Grouting Of Tendons Research Articles

Behavior of a Rock Mass in Uplift Field Tests of Rock Anchors

AbstractRock anchors are high-capacity reinforcement measures used to stabilize large-scale infrastructures. According to the literature, they can fail in one of the four ways: (1) steel tensile failure; (2) tendon–grout interface failure; (3) grout–rock interface failure; and (4) rock mass uplift failure. Rock mass uplift field tests were performed in a limestone quarry to test this fourth failure mode. The tests were designed to induce rock mass failure around rock anchors. The ground surface heaved asymmetrically around the anchors and the pre-existing joints in the rock mass tended to open first. The seismic activity in the rock mass was greatest close to the anchor, decreasing with distance. The failure crater in the rock followed the joint sets in the rock mass, and the shape was partly controlled by the pre-existing joints. The apex angle of the failures was measured to be between 125 and 140$$^{\circ }$$ ∘ . The horizontal stress in the rock mass increased when the anchor was pulled, indicating load arching around the anchor. The observed failure was a combination of rock mass uplift and grout–rock bond failure. The measured anchor capacity was much higher than the estimated rock mass capacity using the recommended design methods of the Norwegian Public Roads Administration.

Reliability of the grouting of tendons under consideration of uncertainties under on-site conditions

This paper contributes to the body of knowledge from German research work Deutscher Ausschuss für Stahlbeton and from author’s experiences, to improve the reliability of cable ducts grouting. The complete and reliable filling of post-tensioned tendons with grout is necessary to protect the prestressing steel against corrosion and for bond between prestressing steel and the concrete structure, which is in both limit states applied. Diagnostics of bridges built in the last century showed the cases of faulty grouting of cable ducts. These faults are cause of corrosion prestressing steel often. Based on these diagnostics, bridges are after 35 to 70 years of service life demolished, although service life of these bridges was to 100 years declared. In the studied research work were investigated the effects of individual components, procedures and conditions of the grout and results of grouting investigated. Tests have been performed both on the experiment cable ducts and the real structures. Based on this paper, certain principles have been recommended that aim to prevent grouting faults and to improve the reliability of the grouting. In these recommendations are suggestions of controls of grouting included.

Study on shear behavior and damage constitutive model of tendon-grout interface

Ground anchors are responsible for maintaining the stability and integrity as well as controlling the deformation, displacement, and crack development in the surrounding ground. Tendon-grout (T-G) interface, which is the weak part of anchorage structures, affects the anchorage performance of the ground anchor during load-transfer processes. To investigate the shear mechanical properties of the tendon-grout interface, a series of pull-out tests were conducted on anchorage element under constant radial stiffness boundary conditions. Moreover, the equivalent calculation for the constant radial stiffness boundary condition was analyzed. The mechanical performance of cement grouts cured for different periods was investigated, including the compressive strength and shear strength. Additionally, the failure modes of tendon-grout systems and effects of different tendon quantity, spacing and offset, were assessed. The failure evolution mechanism of the interface during the pull-out process was clarified. In addition, the microscopic structural characteristics of the tendon-grout interface were investigated. Two interfacial shear stress-displacement relationships were developed based on the interface failure modes, i.e., stress attenuation type and ideal elasto-plastic type. According to the test results, the peak strength of the interface increased with the tendon spacing, while the residual strength decreased. The effect of the tendon offset on the shear stiffness and strength of the interface is significant. A damage constitutive model was proposed to model the shear behavior of the tendon-grout interface. The proposed model verified by comparing with the test results and further adopted in pull-out test simulation. The conclusions will provide a better understanding on the shear behaviors of tendon-grout interface, and facilitate the development of a general evaluation method for ground anchor systems.

