- Peters Chemical Company - http://www.peterschemical.com -

Controlling Road Maintenance Costs Through Surface and Base Stabilization

Posted By admin On 05/21/2012 @ 5:35 pm In | No Comments

Controlling Road Maintenance Costs Through Surface and Base Stabilization

A Report on Calcium Chloride

On unpaved roads, calcium chloride stabilizes the road surface as it controls dust.  For roads that are about to be paved, calcium chloride stabilizes the road base material to provide a better paved surface.  In both those applications, calcium chloride leads to reduced maintenance costs.  And that’s what this brochure is all about.

But the brochure doesn’t stop there.  It goes on to give you some insight into the chemical itself – where it comes from; its different forms; and how it works.

Also included in this brochure is a list of alternatives to calcium chloride and explanations as to why they’re not as effective, testimonials from actual users of CaCl2, and complete tables of specifications and application rates for both unpaved and about-to-be-paved roads.

Lastly, there’s a section in this brochure on other uses of calcium chloride that are of interest to local government officials.

One overriding point will become apparent as you read through this booklet.  That is, when you’re considering calcium chloride for use on paved or unpaved roads, you’re considering a maintenance cost controller.  And that you’re assured of.

What is Calcium Chloride?

A chemical almost too simple to be so useful. There’s nothing very complicated about calcium chloride. It’s simply a material produced from natural brine deposits found underground. The Occidental Chemical Company processes the brine into a colorless, odorless liquid or into solid forms as pure white flakes or pellets. LIQUIDOW*, DOWFLAKE*, and PELADOW* are the trade-marks for these three different forms. CaCl2 is the chemical symbol for calcium chloride.

How does calcium chloride work?

There are three characteristics of calcium chloride which enable it to be so useful in so many road maintenance applications.  First, calcium chloride is hygroscopic, meaning it attracts moisture from the air and fights to keep it as the chemical tries to remain in its natural liquid state.  Second, calcium chloride is deliquescent, which means the solid can dissolve into liquid form by absorbing atmospheric moisture.

When calcium chloride is spread on an unpaved road, usually as a liquid, it coats each particle of dust and gravel to bind them together.  As it fights to remain in its natural liquid state, it resists evaporation to keep the surface damp and the particles bound together even on the hottest, driest days.  The end result is a dust-free, stabilized, unpaved road that stays that way.

On a road that’s about to be paved, calcium chloride works essentially the same way.  When thoroughly mixed with aggregate, calcium chloride holds onto water already in the aggregate, while pulling additional moisture from the air.  This ability to maintain an optimum and uniform level of moisture in the road base material is the key to calcium chloride’s success as a base stabilizer.  It ensures more uniform compaction and a high-density base.  Once the road is paved, it has a higher degree of durability and permanence under traffic, moisture fluctuation and temperature extremes.

The third characteristic of calcium chloride that is important to road officials is not related to stabilization, but rather snow and ice control.  It’s the characteristic of being exothermic, meaning calcium chloride gives off heat as it dissolves and returns to its natural state.  This property is the key in making calcium chloride the most effective, most powerful commonly used chemical deicer for snow and ice control.

Dust on Unpaved Roads: A Mixed Blessing

For years, calcium chloride has been called a dust control agent.  And it’s the best material available to control dust.  But this definition of the material is not totally accurate, because it only hints at calcium chloride’s real value in unpaved road maintenance.  To be more correct, calcium chloride is a surface stabilization material that controls dust as an automatic byproduct. Here’s why.

There’s good dust…

For a moment, let’s consider dust from a totally different perspective than the normal one where it’s simply viewed as a nuisance: view dust as an important part of an unpaved road.

First, those tiny particles of fines are what give a road its stability.  That is, dust acts as a binder agent for the more coarse material to keep unpaved roads dense and compacted.  When a road is stabilized, the aggregate stays in place and the crown remains intact to provide proper drainage.  And if there’s a secret to maintaining unpaved roads, it can be summed up in two words: Proper drainage.  Water that doesn’t drain off the surface of an unpaved road causes soft spots that ultimately become potholes.  Yet, just as the dust binds the coarse material together, it’s imperative to bind the dust particles together.

