Performance of Fiber-reinforced Self-consolidating Concrete for Repair of Bridge Sub-structures and Fiber-reinforced Super-workable Concrete for Infrastructure Construction PDF Download
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Author: Kamal H. Khayat
Publisher:
ISBN:
Category : Bridges
Languages : en
Pages : 181
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Book Description
The proposed research investigates the combined use of self-consolidating concrete (SCC) and fibers reinforcements to develop a novel repair material, fiber-reinforced self-consolidating concrete (FR-SCC) that can be used for the rehabilitation and strengthening of existing structures. Furthermore, the feasibility of using super workable concrete (SWC) reinforced with different types of fibers for new structural cast-in-place applications is investigated. The use of SCC matrix can greatly enhance the workability of fibrous mixtures along with incorporation of greater volume of fibers. SWC is a new type of flowable concrete with lower workability than SCC. Containing lower binder content can be more cost effective than SCC. SWC requires some mechanical consolidation energy to ensure proper filling of the formwork. Eight types of fibers, including a propylene synthetic fiber, five steel fibers and a hybrid steel and polypropylene synthetic fiber were investigated. Fibers were incorporated at a volume of 0.5% in FR-SCC and at 0.5% and 0.75% in FR-SWC. Two types of expansive agents (EA), Type G and Type K, were added to both concrete types to reduce shrinkage and enhance resistance to restrained shrinkage cracking. The optimized mixtures exhibited high workability, mechanical properties, and freeze/thaw durability. The incorporation of fibers with 4% Type-G EA in FR-SCC increased the 56-day flexural strength by up to 32%, and flexural toughness up to 23 times. The incorporation of 0.5% of the 1.18 in. (30-mm) hooked end steel fibers (ST1) in FR-SCC made with 4% Type-G EA increased the elapsed time to cracking determined from restrained shrinkage ring test from 16 to 20 days compared to FR-SCC made with 0.5% ST1 fibers without EA. The use of ST1 steel fibers and 4% Type-G EA decreased the 1-year drying shrinkage by 48% compared to the reference SCC mixture without any fibers and expansive agent. In case of FR-SWC, the decrease in shrinkage was 37% compared to SWC. In addition, 20 monolithic full-scale beams were cast using different types of concrete, including conventional vibrated concrete (CVC), fiber-reinforced conventional vibrated concrete (FR-CVC), SCC, FR-SCC, SWC and FR-SWC. Twelve reinforced concrete beams were cast using CVC to fill two thirds of the beam height. They were then filled with five different types of FR-SCC and SCC to simulate beam repair in the tension zone. Findings indicated that macro fibers can be used with FR-SCC designated for repair with fiber length ≤ 2 in. (50 mm) up to 0.5% fiber volume. Macro fibers can be used with FR-SWC designated for construction with fiber length ≤ 2.6 in. (65 mm) up to 0.75% fiber volume. Fibers had great impact on structural performance of the full-scale monolithic beams. The incorporation of 0.5% of the 1.18 in. (30-mm) hooked end steel fibers combined with 0.5 in. (13-mm) straight steel fibers at ratio 4 to1 (STST) with 4% Type-G EA increased toughness of FR-SWC beams by 95% compared to SWC beams and by 86% in case of 0.75% 5D fibers. Repair using FR-SCC increased the flexural capacity of the beam by 6% and the toughness by 110% in case of using 0.5% ST1 fibers with 4% Type-G EA.
