Posts By: Calvac Paving
Calvac Paving’s commitment to service means that we often have projects that present unique challenges. For a medical center in Menlo Park, there were several problems that had to be overcome. First, the base below the asphalt had become unstable, leading to depressions and potholes in the surface. Due to these conditions the existing asphalt had to be removed, the baserock graded and compacted. Second, the existing asphalt had to be off hauled and new pavement placed over the recompacted baserock. Finally, because it is an active office, we had to complete the removal, replacement and striping in a single Saturday.
When we first arrived, the parking area was riddled with potholes and puddles from the destabilized base. The existing striping and stall design of the parking lot was several years out of step with current ADAS and CBC standards for access. We then scheduled the off haul of recycle and import of hotmix asphalt tonnage and we mobilized the equipment and manpower necessary to complete the job, as well as staging the striping crew. Since we had a very tight window and no margin for error, we knew this had to be done efficiently and correctly the first time, with no delays. After blocking off the area so that we could work safely, we began grinding out the existing asphalt using a specialized milling machine. This pulverized the existing asphalt so that we could haul it to a local recycling plant, while exposing the existing baserock surface. Once that was completed, we graded and compacted the baserock so that Calvac Paving could create a stable, uniform surface that would create the necessary drainage and eliminate the puddles. This process, known as “grading,” is key to establishing a surface safe for vehicles and pedestrians while permitting stormwater drainage, which helps prevent subgrade destabilization by not allowing water to collect and seep through the asphalt.
Once the grade had been established and the baserock compacted to comply with industry standards and project specifications, we placed fresh hotmix asphalt in two 2” layers, or “lifts.” Compacting the asphalt in lifts as it was placed, created an end product that is more durable, less prone to cracking, potholing and other problems seen with asphalt paving. Once the second lift was placed, and we fog sealed the surface, we then had to layout and stripe the parking lot up to current ADAS and California building code requirements for correct access to the building and parking areas.
The result was a very smooth and puddle free, pedestrian, parking and driving surface that is far more stable than the previous paving, as well as meeting the latest standards. At the end of the project, we had removed and replaced more than 150 tons of hotmix asphalt in a single day, which was a quick turnaround for this volume of material and the job specific constraints.
Calvac Paving has been serving the Bay Area for over 45 years, from road rehabilitation projects in Los Altos Hills to this medical center parking lot overhaul in Menlo Park, and we have constructed, repaired or remediated thousands of properties. Each project requires a slightly different approach, due to project requirements, schedules, access concerns and other factors. We pride ourselves as the Bay Area’s solution to those supposedly “challenging” jobs, combining our reputation for safety and efficiency with the attitude that there’s no reason to consider a job “challenging” with the right safety, tools, training and equipment.
We also offer an industry-leading three-year warranty on the finished product to our qualifying clients as proof that we stand behind our product and the workmanship that goes into it. We are committed to providing our clients and stakeholders the best and most efficient results in the business, while making sure that the product that we leave behind is one we can look back at with pride. For more information about how Calvac Paving can help with your job, from a major roadway reconstruction to building an ADA-compliant access point to restriping a parking lot, we invite you to call us at:
(408) 225 – 7700
(650) 694 – 7944
(831) 375 – 7944
Some things in life shouldn’t be left to chance, and the surfaces where you, your family and your clients drive and walk on a daily basis are good examples. When you want the best, done right the first time, every time and on time, you want Calvac Paving, and we want to help!
At Calvac Paving, we think the history and evolution of paving and construction materials over time is just as interesting and important as using them properly to deliver great, durable results for the projects we work on. For this week’s Maintenance Monday installment, we’re going to take a look at the surprising and fascinating history of asphalt and answer a few questions we get a lot from clients and the general public. You might even learn new facts to stump your friends or help your trivia team crush the competition, courtesy of your friends at Calvac Paving!
When Was Asphalt Invented?
The “active” ingredient in asphalt is tar, also called pitch and technically known as bitumen. It is a naturally occurring petroleum byproduct that is formed from the decomposition of buried plants that were ancient when the dinosaurs rose to ascendancy on the planet. It is often found in pitch lakes and oil sands. It is also created as a byproduct of petroleum distillation, which today is the most popular source of bitumen due to global fossil fuel consumption.
