Date of Defense
5-12-2024 4:00 PM
Location
F3-134
Document Type
Thesis Defense
Degree Name
Master of Science in Civil Engineering (MSCE)
College
COE
Department
Civil and Environmental Engineering
First Advisor
Dr. Hilal El-Hassan
Keywords
Basalt fiber-reinforced polymer (BFRP), geopolymer, durability performance, concrete, conditioning, temperature, sustained load, tensile strength, microstructure, Arrhenius concept.
Abstract
The rapid growth of infrastructure projects in the Gulf region has significantly increased the demand for construction in the urban coastal areas of the Arabian Gulf. This harsh coastal environment accelerates the corrosion of steel reinforcement in structural concrete, which leads to severe safety hazards as well as considerable financial losses. The utilization of non-corrodible materials as reinforcement bars in concrete structures would extend their service life and reduce the operation and maintenance expenditure. Basalt fiber-reinforced polymer (BFRP) bars have great potential to replace traditional steel reinforcement and eliminate corrosion-related problems. At the same time, the construction industry is responsible for the excessive consumption of natural resources and the emission of greenhouse gases to produce cement. The complete replacement of cement with waste-derived geopolymer binders promises to alleviate its environmental burdens. Yet, the effect of moist geopolymer concrete on the performance of BFRP bars has not been evaluated. To fill this research gap, the durability performance of BFRP bars embedded in moist geopolymer concrete has been investigated in an extensive testing program. The test parameters included the conditioning duration (3, 6, and 9 months), the conditioning temperature (20, 40, and 60oC), and the stress level of the sustained load (0, 15, and 25% of the ultimate tensile strength of BFRP bars). The BFRP bars were tested for tensile strength, moisture uptake, and matrix digestion. The pH and leachate in the geopolymer concrete pore solution were examined. Additionally, the microstructure of the BFRP bars was evaluated using differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). A durability design model for performance prediction of BFRP bars in moist concrete was developed as well. The results highlighted a progressive deterioration of the BFRP bars under the different environmental conditions, particularly at higher temperatures and sustained loads. After 9 months of conditioning, unloaded BFRP bars retained 50, 34, and 43% of their original tensile strength at 20, 40, and 60°C, respectively. Conversely, the loaded specimens exhibited further reduction after 9 months at 40°C, with tensile strength retention dropping to 33.7% and 18.5% for bars under 15% and 25% sustained load, respectively. The highest moisture uptake (2.7%) and lowest matrix retention (61.7%) were exhibited by the BFRP bars conditioned for 9 months at 40°C under a 25% sustained load. This was associated with an increase of 5.4% in hydroxyl (OH) group absorbance and a decrease of 18.2% in the transition temperature (Tg). In turn, the SEM micrographs confirmed the fiber-matrix interface debonding, hydrolysis reaction, and matrix softening as primary causes of deterioration. The combination of the accelerated aging test data along with the Arrhenius concept was further used to develop a durability design model.
Included in
DURABILITY OF BASALT FIBER-REINFORCED POLYMER BARS IN MOIST GEOPOLYMER CONCRETE
F3-134
The rapid growth of infrastructure projects in the Gulf region has significantly increased the demand for construction in the urban coastal areas of the Arabian Gulf. This harsh coastal environment accelerates the corrosion of steel reinforcement in structural concrete, which leads to severe safety hazards as well as considerable financial losses. The utilization of non-corrodible materials as reinforcement bars in concrete structures would extend their service life and reduce the operation and maintenance expenditure. Basalt fiber-reinforced polymer (BFRP) bars have great potential to replace traditional steel reinforcement and eliminate corrosion-related problems. At the same time, the construction industry is responsible for the excessive consumption of natural resources and the emission of greenhouse gases to produce cement. The complete replacement of cement with waste-derived geopolymer binders promises to alleviate its environmental burdens. Yet, the effect of moist geopolymer concrete on the performance of BFRP bars has not been evaluated. To fill this research gap, the durability performance of BFRP bars embedded in moist geopolymer concrete has been investigated in an extensive testing program. The test parameters included the conditioning duration (3, 6, and 9 months), the conditioning temperature (20, 40, and 60oC), and the stress level of the sustained load (0, 15, and 25% of the ultimate tensile strength of BFRP bars). The BFRP bars were tested for tensile strength, moisture uptake, and matrix digestion. The pH and leachate in the geopolymer concrete pore solution were examined. Additionally, the microstructure of the BFRP bars was evaluated using differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). A durability design model for performance prediction of BFRP bars in moist concrete was developed as well. The results highlighted a progressive deterioration of the BFRP bars under the different environmental conditions, particularly at higher temperatures and sustained loads. After 9 months of conditioning, unloaded BFRP bars retained 50, 34, and 43% of their original tensile strength at 20, 40, and 60°C, respectively. Conversely, the loaded specimens exhibited further reduction after 9 months at 40°C, with tensile strength retention dropping to 33.7% and 18.5% for bars under 15% and 25% sustained load, respectively. The highest moisture uptake (2.7%) and lowest matrix retention (61.7%) were exhibited by the BFRP bars conditioned for 9 months at 40°C under a 25% sustained load. This was associated with an increase of 5.4% in hydroxyl (OH) group absorbance and a decrease of 18.2% in the transition temperature (Tg). In turn, the SEM micrographs confirmed the fiber-matrix interface debonding, hydrolysis reaction, and matrix softening as primary causes of deterioration. The combination of the accelerated aging test data along with the Arrhenius concept was further used to develop a durability design model.