Electrochemical Behavior of Steel in Alkaline Sulfate Solutions with Low Level Chloride Concentrations

Localized corrosion of steel strand in deficient PT grout have been attributed to the accumulation of grout bleed water and more recently to grout segregation with elevated sulfate concentrations [1-4]. Testing of steel in sulfate alkaline solution and grout with high sulfate concentration showed higher corrosion activity and impairment of passive film development. Anodic polarization results showed that in the alkaline solution (pH 12.6), early fixed sulfate presence could be aggressive by disrupting passive film development. Also, electrochemical noise results showed numerous distinct noise events in solutions with >1,300 ppm SO4 2- that were characteristic of metastable pitting and pitting. Pitting events were sustained in solutions above 10 g Na2SO4/L H2O) [5]. Furthermore, chloride ions have often been associated with strand corrosion and limits are specified in material and building specifications [6]. However, even though strand corrosion in segregated grout in field case studies did not coincide with high chloride concentrations [1]. Testing in grout with low-level chloride concentrations (below conventional threshold values) resulted in elevated corrosion rates in presence of the sulfate ions and indicated that the sulfate presence in the grout may reduce its chloride-ion binding capacity. It was posited that there are synergic effects of sulfate ions and vestigial chloride ions in segregated grout that can promote corrosion activity.The electrochemical behavior of steel in simulated grout pore solutions was investigated to elucidate the effect of low level chloride ions in alkaline sulfate solutions on steel corrosion. The electrochemical noise (EN) technique relating to corrosion of metals in aqueous solution has been developed over the past 50 years and was used here to provide a useful mean to elucidate the localized corrosion behavior of steel subjected to alkaline sulfate solutions with low level of chloride concentration. In the testing here, steel specimen were exposed to alkaline solutions simulating pore solutions with pH 12.6 with varying sodium sulfate levels and low level of sodium chloride. Supplemental electrochemical experiments included the steady-state condition (open circuit potential and linear polarization test) and potentiodynamic polarization tests. References Permeh, K.K. Krishna Vigneshwaran, K. Lau, “Corrosion of Post-Tensioned Tendons with Deficient Grout,” Florida Department of Transportation, Final Report, Contract No. BDV29-977-04, October 20, 2016.K. Krishna Vigneshwaran, S. Permeh, M. Echeverría, K. Lau, and I Lasa. “Corrosion of Post-Tensioned Tendons with Deficient Grout. Part 1. Electrochemical Behavior of Steel in Alkaline Sulfate Solutions.” Corrosion 74 (2018) pp.362-371.Permeh, K.K. Krishna Vigneshwaran, M. Echeverría, K. Lau, and I Lasa. “Corrosion of Post-Tensioned Tendons with Deficient Grout. Part 2. Segregated Grout with Enhanced Sulfate.” Corrosion 74 (2018), pp.457-467.Permeh, K. K . Krishna Vigneshwaran, K.Lau., and I.Lasa. “Corrosion of Post-Tensioned Tendons with Deficient Grout. Part 3: Segregated Grout with Elevated Sulfate and Vestigial Chloride Content.” Corrosion 75 (2019) pp.848-864.Permeh, K. Lau, M. Duncan, and R. Simmons, “Identification of Steel Corrosion in Alkaline Sulfate Solution by Electrochemical Noise” Materials and Corrosion, April 2021.DOI: 10.1002/maco.202112347K. Lee, J. Zielske, An FHWA special study: post-tensioning tendon grout chloride thresholds, Federal highway, Final Report, Contract No. FHWA-HRT-14-039, April 2014.

Effect of grout conditions and tendon location on corrosion pattern in PS tendon in grout

Pre-stressed Concrete (PSC) has various engineering advantages like reduction of dead load, enhancement of shear strength, and reducing crack, however tendon corrosion in grout caused by deficient grout and intrusion of chlorides causes a tendon break and the related structural problems. It is important to understand the corrosion pattern varying with grout properties and placement conditions. In the work, TG (Tendon-Grout) systems are prepared considering grout quality, bleeding, tendon location, and crack width. In order to evaluate corrosion pattern in TG systems in a short period, ICM (Impressed Current Method) is adopted for corrosion acceleration for 2 and 4 days of duration. For two types of grout (conventional one and improved grout with reduced water to cement ratio and silica fume), corrosion current and its amounts are evaluated for various conditions. In the TG system with crack, corrosion greatly increases with extension of test duration for both types of grout since crack width on grout is a main channel for ion intrusion. In spite of crack effect, improved grout has better resistance to corrosion considering crack and bleeding condition. When TG system has eccentricity of tendon with small cover depth, no significant differences between conventional and improved grout are measured since cover depth is too small to protect chlorides from outside. Various effects like bleeding, crack, tendon location, and grout quality are discussed in the work. The improved properties in IG like porosity, strength, absorption ratio, and expansion rate are also investigated.

