Strength Grout Research Articles

Mechanisms of fatigue degradation process in axially loaded grouted connections under submerged conditions

Grouted connections in offshore support structures bond overlapping steel tubes using ultra-high strength grout. These connections, used in jacket structures, face dynamic pulsating loads and submerged conditions. Current design guidelines offer simplified S-N curves that do not reflect realistic conditions for offshore wind turbines. This study introduces a new S-N curve for axially loaded grouted connections under submerged conditions, based on large-scale high-cycle fatigue experiments. It also analyses the degradation behaviour of cyclic axially loaded grouted connections to identify critical phase changes: stable, incremental, and progressive. The study examines the impact of different load levels on degradation, focusing on displacement between the pile and sleeve. Lower load levels result in longer stable and progressive phases. As load levels increase, the stable phase shortens and eventually disappears at the highest load levels. Damage within the grout material is categorised into crack-driven and crushing-driven patterns, with the latter linked to longer lifetimes. Even at the lowest load levels, minor damage occurs, precluding an endurance limit. This understanding of degradation mechanisms supports the assessment of grouted connections using monitoring systems.

Seismic performance evaluation of prefabricated concrete shear walls with anchorage defects

In this study, the effects of grouting sleeve anchorage defects on the seismic performance of prefabricated concrete shear walls were studied, and a fast after-damage retrofitting method has been proposed. Six specimens were investigated under cyclic loading. The parameter was the number of grouting sleeve anchorage defects, selected as 0, 2, and 4. The test was divided into two loading stages. During stage 1, the specimen was loaded until the strength dropped below 85 % of its peak strength. After stage 1, the damaged specimens were retrofitted using combined retrofitting method of steel plate and high-strength grouting material, and then subjected to loading tests in stage 2. The resulting damage characteristics, hysteretic behavior, stiffness, strength, and energy dissipation capacity were studied. The strength of the shear wall, considering anchorage defects, was calculated. The results show that anchorage defects reduce the seismic behavior of the specimens. Compared with the two defects, the strength of the shear wall with four defects did not significantly change, though the ductility coefficient and energy dissipation capacity decreased considerably. The combined steel plate-high strength grout retrofitting method could significantly improve the strength and energy dissipation and effectively restore the stiffness of prefabricated shear walls. The calculated strength of the shear wall is in good agreement with the experimental value, confirming that it is reliable and can be used to calculate the strength with anchorage defects. The proposed retrofitting method can provide a new choice for the fast damage repair of the post-earthquake shear walls.

Heterogeneous distribution of lightweight porous ceramic sands in a high strength cement grout

Material heterogeneity may occur to cement grouts especially when lightweight fine inclusions are used, however, the quantitative assessment still remains a challenging task. In this work, a lightweight ceramic sand (LCS) was adopted to partially replace a quartz sand (QS) for fabricating two grouts, namely LCS-GM and O-GM. The impacts of LCS on the flowability, expansion and compressive strength were first measured in laboratory tests. To approach the real construction conditions, the grouting materials were cast in 6-meter-long tubes, and the compressive strength and microstructure of the specimens at different depths were measured. X-ray computed tomography (XCT) was employed to nondestructively quantify the structure and distribution of the pores and LCS particles. Results demonstrated that the partial replacement of QS with LCS can decrease compressive strength, reduce expansion, but increase flowability. Both density and compressive strength increased linearly with depth. The long-tube casting entrapped more air voids for O-GM. Less air voids and LCS particles were detected for a deeper LCS-GM specimen. Tight interactions between the cement matrix and LCS particles were observed. The regimes of water release and air void accommodation by the porous LCS particles may account for the experimental observations. The findings provide a reliable way to fabricate lightweight and high strength grouting materials and deepen the understandings of material heterogeneity in cement-based materials.

