Link to Report: Coming Soon
Background :
Ongoing advances in the understanding of the chemistry and physics of infrastructure materials are making it possible to endow concrete with functional properties that include electrical conductivity, active thermal management, and charge storage. In this proposal, we will exploit these advances to engineer concrete bridge deck materials that can be heated in cold weather to eliminate or prevent ice formation. This functional behavior will be produced by infusing the material with moderate doses of biochar, a nanoporous and electrically conductive additive that will enable the material to conduct electricity and thereby raise the material’s temperature by Joule heating. The advent of electrically conductive concrete (ECC) will greatly reduce or eliminate the need for deicing salts in cold weather, the latter which interferes with traffic patterns when applied and shortens the service life of bridge decks by salt scaling mechanisms. In addition, the formulations will be optimized for ideal self-heating and maximum possible compressive strength.
Objectives :
The primary research goal is to develop biochar-infused ECC that can be implemented in bridge deck de-icing applications. The primary knowledge gap is the unknown performance of biochar as an electrically conductive filler, which hinders the practical application of biochar incorporated ECC to bridge construction and maintenance. A secondary goal is to optimize the material formulation so that it not only possesses sufficient conductivity for self-heating but also has the maximum possible compressive strength. The specific tasks in this project are to characterize the electrical properties of biochar and to identify the relationship between the mixture design variables to mechanical and thermal performances (e.g., heat generation rate and de-icing efficiency) of biochar-infused self-heating concrete.
Scope :
Task 1 – Characterize the physico-chemical and electrical properties of biochar
Commercially available biochar will be chosen for this project. To characterize the physico chemical and electrical properties of biochar, X-ray fluorescence (XRF), thermogravimetric analysis (TGA), scanning electron microscopy (SEM) for morphology, particle size analysis, specific surface area through BET method, and two-probe method for bulk electrical conductivity will be used in this project. We intend to examine water-to-solid mass ratios (w/s) of 0.35 and 0.45, which covers that used for most normal-strength concrete applications. Biochar dosages will be 5 % by mass (used in Cycle 1 research), 10 % by mass, and 20 % by mass (used in Cycle 2 research) replacement for portland cement. The mixtures will be prepared by standard mixing methods using either dry or pre-saturated biochar— keeping the total water content constant—and will be cured under saturated or moisture-sealed conditions. In each case, three replicates will be cured in ambient air. These ranges for the experimental variables are tentative and may be adjusted based on preliminary results to achieve the maximum amount of useable data. In addition, Cycle 2 research on biochar-infused concrete is still early in the development stages. We expect that findings from Cycle 2 in the coming months will also guide the work of Task 1.
Task 2 – Define the percolation threshold of pastes and mortar
The prepared biochar and carbon nanomaterial (CN) will be added to Type I Portland cement paste and/or mortar up to five replacement levels. Three different cases (i.e., biochar only, CN only, and hybrid biochar/CN) will be used to define the percolation threshold of electrical resistance as a function of different filler content. The electrical resistance of paste/mortar samples will be measured with a LCR meter, using an stainless steel electrode setup. A total of 19 mixture designs will be considered in this project to measure the absolute electrical resistance as well as the percolation threshold depending on filler type and dosage.
Task 3 – Optimize self-heating characteristics and compressive strength
We will use the data obtained in Tasks 1 and 2 to determine mixture proportions that maximize the compressive strength while still maintaining acceptable electrical conductivity to ensure adequate Joule heating of the material. The heat generation measurements will be conducted at room temperature using a thermocouple sensor and infrared thermography images under up to three different levels of voltage/current and for three different periods. More realistic de-icing tests will be conducted using plate samples with ice under ambient temperature and/or simulated cold temperature with an environmental chamber. With the data obtained from Task 2, we will extract the influence of biochar content and combination with CN on the self-heating performance of multifunctional concrete materials. The resulting outcomes will be a basis for developing and optimizing the mixture design of biochar-infused self-heating concrete material for potential implementation into bridge de-icing applications.
Research Team :
Principal Investigator: Jeffrey W. Bullard
Co-Principal Investigator: Yong-Rak Kim