Conventional concrete used for construction has neither the inherent ductility nor durability to meet the requirements of modern infrastructure construction. With ageing highway and bridge infrastructure requiring a significant expenditure of capital, it is prudent to explore utilization of so-called high performance materials that have the potential to outperform and outlast their conventional counterparts. This research program is built around the concept of creating a sustainable material that exceeds the performance of conventional concrete through a characteristic enhanced cracking resistance achieved by the introduction of discrete fiber reinforcement combined with an optimized level of workability.

In an effort to meet the existing demand for high performance materials suitable for modern construction practice, self-consolidating features have been developed for a preexisting high performance hybrid fiber reinforced concrete. A parametric study was employed to maximize the fresh state performance benefits of chemical and supplementary cementitious material additives in conjunction with optimization of the fiber reinforcement to meet the flow criteria of self-consolidating type concrete. The resulting composite, Self-Consolidating Hybrid Fiber Reinforced Concrete (SC-HyFRC), is tested under compression, tension and flexure loading independently and in combination with conventional steel reinforcement to illustrate the mechanical performance gains that can be achieved with such composites. The performance enhancements gained in each manner of loading are then combined in the material's application to a structural element that must be designed to undergo a substantial inelastic (cracked) response.

The intrinsic durability of the SC-HyFRC material is tested against two environmental deterioration mechanisms which plague modern concrete. Due to the enhanced crack resistance present in SC-HyFRC, chloride-induced steel reinforcement corrosion is mitigated during both the initiation and the propagation phases. This mitigation is qualitatively and quantifiably measured by suppression of observable cracking and direct electrochemical measurements of the reinforcing steel surface. Similarly, the cracking resistance feature of SC-HyFRC and similar fiber reinforced cementitious composites is judged for mitigation capacity of alkali-silica reaction. The magnitude of internal cracking accompanying the swelling-induced expansion is measured by relative changes in structurally relevant concrete mechanical properties, compressive strength and elastic modulus, with fiber reinforced restraint of expansion observed to correlate well with mechanical property retention. As reinforcement corrosion and alkali-silica reaction are but two of many deterioration mechanisms that induce damage by way of internal expansion, the positive outcomes of SC-HyFRC testing are expected to be transferable to concrete durability in a holistic sense.

The potential benefit of constructing critical infrastructure elements with such high performance materials is a two-fold gain in overall structural life cycle assessment, being better equipped to deal with multiple facets of loading placed on modern structures. This and similar research of SC-HyFRC and other such materials will hopefully validate the upfront costs necessary to build with materials that can generate outsized long term fiscal savings.

This research first focused on developing a green ultra-high performance fiber-reinforced concrete (G-UHP-FRC) to reduce its cement content, and thus its carbon footprint and environmental impact. In this study, 50% of Portland cement by weight was replaced by 25% fly ash (FA) class F and 25% ground granulated blast-furnace slag (GGBFS). A comprehensive study was undertaken to achieve high workability while ensuring a minimum compressive strength of 125 MPa after 28 days of moist curing. The best performing G-UHP-FRC mixtures were selected for flexural as well as large-scale tensile testing. Ductility enhancement was achieved by optimizing a hybrid mechanism through combining three different types of micro and macro fibers.

