Isaac L. Howard’s research while affiliated with Mississippi State University and other places

Over the past several years, the asphalt industry has progressively increased efforts to evaluate mixtures after laboratory conditioning for the purpose of simulating field aging, and has also increased reliance on mixture testing. AASHTO T 401-22 describes Cantabro Mass Loss testing and has an appendix of field aging simulation protocols that can be used to estimate field aging by making use of compacted specimens. T 401-22 is one of the few methods to contain both a field aging simulation protocol and a mixture property index test. This paper uses roughly 1,000 tested specimens from forty-nine mixes (mostly dense-graded asphalt with minor amounts of stone-matrix asphalt) evaluated for up to four years of field aging in a hot and non-freeze climate alongside twenty-five different laboratory conditioning protocols. This paper’s objective is to provide information to improve T 401-22 by way of recommendations to update the appendix of conditioning protocols with more comprehensive assessments of their effectiveness in simulating field aging in a hot, non-freeze climate. The overarching recommendation of this work culminates with four protocols. Two of these protocols use only oven conditioning, whereas the remaining two protocols use a combination of stages exposing specimens to oxidation in ovens, moisture effects in hot water baths, and freeze–thaw cycling. The time required to administer the recommended protocols varies from approximately 6 to 28 days and they simulate between 1 and 5 years of field aging depending on the protocol selected.

This research contributes to long-term structural health monitoring (SHM) by exploring radio frequency energy-powered sensor nodes (RF-SNs) embedded in concrete. The RF-SN captures radio energy from a mobile radio transmitter for sensing and communication, which offers a cost-effective solution for consistent in-situ perception. To optimize the system performance across various situations, we've explored both active and passive communication methods. For the active RF-SN, we implement a specialized control circuit enabling the node to transmit data through ZigBee protocol at low incident power. For the passive RF-SN, radio energy is not only for power but also as a carrier signal, with data conveyed by modulating the amplitude of the backscattered radio wave. To address the challenge of significant attenuation of the backscattering signal in concrete, we utilize a square chirp-based modulation scheme for passive communication. This scheme allows the receiver to successfully decode the data even under a negative signal-to-noise ratio (SNR) condition. Performance modeling and optimization for both active and passive RF-SNs are provided in this study. The experimental results verify that an active RF-SN embedded in concrete at a depth of 13.5 cm can be effectively powered by a 915 MHz mobile radio transmitter with an effective isotropic radiated power (EIRP) of 32.5 dBm. This setup allows the RF-SN to send over 1 kilobyte of data within 10 seconds, with an additional 1.7 kilobytes every 1.6 seconds of extra charging. For the passive RF-SN buried at the same depth, continuous data transmission at a rate of 224 bps with a 3% bit error rate (BER) is achieved when the EIRP of the transmitter is 23.6 dBm.

The plastic mold compaction device (PM Device) was developed in Mississippi to compact cementitiously stabilized soil inside plastic molds to improve soil–cement quality by adding value during design and construction activities. The PM Device has been incorporated as an AASHTO provisional standard (AASHTO PP92-19) and, to date, prevailing activities have been Mississippi Department of Transportation projects and have included controlled laboratory evaluations and field projects. This paper goes beyond previous efforts, to document a field study in which the PM Device was successfully used on an Alabama Department of Transportation project to evaluate its effectiveness within another state’s construction specifications. The PM Device was capable of capturing quantifiable variation in mechanical properties over the duration of the construction project, as well as producing similar mechanical properties to cores taken from the compacted pavement surface. Additionally, molds described in AASHTO PP92-19 were compared with one another to evaluate their potential within the standard practice. AASHTO PP92-19 protocols were sufficient to produce viable, repeatable test specimens within another state department of transportation construction environment for quality control and quality assurance.

This research contributes to long-term structural health monitoring (SHM) by exploring radio frequency energy-powered sensor nodes (RF-SNs) embedded in concrete. Unlike traditional in-situ monitoring systems relying on batteries or wire-connected power sources, the RF-SN captures radio energy from a mobile radio transmitter for sensing and communication. This offers a cost-effective solution for consistent in-situ perception. To optimize the system performance across various situations, we've explored both active and passive communication methods. For the active RF-SN, we implement a specialized control circuit enabling the node to transmit data through ZigBee protocol at low incident power. For the passive RF-SN, radio energy is not only for power but also as a carrier signal, with data conveyed by modulating the amplitude of the backscattered radio wave. To address the challenge of significant attenuation of the backscattering signal in concrete, we utilize a square chirp-based modulation scheme for passive communication. This scheme allows the receiver to successfully decode the data even under a negative signal-to-noise ratio (SNR) condition. The experimental results indicate that an active RF-SN embedded in concrete at a depth of 13.5 cm can be effectively powered by a 915MHz mobile radio transmitter with an effective isotropic radiated power (EIRP) of 32.5dBm. This setup allows the RF-SN to send over 1 kilobyte of data within 10 seconds, with an additional 1.7 kilobytes every 1.6 seconds of extra charging. For the passive RF-SN buried at the same depth, continuous data transmission at a rate of 224 bps with a 3% bit error rate (BER) is achieved when the EIRP of the transmitter is 23.6 dBm.