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.

Cast-in-place Concrete

By Conco  

Cast-in-place concrete is a commonly used building material for commercial and residential structures and accounts for 75% of all concrete used.  The process starts with a temporary form in which reinforcement such as steel bars (rebar) may be added.  The next step is to pour the liquid, ready mix concrete that has been transported to the jobsite (it may in some cases be mixed on site) into the removable forms.

Using cast-in-place offers the same benefits as other types of concrete such as durability, and strength and can use some recycled material.  It is resilient when faced with severe weather conditions such as tornados as well as resistant to mold, rot, bugs, and fire.  The thermal mass of the concrete helps to reduce a building’s energy costs and has the added benefit of acting as a sound insulator.  Moreover the concrete is ready to use once the forms are stripped and does not require any further treatment.

Originally this method was only used for sub-grade walls but the renowned inventor, Thomas Edison, experimented with using cast-in-place concrete on above-grade projects.  He demonstrated the success of his work by constructing several homes that were made entirely out of cast-in-place concrete.  With many improvements and new developments since then, cast-in-place is now used for constructing slabs, walls, beams columns floors, and roofs as well as for forming special architectural features.

The forms need to remain in place until the concrete is self-supporting.  Since one of the primary costs of cast-in-place is the forming process, using prefabricated formwork can help speed up a job and save money.  They are assembled on site and can be reused over and over again.

Conco is a leading supplier 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 steadily taken a leading role as one of the Bay Area’s top concrete contractors. 

The Early History of Concrete

The earliest evidence of concrete is from a naturally occurring event caused by a spontaneous combustion between limestone and oil shale in Israel more than 12 million years ago.  These deposits still exist today.  More recently and manmade, concrete was first used by the Egyptians around 3,000 BC.  They mixed mud with straw to bind dried bricks and later used lime and gypsum mortar for the binding agent when building the Pyramids. 

Through time, concrete was used to build many of the ancient structures of which some still exist today.  The Greeks first used lime mortars around 800 BC, which were much harder than what the Romans would later use.  There is even evidence that the Assyrians used a fully waterproof concrete to construct the Jerwan Aqueduct around 700 BC. 

Modern concrete is derived from the developments made during the Roman Empire.  The Romans widely used concrete from 300 BC - 476 AD, which made possible their revolutionary architectural designs that were structurally very complex and dimensional.  Some of the cement used was from a slaked lime found in volcanic ash called pozzuolana.

The Romans used the concrete to create buildings with arches, vaults and domes.  The most famous examples of building projects include the Roman baths, the Coliseum, the Pantheon in Rome, and the Pont du Gard aqueduct in southern France.  After the fall of the Roman Empire, the art of concrete was lost for many hundreds of years. 

An interesting fact is that modern tests have proven that Roman cement (opus caementicium) had as much compressive strength as modern Portland-cement concrete.  Of course, its tensile strength was much lower without the reinforcement of today’s concrete.

Conco is a leading supplier 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 steadily taken a leading role as one of the Bay Area’s top concrete contractors. Our concrete services include commercial, educational, parking and other construction development as well as public works projects and highways.