Ideal lightweight structures, such as façade and flooring systems provide strength as well as thermal and acoustic insulation while keeping weight to a minimum. Highly porous concrete can be lightweight and have excellent insulating properties; however, increasing porosity, if geometrically disordered, results in rapid strength loss, with strength generally scaling as the cube of the solid volume fraction. Furthermore, recent advances in the development of Ultra-High Performance Fiber-Reinforced Concrete (UHP-FRC) with very high compressive strength (120 to 210 MPa) inspired the development of a lightweight structure by engineering the void spaces in the material, thus taking advantage of porous concrete’s thermal insulating properties while maintaining strength and stiffness. This engineered material is here referred to as Octet-Truss Engineered Concrete (OTEC). To make OTEC structures, UHP-FRC and G-UHP-FRC mixtures were developed and used. 50.8-mm side-length OTEC unit cell specimens with various element diameters as well as 5×1×1-cell OTEC flexural specimens with 8 mm-diameter elements were cast and tested under uniaxial compression and four-point bending, respectively. The compressive strength of the OTEC unit cell specimens with various element diameters (8, 10, and 11 mm resulting in 66.4, 53.6, and 47.5% porosity, respectively) is mainly stretching-dominated, and hence considerably surpasses that of the control foam Green Ultra-High Performance Concrete (G-UHPC [no fibers]) specimens with random pore orientations (by about 180, 290, and 400%, respectively). Furthermore, the flexural performance of polylactic acid (PLA) octet-lattice reinforced Ultra-High Performance Concrete (UHPC) with three different UHPC volume fractions (37.5, 75, and 100%) was briefly investigated. All these results indicate a promising application of UHP-FRC and G-UHP-FRC OTECs as well as PLA octet-lattice reinforced UHPC for lightweight structures, such as façade, flooring, and membrane systems.

UHPC composites, with compressive strengths exceeding 125 MPa, carry tension to much higher levels compared to conventional concrete or High-Performance Fiber-Reinforced Cement-Based Composites (HP-FRCC). This improved strength of UHPC composites, however, leads to a brittle behavior under both tension and compression. Therefore, through addition of fibers in UHP-FRC composites, ductility and strain-hardening is achieved for such materials. During the last few years, however, while many researchers have focused on developing UHP-FRC composites with higher tensile strain values than 0.2–0.4% (strain value of steel rebar at its yielding point), the interaction and synergy between the composite and steel reinforcing bar to large deformations up to fracture remains unknown. In this research, eleven G-UHP-FRC as well as one Hybrid Fiber-Reinforced Concrete (HyFRC) dogbone-shaped specimens reinforced with a single deformed steel rebar in the middle were tested under uniaxial tension up to fracture of the steel reinforcing bar. After the yielding of the steel rebar, a dominant crack is formed at the location of which early strain-hardening and ultimately, fracture of the rebar can lead to an overall brittle failure at much lower strain values than the bare rebar for under-reinforced specimens. Therefore, a minimum longitudinal reinforcing ratio of ~4.0% (A706 Grade 60 mild steel) is recommended for UHP-FRC and G-UHP-FRC composites to ensure multiple macro cracking, uniform bar yielding throughout the specimen, and an overall ductile behavior. For all specimens, Digital Image Correlation (DIC) techniques were utilized based on which different crack formations were recorded, and concrete, rebar, and bond stresses were calculated. Such information then provides for the estimation of flexural strength of reinforced G-UHP-FRC components, which could be later verified through flexural experiments.

Concrete-related construction industry consumes considerable amount of energy, resulting in large CO2 release into the atmosphere. Cement which is used as the main binder in concrete is energy intensive to produce and contributes about 7% to total global anthropogenic carbon emission. Infrastructure across the globe suffers from durability problems and requires frequent repair and maintenance. This brings about high direct cost for rehabilitation and unaccounted indirect cost resulted from loss of productive time, traffic congestion and diversion, and in the process more CO2 emission. In the meantime, buildings which are part of the overall civil infrastructure system require extensive amount of energy to keep the internal environment comfortable to users. The sector accounts for about 40% of global primary energy consumption. With increasing population and demand, actions from various building disciplines are needed to build a more sustainable industry. This research addresses these issues through the development of a new high performance fiber-reinforced concrete, its durability studies and its application to reduce operational energy in buildings. Durability is critical for infrastructure systems whose frequent maintenance and rehabilitation pose adverse impacts to the environment and add considerable costs to the economy. By accounting for sustainability aspects from materials conception to usage and disposal, this study encompasses the concept of sustainability through life cycle consideration. This represents a deviation from conventional sustainable approach where a focus is usually spent on reducing embodied energy of concrete composites.

