Concrete Plug Research Articles

Bending test of long-span ultra-shallow floor beam (USFB) with two lightweight concretes

This paper presents the bending behaviour of a partially encased ultra-shallow floor beam (USFB) with two types of lightweight concrete. The beam was fabricated by welding two asymmetric Tees together along the web to create a beam with multiple circular openings that act as ‘plug shear connectors’ with the concrete encasement. The bending resistance of the plug-shear connection system was obtained by testing a composite USFB for a beam span of 7.2 m, half of the span being made with a lightweight concrete slab and the other half span with an ultra-lightweight concrete slab. Analysis of the four-point bending tests was carried out to determine the increase in bending resistance due to composite action and the contribution of the longitudinal shear connection due to the concrete plug passing through the web openings combined with additional tie bars. Calculations of the properties of the USFB with the two types of lightweight concrete were made according to SCI documentation and Eurocode 4. It was observed that the deflections were predicted accurately by the elastic properties and that the failure mode was by concrete crushing before the plastic bending resistance of the composite section had been developed. It was also shown that the cracked section properties should be used for the deflection analysis.

Experimental determination of deposition velocity of CsOH aerosols on CaCO3 at temperature range 170 - 290 °C

A field assessment at the Fukushima-Daiichi Nuclear Power Station revealed high radioactivity on the concrete shield plugs, which is estimated above 20 PBq for Cs-137 at units 2 and 3. This leads to significant interest in the retention of Cs on concrete during severe accidents (SA). However, the interaction of CsOH, as one of the main Cs forms released in SA, with concrete surfaces at elevated temperatures remains poorly researched. In this study, we have experimentally investigated the deposition behavior of CsOH on CaCO3, which is the primary phase existing on the surface of concrete, under humid atmosphere. As a result, the chemical reaction enhanced deposition rate (N), and increased linearly with CsOH concentration (Cg), as following expression:N(µg/cm2.s)=vdCg, where vd is temperature-dependent deposition velocity as given by lnvd(cm/s) = -3785.8/T + 3.766, for T in the range of 170 and 290 °C.This empirical model can be integrated into severe accident codes to quantify the chemical trapping of cesium on concrete surfaces during ex-vessel release. Moreover, it can contribute to understanding the reasons behind the high dose rate on concrete shield plugs at the Fukushima Daiichi Nuclear power stations and aid in developing effective decommissioning practices for concrete structures.

RESEARCH OF SEALING KNOT OF WELLHEAD

The article covers data on the investigation of line heads, their assortments, and the fixing component used to suspend the security pipes during the wellhead supply subsequent to boring is done, as well as bringing down and solidifying the creation line and penetrating the concrete module the pipeline (would it be a good idea for it be found that a concrete plug exists in the line while estimating the concrete behind the line with an electric thermometer). Keywords: wellhead, security pipeline casing, sealings, wedge, cuff, metal sealing, Hanging - sealing.

Development and assessment of sustainable steel-concrete composite beams with novel demountable shear connections

The design of sustainable steel-concrete composite beams (SSCCBs) with demountable shear connections (DSCs) for deconstructability can improve the problem of construction and demolition waste during these construction activities, and it also strengthens the sustainability of a building by allowing for easy dismantling and the reuse or recycling of structural components at the service load and easy replacing the damaged members to achieve the resilience capacity after earthquake. In this study, the structural configuration and concept design of novel SSCCBs using DSCs were firstly introduced. The nonlinear finite element models (FEMs) using the Abaqus software were validated in terms of the load versus mid-span deflection curves and failure modes of the similar composite beams given by the experimental data. A parametric study was implemented to identify the influence of the following variables: geometric size, strength grade, inclination angle and shape of concrete plug, diameter and strength grade of connected bolt, steel grade and width and grade of slab concrete. It was found that geometric size, grade and smooth shape of concrete plug could optimize the performance level of occupancy while bolt diameter and grade enhanced the reuse behavior at service loads. Additionally, increasing the bolt diameter and steel grade led to an increase by 8–10% in the equivalent ultimate strength and to decrease the ductility of the whole beams obviously. Bolt diameter, steel grade and slab width have quite influences on the stiffness due to increase the interaction degree of these prefabricated components. Based on the theoretical and parametric analysis results, simple design method of ultimate moment capacity for this SSCCBs with DSCs is proposed to facilitate design practice.