…and there’s bad dust

Dust particles that aren’t controlled or bound together eventually become those billowing clouds that people have come to know and dislike.  With a daily dosage of traffic, untreated gravel roads lose about one inch of surface a year.  This is the equivalent of more than 500 tons of material per road mile a year.

To area residents, dust is a nuisance.  To drivers, it’s a hazard.  To crops, it’s detrimental.  And to the environment, it’s a form of air pollution.

Dispersed dust: The first link in a chain reaction

But those are only the immediate problems of dust.  Actually, it’s merely an indication that the road is starting to deteriorate.  And when a road starts to deteriorate, more serious problems are soon to follow.

Picture a car travelling at about 40mph over an unpaved road.  If there’s no dust, it means the road is compacted because the aggregate and crown are intact.  Several weeks later imagine that car travelling at the same speed over the same road, but this time there’s that familiar cloud behind it.  What’s actually happening is the road is losing its stability.  As more dust is lost in the air, the road begins to loosen and valuable aggregate is pushed to the shoulders or kicked into culverts and ditches.

Next the modified A-shape of the crown begins to break down and flatten.  And when it rains, water collects on the surface simply because it can’t drain off into the culverts.

And that brings us to the last link: the collected water forms loblollies, which become potholes when they dry; long stretches of washboard start to develop; the shoulders of the road break down.  And when the road reaches this stage, your maintenance costs are just starting.

A hard look at maintenance costs.

To be certain, every unpaved road needs some type of maintenance at one time or another.  That’s unavoidable.  As are the expenses involved in maintenance.

First you have material replacement costs.  That alone can be staggering.  Consider this for example: of the nation’s 3.8 million miles of roads and streets, 2 million are unpaved.  And it’s estimated that replacing road material can cost anywhere from $500 million to $1 billion annually.  In New York State alone, material replacement costs can run anywhere from $6 million to $15 million a year.

The next cost figure is the actual work of blading and reshaping the road.  This can be looked at in terms of time because the more deteriorated a road is, the longer it takes for repairs to be completed.  For example, a road that’s in a relatively stable condition may only need light blading and the work can be finished within a few hours.  Whereas a badly deteriorated road may need extensive patching and complete reformation of the crown and shoulders.  That can take days or even weeks.

And of course there’s equipment maintenance.  This can include preventive maintenance, routine maintenance, or complete overhauls of machinery.  Obviously, the more often a road needs repair work, the more wear and tear there is on your machinery; hence, your maintenance costs are higher.

That brings us to the crux of maintenance costs: the frequency of road repairs. Let’s say it costs you X dollars per mile of unpaved road for material replacement, actual repairs, and equipment maintenance.  If road repairs are needed once a year, your total cost is simply X dollars.  But if road repairs are called for two and three times a year, it doesn’t take a mathematician to figure out that your costs will double and triple.

By using calcium chloride, you stop this costly chain reaction of problems.  All because you start and stay with a more stable surface.  The need for aggregate replacement, blading and dust control are substantially reduced.

Calcium Chloride: Specifications and Application Rates

LIQUIDOW calcium chloride is a ready-to-use liquid solution that goes on fast and easy.  Sprayed on roads, this chemical helps valuable road material stay where it’s put by keeping fines for binder in place.  The result: Stabilized road surfaces.

It’s likely that your spreader equipment can easily handle the application of calcium chloride without modifications.   Calcium chloride cannot make a bad road good; its purpose is to keep a good road good – crown intact, aggregate in place, etc.  The chart below shows application guidelines for calcium chloride in both liquid and solid equivalents on existing unpaved roads that meet the standards of stabilization.

Specifications LIQUIDOW
CaCl2 – minimum 38% 35% 32%
MgCl2 – maximum 0.2% 0.2% 0.2%
Alkali Chlorides – maximum 3.4% 3.1% 2.8%
Table of equivalents for dry Calcium chloride @ 77°F 38% 35% 32%
1 gallon = pounds of DOWFLAKE calcium chloride 5.70 5.11 4.55
1 gallon = pounds of PELADOW calcium chloride 4.62 4.15 3.69
1 ton DOWFLAKE in gallons 351 392 440
1 ton PELADOW in gallons 433 482 542
1 liquid ton in gallons 172 177 182

One thousand gallons of LIQUIDOW 38% is equal in calcium chloride content to 1115 gallons of LIQUIDOW 35% and 1253 gallons of LIQUIDOW 32%.

