Concrete Finishing Archives | Page 17 of 22

While Conco is justifiably proud of breaking the World record for the largest continuous mat pour, we are even more proud of doing it safely. Our commitment to safety began with the vision from Conco’s Southern California General Manager, Rick Parker. Five months prior to the pour, he invited John Messing, Conco’s Safety Director, to participate in the planning meetings for the Grand Pour. Rick has learned from his years of experience that projects go more smoothly when the safety department is involved early-on to ensure that safety is built into the overall work plan.

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*Photos provided by Gary Leonard

Rick also made the prudent decision to devote the first-quarterly company safety meeting in January entirely to the safety of the pour. During the meeting, Rick Parker and Pumping Manager, Doug Marquis, provided an overview of the Wilshire Grand jobsite along with the challenges, unique project features, and logistical considerations of the job. John Messing spent the balance of the time devoted to discussing the importance of pre-task plans. He assigned three sub-groups to develop such plans regarding the work that they would perform. At the conclusion of the safety meeting, the pumping crew, place and finish crew, and street-level supervisors all had a unique, customized pre-task plan that was used as the basis to ensure their workers understood the hazards of the work and how to mitigate them.

The end result of the successful well-thought out plan was a highly professional team effort from all Conco employees. The entire team—at all levels—executed the plan to perfection, which resulted in zero injuries for this world record continuous concrete pour.

Among the many unique features of the Wilshire Grand mat foundation pour was the thermal control plan. Occasionally we need to make provisions for the heat that is generated in mat foundations. In mass concrete structures there are two thermal properties that must be considered: the maximum temperature and the temperature difference between the center of the structure and surface.

There are multiple ways to control the overall thermal properties of mass concrete. For the Wilshire Grand pour, one of the first things Conco addressed was the concrete mix design. There are a few common adjustments that can be made to the actual mix, but they all have some impact on the production rate when the concrete is being batched. In this case, working with our supplier Catalina Pacific, we increased the proportion of fly-ash which normally results in reduced maximum temperatures.

The next step was to mechanically control the temperatures. Pre-chilling the concrete was not an option due to the rate that we needed to batch and place the concrete. Nor was there a way to feasibly pre-chill 21,200 cubic yards of material ahead of time so we had to consider post-chilling by means of cooling pipes to mechanically remove heat.

For this, we turned to John Gajda of the CTL Group. CTL developed a thermal control plan specific to the mix design, the geometry of the foundation, and the configuration of the rebar. With help from Couts Heating and Cooling, we implemented CTL’s thermal control plan. Ultimately the system we installed to post-chill the concrete was composed of 18 miles of cooling pipes, over 660 tons of chiller capacity, 40,000 gallons of chilled water, multiple pumps, 3 x 500kva generators, and over 2,200 valves. This includes a large amount of contingency and redundancy for reacting to unanticipated thermal phenomena and providing backup during the critical early stages of the thermal control plan.

Subsequently we installed 24 thermal couplers to digitally monitor the thermal properties of the concrete. For assistance, we teamed up with Twining Laboratories who were able to provide hourly readings of the foundation utilizing Intelirock equipment. By monitoring temperatures closely, we could respond by increasing chiller capacity and/or adding insulation if required. Furthermore, monitoring allowed us to determine when the thermal control system could be removed and the concrete core started.

In the end the thermal control system was a success. The maximum temperature was kept below ACI limits and the temperature difference was well within the ranges required to avoid thermal cracking.

To successfully complete the world’s largest continuous mat pour, one of the biggest challenges Conco faced was to find ways to unload 120 – 150 truckloads of concrete per hour. With the need to unload so many trucks in such a short period of time, Conco’s plan called for thirteen points of placement in the mat foundation. However, only two sides of the project were accessible from the street.

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Since the site only provided access for seven pumps to be positioned to pump directly into the building foundation, Conco’s plan needed to have pumps that were pumping into pumps. Pumps were dropped by crane into the excavation site and two placing booms were fed from pumps nearly 400 feet away. In all, fifteen boom pumps, two high-pressure stationary pumps, two placing booms, and more than 2,500 feet of pipe operated throughout the pour to get the concrete to the foundation. Four of the pumps on this project were new along with a brand-new placing boom. In addition to this equipment, three boom pumps were parked in close proximity to the project in case of a breakdown. None of the backup pumps were put into service as the pumps on the job performed near flawlessly.

To complete the rest of this signature project, the two high-pressure stationary pumps will remain on-site for the project’s duration. One of the pumps is a recently purchased electric pump. This pump is the most powerful electric pump operating west of the Mississippi and is capable of pushing concrete to the top of the structure. It provides our client, the Turner Construction Company, with a zero-emission pump that operates with less noise than a typical diesel pump.

