Five Distinct Classes of Chemical Admixtures

The purpose of chemical admixtures is to give concrete additional properties in order to better handle a range of variables such as pumping requirements or placing concrete in extreme weather conditions.  According to the National Ready Mix Concrete Association (NRMCA), admixtures are added to concrete to increase “durability workability or strength characteristics of a given concrete mixture.”  

 

The Portland Cement Association further adds that, “Admixtures are classed according to function. There are five distinct classes of chemical admixtures: air-entraining, water-reducing, retarding, accelerating, and plasticizers (superplasticizers).” 

 

Air-entraining is the process of intentionally inserting microscopic air bubbles into the concrete.  It is done to improve the concrete’s workability as well as to increase its durability in extreme freezing and thawing temperature cycles.  The only downside to air-entraining is that the concrete experiences a 5% reduction in strength for each 1% of air added; however, the segregation and bleeding is diminished or completely eliminated. 

 

Accelerators are another type of chemical admixtures and are used to increase the early strength of concrete by causing it to harden faster.  They are also used to protect concrete from extremely cold weather or if a project has a tight deadline.  Chemical accelerators can be either chloride based or non-chloride based and one common inexpensive example is calcium chloride. 

 

For situations where you need to slow down or delay the hardening process such as requiring a slower pour due to the scope of the project or in very hot temperatures, a retardant may be used.  This gives crews more time to effectively place and finish the concrete.   Sugars, lignin, and citric and tartaric acids are all common retardants. 

 

Chemical admixtures can be in a liquid or powder form and are added to the concrete mix along with portland cement, aggregate and water and typically make up less than 5% of the total concrete mix.  Regardless of whether chemical admixtures are derived from natural or manufactured chemicals, they are added to the concrete either immediately before or during the mixing process.

 

At The Conco Companies, our mission is to be the best supplier of concrete services in the Western United States and to bring our expertise, experience and quality to each project.  We continue to upgrade and expand facilities to better serve the growing market for public works projects, commercial, parking structures, educational, and other construction development. We have offices in California, Washington State, Oregon, Colorado and Nevada.

Sources:cement.org/cement-concrete-basics/concrete-materials/admixtures, nrmca.org/aboutconcrete/cips/15p.pdf

Properly Cured Concrete Offers an Optimal Outcome

Curing concrete is the process that controls the rate and amount of moisture concrete loses during cement hydration.  When concrete is properly cured, it can attain its optimal strength and durability.  Curing can be done at the jobsite once the concrete is placed and finished or during the manufacturing of concrete products.   

 

There are several different methods for curing concrete that are determined by factors such as the type of construction, the concrete mix, and outside temperature and humidity.  Regardless of the technique used, they all strive to keep concrete moist and to prevent the loss of moisture.  Other considerations taken into account are project specifications and/or parameters of the jobsite.  The Portland Cement Association explains that the purpose of curing is to provide the “adequate amount of moisture for continued hydration and development of strength, volume stability, resistance to freezing and thawing, and abrasion and scaling resistance.”

 

Concrete attains its full strength and durability after curing for a number of days, or in some cases, weeks.  Concrete contractors prevent the loss of moisture during curing by leaving the formwork in place and/or to cover the concrete with an impervious paper, plastic sheeting or membrane-forming compounds.  In addition methods such as spraying (or fogging), ponding or wet coverings that cool the concrete as the water evaporates are used.

 

When temperatures are 40ºF and above, the American Concrete Institute (ACI) recommends a curing period of a minimum of 7 days, or until 70% of the specified compressive strength is achieved for most concrete structures.  In temperatures above 50ºF, an accelerant can be used to speed up the hardening process and reduce the curing period to only 3 days.  Additional variables are determined by the weather conditions the concrete will be exposed to during its life-cycle as well as the size, shape and strength requirements.   

 

The Conco Companies are a leading supplier of concrete services for the Western U.S. and got our start in the Bay Area in 1959 by offering clients the best value on a wide range of concrete services and products.  Since that time, we have taken a leading role as one of the top concrete contractors in the region. Our offices serve California, Colorado, Oregon, Washington and Nevada.

Sources:cement.org/for-concrete-books-learning/concrete-technology/concrete-construction/curing-in-construction, concrete.org/TopicsinConcrete/TopicDetail.aspx?id=25&Search=Curing

Is Shotcrete Right for My Project?