Study on macro performance and micro-analysis of high strength grouting material

Wind turbine duct put forward higher requirements for the performance of grouting materials. In order to obtain more economical high strength grouting materials (HSG), three kinds of low price main components, cement, quartz sand (QS) and fly ash microspheres (MS) were utilized and developed. Macro performance and micro-analysis of the HSG were conducted. The macro performance tests revealed that the mix proportion of HSG is determined as, cement: QS: MS: superplasticizer: swelling agent = 80:10:10:0.3:0.12, water binder ratio is determined as 0.26. Compressive and flexural strength of the HSG exceeding 120 MPa and 20 MPa respectively. The HSG also showed good fluidity and homogeneity. The micro-analysis showed that a complete and continuous micro-structure was formed and interface transition zone could not be observed. XRD and TG-DSC results meant that the amount of AFt increased. On the contrary, the amount of Ca(OH)2 decreased. pore diameter of the HSG was mostly 10 nm. The addition of swelling agent and MS did not changed the types of hydration products of HSG, but the pore structure was optimized. Due to the cheap components, HSG contributed higher profits with the lower price, and which perform good economic benefits and market competitiveness.

Influence of the composite interface on the mechanical properties of semi-flexible pavement materials

Semi-flexible pavement (SFP) materials, composed of porous asphalt mixture (PAM) and cement-based grouting material, are multiphase composites commonly used in roadway construction. However, damage frequently occurs at the composite interface of two-phase materials, and most SFP research has focused on the design of grouting material, with insufficient attention given to the composite interface. This paper aims to investigate the effect of bonding properties between organic PAM and inorganic grout on the mechanical properties of SFP. To investigate the different bonding properties of the SFP asphalt-grout interface, a simple method was employed, in which PAM specimens were immersed in a silane coupling agent solution to form a layer of coupling agent on the PAM surface. A series of SFP specimens were created using PAM with a porosity of 28–30%, and different strength grouting materials (40 MPa, 60 MPa, 70 MPa), and three laboratory tests were conducted to evaluate their mechanical properties. The results demonstrated that the interfacial bonding strength between asphalt and grouting material significantly influences the low-temperature splitting tensile strength, uniaxial penetration strength and uniaxial compression strength of SFP. Compared to specimens formed from high-strength grouting materials, SFP specimens immersed in a silane coupling agent solution exhibited superior low-temperature splitting tensile strength (2.06 MPa > 1.97 MPa, 2.63 MPa > 2.34 MPa) and shear strength (7.28 MPa > 6.46 MPa, 7.97 MPa > 7.26 MPa). As a result, this study highlights the importance of considering the bonding properties of the asphalt-grout interface in the design and preparation of SFP. The results of this study can be useful for enhancing the performance and durability of SFP materials in a more economically efficient way.

Numerical model of cumulative damage evolution of offshore wind turbine grouted connection under cyclic axial load

GCs in OWTs are exposed to fatigue loads that can lead to damage of the grout before ultimate limit state is reached. A uniaxial and fatigue compression test of high strength grout material were carried out to obtain the compressive strength, failure mode, fatigue life and load-displacement relationship of test cubes. A uniaxial and fatigue tests were carried out on GCs specimens to study the damage evolution of the GCs. The fatigue test on GC was done by applying six incremental amplitude cyclic load ranges of 30%–80% of ultimate load on the GC. The scalar damage degradation parameter (SDEG) from the result of the numerical simulation was used to estimate a damage index which measured the cumulative damage evolution. The cumulative damage evolutions were influenced by the cyclic load amplitude. The larger the load amplitude, the higher the damage index accumulated. The numerical simulation results compared with the DNV code method showed that the DNV code predicted lower damage values for fatigue loads ratio of up to 0.725 and predicted higher damage values beyond the 0.725 loads ratio for the GC. The proposed numerical model predicted the laboratory test results of the grout cube and the grouted connections.

