Grouting Conditions Research Articles

Effect of grouting quality on flexural behavior of corroded post-tensioned concrete T-beams

The durability of post-tensioned concrete (PTC) bridge structures has been greatly threatened by the corrosion of steel strands, especially in the case of insufficient grouting. In this paper, the effect of grouting quality on flexural behavior of corroded post-tensioned concrete (CPTC) beams is experimentally investigated with two groups of T-beams, i.e., five fully grouted beams in Group A and five partially grouted beams in Group B. Results indicate that when the mass loss of steel strands in Group A ranges from 0 % to 10.47 %, the cracking load decreases by 5.8821.57 %, and the ultimate bearing capacity decreases by 5.45–30.45 %. While for Group B, when the mass loss of steel strands ranges from 0 % to 14.26 %, the cracking load decreases by 3.75–25.00 %, and the ultimate bearing capacity decreases by 7.41–44.91 %. It is observed that as the degree of corrosion increases, both cracking load and ultimate bearing capacity of the beam gradually deteriorate, with the flexural capacity of partially grouted beams deteriorating faster. Built on this and with the model of bond reduction coefficient, an analytical method is proposed to predict the flexural capacity of CPTC beams under different grouting conditions. The developed method provides good predictions compared with experimental results of current study and from literature, paving the way for accurate assessment of the flexural bearing capacity of PTC beams with different grouting qualities in corrosive environments.

Effects of Grout Condition on Galvanic Coupling and Hydrogen Absorption in Post-Tensioned Bridge Tendons Constructed with Galvanized Steel Ducts

There has been concern that prestressing structural steel contained within galvanized bridge tendon ducts may become embrittled due to excessive galvanic coupling with the duct which may be exacerbated by deficiencies within the grout fill. This work strives to quantify the level of galvanic coupling achievable as a function of grout conditions and assess whether such conditions may promote water reduction and hydrogen absorption. Experimental tendon assemblies were used to quantify galvanic coupling considering a single prestressing steel wire and various grout conditions. The results were related to more realistic geometric configurations by simulations considering a range of possible kinetic boundary conditions. A model is used to estimate the amount of hydrogen that may be absorbed as a function of time considering the coupling current density.

Experimental study on grouting inspection of PC tendons by means of Ultrasonic Pulse Echo Tomography method

Evaluation of grouting condition of post-tensioned tendons in Prestressed Concrete (PC) structures is an important problem in a field of maintenance of civil engineering infrastructure. Existing methods of non-destructive testing (NDT) used for grouting inspection have some limitations. For example, Impact-Echo method has comparatively low accuracy and X-Ray method is expensive and time- and labor-consuming. At the same time, there are promising alternative methods of NDT, which can be used for grouting inspection. The authors carried out an experiment using several large-scale specimens simulating PC girders. Commercially available Ultrasonic Pulse Echo Tomography device with an array of dry-contact sensors was used. Several cases of grouting condition, PC sheath diameter and geometry and rebar placement were studied. It was confirmed that amplitude of reflected ultrasonic pulse in the case of not grouted PC sheath is larger, as compared with a case of a grouted PC sheath. However, depending on diameter of PC sheath, distance from PC sheath to concrete surface and presence of nearby reinforcement, evaluating grouting condition based only on amplitude of reflected ultrasonic pulse can be problematic. To solve this problem authors developed a more accurate method of evaluating grouting condition, which uses multiple parameters, such as amplitude of ultrasonic pulse reflected from PC sheath, backwall and phase of reflected ultrasonic pulse.

Experimental Investigation on Nonlinear Flexural Behavior of Post-Tensioned Concrete Bridge Girders with Different Grouting Conditions and Prestress Levels

Experimental Investigation on Nonlinear Flexural Behavior of Post-Tensioned Concrete Bridge Girders with Different Grouting Conditions and Prestress Levels

Reliability of ultrasonic tomography in detecting grouting defects in post-tensioned structures by PoD curves

The present research aims to assess the reliability of Ultrasonic Tomography (UT) of void detection in post-tensioning ducts due to inappropriate execution of grouting. The methodology is based on the construction of the Probability of Detection (PoD) curves for this specific non-destructive technique, by relating the probability of success to identify a specified ungrouted region. The PoD curves are built on data collected during a testing campaign in the laboratory, under fully known grouting conditions. Six walls containing prestressing strands and bars in metallic and plastic ducts with simulated voids of different sizes were designed and executed. Both water-filled (infiltration) and empty voids (ungrouted region) were simulated. The classical frequentist and Bayesian approaches are used to derive the PoD curves. Since the available experimental data are limited, the Bayesian approach provides more reliable data and is, thus, proposed as the best alternative. It is finally concluded that the minimum size of the voids in metallic ducts that UT can detect with 95% confidence and 90% probability, is around 30 cm and this value will be used in future inspection campaigns in posttensioned bridges.

