Key Ingredient in Concrete – Portland Cement

Portland cement is the most common type of cement and typically originates from limestone.  It is the key ingredient in concrete, mortar and stucco and used throughout the world.  When added to concrete, it is the paste that binds the aggregate (consisting of gravel and sand) with the water. 

Scientist Search for Clues to the Formula for Roman Concrete

One of the mysteries that continue to baffle scientists and engineers is how the ancient Romans produced the strongest concrete in the world.  Typically modern concrete buildings last about 50 to 60 years while ancient Roman concrete structures have survived through 2,000 years of environmental damage.   

Conco’s Portland Office is working on Several New Projects

The Conco Companies have recently opened a new office in Portland, OR.  While not new to the area as we have performed services for Portland from our facilities in Kent, WA, this is our first actual office in the city.  The need for the office made sense as we are working on several large projects throughout the city and having a more established presence allows us to better serve our current clients as well as future clients.   

Prestressed, Pretensioned and Post-Tensioned Concrete

Prestressed, pretensioned and post-tensioned are methods used for reinforcing concrete.  Experts define prestressed concrete as the process used to overcome concrete's natural weakness in tension by introducing internal stresses to counteract the tensile stresses encountered in service.  “The stress is usually imposed by tendons of individual hard-drawn wires, cables of hard-drawn wires, or bars of high strength alloy steel.” Prestressed concrete is commonly used to produce beams, floors or bridges that require a longer span than would be safe with ordinary reinforced concrete, and may be pretensioned or post-tensioned. 

 Pretension concrete describes the process of tensioning the steel between anchorages or in a frame and then casting concrete around it.  Once the concrete has sufficient strength the “tension is slowly released from the frame or anchorage to transfer the stress to the concrete to which the tendons have become bonded.”   

In the case of post-tensioned concrete, the concrete has preset ducts or sleeves that are designed to allow tendons to be threaded through them.  The tendons are positioned before the concrete is placed.  Once the concrete has sufficient strength the tendons are tensioned by portable jacks and anchored against the outer edges of the concrete. 

One high-profile problem that was solved by a complex post-tensioning fix was the San Francisco area’s Bay Bridge.  The problem started when the anchor rods that secured the earthquake shock absorbers, known as shear keys, to the deck of the bridge failed.  Since the failed rods were embedded in concrete and inaccessible, replacement was impossible.   A team of experts, including Conco, designed and installed a complex series of steel saddles and post-tensioned jacket walls to provide the required clamping force required to secure the bridge deck framing to the E2 crossbeam.   

The Conco Companies have a reputation for expertly fabricating precision-engineered rebar and post-tension cable in our two state-of-the-art facilities.  To meet the most exacting specification and demand, our plants are outfitted with modern shear lines, benders and post-tension cable manufacturing equipment.  

At The Conco Companies, we are one of the leading concrete contractors in the Western U.S. and offer a wide range of quality services and products.  Our experience includes providing services for commercial, educational, parking and other construction development as well as public works projects.  We serve California, Washington State, Oregon, Colorado and Nevada.

Source:concreteconstruction.net/how-to/prestressed-pretensioned-and-post-tensioned-concrete_o?utm_source=krux&utm_medium=recommended-widget

Understanding How the Aggregate Influences a Concrete Mix

The Portland Cement Association (PCA) states that, “Aggregates strongly influence concrete's freshly mixed and hardened properties, mixture proportions, and economy.”   Furthermore, while choosing the proper aggregate in a concrete mix is important, the type of aggregate used affects the concrete more while it is wet than once it has cured. 

Concrete mixes are made up of aggregate, cement, water, and sometimes chemical admixtures.  The aggregate’s size or type of stone used in the mix can impact the strength, durability, workability, hardening, and ultimately the cost of the concrete.  It also accounts for up to 60 to 75% of the volume and 70 to 85% of the weight.

Most aggregate comes from sand, gravel or crushed stones and helps to determine the amount of cement paste added to the mix, which is the most costly part of concrete.   Before the aggregate is ready to go into the concrete, it is put through a cleaning and grading process.  Fine aggregate is usually defined as a mix of natural sand or crushed stones with a majority of particles smaller than 3/16th of an inch or 5mm (although sometimes it is defined as less than 4.75mm).  For coarse aggregate, the crushed stones or gravel particles are usually larger than 3/16th of an inch or 5mm (or larger than 4.75mm.).     

Aggregate used in concrete is derived from natural sand or gravel pits, rivers, seas or lake beds, hard-rock quarries, and underground mines.  If the gravel used in an aggregate is extremely rough or irregularly shaped, it will require that more water and cement be added to the concrete mix for a proper consistency.

During our many decades in the industry, The Conco Companies have encountered and successfully used a variety of concrete mixes including “green” concrete.  See our website to learn more about our large portfolio of projects.    

At Conco, we are one of the leading concrete contractors in the Western U.S. and offer a wide range of quality services and products.  Our experience includes providing services for commercial, educational, parking and other construction development as well as public works projects.  We serve California, Washington State, Oregon, Colorado and Nevada.

