Behavior Of Grouts Research Articles

Estimation of Viscosity and Yield Stress of Cement Grouts at True Ground Temperatures Based on the Flow Spread Test

The rheology of cement grouts often plays a crucial role in the success of rock grouting. In practice, the rheological parameters should be timely adjusted according to the evolution of grouting pressure, flow rate and injection time. However, obtaining the magnitude of rheological parameters is not easy to achieve under site conditions. More importantly, the ground temperature in deep rock masses is elevated higher than that on the surface or under room conditions, which has been demonstrated to strongly influence the rheological properties of grouts. Reasonable understanding and control of the rheological behavior of cement grouts at true ground temperatures is very important to the quality of grouting. This paper aims to propose a simplified method to approximately estimate the initial yield stress and viscosity of cement grouts for rock grouting under elevated ground temperature that actually exists in deep rock masses, on the basis of the flow spread test. The temperature investigated was controlled between 12 °C and 45 °C to simulate the true ground temperature in rock masses with a maximum depth of 1500 m below the surface. Taking the influences of elevated temperatures into account, a temperature-based model for estimating the initial viscosity of cement grout was successfully developed on the basis of Liu’s model and the results of the flow spread test. However, the yield stress failed to be estimated by the Lapasin model due to the absence of plastic behavior of cement grouts. In contrast, yield stress can be linearly correlated to the measured relative flow area. In this work, it was also found that the dependence of yield stress of cement grouts on relative flow area is a strongly exponential law. The temperature dependence of the viscosity of water was accounted for in both estimations of viscosity and yield stress of grouts. Significantly, it was found that the packing density of cement is dependent on the grout temperature, especially when the temperature is up to 45 °C. The proposed method in this work offers an alternative solution for technicians to reasonably control the rheological properties in the increasing applications of deep rock grouting.

The anoxic corrosion behaviour of carbon steel in anoxic alkaline environments simulating a Swiss L/ILW repository environment

AbstractThe Swiss waste management programme foresees that low‐ and intermediate‐level radioactive waste will be disposed of in a deep geological repository constructed in Opalinus Clay. Gas generation is expected in the repository due to the decomposition of organic materials and the corrosion of metals, with carbon steel being the primary source. The corrosion behaviour of mild steel under anoxic conditions has been studied over the course of several years to better understand the long‐term hydrogen evolution profile under anticipated repository conditions. Steel, either bare or encased within mortar, was tested in water vapour or immersed in electrolytes representative of aged cement waters at 50°C. The corrosion rate was measured indirectly through the hydrogen analysis using a solid‐state probe. The hydrogen evolution behaviour of grout was also monitored to more accurately determine the hydrogen generating from the corrosion of the embedded steel. For steel in water vapour or in alkaline environments, embedded in cementitious material or immersed in simulated aged cement pore water, corrosion rates were invariably <1 nm/year after several years of analysis.

Time-dependent rheological behavior of cement-sand injection grout containing high volume fly ash

Grouting technology is playing an increasingly important role in construction engineering. Various types of grout are available but cement slurry grouts are often selected for injection works due to better workability. Meanwhile, in repair works, cement-sand grout often preferred as the fine aggregates gives better volume stability for large repair area. However, theoretical research on the use of waste material to improve the rheological properties of cement-sand grout is still lacking. For grouts, rheology is a factor of prime importance to the transport, injection and pumping of the material. Cement-sand grouts often have poorer fluidity due to friction created by the sand. Since grouts typically contain cement, therefore fly ash can be a good option to improve the workability of the grout. This paper studies time dependent behaviour of the grout by measuring the flow times and viscosity of cement-sand grout containing high volume fly (HVFA) up to 1 hour from the time of mixing. The result indicates that replacement of HVFA reduces the flow time of the grout and maintained good fluidity up to 1 hour. The viscosity test showed that the grouts, at fresh state, behaved like a Bingham fluid by exhibiting lower viscosities for the mixtures containing fly ash at 0, 60 and 120 minutes. In conclusion, the use of large quantities of fly ash in grouts significantly enhances fluidity of the cement-sand grouts. Methodology comparison also resulted in new knowledge for best method flow test for fly ash grout.