Experimental investigation of the influence of head joints and grouting conditions on the shear strength of concrete block masonry

The nonlinear composite nature of masonry has limited theoretical understanding of material shear strength – especially with concrete block, where minimal experimentation has rendered the influences of two important variables (head joints, presence of grout) unknown. The effects of these variables were investigated experimentally on non-precompressed triplet specimens. Head joints did not influence shear strength statistically significantly: the proportion of grouted cores linearly increased shear strength. The provisions in the Canadian standard lacked accuracy when predicting partially grouted specimen strengths (overestimating up to 135%). Units from tested triplet specimens were also found to have similar compressive strengths to undisturbed units.

Micro-macro investigation on bio-cemented sand under different grouting saturation: An effective enhancement method

Microbial-induced calcium carbonate precipitation (MICP) is a new biotechnology that can be used to improve the strength of soils. Unsaturated soils are common in nature and saturation is a significant factor affecting the efficiency of bio-cementation. This study investigated the properties of MICP under different grouting saturation conditions. Unconfined compressive strength (UCS) tests confirmed that biocemented sand could get higher strength under unsaturated grouting conditions with the same calcium carbonate content which helps reduce the material cost. Scanning electron microscopy (SEM) test results show that at lower saturation, the size and amount of calcium carbonate crystals were insufficient but calcium carbonate mainly gathered between the particles. At higher saturation, larger calcium carbonate crystals were produced and exited in pores and on the particle surface, increasing the filling effect. Energy-dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) test results show that the dominant calcium carbonate morphology detected in samples was calcite, which was the most stable one. X-ray computed tomography (CT) test results show that after cementation, the measured contact surface area became uniform and the coordination number was higher. The flow direction of bacteria and the cementing solution did not induce significant anisotropy in the cementation process. The effective cementation and content of calcium carbonate jointly influenced the improvement of soil mechanical properties.

Numerical analysis method of equivalent deformation parameters for grouted arch dam abutment fractured rock masses considering scale effects and anisotropy

Research on the equivalent deformation parameters of grouted arch dam abutment rock masses has recently emerged as a key in the design, construction and stability assessment of arch dams. With the aim of synthetically considering scale effects and anisotropy of the rock mass equivalent deformation parameters after grouting, in this paper, a practical numerical calculation method is developed. First, the Latin hypercube sampling method is introduced to generate a network of fractures of the arch dam abutment rock mass. Subsequently, the finite element models of the rock masses with different sizes in various directions are constructed. On this basis, equivalent continuum theory and cohesive element model are applied for numerical calculation of grouting fractured rock masses. Then, the scale effect and anisotropy of the deformation modulus of rock mass under different grouting conditions are investigated. Finally, the Jinping super-high arch dam is taken as an example to validate the theoretical significance and application effect of the proposed method. The analysis results indicate that the process of fracture and fragmentation of grouted rock masses is characterized precisely, and the deformation of material units can be described as fully as possible to calculate more realistic equivalent deformation parameters of the fractured rock masses.