One of the most famous natural sources of bitumen is California’s very own La Brea Tar Pits, which also happens to be one of the most notorious and productive Ice Age fossil concentrations in America. This is because water accumulating and floating on the surface of the pits attracted prehistoric animals to drink from it—trapping them in the hot tar and preserving their remains!
The earliest known references to the use of bitumen as a building material date all the way back to ancient Mesopotamia. Bitumen was used to waterproof temple roofs, ritual baths, and rainwater collection vessels, basically serving as an ancient precursor to silicone caulking. The Phoenicians used pitch to protect the hulls of their ships from the ravages of saltwater, weather, wind, and waves, which in turn helped rank them among the world’s most skilled and feared navies of the day. There is a school of thought that suggests the formula for the legendary “Greek fire,” which could burn on water and was primarily developed as a counteroffensive measure against the Phoenicians and other seafaring foes, may have incorporated bitumen in some way, though this cannot be factually substantiated since the actual process for producing this fearsome weapon has been lost to the ages. In Egypt, bitumen was employed as an adhesive for the funerary wrappings of royalty to protect both the earthly bodies and the treasures bound within the linen bandages which formed the shroud.
To the best of our knowledge, Ancient Babylon has the best claim to fame for the first use of asphalt as a paving material, somewhere around 625BCE.
From Babylon and Carthage, the idea caught on with both the Greeks and the Romans. In fact, the word “asphalt” derives from a Greek word, “asphaltos,” meaning “secure.” The Romans used this new Babylonian technology to create smoother, more efficient roads to move goods, supplies, and, naturally, military forces throughout the Empire.
The first use of asphalt as pavement in modern history appears to date to the 1700s, when an Englishman named John Metcalf began laying roads using asphalt around England. A Scot, Thomas Telforld, took up the idea and brought it to Scotland, where it was later perfected by one John Loudon Macadam. Macadam used a combination of crushed rock and bitumen to create his asphalt roads, giving rise to the names “tarmacadam,” “macadam” and “tarmac,” all names which are still in common use on the Continent, and to a lesser extent in the United States, today.
Asphalt in America
The first recorded asphalt roads in the United States were laid in Newark, New Jersey and on Pennsylvania Avenue in Washington, DC by a Belgian chemist, Edmund DeSmedt, in 1870. This was also the year the first hot mix production operation in the United States began. Curiously, the first patent for asphaltic concrete was not filed until 1871! Another patent in 1900 referenced “bitulithic” concrete, a portmanteau term of “bitumen” and “lithos,” the Greek word for “stone,” which set the foundational template for nearly all asphalt mix designs used in America up to the present day.
As early as 1907, the rise of automobiles as a primary transportation method and the increasing demand for gasoline to fuel them had made man-derived asphalt the most popular source of bitumen. In a magnificent twist of ingenuity and synchronicity, the very thing that made cars run also provided the materials on which they could drive!
Today, asphalt or asphaltic concrete, as it is technically known, is by far the most popular paving material for everything from parking lots to interstate highways. It is also used in roofing materials such as asphalt shingles. Raw hot mix can also be applied to the surface of a roof, creating a light, strong, waterproof surface.
Natural asphalt is rarely used these days, partially because asphalt derived as a byproduct of petroleum production is so plentiful and relatively cheap compared to the expense and effort required to distill asphalt into a usable purified form.
Another reason natural asphalt sources go largely untapped is because many of them, like the La Brea Tar Pits, are protected by local, state, and federal laws for their paleontological and cultural value.
Fossil plants, animals, insects, and human artifacts from Native American tribes in these areas have all been found, making their ongoing conservation and preservation a major point of interest to nature and environmental groups, Native American tribes, and government agencies alike.
Finally, asphalt is one of the most recycled substances on earth. An estimated 89.2 MILLION tons (178.4 billion pounds/81.09 billion kilograms) of asphalt were reclaimed and recycled into new mixes in 2019 in America alone according to the National Asphalt Paving Association. This means that overall, asphalt is very environmentally friendly and is not considered an air pollutant by the EPA, even though the fumes from fresh asphalt can be a little overwhelming if you’re not used to them.