As shotcrete is less expensive than traditional cast-in-place concrete walls, you may be wondering if it is right for your project and want to know when and where is it the most appropriate application.  The simple answer is that because it has the same structural characteristics as traditional cast-in-place walls, applications include everything from shear walls, retaining walls, and architectural walls to slope pavement and soil nailing.  Shotcrete is also the first choice for sites that have extreme operating environments including chemical plants, hydroelectric plants and gas-fired electrical generators. 

 

One of shotcrete’s biggest advantages is that it virtually eliminates the forming process all together, and thus reduces labor costs as well as saves time.  Furthermore, over the last several decades, advancements in shotcrete technology have increased dramatically along with many improvements in the equipment that allow for even more varied uses.

 

At the Conco Companies, we have extensive knowledge of the shotcrete process and have had the opportunity to work on numerous projects using the material.  One unique project we did a few years ago was in Washington State in the scenic City of Burien.  The city, which sits just below the Cascade Mountain range and boasts a spectacular view of Mount Rainier, needed to build a parking garage to support their new bus transit center. 

 

Since Burien did not want to build a structure with lots of plain concrete walls, they turned to Conco’s expertise to help turn a parking garage into a piece of art that featured the town’s most visible landmark and the surrounding mountain ranges.  Our team of experts sculpted shotcrete murals along all four sides of the structure that depicted scenes of the Olympics, the Cascades and Mount Rainier.  The project consisted of shear walls that were shot from the outside of the building, and the area where we would do the murals were left with a scratch finish to ensure a proper bonding to the structural shotcrete wall.  We encourage you to visit our website to see the remarkable pictures of the finished project. 

Conco’s mission is to be the best supplier of concrete services in the Western United States and to bring experience, expertise and quality to each project.  We continue to upgrade and expand facilities to better serve the growing market for public works projects, commercial, educational, parking structures, and other construction development.

New Techniques for Dealing with Concrete Cancer

Concrete cancer is a term used to describe the problem of concrete spalling and cracking caused by rebar corrosion in buildings and concrete structures.  When the steel reinforcing within a concrete slab starts to rust, the steel rust can expand up to 7 times its original size, which causes concrete to be displaced and become flakey.  The process intensifies as the steel pushes the concrete away (referred to as concrete spalling), and more water comes into contact with the steel, which compounds the problem. 

 

Beside flaking and cracking, other signs of spalling concrete include rust stains that appear to be coming from within the concrete, leaks, and bubbling.  Often the problem is blamed on weathering or aging concrete, but the problem can be dangerous.  Spalling can cause chucks of concrete to separate from structures such as buildings and bridges and present a real hazard to pedestrians passing by or traffic below. 

 

Structural engineers have wrestled with the problem for years and recently researchers at the University of British Columbia in Canada think they have found a cure for concrete cancer.  Their study suggests that a cure may involve “producing concrete using discarded glass.” Shahria Alam, an associate professor of engineering and one of the authors of the report, says, ““Every year, millions of tons of glass bypass recycling centers and end up in North American landfills.”  He explains that their goal, like many engineers, is to try and make smarter building materials without having to take a new resource out of the ground. 

 

The researchers report that “By partially replacing cement with polymer, fly ash and glass powder, we were able to produce concrete that was more than 60% stronger than what was previously believed possible.”  They are looking to further test their products but hope to eventually replace up to 25% of traditional cement materials, mined from the earth with recycled glass. 

 

The Conco Companies is one of the leading concrete contractors in the Western U.S. and offer a wide range of quality services and products.  While we tackle projects both big and small, our experience includes providing the complete concrete package for the Levi’s Stadium along with other notable projects.  We serve California, Washington State, Oregon, Colorado and Nevada.

Sources: remedial.com.au/structural-repairs/concrete-cancer

Examples of Early Projects Using UHPC

The Portland Cement Association defines Ultra-High Performance Concrete (UHPC) as “high-strength, ductile material formulated by combining portland cement, silica fume, quartz flour, fine silica sand, high-range water reducer, water, and steel or organic fibers. The material provides compressive strengths up to 29,000 pounds per square inch (psi) and flexural strengths up to 7,000 psi.”  The high performance fiber reinforced concrete offers the advantage of strength, ductility, durability without the need of reinforcing steel rebar. 