Author: Kamal H. Khayat
Publisher:
ISBN:
Category : Bridges
Languages : en
Pages : 181
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Book Description
The proposed research investigates the combined use of self-consolidating concrete (SCC) and fibers reinforcements to develop a novel repair material, fiber-reinforced self-consolidating concrete (FR-SCC) that can be used for the rehabilitation and strengthening of existing structures. Furthermore, the feasibility of using super workable concrete (SWC) reinforced with different types of fibers for new structural cast-in-place applications is investigated. The use of SCC matrix can greatly enhance the workability of fibrous mixtures along with incorporation of greater volume of fibers. SWC is a new type of flowable concrete with lower workability than SCC. Containing lower binder content can be more cost effective than SCC. SWC requires some mechanical consolidation energy to ensure proper filling of the formwork. Eight types of fibers, including a propylene synthetic fiber, five steel fibers and a hybrid steel and polypropylene synthetic fiber were investigated. Fibers were incorporated at a volume of 0.5% in FR-SCC and at 0.5% and 0.75% in FR-SWC. Two types of expansive agents (EA), Type G and Type K, were added to both concrete types to reduce shrinkage and enhance resistance to restrained shrinkage cracking. The optimized mixtures exhibited high workability, mechanical properties, and freeze/thaw durability. The incorporation of fibers with 4% Type-G EA in FR-SCC increased the 56-day flexural strength by up to 32%, and flexural toughness up to 23 times. The incorporation of 0.5% of the 1.18 in. (30-mm) hooked end steel fibers (ST1) in FR-SCC made with 4% Type-G EA increased the elapsed time to cracking determined from restrained shrinkage ring test from 16 to 20 days compared to FR-SCC made with 0.5% ST1 fibers without EA. The use of ST1 steel fibers and 4% Type-G EA decreased the 1-year drying shrinkage by 48% compared to the reference SCC mixture without any fibers and expansive agent. In case of FR-SWC, the decrease in shrinkage was 37% compared to SWC. In addition, 20 monolithic full-scale beams were cast using different types of concrete, including conventional vibrated concrete (CVC), fiber-reinforced conventional vibrated concrete (FR-CVC), SCC, FR-SCC, SWC and FR-SWC. Twelve reinforced concrete beams were cast using CVC to fill two thirds of the beam height. They were then filled with five different types of FR-SCC and SCC to simulate beam repair in the tension zone. Findings indicated that macro fibers can be used with FR-SCC designated for repair with fiber length ≤ 2 in. (50 mm) up to 0.5% fiber volume. Macro fibers can be used with FR-SWC designated for construction with fiber length ≤ 2.6 in. (65 mm) up to 0.75% fiber volume. Fibers had great impact on structural performance of the full-scale monolithic beams. The incorporation of 0.5% of the 1.18 in. (30-mm) hooked end steel fibers combined with 0.5 in. (13-mm) straight steel fibers at ratio 4 to1 (STST) with 4% Type-G EA increased toughness of FR-SWC beams by 95% compared to SWC beams and by 86% in case of 0.75% 5D fibers. Repair using FR-SCC increased the flexural capacity of the beam by 6% and the toughness by 110% in case of using 0.5% ST1 fibers with 4% Type-G EA.
Author: Ahmed Abdelrazik
Publisher:
ISBN:
Category :
Languages : en
Pages : 282
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Book Description
"The objective of this document is to design high-performance fiber-reinforced self-consolidating concrete (FR-SCC) for infrastructure repair and fiber-reinforced super-workable concrete (FR-SWC) for bridge construction. The investigated fibers included propylene synthetic fibers, hooked steel fibers, double and triple hooked steel fibers, hybrid crimped steel fiber and polypropylene multifilament fibers, and micro-macro steel fibers. The fiber volume varied between 0 and 0.75%. An expansive agent (EA) was incorporated to compensate for shrinkage and induce compression in the concrete at early age. Two types of EA (G and K) were employed at 0 to 8%, by mass of binder. The investigated FR-SCC and FR-SWC mixtures achieved excellent passing ability and stability. Compared to non-fibrous mixtures, the optimized mixtures exhibited 30% and 110% increase in compressive and splitting tensile strengths, respectively, and developed high toughness. The combined use of EA and fibers led to a synergetic effect of increasing the resistance to restrained shrinkage cracking. Low cracking potential was observed for mixtures made with steel fibers combined with EA compared to high cracking potential in case of non-fibrous SCC. The optimized FR-SWC mixture, with some adjustments to reduce fluidity, was successfully used for the re-decking of a bridge in Missouri. The concrete exhibited high workability and was easily pumped, consolidated, and finished. After 18 months, no signs of cracking were observed in the deck, except for hairline cracks near the intermediate bent. The high-performance fibrous concrete can provide cost saving of up to 55% in areas with high traffic volume but limited savings in the low traffic volume areas"--Abstract, page iii.
