Designing a Concrete Mix

As the most commonly used man-made material in the world, concrete mixes are designed to meet the demands of today’s increasingly complex architectural projects.  A structure’s concrete mix must suit the purpose of the structure as well as accommodate any special features and characteristics of the project. 

In the early planning stages of a project, a concrete mix is designed to meet the criteria for both strength and appearance of the structure.  Additional factors taken into account are local building codes and the kind of weather conditions the structure will be exposed to.  Furthermore, standard molded and standard-cured cylinder samples are used to measure the concrete’s compressive strength.  Other testing methods may include the Hardened Air Void Systems (AVS), Rapid Chloride Permeability (RCP) and Linear Shrinkage limits.  

The slump or consistency of fresh concrete is also considered, and generally there is a trade-off in terms of easy mixing and placement and in achieving the ultimate performance of the concrete.  The design process will include discussion on the type, cost and amount of the various additives to be used in addition to the portland cement.  It will also be decided if the concrete mix will use fine (small) or coarse (larger) aggregates.  Since there is such a wide range of performance requirements for concrete and different types of mixes, sophisticated software programs have been developed to help in the process. 

According to the Portland Cement Association (PCA), “The key to achieving a strong, durable concrete rests in the careful proportioning and mixing of the ingredients. A mixture that does not have enough paste to fill all the voids between the aggregates will be difficult to place and will produce rough surfaces and porous concrete. A mixture with an excess of cement paste will be easy to place and will produce a smooth surface; however, the resulting concrete is not cost-effective and can more easily crack.”   They suggest that a common concrete mix is approximately “10 to 15 percent cement, 60 to 75 percent aggregate and 15 to 20 percent water.”  For concrete mixes with entrained air, it can account for another 5 to 8 percent of the mix.   

The Conco Companies 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 proudly serve California, Washington State, Oregon, Colorado and Nevada.

Sources:en.wikipedia.org/wiki/Types_of_concrete,cement.org/cement-concrete-basics/how-concrete-is-made

The Early Beginnings of Portland Cement

Portland cement, which is one of the key ingredients in concrete, mortar, stucco and many grouts, is the most common type of cement and is used throughout the world.  Most of it is grey colored and referred to as ordinary portland cement (OPC) but there is also a white variety. 

It was in the mid-18^th century during the planning of a lighthouse in Britain that John Smeaton, an English civil engineer, pioneered the use of hydraulic lime which eventually led to the invention of portland cement in the next century.  The lighthouse required a hydraulic mortar that could set and develop some strength in the short time span between high tides. His experiments included working with combinations of different limestones and additives such as trass (a volcanic tuff occurring in the Eifel) and pozzolanas (volcanic ash from Italy).  Smeaton is credited with concrete eventually becoming the building material of choice for the modern world.

Toward the late 18^th century, Roman cement, a natural form of cement made by burning nodules found in clay deposits containing clay minerals and calcium carbonate, was developed and patented by James Parker.  This cement was nothing like the material used by the ancient Romans.  In Parker’s cement, the burnt nodules were ground into a fine powder and mixed with sand to make a mortar that set in as little as five to fifteen minutes.

After several developments in cement during the ensuing years, Joseph Aspdin patented a material he called portland cement in 1824 based on the fact that its color was similar to the famous stones on the Isle of Portland, Dorset. His portland cement was just a first step in the development of the material we use today.  Several decades later his son improved the material by inadvertently producing calcium silicates.   While this resulted in higher production cost with a material that required more lime in the mix and higher kiln temperatures, the concrete that it produced set slowly and developed strength quickly. 

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

Source:  en.wikipedia.org/wiki/Portland_cement 

The Architectural Wonder of the Roman Pantheon

The Pantheon is one of the best preserved structures from Ancient Rome.  The building was constructed around 126 AD during the reign of the emperor, Hadrian and was first a Roman temple and later a Catholic Church.  To this day, the Pantheon is still the world’s largest concrete dome ever to be constructed without reinforcement.   

Since the building is so well preserved we know a lot about how it was built.  Standing on a 1.3 meter high base, the Pantheon is made up of two main parts, the porch and the interior building.  It is believed that stairs originally led to the entrance but in later years the exterior area was reconstructed to eliminate the need for stairs. 