Soil Interaction and Grout Behavior for the NREL Reference Monopile Offshore Wind Turbine

Monopiles for offshore wind are the most used foundations by farm operators due to their low production costs, when compared to other bottom-fixed or floating foundations. In this research, a monopile foundation for offshore wind power was evaluated for its soil interaction and grout behavior, and an appropriate numerical model for the structural analysis of the foundation and tower was developed. FAST 8, an aero-hydro-servo-elastic numerical code developed by NREL, was used to obtain the loads applied on the supporting structures. These loads were pre-processed before they were inputted on the finite element model, developed using the finite element software ANSYS. The considered conical grout connection, which connects the monopile to the transition piece through friction, was modeled under a changing-status nonlinearity condition. To model the soil–pile interaction, a p-y model was applied using the ANSYS APDL commands. Static, modal, and transient structural analyses were produced to study the structure suitability for its use on offshore environments. Different soil interactions were modeled, and their results were then compared within the transient and modal analysis, indicating that the angle of the grout connection strongly affects the loading conditions on the grout. Moreover, scouring affects the dynamic behavior of the overall supporting structures, thus protection against this phenomenon is suggested.

Shear stress limit, rheological properties and compressive strength of cement-based grout modified with polymers

Grouting is a comprehensive technology used in the construction projects due to the rapid development of sub-surface urban infrastructures, the main reasons for grouting soils are strengthened the cohesion-less soils and increasing the shear stress (pure shear) of the grouted soils. Providing high flowability with high viscosity for the cement-based grout in the liquid stage (slurry) and high compressive strength of the cement-based grout in the hardened stage are significant challenges. In this study, the impact of two types of water reducer [polycarboxylate (PCE)] polymer on the rheological properties with the ultimate shear strength and compressive strength of cement-based grout with water-cement ratios (w/c) of 0.6 and 1.0 at two different temperatures 25 °C and 50 °C were studied. XRD and TGA were used to analysis the cement, polymers, and cement modified with polymers. The behavior of cement-based grout in the liquid phase (slurry) and hardened phase modified with different percentages of polymer up to 0.16% (by dry weight of cement) were investigated. The compressive strength of cement-based grout modified with polymer was tested from the young age up to 28 days of curing. Vipulanandan rheological model was used to predict the shear stress-shear strain behavior of cement-based grout slurry and compared to the Herschel–Bulkley (HB) model. The rheological and the compressive strength are increased with increasing the of PCE content. The polymer modification increased the yield stress, apparent viscosity and plastic viscosity of the cement grout by 19–136%, 32–319% and 58–367%, respectively based on the types of polymer, polymer content, w/c, and temperature. The compressive strength of the cement-based grout increased by 94–786% based on the types of polymer, polymer content, w/c and curing time. Increasing the temperature of cement-based grout slurry to 50 °C increased the maximum shear stresses by 110% and 107%, respectively. Effects of polymer content, w/c, curing time and the temperature of the plastic and hardened properties of cement-grout were modeled using a multiple nonlinear regression analysis.

TGA, rheological properties with maximum shear stress and compressive strength of cement-based grout modified with polycarboxylate polymers