Frequency domain full waveform inversion with small‐scale laboratory measurements for reconnaissance in mechanized tunneling

AbstractIn mechanized tunneling, so‐called tunnel boring machines (TBMs) drill through the ground in an automatized manner. Therefore, the drilling process is very efficient but the maintenance costs are high. Seismic exploration seems appropriate to identify changing ground conditions in front of the TBM to reduce costs from damages of the TBM and from the corresponding dwell times. Today's seismic exploration techniques are using only a small amount of the information, which is contained in the seismic records from field observations, whereas full waveform inversion (FWI) tries to use the whole content. The potential of different FWI approaches for the application in mechanized tunneling has been investigated. An analysis of the performance of FWI not only employing synthetic examples but additionally measured waveforms is essential. Since seismic surveys at the construction side are not performed with FWI in mind, the data sets are usually not appropriate for testing the developed algorithms. Nevertheless, a validation of FWI approaches by measured waveforms is possible by using waveform recordings from a small‐scale experimental setup. A small‐scale super high strength grout specimen is constructed for validating an adjoint frequency domain FWI approach. Frequency domain models compute the seismic response of a system for an infinite time interval. The attenuation of the material as well as the attenuation effects at the free surfaces are hard to quantify over an infinite time interval. Therefore, the specimen is designed in a way that four of the six borders can be modeled as absorbing boundaries. For this purpose, the displacement recordings are truncated just before the waves that are reflected at the excluded borders arrive at the measurement points. This design in combination with a notch representing a rectangular tunnel makes the measurements more similar to data from a tunnel construction side. A rectangular hole is embedded in the specimen and acts as material discontinuity, which the FWI approach is aiming to detect.

Influence of Wet or Dry Conditions on the Fatigue Life of Grout Cementitious Materials under Cyclic Loading

Grouting cementing material is a kind of sealing cementing material widely used in underground space. However, the influence of the fatigue life after cementation hardening is often ignored when subjected to, for example, cyclic traffic loads. Therefore, it also often causes engineering problems such as joint cracking, leakage, and plate bottom emptiness. The prediction of fatigue life of grouting cementation material is of great significance to the stability of underground tunnel structure. In this paper, the fatigue characteristics of hardened grout specimens under different fatigue loads and cycle frequencies are studied. Test the cyclic compression load repeatedly in different environments (dry or wet). The results show that the fatigue properties of grout materials are reduced in both air and water and significantly reduced when the stress level is 65% or above of static compressive strength in wet environment, especially when the loading frequency in water drops from 10 to 35 Hz. The main mechanism of fatigue life decline is splitting effect caused by water extrusion in the sample under cyclic loading. Water washes away abrasive action in the cracks. The dry-wet fatigue aging characteristics of superhigh strength grout cement materials lay a foundation for the evolution simulation of underground foundation structures under cyclic loading.

Synergistic effect of polycarboxylate superplasticizer and silica fume on early properties of early high strength grouting material for semi-flexible pavement

Nowadays, the application of early high strength grouting material (EHSG) is in line with the development trend of semi-flexible pavement. In this paper, the synergistic effects of polycarboxylate superplasticizer (PCE) and silica fume (SF) on the properties of EHSG were studied. The results suggest that the flow time of slurry with high fluidity has a linear relationship with its dynamic yield stress. The mechanism of PCE and SF on rheological properties was analyzed via water film thickness (WFT), zeta potential, PCE adsorption, and SEM. It can be found that the crucial role of SF on slurry is to improve the adsorption of PCE on binders. The model describing the synergistic effect of SF and PCE on the particle aggregation of EHSG is proposed. SF addition weakens the interlocking effect and reduces the friction but may form the interparticle bridging effect between cement grains. PCE can not only inhibit the aggregation of cement grains but also mitigate the bridging effect of SF.

Monotonic and cyclic stress-strain models for confined concrete-masonry shear wall boundary elements

Simulation of the seismic response of fully grouted reinforced masonry shear walls (RMSWs) built with reinforced masonry boundary elements (RMBEs) necessitates reliable nonlinear models of their RMBEs. The axial monotonic and cyclic full stress-strain curves of RMBEs are essential for predicting the lateral cyclic response of RMSWs with boundary elements. Therefore, a reliable stress-strain constitutive model for the axial monotonic and cyclic behavior of RMBEs is required. The authors recently investigated the axial monotonic compressive behavior of unconfined and confined RMBEs built with different section configurations, vertical reinforcement arrangements, transverse confinement ratios, and different construction procedures. In the current study, the authors investigated the cyclic behavior of some RMBEs whose counterparts were previously tested under axial monotonic compression. In addition, more specimens with different confinement configurations and different grout strengths were tested. Comparisons of the test results showed that increasing the vertical reinforcement ratio increased the axial load carrying capacity of the tested RMBEs but decreased their strain ductility. In addition, using a low compressive strength grout significantly reduced the strain ductility of the RMBEs. Moreover, monotonic and cyclic stress-strain models for confined and unconfined concrete-masonry boundary elements subjected to axial compression loading were developed. The proposed models showed good-to-excellent agreement with the experimental results, predicting the stress-strain rising curve, stress drop, and postpeak behavior. Furthermore, unloading and reloading curves, strength degradations, and softening of reversal and reloading branches due to cyclic degradations were well captured by the proposed model.

