The Experts below are selected from a list of 285 Experts worldwide ranked by ideXlab platform
Ditao Niu - One of the best experts on this subject based on the ideXlab platform.
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frost durability and stress strain relationship of lining Shotcrete in cold environment
Construction and Building Materials, 2019Co-Authors: Jiabin Wang, Ditao NiuAbstract:Abstract Given the different hydration processes of normal concrete without accelerator, Shotcrete with accelerator has not only a short setting time and high early mechanical properties, but also different hydration products and microstructures. In high latitude and altitude areas, Shotcrete lining structures are subject to freeze–thaw cycles. Thus, the durability, bearing capacity, and service life of lining Shotcrete is critically threatened. In this work, a freezing–thawing durability experiment was conducted using the accelerated frost method. Dynamic elastic modulus, weight, compressive and splitting tensile strength, and the stress–strain relationship of frost–damaged Shotcrete were measured for a study of the durability and mechanical property degradation rules. Microstructures, through pore structure analysis and microscopic characterization, were identified for elucidating the deterioration mechanism of the mechanical properties of Shotcrete. After frost damage, the volume percentage of harmless pores rapidly decreased, whereas porosity increased. Micro-cracks appeared in interfacial transition zone grew into mortars and connected to form main cracks, which accelerated the microstructure damage. Physical and mechanical properties of Shotcrete decreased with prolonged freeze–thaw cycles. However, the peak stress and toughness of Shotcrete decreased, whereas peak strain, initial elastic modulus, and ultimate compression strain increased. Therefore, steel fiber reinforced Shotcrete had improved frost durability and reduced growth ratio of porosity under the bridging effect.
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influence of freeze thaw cycles and sulfate corrosion resistance on Shotcrete with and without steel fiber
Construction and Building Materials, 2016Co-Authors: Jiabin Wang, Ditao NiuAbstract:Abstract Shotcrete with low-alkali accelerator has short final setting time, high early strength, and various hydration products and microstructures because of different hydration processes of ordinary concrete without accelerator. In tunnel operation processes, a Shotcrete single-layer lining structure is subjected to positive and negative temperature alternation and corrosion ions, particularly sulfate ion. The durability and service life of the lining structure are seriously threatened. In this study, the performances, including relative dynamic elastic modulus, mass loss ratio, and mechanical properties after corrosion, were tested to investigate the Shotcrete durability of frost and sulfate resistance. Then, mineral composition, thermal analysis, pore structure, and microscope analysis of the specimen before and after corrosion were characterized. To achieve this objective, ordinary concrete and accelerated Shotcrete with and without steel fiber were fabricated. Results showed that ordinary Shotcrete was more durable under the action of freeze–thaw cycles and sulfate ion attack than that of the ordinary concrete with the same mixture. Thus, steel fiber led to a considerably dense microstructure in the Shotcrete matrix, and it could significantly improve the early-age compressive and splitting tensile strengths. Steel fiber reinforced Shotcrete had the best durability performance in frost and sulfate resistance.
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Mechanical properties, permeability and durability of accelerated Shotcrete
Construction and Building Materials, 2015Co-Authors: Jiabin Wang, Ditao Niu, Yongli ZhangAbstract:Abstract In this paper, the experiment is completed into two phases. In the first phase, the performance of setting time of pastes, mechanical properties of Shotcrete at different hydration age and permeability of Shotcrete at 90 day were tested. Meanwhile, in the second phase, the durability performance of Shotcrete with 10% fly ash and 0.64 vt.% steel fiber was studied under environment corrosion which included freeze–thaw cycle, accelerated carbonation test with and without bending load, sulfate attack, chloride ion diffusion and acid corrosion respectively. The results showed that, in comparison to ordinary concrete (OC) with the same mixture, ordinary Shotcrete (OS) had better durability properties except to chloride ion. Thus, steel fiber (steel fiber reinforced Shotcrete, SFRS) not only led to much denser microstructure in Shotcrete matrix but also could significantly improve the early-age compressive and splitting tensile strength, permeability and durability of Shotcrete.
D R Morgan - One of the best experts on this subject based on the ideXlab platform.