Author: Fodhil Kassimi
Publisher:
ISBN:
Category :
Languages : en
Pages : 377
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Book Description
The use of self-consolidating concrete (SCC) in the concrete industry in cast-in-place applications, including repair applications, is growing given the various advantages offered in both fresh and hardened states. The present study deals with the design and performance of fiber-reinforced self-consolidating concrete (FR-SCC) as a repair material of concrete infrastructure. The study also considers the use of various steel and synthetic fibers (five fibers in total) that were used to produce FR-SCC and fiber-reinforced self-consolidating mortar (FR-SCM) that can be employed for structural and non-structural repair applications. The study evaluates the effect of material properties and mixture composition of the fibrous concrete and mortar on workability, mechanical, visco-elastic, durability, and structural behavior. The investigation that is presented in this thesis included the testing of 28 full-scale beams under four-point flexural loading. The majority of these beams were repaired by casting concrete to fill a relatively thin section along the tension zone of the beams. The repair technique was based on the FR-SCC characteristics including the maximum fiber volume and length. This technique required mixtures of high range of fluidity. The optimized FR-SCC and FR-SCM mixtures exhibited excellent flow characteristics along the 3.2-m long beams without blockage, segregation, nor debonding at the interface of repair-substrate concrete. Based on the structural characteristics of the composite beams, the overall performance of the beams repaired using the FR-SCC and FR-SCM was similar or higher (up to 2.6 times) than that of monolithic beams made with conventional vibrated concrete (CVC). The use of optimized FRSCC mixtures enabled the replacement of 50% of the tension steel reinforcement in repair sections; i.e., the number of bars in the tension zone decreased from three bars to two bars with the addition of fibers in the SCC without mitigating structural performance. The degree of prediction of crack width, cracking load/moment, ultimate loads, and deflection of various FR-SCC and FR-SCM mixture was evaluated using several design and code models. The results indicate that these code models can provide safe predictions for crack and ultimate loads, as well as crack width of FR-SCC. The deflection of FR-SCC is unsafe but predictable by these code models. In total, 18 large-scale beams were tested in four-point for flexural creep. FR-SCC incorporating steel fibers combined with expansive agent provided overall performance up to 10 times of that obtained with CVC with the same fiber type and volume. The cracking under constant load was reduced by 60% to 80% using self-consolidating fibrous mixtures made with or without expansion agents, compared to SCC without fibers. The best combination to reduce the cracking potential when the restrained shrinkage ring test was employed was obtained with SCC mixtures made with steel fibers and expansive agent. Models were elaborated to predict the time-to-cracking for FR-SCC and FR-SCM mixtures based on mixture modulus of elasticity and drying and autogenous shrinkages. The project involved extensive testing of highly flowable fibrous materials to determine drying shrinkage (nearly 260 prisms), modulus of rupture (nearly 180 prisms), as well as compressive and splitting tensile strengths and elastic modulus (nearly 2100 cylinders). Based on the results, models were proposed to predict these key material properties that affect the performance of FR-SCC and FR-SCM used in repair applications. In addition to FR-SCC, the investigation also was set to evaluate the feasibility of using fiber-reinforced superworkable concrete (FR-SWC) in construction and repair applications. Such highly flowable concrete that requires limited vibration consolidation can represent some advantages over FR-SCC (lower admixtures demand, lower risk of segregation, greater robustness, lower formwork pressure, etc.). The energy needed to ensure proper consolidation, using either vibration or rodding, applied on samples made with FR-SWC was determined. The energy requirement took into consideration the development of mechanical properties, the resistance to segregation, and the development of proper surface quality. The study also demonstrated the higher overall structural performance of optimized FR-SWC compared to the corresponding FR-SCC mixtures. The findings of the thesis on the design and performance of highly workable fiber-reinforced cementitious materials should facilitate the acceptance of such novel high-performance material in infrastructure construction and repair applications.