Numerical modelling of a large-diameter sealing structure in a deep radioactive waste repository

Numerical modelling of a large-diameter sealing structure in a deep radioactive waste repository

Scavenging of laser-generated aerosols with electrostatic-charged spray droplets

At the Fukushima Daiichi nuclear power station, high radiation hot spots were found at the concrete shield plugs above the Primary Containment Vessel (PCV), indicating that radioactive material may have flowed into narrow gaps at the upper part of the reactor building. High-power fiber lasers can be the preferred choice for cutting fuel debris and cleaning high radiation hot spots due to their advantages over conventional mechanical removal methods. However, laser decontamination generates submicron radioactive particles that pose a risk of internal dose to workers if dispersed. Effective confinement and scavenging are critical to reducing the risk of radiation exposure during decommissioning processes at the Fukushima Daiichi nuclear power station. Various other industries such as coal, mining, and chemical produce flue gases that contain particles smaller than a micron in size, which are harmful to both the environment and human health. To understand the feasibility of implementing an electrostatically charged spray to capture the aerosol particles in decommissioning applications and other industries, laser cleaning experiments were conducted inside UTARTS (University of Tokyo Aerosol Removal Test with Sprays) facility with a class-4 laser having maximum irradiation power of 1.5 kW. Various test samples made of carbon steel (CS), stainless steel (SS), and concrete were coated with CeO2 and cleaned using the laser. The aerosol particles generated during laser decontamination were confined inside the UTARTS and captured using a spray and electrostatic droplet charging system. The study proposes the use of a charged spray, which proves highly efficient for scavenging aerosols generated through laser irradiation. This technique can be used to efficiently decontaminate radiation hotspots adhering to shield plugs, PCV walls, and structures to ensure the safety of operators in high-dose environments and extend the operating time of electronic devices.

Detection of potential voids in the granulated bentonite mixture and concrete plug in the Full-scale Emplacement experiment using a parallel-wire cable as an extra-long TDR waveguide

For quality control of a concrete plug constructed for the Full-scale Emplacement (FE) experiment at the Mont Terri rock laboratory and to monitor the backfilling of granulated bentonite, a commercial parallel-wire cable designed for audio speakers was applied as an extra-long time-domain reflectometry (TDR) waveguide. A procedure for estimating the length and position of a potential air void was first established based on laboratory test results. Three cables with a length of 8.0 or 8.5 m were installed along the lined perimeter of the tunnel with a diameter of about 2.7 m. The first cable in the granulated bentonite detected the potential presence of two air voids, 0.79 and 1.17 m in length along the cable, on either tunnel shoulder. Their positions suggested that the voids could have resulted from the flow of granules on both sides of the single screw feeder used to backfill the uppermost portion of the tunnel. The second cable in the concrete plug detected a potential air void (0.98 m in length along the cable) at the tunnel crown likely to have formed when fresh concrete was cast. The third cable did not show any sign of an air void in the concrete at the tunnel crown, implying that the void detected by the second cable was likely localized. The cables were also used to monitor resin-based contact grout injection. The data before and after grout injection suggested that the grout did not seep into the granulated bentonite behind the concrete plug and sufficiently filled gaps in the vicinity of the injection lines. Although the outcome above suggests a promising possibility for observation, it is based on our interpretation of the acquired data. There is no direct observation as of yet, thus, our interpretation remains to be verified when dismantling the FE experiment.