Grouting is a comprehensive technology used in the construction projects due to the rapid development of sub-surface urban infrastructures, the main reasons for grouting soils are strengthened the cohesion less soils and increasing the shear stress (pure shear) of the grouted soils. Providing high flowability with high viscosity for the cement-based grout in the liquid stage (slurry) and high compressive strength of the cement-based grout in the hardened stage are significant challenges. In this study, the impact of two types of polycarboxylate (PCE) polymer on the rheological properties with the ultimate shear strength and compressive strength of cement-based grout with water-cement ratios (w/c) of 0.6 and 1.0 at two different temperatures 25 °C and 50 °C were studied. XRD and TGA were used to analysis the cement, polymers, and cement modified with polymers. The behavior of cement-based grout in the liquid phase (slurry) and hardened phase modified with different percentages of polymer up to 0.16% (by dry weight of cement) were investigated. The compressive strength of cement-based grout modified with polymer was tested from the young age up to 28 days of curing. Vipulanandan rheological model was used to predict the shear stress-shear strain behavior of cement-based grout slurry and compared to the Herschel-Bulkley (HB) model. The rheological and the compressive strength are increased with increasing the of PCE content. The polymer modification increased the yield stress, apparent viscosity, and plastic viscosity by 19–136%, 32–319% and 58–367%, respectively based on the types of polymer, polymer content, w/c, and temperature. The compressive strength of the cement-based grout increased by 94–786% based on the types of polymer, polymer content, w/c, and curing time. Based on the Vipulanandan rheological model, increasing the temperature of cement-based grout slurry to 50 °C increased the maximum shear stresses by 110% and 107% respectively. The unprecedented conclusions can be drawn in this study, which is the effect of the polymer content, water-cement-ratio and temperature effect on the plastic viscosity, yield points and shear stress limit in the fresh stage (slurry) of the cement-based grout and also, the impact of the polymer content, water-cement-ratio and curing time on the flexural with compressive strengths in the hardened stages of the cement modified with polymers were modeled.

Time-dependent empirical model for fracture propagation in soil grouting

The fracture grouting method has been widely adopted to strengthen weak rock masses around tunnels and other underground constructions. However, the current understanding of fracture mechanism, especially in relation to the fracture propagation process, is still limited. This paper presents a time-dependent empirical model to describe the fracture propagation process in soil, and to show its change caused by increase of grout injections, which can also be used to obtain empirical solutions for the fracture thickness and grout driving pressure in two grout injections. The relation between grout behavior and soil reaction is modelled through a modified compression and recompression soil model. In case of two grout injections with the same injection point, a novel fracture geometry schematization has been developed, which can be represented as a radial plane with the injection point at the center. A series of numerical examples show that the grout driving pressure in the second injection can be 5–10 times larger than that in the first injection, while the fracture thickness can be 36–42% smaller. Finally, the fracture grouting test is performed to verify the suitability of empirical model to predict the fracture thickness and grout driving pressure in two injections. Comparison of theoretical values and experimental values shows that they match reasonably well with each other.

Rheological behavior of cement-based grout with Algerian bentonite

The rheological parameters, yield stress, flow index, consistency, and plastic viscosity of cement grouts are important parameters for the quality control of these materials. These parameters are assessed from the rheogram using a rheological model. Cement slurries without additive indicated a non-Newtonian type of rheological behaviour with yield stress. On the other hand, the mixtures containing a viscosifying agent exhibit a shear-thinning rheological behaviour which is much more important than the mixtures without a viscosifying agent. In this work, we formulated non-hydrated Algerian bentonite cement slurry in the presence of a superplasticizer. Cement was replaced cement by bentonite in five different substitution rates (2%, 4%, 6%, 8%, and 10%) and the water/binder ratio was fixed at 0.5. For this, various rheological tests were realized by using a controlled stress rheometer. In order to show the influence of bentonite on the rheological behaviour of the different grouts, several flow tests were carried out for a range of shear rates between 0.01 and 200 s−1. To properly adjust the different rheograms, various rheological models were used such as the models of Bingham, Herschel–Bulkley, modified Bingham, Casson, De Kee, Vom Berg, Yahia and Papanastasiou. For the correct choice of the rheological model, it was based on the calculation of the standard error. It was found that the rheological models of Herschel–Bulkley and Papanastasiou made it possible to better describe the flow curves compared to the other rheological models. It has been found that as the content of bentonite increases, the yield stress and the consistency evolve drastically, by cons the flow index decreases progressively.