So the next time you’re driving down the highway or pulling into your own driveway, you might take a moment and spare a thought for the fact you’re driving on the results of an idea older than recorded history!
And of course, for all your concrete and asphalt paving needs, click here to contact Calvac Paving and get the job done right the first time, every time!
Sealcoating is an important process in the maintenance of your all too expensive parking lots. We all know that the costs for paving repairs have increased. This makes it all the more important to protect and preserve your asphalt surface. Calvac Paving has been applying sealcoat for over 45 years, longer than most Bay Area Suppliers have been making asphalt based sealcoats. Each successive generation of sealcoats has provided greater protection from premature wear, moisture intrusion and oxidation. Even with these improvements we strongly recommend the addition of latex and sometimes sand to the existing asphalt sealcoats to extend the life expectancy of these applications. It is also vital for you to have your contractor apply two coats of sealcoat to your property. The first coat, with the added sand and latex, is the filler coat and allows placement of a second coat with added latex only or wear coat.
Preparation of the existing asphalt surface is a very important process in sealcoating your parking lot. Calvac Paving will spend the time necessary to clean and prepare your asphalt to assure a durable and attractive product. We will remove all vegetation, and apply herbicide if appropriate. We will use Power blowers, scrapers, wire brushes and brooms to thoroughly clean the existing asphalt.
This preparation may also include Mobile Sweepers, water trucks or buggies and vacuum trucks. We will burn, scrape and carefully clean the oil spots and apply an oil spot sealer with sand. We will mask utility covers and other structures to protect against coverage. We will apply hot rubberized or coldpour emulsion crackfiller as directed.
The consistency of the asphalt sealer is also very important to the durability of your sealcoat project. Calvac Paving will never exceed the manufacturer’s recommendations for dilution. This addition of water is necessary for the application and actually improves the bonding to the existing asphalt surface. We feel the addition of latex and sand to the asphalt sealer extends the life of the sealer, and we include these admixtures in well over 90% of our sealcoat projects. By extendeding the life of your sealcoat surface with added latex, you reduce the number of times you will need to seal coat and stripe your lot as well as impose upon your tenants over the life of the asphalt.
The combination of effective barricading and traffic control with superior craftsmanship and products will provide you with the best result with the least impact upon you and your tenants.
The saying “They don’t build ‘em like they used to” is literal truth in the concrete industry. For decades, modern science has struggled to work out how ancient societies such as the Romans were able to create buildings, monuments and roadways which are still visible and even in use today, when the average lifespan of modern concrete tends to be far more modest. Now, a team of scientists from the University of Utah believes they may have found the surprising answer to this centuries-old mystery.
Modern concrete uses Portland cement as its base, which is a fine powder created from lime, chalk, sandstone, iron and other materials and then combined with aggregates of varying sizes. However, the Romans used a type of cement created from the ash of certain volcanoes. These volcanoes’ emissions contained a rare combination of mineral elements which only occurs naturally in very specific areas with particular geological profiles. What’s most surprising is that the minerals which make Roman cement different from Portland cement appear to react to seawater, which encourages the crystalline structure of the minerals to continue growing. This actually makes the concrete self-healing and impedes cracking, a feat modern science is still trying to replicate.
This discovery of how Roman concrete was made is important because it could lead to greener and more eco-friendly concrete production and paving technologies, as well as structures with higher strength, structural integrity and longevity under adverse conditions than modern concrete allows for. In addition, Roman concrete did not use reinforcing steel such as a wire mesh mat or rebar, both of which Portland cement will corrode and degrade over time. This may lead to significant cost reductions for new construction on structures like bridges, building footings and other applications.
However, the research team warns it’s too early to get too excited about Roman concrete. First, Roman concrete relies on very specific minerals, namely tobermorite and phillipsite, being present in certain quantities. The researchers say the composition of Roman concrete was largely a matter of luck and being in the right place, at the right time, with access to the right materials. Second, we don’t yet know exactly how the Romans made their cement or what the process was for mixing it with aggregate and placing it. This by itself may leave us several years, or even decades, away from being able to use Roman concrete effectively.
