Paving Questions

What is Hot Mix Asphalt (HMA)?

Hot mix asphalt (HMA) is a bituminous concrete made principally from asphalt binder and aggregate. It is distinguished from other bituminous products by its constituent materials (asphalt and aggregate), mixture design methods and elevated mixing temperature (thus the term "hot mix").

What is Portland Cement Concrete (PCC)?

Portland cement concrete (PCC) is a composite material consisting of aggregate, Portland cement, and water. As a construction material, PCC can be cast in almost any shape desired, and once hardened, can become a structural (load bearing) element.

What is typical Hot Mix Asphalt (HMA) pavement structure?

A typical HMA pavement is composed of several layers of material, i.e., a surface of HMA layer built over a base course and subbase course that rest upon a compacted subgrade (compacted soil). Because HMA pavement structure bends, or flexes, under loading, it is generally categorized as “flexible pavement”.

What is typical Portland Cement Concrete (PCC) pavement structure?

PCC pavement typically consists of a PCC surface course built on top of either the subgrade or an underlying base course. PCC pavement deflects very little under loading due to the high modulus of elasticity of PCC surface course, and is therefore categorized as “rigid pavement”.

What is the difference between the flexible (HMA) and rigid (PCC) pavements?

The essential difference between the two types of pavements, flexible and rigid, is the manner in which they distribute the load over the sub grade.

Rigid pavement, because of concrete's rigidity and stiffness, tends to distribute the load over a relatively wide area of subgrade. The concrete slab itself supplies a major portion of a rigid pavement's structural capacity. Flexible pavement, inherently built with weaker and less stiff material, does not spread loads as well as concrete. Each layer receives the loads from the above layer, spreads them out, then passes on these loads to the next layer below. Therefore flexible HMA pavements usualy require more layers and greater thickness for optimaly transmitting load to the subgrade.

What are the major factors that cause deterioration of pavement?

The combined effects of

• traffic loading,
• the environment (such as air, sun and water, asphalt’s natural enemies),
• improper design/construction

will cause pavement to deteriorate over time.

Maintenance, rehabilitation and reconstruction are what we use to slow down or reset this deterioration process. Definition of Maintenance, rehabilitation and reconstruction : “Maintenance actions, such as crack sealing, joint sealing, fog seals and patching help slow the rate of deterioration by identifying and addressing specific pavement deficiencies that contribute to overall deterioration. Rehabilitation is the act of repairing portions of an existing pavement to reset the deterioration process. For instance, removing and replacing the wearing course in a pavement provides new wearing course material on which the deterioration process begins anew. Reconstructing an entire pavement, however, is not considered rehabilitation but rather new construction because the methods used are generally those developed for new pavement construction.” — WSDOT Pavement Guide.

What is the pavement condition evaluation?

“A pavement condition evaluation is a visual inspection or a mechanical assessment of a pavements condition or properties that usually results in a numerical rating. It is conducted on both Bituminous (HMA) or Portland Cement Concrete (PCC) pavement. There may be many factors involved in rating a pavements condition depending on the intended use of the pavement and the specific informational needs of the managing agency.” — WSDOT Pavement Guide.

Common distresses for asphalt pavement

Surface Defects
Bleeding
Raveling
Polishing
Cracking
Fatigue Cracking
Block Cracking
Edge Cracking
Longitudinal Cracking
Reflective Cracking
Transverse Cracking
Patching and Potholes
Surface Deformation
Rutting
Settling/Shoving
Etc.

Common distresses for concrete pavement

Corner Breaks
Durability Cracking ("D" cracking) Longitudinal Cracking
Transverse Cracking
Joint Deficiencies Joint Seal Damage
Transverse Joint Seal Damage Longitudinal Joint Seal Damage Spalling of Longitudinal Joints
Spalling of Transverse Joints
Surface Defects
Map Cracking & Scaling
Map Cracking Scaling
Polished Aggregate
Popouts
Miscellaneous Blowups
Faulting of Transverse Joints & Cracks Path/Patch Deterioration
Water Bleeding & Pumping
Etc.

Frequently Asked Questions

Roofing Questions

What is the best roof?

Wouldn't it be simple if there was one answer to all roofing problems? Unfortunately there is no magic pill in the roofing market that solves all roofing problems. What the market does offer is a wide selection of good products, each having attributes and faults. The key to selecting the proper roof system is identifying the specific roof design parameters of your building, and how each roof system meets those parameters. A simple example would be: If a building has very heavy foot and wheel traffic on the roof, a 45 mil single ply membrane probably would not be advisable, due to its limited puncture resistance.

