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.

Increasing the Tensile Strength of Concrete

The aggregate in a concrete mix effectively carries the compression load to make concrete strong in compression.  However concrete is weak in tension as the cement holding the aggregate in place is susceptible to cracking and can result in the structure failing.  To carry the tensile load, concrete is reinforced with steel reinforcing bars (rebar), steel fibers, glass fibers, or plastic fibers.

Both brittle and rigid, concrete may crack or break under high pressure conditions and shear stresses caused by wind, earthquakes, and other forces.  By embedding rebar or other reinforcement into the concrete, it provides a higher tensile strength and ductility to the concrete and gives buildings the required strength to stand up to seismic activity. 

Generally concrete only needs a relatively low percentage of rebar to achieve the maximum performance required for a specific construction project.  In a typical concrete beam, about 1% of rebar is added to the concrete, while in a column, it can be up to 6% rebar.  This formula achieves an economical solution for providing strength, ductility, and durability to the construction project since the cost of steel far exceeds the cost of concrete.

Types of reinforced concrete include precast or cast-in-place and are used in the construction of slabs, walls, foundations, beams, and columns.  Many structures built today would not have been possible without reinforced concrete.   Another type of reinforcement is referred to as post-tensioning.   Wikipedia states, “Bonded post-tensioned concrete is the descriptive term for a method of applying compression after pouring concrete and the curing process (in situ). The concrete is cast around a plastic, steel or aluminum curved duct, to follow the area where otherwise tension would occur in the concrete element.” 

Precision-engineered rebar and post-tension cable is fabricated in state-of-the-art facilities such as the plants owned by The Conco Companies.  We utilize the latest technologies to ensure accuracy and increase productivity.  Our plants are outfitted with modern shear lines, benders and post-tension cable manufacturing equipment to meet the most exacting specifications. 

Source: en.wikipedia.org/wiki/Concrete

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.

Today’s Modern Equipment Saves Time on a Jobsite

The Conco Companies are one of the top commercial concrete contractors and independent reinforcing steel and post-tension cable suppliers in the Western United States, and as such, we recognize the need to finish projects on time and on budget.  This is why we continue to purchase and utilize the most up-to-date equipment to help us successfully fulfill our commitments.  

As one of our lesser known pieces of timesaving equipment, Telebelts are designed to move heavy materials on or off a jobsite quickly and easily.  Telebelts are a mobile telescopic belt conveyor that is very versatile and comes in a variety of sizes.  This type of equipment is used to place high volumes of concrete, gravel, rock, and backfill fast and efficiently to save time and labor.  The set-up on a Telebelt is easy to do, and since it is mobile, offers the option to move around a jobsite as needed and is ideal for jobs that would otherwise have few options but to wheelbarrow material by hand.

Telebelts are fast and efficient with outputs up to 5 cubic yards per minute.  They are perfect for use in low clearance areas or under bridges and can go into limited access structures.  One example is a Putzmeister TB 130 that has a horizontal reach of 126’ 6” and a maximum rated capacity of 360 cubic yards an hour.  The unit has a 360 degree hydraulic rotation and a variety of hopper options.   

To demonstrate how we utilize Telebelts in a project, Conco recently had to backfill 2,900 tons of crushed rock in just three 8-hour days.  There was no room for error as any delay in placing the material would impact other jobs on the project.  To finish on time, we brought in our Direct Feed trailer which allows a Superdump, Transfer, End Dump or 10-Wheeler to unload its contents directly into the hopper attached to the trailer.  The material was then fed from the hopper onto one of our Telebelts.  The Telebelt placed the material directly at the point of placement, which all helped in our efforts to meet a tight deadline.

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.

Conco is Committed to Meeting All New Requirements and Regulations

Safety is always in the forefront at The Conco Companies, and in that effort, we recognize the importance of keeping up with any new changes in safety procedures and regulations.  One important update occurred this past March with the publication of ASME’s B30.27-2014 Jobsite Responsibilities for Material Placement System that outlines specific responsibilities on the jobsite. 

The American National Standard’s most notable change came with the addition of language that was taken from the mobile crane standards to now use in concrete placement.  The new regulation includes a translation requirement for companies that import equipment into the U.S. and a clear description of responsibilities for general contractors, pump operators, and concrete mixer truck drivers as well as for anyone else that is a part of the process. 

The publication, Concrete Facts, explains the new regulation as such, “If specialized training is required, it is shown. Expectations of setup locations are spelled out. What an operator should know, and the items a contractor should consider when ordering a machine are listed. The only way everyone can go home safely after the pour is if everyone knows their piece of the safety puzzle and works to accomplish it.”

The new regulations will go into effect next year but the American Concrete Pumping Association (ACPA) has already stepped up to make sure their safety training programs comply with the new regulations.  Their goal is to see to it that concrete pump operators and ready mix drivers meet the safety training and competency requirements spelled out in the ASME B30.27-2014.   

At Conco, we continue to work at creating the safest work environment for all employees, fellow contractors, customers, and the general public.  As one of the largest pumping and belting companies in the U.S., we implement the highest safety standards in the industry.