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REPAIR OF BERTH FACES AT PORT OF MONTREAL WITH FIBER-REINFORCED Shotcrete. IN: HIGH-PERFORMANCE FIBER-REINFORCED CONCRETE IN INFRASTRUCTURAL REPAIR AND RETROFIT
2000Co-Authors: D R Morgan, A. Lobo, L. RichAbstract:This paper describes a prototype construction project in which about two thirds of a berth face, 122 m long and 7.1 m high, was repaired with a synthetic fiber reinforced Shotcrete and the remaining third with a steel fiber reinforced Shotcrete. The synthetic fiber used was a new mono-filament polyolefin fiber, 26 mm long x 0.38 mm diameter added at an addition rate of 1.25% by volume of Shotcrete. The deformed steel fiber, 38 mm long, was added at an addition rate of 0.75% by volume of the Shotcrete. The Shotcrete used was air entrained, silica fume modified, supplied by transit mixers from a central mix plant and applied by the wet mix Shotcrete process. The remedial design, Shotcrete mixture designs, preconstruction mock up production and quality control testing are described as well, and a summary of construction quality control test results is provided.
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DEICER SALT SCALING RESISTANCE OF DRY- AND WET-PROCESS Shotcrete
Aci Materials Journal, 1994Co-Authors: Denis Beaupre, Caroline Talbot, Michel Pigeon, Michel Gendreau, D R MorganAbstract:American Society for Testing and Materials (ASTM) C 672 deicer salt scaling tests were carried out on both dry- and wet-mix Shotcretes. Twenty-five dry-mix Shotcretes and eleven wet-mix Shotcretes were used to fabricate different test panels. The mix variables included cement type, silica fume, latex, polypropylene and steel fibers, and set-accelerating and air-entraining admixtures. All test panels were wet-cured for 7 days except two additional panels, one of which was not cured and the other of which was cured with a curing compound. Water containing 2.5 or 3 percent salt solutions was used for the scaling tests. The scaling residues were collected and weighed to evaluate deterioration. The mass of scaling residues was found to vary between 0.1 and 24.0 kg/m. These tests indicate that the scaling resistance of both dry- and wet-mix Shotcrete improves with an increase in the air content, and that the use of silica fume generally reduces the mass of scaling residues. These tests also indicate that the use of a set-accelerating admixture can significantly reduce the scaling resistance of Shotcrete. The use of Type 30 cement and of an air-entraining admixture was found to markedly improve the scaling resistance of dry-mix Shotcretes.
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Influence of surface preparation on long-term bonding of Shotcrete
ACI Materials Journal, 1994Co-Authors: Caroline Talbot, Denis Beaupre, Michel Pigeon, D R MorganAbstract:Bonding rests were performed to evaluate the capacity of different Shotcrete mires to provide a good and durable joint with concrete surfaces prepared for repair in various ways. A total of 21 slabs (1.2 x 1.2 m) made of ordinary or conventional concrete were covered with a 75- to 100-mm layer of Shotcrete. The concrete surfaces to be covered with Shotcrete were prepared in different ways: sandblasting, chipping with jackhammers, grinding, or hydrodemolition. Both dry-mix and wet-mix Shotcretes were used. Pullout rests, performed after 2 and 6 months, were used to evaluate the strength and durability of the bonding. The results indicate that the type of surface preparation has a strong influence on the strength and durability of the bonding, and that hydrodemolition is probably the best type of surface preparation. The Shotcrete mit composition, however, was found to hare relatively little influence on bonding durability.
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SILICA FUME IN Shotcrete
Concrete international, 1993Co-Authors: D R Morgan, And J. T. WolsieferAbstract:The details are described of a study that demonstrated that all the three forms of silica fume, uncompacted, compacted low density, and compacted high density, can be readily batched, mixed, and applied in both the dry- and wet-mix Shotcrete processes. In the wet-mix Shotcrete process, incorporating silica fume in the mix resulted in signigicant increases in achievable thickness of build-up compared to plain portland cement Shotcrete. In the dry-mix Shotcrete process, silica fume use in the mix resulted in substantial increases in achievable thickness of build-up compared to the plain portland cement Shotcrete. These and other study findings are presented and discussed.
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Advances in Shotcrete Technology for Support of Underground Openings in Canada
1993Co-Authors: D R MorganAbstract:This paper presents a broad overview of the state-of-the-art of Shotcrete technology for support of underground openings in Canada. Advances in Shotcrete technology such as the introduction and use of steel fibre reinforcement (in lieu of conventional wire mesh reinforcement) and silica fume, in both wet and dry-mix Shotcrete are reviewed. Shotcrete mix design procedures and batching, mixing, supply and application procedures are examined. Typical performance characteristics and properties of both plastic and hardened Shotcrete are described. Examples of the use of Shotcrete for support of underground openings in tunneling and mining applications in Canada are presented.
