Pavement & Parking Structures

May 31 2016

Cleaning Concrete

shutterstock_196561019 It’s hard to find a building today without concrete surfaces stained by rust. Rust stains can adversely transform the aesthetics of a beautiful building. How can rust stains be removed? Let’s find out!

Once rust staining has occurred, it is important to remove the stains without altering the color or finish texture of the concrete. Two techniques which can be implemented are dry methods (i.e. sandblasting, wire brushing, grinding, etc.) and wet methods (i.e. waterblasting, chemicals, etc.). If surface texture is not a priority, the dry methods can be a quick and cost-effective way to remove stains. If the final finish is important, as is commonly the case with architectural concrete, chemical treatments are recommended.

Mild stains usually can be removed with an oxalic acid or phosphoric acid solution, applied to a water saturated concrete surface. Deeper stains typically require a poultice, which absorbs the chemical solutions and then forms a paste over the stain. Older buildings require more attention with stain removal because the chemical treatments may remove other contaminants in the concrete, creating a lighter color than the adjacent concrete.

The rule of thumb when putting a cleaning solution on your stained carpet or clothes applies with concrete. Be sure to test different chemicals on small, inconspicuous areas to evaluate the treatment. Also, the longer you let a stain sit, the more difficult it is to remove, so seek help quickly when rust stains appear!

April 12 2016

Don’t Forgo The Soil Sampling

shutterstock_360675260 Occasionally we run into a building owner that regards soil sampling and testing as an unneeded extra expense and asks if we can forgo this effort. Generally, soil is sampled by using a drill rig that bores into the ground up to 40-feet, or more deep. Small samples of the various soils that are found at different levels or strata are taken to a laboratory for testing to determine the composition of the soil, moisture content, and other properties.

In the field, the various soil types encountered are visually classified according to accepted standards and stiffness of the soil at different depths of the boring. These engineering properties are necessary to determine the type of foundation needed for a retaining wall or building, depth of a storm water infiltration facility, or even in the selection of a proper pavement profile.

Nearly all local municipalities will require soil testing for structural retaining walls (over 3-feet tall), storm water infiltration facilities, and buildings. We routinely obtain soil borings to help evaluate suspected building settlement conditions to learn the impact that the soil may have on the apparent building movement and help design the foundation underpinning repairs. If soil is not sampled and tested for its engineering properties, unexpected expenses can arise and the job progress can stop after the excavation begins and unsuitable soil layers are found.

January 18 2016

Carbon Monoxide Check

car exhaust Did you know carbon monoxide (CO) detectors have shorter life span than most household equipment (such as air conditioning units, water heaters, washers and dryers etc.)? On average, carbon monoxide detectors have service lives of about five years. If you have not replaced your carbon monoxide detectors in the past five to six years, they’ve probably stopped working correctly.

Ventilation systems are critical in enclosed parking garages and most systems installed over the past ten years or so are controlled by carbon monoxide detectors. Without properly functioning, accurate detectors the exhaust fans of garage ventilation system will not activate to remove toxic fumes from vehicle exhaust before they reach unhealthful levels.

Carbon monoxide is an odorless, colorless gas that’s a bi-product of combustion, such as occurs in car and trucks engines, standby generating systems, gas-fired furnaces and dryers, etc. CO from such sources can build up in enclosed or semi-enclosed spaces and people therein can be poisoned by breathing it. The most common symptoms of CO poisoning are headache, dizziness, weakness, nausea, vomiting, chest pain, and confusion. High levels of CO can cause loss of consciousness and death.

Given the hazards associated with carbon monoxide, now is the time to replace old sensors in your home and have your garage ventilation systems professionally inspected and tested

December 18 2014

Infrared Asphalt Repairs

Conventional pavement repair entails removal of distressed asphalt, replacing it with new-hot-mix asphalt, and rolling it to achieve compaction and a uniform surface. A major problem with that method is the creation of “cold” joints. The new asphalt will not meld with the in-place material and the joints must be periodically sealed to keep water out.

