Heaving Concrete and Asphalt – Subgrade

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In Minnesota, there are some excellent references that can be used as a guide for the design and construction of residential driveways. However, what is needed is a code that addresses the key elements of a driveway structure. I find it fascinating that there is nothing in the code that addresses the design or the construction of a residential driveway.

In my professional opinion, the key elements to a properly designed residential driveway are as follows: the proper subgrade with the required compaction, a solid base upon which the driveway material will rest (this blog is based on an asphalt driveway), the right asphalt thickness, and once the driveway is constructed, preventing water from entering the subgrade (water management system).

Proper Subgrade

What is a proper subgrade? The answer – one that is NOT prone to frost heaving.  Damage from frost heaving can result in the buckling of garage door trim which can cause the misalignment of your garage door. This misalignment can make it difficult to open and close the door.

Buckling of garage door tripm. Clay soils push concrete soils upward in winter.

Buckling of garage door apron. Clay soils pushes concrete soils upward in winter.

The subgrade should either be granular or con-bit.  Most subgrades today consist of clays and silts, soils that are considered expansive – these materials are not the proper subgrade.  If you have subgrade consisting of clays and silts, it should be removed and replaced with granular material or con–bit (this is normally referred to as a soil correction). Here at CBS we recommend using con-bit rather than granular material. Whether it is con-bit or granular it must be compacted and it should be compacted in lifts. Each lift should be about 8-10 inches. Once the subgrade is prepared then the base is constructed.

Concrete and asphalt can move as much as 8 inches when the soil beneath it freezes.

Concrete and asphalt can move as much as 8 inches when the soil beneath it freezes.

Many driveway problems occur right in front of the garage door. This is an area where the native soils are used for backfilling and they are seldom compacted properly and are often placed wet. This area is prone to becoming “wetter” over time because other elements feed moisture into it (poor water management systems). Disregarding this compaction and allowing the subgrade to become saturated are the key reasons why driveways settle and are subjected to frost heaving.

 

Moisture Intrusion Solutions: Solid Base & Asphalt Thickness

The next element of importance in a pavement structure is the base. The base is the layer directly below the driveway surface (either asphalt or concrete). AS previously stated, this article is based on a hot mixed asphalt driveway. The base material, in my opinion should be a class V material or con-bit (recycled concrete and asphalt). The thickness of the base will depend upon the thickness of the asphalt.

Let me explain – the design of the pavement structure should be based upon a term called “Granular Equivalent” (GE). The granular equivalent concept defines a pavement section by equating the thickness of the base and asphalt layer to an equivalent thickness of granular base material. Note: this is not my term, but a term used by the Minnesota Department of Transportation (MN/DOT) for designing pavement sections.

As an example, a class 5 aggregate base has a granular equivalent of 1 per inch of thickness and an asphalt course has a granular equivalent of 2.25 per inch of material.  So, if I have an asphalt thickness of 3 inches, and a class 5 course of five inches, my granular equivalent would be 11.75 inches. If I had an asphalt thickness of 2 inches and a class 5 base of seven inches, my granular equivalent would be 11.50 inches.

So, you see the granular equivalent can be any combination of asphalt and base. It goes without saying that the higher the GE number, the better the pavement structure (I have personally seen this to be true).  Low GE’s might not show pavement distress in the first few years but within 3-7 years, signs of distress will begin showing up.

The next element in the pavement structure and the ones everyone sees, is the surface course. To be frank, I am not sure what specification most residential paving contractors use for their design mix. I have seen HMA thicknesses from 2” up to 3” used for driveways. I think most paving contractors will use 2”-2 ½”. Especially in large residential developments. If you are an individual homeowner the contractor will probably use 2 ½” – 3”. In my professional opinion, I would recommend 3” – 4”.

Now getting back to the GE. I would recommend a GE between 10.5”-12” for residential driveways. Similarly, for reference – the Minnesota Asphalt Pavement Association (MAPA) recommends a GE of 11.5” for driveways also.

Conclusion:

The building codes govern the applications of these materials and practices. Neither the IBC, nor the IRC include information for residential driveway designs. Nor is there a recognized national standard. Maybe it is far “fetched” of me to think that one could be established, but at the very least, I believe the Minnesota State Building Code should address the issue.