The first area of focus was on the development of a new concrete composite called high performance green hybrid fiber-reinforced concrete (HP-G-HyFRC) reinforced with polyvinyl alcohol (PVA) micro- and hooked-end steel macrofibers. For easy construction and durability, the design criteria were defined to cover high workability, high strength and deflection hardening which is defined as an ability of the composite to carry increasing load after the first crack is formed. It was demonstrated that theoretical analysis could be used to limit the number of trials in determining the critical fiber volume fractions for the deflection hardening behavior in the composite. As compared to conventional self-consolidating concrete (SCC), fine aggregate over coarse aggregate ratio had to be increased in FRC for enhanced workability. Addition of supplementary cementitious materials (SCMs) in concrete especially fly ash helped to improve the composite’s workability. This is attributed to fly ash’s favorable fineness, size distribution and spherical shape which resulted in ball-bearing action provided to other concrete constituents. PVA microfibers controlled propagation of micro cracks inherent in concrete or formed during loading. They also provided toughening around steel fibers and ensured a gradual pullout of steel fibers. The synergy of PVA micro- and steel macrofibers led to a smooth deflection hardening behavior of the composite under flexure at a relatively low fiber volume fractions of 1.5% steel fibers and 0.15% PVA fibers.

A study on corrosion performance of HP-G-HyFRC with accelerated corrosion test with an impressed current was then conducted. It was found that wide cracks ranging from 1.1 to 2 mm were observed in high performance concrete (HPC) without fibers. The presence of hybrid fibers in HP-G-HyFRC, on the other hand, reduced corrosion rates by half, attributable to crack bridging of fibers and the resulting formation of distributed cracks of small sizes. Also, under no applied current, all embedded steel rebars in HP-G-HyFRC were in the inactive corrosion zone even with the presence of 4% NaCl in the mixing water. Microscopic observation at steel-concrete interface showed a densification of corrosion products, which is postulated to limit iron dissolution and subsequently to reduce corrosion rates of the embedded bars. HP-G-HyFRC corrosion samples were also able to retain most of its strength after the accelerated corrosion tests.

As corrosion resistance of HP-G-HyFRC was considered at a composite level, the effects of individual mix component such as slag and fibers on corrosion were yet unknown. The next area of focus was on the influence of high-volume slag as cement replacement, hybrid fibers and steel-concrete interface on corrosion of steel in concrete. The studies elaborated various phenomena observed in the corrosion study of HP-G-HyFRC and also provided a fundamental understanding of different concrete parameters on corrosion.

It was found that due to shrinkage-induced cracking and possibly poor quality passive film due to the presence of reducing agents in concrete pore solutions, samples with 60% slag replacement and with no fiber reinforcement showed an early corrosion initiation and higher mass loss induced by the impressed current. Microstructural imaging showed that the samples with slag, despite having a higher gas permeability, showed a denser matrix but more continuous distributed microcracking in the matrix. This led to its poor ability to accommodate corrosion products at the interface and as a result the concrete experienced an early onset of cracking. Under the same regime of applied current, samples made of slag concrete also experienced higher gravimetric mass losses. This is attributed to a less stable passive film and more intense acidification at the interface due to a reduction in calcium hydroxide (CH) in the matrix. Also, an inclusion of hybrid fibers in concrete slightly increased concrete permeability although this did not adversely affect corrosion initiation performance of concrete. However, under propagation stage achieved by an induced current, hybrid fibers in concrete significantly reduced corrosion rates through confinement and densification of corrosion products at steel-concrete interface. The influence of interface qualities on corrosion of steel in concrete showed conflicting performance in corrosion initiation and propagation stages. It was found that higher porosity at the steel-concrete interface initiated an early corrosion. However, the porous interface could accommodate more corrosion products. This led to a smaller pressure buildup from the corrosion products and less damage to the surrounding concrete. As a result, smaller corrosion rates were observed in the samples with more porous interfaces after impressed current regimes. The finding helps to explain the more extensive damage in high performance concrete (HPC) as compared to normal strength concrete. This warrants the inclusion of fibers in HPC to extend the service life of structures constructed with the composite.