Radioactive Aerosol Control and Decontamination in the Decommissioning of the Fukushima Daiichi Nuclear Power Station

The recent Nuclear Regulation Authority evaluation report suggests that at the Fukushima Daiichi Nuclear Power Station, the concrete shield plugs above the primary containment vessel (PCV) have exceptionally high radiation levels in Units 2 and 3, which may increase the risk of radiation exposure during decommissioning operations. During the cleaning and disassembly of such radiation hot spots, it is expected that a large amount of submicron-sized radioactive aerosol particles will be generated, which may influence the decommissioning operation. In the present study, laser cleaning experiments were conducted at the University of Tokyo Aerosol Removal Test Facility to simulate aerosol scavenging during the laser cleaning process. The facility can reproduce multiple phenomena expected in actual plant decommissioning, such as laser decontamination and simultaneous mist and spraying operations. Through the work, we have developed effective aerosol dispersion control methods and strategies based on the joint use of water mist and water spray to reduce radiation risk in either laser cutting or other means of decontamination methods. Preliminary laser cleaning experiments on various coated samples were conducted to assess the aerosol removal efficiency using water droplets and mist. It was verified that the proposed method effectively cleans the radiation hot spots during the decommissioning process.

Demountable connections for enhanced resilience: An analytical and numerical assessment of steel-concrete composite beams

To improve the increasingly serious environmental pollution problems such as construction dust and waste in the process of construction and reconstruction phase, the full life-cycle demountable structures have attracted increasing interest in earthquake engineering. This paper describes a new type of demountable shear connection for the steel-concrete composite beams to realize reuse in full-life cycle at service loads and rapid return to occupancy after damage under seismic actions. The structural configuration and mechanical feature of this composite beam were first introduced. After the nonlinear finite element (FE) models using the Abaqus software had been validated against experimental data, a parametric study was carried out to understand the effect of bolt diameter, bolt strength grade, precast concrete plug size, strength of precast concrete plug and slab on the shear behavior of demountable shear connections at the component level. The results show that bolt diameter and strength grade have a significant effect on the shear capacity and stiffness, respectively. Besides, bolt strength grade and concrete plug size can improve the performance level of reuse and occupancy. Based on the FE analysis results, simple design calculation method for demountable shear connection is proposed. Finally, behavior of the proposed steel-concrete composite beam was also evaluated under two-point loading to exhibit the performance of reuse and replaceability in engineering practice.

Optimized Structural Design of Concrete Pile Plug in Steel Pipe Piles

Optimized Structural Design of Concrete Pile Plug in Steel Pipe Piles

Study on cesium compound formation by chemical interaction of CsOH and concrete at elevated temperatures

Recently, extremely high dose rates were detected in the three-layer concrete plugs of the units 2 and 3 at the Fukushima Daiichi Nuclear Power Plant. The high dose rates suggest that there are some trapping effects of radioactive materials on shield plugs when gas species and aerosols (e.g., CsOH, CsI) are released from reactor through the plug layers. To determine the trapping mechanism, concrete, rock-forming aggregates and relevant minerals are pulverized and mixed with CsOH monohydrate, followed by heating at different temperatures to clarify the chemical interaction. The results showed that interactions of CsOH and CaCO3 in concrete occurred even at room temperature to form Cs2CO3(H2O)3. The interaction with aggregates occurred above 100 oC and resulted in the formation of CsAlSiO4. Additionally, amorphous and crystalline SiO2 also interacted with CsOH, and formed CsHSi2O5 at around 250 oC. These results suggest that formation of Cs2CO3(H2O)3 might be one of the main trapping mechanisms at shield plugs because CaCO3 is commonly formed on concrete surface and reacts with CsOH at room temperature.

Study of engineering properties of low-pH self-compacting concrete for concrete plug

