ASPIRE is a quarterly magazine published by PCI in cooperation with the associations of the National Concrete Bridge Council. The editorial content focuses on the latest technology and key issues in the Concrete Bridge Industry.

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C O N C R E T E B R I D G E T E C H N O L O G Y 30 | ASPIRE Summer 2018 Many people in the bridge-building community may be surprised to learn that the maturity method, introduced 20 years ago as ASTM C1074 Standard Practice for Estimating Concrete Strength by the Maturity Method, 1 can be incredibly beneficial for every stakeholder in the building process, including contractors, departments of transportation (DOTs), concrete producers, and testing agencies. The maturity method (often just called "maturity") is a vital supplement t o t ra di t io n a l m e t h o d s o f t e s t ing concrete that are required by codes and specifications. Applications in Bridges M a t u r i t y i s r e c o g ni z e d b y m a n y state DOTs as an alternative to field- cured sample testing for determining in-place concrete strength for low-risk applications such as slab-on-grade fast- patch pavement repairs and mainline paving, 2 but its use in bridge construction is not nearly as universal. Using maturity can have substantial benefits for all aspects of concrete bridge construction, especially for high-risk projects where p o s t - t e n s io nin g a n d c o ld - w e a t h er operations are commonplace. Es timating concrete s trength using maturity has been in place for more than 60 years and is based on the fact that concrete gains strength at a rate that is generally proportional to the temperature history of the concrete during the curing process. Maturity/strength relationships are mixture-specific (relationships must be determined for each mixture's p ro p o r t io n s ) , b u t a s l o n g a s t h e mixture constituents and proportions do not change, maturity estimates are remarkably accurate. 3, 4 There are several different ways to collect the field data needed to estimate concrete strength using maturity. Traditionally, sensors embedded in the fresh concrete record concrete temperatures over time via a data-logging device; then, at various ages, the data are "read"; and an assessment of the strength is made with software using the procedures of ASTM C1074. Today, the most innovative maturity-collection systems provide data to the user in real time via the internet. Regardless of the type of maturity data- logging device used, the results are the same: in-place concrete strength estimates that are far more accurate than traditional field-cured samples could ever be. Stakeholder Benefits Each stakeholder in any bridge project has unique criteria to monitor, record, and achieve. The contractor wants to build quickly and safely while turning a profit. The owner (usually a DOT) wants the project done correctly to maximize the service life of the bridge while minimizing disruption to the traveling public. The engineer wants to ensure that the entire structure meets the minimum design requirements. The concrete producer wants to ensure consistent quality and eliminate cylinder breaks that come back too low (often due to improper curing and handling of the cylinders in the field). The regular use of the maturity method on any concrete project can help all stakeholders achieve their goals simultaneously, easily, and reliably, and this is especially true for time-sensitive and high-risk endeavors. Contractors have reported many benefits from routine use of maturity on their projects. They experience lower project costs because construction schedules can be dramatically shortened. They can use knowledge obtained during other projects to estimate their time and staffing requirements more efficiently, which allows for more competitive bids. Their energy costs are significantly lower in cold weather, and their reliance on third-party testing is reduced. Finally, they can earn early-completion bonuses, if available, when they finish work ahead of schedules. Using Maturity Systems to Evaluate Concrete Strength by John Gnaedinger, Con-Cure, and Danielle Shultz, CTL Engineering Black Ankle Valley Bridge for Interstate 69 in southern Indiana. Maturity and temperature were wirelessly monitored for the cast-in-place piers, saving the contractor the costly process of using a lift to collect recorded data. All data were sent wirelessly to the contractor's job-site trailer. All Photos: John Gnaedinger.

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