Sources:

cfawalls.org/concretefacts/2014/06/30/a-new-american-national-standard-for-material-placement-safety/

mydigimag.rrd.com/publication/?i=216900

Conco is one of the leading commercial concrete contractors in the Western United States.  We have four regional offices serving California, Washington, Oregon, Nevada and Colorado and are experts at creating cost-effective solutions that take advantage of the most up-to-date techniques.  Our concrete services include commercial, educational, parking and other construction development as well as public works projects.

A Short History of Shotcrete

 

Shotcrete is pneumatically placed concrete that is used as an economical alternative to traditional cast-in-place walls.  As it almost eliminates the forming process all together, it greatly reduces labor cost and time.  Shotcrete has the same structural characteristics as traditional cast-in-place walls and a wide range of applications including shear walls, retaining walls, architectural walls, slope pavement, and soil nailing. 

Wikipedia reports that shotcrete, originally known as gunite, was first used to repair the crumbling façade of the Field Columbian Museum in Chicago in 1907 by a well-known naturalist, Dr. Carl E. Akely.  He used a process where dry material was blown out of a hose and water was injected from the nozzle.  Mr. Akeley later went on to patent the equipment, which was called a cement gun, and the material called Gunite.  The Cement Gun Company was soon started (now called Allentown Equipment).

It was not until mid-1950 that a wet mix method was introduced to the construction industry.  Right from the start the benefits were recognized and it was successfully used on many projects.  Shotcrete really took off from there 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 during the 1970’s of providing a huge improvement in the applications of shotcrete.  They report that, “The Engineering Foundation organized the first conference for The Use of Shotcrete for Underground Support.”  Furthermore, they write 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 saw advancements in the mixing and batching of ready mix concrete with developments of admixtures that allowed for consistency, hydration and performance.  One of the biggest changes in the shotcrete that is used today is the ability of equipment to pump any slump and to be able to pump it over long distances and up into high rise construction projects.  

* http://en.wikipedia.org/wiki/Shotcrete

* http://www.shotcrete.us/

* source: American Shotcrete Association

Conco is taking a more active role in the Portland area with our expansion of high-quality commercial concrete services.  We bring our years of experience delivering dependable services since 1959, and a vast portfolio of noteworthy and large-scale projects from throughout the Western U.S.  Our work includes commercial, industrial, educational and multi-residential construction as well as public works projects. 

How Concrete Pumps Works

Concrete pumping is a very efficient and reliable means of placing concrete.  One of their advantages is that they provide the ability to access places that other methods would be unable to reach.  A concrete pump can be used for small or large jobs and provides a smooth and even distribution. 

Concrete pumps are the only placement option in very tight, confined spaces or on tall high-rises.  Pumps are the favored method for large volume mat pours and handle these jobs efficiently.  Additionally, concrete pumps can accomplish most placement jobs more economically.  Today’s concrete pumps can place concrete so precisely, there is less need for shoveling and moving it around.  This greatly reduces labor and time.

There are two types of concrete pumps.  One of them is attached to a truck and is known as a boom concrete pump.  It is used on big construction projects to quickly move large volumes of concrete into place.  The pump is operated with a robotic arm that is controlled by a pump operator and is extremely accurate in its placement.  The other type of concrete pump is called a line pump and is mounted on a trailer or truck.  It is operated manually and used on smaller projects such as residential driveways or pools. 

Concrete pump operators are certified by the American Concrete Pumping Association (ACPA), which is the only recognized certification program in the industry.  In order to get certified, an applicant must do the required prerequisite safety training and pass a test before they are given the ACPA endorsement. 

Conco is one of the leading concrete contractors in San Francisco offering a range of innovative, quality services.  We have been honored to work on many high-profile projects and were recently awarded the concrete package for the San Francisco 49ers Stadium.  Our concrete services include commercial, educational, parking and other construction development as well as public works projects.

The Earliest Cranes

A crane is a type of machine that creates a mechanical advantage for moving heavy objects that are beyond the normal capacity of a man.  It can lift and lower objects and move them horizontally to transports heavy materials from one place to another using a hoist or winder, wire chains, and sheaves (wheels or rollers).  A crane is an essential piece of equipment in the construction industry, the transportation industry, and the manufacturing industry.

The invention of the crane has had important implications on the advancement of our civilization.  It is thought that the most powerful hand crane in history could multiply the force it imparted to the operator by 632 times.  When looking at what the Egyptians accomplished with the building of the Pyramid, 50 men were utilized to move a 2.5 ton stone block, which translates to about 50 kg per person.  During the Roman Empire, a Roman crane increased the lifting capacity of a person to about 3,000 kg or 60% higher. 

Historians believe that the Ancient Greeks were the first to invent cranes in the late 600 BC and were powered by men or animals.  Archeologists have discovered distinctive cutting marks on stones from early Greek temples that prove they were lifted by cranes.  These early cranes were made of wood and enabled the Greeks to construct taller buildings. 

The Romans further advanced the development of the crane that allowed for larger and heavier weights to be lifted.  They invented cranes that were powered by groups of men or animals and used extensive pulley and rope systems.  The Roman Polyspastos crane consisted of 3 ropes and 5 pulleys which were worked by 4 men to move 3,000 kg.  

Conco is one of the leading commercial concrete contractors in Sacramento and has been delivering first-rate services in the area since 1959.  We are experts at creating cost-effective solutions that take advantage of the most up-to-date techniques.  Our concrete services include commercial, educational, parking and other construction development as well as public works projects and highways.