Concrete Parking Lots
Concrete parking lots are a potentially lucrative market for concrete contractors and make good economic sense for building owners. Today, about 90% of parking lots are paved with asphalt, but improved equipment and rising prices of asphalt have made concrete more competitive. When you throw in the other advantages of concrete, especially the long-term costs, it is, as Platinum Concrete likes to put it, a no-brainer. We’ve constructed concrete parking areas all over the Bay of Plenty and if we look back at our projects today, we will see that they are still looking amazing. Being low maintenance and having the longevity asphalt doesn’t, our clients have made the right choice when choosing concrete material for their commercial parking solutions.
A concrete parking lot is really nothing more than an exterior slab on ground (or slab on grade). Perhaps what defines it as a parking lot, and what makes it a little different to design and build, is the sloped surface for drainage, the ability to handle heavy vehicular loads, and severe environmental exposure.
Why choose concrete for your parking areas?
Let’s look at how to design and build concrete parking lots and also why concrete parking lots are preferable to asphalt. Contractors need to understand the advantages of concrete parking lots in order to clearly justify them to their customers.
While the initial cost of installing asphalt is still less than that of concrete, rising asphalt prices have narrowed the gap some. For years, contractors have emphasized concrete’s lower life-cycle costs based on its longer life span and lower maintenance needs. When these factors are considered, concrete wins the race.
Even structurally equivalent asphalt pavement that is designed to have the same load-carrying capacity as concrete and has an initial cost that is comparable to concrete, will still need to be resealed and resurfaced. Over its lifetime, the most expensive pavement is a typical asphalt pavement which is cheaper to build initially, but is under-designed in load-carrying capacity and ends up with high maintenance costs.
Here are a few of the reasons why we at Platinum Concrete recommend a main contractor, or building owner should pave his parking lots with concrete:
- Asphalt is similar to concrete except that it uses liquid asphalt as the binder rather than cement. Liquid asphalt is a residue left over from refining crude oil to make gasoline. Improvements in refining techniques have led to asphalt shortages.
- Maintenance costs for concrete are nearly zero—only some joint sealing and annual cleaning. Asphalt parking lots need to be coated with liquid asphalt every few years and be completely resurfaced every 10 years or less, causing interruptions of use of the parking lot for the business.
- Concrete surfaces are much lighter coloured, and hundreds of colour variations are available. Asphalt being limited to a darker colour attracts and generates excessive heat which can be uncomfortable to some users.
- The lighter colour also results in a lower temperature for the parking area during the summer, reducing the heat-island effect and lowering cooling costs for adjacent buildings.
- Concrete pavements can carry heavy loads without rutting or developing potholes. With concrete’s rigidity and high strength it only takes 125mm pavement to provide the same load-carrying capacity as 200mm of asphalt.
- Concrete parking lots can be coloured and textured to meet the owner’s desires.
- Concrete parking lots are green—runoff is low toxicity and cooler than from asphalt surfaces. Also, concrete can contain recycled materials such as fly ash, slag, or recycled concrete aggregate.
- Comparing the combined cost of initial installation and 20-year maintenance costs, concrete is considerably less expensive. Maintenance for an asphalt lot can be as much as 80% of the initial construction cost; and on one Florida project, asphalt was shown to be twice the cost of a concrete lot over 20 years.
When comparing parking lots to other concrete applications, they are obviously subjected to higher loads than floors. The loads are mostly static (or low speed), so flatness and smoothness are not as critical as for streets and highways. With a parking lot, a good subbase, proper thickness, drainage, and traction are more important.
Here are a few things to understand about design of concrete parking lots:
- An important consideration is that there’s more to the parking lot than just pavement. Parking lots include slabs, joints, curbs, light poles, and drainage facilities — and all of these need to work together.
- Parking lots are typically placed directly on the existing soil rather than on a compressed subgrade. The important thing is to get the compaction of the subgrade uniform so that some areas don’t sink and crack the pavement.
- For cars and light trucks, a 100-125mm pavement is generally acceptable. For bigger delivery trucks, the pavement will need to be 125-150mm thick. This is dependent on the subgrade, the total number of load repetitions, and the weight of the vehicles.
- Parking lots generally drain simply to the edge of the pavement or into gutters. Sometimes drains are located within the paving area. In either case, pavements should slope a minimum of 1%; 2% is better; Slope of entrances to the parking lot should not exceed 8% to prevent cars from dragging.
- Jointing in a concrete parking lot is no different than for any slab on grade. Parking lots should be isolated from any buildings, drains, or light post foundations by installing isolation joints. Contraction joints should be continuous (not staggered), in square panels, and spaced at the ideal intervals as determined during the design and planning process.
- The edges of parking lots should be thickened if cars will park close to the edge. Edges can be thickened by using an integral curb or by thickening the bottom (see diagram).
- Parking lots can be given just about any exterior decorative treatment, although large lots would be expensive to stamp or texture. Integral colour is a good option and may keep the lot looking a little cleaner.
As with any slab, there are several ways to construct concrete parking lots. The simplest but least precise method is to simply wet screed the concrete to the desired thickness. Setting side forms and using hand screeds, truss screeds, or other vibrating screeds is another option, and probably the most common. Slip forming is fast and produces very high-quality pavement, although the equipment is expensive and positioning the equipment is difficult except for on very large lots.