Source: cement.org/cement-concrete-basics/concrete-materials/aggregate

Ready-mixed Concrete

While concrete is produced in several different forms, ready-mixed concrete is the most common.  In fact the Portland Cement Association (PCA) states that almost seventy-five percent of concrete is used as a ready-mixed form.  Referred to as RMC, the concrete is batched at a factory or batching plant rather than mixed at the jobsite.  This provides the advantage of producing precise concrete mixes as well as reducing congestion at the jobsite.  The first concrete mixing plants were built in the 1930s.

Each batch of RMC is mixed according to an exact recipe as designated by the contractor to meet the project specifications.  Once the concrete is mixed, it is quickly transported to the job site in concrete mixing trucks.   If the material is mixed during the trip to the jobsite, it is call transit-mixed or truck-mixed.  Sometimes it is partially mixed in-transit and the process completed once it reaches the placement site. 

Often with transit-mixed concrete, the water is kept separate from the cement and aggregate until it is fully mixed right before placement.  According to the Portland Cement Association, the reason behind this approach is “to avoid the problems of premature hardening and slump loss that result from potential delays in transportation or placement of central-mixed concrete.”  Also transit-mixing can be used for those times when the jobsite is a distance from the batching plant. 

The disadvantage to transit-mixing is that the cement mixer cannot carry as large of a load of concrete as it can if the concrete is already completely mixed.  Shrink-mixed concrete, which is the process of partially mixing the concrete at the plant, reduces the volume of the mixture and increases the capacity of the load.  The rest of the mixing is done during transit or at the jobsite.

The Conco Companies are a leading supplier of concrete services for the Western U.S.  We 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. We have four regional offices serving California, Nevada, Washington, Oregon and Colorado.

Source: cement.org/cement-concrete-basics/products/ready-mixed-concrete

Concrete – An Important Resource

Concrete is not only an extremely important resource in the construction industry, but to the very infrastructure of our country.  Almost all larger-sized buildings, bridges and other structures constructed today use reinforced concrete, which is comprised of steel rebar in the form of mesh, spiral and bars or structural fibers from other materials.  Concrete can also be “pre-stressed (reducing tensile stress) using internal steel cables (tendons), allowing for beams or slabs with a longer span than is practical with reinforced concrete alone.” 

The benefits of building with concrete are numerous and concrete mixes of today allow for all kinds of creative projects.  It is one of most sustainable building materials available and lasts for decades, especially when compared to wood, asphalt or other materials.  Furthermore, concrete structures are extremely fire resistant.

Another factor to consider regarding the importance of concrete to our economy is that it is produced here in the U.S; and it is estimated that the concrete industry provides over two million jobs to Americans.  Furthermore, the concrete used for a project is generally produced somewhere near the construction project, which reduces transportation and energy cost.  The Portland Cement Association (PCA) explains that the cement industry is regional by nature and that nearly 98% of U.S. cement is shipped to customers by truck with the rest by barge or train.

Even after several decades of use, concrete can be recycled into an aggregate that has a hundred or more different uses.  The National Ready Mixed Concrete Association (NRMCA) points out the fact that concrete is “green” as it does not have any toxic runoff as asphalt does and is produced locally from abundant local sources.  Thus the mere sustainability of concrete makes it a good choice both environmentally and economically.

At The Conco Companies, we are one of the leading concrete contractors in the Western U.S. and offer a wide range of quality services and products.  Our experience includes commercial, educational, parking and other construction development as well as public works projects.  We serve California, Washington State, Oregon, Colorado and Nevada.

Sources: en.wikipedia.org/wiki/Properties_of_concrete,

cement.org/cement-concrete-basics/how-concrete-is-made, 

nrmca.org/sustainability/Sustainable%20Concrete%20Pavement.pdf

New Developments Drastically Reduce Carbon Emissions in Cement

Concrete is the world’s most common manmade material and is used to construct a majority of buildings, bridges, highways, and much more.  In fact it is used three times more often than steel.  However one of the key ingredients in concrete is cement, which to produce contributes anywhere from one-fifth to one-tenth of industry-generated greenhouse-gas emissions.  Recently a five years collaborative research project from the Massachusetts Institute of Technology (MIT) and CNRS suggests “a way in which those emissions could be reduced by more than half — and the result would be a stronger, more durable material.”

To make portland cement, the most common type of cement used today, calcium-rich material such as limestone is cooked with silica-rich material like clay to extremely high temperatures (up to 1450 °C) in a process called calcination.  The cementitious compounds produce a hard substance called ‘clinker’.  It is a result of the decarbonation of the limestone along with the extreme amount of energy used to heat up the mix that produces the carbon dioxide emissions.  

The MIT research suggests that by reducing the ratio of calcium to silicate, it would not only cut present day levels of emissions, but would also help to produce a better, stronger concrete.   The study looked at the entire conventional calcium-to-silica rations that range from 1.2 to 2.2 with 1.7 identified as the accepted standard.  They then built a database of the rations and discovered that the optimum mixture was not today’s standard but rather a ratio of approximately 1.5. 

In fact they found that the ratio of 1.5 parts calcium for every one part silica to be “a magical ratio.”   They further noted that “at that point the material can achieve two times the resistance of normal cement, in mechanical resistance to fracture, with some molecular-scale design.”  The researchers believe that this minor change in the calcium levels could help to reduce carbon emissions by as much as 60 percent.

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

Source: news.mit.edu/2014/stronger-greener-cement-0925