Engineered Barrier Systems (EBS) is the primary concept in the design of the Geological Disposal Facility (GDF). In the design of EBS, bentonite is usually used as a buffer/backfill material. Due to its unique design, the concrete plug, used to close the junction between the transport tunnel and the disposal tunnel, is made of self-compacting concrete. Because the high pH solution in normal concrete reduces the performance of bentonite, low-pH self-compacting concrete with pH value less than 11 must be used to manufacture concrete plug. The silica fume (SF) and fly ash (FA) were used as mineral admixtures to discuss the effect of the mineral admixture addition level, Increased use of cementitious materials, and w/p on the engineering properties of Low-pH Self-Compacting Concrete (LPSCC). The test result shows that adding SF and FA could effectively prolong the setting time. Using only SF, the initial setting time of the mix increased up to 4.2 h with the addition of 40 wt% SF, while the combination of 40 wt% SF + 10 wt% FA could also increase the initial setting time to 3.92 h, which was much longer than 2 h working time requirement. Furthermore, at 90 days of curing, the pH value of each mixture was lower than 11, while the compressive strength enhanced to 118–132% compared to the control group. This addition could increase compactness, which leads to relatively strong sulfate resistance. The compressive strength could be enhanced by increasing the cementitious materials, which in turn, increases the pH and dry shrinkage. The LPSCC would lose strength when the w/p was reduced. The SF reacted with Ca(OH)2 in the LPSCC to generate a C-S-H gel. It was the primary factor in the drop of pH. The existence of SF and FA improved the pore structure in the matrix, compacting the structure of LPSCC. All that has been stated above are the dominant mechanism for improving the engineering properties. The pH value of mixture B300W29 was only 10.6 at 90 d, and the compressive strength could reach 61.66 MPa. Moreover, its drying shrinkage was about 0.047% at 90 d, and 0.055% at 150 d. Therefore, it should be considered as a potential material for concrete plug. The swelling property of bentonite was tested to validate the LPSCC material. No evident influence on the swelling property of bentonite was found. Replacing the conventional concrete with the designed material in disposal facilities can effectively enhance safety.

Developments of prefabricated steel-concrete composite beams with novel steel-yielding demountable bolt connectors

This paper developed prefabricated steel-concrete composite beams (PSCCBs) with novel steel-yielding demountable bolt connectors (SYDBCs). This new connecting system adopted the post-installed bolts and concrete plug blocks to interlock the prefabricated concrete slab and underneath I-beam, which significantly improves the construction efficiency. The concept design of the PSCCBs with SYDBCs was firstly introduced. Followed, four push-out tests with PSCCBs using SYDBCs were tested to investigate their shear behaviours at the component level. Push-out test results showed that compared with the casted-in bolt connectors, the developed SYDBCs slightly reduces the shear stiffness (about 20%) and yielding load, but does not affect their ultimate shear strength. Moreover, the SYDBCs exhibit better shear ductility than the casted-in bolt connectors with the same size. Two PSCCBs designed with post-installed normal bolts (NBs) and SYDBCs were also tested under two-point loading to study their ultimate strength behaviour. Test results showed that PSCCBs using SYDBCs exhibited reduced elastic stiffness (by about 22%), but equivalent ultimate strength (difference is 3%) to those PSCCBs using casted-in bolt connectors. Finally, two T-joints using the casted-in steel-concrete composite beams and PSCCBs with SYDBCs were tested under cyclic loading to study their seismic performances. Using SYDBCs has quite limited influences on the stiffness, ultimate bending resistance, and energy dissipation of the T-joint with composite beams (reductions equal to about 10%). This further confirms the applicability of the developed SYDBCs for the PSCCBs in steel framed buildings.

Optimization design of a large-scale seepage control system at a high arch dam site

The Baihetan Hydropower Station, located in the lower reaches of Jinsha River in southwest China, is the second largest hydropower station in the world. The site is characteristic of extremely complex geological and hydrogeological conditions, with fractures, faults, and shear zones that make water tables wedge-shaped. A large-scale seepage control system that contains grouting curtains covering an area of 780,000 m2 and 12,300 drainage holes, together with concrete plugs, were designed to control the seepage in the dam foundation and in the underground powerhouse areas as the reservoir water level will be raised by 225 m during operation. How to assess the performance and optimize the design of seepage control system becomes a key technological issue in the design and construction of this project. In this study, a three-dimensional finite element model that well represents the site conditions is established. The drainage holes are modelled with a substructure technique and the seepage field is solved with the variational inequality method of Signorini’s type. A procedure is proposed to optimize the layout of the seepage control system by taking the amount of leakage, the distribution of uplift pressure, the risk of seepage erosion and cost into account. Numerical results yield the appropriate parameters for the seepage control system, including the extension and depth of grouting curtains, and the spacing of drainage holes. With these optimized parameters, the seepage control system is effective in lowering the phreatic surface and limiting the amount of leakage at the dam site.