Experimental research and finite element analysis on the seismic behavior of CFRP-strengthened severely seismic-damaged RC columns

This study describes a new strengthening technique that involves the combination of CFRP jackets, CFRP sheets and high- strength grouting material. Three different strengthening alternatives were employed to strengthen three severely damaged RC columns. Based on the experimental results, the failure mode, hysteresis curve, skeleton curve, ductility, energy dissipation ability, stiffness degradation and strength degradation of both the original and strengthened test specimens were compared and discussed. All three strengthened test specimens exhibited similar damaging processes, yielding of longitudinal reinforcement, cracks on CFRP jackets, rupture of CFRP sheets and collapse of high-strength grouting material were successively observed in the loading procedure. The results showed that the three strengthened seismic damaged concrete columns all presented a bending failure mode and met the “strong shear, weak bending” design attributes. Compared with the original columns, the ductility and energy dissipation capacity of the three strengthened test specimens were significantly improved, while the capacity and stiffness were not fully restored. Strengthened test specimen Z3-R, which was strengthened by the combination of CFRP jackets, CFRP sheets and high-strength grouting material, showed the best seismic performance among all three strengthened test specimens. A finite element model based on OpenSees was developed and validated by a comparison with experimental results. The effects of the axial compression ratio and thickness of CFRP sheets were also discussed through parametric studies.

The Behaviour of Shear Anchors with Different Grout Properties

AbstractDuring the assembling of a steel structure with anchors, grout should be used in connections between steel elements and a reinforced concrete support element. In horizontal and vertical joints, grout is used as a good construction practice for solving geometric tolerance problems. Grout can be used with cast‐in anchors or post‐installed anchors. However, the relation between anchor shear resistance and characteristic grout compressive strength is not described in detail in technical regulations. The behaviour of a connection considering achieved slip tolerances should match the boundary conditions set in the global analysis. In the support joint, grout properties could influence the value of the slip between a steel part and a concrete part of the joint. Slip value could be significant for the relevant design cases featuring the interaction of shear force and tension force. In this paper, results of the push‐out test conducted on anchors are presented. Based on the experimental test, the finite element analysis was performed to investigate the shear connection behaviour. According to the preliminary results, it can be concluded that a grout strength and a grout thickness influence the connection response when serviceability loads are applied, although they do not influence the ultimate load bearing capacity of anchors. In some cases, using the contemporary solutions of high strength grout materials, the slip between steel and concrete parts in the connection could be reduced.

GROUTED SLEEVE CONNECTION FOR PRECAST CONCRETE MEMBERS

Precast concrete structures have gained preference in the modern construction industry because of the multiple advantages they offer. The connection of precast members is an important aspect to consider in the design of structures with precast components. Grouted Sleeve connection, one of the famous connector types, is made of the trio of reinforced bars, high strength grouting materials and a ductile iron cylinder. This article compares the finding of recent experimental research findings on grouted sleeve connection and establishes the relationship between the three components of the connector to enhance the performance of the splicing agent. It is found that the tensile performance of the connector increases with the embedded length of the bar for a normal sleeve. An effective embedded length set between 6 and 8 times the diameter of the bar will maximize the tensile performance of the connector. The increase in diameter of the sleeve cylinder, the compressive strength of the grout and the length of the bar embedded and its surface will affect the bond performance and the mode of failure under tensile load.