Transient Response of RC Panel Protected with Slurry Infiltrated Micro Reinforced Concrete Jacket Under Blast Loading

With increase in terrorist attacks, there are definite priority to protect the important infrastructure facilities against possible terrorist attacks. In order to improve blast resistance capacity of RCC panel, in present study, it was strengthened with Slurry Infiltrated Micro Reinforced Concrete (SIMRC) jacket. . The SIMRC jacket strengthened RC panel was analyzed under blast load scenario using finite element method based application, ABAQUS. The dynamic behavior of concrete and grout of SIMRC was modeled using concrete damaged plasticity model. The structural response of RC panel without any strengthening was compared with SIMRC strengthened RC panel to investigate effectiveness of SIMRC jacketing to resist blast load. Parametric study was carried out considering SIMRC jacket on single side or both side of RC panel, with different ratio of thickness of jacket to thickness of RC panel (t/D) and different percentage of wire mesh reinforcement for jacket. Simulation of various analysis results were presented in form of displacement time history, distribution of tensile/compressive damage variable explaining the pattern of failure in the RC panel, comparison of distribution of tensile damage variable on front and back jacket, compression damage variable of RC panel. It was observed that for panels with strengthening displacement and damaged areas are reduced as compared to conventional RC panel. The increase in thickness ratio (t/D), percentage of wire mesh reinforcement in jacket also contribute to increase blast resistance capacity of SIMRC Jacket. It was also observed that the jacketing on both side of RC panel is more effective in reducing the displacement and the damage is observed to be spread over the support areas. Obtained results through present study demonstrate the effective use of SIMRC jacketing as blast mitigation measure.

Laboratory Investigation of Foam Grout Performance under Freeze and Thaw Conditioning

Foam grout is a fluid, self-leveling, and lightweight material with excellent load spreading and thermal insulation properties. These properties have contributed to foam grout being considered over its regular cement/water grout counterparts for many projects. Although applied in many successful cases, not much has been done to compare foam and regular grout behavior in cold regions. This research focused on the compressive strength of both materials before and after freeze/thaw cycles. Specimens were cured for different durations in a moisture room and conditioned for diverse freezing/thawing cycles to assess short- and long-term performance. The impact of immediate freezing was also evaluated for both materials. Foam grout’s ability to resist cold environments was explained using test results and visual analysis. At the end of the process, a material cost versus strength analysis was conducted with the intent of providing a reliable source of information when selecting materials to fulfill minimum industry specifications.

Influence of Segregation on the Rheological Behavior of Cement Grouts Determined by Coaxial Cylinder Rheometer

Influence of Segregation on the Rheological Behavior of Cement Grouts Determined by Coaxial Cylinder Rheometer

Filtration Behaviour of Cement-Based Grout in Porous Media

Filtration behaviour of cement particles, especially under the high grouting pressure with a rapid grout flow velocity, has a significant effect on the grout injection. However, there have been few studies on this field where the governing equation of this behaviour remains unclear. In the present study, a novel experimental procedure for grout injection was adopted to acquire the spatial and temporal variations in porosity and viscosity of high-speed grout flow in coarse sand. Experimental observations showed that there were dramatic variations in viscosity and porosity during the grout penetration within the first 50 s, suggesting that the high velocity had a significant influence on the distribution of the filtration coefficient. A model based on the Stokes–Brinkman (S–B) equation and advection–filtration equations was established to describe the filtration of grout flow in porous media. Meanwhile, numerical solutions from both the proposed model and traditional Darcy’s law were compared with experimental results. The comparative results showed that the proposed approach can match the laboratory tests well; the analysis indicated that Darcy’s law was unable to properly describe high-speed grout flow in porous media due to the lack of a shear force and the inertial term. Nonuniform filtration behaviour of cement grout flowing in porous media was revealed. Due to the nonuniform distribution of the pore velocity isoline caused by Poiseuille flow, it led to a heterogenous distribution of porosity as well. Parametric studies on the applicability of Darcy’s law and S–B equation for grout flow were discussed, in which an error of less than 10% was calculated when the Reynolds number was less than 2.5.

