Date of Defense
27-11-2024 10:00 AM
Location
F3-134
Document Type
Thesis Defense
Degree Name
Master of Science in Civil Engineering (MSCE)
College
College of Engineering
Department
Civil and Environmental Engineering
First Advisor
Dr. Hilal El-Hassan
Keywords
Geopolymer concrete, recycled concrete aggregates, glass fibers, fly ash, slag, performance, shear capacity .
Abstract
This study aims to investigate the potential use of geopolymer concrete (GC) incorporating recycled concrete aggregates (RCA) and glass fibers (GF) as a sustainable alternative to traditional cement-based concrete. It comprehensively evaluated the impact of RCA and GF on the fresh, physical, mechanical, and durability properties. A blended precursor binder consisting of ground granulated blast furnace slag and fly ash was utilized. To mitigate the challenges associated with the brittle behavior and low crack resistance of GC, mainly when incorporating RCA, two types of GF were used. Type A had a length of 24 mm, while Type B exhibited a length of 45 mm, with a consistent diameter of 0.7 mm. The workability of produced mixes was evaluated using the slump cone test, while the mechanical performance was characterized by compressive strength, tensile strength, and flexural strength. Durability tests such as water absorption, sorptivity, abrasion resistance, ultrasonic pulse velocity, bulk resistivity, and resistance to hydrochloric acid attack were conducted to evaluate the long-term performance of the material and its potential behavior under harsh environmental conditions. Moreover, the shear behavior of GC beams made with RCA and GF was examined through full-scale experimental testing. The results highlighted that 100% RCA led to significant losses in compressive, tensile splitting, flexural, and shear properties. This trend of lowering mechanical properties was observed consistently across all the tested parameters, with each showing a decline as the RCA content increased. Nevertheless, GF incorporation into GC mixes countered the RCA-induced reductions in the mechanical performance to the extent of even exceeding the control mix made with natural aggregates (NA). Notably, the inclusion of GF in RCA-based GC, beyond 1 and 2%, not only offset the negative impacts associated with RCA but also restored literally 95 and 97% of the compressive strength, respectively, of a comparable plain mixture made with NA. This enhancement was consistently observed across all types of GF, highlighting their uniform effectiveness in improving overall characteristics of GC (e.g., compressive strength, tensile strength, modulus of elasticity, etc.). In fact, of the different combinations and volume fractions investigated, the hybrid mix made with both types of GF at a volume fraction of 1% yielded superior performance. Similar findings were noted for the durability of GC upon RCA replacement and GF incorporation. In turn, the full-scale concrete beam testing showed that GF improved the shear and deflection capacity to the extent of potentially replacing steel stirrups, especially with 1% volume fraction of Type B GF. For example, the shear strength improved by 15 and 19% upon the addition of 1 and 2% Type A GF, respectively. Meanwhile, the inclusion of Type B GF at a volume fraction of 0.5 and 1% resulted in 9 and 21% higher shear strength. Notably, the optimal GF-reinforced beam, composed solely of 1% Type B GF, exhibited a shear capacity that was approximately 80% of that achieved by an RCA-based beam reinforced with steel stirrups. The validity of published analytical models to predict the shear capacity of RCA-based GC beams, both with and without GF, was examined.
Included in
PERFORMANCE OF GEOPOLYMER CONCRETE INCORPORATING RECYCLED AGGREGATES AND GLASS FIBERS
F3-134
This study aims to investigate the potential use of geopolymer concrete (GC) incorporating recycled concrete aggregates (RCA) and glass fibers (GF) as a sustainable alternative to traditional cement-based concrete. It comprehensively evaluated the impact of RCA and GF on the fresh, physical, mechanical, and durability properties. A blended precursor binder consisting of ground granulated blast furnace slag and fly ash was utilized. To mitigate the challenges associated with the brittle behavior and low crack resistance of GC, mainly when incorporating RCA, two types of GF were used. Type A had a length of 24 mm, while Type B exhibited a length of 45 mm, with a consistent diameter of 0.7 mm. The workability of produced mixes was evaluated using the slump cone test, while the mechanical performance was characterized by compressive strength, tensile strength, and flexural strength. Durability tests such as water absorption, sorptivity, abrasion resistance, ultrasonic pulse velocity, bulk resistivity, and resistance to hydrochloric acid attack were conducted to evaluate the long-term performance of the material and its potential behavior under harsh environmental conditions. Moreover, the shear behavior of GC beams made with RCA and GF was examined through full-scale experimental testing. The results highlighted that 100% RCA led to significant losses in compressive, tensile splitting, flexural, and shear properties. This trend of lowering mechanical properties was observed consistently across all the tested parameters, with each showing a decline as the RCA content increased. Nevertheless, GF incorporation into GC mixes countered the RCA-induced reductions in the mechanical performance to the extent of even exceeding the control mix made with natural aggregates (NA). Notably, the inclusion of GF in RCA-based GC, beyond 1 and 2%, not only offset the negative impacts associated with RCA but also restored literally 95 and 97% of the compressive strength, respectively, of a comparable plain mixture made with NA. This enhancement was consistently observed across all types of GF, highlighting their uniform effectiveness in improving overall characteristics of GC (e.g., compressive strength, tensile strength, modulus of elasticity, etc.). In fact, of the different combinations and volume fractions investigated, the hybrid mix made with both types of GF at a volume fraction of 1% yielded superior performance. Similar findings were noted for the durability of GC upon RCA replacement and GF incorporation. In turn, the full-scale concrete beam testing showed that GF improved the shear and deflection capacity to the extent of potentially replacing steel stirrups, especially with 1% volume fraction of Type B GF. For example, the shear strength improved by 15 and 19% upon the addition of 1 and 2% Type A GF, respectively. Meanwhile, the inclusion of Type B GF at a volume fraction of 0.5 and 1% resulted in 9 and 21% higher shear strength. Notably, the optimal GF-reinforced beam, composed solely of 1% Type B GF, exhibited a shear capacity that was approximately 80% of that achieved by an RCA-based beam reinforced with steel stirrups. The validity of published analytical models to predict the shear capacity of RCA-based GC beams, both with and without GF, was examined.