Developing Eco-friendly Concrete with Sustainable Supply: The Potential of Using Whole Recycled Gypsum Drywall
Presented By: Alireza Jafari
Affiliation: Dalhousie University
Description: Fly ash is the most common cement alternative used to reduce demand for cement in cementitious composites and, thereby, their environmental impacts. Studies show that incorporating up to 10% fine recycled gypsum drywall (RGD) in high-volume fly ash concrete (HVFA) maintains mechanical strength while reducing cement demand. However, using only fine RGD returns almost 70% of the RGD into landfills, causing ecosystem contamination. This study examines incorporating whole RGD in high-volume fly ash concrete with 40% (F40) and 50% (F50) fly ash by testing 36 concrete cylinders for mechanical strength, unit weight, and porosity at 7, 28, and 90 days. The data revealed that replacing fine RGD with the whole RGD increased the 7-day by 11 and 10% in the F40 and F50, respectively. However, the strength of specimens containing fine RGD surpassed those containing whole RGD by 1 (in F40) and 4.4% (in F50) at 90 days, respectively. Comparing F50 and F40 specimens with 10% RGD, the 7-day strength of specimens decreased by 35.1 (whole RGD) and 41.98% (fine RGD) compared to F50. However, the superior strength improvement of the RGD narrowed the difference to less than 8%. The data also suggested that adding RGD could increase the porosity of the concrete, identified by a reduction in ultrasonic pulse velocity and unit weight. Accordingly, while the study showed the potential of whole RGD, findings proposed the whole RGD as an efficient alternative for fly ash in HVFA, especially critical given environmental regulations limiting biomass combustion and fly ash availability.
Behavioral Analysis of Bent-to-Column Connections under Lateral Load: Insights into Current Design Practices
Presented By: Terence Briscoe
Affiliation: University of Austin Texas
Description: This presentation highlights the results of an experimental and analytical research program investigating the behavior of bent-to-column connections. Nine large-scale tests were conducted under monotonically increasing lateral load and constant axial load. Different anchorage methods of the column longitudinal reinforcing bars were explored, including straight, headed, and hooked bars. In addition, the influence of hoop confinement in the joint region was also investigated. Specimens with both precast and cast-in-place bent caps were tested, and two different types of boundary conditions were explored. Experimentally measured responses such as moment-displacement, load-displacement, strain profiles at the critical region, maximum crack widths and slip of the longitudinal column bars were used to evaluate the performance of the specimens. To gain additional insight into the governing mechanisms influencing the behavior, nonlinear finite element analyses were conducted. The findings suggested that all connections effectively transferred the moment between the bent cap and column, resulting in a ductile flexural failure. Moreover, confinement in the joint region, whether external due to the boundary conditions or internal provided by hoop reinforcement, along with anchorage methods such as headed or hooked bars, significantly enhances the maximum moment capacity and ductility of the connections. Additionally, the findings revealed that current AASHTO LFRD and ACI 318 provisions for the development length of column longitudinal bars are conservative for connections where the column is flexural-critical.
Monitoring Buildability of 3DPC Using Ultrasonic Guide Wave Technique
Presented By: Geetanjali Chandam
Affiliation: Ulsan National Institute of Science and Technology
Description: Recent advancements in the 3D printing of concrete structures have highlighted its numerous advantages over traditional construction methods. However, ensuring quality during the printing stage remains essential to achieving optimal buildability. To address this, we propose the use of an ultrasonic guided wave technique for monitoring 3DPC during this critical phase. Guided wave techniques have been adopted for numerous studies of traditional concrete however the recent technology is yet to benefit from this technique. Two plates of different materials, i.e. aluminum and acrylic, were selected as waveguides. Piezoelectric (PZT) sensors with different center frequencies, i.e. 100 kHz, 200 kHz accordingly matched with the thickness of the wave guide were permanently mounted on these plates. The wave guides were then attached to the side of the lower layers of the 3DPC structure. This setup enables real-time monitoring of the development of stiffness for the 3DPC, based on the principle of energy loss due to wave leakage from the waveguide into the 3DPC. Experimental tests were conducted over a 2-hour period following the printing of the first layer. From the selected waveguides, acrylic was found to be more efficient to monitor the stiffness development of 3DPC even during this very early age. The results demonstrated a strong correlation between energy attenuation and the development of material stiffness over time, with a linear attenuation loss of up to 5 dB.
Advanced Machine Learning Modeling of Chloride Ion Penetration and Service Life Prediction in Internally Cured Concrete
Presented By: Ali Akbar Shakeri
Affiliation: Tarbiat Modares University
Description: This study presents a numerical model that uses machine learning to predict chloride ion penetration and the service life of concrete based solely on commonly measured properties. The proposed method intends to link such properties to the results of experimental chloride penetration measures. The model integrates data on concrete properties (density, compressive strength, porosity, cement content, and curing conditions) with machine learning algorithms to provide practical and accurate relationships for predicting chloride penetration. Although this research focuses on internally cured concrete containing lightweight expanded clay aggregate (LECA), the final model is adaptable and can be extended to predict chloride penetration in concrete subjected to various curing conditions, making it a versatile tool for durability assessment. The results demonstrate that this model can give engineers a powerful tool for predicting concrete durability in corrosive environments.
Additive Construction of Low Embodied Carbon Concrete: Geopolymer Concrete
Presented By: Anthony Mackin
Affiliation: Rowan University
Description: Additive construction provides key benefits over traditional methods; however, conventional concrete production significantly impacts the environment due to carbon emissions from Portland cement. This study explores geopolymer concrete a cement-free alternative made from industrial by-products activated by alkali activators, for additive construction. The research focuses on: (1) developing geopolymer mixtures for additive construction, (2) establishing a reliable 3D printing process, and (3) demonstrating the printability of 3D printed geopolymer structures. Results show that the mixtures enabled successful printing of complex forms like circular paths, slopes, and varying cross-sections, proving their suitability. Additionally, findings indicate that increasing slag content enhances compressive strength, controlling the temperature of the alkaline activator optimizes setting time and printability, and allowing idle time before printing helps achieve a printable consistency.
Using an Embedded Sensor to Measure the Formation Factor of Concrete
Materials
Presented By: Nima Kargah-Ostadi
Affiliation: Callentis Consulting Group
Description: This presentation will discuss test results of a novel sensor system for measurement of the concrete Formation Factor (FF). Calculated as the ratio of the electrical resistivity of the concrete mixture over the concrete pore solution resistivity (PSR), FF is an indication of concrete transport properties, used to predict service life. Funded by the USDOT FHWA, this embedded sensor system was developed to measure both the mixture resistivity and the PSR inside cylindrical concrete samples to calculate the concrete FF. This presentation discusses test results using sensors in several concrete mix designs exposed to different curing methods. The use of the sensor in cylindrical concrete samples will improve concrete mix design and construction quality control to produce concrete materials that are more resilient against ingress of aggressive ions, which can corrode steel reinforcement and accelerate deterioration. The sensor system can also be used to evaluate the impact of various additive materials on the durability of concrete mixtures.