The study ended with a proposed application of HP-G-HyFRC in an innovative double skin façade (DSF) system in place of a conventional solid façade system to enhance operational energy performance of buildings. It was found that although the DSF is more energy intensive and more costly to construct, it allowed for a full recovery of the additional embodied energy within the first year of operation and cost recovery within the first 6 years of operation. The overall study exemplifies a life-cycle consideration adopted for materials design, durability investigation and application to ensure more sustainable infrastructure and buildings for our society.

For a reinforced concrete structural member, sufficient bond between steel reinforcing bar and concrete guarantees a steel/concrete composite behavior, which is essential for a good overall member performance. Under severe loading, high slippage between rebar and concrete leads to matrix cracking and crushing in the bond region followed by degradation of the rebar/matrix bond. Fiber reinforcement provides a fiber bridging mechanism to resist such cracking behavior by modifying the tensile properties of the matrix. This thesis investigated a deflection hardening hybrid fiber reinforced concrete (HyFRC) with micro/macro fiber hybridization and recommends it as a matrix to enhance the rebar/matrix bond by utilizing its superior crack resisting ability.

In the experimental phase, the rebar bond behaviors in ordinary concrete (OC), HyFRC without/with high volume fly ash and Engineered Cementitious Composites (ECC), another type of fiber reinforced cement-based composite (FRCC) with hardening behavior, were studied. The experimental program consists of monotonic and cyclic rebar pull-out test series and was supported by digital image correlation (DIC) and vibration test techniques. Different specimens were made by varying some conditions such as rebar size (no. 4 and no. 8) and absence/presence of transverse reinforcement (spiral) so the effect of such conditions in regards to bond between rebar and different matrices can also be studied. In addition to experiments, Finite element models were developed to further investigate the mechanical behavior of the HyFRC matrix during rebar pull-out and to examine how a transverse steel reinforcement affects such behavior.

The experimental results showed that HyFRC can improve the rebar pull-out behavior by changing the failure mode from brittle splitting failure to a more ductile frictional pull-out failure compared to the OC material. The HyFRC material without fly ash provided better rebar bond performance compared to OC with spiral reinforcement and other type of FRCC under investigation. Compared to the monotonic rebar pull-out behavior, only minimal amount of additional damage was induced in such HyFRC material by repeated loading and unloading process from cyclic loading protocol.

DIC measurement indicated that the width of the splitting cracks that form in HyFRC matrices due to rebar pull-out could be further reduced when such specimens were confined by spirals. The finer the splitting cracks, the higher the rebar gripping stress and hence the higher the rebar pull-out resistance. The DIC measurement was consistent with the results from finite element analysis because both of them showed that confining the HyFRC matrix with transverse steel reinforcement led to a more uniform distribution of the splitting crack width during rebar pull-out. The vibration test showed that rebar pull-out induced similar degree of damage in the bond regions of HyFRC with and without transverse reinforcement.

If severe macrofiber pull-out occurs within the cracks induced by rebar pull-out, the macrofibers become less effective in resisting such cracks. Therefore, good macrofiber pull-out resistance in HyFRC is essential for an improved rebar pull-out performance. To investigate the macrofiber pull-out behavior and how it is affected by the presence of PVA microfibers in HyFRC, single fiber pull-out tests were conducted for various mortar mixtures. In some of these mortars, the cement was replaced by industrial by-products, such as fly ash and slag. In addition, macrofiber pull-out behavior in an ultra-high strength concrete with and without steel microfiber reinforcement was also studied.