Axial load behavior of unreinforced and reinforced hollow interlocking compressed stabilized earth block masonry walls

This study investigates the axial load behavior of unreinforced and reinforced hollow interlocking compressed stabilized earth block masonry walls. Sixty walls were constructed and tested under axial compression. The variables include block type (unreinforced and coir fibre reinforced), grout condition (ungrouted and grouted), channel blocks, reinforcement type (steel bars and bamboo splints) and configuration (vertical and mesh type). The results show that addition of coir fibres significantly increase the axial load capacity and ductility of walls, regardless of all other variables considered. Grouting of masonry cores increases the load capacity of unreinforced and fibre-reinforced walls (without bamboo/steel reinforcement), however slightly affecting the deflection capacity. The channel block had a detrimental effect on the load and deflection capacity of both unreinforced and reinforced walls. Bamboo/steel reinforced vertically significantly contributed to the axial load and deformability of walls, despite the presence or absence of channel blocks. Both bamboo and steel reinforced walls behaved in a similar manner; yet bamboo splints showing slightly lesser load and deflection capacity than steel. The axial load and deflection capacity of bamboo reinforced grouted walls are about 78.54% to 90.00% and 79.50% to 94.60% respectively as compared to steel reinforced counterparts. Bamboo/steel mesh reinforced walls with channel blocks exhibited better performance compared to corresponding specimens with only vertical reinforcement. However, the improvement was marginal, due to larger spacing between the horizontal reinforcement. Nevertheless, the presence of horizontal reinforcement greatly improved the failure behavior by restraining the buckling of vertical reinforcement. Overall, fibre and vertical steel reinforced grouted wall specimens without channel blocks (FSVRGMW) showed the best performance in terms of compressive strength. The design equations in MSJC-11 predicted the load capacity of unreinforced and reinforced masonry walls more conservatively. Finally, it can be stated that MSJC-11 recommendation of internally reinforced grouted walls must be treated as unreinforced walls, if no horizontal reinforcements was provided, is not reasonable.

Experimental Study on the Proportioning of Grouting Materials for Fractured Roadways

For broken, low overall strength roadways, anchor cable and anchor mesh support are generally adopted. Sometimes, grouted anchor cable support is both an economical and safe support method. Therefore, the design of grouting materials and ratios plays a stewardship role. Through the proportioning experiments of cement slurry and water glass, a suitable proportioning scheme and the determination of various parameters were identified. According to the analysis of the test results, a slurry mixture of ordinary silicate cement with a water-cement ratio of 0.8 and water glass with a volume ratio of 1:0.5 is more suitable for the site grouting conditions.

Mechanical behaviour of grouted sands with acrylates and polyurethane resins

Chemical grouting is a technique where solution-based binders are used to improve both mechanical and hydraulic properties of the soil or rocks. The following research study shows an extensive laboratory programme where a polyurethane (PU) and an acrylate (AC) were grouted in a tertiary sand under different water contents and relative density, with different gelling time and grouting conditions. Unconfined compressive strength, splitting tests, triaxial tests and creep tests on the grouted materials were conducted. A statistical interpretation considering the kernel probability density function was performed in order to understand the interdependency of the changing parameters. In general, PU-consolidated samples provide higher mechanical properties with respect to ACs; however, the effects and the dependency on the geotechnical base parameters are different.

Study of Bearing Characteristics and Damage Law of Grouting-Reinforced Bodies

To explore solutions for reinforcement problems of broken rock masses in deep roadways, it is necessary to study the performance of cement-based grout and its reinforcement effect. In this study, grouting-reinforced specimens with different particle sizes of broken coal were made, which revealed the reinforcement effect of grouting on the bearing capacity of broken coal and the mechanism for secondary bearing damage and the instability of the reinforced specimens. First, it was determined that the appropriate water–cement ratio (W/C) to meet the field grouting conditions is 0.45. Second, the uniaxial compression of the grouting-reinforced specimens with 0.45 W/C was carried out, and acoustic emission equipment was used to detect it. Finally, through indoor experiments, this study investigated the differences in failure modes, stress–strain curves, and acoustic emission signal characteristics among intact coal samples, grouting-reinforced bodies with different particle sizes, and grouting-reinforced bodies after anchoring. The deformation and failure patterns of grouting-reinforced bodies were revealed, and the failure mechanisms of grouting-reinforced bodies with different particle sizes were elucidated.

