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Welcome to our newsroom! Here you will find the latest information about our company, projects and people. Browse articles published by our engineers and scientists in national publications and conference proceedings, view our press releases and read through news coverage of Terracon.

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Calling All Bats, We Hear You: Acoustic Sampling for Endangered Bats

Eastern Red Bat

Bats might not be the first thing that come to mind when planning a development project, but these unique and often protected creatures play a vital role in their ecosystem. In the summer of 2016, a team of scientists, biologists, and geologists were contracted to conduct a threatened and endangered (T&E) bat survey of a 590-acre wooded project site near Nashville. These types of presence or absence surveys are used to collect data, to determine a project’s potential impacts on area habitat, and, if a habitat is verified, provide recommendations for safe site development.

Due to the quantity of wooded land within the project, habitat was assumed to be present by U.S. Fish and Wildlife Service (USWFS). The site is located within the range of known federally-endangered Indiana bats and threatened Northern long eared bats.  As such, we knew on-site evaluation would be required to satisfy USFWS and the U.S. Army Corps of Engineers (USACE) requirements before federal permits could be released for the project.

Evaluating Options for Evaluation Survey

Typically for endangered bat evaluations, first a survey is conducted to determine if the project has bat-conducive habitat. Federal survey guidelines for bat evaluations allow two options for evaluating if T&E bats are present; mist netting or acoustic surveys. These guidelines are designed to determine if any of the trees within the project area are serving as a maternity roost. At times up to 100 adult bats can be found in these particular trees, which can be used year after year. If such a tree is located, it can be protected by federal statutes similar to a Bald Eagles nest depending on the species.

Anabat Acoustic RecordersBoth mist netting and acoustic surveys have limitations. Mist netting has been a standard method for evaluating bat populations for decades. This methods places thin-laced netting in a narrow tree corridor where bats are likely to fly at night. Scientists wait and during periods of bat activity, capture and identify bats. It is simple, safe, and effective method. However, issues arise in that many species won’t happen to fly through the selected corridor. The other major challenge is cost. Mist netting guidelines for central Tennessee recommend 9 net nights per 123 acres. This means two scientists staying approximately 45 nights – a method of evaluation quite costly for such a large area.

Acoustic survey sampling consists of setting up data recorders to monitor for sub-sonic sounds bats make to navigate at night while feeding. Each species has a particular set of calls, which can be identified by computer software with an accuracy rate of 75-80 percent. Guidelines for acoustic recording in the area recommend 4 detector nights per 123 acres or approximately 20 nights. In this sampling setup detectors are preset to record in the evenings and retrieved in the morning, eliminating overnight field stays and providing a more cost-efficient option.

Sampling Protects Natural Habitat

Grey Bat

One night of acoustic sampling yields approximately 2GB of data, which bat call computer software can filter in about two hours. During the project, Anabat II acoustic recorders collected 94,315 bat pulses, which the software filtered down into 2,074 total bat passes and identified 11 species, including one potential endangered Indiana bat. After consultation with USFWS, it was deemed only a few nights of mist netting were needed in limited locations to verify if endangered Indiana bats were actually present. The mist netting captured five species though none were Indiana bats. A federally-endangered Gray bat was captured, but as its roost habitat occurs only in caves, no impacts to the species were expected.

By combining the acoustic survey data with a traditional sampling method, Terracon was able to assist our client in navigating environmental rules and regulations while reducing the total cost of the project. The T&E survey provided conclusive results demonstrating that endangered species of bats would not be impacted and created a viable option for private development.

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Real-time Information Saves Time and Money: Maturity Meter Speeds-up Completion of Concrete Construction Projects

Maturity MeterMany materials testing activities are used to evaluate when certain construction activities can move to the next stage. Soil compaction testing of fill materials determine if additional fill can be placed or paving or foundation work can begin and concrete compressive strength testing will dictate whether post-tension cables can be stressed or concrete formwork can be removed are a few examples. Failing tests or insufficient test results can delay construction activities and impact the overall construction schedule.

