Almost all drilling cements are made of Portland cement, a calcined (burned) blend of limestone and clay. A slurry of Portland cement in water is used in wells because it can be pumped easily and hardens readily, even under water. It is called Portland cement because its inventor, Joseph Aspdin, thought the solidified cement resembled stone quarried on the Isle of Portland off the coast of England. Portland cements can be modified easily, depending on the raw materials used and the process used to combine them. Proportioning of the raw materials is based on a series of simultaneous calculations that take into consideration the chemical composition of the raw materials and the type of cement to be produced: American Society for Testing and Materials (ASTM) Type I, II, III, or V white cement, or American Petroleum Institute (API) Class A, C, G, or H.  The basic raw materials used to manufacture Portland cements are limestone (calcium carbonate) and clay or shale.
Shibayama, Atsushi (Central Research Institute of Electric Power Industry) | Miyagawa, Yoshinori (Central Research Institute of Electric Power Industry) | Kihara, Naoto (Central Research Institute of Electric Power Industry) | Kaida, Hideki (Central Research Institute of Electric Power Industry)
The damages of the gigantic tsunami that followed the 2011 Great East Japan Earthquake were confirmed on reinforced concrete (RC) structures (Nandasena et al., 2012). Moreover, the damages caused by the tsunami debris collision were confirmed in addition to the damages caused by only the tsunami. Therefore, it is important to clarify the response characteristics of the structure subjected to the tsunami wave force and collision force, and to establish a response evaluation method by numerical analysis. However, the response characteristics of RC structures subjected to two external forces with significantly different timings of actions--namely, wave pressure and collision forces--have not been clarified. Furthermore, to assess the responses of RC structures using numerical analysis, the two different types of superimposing external forces must be considered. However, the applicability of numerical analysis under such external force conditions has not been sufficiently verified. In this research, a large-scale debris collision experiment was first conducted to experimentally investigate the response of an RC vertical wall subjected to the wave pressure and debris collision forces. Next, a reproducibility analysis of the experiment was performed with nonlinear finite element analysis to examine the adaptability of the finite element analysis.
This NACE International standard practice establishes the general principles to be adopted to minimize the effects of stray current corrosion caused by direct current (DC) and/or alternating current (AC) from external sources on steel reinforced concrete (RC) and prestressed concrete (PC) structures or structural elements. The standard practice offers guidance for the design of concrete structures that may be subject to stray-current corrosion; the detection of stray current interference; the selection of protection measures; and the selection of mitigation methods. The standard practice is intended for use by designers of RC and PC structures, professionals working with electrochemical techniques (e.g., cathodic protection [CP], realkalization, and electrochemical chloride extraction [ECE]); owners of structures with the risk of reinforcement corrosion caused by stray currents; owners of systems that could generate stray currents to concrete structures; engineers; and other interested parties.
This NACE International standard practice establishes the general principles to be adopted in order to minimize the effects of stray current corrosion caused by direct current (DC) and/or alternating current (AC) from external sources on steel reinforced concrete (RC) and prestressed concrete (PC) structures or structural elements. The standard practice is intended to offer guidance for: the design of concrete structures that may be subject to stray-current corrosion; the detection of stray current interference; the selection of appropriate protection measures; and the selection of appropriate mitigation methods.
The standard practice is intended for use by designers of RC and PC structures, professionals dealing with electrochemical techniques (e.g., cathodic protection [CP], realkalization, and electrochemical chloride extraction [ECE]), owners of structures with the risk of reinforcement corrosion caused by stray currents, owners of systems that could generate stray currents to concrete structures, engineers, and other interested parties.
The technical background for this standard is published as NACE Publication 01110, prepared by Task Group (TG) 356.1
This standard practice was prepared in 2019 by NACE TG 356, “Reinforced Concrete: Stray-Current-Induced Corrosion.” This TG is administered by Specific Technology Group (STG) 01, “Reinforced Concrete”; and is sponsored by STG 05, “Cathodic/ Anodic Protection.” This standard practice is issued by NACE International under the auspices of STG 01.
Experimental uniaxial compression loading tests and scanning electron microscope (SEM) tests are carried out on rock-like specimens containing single pre-existing cracks to study the mechanical properties and microscopic damage evolution. The present study has distinguished tensile or shear cracks based on different SEM observations on a micro scale. Specifically, six typical micro patterns are defined according to their geometry shapes, namely, flocculent, flaw, circle, flow, layered, and broken circle pattern. These micro patterns display distinct characteristics on structure surfaces, boundary lines, and the distribution of grain debris. Moreover, the microscopic damage of both tensile and shear cracks is quantitatively studied using the image post-processing technique. The damage evolution, which associates the macroscopic cracking processes, has been investigated. It is indicated that the microcracks develop from the pre-existing cracks prior to the initiation of any macroscopic observable cracks, and the damage is not rapidly accumulated after the initiation of both tensile and shear cracks.
