Reinforcing Steel in Concrete

Reinforcing steel is used in the construction of bridges, buildings, skyscrapers, residential homes, warehouses, foundations and roads to increase the strength of the concrete in addition to providing the support to hold the structure up.  It offers many economic advantages, and the high-tech process used to create the steel bars of today has been totally transformed from the reinforced concrete building that was done in the late 1800’s. 

As reinforced concrete is typically a locally sourced material as well as the fact that the steel comes from recycled scrap, makes it both a sustainable and environmentally friendly product.  In addition once a structure is no longer viable, the reinforcing steel and concrete are separated and both materials are recycled to be used again. 

The reinforcing steel bars known as rebar are installed inside the concrete, and work to help the concrete maintain its shape.  It is both an economical way to increase the strength of the concrete and provides the opportunity to build structures that could not have been done without it. 

The Concrete Steel Reinforcing Institute (CSRI) explains that, “Steel Reinforcing bars are produced by pouring molten steel into casters and then running it through a series of stands in the mill, which shape the steel into reinforcing bars. The cross hatchings, called "deformations," help secure the steel and transfer the load between it and the concrete.” 

Reinforced concrete offers the durability and strength of the concrete and the reinforcing bar working together.  The CSRI adds that, “The concrete provides the material's compressive strength, while the steel — in the form of embedded reinforcing bars — provides tensile strength.”

Sources:  crsi.org/index.cfm/steel/about

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.

 

 

More Concrete Terminology

 

 

The Conco Companies have been providing the best value on concrete services and products along the West Coast since 1959.  We are honored to be a part of many noteworthy projects being constructed throughout the area and bring that same commitment to all of our projects regardless of the size.  Our vast portfolio includes work on parking structures, educational and healthcare buildings, high-rises as well as public sector work.

We have taken the opportunity to do a couple of blogs providing definitions for some concrete specific terms.  Here is our last post regarding some indispensable concrete terminology that is taken from the American Concrete Institute’s ACI Concrete Terminology. 

Load balancing — a technique used in the design of prestressed-concrete members in which the amount and path of the prestressing is selected so that the forces imposed upon the member or structure by the prestressing counteract or balance a portion of the dead and live loads for which the member or structure must be designed.

Mass concrete — any volume of concrete in which a combination of dimensions of the member being cast, the boundary conditions can lead to undesirable thermal stresses, cracking, deleterious chemical reactions, or reduction in the long-term strength as a result of elevated concrete temperature due to heat from hydration.

Metakaolin — a natural pozzolan produced by heating kaolin-containing clays

Natural pozzolan — a raw or calcined natural material that has pozzolanic properties

No-slump concrete — freshly mixed concrete exhibiting a slump of less than 1/4 in. (6 mm).

Plastic shrinkage — shrinkage that takes place before cement paste, mortar, grout, or concrete sets.

Portland cement — a hydraulic cement produced by pulverizing portland-cement clinker and usually with addition of calcium sulfate to control setting

Pozzolan — a siliceous or silico-aluminous material that will, in finely divided form and in the presence of moisture, chemically react with calcium hydroxide at ordinary temperatures to form compounds having cementitious properties (there are both natural and artificial pozzolans).

 

Precast concrete — concrete cast elsewhere than its final position

Reinforced concrete — structural concrete reinforced with no less than the minimum amount of prestressing steel or nonprestressed reinforcement as specified in the applicable building code.

Scaling — local flaking or peeling away of the near-surface portion of hardened concrete or mortar

Slump — a measure of consistency of freshly mixed concrete, mortar, or stucco equal to the subsidence measured to the nearest 1/4 in. (5 mm) of the molded specimen immediately after removal of the slump cone

Sources:  concrete.org/tools/concreteterminology.aspx  

Discover the experience of working with one of the top professional commercial concrete contractors in Northern and Southern California, Nevada, Oregon, Colorado and Washington.  Conco has been in business since 1959 delivering first-rate concrete services and has all the experience and expertise to handle even the most challenging projects.

Air-entrained Concrete

The Portland Concrete Association (PCA) defines air-entrained concrete as containing billions of microscopic air cells per cubic foot.  These tiny chambers or microscopic bubbles act as reservoirs to allow water to expand when subjected to freezing temperatures and helps to relieve some of the internal pressure on the concrete. 

Air-entrained concrete is not only designed to make concrete more resistant to freeze/thaw cycles but also to make it more deicer-scaling resistant.  In addition the air-entraining concrete acts as a lubricant in the mix to improve the workability while the concrete is still plastic and increases its slump (a measure of the consistency of fresh concrete). 

