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Shotcrete : materials, performance and use
\"This comprehensive textbook covers current state-of-the-art shotcrete technology. It provides an overview of the many and various uses of shotcrete. It includes chapters with case histories on shotcrete materials and mixture proportioning, performance, shotcrete research, equipment and shotcrete application\"-- Provided by publisher.
Book
An overview of the research trends on fiber-reinforced shotcrete for construction applications
In this study, data mining, followed by the scientometric analysis of fiber-reinforced shotcrete (FRS), was carried out for knowledge mapping, co-citations, and co-occurrence. The information needed for the analysis was retrieved from the Scopus search engine. Important publishing sources, keyword analysis, writers with the most contribution in citations and publications, the most-cited articles, and the regions most actively engaged in FRS research were identified throughout the data review process. Moreover, the need for FRS, the major constraints associated with their usage, and their possible solutions were discussed. The analysis of the bibliographic data showed that research publications on FRS progressed inconsistently till 2015, and over the past 6 years (2016–2021), publication numbers increased steadily, which exhibited the interest of academics in fiber-reinforced materials. The analysis of keywords in the field showed that the most common FRS research keywords are shotcreting, shotcrete, steel fibers, FRS, and fiber-reinforced materials. Keyword analysis showed that FRS is typically used for tunnel rock support and lining. Based on the review of relevant literature, research gaps have been identified, and future research has been suggested.
Journal Article
The Effect of Accelerator Dosage on Fresh Concrete Properties and on Interlayer Strength in Shotcrete 3D Printing
Recently, the progress in 3D concrete printing has developed enormously. However, for the techniques available, there is still a severe lack of knowledge of the functional interaction of processing technology, concrete rheology and admixture usage. For shotcrete 3D printing technology, we present the effect of accelerator dosages (0%, 2%, 4% and 6%) on fresh concrete properties and on interlayer strength. Therefore, early yield stress development up to 90 min is measured with penetration resistance measurements. Deformation of layers under loading is investigated with digital image correlation and a mechanical testing machine. One point in time (10 min after deposition) is examined to quantify vertical buildability of elements depending on the accelerator dosage. Four different interlayer times (0, 2, 5 and 30 min), which occur for the production of small and large elements as well as due to delay during production, are investigated mechanically as well as quantitatively with computed tomography regarding the formation of cold joints. With increased accelerator dosage, an instantaneous increase in early age yield stress and yield stress evolution was observed. An increase in interlayer time leads to a reduced strength. This is mainly attributed to the observed reduced mechanical interlocking effect of the strands. Finally, a model to describe interlayer quality is presented. In the end, advantages as well as limitations of the findings are discussed.
Journal Article
Determination of Stiffness of Circumferential Yielding Lining Considering the Shotcrete Hardening Property
The safety of circumferential yielding lining is influenced significantly by the shotcrete hardening property. However, presently, negligible research attention has been paid to this topic. This study aims to establish an analytical model for determining the support stiffness of circumferential yielding lining. Here, the shotcrete hardening property is considered. The entire deformation process of circumferential yielding lining is divided into three stages according to the mechanical characteristic of the yielding elements. A comparison of the element yield time and shotcrete age yields two cases that need to be discussed. Furthermore, analytical solutions for the time-dependent lining stiffness in different cases are proposed based on the previous shotcrete hardening equations. The corresponding equation for the lining pressure is also provided to evaluate the safety of shotcrete lining. The proposed analytical model is applied effectively in the Saint Martin La Porte access adit and predicts the average response of the monitoring tunnel convergences. Finally, a comprehensive parametric investigation is carried out, which includes the effects of yield stress, elastic modulus and length of yielding elements and ground stress on the shotcrete lining safety. Certain inspiring findings and effective recommendations for the design of circumferential yielding lining are provided.HighlightsEquations for time-dependent stiffness of circumferential yielding lining are proposed.The real-time evaluation of shotcrete lining safety is performed.The influences of yielding element parameters and ground stress are discussed.
Journal Article
Interfacial Transition Zone between Young Shotcrete and Hard Rock
Shotcrete (sprayed concrete) differs from ordinary cast concrete through the application technique and the addition of set accelerators that promote immediate stiffening. The bond strength development between shotcrete and rock is an important property that depends on the texture of the rock, the type of accelerator, and application technique. This investigation focuses on the development of the microstructure in the interfacial transition zone (ITZ) and the strength of the bond at the shotcrete-hard rock boundary. The results show that the bond strength is related to the hydration process--that is, the strength gain of the shotcrete--and remains low before the acceleration period of the cement hydration. With a scanning electron microscope (SEM), it is possible to observe changes over time for the early development of the interfacial zone, both before and after proper cement hydration. Results from tests with wet-sprayed concrete on granite rock are presented. The test method--using both bond strength and the SEM to investigate the development of the microstructure at the ITZ--is interesting, but has to be more broadly examined. Different mixtures, accelerators, and rock types have to be used. Keywords: bond strength; ettringite; interfacial zone; microstructure; set accelerator; shotcrete.