Execution of Safe Blasting Under Adverse Conditions of a Powerhouse Complex: A Revisit to Sardar Sarovar Project, India

When the excavation of the underground powerhouse of the Sardar Sarovar Project, India was nearly complete, cracks were observed on the upstream and downstream walls of the powerhouse, and the installed instrumentation readings sounded an alert for the instability of the powerhouse cavern that could possibly derail the project, further excavation in the powerhouse cavern was halted. After completing stabilisation measures, the remaining underground excavations by drill and blast method were to be completed. This paper revisits case studies of controlled blasting for the remaining excavations, namely a construction ramp, turbine pits, draft tube tunnels connecting the powerhouse, and the concrete plugs erected at the exit ends of the draft tube tunnels. To ensure overall stability around the excavations, blast vibration was controlled by planning the excavations in proper sequences. The damage outside the planned line of excavations was controlled by adopting modified line drilling/smooth blasting techniques. The details of the sequence of excavations, drilling and blasting parameters, compiled from previous publications, are presented in this paper. This paper also describes the reasons why concrete plugs were erected in the draft tube tunnels, the details of the concrete plugs, the optimised drilling and blasting procedure for safe removal of the plugs, and the method adopted to quantify the damage.

Experimental Insights into Concrete Flow-Regimes Subject to Shear-Induced Particle Migration (SIPM) during Pumping.

In this paper, the authors have focused on shear-induced particle migration (SIPM), its effect on concrete flow patterns, and lubricating layer formation during pumping. For this purpose, various volume-fractions ϕ of aggregates were selected. The particle migration was analyzed by applying two methods: sampling hardened concrete exposed to pumping and performing X-ray microcomputed tomography (μCT) and image analysis to determine the thickness of the lubricating layer due to SIPM. The results indicate that the first approach is unsuitable due to the nearly equal molecular density of particles and matrix. The second approach indicated that the actual thickness of the lubricating layer depends on the discharge rate as well as on ϕ and viscosity of concrete bulk; hence, it cannot be defined as a constant parameter for all concrete mixtures. Additionally, the concrete pipe-flow pattern, i.e., plug versus shear flow, was captured and studied while considering pumping pressure and discharge rate. It was concluded that particle migration is essential in the cases of both flowable and very flowable concretes with a high volume-fraction of solids. The changes in rheological properties caused by SIPM are severe enough to influence the definition of the flow pattern as plug or shear and the discharge rate of pumped concrete as well.

Comprehensive Method to Test the Stability of High Bedding Rock Slop Subjected to Atomized Rain

In the construction of high dams, many high rock slope failures occur due to flood discharge atomized rain. Based on the steel frame lifting technique and strength reduction materials, a comprehensive method is proposed in this paper to study the stability of high bedding rock slope subjected to atomized rain. The safety factor expression of the comprehensive method and the evaluation method for deformation instability were established according to the similarity theory of geomechanical model, failure criterion, and mutation theory. Strength reduction materials were developed to simulate the strength reduction of structural planes caused by rainfall infiltration. A typical test was carried out on the high bedding rock slope in the Baihetan Hydropower Station. The results showed that the failure modes of the bedding rock slope were of two types: sliding–fracturing and fracturing–sliding. The first slip block at the exposed place of the structural plane was sliding–fracturing. Other succeeding slip blocks were mainly of the fracturing–sliding type due to the blocking effect of the first slip block. The failure sequence of the slip blocks along the structural planes was graded into multiple levels. The slip blocks along the upper structural planes were formed first. Concrete plugs had effective reinforcement to improve the shear resistance of the structural planes and inhibit rock dislocation. Finite element method (FEM) simulation was also performed to simulate the whole process of slope failure. The FEM simulation results agreed well with the test results. This research provides an improved understanding of the physical behavior and the failure modes of high bedding rock slopes subjected to atomized rain.