Air-entrained concrete is produced by using air-entraining portland cement or by the introduction of air-entraining agents (chemical admixtures).  The amount of air bubbles are generally in the range of 10 to 500 micrometres in diameter (0.0004 to 0.02 in) and are spaced very closely together.  These air pockets or bubbles relieve much of the pressure from the freezing water by giving it a place to safely flow into.  The PCA explains that, “The amount of entrained air is usually between four and seven percent of the volume of the concrete, but may be varied as required by special conditions.”

The procedure was first started in the 1930’s, and today, most concrete is air-entrained particularly the concrete that is used for exterior projects in colder climates.  Another advantage it offers is that with the increased slump, it allows less water to be used in the mix to produce a higher strength concrete.  The benefit of less water in the mix also means there is less drying shrinkage.  Air-entrained concrete is also used to protect against sulfates and alkali-silica reactivity.

Sources:

cement.org/cement-concrete-basics/working-with-concrete/air-entrained-concrete
en.wikipedia.org/wiki/Air_entrainment
nrcs.usda.gov/Internet/FSE_DOCUMENTS/nrcs141p2_023438.pdf

The Conco Companies are 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 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.

Building Facts for the Salesforce Tower

 

The Salesforce Tower in downtown San Francisco is one of The Conco Companies more recent projects and we are currently preparing to do another huge mat pour for the Tower.  This new undertaking will be the largest continuously pumped mat pour done in San Francisco, and by the end of the pour, we will have placed nearly 14,000 cubic yards. 

In recent interview done by the San Francisco Business Times with Michael Tymoff, the senior project manager for the development company, Boston Properties, mentioned that the building could exceed LEED Platinum certification.  Presently the building is pre-certified for LEED Platinum but is intending to add features that are certain to increase the energy efficiency of the Tower such as wind turbines on the roof and other power saving ideas. 

The building is loaded with high-end features that include tall ceilings on each floor that will be as high as 13 feet tall, and 10 foot-high windows throughout the building to offer fantastic views.  Furthermore in an effort to provide exceptional air quality, every floor will have 100% natural air pulled into the building by units that are located on the floor.   

The $1.1 billion project is expected to be complete in 2017 and with a height of 1,070 feet; it will become the second tallest skyscraper west of the Mississippi, just behind the Wilshire Grand Tower.  In addition to the mat pour, Conco was awarded the concrete and rebar contracts for the building.  The building will consist of a concrete core with a structural steel frame that will require lightweight concrete to be pumped to the kinds of heights we have successfully been doing for the Wilshire Grand Tower project in Los Angeles.  

Sources:  bizjournals.com/sanfrancisco/blog/real-estate/2014/07/salesforce-tower-boston-properties-hines-transbay.html?page=all  

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 contract for the San Francisco 49ers Stadium.  Our concrete services include commercial, educational, parking and other construction development as well as public works projects.

How Pozzolan Additives are Used in Concrete?

 

 

To understand what a pozzolan is and how the addition of one can benefit concrete, we need to define the term.  The American Concrete Institute defines a pozzolan as, “a siliceous or silico-aluminous material that will, in finely divided form and in the presence of moisture, chemically react with calcium hydroxide at ordinary temperatures to form compounds having cementitious properties”  Pozzolan are found in natural, artificial and silica fume substances.  To have pozzolanic properties, the material must be amorphous (lacking a crystalline structure, without solid form) to create the required chemical reaction. 

The word “pozzolan” comes from the name of a town in Pozzuoli, Italy that is located near the site of Mount Vesuvius and is where the Romans mined ash from the volcanic activity to use in the construction of many of their buildings.  Natural pozzolans are found in materials such as volcanic ash, pumice and tuffs as well as inorganic material such as calcined clay and shale and metakaolin.  

 

Artificial pozzolans are found in materials that include Class C fly ash, Class F fly ash, ground slag, and silica fume and rice hull ash.   All of these materials are waste or by-products of industry.  Silica fume is a waste product of the silicon metal industry while fly ash results from the burning of coal in electric power plants. 

The addition of pozzolans to concrete has many benefits.  One of the foremost benefits is they offer an economic savings as they replace a substantial portion of the more costly portland cement.  Pozzolans can also create a higher strength concrete and increase durability by being more resistant to the environment.  Furthermore since they decrease the water content that is needed in the concrete, they help to reduce drying shrinkage.    

Sources:

concrete.org/topicsinconcrete/topicdetail/pozzolans
en.wikipedia.org/wiki/Pozzolan
ferrocement.net/ferro/files/pozzolans-uwe.html

Since 1959, The Conco Companies have been leading commercial concrete contractors in the Western U.S. offering a wide range of innovative, quality services.  We have built a reputation on superior concrete formwork, reinforcing, place and finish, shotcrete and other ancillary services that benefit from our vast experience.  Our regional offices are in Southern and Northern California, Washington, Oregon, Nevada and Colorado. 