Problems with Continuous Spliced Posttensioned–Prestressed Concrete Bulb-Tee Girder Center Spans at West Point, Virginia

The Lord Delaware and Eltham Bridges carry traffic on US-33 over the Mattaponi and Pamunkee Rivers in Virginia. Completed in 2006 and 2007, respectively, the bridges are similar in that they have prestressed, precast tee-beam approach spans and two four-span continuous spliced posttensioned–prestressed precast bulb-tee girder center spans. Constructed with the latest prestressed–posttensioned precast technologies, the structures were expected to provide relatively maintenance-free performance for more than 100 years. In May 2015 during a biannual inspection, a spall that exposed a tendon duct was reported in the web of an exterior girder of the Lord Delaware bridge, raising concerns about the life of the of the posttensioned lightweight concrete girders. The tendon grout was a high-performance prepackaged mixture. In-depth inspections identified cracking, leaking, and spalling in the webs of the beams and problems with the grouted tendons that included voids, soft grout, water, and corroding strands. Ground-penetrating radar worked well to locate the tendons, and impact echo worked well to determine the condition of the grout. Destructive drilling and sampling were used to confirm the impact echo readings and to evaluate the condition of the grout. Access to the strands at the anchors and over the piers where voids are typically located was not possible because at the anchors the web thickness was the same as the flange, and over the piers the tendons were in the top flange of the beams. A suitable repair has not been determined.

An analytical solution for stresses induced by a post-tensioned anchor in rocks containing two perpendicular joint sets

A new analytical approach for the analysis of stress around a post-tensioned anchor in rock with two perpendicular joint sets is presented. The solution considers nonlinear shear stresses developed along the anchor bond length as well as debonding at the tendon–grout interface. The bearing plate effects are also considered in the analyses. The following assumptions are made: (1) homogeneous and orthotropic elastic rock; (2) half-space rock mass with plane strain conditions; (3) trilinear bond-slip model for the behavior of the tendon–grout interface; (4) an elastic anchor. The employed methodology is to decompose the anchor problem into two problems of simpler loadings: stresses produced under a rigid bearing plate and stresses induced by interfacial shear stresses mobilized along the bond length. Based on the proposed solution, an illustrative example is given and the results show that a large compressive region is formed around the anchor free length. Tensile stress concentrations are also observed around the bond length and near the rock surface outside the bearing plate. A parametric study is also conducted to investigate the effects of joint properties on the induced stresses. The results show that as the number of joints intersecting the anchor axis increases, the magnitude of compressive stresses in the free zone decreases, while the size of compression zone around the anchor increases. To verify the results of the analytical approach, a comparison is made with numerical results obtained by using the finite element method. The analytical solutions compare very well with the results obtained by numerical method.

Debonding along the fixed anchor length of a ground anchorage

Ground anchorages are the main means of support used for safety aspects in mining and tunnelling industry. Poor installation of ground anchorages can result in partial debonding between the tendon and the grout. The effects of debonding on the load carrying capacity of a model anchorage are examined by pull out tests. The load carrying capacity is found to decrease with increasing length of pre-existing debonding at the tendon–grout interface. The fracture toughness of the tendon–grout and of the ground–grout interfaces is measured over a wide range of mixed-mode loading and the results are used to assess the likelihood of debonding at the interfaces in a ground anchorage system.

Natural hydraulic lime based grouts – The selection of grout injection parameters for masonry consolidation

The goal of this research was to develop a methodology for grout composition optimization concerning specific applications. It could be developed for masonry consolidation or bonded prestressed tendon grout, pre-placed aggregate grout, among others. The grout development does not only depend on its intrinsic properties but also on the nature and features of the support. The purpose of a grout injection technique applied in a multiple leaf wall is to increase the compactness and create links between the internal and external leaves, which improve not only shear and flexural resistance but also the compressive strength. In practice, the variability of voids within masonries requires an ability to fine tune the rheological properties of the grout in order to optimally fill the voids. The methodology proposed here for testing grout injectability in a porous media like masonry is a logical tool to use in grout optimization. It shows that several grout parameters should be controlled for a successful injection. Concerning the support and its typology, the mortar between stones plays a fundamental role in the effectiveness of the intervention, due to its reduced porosity and composition. Besides that, earth and mortar, for example, can be present in the interior of masonry and make difficult, with their absorption, the injection. Thus, the water retention capacity of grout should be controlled to prevent that problem, as it was made in this work, using the optimized mixing procedure that takes into account that and other fresh grout properties. This study analyses some relevant grout properties such as yield stress, plastic viscosity, flowability and injectability for natural hydraulic lime based grouts in different porous media. The research shows that there are differences in the grout behaviour, especially in rheological properties, when different mixing procedures and/or grout composition (different water/binder or fly ash/binder ratios) are used and that fresh grout properties may be optimized for injection purpose.