Failure analysis and design of grouted fibre-composite repair system for corroded steel pipes

Grouted fibre-reinforced composite stand-off sleeve repair is a light-weight and easily deployable repair system for steel pipelines with localised metal loss. The effectiveness of this type of repair system is dependent on the load transfer through the grout layer, which is weaker than neighbouring components and susceptible to failure due to stresses developed from applied internal pressure. In this study, three dimensional (3D) Finite Element Analyses (FEA) of a full-scale pipe with different levels of metal loss were implemented to evaluate the failure behaviour and capacity of grouted composite repair system. Steel pipes with a localised defect ranging from 20% to 80% metal loss and repaired using two infill grout systems reinforced with carbon and glass sleeves of different thicknesses were considered. The results indicated that the performance of the repair system is governed by the tensile cracking of the infill grout. A thicker sleeve and higher tensile strength grout delivers higher pipe capacity in the repair system. On the other hand, a high modulus grout provides a more effective load transfer from steel to sleeve. Using a high tensile strength grout, the composite repair system can restore the capacity of the steel pipe with defect up to about 70% metal loss.

Evaluation of the bonding and fatigue properties of an innovative rapid repair structure for concrete pavement

Deterioration and damage of pavements require rapid and durable full-depth repair. This study proposes an innovative rapid repair structure for the incorporation of precast slabs, graded gravel bases, and grouting technology in concrete pavements. Two representative grouting materials and two types of graded gravel bases with different particle size compositions were selected to construct four types of rapid repair structures. Static stepwise loading, fatigue loading, and lateral loading tests were conducted to evaluate both the effectiveness and feasibility of the rapid repair structures by measuring deformation, strain, and pressure as well as by examining the failure modes of the repair structures. The results indicated that the high strength grouting material contributes to the mechanical properties and bonding performance of the repair structure. Moreover, a well-compacted base is critical for the deformation uniformity of the repair structures and a graded gravel base with large particle size provides firm support, which is conducive to the infiltration of grouting material. The rapid repair structure proposed in this work not only reduces the time and cost required to re-open traffic, but also meets the requirements of a semi-permanent repair of concrete pavement. However, a full-scale investigation needs to be conducted to assess the mechanical properties for rapid repair structure.

Selective weakening of mineralised synthetic particles by high voltage pulses

The phenomena of high voltage pulse (HVP) selective breakage and HVP weakening have been reported separately in the literature, but the relation between the two HVP applications has previously not been investigated. Synthetic particles made of Epirez high strength grout were cast with and without embedded metalliferous minerals of chalcopyrite and pyrite and used in a study of HVP selective breakage and weakening. When metalliferous grains were embedded in the grout, there were added either as a single grain occurrence or as a fine disseminated texture. The HVP products were assessed using the JKRBT breakage characterisation method for the mineralised particles and the barren particles (with no metalliferous minerals contained), respectively. It has been found that the HVP weakening effect mainly occurs in the mineralised particles, with a reduction in particle competence (indicated by the relative change in A × b value) between 172% and 200% for the pyrite fines dispersed synthetic particles, and 70% relative reduction for the single chalcopyrite grain embedded synthetic particles. The barren synthetic particles do not exhibit a statistically significant weakening effect and appear much more competent than the mineralised particles after HVP treatment. This finding suggests that in mineral processing circuit design utilising the HVP technology, benefits associated with HVP weakening on the downstream comminution process would be maximised by combining the HVP pre-concentration and weakening applications, in doing so removing the barren unweakened rocks from the process.

Modeling of Buckling Restrained Braces (BRBs) using Full-Scale Experimental Data

Hysteretic performance of buckling restrained braces (BRBs) having various core materials, namely, steel and aluminum alloy and with various end connections are numerically investigated. As a computational tool, nonlinear finite element analyses (FEAs) are performed to better model the hysteretic behavior. For the simulation, various aspects such as 1) stress — strain relationship including the strain hardening effect 2) von Mises yield criterion 3) contact surface parameters between the core metal and surrounding high strength grout and 4) friction are defined. Experimental results from near-full scale cyclic tests on two steel core BRBs having steel casing as a restraining environment (named as BRB-SC4 and BRB-SC5) and an aluminum alloy core & aluminum alloy casing tube (named as BRB-AC3) are used in the analyses. All cyclically tested specimens have been designed according to AISC Seismic Provisions. Numerical results obtained from 3D models developed in ANSYS-Workbench give satisfactory response parameters when compared with the experimental ones (e.g., hysteretic curves, dissipated energies). Further, a convergence analysis regarding element numbers in the developed model is conducted for each BRB specimen. Finally, key issues that influence the hysteretic modeling of BRBs are identified.