Factors affecting the performance characteristics of cementitious grouts for post-tensioning applications

In grouted post-tensioned (PT) systems, cementitious grouts are supposed to completely fill the interstitial spaces between the strands and act as the ‘last line defence system’ against corrosion. However, use of poor quality grout materials and grouting practices result in voided grout systems, ultimately leading to premature failure of tendons in many bridges around the world. To ensure an intact system, the grout must have excellent fresh properties, in particular the flow properties. Such high-performance grouts are not available in many developing countries, where grouting for post-tensioned structures is still a nascent technology. In this research, a two-stage test program was carried out to evaluate the fresh and hardened properties of seven commercial grouts, which includes three Pre-Packaged Grout mixes (PPG); three Site-Batched Grout mixes (SBG) and one standard Ordinary Portland Cement grout mix (PCG). Further, one PPG mix and SBG mix were chosen and their properties were evaluated for three levels of mixing speed and two ambient temperature conditions. Fresh properties such as wet density, efflux time and its retention, standard bleed, wick-induced bleed and pressure bleed, as well as set/hardened properties such as setting time, compressive strength and volume change were evaluated. Three batches of grout were tested for each grout material, to ensure reliability of results. The influence of binder fineness on the performance of grouts was also evaluated. The study serves as a strong evidence in substantiating that the most commonly used grout materials for PT system in developing countries, fail to meet the standard requirements and even the manufacturer’s own specifications. It is also found that the performance of the grout is influenced by mixing speed, ambient temperature, and fineness. The study emphasises that the evaluation of the grout behaviour under simulated field conditions is essential to ensure void free and durable PT systems.

A study of the shear behavior of a Portland cement grout with the triaxial test

Numerous research has been conducted on the axial performance of cement-based grouts. However, much less work has been focused on the shear behavior of cement-based grouts. In this study, the shear behavior of a Portland cement grout was investigated with the triaxial test. Cylindrical samples with two different water-to-cement (w/c) ratios: 0.42 and 0.35 were cast and prepared. In the test process, a series of confining pressures was applied on the samples and the confining pressure was ranged from 1 MPa to 35 MPa. The results show that there is a bi-linear relationship between the maximum vertical stress and the confining pressure independent of the w/c ratio. Low w/c ratio can effectively increase the maximum vertical stress of grouts. Mohr-Coulomb models were used to fit the shear strength envelopes of grouts. The results show that the shear strength of grout with a w/c ratio of 0.35 is much higher than that with a w/c ratio of 0.42. When a w/c ratio of 0.42 was used, the grout has a cohesive strength of 31.4 MPa and an internal friction angle of 15.1° while when the w/c ratio was decreased to 0.35, the cohesive strength of grout increases to 34.2 MPa and the internal friction angle rises to 24.3°.

Shear behaviour of a cement grout tested in the direct shear test

Portland cement grouts are widely used in the mining industry to bond cable bolts with the surrounding rockmass. Numerous laboratory and field tests showed that bond failure of the cable/grout interface is the dominant failure mode. Previous research has found that shear behaviour of the grout along a pre-defined plane plays a significant role in determining the nature of the bond failure in a cable bolt reinforcement system. In this study, the shear behaviour of a Portland cement grout was investigated based on a direct shear test. Two different boundary conditions were considered being a constant normal load (CNL) and constant normal stiffness (CNS). Under CNL condition, five different normal pressures between 0.1 MPa and 6.0 MPa were examined. While under CNS condition, the initial normal pressure was set to value within the same range. Also, a CNS of 10kN/m was added. The cohesion, internal friction angle and shear strength of the grout were acquired. The results showed that there is a linear relationship between the shear strength of the grout and resultant normal pressure. However, under the CNS condition, the shear strength of the grout was found to be generally higher comparing to the CNL condition, most likely because sample dilation resulted in an increase in the normal pressure. Consequently, shear strength of the grout also increased.

Strength and filtration stability of cement grouts at room and true tunnelling temperatures

The overall objective of this work, carried out under the research project “True Improvement in Grouting High pressure Technology for tunnelling (TIGHT)” is to understand the behavior of cement grouts under true tunnelling conditions. This paper describes a systematic laboratory study to characterize uniaxial compressive strength (UCS) and filtration stability of grouts made up of three types of cement commonly used for tunnel grouting in the Nordic countries. Since in-situ tunnel conditions are different from those of the laboratory in terms of temperature, we made various cement grouts at different temperatures and tested in the laboratory. The water cement ratios of 0.6, 0.8, 1.0 and 1.2 were used for all three cements and grouts were made and cured at two temperatures; 8°C and 20°C. Strength of a total of 96 cylindrical specimens of 4 and 7days age and permeability of four specimens of 7days age were measured. Filtration tests were done for 36 cement grouts. Results of the laboratory tests show that strength of samples cured at 8°C is lower than those cured at 20°C. Strength of grout specimens decreases dramatically with increasing w/c ratio. Filtration of cement grouts at 8°C is not that different from those at 20°C and filtration stability increases with increasing water-cement ratio. Permeability of cylindrical specimens of different types of cement varies several orders of magnitude; from nano- to milli-Darcy.

