Currently, in Texas, there is a need for different repairs on pavements and bridge decks; rapid repair materials designed for these repairs are available but the service life and durability of these products are often inadequate. Thus, the goal for the Texas Department of Transportation (TxDOT) is to implement repairs with an extended service life in a timely manner, in order to cause minimal disruption. Research performed under TxDOT Project 6723 (Development of Rapid, Cement-based Repair Materials for Transportation Structures) evaluated a wide range of rapid repair materials, including calcium aluminate cement (CAC), calcium sulfoaluminate cement (CSA), fly ash alkali activated blends, and ordinary portland cement. Some of the properties which contribute to a long-term service life are: mechanical properties, early-age volume change, and the heat evolution; often, the early-age development of these repair materials can cause later durability issues. These properties were examined through a variety of experiments and test in the laboratory, as well as, in the field. / text

Concrete repair materials are being widely used to restore and extend the service life of structures. While most cement-based repair materials are compatible with concrete structures, their durability properties do not attract much attention which it deserves from researchers. Since repair materials can deteriorate like conventional concrete, the search for reliable, long-lasting concrete repair materials is becoming more intensive. Amongst other factors, concrete permeability and chloride diffusivity within concrete are believed to play a major role in determining the durability and success of the repair. These two parameters determine the penetration rate of aggressive substances into concrete and how fast degradation could take place. A number of test methods have been proposed to study these two factors, and the commonly used test methods are water penetration, surface/bulk electrical resistivity, rapid chloride permeability (RCP), and half-cell potential. However, the relationship between each durability test method and their correlation with compressive strength measurement have not been fully understood. So, in this study, we aim for using multiple testing techniques, destructive and non-destructive, to evaluate the durability of concrete repair materials as well as correlating different test methods. Three types of commercially available cement-based materials are tested and evaluated, and results have indicated that cementitious concrete mortar (termed as Mix M) amongst others has the best durability performance which means low water permeability, high resistivity, and compressive strength. Whereas, the flexural performance of Mix M still needs some improvement in terms of flexural strength and flexural toughness. For various durability testing methods, surface resistivity is found to have a strong linear relation and a polynomial relation to bulk resistivity and water permeability respectively. No relationship is established between concrete resistivity and compressive strength, though high-strength concrete tends to have a high resistivity in our study. RCP test results do not correlate well with resistivity measurements, which requires further study to overcome its heating and binding effect when measurements are being taken. Half-cell potential method is used for validating test results but it reveals no difference for materials with different permeability and resistivity. A model is proposed to counteract temperature’s effect while calculating the coefficient of diffusion, which indicates the concrete to resist chloride diffusion. It is found that this model can shift the RCP measurement slightly closer to its theoretical prediction but the difference between them is still large. Therefore, further research is required for acquiring more raw data from RCP measurements as the regression analysis input. In addition, a more comprehensive model that involves more correction factors for binding effects, etc., is also needed. / Graduate / 2020-04-30