Journal Article
Key features of numerical models for the FE-simulation of deep tunnel advance by the NATM
In the present work, important aspects of time-dependent nonlinear 3D finite element (FE) models for deep tunnel advance by the New Austrian Tunneling Method (NATM), characterized by repeated sequences of excavation, securing, and idle periods, are discussed on the example of a 3D finite element model of a stretch of the Brenner Base Tunnel, which is currently constructed between Austria and Italy. Nonlinear material models are utilized for representing the surrounding rock mass and the shotcrete shell. Based on the finite element model, strategies for the efficient implementation into a parallel distributed memory numerical code are proposed. They are essential to achieve reasonable computation times for numerical simulations of tunneling based on large 3D FE models. In particular, the implementation of the construction procedure, parallel computing and communication specific details, and efficient linear solvers for the global equation system within the incremental-iterative Newton–Raphson scheme are addressed. Furthermore, possible extensions of the material models for rock mass and shotcrete, used in the 3D FE model, are presented. They concern (i) a gradient-enhanced model for transversely isotropic rock and rock mass, taking into account hardening and softening behavior and (ii) the extension of the shotcrete model to nonlinear creep and damage due to creep. The possible benefits of the model extensions in numerical simulations of tunneling by the NATM are discussed.
Journal Article
Mass Shotcrete Wall Construction and Thermal Control Plan
Wet-mix shotcrete has been used more and more for structural applications in the past few decades. Recently, wet-mix shotcrete was successfully used to construct a mass structural wall with congested reinforcement and minimum dimensions of 1.0 m in a sewage treatment plant. A low-heat shotcrete mixture that included up to 40% slag was proposed for shotcrete application. A preconstruction mockup was shot to established proper work procedures for shotcrete application and qualify the shotcrete mixture and shotcrete nozzlemen. Extraction of cores and cut windows from the mockup confirmed proper consolidation around the congested reinforcement. A thermal control plan was developed, which included laboratory and field testing requirements, thermal analysis modeling with a three-dimensional (3-D) finite element program, and thermal control requirements, including installation of cooling pipes and thermal blankets. Shotcrete proved to be an efficient means for mass concrete structural construction. Thermal control for mass shotcrete construction was studied, and the proposed thermal control plan was proved to function properly. The general guidance for mass shotcrete construction is provided. Keywords: compaction; consolidation; encapsulation; mass concrete; mass shotcrete; nozzleman; shotcrete; temperature differential; thermal control plan.
Journal Article
Study on the mechanics and self-sensing properties of ultrahigh-performance shotcrete containing waste glass aggregates
To promote the recycling of waste glass and satisfy the demands of environmental sustainability for ultrahigh performance concrete (UHPC), in this study, glass sand was employed to partially or entirely replace machine-made sand, and steel fibres were incorporated to fabricate ultrahigh performance shotcrete (UHPS). The effects of glass sand and steel fibres on the mechanical and electrical properties of composite materials were analysed in this study. Furthermore, alkali‒silica reaction (ASR) tests and microstructural analyses were conducted. The results indicate that at higher steel fibre contents, the incorporation of glass sand does not reduce the compressive strength of the UHPS and that glass sand has no significant effect on the split tensile or flexural strength. When the steel fibre content is 2% and the replacement ratio of glass sand reaches 100%, the mechanical properties of the UHPS reach their maximum. The addition of glass sand negatively affects the electrical properties, whereas the use of steel fibres improves them. The results of the alkali‒silica reaction tests confirm that the use of glass sand does not induce harmful expansion reactions. The study revealed the trends in the mechanical and electrical properties of concrete from a microstructural perspective and provided explanations for the alkali‒silica reaction outcomes. This study provides technical support for the application of UHPS to tunnel linings.
Journal Article
Influence of Fiber Geometry and Type on Creep Rupture of Cracked Fiber-Reinforced Shotcrete Mixtures
It is well known that creep can affect the serviceability of concrete structures, including tunnel linings made using fiber-reinforced shotcrete (FRS). However, the possible effect of creep on the strength of structures is seldom explicitly considered in design. For cracked FRS loaded in tension or flexure, creep rupture of the fiber-concrete composite, either by pullout or rupture of fibers, can lead to structural collapse, at least when no alternative load path exists. In the present investigation, the influence of fiber geometry and surface roughness on creep rupture (expressed as the time-to-collapse) of FRS panel specimens subjected to a sustained flexural-tensile load has been assessed. The results suggest that geometric aspects of fiber design influence the propensity of the fiber composite to suffer creep rupture at a crack, and that collapse primarily occurs as a result of fiber pullout rather than tertiary creep of individual fibers. For the fibers presently investigated, geometric aspects of fiber design appear to exert a greater influence on creep rupture of the fiber composite than the properties of the material comprising the fibers. Keywords: creep; fiber-reinforced shotcrete; macrosynthetic fibers; pullout; rupture; slippage; steel fibers; testing; time-dependent behavior.
Journal Article