By the end of Conco’s record breaking mat pour, the pumping work all went successfully according to plan. Special recognition goes to our ACPA trained pump operators, and our mechanics that spent countless hours preparing the equipment for the pour.

*Photos provided by Gary Leonard

Starting at 4:47 p.m. on Saturday, February 15, 2014, Conco broke the Guinness World Record for the largest continuous mat pour in 18 ½ hours (1 ½ hours under the projected time). To verify the event, there was an official Guinness World Records adjudicator on-site. The mat pour was for the new Wilshire Grand Center that is being constructed in downtown Los Angeles, and is slated to become the tallest building in the U.S. west of the Mississippi.

*Photos by Gary Leonard

After some 5 months of excavation and shoring, Conco was finally ready to begin the preliminary mat foundation work. Starter footings and elevator pits had to be constructed before the nearly 7 million pounds of mat reinforcement was installed. Then came 18 miles of cooling pipes for thermal control. We were ready to go with a couple of days to dot the i’s and cross the t’s. We began the set ups for pumping which involved strategically placing 19 pieces of concrete placing equipment in and around the construction site. It was now time to place this nearly 20 foot thick mat foundation.

The massive mat pour required a fleet of 208 trucks that each made 10 to 14 concrete drops for a total of 2,100 trips over the 18 ½ hour period. All of the concrete was provided by eight concrete batch plants operating at full capacity and located within a 20-mile radius of the job site. The success of the pour depended upon everything going exactly as planned and with contingencies in place to reroute trucks around any traffic jams. Trucks had to arrive on time since concrete needs to be poured 90 minutes after it is mixed. Several streets in the area were closed off to traffic.

Prior to this record breaking event, the largest continuous mat pour had been for the Venetian Hotel in Las Vegas in 1999. During that event, 21,000 cubic yards of concrete were poured. For the Wilshire Grand, 21,200 cubic yards of concrete were poured with an official finish time of 11:30 a.m. Sunday morning. The skyscraper is expected to be completed in 2016 and opened to the public in 2017. The Wilshire Grand will be 1,100 ft. tall, to include a 900-room hotel, office and convention space as well as five levels of subterranean parking.

After the highly publicized reports from this past summer regarding the failure of 32 anchor rods on the eastern span of the new Bay Bridge, the highly regarded concrete contractor, Conco was retained by the general contractor, American Bridge/Fluor Enterprises, Inc. JV, to assist with the repair work. Based on their earlier performance with other critical and technically challenging components of the new bridge structure, Conco was the logical choice. “Every aspect of this project had complex technical challenges.” said Brian Petersen, the contractor’s Project Director, and “Conco’s skill and expertise was a great asset to our team.”

The defective anchor rods were supposed to secure the bridge deck to the concrete crossbeam support. Since the failed rods were embedded and inaccessible, replacement was not feasible. After extensive collaboration and analysis, a fix was designed. It involved a complex series of steel saddles and post-tensioned (PT) jacket walls that would provide the required clamping force to secure the bridge deck framing to the E2 crossbeam. Temporary steel shims were inserted into the stabilizers while the repairs were being done, and in order for the Labor Day opening to go forward as planned. “The SAS bridge is part of a world-class megaproject which features a large amount of challenging concrete work associated with temporary support structures that are not part of the completed bridge,” noted Jim Klinger, Conco’s project manager.

For this very complicated problem, Conco’s first task was to close in a steel-framed trestle platform to give work crews access to the site and eliminate the potential for materials to fall into the San Francisco Bay. Once the platform was complete, crews roughened the crossbeam surface and epoxied over 3,000 drilled dowels into place. Reinforcing steel and PT cable ducts were then installed by Harris Salinas. Conco crews followed behind them, placing custom-made PT trumpet blockouts and setting forms for the jacket walls.

The concrete jacket wall structures were placed in three pours totaling 380 cubic yards. Due to restricted access and rebar congestion, much of the concrete had to be pumped 250 feet and then injected into the forms through ports at strategic locations. Conco worked closely with concrete supplier, Central Concrete, to develop an injectable SCC mix with silica fume that would meet the project’s specifications. A full-scale mockup was constructed and successfully tested to ensure the long-distance pumping and injection of the highly-flowable SCC mix would work.

“Almost all of the concrete work items Conco was asked to perform by ABFJV were custom, one-of-a-kind scopes that we will probably never see again,” said Klinger. In late November, the third and final injection was finished and the repairs were completed successfully.

Conco is a leading supplier of concrete services for the Western United States. As one of the leading commercial concrete contractors in the Bay Area, we have been involved with large-scale projects in the area including the new 49ers Stadium. Our concrete services include commercial, educational, parking and other construction development as well as public works projects and highways.