Author: Corey Michael Wirkman
Publisher:
ISBN:
Category : Concrete bridges
Languages : en
Pages : 200
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Book Description
Author: Gabriel Jen
Publisher:
ISBN:
Category :
Languages : en
Pages : 134
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Book Description
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.
Author: Michael Carey Brown
Publisher:
ISBN:
Category : Self-consolidating concrete
Languages : en
Pages : 19
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Book Description
The rising cost of materials and labor, as well as the demand for faster construction, has prompted development of cheaper, faster alternatives to conventional building techniques. Self-consolidating concrete (SCC), a high performance concrete characterized by its ability to flow without segregation under its own weight, promises to speed construction while reducing the need for skilled labor. However, experience has shown that SCC may be prone to shrinkage cracking, which may compromise its durability. In conventional concrete, fiber reinforcement has been used to control cracking and increase tensile and flexural strength. This study evaluated the feasibility of fiber-reinforced SCC (FR-SCC) for structural applications. Tests were conducted in the laboratory to assess the fresh and hardened properties of FR-SCC containing various types and concentrations of fibers. The results indicated that an SCC mixture can be prepared for use in transportation facilities that combines the properties of a high flow rate and some residual strength that would be beneficial for crack control. The residual strength is contributed by the internal fibers and provides load-carrying capacity after initial cracking of the concrete. At optimum fiber additions, FR-SCC mixtures can have the same fresh concrete properties as traditional SCC mixtures. FR-SCC also demonstrated a considerable improvement in the residual strength and toughness of a cracked section, which is expected to lead to the control of crack width and length. The improved performance of the FR-SCC cracked section indicated that it can be expected to have more durability in service conditions than would an identical SCC with no reinforcement. The study recommends that the Virginia Department of Transportation's Structure & Bridge Division evaluate FR-SCC in field applications such as link slabs and closure pours in continuous concrete decks; formed concrete substructure repairs; or prestressed beams where end zone cracking has been an issue. In such applications, construction with FR-SCC has the potential to be faster than with SCC, as traditional steel reinforcement may be reduced or eliminated, yielding reduced labor and materials costs for reinforcement placement. Enhanced public and worker safety may result from the reduction of overall construction time and required maintenance of traffic. The next step toward implementation of this technology would involve coordination with VDOT's Materials Division and Structure & Bridge Division to create special provisions or standard specifications regarding the use of FR-SCC and to identify candidate projects for field trials.
Author: Kamal H. Khayat
Publisher:
ISBN:
Category : Bridges
Languages : en
Pages : 70
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Book Description
A fiber-reinforced super-workable concrete (FR-SWC) made with 0.5% micro-macro steel fibers and 5% CaO-based expansive agent was used for the new deck slab of Bridge A8509. The selected FR-SWC had a targeted slump flow of 20 in. at the casting location. Multiple trial batches were performed, in collaboration with the concrete supplier, to adjust the mixture composition to meet the targeted performance criteria. This was followed up by casting the fibrous concrete in a mock-up slab measuring 10 x 10 ft that was prepared to simulate the tight rebar and the roadway crown slope in the transverse direction. The results indicated the necessity to lower the concrete slump from the intended value for FR-SWC to hold the 2% crown slope of the bridge deck in the transverse direction. The final mixture that was selected following the trial batches and mock-up placement had a slump consistency of 8 plus or minus 2 in. (FRC). Six sensor towers were installed in the slab within 18 ft to the East and West sides of the intermediate bent to monitor in-situ properties of the concrete. Each tower had three humidity sensors, three thermocouples, and 12 concrete strain gauges. The slump values varied between 6 and 10 in. Slump values were around 8.5 in. The fresh air volume ranged from 4.4% to 5.8%, and the concrete temperature ranged from 85 to 97 degrees F. At 56 days, the compressive strength ranged from 7,020 to 8,360 psi and had a mean value of 7,770 psi. Data up to 260 days are reported at the time of the preparation of this report. The in-situ concrete temperature was shown to increase around 45 degrees F during the first day, reaching a maximal temperature of 140 degrees F. The temperature then dropped to ambient temperature of approximately 95 degrees F during the second day. It then varied on a daily basis with the ambient