The results of the single fiber pull-out tests revealed that the presence of PVA microfibers in a mortar mixture designed based on the HyFRC mixture enhances the steel macrofiber pull-out resistance. This synergy between micro and macrofibers provided a more effective control of the splitting cracks and was responsible for the superior rebar bond performance. Hence, the research revealed a multi-scale bond enhancement in a HyFRC member reinforced by steel rebar. The macrofiber pull-out behaviors from mortars in which 45% and 15% of cement were replaced by slag and fly ash, respectively, showed that slag densified the steel macrofiber/matrix interface and hence, improved the pull-out resistance for the macrofiber. On the other hand, test results of fiber pull-out specimens in which 55% of cement was replaced by fly ash showed that increasing curing age made the PVA microfiber reinforcement less effective in resisting steel macrofiber pull-out. Such characteristic showed how high-volume fly ash weakened the PVA fiber/matrix bond. This mechanism induced by fly ash made PVA fibers in HyFRC less effective in improving steel macrofiber pull-out resistance and hence, reduced the micro/macro fiber synergy, which is beneficial for the rebar bond behavior. Therefore, using high volume fly ash decreased the rebar pull-out resistance in HyFRC. When steel macrofibers were pulled out from extremely strong matrices, almost no microcracks formed around macrofibers and the steel microfiber reinforcement didn’t affect the macrofiber pull-out behavior because such microfibers function by bridging the microcracks.

Concrete is the most-used construction material in the world, yet on its own it is not ductile. It relies on carefully detailed steel reinforcing bar (rebar) cages to provide the tensile capacity and confinement needed to behave in a ductile manner. Building codes supply research-backed provisions that dictate how a reinforced concrete (RC) structure should be designed in order to meet ductility demands. Observations from seismic events within the last ten years reveal deficiencies in the code provisions in cases where large compressive strains are required. Subsequent experimental investigations found that in certain cases no practical amount of reinforcing steel could prevent brittle failure. To meet these demands it is necessary to stray from conventional paths and search for creative solutions to provide the requisite ductility.

Research presented in this document explores an alternative approach to provide compressive ductility in reinforced concrete elements using Hybrid Fiber Reinforced Concrete (HyFRC). This material utilizes fiber hybridization to achieve deflection-hardening and a small amount of tensile strain-hardening. The goal is not to completely replace the steel reinforcing cages embedded in RC elements, but to enhance it in such a way that it maintains load-carrying capacity at large deformations. Response of experimental specimens is examined at a global and local level in order to provide a comprehensive understanding of the interactions and overall performance. One large-scale and one small-scale experiment is performed, and these data are used to construct and validate a predictive computational model that can be used to evaluate the behavior in other scenarios.

Results of a large-scale compression test on a high aspect ratio column representative of a special shear wall boundary element demonstrate improved performance when constructed with HyFRC in place of conventional concrete. Control specimens lose confinement due to rebar buckling and opening of the lateral reinforcement which initiates upon cover spalling. Cover in the HyFRC specimen does not exhibit spalling, but instead shows a stable crushing behavior while leaving the cover material intact. This retained cover material delays the onset of longitudinal rebar buckling and provides additional confinement to the core. Due to this behavior toughness up to failure for the HyFRC specimen is, on average, 1.9-times higher than that of control specimens constructed with conventional concrete.

Rectangular column specimens with embedded rebar are tested to isolate the behavior of longitudinal rebar buckling when embedded in HyFRC. Specimens are built with tie spacings of four-, six-, and twelve-bar diameters (db) and tested in uniaxial compression until failure. Results show that HyFRC slows the progression of buckling compared to conventional concrete and yields a more ductile, predicable behavior. At 2% normalized axial displacement the HyFRC specimens with 6-db tie spacing exhibited, on average, 34% higher toughness than the control specimens with the same spacing. At the same level of displacement, HyFRC specimens with 12-db tie spacing had, on average, 8% higher toughness than the control specimens with 6-db¬ tie spacing. These results provide evidence that replacing conventional concrete with HyFRC could enable minimum lateral tie spacing requirements to be relaxed up to 12-db while still maintaining a ductile response with respect to buckling.