Infrared repair utilizes equipment that heats the in-place asphalt adjacent to the repair area to a plastic (workable) state and new hot-mix asphalt is placed. The new asphalt would be maintained at a similar temperature and consistency, so the materials readily blend. The asphalt can be raked to enhance consolidation and then compacted.

Done properly, the result is a seamless patch, but there are limitations. For older pavements (15 years old or older), the asphalt binders are probably too depleted or degraded to undergo infrared patching. In some instances, binder constituents can be replenished, but that’s not practicable if the asphalt is too brittle. Also, it may not be financially beneficial to spend a lot of money patching pavement that’s near the end of its useful life.

Infrared patching is not suitable for full-depth distress. Only the top two, to two and one-half inches of asphalt can be sufficiently heated to permit consolidation. Trying to raise the temperature of deeper material would likely overheat the surface asphalt and degrade the binder. Accordingly, full-depth distress must be full-depth patched. The topmost layer of a full-depth patch could be blended in with the infrared process.

Infrared methods have been employed as rehabilitation, in lieu of overlayment; however, it’s unlikely they achieve the same results in every circumstance. As noted above, the in-place asphalt must be in relatively good condition to withstand heating and binder replenishment won’t produce “new” asphalt.

November 21 2014

Cracks Happen

Cast-in-place concrete will, more often than not, crack. In a nod to that characteristic, weakened planes (control joints) are formed or cut into conventionally-reinforced concrete slabs and sidewalks to influence where cracks occur. Cracking outside of control joints can indicate shortcomings in concrete placement, finishing, and/or curing, as well as influences from without. Cracks can manifest in a number of forms, most of which are of no structural concern.

Shrinkage cracks are most common and those for which control joints are used. Excessive shrinkage cracks can be caused by high water content in the concrete mix or poor control joint layout.

Plastic-shrinkage cracks are usually shallow and occur when surface water evaporates from the surface of plastic (soft) concrete faster than bleed water from below can replace it. Accelerated evaporation can occur under conditions of low relative humidity, high heat, when wind speeds exceed 5 MPH, or a combination thereof. Plastic shrinkage cracking can be controlled by various methods, including the use of wind breaks, shading provisions, water misting, etc.

Crazing or map-cracking is characterized by interconnected shallow cracks and can be caused by the same conditions that cause simple plastic shrinkage cracks. They can also be caused by poor finishing, particularly on steel-trowel finished concrete. Over-finishing can depress large aggregate and draw excessive paste and fines to the surface. High water content and rapid curing can also produce crazing.

Durability (D)-cracking is caused by the use of porous large aggregates (usually sedimentary materials such as limestone, sandstone, dolomite, shale, etc.) in regions that experience freezing temperatures. It occurs when absorbed water freezes and the resulting expansion (ice occupies about 9% more space than liquid water) breaks the aggregate. The greatest harm is caused by freeze-thaw cycling. The mid-Atlantic region experiences temperatures near the freezing point of fresh water more frequently than most other parts of the country and therefore experiences more freeze-thaw cycles. Deicing agents (such as road salt) creates brines, which have lower freezing points and thereby further increase freeze-thaw cycles.

D-cracking usually occurs near joints and can be partial or full-depth. It will often cause severe spalling and it is considered a terminal, incurable condition.

Displaced or offset cracks are characterized by a height differential on either side of a crack. When they occur at slabs-on-grade, the cause is usually a poorly prepared or unsuitable sub-grade or displacement by tree roots. Significant displacement (one-half-inch, or greater) can present tripping hazards.

Offset cracks in elevated (bridging or cantilevered) slabs could indicate a structural instability. Embedded steel reinforcement would normally prevent displacement and its failure to do so could have serious consequences.

July 29 2014

What’s In A Word?