The Addition of Fly Ash to Concrete

Over the last several years the use of fly ash in concrete has been fully documented to demonstrate a benefit in both the mechanical and durable properties in concrete structures according to the National Ready Mixed Concrete Association (NRMCA).  So what is fly ash and how wide-spread is its use in concrete?

Fly ash is defined by the Cement and Concrete Terminology (ACI Committee 116) as “the finely divided residue resulting from the combustion of ground or powdered coal, which is transported from the firebox through the boiler by flue gases.”  It is the ash that is produced from the combustion of coal-fired electric generating plants and there are two classifications of fly ash produced depending on the type of coal that is used. 

All fly ash has a significant amount of silicon dioxide (SiO2) and calcium oxide (CaO) but Class F fly ash is produced from anthracite and bituminous coal and Class C fly ash from burning younger lignite or subbituminous coal.  It is Class C fly ash that is preferred by the Green Building Guide and is the most common type offered in ready-mix concrete. 

Sources on Wikipedia cite the benefits of Class C fly ash as, “in addition to having pozzolanic properties, it also has some self-cementing properties. In the presence of water, Class C fly ash will harden and gain strength over time.”  Another benefit of Class C fly ash is it does not require an activator unlike Class F fly ash.

Not only does fly ash offer an environmental benefit of using a by-product of the coal industry but it also improves the performance and quality of concrete.  It is used in the range of 10 to 25% of the cementitious portion of concrete mixtures and more than 75% of concrete uses some portion of fly ash. 

Sources:  nrmca.org/research/cif%20spring%2008%20fly%20ash.pdf

flyash.sustainablesources.com/
precast.org/2013/10/future-fly-ash-use-concrete/

The Conco Companies are 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 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.

More Concrete Terms

Looking for exceptional commercial concrete services?  The Conco Companies are a leading provider in the Western U.S. and have years of experience in the industry.  We assist our clients with eliminating or reducing technical difficulties and costly delays by creating a solid foundation.  Our excellent in-house services mean you are guaranteed to get the best job.    

In order to understand the industry, it helps to become familiar with some of the concrete terminology.  The following is another list of some important concrete terminology that is taken from the American Concrete Institute’s ACI Concrete Terminology.   

Dense-graded aggregate — aggregates graded to produce low void content and maximum density when compacted. (See also well-graded aggregate.)

Elastic design — design based on a linear distribution of flexural stresses and strains and corresponding limiting elastic properties of the material

Evaporation retardant — a material applied to the surface of concrete before initial setting to reduce the evaporation rate of water without interfering with finishing operations (also called evaporation reducer). (See also monomolecular.)

Fiber-reinforced polymer (FRP) — a general term for a composite material comprising a polymer matrix reinforced with fibers in the form of fabric, mat, strands, or any other fiber form. (See composite.)

Fine aggregate — (1) aggregate passing the 9.5 mm (3/8 in.) sieve, almost entirely passing the 4.75 mm (No. 4) sieve, and predominantly retained on the 75 mm (No. 200) sieve; (2) that portion of aggregate passing the 4.75 mm (No. 4) sieve and predominantly retained on the 75 mm (No. 200) sieve

Flowing concrete —cohesive concrete mixture with a slump greater than 7-1/2 in. (190 mm)

Fly ash — the finely divided residue that results from the combustion of ground or powdered coal and that is transported by flue gases from the combustion zone to the particle removal system.

Formwork — total system of support for freshly placed concrete including the mold or sheathing that contacts the concrete as well as supporting members, hardware, and necessary bracing

Green concrete — concrete that has undergone final setting but not hardened appreciably

High-performance concrete — concrete meeting special combinations of performance and uniformity requirements that cannot always be achieved routinely using conventional constituents and normal mixing, placing, and curing practices

High-strength concrete — concrete that has a specified compressive strength for design of 8000 psi

(55 MPa) or greater

Lightweight concrete — concrete of substantially lower density than that made using aggregates of normal density; consists entirely of lightweight aggregate or a combination of lightweight aggregate and normal-density aggregate; its equilibrium densities are generally between 70 and 120 lb./ft3  (1120 and 1920 kg/m3).

Moisture content of aggregate — the ratio expressed as a percentage of the mass of water in a given quantity of aggregate to the dry mass of that quantity of aggregate.

Sources:  concrete.org/tools/concreteterminology.aspx

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 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.