Despite these hurdles, the concepts behind Roman concrete and other green discoveries from the ancient world are constantly being studied, evaluated and applied to our modern understanding of how to build things that last. At Calvac Paving, we’ve been serving the Bay Area for over 45 years in the most environmentally friendly, safe and expedient way possible. We’re always on the lookout for new developments, technologies and ideas which will let us do our jobs more effectively, with less impact on the world we all share. To learn more about our commitment to the environment, or how Calvac Paving can help you with your next project, contact us at:
2645 Pacer Ln
San Jose, CA 95111
With the wetter, cooler conditions of fall upon us and winter in full swing, it’s a good time to check your parking lot and other asphalt applications for signs of poor drainage and damage. It’s much easier and less expensive to catch a problem early and correct it than it is to wait until that small cracked area spreads to half the lot. With this in mind, here are four signs you should look for to check if your parking lot drainage is working as it should.
- Rocks or sand in unusual places
If, after a heavy rain, you notice rocks or sand in low-lying areas, this may be an early warning sign that something’s wrong with your drainage. The water from the rain may actually be eating away at the asphalt and flushing away the solid particles of sand and rock aggregate that make up asphalt. To make sure it’s not runoff from the street or areas higher up, look for consistent ripples or waves in the deposits which are larger at the higher end and taper off toward the lower side of your lot. If you see this, your lot is probably okay, unless you see large areas where the sediment and rocks have gathered. This indicates possible low spots which could cause problems later.
- Pools of water or flow down the middle of the lot
Most asphalt parking lots today are designed along a slight but apparent slope to facilitate runoff. Likewise, they are usually built with an engineered high point called a “crown,” which is intended to direct water away from the middle of the lot and down toward the drain points. Pooling and water flowing directly down the middle of the lot suggests the crown has been compromised or a possible issue with the subgrade, which will need to be addressed before the asphalt begins to buckle.
If you start to see cracks developing, especially in areas where you also see heavy water flow and/or residue such as described above, this is a sign the asphalt is beginning to fail because the water is breaking down the bitumen binder. This may also be a sign of traffic outside the asphalt’s design tolerances being present, such as large amounts of heavy trucks or construction equipment. In either case, once cracking begins, water can infiltrate the asphalt surface and accelerate the rate of failure, making repairing it a priority before it gets out of control.
- Are your drain inlets working as they should?
Periodically, it’s a good idea to check your streetside and in-lot drainage inlets to ensure they’re clear of obstructions and debris which may prevent them from working as expected. In many cases, asphalt failure can be traced back to a blocked drain inlet which hasn’t been corrected. Regular property walkthroughs can help you spot problems like this before they become severe enough to warrant repair or rehab of your parking lot, and keep it working the way you expect it to for years to come.
For more information about drainage or to speak with Calvac Paving about your parking lot or other asphalt and concrete construction needs, click here to contact us!
Calvac Paving recently undertook a paving rehabilitation project for the San Harbour South HOA association located at 906 Beach Park Boulevard in Foster City, California. The existing pavement was over 45 years old and was starting to exhibit severe cracking and base failures.
Primary Client Concerns
The primary client concerns included:
Continuous access during the milling, repaving and striping operations
Schedule and time management
Quality surface at the project’s end
After reviewing the jobsite in person, we came up with a range of possible solutions that would meet the client’s needs.
Milling and grading operations
Tearout and rebuilding of existing valley gutter
Due to sub-grade issues. We proposed milling the existing pavement down 2” from the existing surface and laying approximately 2,500 tons of ½” aggregate hot mix, in addition to the replacement of 1,500 linear feet or 90 cubic yards of concrete valley gutter. Our recommendations and proposed fix were accepted by Calvac’s client and HOA Board. The job was undertaken in phases as to not disrupt the community at one time.
The end result of the San Harbour South HOA project looked fantastic! The project went off without any difficulty and was completed within the stated schedule and budget.