Bringing a road up to standard

To start, it’s best to determine if fines for binder and aggregate for stability are needed. Where the surface has loosened or raveled, add more material or pull in binder that has worked out to the shoulders. New binder should be placed in a windrow, then dry-mixed with the aggregate.

Add fine aggregate to road sections that become slick in wet weather. Strengthen soft spots by adding graded aggregate, then consolidate the surface by applying calcium chloride at a rate of 1.65 pounds per square yard.

When adding new materials, scarify the surface and mix in the new materials. Apply calcium chloride at a rate of .65 lb. per square yard per inch of depth. The minimum amount to be 1.65 lbs. per square yard for the first three inches of depth. (Figures based on Dowflake Xtra 83 – 87% calcium chloride content.) Then blade the road material and calcium chloride from side to side for a thorough mix.

Crown the road to a modified “A” cross section, then compact it. After the road is firm, apply calcium chloride at a rate of ½ to 1 pound per square yard for dust control.

Application Chart – Dust Control 38% Solution†

Width of Spread Gallons per Sq. Yard Gallons per Mile Miles per 8000 gallons Miles per 10,000 gals.
4 ft. 0.09 211 37.9 47.3
0.18 422 18.9 23.6
0.27 633 12.6 15.7
8 ft. 0.09 422 18.95 23.69
0.18 844 9.48 11.84
0.27 1266 6.32 7.89
12 ft. 0.09 633 12.63 15.8
0.18 1266 6.32 7.9
0.27 1899 4.21 5.27
16 ft. 0.09 845 9.47 11.83
0.18 1689 4.74 5.92
0.27 2545 3.16 3.95
18 ft. 0.09 950 8.42 10.53
0.18 1900 4.21 5.26
0.27 2850 2.81 3.51
20 ft. 0.09 1056 7.58 9.47
0.18 2112 3.79 4.73
0.27 3168 2.53 3.16
22 ft. 0.09 1162 6.88 8.61
0.18 2323 3.44 4.3
0.27 3485 2.29 2.87
24 ft. 0.09 1267 6.31 7.89
0.18 2534 3.16 3.95
0.27 3802 2.1 2.63

The calcium chloride content of 1.65 lbs. of Dowflake Xtra (83-87%) or 1.27 lbs. of Peladow (94-97%) is equal to the calcium chloride concentration in 0.27 gallons of Liquidow 38%.

The application rates shown in this chart are intended as general guidelines only. Varying factors such as traffic count and road and weather conditions may require increased or decreased dosages.

Calcium Chloride for Base Stabilization

And base stabilization for better paved roads

To produce better paved roads, it used to be that most attention was directed at improved construction practices. But now road engineers know that how a road performs after it’s paved is largely determined by the condition of the base course before the road is paved. That means stabilization of the subgrade has become the attention-getter. And that’s where calcium chloride comes in.

What does stabilization of the subgrade include? Specifically road engineers look for high density, easy compaction, moisture retention, retention of fines, and resistance to frost action; in general, a stronger base course. And how does calcium chloride help stabilize the subgrade? For all practical purposes, it stems from the chemical’s ability to attract and retain moisture while lowering the freezing point of moisture in the base material. Moisture limits for a road base are strict. For example, a variation of only 1% from optimum can reduce density by 2 lbs. per cubic foot and increase voids by as much as 8%.

It’s hard enough to build a road in the summer heat without having to rework a base course that has fluffed because it dried out. Calcium chloride helps prevent this problem as it coats the individual fines to keep them in place. This binding action that calcium chloride has on the fines adds density to the base course; hence it’s much easier to compact the material in a uniform manner. And uniform compaction is one thing that gives a road its resistance to frost action. The other is the calcium chloride itself as it lowers the moisture’s freezing point to -60°F.

In recent laboratory studies conducted by Dr. Dan Marks, Department of Civil Engineering, University of Tennessee, calcium chloride was added in various percentages by weight then tested under several methods. Tennessee grading D, a non-cohesive limestone, was used in the research with calcium chloride added at levels up to 2.0% in 0.5% intervals. Compacted at equal effort and at optimum moisture content, the treated and untreated base material samples were tested for strength and density by the standard California bearing ratio (CBR), spherical bearing value (SBV), and triaxial tests. In addition, both samples were tested again by triaxial methods after 24 hours of accelerated drying.