A computational model is developed to predict the buckling behavior of longitudinal rebar in compression. This model accounts for the effects of transverse reinforcement and HyFRC cover. Experimental results from the large- and small-scale experiments are used to validate the model, which is then used to evaluate test cases with other geometries and materials. These results show that HyFRC improves the compressive response of large diameter rebar and high strength rebar with a nominal yield strength of 689-MPa (100-ksi).

The deteriorating quality of the United States’ infrastructure will result in the construction of new civil engineering structures, particularly bridges, in the coming decades. This future construction presents an opportunity to modify current designs with novel materials that are more damage-resistant and durable than conventional materials.

Hybrid fiber-reinforced concrete (HyFRC) is proposed for implementation in reinforced concrete structures. This material utilizes a multiscale crack control scheme to achieve greater ductility and toughness than plain concrete, allowing for progressive crack resistance from microcrack initiation to macrocrack propagation. In this dissertation, reinforced HyFRC (i.e. HyFRC with embedded steel reinforcing bars) was investigated to evaluate realistic expectations of mechanical and durability performance of constructed structural elements.

Two primary sources of damage in reinforced HyFRC bridge structures were considered for study. The first source relates to earthquake events while the second source relates to corrosion of embedded steel reinforcing bars. Regarding earthquakes, which induce high deformations on reinforced concrete, reinforced HyFRC was investigated for its fracture behavior under direct uniaxial tension. Prismatic samples with a low longitudinal reinforcement ratio were tested to evaluate the feasibility of reducing reinforcing bar congestion in construction through the use of fiber-reinforced concrete. The overall deformation capacity of the reinforced composite was largely dependent on HyFRC cracking characteristics, which generally consisted of localized dominant cracking and longitudinal splitting crack suppression. For ductility enhancement, sufficient load capacity from strain hardening of steel reinforcement is required to offset load softening from fiber pull-out processes at a dominant crack.

A 1:4.5 scale bridge column utilizing a precast HyFRC tube, which contained all of the column’s steel reinforcement, was laterally loaded to evaluate simulated seismic damage behavior. The experimental column was subjected to static, unidirectional, cyclic loading and utilized a base-rocking design for further ductility enhancement. At the conclusion of the test, the column reached a peak drift ratio of 13.1% and showed minor damage, including elimination of cover spalling. The HyFRC tube column design contributed effective resistance against longitudinal reinforcing bar buckling, allowing the column to maintain 93% of its peak load capacity at 9.5% drift. Compared to a monolithic HyFRC column, the precast HyFRC tube design showed no reduction in seismic performance despite being fabricated with 43% less HyFRC volume.

Steel reinforcement corrosion is an additional source of severe reinforced concrete bridge damage. Because cracking can occur in a structure prior to corrosion activity, as from seismic loads or other service loads, corrosion studies in this dissertation considered the effect of both preexisting (i.e. applied load-induced) and corrosion-induced cracks on corrosion activity. In a study focused on electrochemical polarization, samples with a single steel reinforcing bar were exposed to a chloride environment for 2.5 years while in a continuous tensile stress state or in a nonloaded condition, and were periodically monitored for electrochemical behavior. Electrochemical impedance spectroscopy (EIS) was additionally preformed at the conclusion of the test program. The severity of corrosion-induced splitting matrix cracks along the length of embedded steel reinforcing bars and subsequent formation of anodic surfaces were found to be the primary factors dictating the magnitude of corrosion current. Cathodic and anodic Tafel coefficients and Stern-Geary coefficients for passive and active samples are also reported.