Calvac Paving is proud to have served the Bay Area for over 45 years with a wide range of paving, concrete and ADA access planning and implementation solutions. Why gamble with the outcome of your project? Make sure your contractor can get it done right the first time, every time. To learn more about how Calvac Paving can help service your construction job or to obtain a quote for services, please call us at 408-225-7700.
2645 Pacer Ln
San Jose, CA 95111
Asphalt pavement is one of the most durable and resilient materials currently used in modern construction. It’s easy to place, maintain and recycle when its service lifespan has expired, helping to reduce manufacturing costs and greenhouse gas emissions associated with asphalt paving production. Asphalt surfaces are also very flexible relative to other paving materials, which is just one reason why asphalt parking lots have become so popular. But, like any other construction material, asphalt and concrete paving don’t last forever. A well-placed asphalt surface can last 10-20 years or more with proper pavement maintenance. As we move into the wetter, colder months, you’ll want to be on the lookout for these 7 signs your parking lot needs repair.
1. Look for cracking and crumbling edges.
You’re most likely to see these signs of asphalt deterioration around joints in the parking lot paving and the curb and gutter areas of industrial parking lots and asphalt driveways, although they can occur anywhere. When this happens, it could indicate that people are driving too close to the edge, the asphalt is not properly supported at the edges or the asphalt is beginning to age out of effective service. If not sealed or repaired, the cracks can spread throughout the entire surface. Crack sealing early can help extend the life and performance of the asphalt surfaces.
2. Potholes and sunken areas
These commonly occur when water seeps into cracks in the parking lot’s surface. Over time, the water undermines the subbase, causing the paving in that area to sag and crack. One key symptom of an incipient pothole is the presence of pooling water on the surface. If you notice this, a spot asphalt repair can help prevent larger and more costly problems later.
Alligator cracking, named for its distinctive appearance, is a sign of too much stress on the asphalt. If your asphalt surfaces look like the skin of an alligator, it can indicate the subbase was improperly prepared by the original paving contractor and/or the pavement is routinely subjected to heavier traffic than it was designed to withstand, such as parking large trucks on a residential driveway. When you see this, you need parking lot and driveway repair or replacement right away.
The binding agents in asphalt which give it its flexibility and strength don’t last forever. In fact, from the moment asphalt is laid, the sun, wind, water, weather, and oil and chemical leaks from vehicles begin to eat away at them. This is why asphalt’s color fades from black to gray and the aggregate begins to peek out of the surface. Depending on the size of the area and whether other signs of damage are present, asphalt seal coat, asphalt milling, and parking lot resurfacing may all need to be considered.
5. Improper drainage
Evidence of improper drainage can be an early sign asphalt repairs are needed. If water can’t drain off your parking lot or driveway it can damage the asphalt surfacing and cause larger problems later. Blocked storm drain inlets can lead to damage as well, so it’s important to inspect them regularly and make sure the runoff from your lot or driveway can go to where it’s intended.
Proper parking stall and line marking make your property look better and more user-friendly. It’s also a requirement of the Americans with Disabilities Act. In addition to directing traffic, striping often works as a sort of visual canary for indicating potential issues which might otherwise go unnoticed. If your parking lot’s striping is looking worn, difficult to read, or hard to understand, you need to take a closer look at the entire area for other potential issues.
If you can’t remember the last time you had any repairs or maintenance on your driveway or parking lot, it’s probably time. For best results, your asphalt surfaces should be seal coated at least every 4-5 years to help keep them looking their best and preventing chemicals, motor oil, and water from infiltrating the surface. If there are no major issues with the asphalt surfaces, minor crack sealing and spot repairs can also be made before sealing the surface again. It’s also a good opportunity to update your parking layout and striping to comply with ADA guidelines if they don’t already!
Keeping your asphalt paved surfaces in good repair isn’t just about making your property look and perform its best. Driveway or parking lot problems could also present ADA compliance issues with hefty associated fines and even open your company to workers’ compensation claims or civil lawsuits arising from injuries and vehicular damage. By making timely preventative asphalt repairs you can save time, money, and worry while presenting a more professional face for your business. At Calvac Paving, we know you have a choice of commercial asphalt and concrete paving contractors in the Bay Area, which is why we’re committed to delivering the finest in asphalt repair and driveway and parking lot construction. For your next parking lot repairs or to learn more about how Calvac can help you get the maximum life from your asphalt paving, click here to contact us.