Incidentally, I have over 30 years of experience with the Hennepin County Department of Transportation dealing with bridge and roadway designs.

 

 

 

Boulder Retaining Wall and Related Drainage Issues

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Boulder retaining wall

The above picture demonstrates how a boulder retaining wall has moved along side the foundation of a home since its initial construction.  Boulder retaining walls are a common landscaping and erosion control method used in many homes.  If a foundation wall is over 48 inches, it needs to be designed by an engineer and requires plans for ordinance and structural review by the local governing body.

There are many elements that can encourage boulder wall movement, but here are

the three main causes:

1.) Often, the wall has been built on unsuitable soils that lacked compaction and ultimately could not support the weight of the wall. Contributing further to this problem, is the added pressure from the soil and related area behind the wall.

2.) Secondly, sometimes retaining walls are built with improper drainage behind it, including no installation of drain tile, drainage material behind the rocks and/or fabric to hold that material in place.

3.) Thirdly, the poor drainage of rain water behind the wall causes erosion to take place and further soil settlement under the boulder wall itself.  This water often comes from a roof or rain gutter that empties behind the wall.

In this case, as the picture depicts, some of those elements were present. This wall had movement subsequent to its initial construction.  This resulted in damage to the outside parge coat on the foundation wall of the home and a leak developed in the basement adjacent to this boulder wall.

Here are some of the things to consider when constructing a boulder retaining wall:

  1. How high is the rock wall going to be? Will it need to be engineered?
  2. Location of the rock wall, asking is it on stable slopes, consisting of firm, undisturbed soil?
  3. The ground surface above the Boulder Wall. How much water will come through this area?
  4. The proper angle of the rockery face of the Boulder Retaining Wall.
  5. The proper rock size should be used to construct the wall.
  6. Rock placement including the rocks to be embedded into the soil at the base to provide maximum stability.
  7. The drainage must be provided behind the wall to assure that water will not erode the soil behind or underneath he boulders. This includes the use of a drain tile system, erosion fabric, and drainage material such as gravel behind the boulder wall itself.

As a homeowner, before taking on construction of a boulder wall, you may want to check with experts in this area.

 

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Choosing Ice-Melts

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Ice-Melts

As we speak, our social media newsfeeds are blowing up with snow warnings, schools are closing, business meetings are being rescheduled, and families are stocking up for the incoming storm in Minneapolis.  If you are making last minute runs to the store, be sure to acquire the proper ice-melt that fits your home’s needs. Below is a chart, put together by Consumer Reports, that can help you determine which product is right for your home.

Keep in mind that certain products effect asphalt and concrete differently. According to a recent study, magnesium products “are the most damaging to the concrete”, specifically Calcium magnesium acetate (Lee, 5). Within the same study, sodium chloride products were discovered to be the least detrimental to concrete.  As far as asphalt is concerned, acetate products can be disadvantageous because of their tendency “to break down the bonds between aggregate and asphalt binder” (consumer reports, 1).  The chart below provides many options for safe asphalt de-icers.

Ice-Melts Comparison

For more information and tips on de-icing best practices, check out the following link: http://www.consumerreports.org/cro/2014/02/best-ice-melts/index.htm .

 

If you are noticing large build-ups of ice around your home check out what our engineer and consultants have to say http://cbsmn.com/blog/?p=149 about PERMANENTLY fixing the problem.  

 

Sources:

“Best Rock Salt and Ice Melts Review – Consumer Reports.” Best Rock Salt and Ice Melts Review – Consumer Reports. N.p., Feb. 2014. Web. 02 Feb. 2016.

Lee, H., R. D. Cody, A. M. Cody, and P. G. Spry. EFFECTS OF VARIOUS DEICING CHEMICALS ON PAVEMENT CONCRETE DETERIORATION. Proc. of Mid-Continent Transportation Symposium 2000, Center for Transportation Research and Education, 2711 South Loop Drive. N.p.: n.p., 2000. 151-55. Print.