To no one’s surprise, the material treated with calcium chloride compacted to a higher density; its bearing strength increased as measured by the CBR, and cohesion increased according to triaxial tests. The outcome of these tests showed that a calcium chloride level of 0.6% by weight achieved optimum strength at minimum cost.

Yet as any road engineer knows, laboratory testing conditions do not always give a true representation of actual use conditions.

So in Montgomery County, Tennessee, a portion of interstate highway was built with and without a calcium chloride treatment of the base course. Prior to paving, Benkleman beam deflection data (another measure of strength) were taken and used to calculate layer coefficients by the AASHTO method for each layer. Results? The untreated base course material had a layer coefficient of 0.12 while the layer treated with calcium chloride had a coefficient of 0.16 – a 33% increase in strength.

If that statistic fails to convince you that calcium chloride helps stabilize the base course material for better paved roads, perhaps this example on road longevity will: A road with two inches of asphalt and six inches of base course which has loadings of 700 18KIP/year can be expected to last 15.2 years when treated with calcium chloride; 6.7 years if left untreated.†

†Based on AASHTO calculations.

Application Rates for Base Stabilization

Calcium chloride content is usually specified as a weight percentage of calcium chloride in dry base course material. In practice, calcium chloride can be added in a variety of forms which contain varying amounts of water.

The chart below gives the quantity (in pounds or gallons) of the different calcium chloride products which may be added to a ton of dry aggregate to give proper weight percentages of calcium chloride. The quantity of water added with calcium chloride should be considered when adjusting the treated base course material to reach the optimum moisture level.

Application Rates of Calcium Chloride for Base Stabilization

Type of Calcium Chloride Product Amount of CaCl2 added (lbs. or gals.) to reach percentages per ton of aggregate as follows:
  0.6% 0.8% 1.0%
PELADOW (pounds) 12.8 17.0 21.3
DOWFLAKE (pounds) 15.6 20.8 26.0
LIQUIDOW 32% (gallons) 3.4 4.5 5.7
LIQUIDOW 35% (gallons) 3.0 4.0 5.0
LIQUIDOW 38% (gallons) 2.7 3.6 4.5

Readying the road for paving

There are two methods of mixing calcium chloride with the road base material: Road mixing and plant mixing. Road mixing involves the use of trucks, patrol grader, spreader, water wagon, and roller, or a travelling rotary mixer. Plant mixing is more advantageous because it assures a more uniform mix, less chance for segregation of materials, and better control of gradation and moisture.

Road mixing: First on the agenda is placing the coarse material on the road and then comes the fine for binder. After dry-mixing the two, distribute the material in layers to prevent segregation. Using a pressurized system, apply LIQUIDOW calcium chloride.

Thoroughly mix the aggregate and calcium chloride by blade or travelling rotary mixer. It may be necessary to add water to assure optimum moisture. If the material is too wet (as a result of rain), you can aerate the mixture by blading. Keep in mind, rolling base material that’s too dry causes low density and poor stability; rolling base material that’s too wet causes the material to build up under the roller.

The next step is blading the material to the proper crown. If the road is to be paved right away, make the crown identical to the finished pavement. If the base is to be used as a wearing course, blade the crown as a modified “A” with a slope of at least ½-inch per foot of width.
After shaping, roll and compact the base with a rubber tire or steel roller.

Plant mixing: With the pre-mixed base material ready to go, place the material on the road uniformly using a mechanical spreader. No more than six inches of loose aggregate should be placed in each layer. Compact and shape the base in the same manner described for road-mixed material.

Other Dust Control Applications

Mining haul roads

Considering that 40% of all time lost by hauling units is due to poorly maintained haul roads, it’s easy to understand why calcium chloride plays an important role in the mining industry. On haul roads, calcium chloride keeps dust down first, then goes on to stabilize the road. As a result, haul units keep rolling at top speed.

Oil and gas access roads

There are two benefits derived from the use of LIQUIDOW calcium chloride on access roads: Improved visibility as a result of controlled dust is one. This lets the heavy equipment used near these areas move in and out quickly and safely.

