When designed and properly constructed, concrete parking lots are the strongest and longest-lasting parking/pavement surface available. Just like any other surface, however, it does have a lifespan and will not last forever. The key is to recognize the signs (besides normal wear and tear) that your parking lot is nearing its end and addressing it before significant deterioration occurs.
Faults are elevation changes that form between two or more adjacent slabs of concrete at the joints and/or cracks. Signs of faulting are 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.
Conditions of the fault will likely worsen and spread to other areas of the lot. Addressing this issue involves removal of existing pavement panels, replacement/restoration/consolidation of the subbase and repaving.
Until the use of synthetic and steel fibers, many concrete parking lots utilized steel mesh for secondary reinforcement. As cracking occurs in concrete over time, water (and salt) infiltrates these cracks and corrodes the mesh, leading to breakdown/failure in the steel.
If the mesh is visible from the surface through cracks or large spalls, it is a good indication that the concrete is in a compromised state and will need to be replaced, whether in specific areas or wholesale replacement. When repaving your parking lot, it is highly recommended to use fiber reinforcement as opposed to steel mesh.
Significant cracking in parking lots comes in many forms (transverse, longitudinal, corner and map cracking). Size and frequency of the cracks are often the result of excessive fatigue over time, instability of the subbase, and thin spots in the concrete (less than design depth). Addressing severe cracking conditions include repaving the lot entirely or applying significant patchwork.
Forms of durability issues include salt attack and Alkali-silica reactivity (ASR). Salt attack comes from deicing salt infiltrating concrete and breaking it down over time. Negatives effects from salt attack include weakening 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.
Alkali-silica reactivity (ASR) is a network of smaller cracks throughout the pavement as 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.
These durability issues can be avoided through the application of supplementary cementitious materials (SCMs) in the concrete design mix. SCMs, predominately type F fly ash or slag cement, bind the alkalis in the Portland cement and remove/reduce the effects of salt attack and/or ASR. SCMs help to produce a denser, stronger, and more durable concrete product overall.
Freeze-thaw damage occurs when water trapped inside concrete freezes and has nowhere to expand, building pressure internally and ultimately breaking the bond between the concrete paste and aggregates. As this process repeats over time, the concrete deteriorates. Results of freeze-thaw damage includes random cracking, severe surface scaling and joint deterioration.
To alleviate internal pressure from freeze-thaw, air entrainment is applied to the new concrete. Through air entrainment, billions of microscopic bubbles are introduced into the mix, resulting in billions of small voids in the hardened concrete. These voids allow room for ice to expand and reduce internal pressure in the concrete. Air entrainment is crucial in any concrete pavement exposed freeze-thaw conditions, which includes all outdoor pavement in the Midwest.
It is important to be aware of the type of loading any existing parking lot experiences. For example, a lot that has mainly supported pedestrian vehicles since being built is now expected to accommodate much heavier semi-trucks and construction equipment. Most likely, it was not built to accommodate this heavy loading and may crack under pressure or fatigue at a quicker rate. Thicker pavement with stronger secondary reinforcement may be required to make sure it can support its future occupants.
Decisions to repave a parking lot could come down to acknowledgement of its age. If signs of wear and tear occur and the lot is 30+ years old, it could be time to consider repaving the lot before significant deterioration occurs. This is all a matter of personal preference though, as some concrete lots have been known to last 50+ years (given certain conditions and exposure to elements).
There are many types of cracks, popouts, significant scaling and normal wear and tear in concrete that will have little to no impact on a parking lot’s strength and durability. Its aesthetic appeal, however, ultimately comes down to owner preference. One lot may not necessarily meet any of the above critical conditions, but when making a statement to clients or customers, a new concrete lot will always attract positive attention.
After paving a new parking lot, it is important to use any preventative measures to keep excess water away from the concrete. Make sure that no standing water (or pond water) is present and that the lot in its entirety is well-drained. In addition to drainage, sealers can also be applied to the surface to repel water. If well-maintained, a concrete parking lot can easily last 50+ years.
For a more detailed breakdown of how to maintain and preserve your concrete parking lot, download our Quick Guide to Concrete Parking Lots.