Mechanism of Filtration Behaviors of Cement-Based Grout in Saturated Sand under Different Grouting Conditions

Cement-based grout has been widely used in various civil engineering applications. However, the filtration behaviors of it when grouting the porous geological masses vary a lot under different grouting conditions, which significantly influences its penetration and the enhancement effect. The purpose of this work was to better understand the filtration of cement-based grout in porous sand by conducting a series of visualized laboratory tests and EDTA titration tests. The experimental results show that the cement filtration, including the penetration, retention, and formation of cement filter cake above the grouting body, is collectively influenced by different grouting factors. With the increase of the soil samples’ pore size and the cement slurry’s water-cement ratio, the penetrated distance and amount of cement in sand increase. However, the penetration does not increase monotonically with the grouting pressure. Too excessive grouting pressure (e.g., 300 kPa in this study) accelerates the formation of cement filter cake and thus stops the subsequent cement infiltration. The mechanisms of different filtration behaviors were explained from microscopic particle clogging in the pore throat of the porous media. Furthermore, the reduced permeability of the sand column with the retained cement due to filtration was discussed, and the dewatering phenomenon of the cement slurry after filter cake formation was first revealed.

Using 3-D velocity contour plots to detect voids in grouted tendon ducts in post-tensioned concrete construction

3-D velocity contour plots are constructed to detect voids in grouted tendon ducts by a stress-wave test method requiring a receiver and a small instrumented hammer. Each time-domain waveform due to hammer impact is processed using the short-time Fourier transform to obtain the spectrogram (frequency-time relationship), which is enhanced using the reassignment method. The reassigned spectrogram is used to obtain the dispersion curve (velocity-wavelength relationship). The results from all test points are assembled to develop wave-velocity contour plots at different wavelengths. A wall specimen containing ducts with five different grouted conditions was constructed. Two types of test grids were used, namely latticed grids covering the entire wall surface and vertical grids directly above the ducts. For the former method, 3D contour plots of a large area can be constructed with few testing lines. For the latter method, the wave velocity contour plots can distinguish different grouting conditions. Finally, the wave velocity reduction to be expected for different grouting conditions and cover depth is provided.

Deformation recoverability of longitudinal joints in segmental tunnel linings: An experimental study

The shield-driven tunnel is a fabricated lining structure. The existence of longitudinal joints between segments in a ring makes the entire tunnel lining vulnerable to deformations, because the rigidity of longitudinal joints is lower than that of the main concrete segments. Large transverse deformation, accompanied by joint opening, is a common disease of shield tunnels. The aim of this work is to explore the deformational behaviors and mechanical properties of tunnel longitudinal joints under overloading, unloading, and soil grouting conditions, with emphasis on the recoverability of joint deformation. For this purpose, a series of laboratory tests have been carried out on the full-scale longitudinal joints at tunnel crown adopted in Shanghai metro tunnels, including three parallel tests with different overload levels and one cyclic overloading and unloading test. The full-scale testing considers the actual stress state of the longitudinal joint under different working conditions in real environments. The specimen of the longitudinal joint at tunnel crown adopts the actual three-segment-two-oblique-seam structure, which is different from the simplified two-segment-one-straight-seam form used in previous studies. Multiple deformation indicators, including joint opening, concrete strain, and bolt strain, are monitored and analyzed. Based on the test results, the effects of restoration actions, i.e., unloading and soil grouting, on joint deformation recovery under different overload levels are discussed. The change of recovery efficiency with the degree of joint deformation is also obtained. In addition, the deformation recoverability and rotational stiffness are compared between the longitudinal joint at tunnel crown which is subjected to positive bending moment and the longitudinal joint at tunnel springline which is subjected to negative bending moment. The test results show that the larger the joint deformation caused by overload, the lower the recovery efficiency. From a mechanical perspective, soil grouting is an effective measure to recover the large deformation of shield tunnels.

Improved technical guide from physical model tests for TDR landslide monitoring

Time-domain reflectometry (TDR) can help observe the initiation and evolution of localized shear planes in both rock and soil slopes, and has temporal and spatial resolutions suitable for landslide monitoring. An improved and standardized technical guide for TDR cable installation and data interpretation is needed to utilize it better. TDR technique involves sending an electromagnetic pulse into a coaxial cable grouted in a pre-drilled borehole, and capturing the reflected signal from cable deformity, which is triggered by the localized shear deformation in the underground. This study developed a large direct shear box for testing TDR responses in various cable-grout-ground assemblies, in order to reliably model the cable-grout-ground interaction at the localized shear. Different combinations of cable type, grout condition, soil type, and shear bandwidth were tested using the new physical model to re-examine TDR's response to ground deformation in sliding mode. The results revealed some misconceptions in previous studies that used cable-grout assemblies without considering the entire interaction with the ground. The implications of the experimental results are carefully considered and new technical recommendations are provided for cable installation and data interpretation to foster the improved use of TDR. A new data reduction method that involves data filtering, differential waveform, and three-sigma rule is proposed to support the recommended installation setup for robust early detection of a localized shear plane.

