Portland cement is the basic ingredient of concrete. Concrete is formed when portland cement creates a paste with water that binds with sand and rock to harden.

Cement is manufactured through a closely controlled chemical combination of calcium, silicon, aluminum, iron and other ingredients. Common materials used to manufacture cement include limestone, shells, and chalk or marl combined with shale, clay, slate, blast furnace slag, silica sand, and iron ore. These ingredients, when heated at high temperatures form a rock-like substance that is ground into the fine powder that we commonly think of as cement.

The most common way to manufacture portland cement is through a dry method. The first step is to quarry the principal raw materials, mainly limestone, clay, and other materials. After quarrying the rock is crushed. This involves several stages. The first crushing reduces the rock to a maximum size of about 6 inches. The rock then goes to secondary crushers or hammer mills for reduction to about 3 inches or smaller.

The crushed rock is combined with other ingredients such as iron ore or fly ash and ground, mixed, and fed to a cement kiln. The cement kiln heats all the ingredients to about 2,700 degrees Fahrenheit in huge cylindrical steel rotary kilns lined with special firebrick. Kilns are frequently as much as 12 feet in diameter—large enough to accommodate an automobile and longer in many instances than the height of a 40-story building. The large kilns are mounted with the axis inclined slightly from the horizontal.

The finely ground raw material or the slurry is fed into the higher end. At the lower end is a roaring blast of flame, produced by precisely controlled burning of powdered coal, oil, alternative fuels, or gas under forced draft.

As the material moves through the kiln, certain elements are driven off in the form of gases. The remaining elements unite to form a new substance called clinker. Clinker comes out of the kiln as grey balls, about the size of marbles.

Clinker is discharged red-hot from the lower end of the kiln and generally is brought down to handling temperature in various types of coolers. The heated air from the coolers is returned to the kilns, a process that saves fuel and increases burning efficiency.

After the clinker is cooled, cement plants grind it and mix it with small amounts of gypsum and limestone. Cement is so fine that 1 pound of cement contains 150 billion grains.  The cement is now ready for transport to ready-mix concrete companies to be used in a variety of construction projects.

Although the dry process is the most modern and popular way to manufacture cement, some kilns in the United States use a wet process. The two processes are essentially alike except in the wet process, the raw materials are ground with water before being fed into the kiln.

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:

Calvac Paving
2645 Pacer Ln
San Jose, CA 95111
(408) 837-9021

 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.

Modern technology and paving practices have revealed faster, more cost-effective solutions to problems that once would have required expensive tear-out and repaving operations. One of the best examples we at Calvac Paving have ever seen was the rehabilitation of the Redwood Shores parking lot we recently undertook. This project mixed new technology with time-tested techniques to deliver a great result for the client, faster and more efficiently than conventional paving methodology.

The parking lot itself was old, cracked and weathered from years of use, but not so bad as to need a complete removal and replacement. Age and oxidation from poorly placed asphalt atop moisture-sensitive base material had caused the asphalt to crack and dry out, reducing its flexibility and its resilience. The parking lot was in need of a major face-lift, and Calvac Paving had the perfect product and the years of specialized talents to make it happen. This was a very unique project in that it perfectly fit the criteria for a very specific application: a Petromat overlay.

 

Petromat is a non-woven reinforcing fabric that is applied using a liquid asphalt binder known as RS1, which works as a penetrating adhesive and moisture barrier. The Petromat fabric helps to retard the existing cracks from reflecting through the new asphalt surface and gives the finished surface a higher tensile strength, thereby distributes the weight of heavy truck traffic over a greater area. After that, a full two-inch placement of hot ½”fine asphalt is placed with self-propelled paving machines.  Once the asphalt has been placed, the compaction equipment follows immediately behind the paving equipment. These very large and heavy smooth drum rollers compact the hot asphalt to a dense, smooth and uniform finish.

Once the compaction process is completed and the hot asphalt has cooled, we then apply a fog seal mixture of 50% SS1 and 50% water. This is designed to help bond the top layer of new asphalt and give it that black shiny “new pavement” look. After the Petromat overlay is 100% completed to our satisfaction, we can proceed with striping and stenciling operations.