When damaged, military airfields must be repaired quickly so that flying operations can resume. Due to their rapid-setting and high-strength properties, epoxy-based polymer concretes (PC) may provide a good alternative to the portland cement concrete (PCC) rapid repair mixes currently used by the United States Air Force (USAF) for their Rapid Airfield Damage Recovery (RADR) operations. Epoxy-based PCs use epoxy polymers in place of portland cement to bind together aggregate and form the composite concrete. A commercially available epoxy-based PC, referred to as Commercial Product "B" in this thesis, was tested according to the procedures stated in the Tri-Services Pavements Working Group (TSPWG) Manual M 3-270-01.08-2. This manual defines testing protocol to be used for rapidsetting rigid repair materials intended for use on rigid airfield pavement spall repairs. These tests include various ASTM standards for compressive strength, flexural strength, slant-shear bonding strength, modulus of elasticity, coefficient of thermal expansion, and slump. Commercial Product "B" was not able to set and cure within the time limits set by the TSPWG manual, but otherwise surpassed final compressive strength, flexural strength, slant-shear bonding strength, and slump requirements. However, its modulus of elasticity was below the acceptable range, and its coefficient of thermal expansion was several times higher than the maximum allowed value. In addition, a second epoxy-based PC currently under development by Luna Labs and D.S. Brown was tested for compressive strength and, in most mix designs, surpassed the minimum requirements. This PC was also field tested in a series of four (4) 2-feet by 2-feet by 8-inch deep patches placed within an 8-inch thick PCC slab. Three of these patches did not meet minimum compressive strength requirements and none of them exhibited good bonding between the PC repair material and the original PCC slab. Finally, the effect of the surface moisture content of PCC on the bonding strength and chloride ion penetration resistance when PCC is bonded to PC was tested by casting Commercial Product "B" against ordinary PCC under two different moisture conditions: surface saturated dry (SSD) and PCC that had been conditioned at 10% relative humidity (RH) for 48 hours. The bonded samples underwent three- and four-point bond flexural testing and rapid chloride penetration testing (RCPT). The bond flexural testing showed that Commercial Product "B" bonds to PCC better when the PCC has been conditioned at 10% RH rather than being at SSD conditions. No statistically significant difference was detected for RCPT between bonded samples cast under the two surface moisture conditions, but did show that samples of PCC bonded with Commercial Product "B" are less susceptible to chloride ion penetration than samples comprised entirely of PCC. The results of this thesis show that PC may be useful to the USAF for repair airfields as short term repairs, but further work is required to ensure they meet all standards set by TSPWG for rapid repair materials. They also demonstrate that, when possible, a PCC repair surface should be dried completely before PC repair material is cast against it. / Master of Science / When damaged, military airfields must be repaired quickly so that flying operations can resume. Due to their rapid-setting and high-strength properties, epoxy-based polymer concretes (PC) may provide a good alternative to the portland cement concrete (PCC) rapid repair mixes currently used by the United States Air Force (USAF) for their Rapid Airfield Damage Recovery (RADR) operations. Epoxy-based PC use epoxy polymers in place of portland cement to bind together aggregate and form the composite concrete. To test whether epoxy-based PC can be used for RADR or other airfield repair operations, a commercially available epoxy-based PC, titled Commercial Product "B" in this thesis, underwent a battery of tests as specified for potential rapid repair materials in the Tri-Services Pavements Working Group (TSPWG) manual for testing protocol for rapid-setting rigid repair materials. Commercial Product "B" was not able to set and cure within the time limits set by the TSPWG manual but otherwise surpassed final strength, bonding, and workability requirements. However, it is not nearly as stiff as ordinary PCC and it expands and contracts far more than PCC when it undergoes temperature changes. In addition, a second epoxy-based PC currently under development by Luna Labs and D.S. Brown was tested for compressive strength and, in most mix designs, surpassed the minimum requirements. This PC was also field tested in a series of four (4) patches placed within a PCC slab. Three of these patches did not meet minimum compressive strength requirements and none of them exhibited good bonding between the PC repair material and the original PCC slab. Finally, the effect of the surface moisture content of PCC on the bonding strength and resistance to chloride ions, often found in de-icing agents, when PCC is bonded to PC was tested by casting Commercial Product "B" against ordinary PCC under two different moisture conditions: surface saturated dry (SSD) and PCC that had been conditioned at 10% relative humidity (RH). The bonded samples underwent bond flexural testing and rapid chloride penetration testing (RCPT). The bond flexural testing showed that Commercial Product "B" bonds to PCC better when the PCC has been conditioned at 10% RH rather than being at SSD conditions. No statistically significant difference was detected for RCPT between bonded samples cast under the two surface moisture conditions but did show that samples of PCC bonded with Commercial Product "B" are less susceptible to chloride ion penetration than samples comprised entirely of PCC. The results of this thesis show that PC may be useful to the USAF for repair airfields as short term repairs, but further work is required to ensure they meet all standards set by TSPWG for rapid repair materials. They also demonstrate that, when possible, a PCC repair surface should be dried completely before PC repair material is cast against it.