Corrosion activity monitoring of reinforced HyFRC was further extended to beam elements containing a steel reinforcing bar of interest and a larger secondary reinforcing bar, which lumped the galvanic corrosion effects of electrically connected reinforcing bars expected in a steel reinforcement cage on the bar of interest. Samples were mechanically loaded to induce varied matrix cracking characteristics prior to a 2.2-year chloride exposure duration. When precracked, time to corrosion initiation was governed by flexural stiffness degradation. After corrosion initiation, HyFRC restricted corrosion-induced cracking, caused more extensive diffusion of corrosion products into the bulk cement paste, and lowered overall steel reinforcing bar mass loss. Any corrosion damage incurred by reinforced HyFRC had negligible effects on flexural stiffness.

To visualize the progressive in-situ corrosion damage of reinforced fiber-reinforced cementitious composites, X-ray micro-computed tomography (µCT), a non-destructive, 3D imaging technique, was performed. Similar to larger scale experiments, samples in this study were preloaded to induce cracking prior to environmental conditioning for 44 weeks. Corrosion damage of embedded steel bars was monitored at different environmental exposure times, with plain cementitious composites exhibiting splitting cracks that caused widespread corrosion of the steel bar. In contrast, the high splitting crack resistance of the fiber-reinforced cementitious composite restricted corrosion propagation to near the initial site of corrosion. The localized corrosion rate was determined based on actual steel mass loss and actual corroded surface area.

The experimental results and conclusions reported in this dissertation indicate that HyFRC composites can significantly enhance the damage resistance and durability of reinforced concrete structures, though HyFRC performance is most optimized under certain conditions.

Given the state of aging infrastructure in the United States, reinforcement corrosion is proving to be costly in direct maintenance and replacement costs, as well as indirect costs, such as traffic delays and loss of productivity. Seismicity complicates this issue due to the looming threat of extreme loading on the heavily-used bridge structures that connect our communities. It is important to understand mechanisms of corrosion damage and their impacts on structural behavior in order to ensure that future repairs and new designs are sustainable, long-term solutions. The research presented in this dissertation investigates the combined action of corrosion and seismic loading on bridge columns. Fiber reinforcement is proposed as a means of extending the service life of reinforced concrete components and providing resistance to damage from environmental and mechanical action. Hybrid Fiber Reinforced Concrete (HyFRC) and its self-consolidating variant, SC-HyFRC, were utilized in these experiments to investigate their durability against the expansion of corrosion products and their ductility during mechanical loading. Of specific interest in this research is the intersection between corrosion damage in reinforced concrete and HyFRC column elements and mechanical behavior under seismic loading.

Steel reinforced self-consolidating concrete (SCC) and SC-HyFRC columns are exposed to corrosion damage through long term exposure in a chloride-contaminated environment, in which 2% chloride by weight of binder materials was admixed when column elements were cast to investigate the corrosion propagation phase in isolation. Corrosion rate and surface cracking behavior was monitored during a 125-week corrosion exposure period. Mechanical behavior was then investigated through compressive testing of corrosion-damaged column elements and tensile testing of corroded reinforcing steel. While the SC-HyFRC clearly exhibited less corrosion damage compared to the SCC control specimen, the large difference in compressive strength between the SC-HyFRC and SCC implies that a difference in their matrix/rebar interfaces made a comparison in their crack propagation behavior less conclusive.

Hybrid Simulation (HS) is utilized to investigate the system-level seismic performance of reinforced concrete structures with corrosion damaged components. This technique combines physical testing with computer simulation to impose realistic, dynamic loading conditions on a physically manageable test-specimen. An HS test procedure was developed to investigate the seismic behavior of a single-column highway bridge, where the lower portion of the column serves as the experimental element. The setup was validated and calibrated using a steel hollow structural section (HSS) column element. The HS procedure was also utilized with reinforced concrete and HyFRC column elements that were exposed to an applied current to accelerate corrosion damage prior to testing. HyFRC columns were more effective at preventing spalling as well as retaining their stiffness following severe seismic damage, even with pre-existing corrosion damage.