To assist our clients Terracon focuses heavily on getting critical information to the project team quickly so a timely decision can be made. Our use of technology to efficiently collect and report our test results is key in making this happen. In addition, we also use technology to support how testing is performed to further create efficiencies in the testing construction schedule and accelerate the decision making process as well. One area where we can do this is related to the testing of field cured cylinders for concrete form removal and or post-tension cable stressing. Terracon can use the maturity meter method (ASTM Standard is C 1074 “Standard practice for estimating concrete strength by the maturity method”) to provide real-time data to be used to assess when form removal or stressing operations can occur or be used to augment when field cured cylinders should be tested.

We have found that with proper application, use of a maturity meter has the potential to save an average of one day per impacted concrete pour on typical commercial projects.  In some cases, this has resulted in reducing a project schedule by months and providing savings in thousands of dollars in construction costs.


By taking time prior to the start of concrete placements or during initial concrete placements to use the maturity meter on initial batches of the approved concrete mix, maturity index values can be correlated with the compressive strength of early-age cylinders. This in turn provides the baseline for future placements and the critical decision making process of when to remove formwork or when to stress post-tension cables by the construction team in a timely manner.

The basis of the maturity value of concrete is dependent upon the time and temperature history during the concrete curing period. A calibration curve is typically developed in the laboratory for a specific concrete mix design by recording the time-temperature history or “maturity value” of the concrete versus the early-age compressive strength of test cylinders. The maturity calibration curve allows for the accurate determination of early-age compressive strengths at the project site for a specific concrete mix design.

The initial costs in trail batches and correlation testing to develop the maturity curves and the actual maturity monitoring during placement is a minimal and worthwhile investment that can be quickly recovered. The form removal and stressing decision process, the significant time savings in the construction schedule, as well as reduction in the number of cylinder test specimens required per the project, all result in cost and time savings to the project.


Using the maturity meter method for early strength assessment can provide more accurate data in assisting in assessing when:

  • Post-tensioned tendons may be stressed
  • Concrete formwork may be removed
  • Shoring and re-shoring operations can begin
  • Floor slabs and pavements may be opened to traffic

In addition, maturity meter can also be used to measure:

  • Concrete curing temperatures
  • Cold-weather temperature effects on the curing process

Temperature differentials in mass-concrete placements

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Transportation Engineers Association of Missouri

Transportation Engineers Association of Missouri
March 22-29, 2017
Branson, MO

For more information on the conference, click here.

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DBIA: Design-Build in Transportation

March 27-29, 2017
Minneapolis, MN

Come visit us at booth 420! For more information, visit the conference website here.

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NSBE Annual Convention

March 29-April 2, 2017
Kansas City Convention Center
Kansas City, MO

We will be hosting a Kansas City themed reception Friday, March 31. For more information on the conference, click here.

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ABCD Spring Seminar

March 31, 2017
Batavia Downs
Batavia, NY

Matthew Silveston, PE LEED AP, will be presenting Quality Control Testing of Drilled Shafts through Thermal Integrity Profiling. For more information on the conference, click here.

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GPA Midstream Convention

April 9-April 12, 2017
Marriot Rivercenter San Antonio
San Antonio,TX

For more information on the conference, click here.

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Texas Alliance of Energy Producers Oil and Gas Expo (TAEP)

Texas Alliance of Energy Producers Oil and Gas Expo (TAEP)
April 25-26
Wichita Falls, TX

For more information on the conference, click here.

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API Pipeline Conference and Control Room Forum

April 25-April 27, 2017
Hyatt Regency Hill Country
San Antonio,TX

For more information on the conference, click here.

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TCEQ Environmental Trade Fair

TCEQ Environmental Trade Fair
May 16-17, 2017
Austin, TX

For more information on the conference, click here.