The Aggregate in Concrete

The Conco Companies offer a range of services that include quality concrete formwork, reinforcing, place and finish, and shotcrete.  We also own a fleet of construction hauling trucks and operate one of the largest pumping companies in the U.S.  Our many years in the industry and extensive experience mean we have dealt with all types of concrete mixes.

Concrete is a mixture of cement, aggregates, and water and it is important to use the right type of aggregate as it influences the concrete mix in strength, durability, workability, hardening, and ultimately the cost.  The aggregate is an inert material that accounts for 60 to 75% of the volume, 70 to 85% of the weight and originates from sand, gravel or crushed stones.   Fine aggregate is typically defined as a mix of natural sand or crushed stones with a majority of particles smaller than 3/16^th of an inch or 5mm (although some define it as less than 4.75mm).  Coarse aggregate is crushed stones or gravel particles that are larger than 3/16^th of an inch or 5mm (or as some define it as larger than 4.75mm.).  

Generally the aggregate used in concrete mixes comes from natural sand or gravel pits, rivers, seas or lake beds, hard-rock quarries, or underground mines.  The type of materials used as the aggregate effect the concrete more when it is wet than once it has cured.  When the gravel is extremely rough or irregularly shaped, it requires more water in the mix as well as more cement to give it the proper consistency. 

Aggregate is prepared by crushing, washing, and putting it through a grading process.  Grading is important as it determines the paste requirements for the concrete and regulates how much of the costly cement will be needed.  According to the Portland Cement Association, “Although some variation in aggregate properties is expected, characteristics that are considered include: grading, durability, particle shape and surface texture, abrasion and skid resistance, unit weights and voids, and absorption and surface moisture.”

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

When your project demands exceptional services and the best value, Conco can deliver.  We have been offering premium concrete services throughout the Western U.S. since 1959, and have four regional offices serving California, Washington, Oregon, Nevada and Colorado. With state-of-the-art equipment and modern facilities, we work diligently to meet goals and stay within budget.

The Development of Shotcrete

Conventional cast-in-place concrete and shotcrete share many of the same properties but shotcrete provides an advantage in placement.  It bonds with most substrates instantly or very rapidly, which makes it a good choice on complex forms or shapes.  Similarities to conventional concrete include high strength, low permeability and high durability.  It has a wide range of applications that include repair or restoration, ground support, architectural and landscape restoration, new construction and much more. 

Shotcrete, originally known as gunite, was developed by Dr. Carl E. Akely.  In his process, the dry material was blown out of a hose and water injected at the nozzle.  Akeley went on to patent his cement gun and the material he called Gunite.  During that period, he created the Cement Gun Company (now called Allentown Equipment).

In the mid-1950s, a wet mix method was introduced to the construction industry.  The benefits were recognized immediately and it was used on many projects.  Shotcrete became even more popular with the development of a rotary gun that had an open hopper which allowed the material to be continuously fed.   

The American Shotcrete Association credits the technical advancements in materials and equipment made in the 1970’s of providing an enormous improvement in the application of shotcrete.  They state that, “Perhaps the most significant step in this period was the development of efficient concrete pumps that could be used for wet shotcrete application.”

The 1980’s continued with advancements in the mixing and batching of ready mix concrete and the development of admixtures that allowed for consistency, hydration and performance.  Today one of the biggest changes to shotcrete applications is the ability of modern equipment to pump any slump as well as to pump it over long distances and up into high-rise construction projects.  

Sources:en.wikipedia.org/wiki/Shotcrete,shotcrete.us/,shotcrete.org/whyshotcrete/index.htm

The Conco Companies are leading suppliers of concrete services for the Western United States. 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, Washington, Oregon, Nevada and Colorado.

Retrofitting Historic Buildings Against Earthquakes

New construction is being built better than ever to withstand the threat of earthquakes.  Moreover since earthquake activity is not limited to the West Coast, local building codes throughout the country mandate that new construction be resistant to the strongest earthquake activity that is believed possible in an area.  This task has become easier with new high-tech materials that are available such as fiber-reinforced polymers, fiber reinforced concrete and high strength steel.  

One of the on-going phases in creating safer buildings is the seismic retrofitting of older structures to be more resistant to seismic activity and ground motion.  Among these projects include significant historical buildings that have the additional task of ensuring the structure is stronger while still preserving the distinctive characteristics that make the buildings special.  