 

 

The Vices of Ices: How to get Rid of Ice at your Home

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Ice Dam Prevention MN

Minnesota winters produce harsh winds, dark skies, and snow. But, the most precarious weather consequence affecting, not only the elderly population, but all generations, is ice.  Ice is a rigid structure maintained by hydrogen bonds and forms when water is cooled below 32°F (0°C). It hosts many of our states favorite pastimes (shout out to the Minnesota Wild), but also poses danger to drivers, pedestrians, and homeowners who are simply trying to maneuver through the labyrinthine byways of a once secure driveway. Needless to say, this challenge is not always a success.

Incidentally, the leading cause of brain injuries in the state of Minnesota is from falls. The Minnesota Brain Injury Alliance and the Minnesota Department of Health say, falls are responsible for 38% of all brain injuries annually (https://www.braininjurymn.org/aboutBrain/falls.php). That is a huge number! Ideally, we would like to completely eradicate ice in order to decrease the injuries that coincide, but this is not realistic. However, individually, we can take measures to drastically decrease the problem within our own home.

First, one must be aware of the drainage system on their roof. A functioning roof system will shed moisture off the roof and into gutters where it can be properly filtered away from your foundation and walkways. If you have noticed ice dams, your roof is unable to perform because an issue exists within in your attic. It is important to note that a permanent solution, which does not require continual snow removal of the roof, exists and will increase the life of your roof and structural components of the attic. Check out our blog on attics & energy loss to learn more about the attic system http://cbsmn.com/blog/?p=121. At CBS, we specialize in these exact issues and offer lasting solutions to ensure peak energy efficiency, life span, and performance of your roof and attic.

Roof Ice Dams Solution

*This ice dam is preventing the roof’s drainage system from functioning properly.

A second factor to consider is the foundation of your home. It is paramount that water be directed away from the foundation to avoid ice build-up, but to also prevent basement leakage.

Charles Glossop, owner of Minnesota’s most highly esteemed commercial snow, landscaping, and consulting company, Hantho Farms, LLC, provided us with some of his methods (which CBS highly supports) for the best ways to prepare for this phenomena pre-winter: 1) Downspouts and gutters must be efficiently draining water away from entrances and walkways and 2) A positive slope must exist around the foundation, walkways, and driveways with at least a  6” drop in elevation within the first 10 feet of the foundation (International Residential Code). This positive slope encourages water to move away from your home and 3) Consult a professional before planting trees near your home. If trees are too close, their roots can actually grow into the foundation, causing cracks, and will retain water near the base of the home. If you combine a negative grade and trees in close proximity to a foundation, the tree roots will actually follow the water (which is trapped near foundation from negative grade) and may cause serious damage to the home’s foundation (International Residential Code).

Bad-grading

*The above photo demonstrates a gutter that is not draining water away from the foundation and a negative grade that is holding water near the foundation.

Now, we know it is mid-winter and your negative grade issues cannot be addressed until spring. However, there are some measures you can take NOW to prevent ice build-up. Charles Glossop suggests using a liquid brine BEFORE it snows to “prevent the bonding of snow to the pavement.” Check out Hantho Farms website http://www.hanthofarms.com to learn more about the liquid brine they make and use for commercial snow removal.

To recap, the two main sources that propagate ice are 1) an insufficient roof drainage system and 2) Improper drainage system of your foundation. After the recent snows, and upcoming freeze/thaw cycle, you will quickly know if there are problems within these drainage systems. If you have ice dams, slippery sidewalks, ice build-up on driveways, or around other areas of your home, you may need to start planning for next year. Call CBS to come inspect your property and start working towards a plan to create an efficient and safe environment at your home.

Why not Building Codes for residential driveways?

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Our company, Complete Building Solutions, investigates construction defects – including but not limited to the building envelope, water management issues, soil issues, settlement problems, concrete issues, and driveways. We also can provide engineering services and construction oversight.

As we conduct our investigations we have found that many of the defects observed do not comply with the building codes.  And, as most people know, the building industry is governed by codes. We rely on the International Building Code (IBC), the International Residential Code (IRC), and the Minnesota State Building Code as our references when conducting our investigations as we look for construction defects. They all do a good job of addressing all facets of a building. But, there is nothing in the code that addresses the design or the construction of a residential driveway.