Seepage characteristics of chemical grout flow in porous sandstone with a fracture under different temperature conditions: An NMR based experimental investigation

In this study, the low-field nuclear magnetic resonance (NMR) testing technique was adopted to experimentally investigate the seepage processes of chemical grout flow in fractured rock under various temperatures and confining pressures. The variations in the NMR parameters, including the tested porosity, transverse relaxation time (T2) distribution and T2 peak area, were quantitatively analysed to study the seepage characteristics under different grouting conditions. The changes in the grout viscosity as a function of the temperature were studied. Then, the effects of injection pressures and temperatures on the seepage characteristics of porous sandstone with a single fracture and a constant confining pressure of 20 MPa were systematically investigated. The results indicated that the viscosity of the grout shows obvious time-dependent and temperature-dependent characteristics. The flow pattern of the grout is greatly dependent on the injection pressure, whereas it is less affected by the temperature. The permeability of the sandstone shows an increasing trend as the injection pressure increases and the temperature decreases.

Practical Cross-Section Imaging of External Tendons to Reveal Grout Deficiencies Relative to Strand Pattern

External post-tensioned tendons in concrete segmental bridges have had strand corrosion failures due to grouting deficiencies such as voids or bleed water. Nondestructive assessment of the grout condition is thus often needed, preferably by a cross-section imaging method. Here, a magnetic sensing approach to image the position of the steel strand bundle is combined with an electric impedance method to evaluate the condition of the grout space. Both are embodied in a device that images the tendon’s cross section. The magnetic sensor travels around the circumference of the tendon and measures the force of attraction to the steel strands from which an image of the strand pattern inside the tendon is created. Simultaneously, a traveling plate rotates around the tendon, and variations of the electric impedance between the plate and strands identify grout deficiencies. The impedance and strand position data create a complete color-coded image of the tendon cross-section flagging grout deficiencies. The approach was validated by experiments with tendon specimens with known deficiencies and under field conditions. The method is rapid, economical, easy to replicate, with a small and safe device not requiring specialized operator training.

Ultrasonic inspection of grouted splice sleeves in precast concrete structures using elastic reverse time migration method

Precast concrete (PC) structure has been widely employed for building construction in recent years, and grouted splice sleeve is commonly used for component connection. The compactness of the grouted splice sleeve connections plays a decisive role in structural safety, especially for its capacity to resist an earthquake. In this study, an ultrasonic imaging method is proposed for inspecting the grouted splice sleeves in PC structures using reverse time migration (RTM) algorithm based on an elastic wave equation. Numerical and laboratory experiments are carried out to assess the feasibility of our proposed method. In the numerical experiment, three numerical models, i.e. three-quarter grouted, fully-grouted, and non-grouted, are established. The results show that the proposed RTM method can reconstruct images of the buried sleeves with a higher resolution and a greatly-improved accuracy, compared with the traditional ultrasonic imaging method. Moreover, the grouting condition in the three models can be readily distinguished and even the interface between the grouting material and the air defect in the three-quarter grouted model can be clearly identified. In the laboratory experiment, two sleeves, one is fully-grouted and the other one is insufficiently-grouted with certain air defects, are embedded in a concrete model. The top of the two sleeves can be clearly imaged, and the insufficiently-grouted sleeve has a reflection, which is about 9 dB stronger than the other one. We conclude that the proposed ultrasonic imaging method can be used for inspecting the grouting quality of splice sleeves in PC constructions in field.

Value of additional vertical deformations of foundations depending on injection grouting conditions

The possibilities of new construction in the center of Saint Petersburg are quite limited by the requirements for preserving the historical center and by the height restrictions, so the construction of underground space is of great importance for the developing city. Investors are ready to deepen basements and to excavate foundation pits in the courtyards of existing buildings to increase usable space, but before starting such works, a number of compensatory measures are required, one of which is strengthening of foundation bed and foundation body of affected buildings.