Obviously first and foremost human safety is addressed and then the focus switches to work on retaining the distinct architectural features of the building. Common weaknesses in historic buildings when faced with earthquake activity include unreinforced masonry and structural connections between walls, floors, and foundations.  Older construction used unreinforced bearing walls that offer inadequate lateral resistance and ductility or flexibility when subjected to seismic activity.     

According to the NPS Department of Interior’s Preservation Briefs, it is imperative to put together a team of experienced engineers, architects, and building code officials as well as consulting with their agency’s administrative staff.  They state that, “Historic materials should be preserved and retained to the greatest extent possible.”  Also that, “New seismic retrofit systems, whether hidden or exposed, should respect the character and integrity of the historic building and be visually compatible with it in design; and that, seismic work should be ‘reversible’ to the greatest extent possible to allow removal for future use of improved systems and traditional repair of remaining historic materials.” 



 

Conco is a leading supplier of concrete services for the Western United States. We have built our reputation in the Los Angeles area with superior concrete formwork, reinforcing, place and finish, shotcrete and other ancillary services that benefit from our vast experience.  Our concrete services include commercial, educational, parking and other construction development as well as public works projects.

 

Skyscrapers Keep Pushing the Limits

Early this year, Conco will provide concrete services for a record breaking skyscraper being built in downtown L.A.  Not only will Conco execute the largest continuous mat pour ever done over the course of three days, but the new Wilshire Grand Center will become the tallest building in the U.S. west of the Mississippi.   

According to a global forecast from the Council of Tall Buildings and Urban Habitat  (CTBUH), 2013 was a robust year for new skyscrapers and 2014 is looking to be even better.  In 2013 the One World Trade Center, after much controversy, was designated as the tallest building in the U.S. at 1,776 feet.  The new tower is scheduled to open in 2014 and has replaced the Willis Tower in Chicago as the tallest building in the U.S. 

The CTBUH’s job is to document the progress and trends of skyscrapers built throughout the world.  Their publication estimates that 75 skyscrapers at least 650 ft. tall or higher were completed in 2013, and that there will be approximately 100 buildings at least that height or taller that will be finished by the end of 2014. 

The editor of CTBUH, Daniel Safarik, cites their reasons for the increased activity in skyscrapers as, “The advancement in high-strength concrete technology, combined with land scarcity and plenty of billionaires willing to spend a great deal of money for single-or double floor unity high in the sky has made this a new reality.”

 

One of the newer trends in skyscrapers is to build extremely narrow, very tall structures that carry a small footprint.  Several examples are currently being built in New York City.  Another new construction trend is prefabrication, which is helping to speed up the building process.  Furthermore there is a concerted effort to develop fully sustainable skyscrapers referred to as zero net energy buildings that have zero net consumption and zero carbon emissions annually. 

Mumbai and China will be the strongest markets for new skyscrapers in 2014 with continued growth in skyscraper construction throughout the Middle East.  

Conco is a leading supplier of concrete services for the Western United States. We have built our reputation in the Los Angeles area with superior concrete formwork, reinforcing, place and finish, shotcrete and other ancillary services that benefit from our vast experience.  Our concrete services include commercial, educational, parking and other construction development as well as public works projects and highways.

How is Concrete Recycled?

Concrete is used in many countless applications and is the most widely used man-made material in the world.  Even after the many decades it serves as a building or as a part of a highway, the concrete is easily recycled. 

In the past, concrete was not reused and was just taken to landfills for disposal which was wasteful and took up space.  Now concrete is routinely recycled and the aggregate that is produced is used to create new concrete or for a multitude of other purposes. 

Once a building is demolished, crews prepare the concrete by removing as many contaminates as possible such as roofing, trash, wood, and other materials.  The care that is taken at the site helps to ensure how good the product will be down the road and recycling facilities will not accept concrete that has not been reasonably cleaned.    

The reinforced steel (rebar) in the concrete is removed at the recycling site.  Huge magnets are used to attract and identify the steel for removal.  After removal, that too is targeted for recycling and sent to facilities that specialize in steel materials. 

At the recycling plant, the concrete goes through several steps that involve crushing, pre-sizing, sorting, screening and further elimination of contaminants.  It is cleaned by a water method to get rid of dirt and other remaining materials.  Especially important is getting rid of things like asphalt, sealant, chlorides and gypsum.  

There is also a market for used concrete that has not processed and screened as carefully. This aggregate can be used for fill, drainage, or as sub-base gravel before asphalt or new concrete is poured.

Conco is a leading supplier of concrete services for the Western United States. We have built our reputation in the Los Angeles area with superior concrete formwork, reinforcing, place and finish, shotcrete and other ancillary services that benefit from our vast experience.