temperature. The relative humidity of concrete ranged between 90% and 100% initially, then decreased with time until reaching approximate values of 80% to 85%. The loss of humidity was higher in magnitude and rate near the top surface of the bridge deck compared to the middle and bottom of the slab. A 3D finite element model (FEM) was developed to predict the top and bottom structural strain values in the concrete deck that can be developed due to the weight of the bridge. The estimated strain values were compared to those recorded by the in-situ sensors in the longitudinal and transverse directions. In the longitudinal direction, the stresses were shown to reach the maximum positive values at the points of contact of the girder with the concrete diaphragm. The values decreased gradually along the length of the bridge to reach the maximum negative values approximately at the mid-span of the bridge deck. The area under consideration, where the towers are located, was in complete tension in the longitudinal and transverse directions. The highest tensile strain values reached 2100 micro-strain at the intersection of the intermediate bent with one of the pre-cast concrete girders. A strain model was proposed to evaluate the strain data collected from the embedded sensors. The model represents the total strain as a summation of strains due to thermal deformation, drying and autogenous shrinkage, and structural deformation. The model was used to evaluate strains and estimate values of the concrete shrinkage during the first 30-36 hours, which corresponded to the time of demolding of the shrinkage samples as well as the load distribution factor between the concrete slab and the steel corrugated sheet that varied with concrete age. Findings indicated that the load distribution factor increased with concrete age reaching a value of 0.98 at 260 days. The concrete shrinkage during the first 30-36 hours was then estimated to be 75 micro-strain.
Author: Bikash Sigdel
Publisher:
ISBN: 9780355044782
Category : Fiber-reinforced concrete
Languages : en
Pages : 312
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Book Description
The first part of this study aims at developing hybrid fiber reinforced self-consolidating concrete (HFRSCC) made with a very high volume of supplementary cementitious materials (SCMs). Self-consolidating concrete (SCC) is a highly workable concrete that can easily flow through heavily reinforced concrete sections without the need for mechanical vibration. The percentages (by volume) of fibers considered were 0.1% and 0.2% hybrid combinations of nylon (PVA) and steel fibers, respectively. Cement was replaced by various percentages of SCMs by up to 70%. The mechanical properties (compressive strength, modulus of elasticity and tensile strength) and unrestrained drying shrinkage of the developed mixtures were evaluated and compared to the standard specifications. The second part of this study aims at evaluating the mechanical properties (compressive strength, modulus of elasticity, tensile strength, and modulus of rupture), thermal properties and unrestrained drying shrinkage of the paving and structural concrete mixtures being used in the six districts of the State of Idaho. The focus of this evaluation was to develop a material database required for the implementation of the "AASHTOWare Pavement ME Design" (ME) Software which is used to design rigid Portland Cement Concrete (PCC) pavements. The data developed and examples of its implementation in the ME software were conducted, evaluated, and presented.
Author: Antoine E. Naaman
Publisher: RILEM Publications
ISBN: 9782912143372
Category : Cement composites
Languages : en
Pages : 580
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Book Description
Author: Dennis R. Mertz
Publisher: Transportation Research Board
ISBN: 0309087694
Category : Political Science
Languages : en
Pages : 88
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Book Description
Rising awareness of and increased attention to sexual harassment has resulted in momentum to implement sexual harassment prevention efforts in higher education institutions. Work on preventing sexual harassment is an area that has recently garnered a lot of attention, especially around education and programs that go beyond the standard anti-sexual harassment trainings often used to comply with legal requirements. On April 20-21, 2021, the National Academies of Sciences, Engineering, and Medicine hosted the workshop Developing Evaluation Metrics for Sexual Harassment Prevention Efforts. The workshop explored approaches and strategies for evaluating and measuring the effectiveness of sexual harassment interventions being implemented at higher education institutions and research and training sites, in order to assist institutions in transforming promising ideas into evidence-based best practices. Workshop participants also addressed methods, metrics, and measures that could be used to evaluate sexual harassment prevention efforts that lead to change in the organizational climate and culture and/or a change in behavior among community members. This publication summarizes the presentations and discussion of the workshop.