The porch is done in the classic Greek style with eight Corinthian columns along the front that are 39 ft. (11.8 m) high.  The material used to build the columns is granite that was brought over from Mons Claudianu, Egypt.  Since the columns are 5 ft. in diameter and weigh 60 tons, getting them to the jobsite required much effort.  First they had to be dragged down to the banks of the Nile River on wooden sledges, put on barges to be transported downriver and then placed on ships to be go across the Mediterranean Sea.  From there they were again put on barges and pulled up the Tiber River to Rome.  Finally the columns were taken off the barges and moved 700 meters to the site of the Pantheon. 

 

In the main building, Roman concrete was used to construct the dome that measures 142 ft. (43.3 m) in diameter and is 142 ft. from the floor to the top of the dome.  The oculus of the dome is 30 ft. in diameter.  The thickness of the concrete walls varies from 21 ft. at the base to only 3.9 ft. around the oculus.  Tests done on other Roman ruins lead experts to hypothesis that the Pantheon’s tensile strength is 1.47 MPa (213 psi) with a “maximum tensile stress of only 128 kPa (18.5 psi) at the point where the dome joins the raised outer wall.”   

At The Conco Companies, our goal is to be the best provider of concrete services for the Western United States. We have built our reputation on superior concrete formwork, reinforcing, place and finish, shotcrete and other ancillary services that benefit from our vast experience.  Currently we serve Northern and Southern California, Oregon, Colorado, Washington, and Nevada.  

Source:en.wikipedia.org/wiki/Pantheon,_Rome, ancient.eu/Pantheon/ 

Conco is Seeking Qualified Project Superintendents

The Conco Companies are looking for a few select individuals to join our team in the position of Project Superintendents for our Northern and Southern California locations.  Working for one of the leading companies in the industry, you will have the opportunity to work on some of the most notable projects being constructed throughout the Western United States. 

As a Project Superintendent, you will take the lead role in safely delivering projects that meet Conco’s high standards of quality, and that are on time and on budget.  The job is done as a team effort along with the Project Manager.

Conco’s requirements include all candidates having at least 10 years of supervisory experience in the concrete industry as well as a proven record of expertise in multi-story cast-in-place construction.  Project Supervisors must be competent in current industry safety practices and technology. 

In addition applicants must have a thorough and broad knowledge of concrete-construction documents, concrete materials, and characteristics.  They also need to be knowledgeable in matters regarding concrete pumping, concrete formwork systems and equipment utilization.  Duties include supervising and developing hourly man-power labor, and discussing with and directing supervisory personnel and subcontractors.  Furthermore, all candidates must possess the ability to work as a team and need to have excellent verbal and written communication skills.   

As a Superintendent, it is imperative that you adhere to all safety standards as well as ensure that subcontractors are compliant with all applicable safety codes and regulations.  You will be responsible for completing projects in a timely fashion through efficient scheduling, deliveries, management of materials and document submittals.  Please refer to the Conco website for contact information and full job description. 

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.

Qualified Project Managers Needed at Conco

As one of the foremost, national commercial concrete contractors, The Conco Companies are looking for talented people to join our team.  We currently have positions open for experienced carpenters, cement masons, ironworkers, laborers and operating engineers at all of our locations which include Northern California, Southern California, Washington and Colorado.

In addition we also have exciting career opportunities for experienced, full-time Project Managers.  These positions require individuals who possess strong leadership skills and know how to safely bring projects in on time while still maintaining the highest quality, and on budget.  They must be able to work in a team effort with the Project Superintendent. 

The job of a Project Manager requires a person who knows how to develop and maintain a project schedule.  They must be able to coordinate the various aspects of concrete construction with an owner and general contractor. Range of duties includes submitting and coordinating all project schedules, pay applications, change orders, submittals and approvals, and RFIs.  In addition it is the responsibility of a Project Manager to direct and coordinate activities to ensure a project stays on schedule and budget.  It is important that a Project Manager knows how to reduce risk and knows how to work efficiently and effectively.   

Job requirements include a four-year Management or Engineering Degree, or the equivalent combination of technical training and related experience.  Furthermore, we need someone who has a thorough and broad understanding of concrete-construction documents, concrete materials, and characteristics as well as concrete formwork systems and equipment utilization.  They also need to know how to schedule and manage sub-contractors.  Since Project Managers interact with many different groups, they must be able to work well as a team and have good communication skills both verbally and written.   Please see Conco’s website for the contact information and complete job description. 

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.