With winter and its accompanying rainfall on the way, the fall is a good time to take a look at your existing pavement and make sure it’s ready for the weather to come. Calvac Paving has been in the business for over 45 years, and in that time, we’ve learned a thing or two about how to solve small problems before they have a chance to become big ones. Now, we’re pleased to present this list of simple things you can watch for so your pavement lasts longer and looks and performs better in the process, even when the worst of the California winter weather strikes!
Do a routine walkthrough of your paved areas.
Parking lots and other paved areas should be checked at least semiannually for problems. Things to look for include:
- Areas of standing water. Water can break down the asphalt binder and leak down into the subgrade, eroding it over time. This is also an indication that the pavement or subgrade may already be failing, because modern grading techniques are designed to establish a grade that flushes water away from the parking area and toward designated drainage points.
- Oil or other chemicals that leak directly onto the pavement. Just like water, some chemicals associated with vehicles can cause binder breakdown and lead to subsurface problems. Cleaning up oil and other chemical spills as quickly as possible can help prevent this and keep your asphalt in better condition.
- Cracks, divots or uneven areas. These can be caused by weeds growing beneath the surface, freeze/thaw patterns, standing water and oil or ongoing heavy truck traffic. Small cracks and divots are often the first visible sign of possible asphalt breakdown, and it’s more cost-efficient and less intrusive to fix them when they’re small by seal coating or spot patching than it is to do a complete tearout and reinstall of the paving.
- Striping: Old, dull or worn striping and pavement-level signage such as fire lane indicators and other information may be harder to see and read during winter months. Especially in ADA stalls, the striping and signage should always be clearly visible to make sure people know where these areas are.
Clear debris from drainage channels and curbs.
If water has nowhere to go, it doesn’t matter how good the drainage plan for your lot is. Making sure the drainage channels, storm sewers and other inlets to the runoff system near your property are clear of leaves, branches, garbage and other obstructions will help the water flow better and make it less likely to pool up on your property.
Limit or restrict heavy-vehicle traffic as much as possible.
Large trucks such as semis, garbage trucks and other heavy vehicles can place a lot of stress on asphalt. By itself this shouldn’t be a problem, but when the base course and subgrade are compromised by water or plant intrusion, it could speed up the breakdown process for the asphalt. If at all possible, try to limit, restrict or even out the traffic pattern for such vehicles within your lot to minimize the time they spend on your pavement.
Be sure it’s sealed.
Even if your parking area is free from cracks and other problems, it is a good idea to have it seal coated every 4 to 5 years at the minimum. This is because seal coating helps rejuvenate the asphalt binder at the surface, adding an extra layer of protection against traffic, water and other spills. Even better, it will help make your parking lot and driveways look newer, especially when you redo the striping at the same time. This makes your property more attractive, safer to navigate and less likely to fail for the long haul.
Seek professional help.
If you’re not sure if the paving problems you’ve identified are “big enough,” or if you think your pavement needs a facelift or a complete overhaul, Calvac Paving can help. We’ve been serving the Bay Area for over four decades with quality construction solutions including:
- Curb and gutter remediation, repair and replacement
- Paving rehabilitation, tearout and reconstruction
- ADA access compliance and signage
- And much more!
We take great pride in delivering a great product for your project, within the schedule and budget we agree upon. For more information about how Calvac Paving can help you with your paving or asphalt project, please contact us for a no charge estimate.
2645 Pacer Ln
San Jose, CA 95111
One question we hear a lot at Calvac Paving, usually from private homeowners and people who don’t work in construction, is what the difference is between cement and concrete. After all, many people call concrete trucks “cement mixers” and refer to the finished product as “cement.” The problem is, this isn’t just inaccurate, but it can cause a lot of unnecessary confusion between contractors, engineers, and the general public. To explain why this matters, let’s start by taking a closer look at how cement, the key ingredient in concrete, is made.