A new prediction method for the rheological behavior of grout with bottom ash for jet grouting columns

Among the many variables involved in jet grout technology, dealing with the complex phenomena of grout flow, specifically related to the pumping pressure (shear stress), the pumping rate (shear rate) and the viscosity, mostly becomes a difficult task for grouting in practice. Thus, this study presents the capability of a new methodology in soft computing techniques, called gene expression programming (GEP), to predict the rheological behavior (i.e., the shear stress versus the shear rate and the viscosity versus the shear rate) of grout with bottom ash for jet grouting columns, as an alternative approach to traditional methods. For this purpose, shear stress and viscosity formulas, including the main input variables of the shear rate and bottom ash proportion, are derived using GEP modeling through the stages of production and testing. Then, the performances of the GEP formulas are compared with the measured data and the regression and conventional rheological models (De Kee and Robertson-Stiff) for use in practice. The results indicate that the GEP formulas are able to yield estimations with good precision resulting in better predictions (R≥0.96) compared to the regression model. A successful description of the pseudoplastic response of rheological behavior is given, and a response consistent with conventional rheological models is obtained. Moreover, the measured data (shear stress and viscosity) generally follow the GEP modeling well, but the level of satisfaction is more favorable at high proportions of bottom ash. In conclusion, the study reveals that the derived GEP formulas are relatively promising for estimating the pumping pressure, the viscosity and the pumping rate of grout with bottom ash for jet grouting columns, at least in assisting conventional methods for preliminary designs.

Properties of cement grout modified with ultra-fine slag

The purpose of the study is to obtain a cement grout with improved performance. The grout mixes of the present study contain cement, ultra-fine slag (UFS), super plasticizer and water. Properties like flowability, bleeding, compressive strength and shrinkage of cement grouts have been studied. Rheological parameters were also studied in order to explain the grout workability. The results show that, cement replacement with slag in grouts could reduce bleeding substantially without affecting the workability of the mixes. Introduction of slag enhanced the compressive strength and reduced shrinkage reasonably. Ultra-fine slag can be used as a supplementary cementitious material in cementitious grouts in order to improve the grout behavior.

Model study and 3-D numerical analysis of vertical micropile subjected to oblique pullout loads

Details of three-dimensional numerical study on 20 mm gravity grouted and centrally reinforced vertical micropile of 600 mm length in uniform sand bed subjected to pull-out loads of inclinations 0°, 5°, 10°, 15°, 20°, 30°, 45°, 60°, 75° and 90° carried out through ABAQUS are presented in this paper. The results of the model study carried out by the same authors on the same micropile subjected to pull-out loads at the same inclinations were used to calibrate the numerical model as well as to compare the analysis results. Axial and lateral load results of the model study were used to calibrate the numerical model. The calibrated numerical model was used to understand the behaviour of micropile at various inclinations of pull-out load. The results of experimental and numerical studies were compared. A reasonably good agreement was found between the two studies. To simulate the behaviour of soil i.e. sand, Mohr–Coloumb constitutive law was used while linear elastic model was used for modelling of reinforcement bar. Linear elasto-plastic constitutive model was used to define the stress–strain behaviour of grout. Interactions between the grout and sand as well as grout and reinforcement bar were modelled using surface-to-surface contact elements approach based on slave–master concept. The results are shown in terms of load-displacement curves. To gain further insight about the behaviour of micropile, horizontal displacement, bending moment and net lateral soil pressure profiles along the length of micropile were also plotted for different inclinations of pull-out load from the numerical study results.

Full-scale modeling tests and numerical simulation of infilling behavior of plastic grout

Full-scale modeling tests and numerical simulation of infilling behavior of plastic grout