This dissertation presents a literature review of the state-of-practice for the use of IC in concrete mixtures and how structural engineers and construction engineers can adapt IC to their present and future work. Current high early strength concrete mixtures have natural cracking and shrinkage problems due to the high content of cementitious material or their chemical components. Using IC allows for early strength, enhanced durability, reduced shrinkage and a better curing by providing water that can be absorbed by the cement past after the final set. Rapid hydration and high early strength Portland cement and calcium sulfoaluminate (CSA) concretes are commonly used as pavement repair media. The fresh properties (slump, setting time), mechanical properties (elastic modulus, compressive and tensile strength), and volume stability (autogenous shrinkage, drying shrinkage, restrained ring shrinkage, and creep) of rapid repair media were evaluated with and without internal curing with saturated lightweight aggregate. Significant improvements in volume stability were also noted. Results indicate that internal curing can successfully improve volume stability and mitigate restrained shrinkage cracking in rapid repair media without compromising fresh properties or ultimate mechanical strength. Maturity was observed for CSA mixtures and exhibited a correlation with compressive strength development which could be beneficial for rapid repair media on the field.

Good bond strength between overlay and substrate is a key factor in performance of concrete repairs. This thesis was aimed at studying the evaluation of bond strength between repair material and substrate at the interface. Many factors such as surface roughness, existence of micro cracks, compaction, curing etc influence the bond strength. The quality assurance of the bond strength requires test methods that can quantify the bond strength as well as identify the failure mode. There have been numerous investigations led to development of different test methods. The forces which are applied in each test and the failure mode are important in order to choose the proper test. An interpretive study on test methods is presented. While this study can provide individually useful information on bond strength and bond characterization, it also contains discussions about each test and comparison of test methods.

This study is part of a VDOT sponsored project focusing on repair techniques for impact damaged prestressed bridge girders. The investigation included evaluation of the repair installation and flexural strength of four AASHTO Type III girders that were intentionally damaged and repaired. In addition, nonlinear finite element modeling was used to aid in the development of design protocols for each repair method. This report discusses two of the three repair techniques. Three Master of Science students report on the project results: Justin Liesen, Mark Jones, and Michael Gangi. Liesen and Jones (2015) had responsibility for the installation and testing of the repaired girders and Gangi (2015) performed the finite element modeling of the girders. Three repair methods were identified for experimental investigation: strand splice, bonded FRP, and FRCM. During this investigation the repair methods were evaluated by conducting six flexural tests on four AASHTO Type III girders. Flexural tests were conducted instead of shear tests because typical impact damage from overheight vehicles occurs around the mid-span and flexural strength dominated region of bridge girders. The cracking and failure moments for each test were evaluated and compared to predictions of the girder's behavior using AASHTO calculations, a moment-curvature diagram, and non-linear finite element modeling. / Master of Science

Highway bridges in the United States are frequently damaged by overheight vehicle collisions. The increasing number of prestressed concrete bridges indicates that the probability of such bridges being impacted by overheight vehicles has increased. This thesis, sponsored by the Virginia Center for Transportation Innovation and Research (VCTIR), investigated three repair techniques for impact damaged prestressed bridge girders: strand splices, fiber reinforced polymer (FRP) overlays, and fabric reinforced cementitious matrix (FRCM) overlays. The flexural strength of four AASHTO Type III girders, three of which were intentionally damaged and repaired, was evaluated. Six experimental tests were performed on these girders: one undamaged girder test and five repair method tests. Nonlinear beam models and three-dimensional finite element (FE) models were created to predict the behavior of the beams under flexural testing, and subsequently validated and calibrated to experimental test data. The very good accuracy of the beam models indicated that they can be used alone for the performance assessment of damaged and repaired girders. Of course, the analyst must always be aware of the fact that a beam model cannot explicitly account for potentially crucial effects such as diagonal cracking. A direct comparison between repair methods was made by creating analytical models of a prototype girder setup. FRP overlays were seen to restore the most strength, while strand splices were seen to restore the most ductility. From observation, combining repair methods resulted in an additive effect on strength, but the deformation at onset of failure will be governed by the less ductile method. / Master of Science

One of the benefits of calcium sulfoaluminate (CSA) cements is that these materials gain strength rapidly, where strength development is often measured in hours instead of days. This property makes these materials desirable for use in temporary, non-reinforced repairs of roadways, airfields, and navigable locks. The rapid repair of these infrastructure elements is critical to transporting supplies into regions devastated by disaster. In these austere environments, potable water may not be available in sufficient quantities to make vital repairs, and the use of impure water in the production of CSA cement-based concrete would be advantageous. However, the hydration products formed by CSA cement are substantially different from those formed by portland cement and may react differently to impurities that water sources may contain. This Thesis investigates the impact of various salts and impure water sources on the early-age strength development of commercially-available CSA cement-based concrete.