The recipients of the other benefit are the workers themselves. With dust kept on the road and not in the air, workers aren’t constantly breathing in those particles day after day. Result: Healthier working conditions.

Logging roads

By their sheer weight, logging trucks can flatten out the A-shape crown of an unpaved road. And when the crown goes, so goes the road: Aggregate is lost, water can’t drain off properly, and potholes and washboard develop.

With an occasional treatment of LIQUIDOW calcium chloride, logging roads stay in solid, stabilized condition longer to support those heavy trucks better.

During road construction

Dust is a problem in areas where paved roads, sewers and other structures are under construction. And by adding calcium chloride to the aggregate you control dust.

Quarries

Dust as a hazard and nuisance can also be found at rock quarries. That is unless calcium chloride is used to control it. Here, too, calcium chloride keeps working environments safer and healthier.

Stabilizing Railroad Track Beds

Perhaps no other vehicle route takes the stress and pounding of railway track beds. So no other needs protection from stabilization at the same high level. And the use of calcium chloride can build in that high level of stability.

And more

Wherever there’s dust, there’s a need for LIQUIDOW calcium chloride. In parks, playgrounds, other recreational areas … on cemetery roads, walkways, driveways … parking lots, drive-ins, tennis courts and baseball diamonds. Anywhere dust can rise, calcium chloride keeps it down.

Other Uses of Calcium Chloride

Control snow and ice with less chemical deicer

Another way calcium chloride helps maintain roads is through snow and ice control. Calcium chloride enables salt to work faster and at lower temperatures than it can alone. That’s because it must be in contact with moisture before it can start deicing. With calcium chloride, it’s just the opposite. It absorbs moisture from the air so it becomes an effective deicing brine more quickly.

And while salt is effective at melting ice down to 20°F (-6.7°C), calcium chloride melts at temperatures as low as -30°F (-34.4°C). The result is a deicing combination that’s effective more quickly; that remains effective over a wider temperature range. And that keeps total deicer costs down because less material is needed. A 1977 study reports a 30% reduction of salt is a minimum you can expect, while one actual case shows a 50% salt reduction.

Maintains shoulders on paved highways

Paved highways built to a high standard need unpaved shoulders that meet the same density and stability requirements as the road base. Also, the unpaved shoulder must remain tight against the pavement for safety reasons. Calcium chloride fits naturally into these needs because of its strong binding qualities..

Concrete modification

Calcium chloride has been used as a concrete additive for nearly a hundred years. It acts as an accelerator so that concrete has a faster strength gain. This can be especially valuable in winter because it shortens the time tender material requires protection from cold weather.

Tire weighting with calcium chloride

Calcium chloride can extend the life of tires because it adds about 30% more weight to a gallon of water. This added weight increases drawbar pull by putting weight at the lowest possible point.

Weighted tires enable the tread to grip the road more firmly for maximum traction and less slippage. The result is increased tire life and thousands of dollars saved.

Calcium Chloride: Specifications and Application Rates

LIQUIDOW calcium chloride is a ready-to-use liquid solution that goes on fast and easy. Sprayed on roads, this chemical helps valuable road material stay where it’s put by keeping fines for binder in place. The result: Stabilized road surfaces.

It’s likely that your spreader equipment can easily handle the application of calcium chloride without modifications. Calcium chloride cannot make a bad road good; its purpose is to keep a good road good – crown intact, aggregate in place, etc. The chart below shows application guidelines for calcium chloride on existing unpaved roads that meet the standards of stabilization.

Specifications LIQUIDOW
CaCl2 – minimum 38% 35% 32%
MgCl2 – maximum 0.2% 0.2% 0.2%
Alkali Chlorides – maximum 3.4% 3.1% 2.8%
Table of equivalents for dry Calcium chloride @ 77°F 38% 35% 32%
1 gallon = pounds of DOWFLAKE calcium chloride 5.70 5.11 4.55
1 gallon = pounds of PELADOW calcium chloride 4.62 4.15 3.69
1 ton DOWFLAKE in gallons 351 392 440
1 ton PELADOW in gallons 433 482 542
1 liquid ton in gallons 172 177 182

Article printed from Peters Chemical Company: http://www.peterschemical.com

URL to article: http://www.peterschemical.com/controlling-road-maintenance-costs-through-surface-and-base-stabilization/