Investigation into the freeze–thaw durability of semi-flexible pavement mixtures

Semi-flexible pavement (SFP) is made of a composite material that consists of porous asphalt concrete (PA) filled with highly flowable grouting material. At present, most researches on SFP focuses on the materials design and pavement performance characterisation, and very limit effort has been made on evaluating its freeze–thaw durability, which limits the application of SFP in cold regions. The present paper was to fill this gap. In the study, two SFP mixes made with a given PA but two different grouting materials (early-strength (ES) and high-strength (HS) grouting materials) were evaluated. ASTM C666 freeze–thaw durability tests were performed not only on the SFP mixes but also on each of SFP component (PA, ES and HS grouting materials), where relative dynamic modulus and mass loss of the tested samples were measured. In addition, indirect tensile strength of the samples was also tested, and the stiffness and strain–stress behaviour of the samples were evaluated. The results indicate that the order of the freeze–thaw resistance of the individual components was the PA matrix < ES grouting material (4.9 MPa at 3 h and 25.4 MPa at 28 days) ≪ HS grouting material (82.4 MPa at 28 days). The relative dynamic elastic modulus and strain–stress behaviours of SFP-ES samples were very similarly to those of PA, indicating the loss of integrity of the composite during freeze–thaw cycling. Differently, relative dynamic elastic modulus and strain–stress behaviours of SFP-HS samples were close to those of HS grouting material, indicating that enhanced freeze–thaw resistance of a SFP mix can be achieved by incorporating a high strength grouting material into a PA matrix.

Impact of soil erosion voids on reinforced concrete pipe responses to surface loads

This paper discusses the results of controlled, full-scale laboratory experiments on 0.9 m (36 in.) internal diameter reinforced concrete pipes (RC pipes) in the presence of simulated erosion voids. This study introduces a novel, yet practical, experimental method to simulate erosion voids near buried pipes. Using this method, the paper focuses on capturing the circumferential moment changes experienced by a 0.9 m (36 in.) internal diameter RC pipe buried at 0.9 m depth as voids of different sizes (approximate cross-sectional areas of 0.16 m2 and 0.31 m2) develop beside it, which have not been investigated before in such tests. The tests were also repeated after the erosion voids were repaired using a low strength grout (∼2 MPa) to characterize it as a potential rehabilitation solution, and the moment changes were recorded. The presence of erosion voids resulted in an overall increase in bending moment with the invert moments being affected the most (e.g., 70% increase in the invert moment between the intact soil result and the small void result and a 26% increase in the invert moment between the intact soil result and the extrapolated large void results). While, grouting the erosion voids resulted in an overall improvement in the pipe responses, there was still a 50% increase in the invert moment between the intact soil result and the grouted small void result and a 22% change between the grouted large void and the intact soil tests. The large void tests showed that soil collapse is the dominant failure mechanism at high loads. Comparing the modified bedding factor values for pipes with different void sizes and void condition (pre- and post-grouting), the intact soil always featured the highest bedding factor, followed by grouted large void (approximately 22% reduction in bedding factor), grouted small void (approximately 36% reduction), and small void before grouting (approximately 39% reduction).

Effects of mortar ratio on the properties of super early strength grouting materials by ternary complex system

An innovative research on preparation of super early strength grouts is presented. A ternary complex system of sulphoaluminate cement, aluminate cement and gypsum was used in the grouts combined with a variety of additives. The effect of mortar ratio on the properties of grouts was studied, and the microstructure was observed. The results show that high mortar ratio can prepare super early strength grouts; 2h and 90d compressive strength of the grouts is 42.6 and 105.6MPa, respectively. Furthermore, the grouting material has no retraction of late strength and possesses micro-expansion property, which attribute to the formation of ettringite.