Everything You Need to Know About Cement
Cement is not the only ingredient in modern concrete, but it is the base agent. The most commonly used type of cement is known as Portland cement, because of the end product’s resemblance to an ancient building material found on the island of Portland, off the British coast. This method of creating concrete was first patented by an English stonemason in 1824, meaning modern cement is two hundred years old!
Portland cement is created by burning and then grinding down a mixture of limestone and either shale or clay. This forms a fine, gray powder with hydrophilic properties, meaning it attracts and binds readily to water. When it is mixed with water and allowed to cure, it creates a stonelike surface, similar to plaster of Paris but far stronger and less brittle.
The problem with hydrophilic cement is that it’s both fairly volatile in terms of how readily it reacts with water and can take a long time to cure. Because of this, it has to be carefully stored in a cool, dry place to keep it in powder form until it’s ready to be made into concrete. Admixtures that help reverse the cement’s hydrophilic properties are often added to the matrix during the mixing stage to reduce the cure time and boost its strength, flexibility, and resilience.
How Concrete is Made
Now that we know how Portland cement is made, it’s time to take a look at how concrete is created, which is really quite simple. By adding water, aggregates from fine sand to large crushed rocks, and in many cases chemicals to the Portland cement, you can create a concrete mix that will meet target strength and flexibility profiles, a specified air content range, and even make concrete in different colors!
The quantity and percentage of cement, water, and aggregates of different sizes to be added will depend largely on what the concrete mix is intended for. On a freeway bridge where asphalt paving is not desirable, you will probably want a fairly lightweight, smooth mix. This typically requires more sand and chemicals with a larger quantity of smaller aggregates than an ornamental walkway, which obviously won’t be expected to stand up to the same stresses as a highway.
The various dry materials are loaded onto the concrete truck at a batch plant. Each truck is supplied with a batch ticket, which shows the percentage and weight in pounds of the various dry ingredients and chemicals. Once the dry materials are loaded, the driver will add a specified amount of water. With the water added, the concrete has to be constantly agitated by rotating the drum to keep it from hardening in transit. If the mix cures on the truck, it’s nearly impossible to remove. If you’re a fan of the show Mythbusters, you may remember they did an episode where they tested a myth about using dynamite to clean out a drum full of concrete that had been set up en route to a job site.
Yes, concrete really does get THAT hard!
Concrete on the Jobsite
Once the mixture reaches the placement location, the tickets are often collected by the technicians who sample and test the concrete to ensure compliance with the project parameters. These technicians may be employed by the company supplying the concrete, a private third-party laboratory, or local, state, and federal authorities. About halfway through the load, if required, they will take a sample from the truck for testing.
Some common concrete tests include:
- Slump Test: Too little or too much water means the concrete may not perform to specifications when it hardens. Many companies send their concrete from the batch plant with the minimum water possible added, because it’s far easier to add water to a drier load than it is to get water out of an overly wet one! A slump test is performed by using a steel cone to form the raw concrete into a 12-inch-high cone and then pulling the steel form away. Upon removing the cone form, the concrete cone should fall. By measuring the amount the cone falls, or “slumps,” when the cone form is removed, the technician can determine whether the concrete’s water concrete is within the proper range for the mix design to perform as expected.
- Unit Weight and Air: These tests allow a laboratory to extrapolate from a given sample about whether the mix design as loaded on an individual truck is within the parameters specified for a given project or application. The air test is particularly important and most commonly done on high-traffic roadways which will receive a lot of exposure to the elements and temperature extremes, because too much air in the mix may allow for air bubbles to form, allowing moisture and frost to infiltrate the matrix and over time, break it up.
- Cylinder Tests: When you hear someone talking about “pulling cylinders” on a concrete pour, it’s almost certain they’re talking about this test. The raw concrete is formed into cylinders of a specific size and depth using plastic molds and allowed to cure onsite in a temperature-controlled environment such as a cooler for at least 24 hours. After this, the cylinders are taken back to the lab, “stripped” out of the molds, and placed in a high-humidity environment to cure until it’s time to break them. Commonly, a set of four cylinders is taken from a given load. This includes one to be broken at 7 days, at which point the concrete mix should meet 70% of the intended break strength; 2 to be broken at 28 days when the concrete should have reached 100% of the specified break strength; and one cylinder to be kept on hold in case one of the 28-day breaks fails to meet the specified strength, in which case it will be broken at 56 days or as directed by an engineer. Note: Your project may have different requirements, so be sure to check with the Engineer of Record for the exact testing protocols!