Words can have a number of meanings and can even change meanings with time. This is especially true of terms specific to a technology or industry. Following are definitions of a few roofing and paving terms that people outside those trades (such as board members) may hear and not fully understand.

Overlayment – Placement of a new roof over an older covering or placement of a new asphalt surface course over an existing pavement.

Resurface – Install a new layer of asphalt (overlay) onto an existing pavement. Should not be confused with seal coat.

Seal coat – Apply a coal tar or asphalt slurry over asphalt pavement.

Tar – Stuff that dinosaurs got stuck in; the nasty stuff in cigarettes. Should not be confused with asphalt used in paving and roofing.

Coal tar – A byproduct of steel smelting used for producing pavement seal coating and interply waterproofing in some roofing systems.

Fishmouth – What a fish eats with; distorted membrane lap in roofing, resulting in an opening.

Shark fin – A closed fishmouth in roofing.

Spud – Tool for removing aggregate surfacing from a roof; the act of removing the aggregate; tater.

PRMA roof – Protected Roof Membrane Assembly, wherein the membrane is adhered, applied or laid onto the roof deck and is covered with a layer of insulation and ballast.

Ballast – Heavy materials (typically stone, concrete pavers, etc.) placed on a roof to hold down insulation or loose-laid membranes that might otherwise be blown off by wind.

Loose-laid – Not fastened or adhered.

Mud – Roof cement.

#$%! Gooey %&*@ – Roof cement.

Alligatoring – Interconnected cracking in pavement; pattern characteristic of depleted asphalt flood coat in roofing.

Flood coat – Hot (liquid) asphalt applied over top ply in built-up roofing system, usually followed by small aggregate surfacing.

Stoning – Installing aggregate surfacing in a flood coat on a built-up roof.

Resaturant – Material intended to rejuvenate asphalt in pavement or roofing by replacing depleted volatile constituents; waste of money.

Consultant – Someone who knows a hundred ways to make love, but doesn’t know any women.

Pitch pocket – Roof flashing consisting of a receptacle for sealant (or pitch), placed around an opening through which utility lines or other items penetrate a roof.

July 3 2014

More on Pervious Concrete

A previous blog entry “Escaping the Hardship of Hardscapes” was an introduction to pervious pavement. Here we get a little more in depth.

We hear a lot about impervious surfaces such as parking lots, creating run-off that can be detrimental to both human and environmental health. One of the solutions being used increasingly is pervious concrete.

Pervious concrete uses many of the same ingredients that normal concrete uses- cement, water and gravel. The main difference is that little to no sand is used in the production of pervious concrete. This creates voids that allow water to flow through the pavement quickly. Typically, 15-25% voids are achieved, which allows for the flow rate of water through the concrete to be between 3-8 gallons per minute per square foot. The water is then stored in a coarse gravel layer underneath or allowed to percolate into the underlying soil.

So the main question: Is porous concrete strong enough to be do the job of normal concrete?

The answer is yes. Normal concrete used for pavement has an average compressive strength ranging between 3,000 to 5,000 psi, which is the same for pervious concrete. While it cannot be used for all applications, it can be used for a wide range of projects. The most common applications include parking lots, driveways, sub-division streets and sidewalks. Unfortunately, pervious concrete is not a viable option for highly traveled pavement. Pervious concrete has a rough textured, honeycomb surface, so when there is a large amount of traffic on this concrete, tire shear can loosen the aggregate on the surface.

Watch for an upcoming article about the special maintenance procedures needed for pervious pavements!

February 6 2014

Prevent Expensive Replacement Projects!

During a recent plaza repair project, we were reminded why cleaning storm drain pipes on a regular basis is a good idea. Solids, such as minerals that may leach from building materials (concrete or brick) or small fines and debris (particularly in planters), may be picked up by surface runoff and deposit into drains and corresponding drain lines. Over time, these deposits may congest the drain pipe, which leads to blockages and decreased drainage flow. Severe build ups may become hardened to the point where replacement of the pipe is the only option to restore proper drainage.