Many reinforced concrete bridges are simultaneously exposed to the combined hazard of seismicity and corrosion damage. It is of great importance to improve the understanding of existing infrastructure so that we can develop efficient and long-lasting repair or replacement strategies to keep communities safe while more effectively utilizing innovative materials to extend the service lives of structures. HS improves accuracy by incorporating the true behavior of a physical specimen into a numerical model to capture the full response of the structure, even if some components are difficult to explicitly model. This also increases efficiency of experimental testing as a large portion of the structure can remain as a computational model, eliminating the need perform expensive system-level tests.

Modern reinforced concrete bridges are designed to avoid collapse and to prevent loss of life during earthquakes. To meet these objectives, bridge columns are typically detailed to form ductile plastic hinges when large displacements occur. California seismic design criteria acknowledges that damage such as concrete cover spalling and reinforcing bar yielding may occur in columns during a design-level earthquake.

The seismic resilience of bridge columns can be improved through the use of a damage resistant hybrid fiber reinforced concrete (HyFRC). Fibers delay crack propagation and prevent spalling under extreme loading conditions, and the material resists many typical concrete deterioration mechanisms through multi-scale crack control.

Little is known about the response of the material when combined with conventional reinforcing bars. Therefore, experimental testing was conducted to evaluate such behaviors. One area of focus was the compression response of HyFRC when confined by steel spirals. A second focus was the tensile response of rebar embedded in HyFRC. Bridge columns built with HyFRC would be expected to experience both of these loading conditions during earthquakes.

The third focus of this dissertation was the design, modeling, and testing of an innovative damage resistant HyFRC bridge column. The column was designed to rock about its foundation during earthquakes and to return to its original position thereafter. In addition to HyFRC, it was designed with unbonded post-tensioning, unbonded rebar, and headed rebar which terminated at the rocking plane. Because of these novel details, the column was not expected to incur damage or residual displacements under earthquake demands exceeding the design level for ordinary California bridges. A sequence of scaled, three dimensional ground motion records was applied to the damage resistant column on a shaking table. An equal scale reinforced concrete reference column with conventional design details was subjected to the same motions for direct comparison.

Compression tests showed that the ductility of HyFRC is superior to concrete in the post-peak softening branch of the response. HyFRC achieved a stable softening response and had significant residual load capacity even without spiral confinement. Concrete required the highest tested levels of confinement to achieved comparable post-peak ductility. Tension tests showed that HyFRC provides a substantial strength enhancement to rebar well beyond their yield point. Interesting crack localization behavior was observed in HyFRC specimens and appeared to be dependent on the volumetric ratio of rebar.

The damage resistant HyFRC bridge column attained its design objectives during experimental testing. It exhibited pronounced reentering behavior with only light damage under earthquake demands 1.5 to 2.0 times the design level. It accumulated only 0.4% residual drift ratio after seven successive ground motions which caused a peak drift ratio of 8.0%. The conventional reinforced concrete column experienced flexural plastic hinging with extensive spalling during the same seven motions. It accumulated 6.8% residual drift ratio after enduring a peak drift ratio of 10.8%.

Significant progress was achieved with the application of Rietveld method to characterize the crystalline, and nanocrystalline phases in portland cement concrete. However, to obtain detailed information on the amorphous phases present in concrete, it is necessary to analyze the total scattering data. The pair distribution function (PDF) method, that takes the Sine Fourier transform of the measured structure factor over a wide momentum transfer range, has been successfully utilized in the study of liquids and amorphous solids. The method provides a direct measure of the probability of finding an atom surrounding a central atom at a radial distance away. The obtained experimental characteristic distances can be used to validate the predictions by the theoretical models, such as, molecular dynamics simulations. This research focuses on obtained results of PDF analysis on silica fume, rice husk ash, fly ash, alkali-silica reaction gel, and opals.