 

One of the first projects to use UHPC was the Shawnessy Light Rail Transit (LRT) Station in 2003 in Calgary, Alberta.  The project consisted of a roof designed with 24 thin-shelled canopies 16 x 20 feet.  Designed by Enzo Vicenzino of the CPV Group Architects Ltd, the precast UPHC shell was only .79 inches thick and had a specified requirement of 19,000 psi.  By using the UPHC, it provided the project with features such as superior ductility, strength, and durability. 

 

Another project that used UPHC as its construction material was the Mars Hill Bridge in Wapello County in Iowa.  Opened in 2006, the bridge is a simple, single-span bridge constructed with three 110-foot long precast UPHC girders that do not contain any shear reinforcement.   The beams are topped with a cast-in-place concrete bridge deck. 

 

The Federal Highway Administration reports that UHPC is being studied for use in a wide variety of highway infrastructure applications. They state that, “the high compressive and tensile strengths allow for the redesign and optimization of structural elements.” They further explain that the “enhanced durability properties facilitate a lengthening of design life and allow for potential use as thin overlays, claddings, or shells.”  Currently UHPC is being used in prestressed concrete girder simple-span bridges, precast concrete deck panels, and field-cast connections between prefabricated bridge components.

 

The Conco Companies’ mission is to be the best supplier of concrete services in the Western United States and to bring expertise, experience and quality to each project.  We continue to upgrade and expand facilities to better serve the growing market for public works projects, commercial, parking structures, educational, and other construction development. We have offices in California, Washington State, Oregon, Colorado and Nevada.

Sources:cement.org/for-concrete-books-learning/concrete-technology/concrete-design-production/ultra-high-performance-concrete 

sustainableprecast.ca/downloads/USE_OF_UHPFRC.pdf

fhwa.dot.gov/research/resources/uhpc/

Improvements in Concrete’s Strength and Longevity

Technological advancements in the last several decades have led to improvements in the quality of concrete being produced, including longevity.  Experts in the field suggest that today’s concrete is designed to last for hundreds of years, not just decades.  The website, AggregateResearch.com states that, “new concretes have better corrosion resistance, equal or higher compressive and tensile strengths, higher fire resistance, and rapid curing and strength gain. In addition, the production and life cycle of these new concretes will reduce greenhouse gas emissions by as much as 90%.”

 

So along with an improved performance for a broader range of applications, concrete is also becoming “greener”.  By using new materials in the production process, an increase in recycling, and a change in mixture proportioning, concrete’s environmental impact has been reduced and the durability improved.  New concrete mixtures such as High Performance Concrete (HPC), Ultra-High Performance Concrete (UHPC), and geopolymer concrete offer several advantages over traditional concrete and have few disadvantages. 

 

HPC and UHPC are some of the concrete mixes that are produced using industrial waste by-products such as fly ash from coal burning, blast furnace slag, and silica fume.  Using these by-products reduces the amount of portland cement required in the mix, which thereby cuts down on the amount of carbon dioxide emissions emitted while producing the cement.  Another benefit to the by-products is that as they are plentiful, they generally are less expensive than portland cement.

 

Other new technologies include creating fiber reinforced concrete that is premixed with dry components to create higher tensile and flexural strength than in standard concrete.  Some of the new concrete uses steel or other organic fibers.  This concrete is denser and lighter weight that concrete reinforced with steel rebar and is being tested for use in earthquake resistant structures, bridges, and nuclear containment structures. 

 

The Conco Companies are a leading supplier of concrete services for the Western U.S. and got our start in the Bay Area in 1959 by offering clients the best value on a wide range of concrete services and products.  Since that time, we have taken a leading role as one of the top concrete contractors in the region. Our offices serve California, Colorado, Oregon, Washington and Nevada.

Concrete Pumps Offer Accurate, Precise Placement

There is such a wide variety of concrete pumps on the market today that there is one designed to handle almost any job specifications.  By having the advantage of the long reach of a boom pump on hand, it allows access to areas on the jobsite that would otherwise be difficult to get to.  Boom pumps also provide solutions for placing concrete up onto the highest floors of tall skyscrapers as well as other projects that otherwise might have been impossible before the advent of today’s sophisticated pumps.    

 

Boom pumps also can place concrete faster and with more precision than any other method of placement.  Pumped concrete requires less handling as the pump can place it directly where it is needed and a project can be finished not only faster but by using less manpower.  Since accuracy is improved in the pumping process, it typically results in fewer delays along the way and produces a more professional outcome.   