Natural rock contains discontinuities, including fractures, pores, and other defects, which govern the fracturing behaviors of the rock masses under loading. Numerous theoretical, experimental, and numerical studies have been carried out to study mechanical properties of jointed rocks or other rock-like materials (Griffith, 1921; Brace and Bombolakis, 1963; Horii and Nematnasser, 1985; Bobet and Einstein, 1998; Wong and Einstein, 2009a; 2009b; 2009c; Park and Bobet, 2010; Zhang and Wong, 2012; 2013; Gonçalves da Silva and Einstein, 2013; Haeri et al., 2014; Yang et al., 2017; Zhao et al., 2018). In these researches, tensile and shear cracks are always be regarded as two basic crack types and fundamental of the rock mechanic. (Cheng and Wong, 2018). Bombolakis (1963) firstly observed the propagation of tensile wing cracks from straight cracks under uniaxial compression, which consists well with the Griffith theory. Lajtai (1974) carried out uniaxial compression loading tests on plaster of Paris, the results consist of five crack types, including both tensile and shear cracks. Petit and Barquins (1988) observed that shear zones develop extensively in addition to the occurrence of tensile wing cracks. Using scanning electron microscope (SEM), Sagong and Bobet (2003) investigated tensile and shear cracks in gypsum specimens on a micro scale. Li et al. (2005) conducted experimental tests on marble specimens, and they discovered two cracking phenomena: wing cracks and secondary quasi-coplanar cracks. Although the mechanical properties of these two cracks were not clearly identified by the authors, it is accepted that wing cracks are tensile cracks and secondary cracks are shear cracks. Wong and Einstein (2009a) systematically characterized the tensile/shear cracks which emanate from a single pre-existing crack. Seven different crack types (including three tensile types, three shear types, and one mixed type) were identified based on geometry and propagation mechanism. Subsequently, they studied the orientation of microcracking zones of the wing cracks (Wong and Einstein, 2009c). As a summary, the previous studies focused on the differences between tensile cracks and shear cracks in three main aspects (Cheng and Wong, 2018): First, the tensile/compressive stress concentration phenomenon around the pre-crack tips; Second, the initiation direction and propagation trajectories of observable cracks; Third, the microscopic observation of the crack surfaces.
The failure behaviour of a plaster beam when coated with a thin layer of polymeric liner was studied both experimentally and numerically. Plaster beams without any liner coating were tested to failure in a four-point bend test scenario and were found to fail in tension at the mid span of the beam. To assess the support mechanisms of thin spray-on liners when adhered to a rock surface, the plaster beams were coated with a 5 mm thick fibreglass reinforced polymer liner. These beams were tested to study the effect the polymer liner has on restricting tensile failure of the beam. Results of flexural tests on plaster beams with a reinforced polymer liner showed failure originating near the support points and extending to the loading points with some delamination of the polymer liner at higher loads. This ability of a thin polymeric liner to resist crack propagation at the interface of the liner was simulated numerically using a cohesive zone model. The model developed predicted the failure behaviour accurately and the numerical results obtained were comparable to the experimental results.
Thin spray-on liners (TSL) form a composite skin layer and support the rock after application (Stacey, 2001). It has performance characteristics that lie between those of shotcrete and mesh. Liners like TSL and shotcrete, which are well adhered to the rock surface can restrict small movements of already fractured and loosened rock mass. However, the TSL being more flexible than shotcrete can generate more support resistance over a full range of rock deformations (Tannant, 2001). Laboratory tests were undertaken to quantify the strata skin reinforcement using a polymer based TSL. The polymer liner was adhered to plaster beams and then flexural tests were conducted on the polymer-plaster composites. Similar tests were also done on plaster only samples. The support resistance provided by TSLs was demonstrated by comparing the flexural strength of the polymer-plaster composite with that of plaster only beams.
The results of flexural tests on plaster only and a TSL coated plaster composite were simulated numerically using finite element modelling (FEM) and the failure behaviour was compared with experimental results. Cohesive zone interaction, available in Abaqus library (Abaqus, 2014), was used to model the interface between the plaster and polymer layers. The interface properties required for defining the cohesive zone interaction were from the work carried out by earlier researchers (Qiao et al., 2015, Shan, 2017) at the University of Wollongong.
To simplify sample preparation, hydrostone, gypsum plaster and 5% Portland cement, was used to simulate the substrate instead of rock. Plaster beams having dimensions 160 mm by 40 mm by 40 mm were cast and textured to mimic rock beams. All hydrostone samples were prepared by mixing in a ratio of 3.5:1 by weight of plaster to water. The samples were then allowed to cure at 40° C in an oven for two weeks.
