Fast-paced construction schedules often expose concrete pavement and/or structures to undergo substantial loading conditions even at its early age, which causes pre-mature failure or a significant reduction in the life span of pavement and bridges. The current methods for determining traffic opening times can be inefficient and expensive, causing construction delays and cost overruns. For instance, maturity testing and flexural strength of concrete are two commonly used methods. The maturity test requires extensive calibrations of the maturity meter and trial batches for each different mix design, causing inefficiency and high costs. The flexural strength testing of concrete beams often provides unreliable results due to the differences between laboratory and field conditions, and is very time consuming. To address this critical need we developed an in-situ nondestructive sensing method that enables an accurate and efficient understanding of early age properties of concrete using electromechanical impedance (EMI) method coupled with piezoelectric sensors. The EMI method is based on the electric impedance–frequency spectra variation of a piezoelectric sensor to measure the opposition of the material to flow of electricity, which provides accurate measurements of many concrete properties including hydration, stiffness, compressive strength, etc. Through support from Indiana Department of Transportation (INDOT), the project team has conducted research and developed the proposed sensing technology for in-situ monitoring of concrete strength gain at lab-scale. The technology has proved to be feasible and reliable at the laboratory scale for in-situ monitoring of the hydration behavior and hardening properties of concrete with and without pozzolanic material supplements (e.g. fly ash, slag and silica fumes). We have also set a precedent for the reported strength property of concrete at the very early age of 4-8 hours. These properties could not be obtained using conventional cylinder testing as concrete is often not hard enough to be demolded at this point. The correlation of experimental results obtained from proposed sensing methods with conventional compressive testing (using ASTM C109) has reached over 95% regardless of the mix designs. This has also proved that the sensing method does not need any calibrations for different concrete mix designs during each test run, which has previously been significantly cumbersome for maturity testing. The research work has published in top research journals and 2019 TRB conference [1-4]. The goal of this pooled-fund study is to develop the field-ready sensing method, implement it in all participating states and develop AASHTO ready specifications for using this method. We will extend the test methods to examine the concrete hydration process, hardening behaviors, and stiffness. The specific properties will be monitored including the set time, hydration, hardening behavior, stiffness and strength properties of concrete. Unlike conventional time-consuming lab and field concrete testing we will monitor the variations in electromechanical impedance of the concrete to determine the early properties of concrete, via the induced change in electrical impedance of a piezoelectric sensor. A detailed cost/benefit analysis of this method will be conducted during the program.

The aim of this project is to develop a reliable in-situ sensing method to evaluate the concrete properties for determining optimal traffic opening time of patching job or new construction with fly ash or other supplementary cementitious materials. This goal will be achieved by using piezoelectric sensors coupled with electromechanical impedance (EMI) analyzers to determine the very early age properties of concrete (i.e. Stiffness, setting time, hydration, etc.). This novel method will address the deficiency of current testing methods for determining traffic opening, for instance extensive calibration of maturity test and inefficiency of flexural strength test. The impact of this study can be revolutionary as it does not require any conventional mechanical testing and expensive and heavy test setups in the field. It only requires commercially available piezoelectric sensors (~$10 per sensor) and a portable EMI analyzer for data analysis and interpretation. There is no need for calibration for each different mix design. The associated benefits of using this novel non-destructive sensing method include 1) determining optimal traffic opening time based on reliable data of concrete properties; 2) reducing pre-mature failure of concrete pavement, bridge deck, patching, and other concrete structures; 3) enabling significant cost and schedule savings in construction projects due to reduced testing samples and testing time; and 4) reducing construction worker safety issues and jobsite accident rates in construction zones.

The objectives of the proposed pooled-fund study are as follows: 1) Develop a field-ready smart sensing method using piezoelectric sensors to assess the in-situ properties of concrete including the strength gain, elastic modulus (stiffness), and hydration behavior at any time period of interest. 2) Develop a user-friendly graphical user interface (GUI) for data interpretation. 3) Implement the smart sensing methods in all participating states and train state engineers to effectively use the sensing methods. 4) Provide guidance of how to use EMI methods to determine the optimal traffic opening time of concrete pavement and the suggested specifications for the measurement system and sensor, based on data gathered nation-wide. 5) Develop AASHTO ready specifications for evaluating the concrete properties using the proposed smart sensing technology. Research Tasks To achieve the proposed objectives, the following tasks are proposed: Task 1- Develop a field-ready smart sensing method to evaluate the in-situ properties of concrete. To implement the piezoelectric based EMI testing method in the field, understanding the environmental condition effects of this method is very important. Although the research team has proven the feasibility of the EMI method for evaluating the concrete strength gain at the early age using typical INDOT concrete mixes, the environmental conditions such as temperature, humidity, external vibration(noise), etc. will be addressed in this task. Moreover, the specific piezoelectric sensor being used needs to be evaluated as it requires good durability to withstand the variation of the weather and environmental conditions, sensors with different polymer coatings will be compared. In addition, the specific dimensions of the piezoelectric sensor will be evaluated to determine the effective sensing area of the sensors. This study will determine the specification for piezoelectric sensors to obtain cost-effective results. Task 2- Develop a user-friendly graphical user interface (GUI) for data interpretation. In practical applications a good testing method should be easy for implementation and be user friendly. A Proper device with convenient software is essential to develop a good test method. In this task, different measurement systems will be evaluated including conventional impedance analyzers and portable impedance analyzers. In addition, the research team will develop the data processing program using MATLAB. This program will be further improved by the addition of a user-friendly GUI to enable easy field implementations. Task 3- Implement the smart sensing methods in all participating states and train field engineers to use the test methods. Once the basic measurement system and software has been developed we will move to large-scale testing using the multi-sensing method to enable the practical application of these methods in highway construction, which are typically hundreds of miles long. During this task, the optimal embedded depth, deployment, and optimal amounts of sensors per mile will be studied using network optimization and machine learning methods. Task 4- Provide guidance and training materials for using smart sensing methods The research team will develop training modules, guidelines, suggested specifications for the measurement system and sensors to accompany smart sensing methods that determine the hydration and mechanical properties concrete properties based on the data gathered nation-wide. Task 5- Develop AASHTO ready specifications for evaluating the concrete property using the proposed smart sensing technology. The team will further extend field testing measurements to include interstate highways to get feedback for improvements. The standard operation procedure for this new testing method will be developed. The team will work with FHWA to draft the AASHTO Guide Specifications on piezoelectric sensors based testing methods.

Deliverables: 1) A reliable in-situ sensing method using piezoelectric sensors to assess the properties of concrete without any calibrations for each different mix design. 2) A complete index database to quantify the hydration, setting time and strength of various concrete mix design with and without supplementary cementitious materials. 3) Onsite testing of samples from all participating DOT, cities and federal agencies. 4) Recommendations for determining optimal traffic opening time to all participating parties based on the test results obtained from this program. 5) A training module and guideline of how to use sensing methods to determine concrete properties for optimal traffic opening time to all participating parties. 6) Reports of initial implementation results of the testing methods with recommended practice for further improvement. 7) Technology transfer to all participating states’ concrete engineers, construction engineers and any other related engineers through a well-developed training module. The funding level requested per partner is $25k per year for three years to facilitate Tasks 1 through Task 6. As stated, the research team will develop the technology and field implementations in all participating states. The full-scale field implementation for highways, and other major transportation projects in all participating states are included. The total estimated minimum funding level is $550,000 for 3 years.