Why does my roof leak?

Well a cynic might answer that there are two kinds of roofs, those that leak and those that will leak. Roofs leak from a break in the waterproofing layer, sometimes caused by mechanical damage (ie, someone dropping an HVAC access panel on the roof), sometimes from an opening in the sealant, such as pitch pans and caulking, and sometimes from deterioration or defects in the roofing material. The key roof management task is leak avoidance. Find and correct defects before they leak.

How long should a roof last?

Like any building component, roofs degrade at different rates depending on a large number of factors. Here are just a few:

• the quality of original construction
• the level of abuse
• the level of maintenance
• appropriateness of design

So how long should a roof last? We have seen poorly designed and installed roofs go as few as six or seven years before they failed, and we have seen old coal tar built up roofs that were over 60 years old. Most building owners, roofing contractors and designers feel 20 years is an acceptable service life.

Can I cover over my existing roof?

Installing a roof over the top of an existing roof is generally acceptable under these guidelines:

• A building cannot have more than two roofs
• No wet insulation can be left in place
• The roof structure must be able to handle the additional roof load
• The new roof must be attached to the roof deck to meet wind loads (it is not generally acceptable to adhere the new roof to the old roof

How many roofs can I put on?

Most building codes allow a structure to have two roof membranes in place, but not a third. The codes are also now requiring all roof layers to be removed once the two roof limit has been reached.

When is the best time to put on a new roof?

This question could be interpreted two ways, so we'll answer each question.

1) What time of year is the best time to install a roof?
The optimum time to install a roof is when the temperatures are above freezing and the wind and rain are at the lowest intensity and frequency. This allows the roofer the best conditions for installation, with the fewest interruptions and lowest risk of leaking. Unless you are very fortunate, sometimes you cannot schedule the roofing work during these periods, and you may need to install the roof in cold temperatures, or in the rainy season. If you know this in advance, it may be possible to choose a roof system that is more tolerant of inclimate weather.

2) "How do I know when my roof has failed?"
Different roof types fail at differing rates and with different failure modes. Without going into a long dissertation, the several general failure clues are: 1. Does the roof leak in numerous locations?

1. Do leaks continue, despite repeated repair attempts?
2. Do repairs seem to make leaks worse, or do new leaks develop after repairs?
3. How tolerant is the occupancy to leaks? Low leak tolerance generally means the "failure" decision is reached earlier.

It is generally better to reroof at the appropriate juncture, rather than pouring money and time into ill advised repairs, but there are exceptions.

How much does a new roof cost?

How much is a new car? Well, the answer to both questions is, "That depends." We find the cost of reroofing is less dependent on the type of roof membrane, than the project's relative size (large projects cost less per SF than small ones, building height (tall buildings cost much more than short buildings), number of roof penetrations (more penetrations = more money).

In our recent project bids, our roofing costs ranged between $3.15 per square foot and $53.00 per square foot. Does that narrow it down?

How often should my roof be inspected and by whom?

We recommend a thorough inspection every two years by a roofing professional, with "walkover inspections" by plant or building maintenance personnel at least twice per year. Roofs that are heavily trafficked or generate roof debris (paper companies, food processors, etc.) may require more frequent inspections. Roofs with many penetrations and lots of roof traffic are going to require more frequent maintenance than roofs with no penetrations and low levels of traffic. There are a number of "musts" on every roof however, including keeping drainage devices open and clear of debris, removing foreign objects, and conducting regular inspections. Some roofs require more maintenance than others, and each should have a maintenance/inspection schedule.

Which roofing manufacturer should I use?

There are a lot of things to consider when choosing a roofing manufacturer. Do they offer the roof membrane/system that best fits your needs? Is their product quality the best of that generic type? What is their commitment to after-the-sale service? Some of the best products and service come from mid-size or smaller companies.

How do I get a fair quote and a good contractor for a new roof?

As self-serving as this sounds, a knowledgeable roof consultant can steer you through the many pitfalls of buying a new roof. With their help, you can pick the right roof system, communicate your design intent through project specifications, and bid to qualified contractors. The good contractors appreciate bidding well designed roofs, and bid with confidence that no one will "backdoor" the project and bid something not otherwise specified.

Please submit additional roofing and paving questions to
askus@benchmark-inc.com.