Is that concrete coming out of a hose?

Shotcrete is concrete that is applied with a pressure hose, which may contradict your perception that concrete is something that is always “poured” into place. It is projected at a very high velocity onto a surface. At the Kravis Center, we’ve been using shotcrete for basement walls. In the pressure hose, the concrete is placed and compacted at the same time, which is especially helpful for spraying onto vertical areas. To date we have placed approximately 10,000 Cubic Yards of concrete utilizing the shotcrete method.

Interestingly, a taxidermist, not an engineer nor construction worker, invented shotcrete in the early 1900s. The taxidermist would blow dry material out of a hose with compressed air, wetting it as it was released. The method was quickly applied to construction and was first use to “patch up” weak buildings. In 1911 a patent was made for a “cement gun.”

When working with concrete, builders chose from a concrete pump or a shotcrete pump. Shotcrete is utilized for larger jobs that demand more durability and long distances. Additionally, concrete pumps use thinner mixes than shotcrete pumps.

Seem familiar? Shotcrete is frequently used for swimming pools, so you might have seen this performed in your backyard. Shotcrete is also used for dams, tunnels, retaining walls, shear walls and seismic reinforcing.

Whether you’ve seen it before or not, you’ll enjoy watching the shotcrete video of work going on at the jobsite. With the set-up used at Kravis Center for shotcrete, we are able to place approximately 1700 Cubic Yards of shotcrete per day. Once the shotcrete is allowed to setup it is finished with a rubber float or hard trowel depending on the finished look the architect requires. The walls shown in the video took 8 hours to place the 1,500 cubic yards.

Green Progress at CMC

Bernards is excited to make the Kravis Center the second LEED® certified building on Claremont McKenna College’s campus. CMC and our team are shooting for LEED® Gold on this project and are committed to finding real, sustainable building solutions to lessen the negative environmental impacts of construction. Bernards has 4 seasoned team members on-site that are LEED® Accredited Professionals, and 42 company-wide, that are well versed in sustainable building.

Claremont Residence Hall

LEED®, or Leadership in Energy and Environmental Design, is managed by the U.S. Green Building Council, and provides a set of standards for new construction and renovations to make construction greener. Increased momentum toward sustainable building has turned LEED® into a bit of a “buzzword,” so we want to dig a little deeper and tell you exactly what areas we’re working on to achieve LEED® Gold.

LEED® identifies six categories for builders to improve their construction process: sustainable sites, water efficiency, energy & atmosphere, materials & resources, indoor environmental quality, and innovative design. In our last blog, we touched on the “materials & resources” when we told you about the recycled content in our concrete and rebar.

At the Kravis Center, we’re doing a number of things to increase energy efficiency. With innovative designs, we will cut our energy usage 44% more than minimum LEED® requirements. Our Modular Active Chilled Beams (MAC Beams), which are responsible for cooling the building, plays a key element in reducing energy consumption. After all, typical heating and air conditioning is responsible for about 30% of total energy consumption in the United States, according to the Energy Information Administration (U.S. Government). Utilizing chilled beams will help reduce this number.

Active chilled beams have been used since the early 1990s and have been more prominent in Europe. Unlike traditional air conditioners that force air into the room at the desired temperature, chilled beams are more efficient and quieter because there are no moving parts in the rooms they are cooling. Simply put, warm air rises to the beams, which are similar in size and shape as a light fixture, air is chilled over the coil, so fresh, cool air is disbursed into the room.

Stay tuned as we share more green building innovations used at the Kravis Center.

Concrete is one of the most versatile, durable and cost-effective building materials known to man. It is also environmentally sustainable, with green credentials that outperform steel and timber. Concrete is used extensively throughout the Kravis Center, from our large concrete spread footings to the 24” thick, post tension floor slabs.

Concrete has excellent thermal mass energy consumption that can help reduce greenhouse gas emissions. This relates to how concrete absorbs and releases the heat from the sun. Because of its slow rate of heat transfer, a concrete building stays cooler during the day (meaning less air conditioning) and slowly emits the built up heat during the evening (meaning less heating costs). This slow rate of heat transfer, coupled by the fact concrete is completely non-combustible; it is an incredibly effective barrier to the spread of fire.

The first form of concrete was used by the Romans, but the method was lost for centuries, until its use was renewed by the British in the late eighteenth century. However, the modern mixture known today is only about 175 years old. The greatest improvement to the use of concrete is the application of rebar.

Reinforced concrete utilizes steel reinforcement bars, commonly referred to as “rebar.” Rebar provides the structure with more tensile strength (prevents bending and resists compression) and is included in most construction components, including slabs, walls, beams, columns and foundations.

The Kravis Center is striving to achieve a LEED® Gold Certification. LEED is a Green Building Rating System that judges the extent of a building’s environmental sustainability. As part of meeting our LEED goals, all of our concrete mixture and rebar comes from recycled materials. Our concrete is from 100% post-industrial recycled materials and our rebar is from 20% post-industrial and 80% post-consumer recycled materials. We also use locally harvested materials, reducing the distance work trucks must transport our materials for concrete.

In this photo above, concrete is being conveyed through a hydraulic Boom placement pump. Concrete is batched at a remote location (a few miles down the road from CMC), and we have about 90 minutes from batching to placement. In a future blog, we'll explore more about the various ways concrete is placed.

116' Above Claremont

This week, some of our Bernards team members climbed atop our 116 ft. tall tower crane. You can see our crane from all around the Claremont area, but do you know where these cranes started?

Adapted from shipyards, tower cranes became vital in the reconstruction of Germany after WWII. Business owner and inventor, Hans Liebherr, remodeled tower cranes in a way to make them more affordable and practical for use. Since the late 1940s, tower cranes have been the lifeblood of construction in Europe, Asia and the Middle East, because they're convenient for hoisting materials in tight, urban areas. Their popularity in the United States has drastically increased over the last decade, with Engineering News Record estimating they've tripled in use.

Tower cranes are used to lift steel, concrete, large tools and a wide variety of building materials. Although erecting and operating the crane can be costly, it's incredibly time effective.

The jib, this long "working arm" that extends horizontally, carries the load (items being lifted by the crane). A trolley runs along the jib to move the load in and out from the crane's center. On the opposite side, is a shorter "arm" that carries counterweights. Our crane, at the very end of the jib can carry 17,181 lbs!

The crane operator sits in a cab at the top of the tower, and in order to hook and unhook loads, the operator works with a signaler, or "rigger." They are constantly in radio contact and using hand signals. The rigger is responsible for the safety of the rigging and loads.

The size and structure of the tower crane can seem a little unnerving, after all, why doesn't it just fall over? The stability comes from a large concrete pad, which is poured before the crane is erected. On our site, the pad measures 24' by 24' by 3'-4". There are also blots that connect the tower structure to the pad. Safety is a top priority for us, and before our crane was used, it was inspected by a third party and Cal OSHA.

Our tower crane will be standing tall until about March 2010. You can take a look at how the crane was erected at the end of June 2009 in the video below.