Because of the unique considerations and time constraints of the job, Calvac Paving recommended a 2” Petromat overlay over the entire parking lot, measuring approximately 63,500 square feet. This offered the best results for the budget and gave them similar benefits to getting a brand-new parking lot for years to come, without the hassle, expense and lost time of a complete remove and replace. This project also had some very unique parking design restrictions, offering a perfect opportunity for Calvac Paving to design a new layout for the regular and ADA stalls. This redesign included larger stalls, which helped prevent unnecessary dents in car doors, making both the tenants, and owners happy with their new parking lot investment.

Please feel free to drive by and see what a truly professional paving project should look like, and what your commercial parking lot can look like too! From a private roadway rebuild to a complete parking lot rehabilitation and much more, there are very few jobs Calvac Paving cannot do. We’ve been serving the Bay Area for more than 40 years. Now let us serve you! To find out more about Petromat or how we can help with your next project, contact us by email or by phone at:

(408) 225 – 7700

(650) 694 – 7944

(831) 375 – 7944

When you need the best, don’t leave the results to chance. Contact Calvac and have the job done right the first time, every time!

At Calvac Paving, we support technologies and construction methodologies that offer a more environmentally sound and sustainable way of creating the things we as human beings have come to rely on. From asphaltic concrete recycling to innovations such as self-healing concrete, we are always on the lookout for trends and techniques that change how we operate for a greener, healthier planet. This is why we are so excited about the possibility of roads that actually recharge electric cars as they drive! These specially designed roadways will reduce pollution, increase the performance and range of electric cars to unheard-of levels, and reduce or entirely eliminate the need for charging stations.

In the UK, this seeming science fiction is becoming science fact, as the government moves to experiment with charging roads. Operating on the same principle as a wireless phone charger, the roads will charge cars through magnetic induction resonance. Cables implanted in the material of the roadway generate a specialized electromagnetic field that the car can convert into usable energy. The roads will also include communications equipment attuned to the unique energy signature of an electric car, alerting the road that an electric vehicle is present and to initiate the power generation process. This will allow properly equipped electric vehicles to recharge on the go, without needing to stop for extended periods to recharge, one of the biggest stumbling blocks cited in the adoption of electric vehicles thus far.

The roads the UK are experimenting with will be restricted for the time being, ensuring that regular vehicles do not impede the testing process. The government is committing 500 million pounds, or roughly $779 million, to these experimental roads over a five-year span. This technology is already in use in South Korea, powering rail systems with ranges of up to 15 miles, and will be combined with an added initiative to provide charging stations every 20 miles in the UK. The combination of options for drivers will help eliminate so-called “range anxiety,” which one advocate described as a combination of running low on gas and having one’s cell phone be low on battery simultaneously.

Magnetic induction resonance works in much the same way as a powerful operatic voice can shatter crystal. When the voice and the crystal reach a similar resonance, the molecules in the crystal begin to vibrate rapidly and cause it finally to break. Instead of shattering or rupturing the battery, however, the cables the charging roads utilize will create a harmonic resonance within the battery that allows it to transform the signal from the roadway into usable power.

Because many roadways contain metal in addition to the native subgrade, road base and asphalt in the form of rebar, wire-mesh matting and metallic joints between road sections, the cables can use this metal as a part of the transmission system for the power. The metal components of the electric car can be employed as a receiver, directing the transmitted energy to the battery without the driver needing to stop, handle any charging devices or worry about whether or not the car will make it to the next charging station.

Major car production companies such as Audi are leading the research into this technology, which they believe will relegate internal-combustion vehicles to the status of horse and buggy. By working together to create a standardized plug-in system for use in garages, parking structures and ultimately at-home use, these car manufacturers believe they can make charging stations easier to find and thus make electric cars more attractive. The idea of “switching stations,” where a person can simply replace a drained battery with a fresh one and continue on, and the increased range of electric cars to around 250-300 miles per full charge depending on the type of car and battery size, will help expedite this process.

While paved roads are still very much a part of the future landscape, what drives over those roads and what lies beneath them may soon play a more crucial role than ever in our environmental integrity and ability to move people and cargo. Calvac Paving will be watching the trials in the UK with a great deal of interest, because we want to see if this technology truly is feasible and what the implications will be for the paving industry. If everything pans out as the equations and scientists claim, this could be a major breakthrough and a huge tectonic shift in how things are designed in both construction and automotive industries, as well as manufacturing and transportation as a whole. We think that’s a pretty big win, and look forward to this technology here at home!