In Minnesota, there are some excellent references that can be used as a guide for the design and construction. However, what is needed is a code that addresses the key elements of a driveway structure. In my opinion the key elements are having the proper subgrade with the required compaction, a solid base upon which the driveway material will rest (incidentally this blog is based on an asphalt driveway), the right asphalt thickness, and once the driveway is constructed keep the water from entering the subgrade (another words – a good water management system).

What is the proper subgrade? The answer – one that is not prone to frost heaving.  Damage from frost heaving can result in buckling your garage door trim to causing the misalignment of your garage door making it difficult to open and close.

Complete Building Inspections In MN

The subgrade should be either granular or should be con-bit.  I can tell you that most subgrades under driveways consist of clays and silts, soils that are considered expansive – those are not the proper subgrade.  So if you have subgrade consisting of clays and silts, it should be removed and replaced with granular material or con–bit (this is normally referred to as a soil correction). Here at CBS we recommend using con-bit rather than granular material. Whether it is con-bit or granular it must be compacted and it should be compacted in lifts. Each lift should be about 8-10 inches. Once the subgrade is prepared then the base is constructed.

The area where we see most of the driveway problems is right in front of the garage door. This is an area where the native soils are used for backfilling and they are seldom compacted properly and are placed wet. It is the area where the contractor has to excavate in order to install the footing and construct the foundation. Typically the excavation extends out from the building’s foundation several feet and extends down to the footing.

That is also the area that is most prone to become wetter over time because other elements feed moisture into it (poor water management for one). Disregarding compaction and allowing the subgrade to become saturated are the key reasons why driveways settle and are subjected to frost heaving.

Moisture Intrusion Solutions

As previously noted, poor water management can affect driveway behavior. Since the presence of water reduces the strength of the pavement structure, it is important to not let water enter it. I can’t tell you how many times I have seen downspouts dump huge amounts of water right next to the driveway.

The next element of importance in a pavement structure is the base. The base is the layer directly below the driveway surface (either asphalt or concrete). AS previously stated, this article is based on a hot mixed asphalt driveway. The base material, in my opinion should be a class V material or con-bit (recycled concrete and asphalt). The thickness of the base will depend upon the thickness of the asphalt.

Let me explain – the design of the pavement structure should be based upon a term called “Granular Equivalent” (GE). The granular equivalent concept defines a pavement section by equating the thickness of the base and asphalt layer to an equivalent thickness of granular base material. Note: this is not my term, but a term used by the Minnesota Department of Transportation (MN/DOT) for designing pavement sections.

As an example, a class 5 aggregate base has a granular equivalent of 1 per inch of thickness and an asphalt course has a granular equivalent of 2.25 per inch of material.  So, if I have an asphalt thickness of 3 inches, and a class 5 course of five inches, my granular equivalent would be 11.75 inches. If I had an asphalt thickness of 2 inches and a class 5 base of seven inches, my granular equivalent would be 11.50 inches.

So you see the granular equivalent can be any combination of asphalt and base. It goes without saying that the higher the GE number, the better the pavement structure (I have personally seen this to be true).  Low GE’s might not show pavement distress in the first few years but within 3-7years, signs of distress will begin showing up.

The next element in the pavement structure and the ones everyone sees, is the surface course. To be frank, I am not sure what specification most residential paving contractors use for their design mix. I have seen HMA thicknesses from 2” up to 3” used for driveways. I think most paving contractors will use 2”-2 ½”. Especially in large residential developments. If you are an individual homeowner the contractor will probably use 2 ½” – 3”.

In my professional opinion, I would recommend 3” – 4”.

Now getting back to the GE. I would recommend a GE between 10.5”-12” for residential driveways. Similarly, for reference – the Minnesota Asphalt Pavement Association (MAPA) recommends a GE of 11.5” for driveways also.

Conclusion:

Neither the IBC, nor the IRC include information for residential driveway designs. Nor is there a recognized national standard. Maybe it is far “fetched” of me to think that one could be established, but at the very least, I believe the Minnesota State Building Code should address the issue.

Incidentally, I have over 30 years of experience with the Hennepin County Department of Transportation dealing with bridge and roadway designs.

Bruce Polaczyk, P.E.