<p>Aging public infrastructure in North America continues to challenge engineers and scientists to develop repair and rehabilitation strategies that are practical, durable and cost effective. Of specific interest is the state of concrete and concrete repair in buildings and civil engineering infrastructures that are in deteriorating condition. In particular, cracks pose a threat to the durability and ultimately the structural integrity of concrete. Cracks in concrete may form for several reasons, e.g. plastic shrinkage, thermal contraction, mechanical loading or as a result of overloading. Once formed, cracks present a combination of problems to the service life and performance of the structure. Therefore cracks must be repaired for the following reasons: to prevent the ingress of deleterious agents such as water, other liquids, vapour, gas, chemicals and biological agents; to either restore or increase the structural load-bearing capacity of the cracked concrete member; to restore the aesthetic condition of the structure.</p> <p>The effectiveness of two different repair methods, crack injections and cementitious overlays, were examined. Two repair materials, a low viscosity epoxy and polyurethane were injected into the cracks, and a thin polymer-modified cementious overlay was applied on the cracked surface. Two types of cement were used, an ordinary Portland cement and a blended cement with 8% silica fume. The specimen properties were evaluated using non-destructive testing, prior to being subjected to a series of freeze-thaw conditioning regimes. From the experimental program, it was determined that the epoxy injection repair was more effective in restoring the air tightness than the thin overlay. The polyurethane material was unsuccessful. Following the freeze-thaw regimes, an overall improvement of conditions for all three repairs was observed, with the cementitious overlay seeing the greatest improvement in air tightness. These results indicate that the on-going cement hydration mechanism had a greater effect on the performance in comparison to the deleterious effects of the environmental loads.</p> / Master of Applied Science (MASc)

This research involves the study of the short term loaded behaviour of mechanically degraded reinforced concrete (RC) flexural elements, which are strengthened with fibre reinforced polymer (FRP) composites. The two main objectives have been: (a) to conduct a series of realistic tests, the results of which would be used to establish the design criteria, and (b) to carry out analytical modelling and hence develop a set of suitable design equations. It is expected that this work will contribute towards the establishment of definitive design guidelines for the strengthening of reinforced concrete structures using advanced fibre composites. The experimental study concentrated on the laboratory testing of 30 simply supported, and 4 two-span continuous full size RC beams, which were strengthened by either FRP plates or fabric sheets. The failure modes of these beams, at ultimate limit state, were examined and the influencing factors were identified. A premature and extremely brittle collapse mechanism was found to be the predominant type of failure for beams strengthened with a large area of FRP composites. A modified semi-empirical approach was presented for predicting the failure load of such over strengthened beams. Despite the lack of ductility in fibre composites, it was found that the FRP strengthened members would exhibit acceptable ductile characteristics, if they were designed to be under strengthened. A new design-based methodology for quantifying the deformability of FRP strengthened elements was proposed, and its difference to the conventional concept of ductility was discussed. The available techniques for ductility evaluation of FRP strengthened concrete members were reviewed and a suitable method was recommended for determining ductility level of FRP strengthened members. A non-linear material based analytical model was developed to simulate the flexural behaviour of the strengthened and control beams, the results were seen to match very well. The parametric study provided an insight into the effects of various factors including the mechanical properties and cross sectional area of FRP composites, on the failure modes and ductility characteristics of the strengthened beams. Based on the findings of the experimental and analytical studies, design equations in the BS 8110 format were developed, and design case studies have been carried out. It was concluded that fibre composites could effectively and safely strengthen mechanically degraded reinforced concrete structures if appropriately designed. The modes of failure and the degree of performance enhancement of FRP strengthened beams depend largely on the composite material properties as well as the original strength and stiffness of the RC structure. If the FRP strengthened elements were designed to be under-strengthened, then the premature and brittle failure mode could be prevented and ductile failure mode could be achieved. It was also found that existing steel reinforcement would always yield before the FRP composite reached the ultimate strength. Furthermore, a critical reinforcement ratio, above which FRP strengthening should not be carried out, was defined. It was concluded that FRP strengthening is most suitable for reinforced concrete floor slabs, bridge decks, flanged beams and other relatively lightly reinforced elements. The study also revealed that to avoid a brittle concrete failure, existing doubly reinforced members should not be strengthened by FRP composites.