In order to prevent solid build-ups and pipe replacement, it is important that drain lines, particularly those serving roofs, terraces, plazas, and garages, be hydro-jet cleaned every few years. The hydro-jet cleaning process utilizes high pressure streams of water to remove the solid deposits from the pipe walls and returns the pipe to a free flowing condition. Cleaning drain lines as part of a regular preventative maintenance plan is an effective way to extend the service life of your drain lines and inspect pipe conditions, which may prevent large (expensive) replacement projects in the future

September 25 2013

Pavement Seal Coats

For many years the gold standard in pavement seal coats was coal-tar emulsion. It’s far more resistant to water than asphaltic products and virtually invulnerable to attack by petroleum-base automotive fluids. Superior performance notwithstanding, coal tar is now banned in many jurisdictions and will probably go the way of asbestos and lead paint. It’s been identified as a health risk and potential carcinogen in its uncured (volatile) state.

The most common alternatives to coal tar are polymer-modified asphaltic products, purported to be comparable to coal tar with respect to cost and performance. New formulations reach the market with regularity, but as with any new product, long-term performance is uncertain.

Another possible alternative to seal coating could be application of a pavement “rejuvenator”. Rejuvenators will not, as the term implies, counteract aging or restore pavement to new condition. These product typically penetrate to depths measured in fractions of an inch, but that’s enough to help reverse surface oxidation and the affected layer does present a barrier to water.

Similar to seal coats, their effectiveness is affected by pavement condition, but they are more forgiving with respect to weathering and surface wear. They also form a chemical bond with the asphalt constituents, whereas seal coats rely on surface adhesion.

Application costs tend to be higher for rejuvenators than for asphaltic seal coats, but not dramatically so. Rejuvenators will not repair distressed pavement, but they could be a viable alternative to conventional seal coating.

April 1 2013

Attack of the Road Salts!

Parking garages in this region are attacked by road salts and water throughout much of the year. The cost to repair deteriorated concrete can be quite high and the project can cause significant inconvenience to garage users. So, as part of a parking garage restoration project, we recommend and our clients tend to include, application of a vehicular-traffic-bearing membrane on the structural slabs to help protect their investment and extend the service life of the garage.

There are two basic classes of products commonly used to protect garage slabs, one of which is penetrating sealers. Penetrating sealers include materials such as silanes and siloxanes, which are silicone-based water repellants. These compounds penetrate into the concrete and react with the silica to create a water repellant barrier that also retards chloride migration.

Penetrating sealers are breathable so they do not create a vapor barrier and are relatively inexpensive. However, they do not seal cracks and require frequent reapplication as their effectiveness decreases with wear and time. These materials usually need to be renewed on a three to five year schedule.

The other class is traffic-bearing membranes, which are liquid-applied materials in several layers of cementitious, epoxy, or urethane compounds. These systems are all relatively thick (up to about 90 mils) and are designed with the properties needed to withstand the destructive forces imposed by vehicles tires.

Cementitious products are generally robust, breathable, and well suited for on-grade or elevated slabs, especially those with steel decking supports.

Epoxies are very durable and offer outstanding abrasion resistance, but are not breathable and are less flexible. So they are prone to cracking when slabs move/crack over time. They are well suited for on-grade slabs and areas where chemical and/or extreme wear resistance is needed.

Urethanes are softer, non-breathable, and more flexible so they have the ability to bridge cracks, which makes them ideal for elevated, reinforced concrete slabs. Some systems include an epoxy primer so that the urethane can be applied to on-grade slabs. Systems from reputable manufacturers are generally warranted for five to ten years and can remain serviceable longer, if properly maintained. Most membrane systems offer fast-cure and low-odor formulations, if the project has special requirements.

Consult your trusted restoration engineer before embarking on a garage coating project, as picking the right coating system can make the difference between a successful and not-so successful result.