A detailed investigation on thermal behaviour of slim floor beams with web openings at elevated temperatures

Purpose In recent times, the use of steel sections with web openings has become common as slim floor beams because they offer a reduction in weight of the steelwork, accommodate services within the floor depth and provide the composite action. The composite action in these beams is achieved either through the concrete dowels or through concrete plugs. Though these web openings offer several benefits in slim floor beams, they induce the material discontinuity in the steel web, which may affect their shear capacity and/or thermal behaviour. The purpose of this study is to investigate the thermal behaviour of slim floor beams with web openings in fire. Design/methodology/approach This research presents findings from experimental and analytical investigations conducted to study the thermal behaviour of slim floor beams with web openings in fire. For this purpose, an experimental investigation was conducted, which shows that the presence of web openings has a major influence on temperature development across the steel section as well as along the span of these beams. The behaviour of the tested slim floor beam is validated using finite element modelling. The validated finite element model is then used to conduct a sensitivity study to analyse the influence of different opening spacings, sizes and shapes on the thermal performance of slim floor beams in fire. Findings Test results show that the presence of web openings has a major influence on temperature development across the steel section as well as along the span of these beams. Temperatures on the web below the openings are found to be higher as compared to those recorded on the adjacent solid steel web. It is also observed that temperatures on the steel web above the openings are lesser than those on the adjacent solid steel web. Parametric studies conducted using the verified analytical modelling methods show that different opening spacings, sizes and shapes have a variable impact on the thermal behaviour of slim floor beams in fire. Closely spaced and larger opening sizes were found to have a more severe influence on their thermal behaviour in fire as compared to widely spaced and smaller openings. It was also found that the behaviour of these beams is influenced by the shape of the openings with rectangular openings resulting in more severe thermal distributions as compared to circular openings. Originality/value The findings from this research study are highly valuable as they contribute to the existing knowledge database. There is a lack of experimental and analytical investigation on performance of slim floor beams with web openings at elevated temperatures. The results and conclusions from this study will help in developing innovative designs for slim floor beams and will help in reducing the fire related risk associated with structures comprising of slim floor beams with web openings.

Experimental and numerical investigation on bearing mechanism and capacity of new concrete plug structures

The stability and safety of concrete plug structure of diversion tunnel is crucial for the impoundment of upstream reservoir in hydropower projects. The ongoing Wudongde hydropower plant in China plans to adopt straight column plugs and curved column plugs to replace the traditional expanded wedge-shaped plugs. The performance of the proposed new plug structures under high water head is then a critical issue and attracts the attentions of engineers. This paper firstly studied the joint bearing mechanism of plug and surrounding rock mass and found that the quality and mechanical properties of the interfaces among plug concrete, shotcrete, and surrounding rock mass play a key role in the performance of plug structures. By performing geophysical and mechanical experiments, the contact state and the mechanical parameters of the interfaces were analyzed in detail and provide numerical analysis with rational input parameters. The safety evaluation is carried out through numerical calculation of plug stability under both construction and operation period. The results indicate that the allowable water head acting on columnar plugs is 3.1 to 7.4 times of the designed water head. So the stability of the new plug structure meets the design code requirement. Based on above findings, it is concluded that for the studied project, it is feasible to adopt columnar plugs to replace the traditional expanded wedge-shaped plugs. It is hoped that this study can provide reference for other projects with similar engineering background and problems.

Controlled blasting in underground construction: A case study of a tunnel plug demolition in the Neelum Jhelum hydroelectric project

Blasting is a popular method of excavation in underground construction. Blast-induced vibrations, however, if not properly controlled, can negatively affect the rock mass surrounding the tunnel. During the drill-and-blast (D&B) excavation of twin headrace tunnels through a major fault zone below the Jhelum River, a 180-m3/h groundwater inflow occurred from the tunnel invert. A 610-m3 concrete plug and high-pressure grouting around the tunnel periphery were formed to stabilize the tunnel and control inflow. To complete the tunnel, the temporary tunnel plug was ultimately demolished using controlled blasting. Ground vibration monitoring data from the regular D&B operations were used to develop a site-specific vibration attenuation model. Using geotechnical data from the feasibility stage and tunnel mappings during construction, a critical particle velocity above which tensile cracking could be initiated was determined for the rock mass surrounding the plug. The critical particle velocity was incorporated into the vibration attenuation model to obtain permissible charge weights to limit blast damage to within a short distance from the charge. Using this approach, an innovative blasting pattern was adopted in which the tunnel plug was sequentially demolished by detonating a burn cut and separate contour blast rows. During blasting, rigorous supervision and data collection helped to record, evaluate, and when needed, adjust the blasting program. Overall, the tunnel plug demolition was completed in a safe and cost-effective manner.