Intermittent jointed rocks, widely existing in various mining and civil engineering structures, are quite sensitive to dynamic cyclic loading conditions. Understanding the dynamic mechanical properties of jointed rocks is beneficial for the rational design and the long-term stability assessment of rock engineering projects. This study experimentally investigates the dynamic mechanical properties of synthetic jointed rock models under different cyclic conditions, regarding four loading frequencies, four maximum stresses and four amplitudes. Our experimental results reveal the influence of the three cyclic loading parameters on the mechanical properties of jointed rocks, including the fatigue deformation characteristics, the fatigue energy and damage evolution, and the fatigue progressive failure behavior. Under lower loading frequency or higher maximum stress and amplitude, the jointed rock is characterized by higher fatigue deformation moduli and higher dissipated hysteresis energy, leading to higher accumulative damage and lower fatigue life. The accumulative fatigue damage of jointed rocks exhibits an inverted S-shape with a three-stage evolution, i.e., initial, steady and accelerated stage. The fatigue failure modes of jointed rocks are independent of cyclic loading parameters; all tested jointed rocks feature a prominent tensile splitting failure mode. Three different crack coalescence patterns are classified between two adjacent joints. Furthermore, different from the progressive failure under static monotonic loading, the jointed rocks under cyclic compression fail more abruptly without evident preceding signs. The tensile cracks on the front surface of jointed rocks always initiate from the joint tips, and then propagate at a certain angle with the joints towards the direction of maximum compression.
The mechanical characteristics of intermittently jointed rocks play a dominant role in the overall mechanical behavior of many mining and civil engineering structures, such as underground tunnels, bridge abutments and road foundations. Since these rock structures are likely to be subjected to cyclic loading resulting from earthquakes, quarrying and rockbursts, it is thus crucial to characterize the fatigue properties and failure mechanism of intermittently jointed rocks for the rational design and long-term stability analysis of rock structures under different cyclic loading conditions.
Natural rock contains discontinuities, including pores, fractures, and inclusions or other defects. The original defects have significant influences on the physical properties and mechanical properties of rock materials, most of the rock failures are due to the initiation, propagation, coalescence of the original cracks. In the classical linear fracture mechanics theory, the stress-strain field at crack tip of rock materials is singular. In order to solve this problem, we introduce the weight function which considering the internal characteristic length of material to modify the stress field. Based on the connection between micro-structures with damage evolution of material, we established stress function which considering the damage evolution of material. Then apply the modified stress function to the existing failure criterion and obtain the strength criterion that considers the micro-structure damage evolution of material. SEM method is also applied to fracture section of pre-existing crack specimens which are fractured under uniaxial compression test. The damage degree at initiation stage of specimens are obtained based on the SEM image. Then apply the damage degree to stress function, we obtained the initiation stress at crack tip. The results shows that the initiation stress at crack tip varies with crack inclination angles, and the maximum initiation stress at the crack inclination angle of 45°.
Natural rock contains discontinuities, including pores, fractures, and inclusions or other defects, which govern the mechanical behavior of the rock mass (Goodman, 1989). The existence of internal defects in the rock mass leads to the stress concentration in the defect area. The stress field function at crack tip of rock originated from the fracture mechanics theory of the metal material. Inglis (1913) studied the stress of an elliptical hole in an infinite plate and pointed out that the stress at the crack tip was infinite and could not bear the load. Griffith (1921) introduced the surface energy to explain the phenomenon that “the tensile strength of crystals is far less than the theoretical strength”, and established the linear elastic fracture mechanics. Irwin (1957) proposed the stress intensity factor (K) in considering the singularity of stress at crack tip, and classified the cracks into three types according to the mechanical characteristics of crack: type I, II, III. However, According to the classical linear fracture mechanics theory, the stress-strain field at crack tip is singular.
Fibre Reinforced Sprayed Concrete (FRSC) is a key technology in the tunneling industry.
To analyze the performances of fibre concretes, we must take into account the combination of fibre and concrete as a composite material, which means integrating the transfer of the concrete matrix to the fibres network.
Furthermore, the different ways to check the energy absorption and residual strength are often less well known, and lead to confusion.
The European standard EN 14487-1 mentions the different ways of specifying the ductility of fibre reinforced sprayed concrete in terms of residual strength and energy absorption capacity. It also mentions that both ways are not exactly comparable.
The main purpose of this presentation will be to offer an insight into the different main testing procedures used for fibre reinforced spray concrete projects to guide the actors on the market to choose the right testing method, the right performance for the right application
The paper will provide very last investigation realized in different lab to better understand the use of the three point bending test on square panel with notch currently endorsed by EFNARC committee and discuss with CEN.
Sprayed concrete technology has dramatically improved in terms of the use of advanced admixtures and application methods to give durable and high performance concrete.
With this improvement in sprayed concrete quality, tunnel linings were constructed using permanent l fibre reinforced sprayed concrete instead of conventional in-situ concrete within the temporary sprayed concrete linings, lowering costs and significantly reducing the construction time, particularly in sections of complex geometry such as step plate junctions.
Currently modern sprayed concrete technology equips the tunnelling industry with a more economic tunnel lining system in the form of a single shell of permanent sprayed concrete. This technology provides a structural lining that is durable, watertight and can be surface finished to a degree that is similar to cast concrete.