. The new seal material is then placed. Joint sealant materials or types include hot rubber, silicone and preformed seals.

Full-depth replacement when necessary. When an area of pavement—up to a full panel or two—is experiencing a severe enough level of distress (such as cracking), it is time to replace that section. The affected concrete should be cut out and removed and the support soils should be reconditioned. New dowels and tie bars should be installed as necessary. Finally, the concrete should be replaced along with the necessary joints and seals.

WHEN TO REPAVE PARKING LOTS

Every pavement has a life cycle—even concrete! There may come a time when the entire lot needs to be repaved. The key is to recognize signs of distress and address them before significant deterioration occurs.

Faulting. Faults are elevation changes that form between two or more adjacent slabs of concrete at the joints and/or cracks. Faulting is an indication of an unstable subbase—when the subbase begins to settle or shift, it creates a non-level surface for the concrete. A saturated subbase subjected to freeze-thaw conditions can compound the differential movement of the slab. If not addressed, conditions of the fault will likely worsen and spread to other areas of the lot. Fixing this issue involves removing the existing pavement panels, replacing/restoring/consolidating the subbase and repaving.

Exposed steel/wire mesh. Until the use of synthetic and steel fibers, many concrete parking lots had steel mesh for secondary reinforcement. As cracking occurs in concrete over time, water (and salt) infiltrates the cracks and corrodes the mesh. Steel mesh that is visible from the surface through cracks or large spalls is a good indicator that the concrete is in a compromised state and needs to be replaced, whether in specific areas or the entire pavement. When repaving your parking lot, it is highly recommended to choose fiber reinforcement as opposed to steel mesh.

Significant cracking. Severe cracking in parking lots comes in many forms (transverse, longitudinal, corner and map cracking), caused by excessive fatigue over time, instability of the subbase and thin spots in the concrete (less than design depth). Fixing these cracking conditions include repaving the lot entirely or applying significant patchwork.

Durability issues. Pavement durability can be weakened by salt attack and alkali-silica reactivity (ASR). Salt attack comes from deicing salt infiltrating concrete and breaking down the concrete paste and aggregates (due to its mild acidity), attracting additional water into the concrete (leaving less room to accommodate freeze-thaw) and accelerating corrosion of any exposed steel mesh.

ASR is a network of smaller cracks throughout the pavement formed as a result of the reaction between silica found in aggregates and alkalis in portland cement in the presence of moisture. This reaction breaks down the aggregate and surrounding paste, resulting in long-term deterioration.

Freeze-thaw damage. When water gets trapped inside concrete and freezes with nowhere to expand, it builds pressure internally and ultimately breaks the bond between the concrete paste and aggregates. As this process repeats over time, the concrete deteriorates. Results of freeze-thaw damage include random cracking, severe surface scaling and joint deterioration.

Loading changes. It is important to be aware of the type of loading your parking lot experiences. For example, a lot that was built to support personal vehicles may not be able to accommodate the heavier loads of semi-trucks and construction equipment. Thicker pavement with stronger secondary reinforcement may be required for changes in traffic loads.

Age. If signs of wear and tear occur and the lot is more than 30 years old, it could be time to repave before significant deterioration occurs. This is an arbitrary decision based on aesthetic appeal and personal preference.

A well-maintained concrete parking lot can easily last 50 years or more. Find a concrete contractor for your parking lot project—and download our Quick Guide to Concrete Parking Lots for more on maintaining and preserving your pavement.