Once these tests and any others the project specifications require are done, the concrete can be certified as meeting the project parameters and construction can continue.
Putting It All Together
Now that you know how cement and concrete are made, you can see they’re not the same thing. It’s easy to understand why some people persist in calling concrete mixers “cement mixers,” even though this isn’t entirely accurate. It’s also obvious why some people stick with calling concrete “cement,” since it’s the Portland cement that cures and makes concrete a durable building and paving material rather than just a jumble of wet rocks and sand.
However, it’s important to understand that when you ask for “cement” and you mean “4500-PSI blue concrete for an exposed-aggregate walkway,” you’re at the minimum going to cause some confusion and brand yourself as an amateur. At the worst, you’ll wind up with a pile of dry Portland cement, which on its own will certainly do you no good when you’re building a roadway or a sidewalk.
But now that you know and understand the difference, you’re far less likely to have that problem—and you’ll sound just like the experts!
Every year, about 6 trillion cigarette butts are produced worldwide, or about 800 discarded butts for every man, woman and child on the planet. Not only are these butts an unsightly and expensive waste disposal problem, but the toxic chemicals which the filters trap and contain leach out over time to poison soil, groundwater, rivers and oceans. Now, a researcher at RMIT in Melbourne, Australia says he may have found a surprising answer to this problem: incorporate cigarette butts into asphalt aggregate!
According to the researcher, by coating the butts with a combination of paraffin wax and bitumen, the black substance also known as “tar” that gives asphalt its distinctive properties, it is possible to trap toxins which used butts contain while repurposing them as a lightweight, flexible asphalt aggregate component. This reduces the overall weight of an asphalt mix design while removing a potential 1.2 million metric tons of waste from the planet’s biosphere.
Another interesting side effect of adding cigarette butts to asphalt is the reduction of heat. Asphaltic concrete has been directly linked to the so-called “urban heat island” effect, caused by vast amounts of asphalt in a relatively small area. Cigarette filters are mostly made from cellulose acetate, a fibrous material which is spun down to look and feel like cotton. This material serves as an insulator which filters out toxins in cigarette smoke while helping prevent burnt fingers for those who simply must light up. These filters reduce thermal conductivity and reduce the thermal density of the mix. When placed as part of a roadway the asphalt containing the filters absorb and diffuse more heat, resulting in a cooler surface temperature and less radiant heat being redirected into the environment.
The final paper on this study states that butts coated with bitumen satisfied requirements for medium- and heavy-traffic mix designs. This would apply to interstates and surface streets with heavy commercial volume. Streets in residential neighborhoods, parking lots not marked for commercial vehicles and similar applications might use paraffin-coated butts. In the study, the research team used 10kg, 15kg and 25kg (about 22, 33 and 55lbs respectively) of encapsulated cigarette butts per cubic meter (1.30795cu.yd) to determine the ideal asphalt mix.
Since cigarette smoking on a global scale isn’t likely to go away anytime soon, finding new ways to deal with this waste is becoming a more pressing problem every day. Estimates claim that the mass of discarded cigarette butts may increase by as much as 50% by 2025 because of the increase in global population. Knowing this, recycling these butts into asphalt and other lightweight construction materials, as the author of the study proposes, may help us all breathe just a little bit easier.
At Calvac Paving, we know we only have one planet, and it’s up to all of us to care for it the best way we know how. There’s no reason that building a solid product and being ecologically responsible should be mutually exclusive, and we’re always on the lookout for new ways to incorporate green ideas into our building design.. We will keep a close eye on this and other “green” developments in construction materials, so we can continue to deliver the most environmentally sound products and processes possible without compromising on quality or durability. It’s all part of our commitment to make the communities we serve, and the world we all share, a safer and healthier place for everyone.