Jiabin Wang - One of the best experts on this subject based on the ideXlab platform.
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frost durability and stress strain relationship of lining Shotcrete in cold environment
Construction and Building Materials, 2019Co-Authors: Jiabin Wang, Ditao NiuAbstract:Abstract Given the different hydration processes of normal concrete without accelerator, Shotcrete with accelerator has not only a short setting time and high early mechanical properties, but also different hydration products and microstructures. In high latitude and altitude areas, Shotcrete lining structures are subject to freeze–thaw cycles. Thus, the durability, bearing capacity, and service life of lining Shotcrete is critically threatened. In this work, a freezing–thawing durability experiment was conducted using the accelerated frost method. Dynamic elastic modulus, weight, compressive and splitting tensile strength, and the stress–strain relationship of frost–damaged Shotcrete were measured for a study of the durability and mechanical property degradation rules. Microstructures, through pore structure analysis and microscopic characterization, were identified for elucidating the deterioration mechanism of the mechanical properties of Shotcrete. After frost damage, the volume percentage of harmless pores rapidly decreased, whereas porosity increased. Micro-cracks appeared in interfacial transition zone grew into mortars and connected to form main cracks, which accelerated the microstructure damage. Physical and mechanical properties of Shotcrete decreased with prolonged freeze–thaw cycles. However, the peak stress and toughness of Shotcrete decreased, whereas peak strain, initial elastic modulus, and ultimate compression strain increased. Therefore, steel fiber reinforced Shotcrete had improved frost durability and reduced growth ratio of porosity under the bridging effect.
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influence of freeze thaw cycles and sulfate corrosion resistance on Shotcrete with and without steel fiber
Construction and Building Materials, 2016Co-Authors: Jiabin Wang, Ditao NiuAbstract:Abstract Shotcrete with low-alkali accelerator has short final setting time, high early strength, and various hydration products and microstructures because of different hydration processes of ordinary concrete without accelerator. In tunnel operation processes, a Shotcrete single-layer lining structure is subjected to positive and negative temperature alternation and corrosion ions, particularly sulfate ion. The durability and service life of the lining structure are seriously threatened. In this study, the performances, including relative dynamic elastic modulus, mass loss ratio, and mechanical properties after corrosion, were tested to investigate the Shotcrete durability of frost and sulfate resistance. Then, mineral composition, thermal analysis, pore structure, and microscope analysis of the specimen before and after corrosion were characterized. To achieve this objective, ordinary concrete and accelerated Shotcrete with and without steel fiber were fabricated. Results showed that ordinary Shotcrete was more durable under the action of freeze–thaw cycles and sulfate ion attack than that of the ordinary concrete with the same mixture. Thus, steel fiber led to a considerably dense microstructure in the Shotcrete matrix, and it could significantly improve the early-age compressive and splitting tensile strengths. Steel fiber reinforced Shotcrete had the best durability performance in frost and sulfate resistance.
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Mechanical properties, permeability and durability of accelerated Shotcrete
Construction and Building Materials, 2015Co-Authors: Jiabin Wang, Ditao Niu, Yongli ZhangAbstract:Abstract In this paper, the experiment is completed into two phases. In the first phase, the performance of setting time of pastes, mechanical properties of Shotcrete at different hydration age and permeability of Shotcrete at 90 day were tested. Meanwhile, in the second phase, the durability performance of Shotcrete with 10% fly ash and 0.64 vt.% steel fiber was studied under environment corrosion which included freeze–thaw cycle, accelerated carbonation test with and without bending load, sulfate attack, chloride ion diffusion and acid corrosion respectively. The results showed that, in comparison to ordinary concrete (OC) with the same mixture, ordinary Shotcrete (OS) had better durability properties except to chloride ion. Thus, steel fiber (steel fiber reinforced Shotcrete, SFRS) not only led to much denser microstructure in Shotcrete matrix but also could significantly improve the early-age compressive and splitting tensile strength, permeability and durability of Shotcrete.
Günter Hofstetter - One of the best experts on this subject based on the ideXlab platform.
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Correction: An Extended Damage Plasticity Model for Shotcrete: Formulation and Comparison with Other Shotcrete Models
Materials, 2018Co-Authors: Matthias Neuner, Peter Gamnitzer, Günter HofstetterAbstract:The aims of the present paper are (i) to briefly review single-field and multi-field Shotcrete models proposed in the literature; (ii) to propose the extension of a damage-plasticity model for concrete to Shotcrete; and (iii) to evaluate the capabilities of the proposed extended damage-plasticity model for Shotcrete by comparing the predicted response with experimental data for Shotcrete and with the response predicted by Shotcrete models, available in the literature. The results of the evaluation will be used for recommendations concerning the application and further improvements of the investigated Shotcrete models and they will serve as a basis for the design of a new lab test program, complementing the existing ones.