Performance of Segmental and Posttensioned Bridges in Europe

With a history a decade or two longer than in the United States, the October 1999 Scanning Tour by the Federal Highway Administration was to examine European performance, durability and maintenance of prestressed concrete, segmental, and cable-stayed bridges to help identify possible concerns and to estimate future needs for maintenance, repair, retrofit or replacement in the United States. All countries reported corrosion of prestressing tendons, concrete, or reinforcing steel—but generally in a minority (2% or so) of structures—from poor quality grouting of tendons or honeycombed concrete allowing ingress of water and chlorides. For new construction, improved grouts and stringent practices have been introduced. Both external and internal tendons are used in European segmental construction. More “robust” ducts of durable polyethylene are being introduced (Switzerland) and new “greased and sheathed” monostrands find favor for repair or retrofit. Where appropriate, new fiber composite materials are used for rehabilitation as in the United States. Widespread European policy is to apply waterproof membranes, drainage, and protective overlays to bridge decks of all types of construction. Less aggressive deicing is being introduced. Structures have been replaced mostly for functional obsolescence rather than deterioration. Maintenance inspection is similar to that in the United States but with a greater commitment to upkeep. Available nondestructive investigation techniques for tendons and cable-stays include X-ray, ultrasonic, electrical resistance, magnetic perturbation, georadar, etc., but their use requires engineering expertise and interpretation. Instrumentation with remote monitoring is occasionally installed on major structures. European cable-stay structures are performing well. Current trends are to greased and sheathed monostrands in high-density polyethylene pipes. Wind-rain vibrations are suppressed by ribbed stay-pipes and/or various types of damping installed during or after construction. Segmental and cable-stay developments in Europe and the United States are moving in parallel directions and improved technology. With appropriate attention to improved grouting, these types of structures continue to be built and will serve well into the foreseeable future.

Grouting of tendons in stressed concrete : 3F Park, R N.Z. Engng, Nov. 1975, P315–320

Grouting of tendons in stressed concrete : 3F Park, R N.Z. Engng, Nov. 1975, P315–320

TO NEW FRONTIERS FOR PRESTRESSED CONCRETE DESIGN AND CONSTRUCTION

The art and practice of prestressing concrete structures has stirred the imagination of civil engineers during the past 30 years. This challenge will continue and the future outlook for prestressed concrete promises even greater interest and excitement. Freyssinet's imaginative idea, to use high strength steel wire with more than 4000 kg/cm2 (56,000 psi) allowable prestress, led to great success and progress in prestressed concrete construction. His first publication on prestressed concrete was titled Une Revolution dans l'Art de Batir (A Revolution in the Art of Building). Indeed; a revolution was started which opened large new fields of application of concrete as a construction material. The prestressing revolution began with a period of creativity mainly by European engineers, inventing different prestressing systems, developing special prestressing steels and providing larger and larger tendons allowing forces up to 1000 tons (2200 kips) or concentrated tendons with prestressing forces of more than 10,000 tons (22,000 kips). Special hydraulic jacks and other special equipment for stressing, anchoring, coupling, and grouting of tendons were invented. Practical experience, systematic research, and special design theories combined to provide a reliable body of knowledge of the behavior and the load carrying capacity of prestressed concrete structures. Principles and recommendations for design could be established, and the joint effort of FIP and CEB (Comite Europeen du Beton) produced a universal code to guide the design of thousands of prestressed concrete structures throughout the world. This revolutionary period is essentially ended, the pace of new inventions in the field has slowed, and we are now entering a period of optimization, that is, selecting the technically and economically best systems and methods, free from patent prestige or other nonrational criteria. A variety of systems will still remain because their unique technical properties and advantages are needed for different applications.