 

Furthermore, when large boom pumps are used, it means that fewer smaller pieces of equipment are needed, and this too saves time by not having to move smaller machinery around a site and then have to set it up again.  In addition pumped concrete offers better quality control that produces a more durable, stronger finished product.  Also as less water is required for pumped concrete, it helps to prevent or mitigate the shrinking and cracking problems that are common in concrete.  Finally pumped concrete is not as affected by weather conditions as other methods that often result in work stoppages and delays.  Please take a look at ourwebsite to view the broad range of projects that Conco has had the honor to serve as a placement specialist.    

 

The Conco Companies are a leading supplier of concrete services for the Western U.S. and got our start in the Bay Area in 1959 by offering clients the best value on a wide range of concrete services and products.  Since that time, we have taken a leading role as one of the top concrete contractors in the region. Our offices serve California, Colorado, Oregon, Washington and Nevada.

Articulating Concrete Boom Pumps

Concrete boom pumps are a common sight on today’s construction jobsites.  While there are several different types of concrete pumps, they are all capable of moving a variety of material quickly and efficiently, saving both time and money.

 

During our many decades in the business, The Conco Companies have been at the forefront of implementing the latest concrete technologies and developments.  We are helped in this endeavor by owning and operating a fleet of the latest, state-of-the-art concrete pumping equipment.

 

One type of pump that is an important addition to Conco’s fleet is our articulating booms.  Known also as roll-and-fold or Z-fold, they come in four-section multi-Z booms or five-section Z-Fold booms and offer versatility and a large working range.  The booms provide easy maneuverability around obstacles, yet are ideal for hard-to-reach places as they have a good vertical reach (the exact amounts depends on the model).  Another advantage of articulating booms is they fold into a compact size for easy transportation.   

 

The Putzmeister 28Z is a perfect example of the versatility of articulating boom pumps, which is why Conco has one stationed at all of our pumping locations including Southern California, Northern California and Washington State.  The pump provides a smooth concrete flow, while at the same time, has the smallest front outrigger footprint of all the models in its class.  Furthermore, since the 28Z does not require a large vertical clearance to unfold, it can even be setup inside a building if desired.  In addition the setup is quick and easy. 

 

Furthermore, by featuring longer straight pipe for less stressful concrete flow and better wear on parts, these light and resilient pumps are readily adaptable to a variety of material.  The multi-Z configuration can even pump if the boom is not fully extended, and fully extended it offers 89 ft. 7 in. of vertical reach for placing concrete in hard-to-reach places.

 

The Conco Companies is one of the leading concrete contractors in the Western U.S. and offer a wide range of quality services and products.  While we tackle projects both big and small, our experience includes providing the complete concrete package for the Levi’s Stadium along with other notable projects.  We serve California, Washington State, Oregon, Colorado and Nevada.

Need a Concrete Pump? We Can Help

If you follow our blog posts or keep up with The Conco Companies’ numerous projects found on our website, you know we have a reputation for tackling some big ones.  Part of our success lies in the fact that we continue to invest in expanding our state-of-the-art fleet of concrete pumps as well as to assemble a team of the top professionals in the field. 

 

Our track record for bringing jobs in on time and on budget is helped by our owning and operating one of the largest pumping companies in the U.S. for more than 40 years.  Furthermore, we strategically house concrete pumps and ancillary equipment up and down the West Coast to efficiently serve the needs of our customers.  For the Southern California area alone, our inventory consists of 15 pumps that are manufactured by the two best names in the industry, Putzmeister and Schwing. 

 

Once you are ready to order a concrete pump from Conco, our experts will help you determine which pump is the most efficient and cost-effective for your project.  We will customize a specific plan and calculate the needs of the job right down to the type of equipment to use to best handle problems such as access difficulties or tight timelines.  The pump size is determined by the concrete output required to get the job done and the delivery output needed in cubic yards per hour to meet the specifications.

 

Other factors we take into account are conditions at the jobsite including the size and access points, overhead obstacles, amount of congestion on the site, and any obstacles along the sides of the area.  Contact us for more information on how to give your project the benefit of using one of the top commercial concrete contractors in the nation. 

 

Conco’s mission is to be the best supplier of concrete services in the Western United States and to bring expertise, experience and quality to each project.  We continue to upgrade and expand facilities to better serve the growing market for public works projects, commercial, parking structures, educational, and other construction development. We have offices in California, Washington State, Oregon, Colorado and Nevada.