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Influence of the Constitutive Model for Shotcrete on the Predicted Structural Behavior of the Shotcrete Shell of a Deep Tunnel.
Materials, 2017Co-Authors: Matthias Neuner, Magdalena Schreter, David Unteregger, Günter HofstetterAbstract:The aim of the present paper is to investigate the influence of the constitutive model for Shotcrete on the predicted displacements and stresses in Shotcrete shells of deep tunnels. Previously proposed Shotcrete models as well as a new extended damage plasticity model for Shotcrete are evaluated in the context of 2D finite element simulations of the excavation of a stretch of a deep tunnel by means of the New Austrian Tunneling Method. Thereby, the behavior of the surrounding rock mass is described by the commonly used Hoek–Brown model. Differences in predicted evolutions of displacements and stresses in the Shotcrete shell, resulting from the different Shotcrete models, are discussed and simulation results are compared to available in situ measurement data.
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An Extended Damage Plasticity Model for Shotcrete: Formulation and Comparison with Other Shotcrete Models.
Materials (Basel Switzerland), 2017Co-Authors: Matthias Neuner, Peter Gamnitzer, Günter HofstetterAbstract:The aims of the present paper are (i) to briefly review single-field and multi-field Shotcrete models proposed in the literature; (ii) to propose the extension of a damage-plasticity model for concrete to Shotcrete; and (iii) to evaluate the capabilities of the proposed extended damage-plasticity model for Shotcrete by comparing the predicted response with experimental data for Shotcrete and with the response predicted by Shotcrete models, available in the literature. The results of the evaluation will be used for recommendations concerning the application and further improvements of the investigated Shotcrete models and they will serve as a basis for the design of a new lab test program, complementing the existing ones.
Pin Liu - One of the best experts on this subject based on the ideXlab platform.
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Shotcrete performance loss due to seepage and temperature coupling in cold region tunnels
Construction and Building Materials, 2020Co-Authors: Shengai Cui, Pin LiuAbstract:Abstract Road and railway tunnels in cold regions are often affected by water leakages and freezing temperatures, which increase the risk of severe damage in Shotcrete linings. Within this context, two environmental conditions are investigated in this paper with reference to a low-alkali-based Shotcrete; i.e., the coupling of seepage and temperature (named the “open system”) and the temperature uncoupled with seepage (named the “closed system”). Based on the physical and mechanical tests performed on two Shotcrete slabs, the previously mentioned environmental conditions are analyzed with reference to concrete mechanical properties, strain characteristics and pore structure. The results are summarized as follows: (1) The stiffness and compression strength of Shotcrete are weakened due to water continuously seeping through the Shotcrete during the freezing and thawing process. (2) The residual tensile strain of the open system is significantly higher than that of the closed system. (3) The seepage and temperature coupling favors the deterioration of micro-pore structure, which has adverse effects on the mechanical performance of Shotcrete matrix.
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Exploratory study on improving bond strength of Shotcrete in hot and dry environments of high geothermal tunnels
KSCE Journal of Civil Engineering, 2017Co-Authors: Shengai Cui, Deli Xu, Pin Liu, Yuezhong YeAbstract:To solve the problem on the serious loss of bond strength of Shotcrete in hot and dry environments, the measures for improving the bond strength were explored by mixing mineral admixtures or fiber materials into Shotcrete mixture. The bond strengths between Shotcrete and rock in hot and dry environments were measured by splitting method, and macroscopic, mesoscopic and microscopic analyses were carried out on Shotcrete specimens. The results show that: in hot and dry environments, the bond strengths all decrease when mixed with mineral admixtures, and especially for the fly ash, with which the bond strength of Shotcrete decreases by 36.7%. Mixing polypropylene fibers into Shotcrete makes its bond strength decrease by 10.2%, but for steel fibers, it will be improved by 41.8% compared with basic mix proportion. Moreover, according to submicroscopic measurement and microscopic analysis, the influence mechanisms of mineral admixtures and fiber materials have been explored to some extent. Therefore, it’s feasible and effective to improve the bond strength by adding steel fibers in hot and dry environment.
