Wilhelm Construction saves over a month on post-tensioning schedule with intelliRock

Real-time strength estimates from intelliRock allowed Wilhelm to post-tension the floor slabs of this 38-story structure at the earliest opportunity.

Wilhelm Construction used the intelliRock system to optimize the mix,post-tensioning workflow and minimize the potential for blowouts.

The Situation

The tallest hotel in Indianapolis endorses Wilhelm Construction’s work as a concrete and masonry contractor. This $41.8 million JW Marriott is a cast-in-place, post-tension concrete structure rising 38-stories into the Indianapolis skyline, containing 1,005 guest rooms with 104,000 square feet of meeting space. Wilhelm used the intelliRock concrete maturity system to estimate the real-time strength of the placements. This strength data helped accelerate project workflow, allowing Wilhelm to post-tension slabs at the earliest opportunity, saving over a month on the project’s post-tension stressing schedule. The intelliRock system also helped optimize the mix for the project by confirming the desired rate of strength gain for a less expensive mix.

Limitations of Traditional Testing

This success story begins at the 2009 World of Concrete when Wilhelm Quality Manager Ryan Decker investigated concrete maturity technology vendors and found the Engius intelliRock system. He secured approval to purchase a system for use on the JW Marriott project. “We didn’t plan to use intelliRock to replace concrete testing on the project,” says Decker. “The testing agency’s view was that intelliRock unnecessarily added expense Wilhelm Construction saves over a month on post-tensioning schedule with intelliRock Real-time strength estimates from intelliRock allowed Wilhelm to post-tension the floor slabs of this 38-story structure at the earliest opportunity. to the project. I sat down with my team and explained that due to the nature of an elevated, post-tensioned structure, it would benefit us to use the maturity method to reduce the potential of blowouts from stressing cables that sometimes result from traditional testing methods. I also looked at how intelliRock would help us with the post-tensioning schedule.”

Optimizing the Mix

Decker took intelliRock to the project’s Ready Mix provider to aid in setting up the mix. They generated maturity curves for various mixes to develop a greater understanding how changing mix components, such as non-chloride accelerators, would affect the mix’s performance in various weather conditions. The goal was to use a mix that would allow post-tensioning within 18 hours so the project could stay on schedule. “Using maturity with intelliRock let us select the best mix and know exactly how it was going to perform so we could stay within the ideal post-tensioning window,” states Decker.

Post-Tensioning Workflow

Construction of a typical floor involved two pours. Wilhelm Construction Superintendent Brian Allison placed two intelliRock maturity loggers in each pour to get the strength information needed to determine the ideal window for post-tensioning. “Within 18 hours of pouring, we want to post-tension and start jumping forms right away,” says Decker. “The intelliRock system let us know when we were at the ideal strength to do this.” During this project, Superintendent Allison would arrive at the site about 4:00 am each morning, review the intelliRock strength data and estimate when to begin stressing the slabs without having to wait for results from the testing facility. He didn’t have to climb into the structure to get this data because it was transmitted directly to the project’s PC via intelliRock wireless.

Cold-Weather Assurance

The data intelliRock provided about the structure’s strength was even more important during the winter months when the risk is higher of having a false, low-strength indication from a cylinder break. “There were one or two instances in the winter time that showed low strength based on cylinder breaks,” says Decker. “We had a conference call with the testing agency and got concurrence to go ahead and stress slabs based on intelliRock maturity readings. The testing agency acknowledged that the cylinders had probably frozen.” Had intelliRock not been in use, the Wilhelm team would either have missed the ideal stressing window or post-tensioned anyway, risking a cable blowout if the strength really was low. “We would have had to follow the ASTM specifications to core the slab, paying an agency to locate rebar and cables. If this testing process revealed low strength, we ultimately would have to take the slab out. It is a long, arduous process.” The intelliRock data assured Decker that the slab had not frozen and the strength was in the ideal range for post-tensioning. “We based all the tensioning work for this project on intelliRock maturity readings and never missed a single post-tensioning stressing schedule. In the end, we beat the schedule by over a month and never lost schedule time because of not making a post-tensioning activity. This let us remove form work and fly it to the next level as soon as possible.”

Other Benefits

The value of intelliRock real-time strength data has led to its use on other projects, including a multi-story parking structure. “As we were setting up the mixes and establishing a maturity curve for the project, the mix wasn’t gaining strength as fast as we expected based on history,” Decker relates. “Our Ready Mix provider changed cement vendors as a result. If we hadn’t detected this strength issue, it would have prevented us from hitting our scheduled time frame for post-tensioning and delayed the project.” Wilhelm is experiencing another intelliRock benefit on a 6-story, cast-in-place pan-deck. Data from intelliRock confirmed the structure had achieved a strength that allowed the superintendent to shut off temporary heat a day earlier than expected for almost every pour, saving the company $1,297 per day in fuel costs.

When Decker initially purchased an intelliRock system, he acknowledges that they “were just kicking the tires to see if the solution would work for future projects.” Now, intelliRock is a known quality assurance check of in-place concrete strengths. It has become a valuable management tool that helps superintendents accelerate workflow and complete projects on or ahead of schedule.

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