Portland Cement Grout Research Articles

Study on cementitious grout for scour protection of offshore wind turbine foundations

To study scour-resistant applicability, 6–10% mass ratio of polyurethane (PU) was added to sulphoaluminate cement (SAC) and ordinary Portland cement (OPC) grouts to generate OPCPU and SACPU. Sodium silicate (SS) with slurry volume ratio of 1:1–5:1 was added to SAC and OPC grouts to generate OPCSS and SACSS. The water-cement ratio (w/c) of grout was 0.8–1.5. Fresh-state properties and mechanical properties were investigated. Hydrated minerals and microstructures were analyzed, scouring tests were conducted considering key formulations. The results indicated that SACSS and OPCSS have a shorter setting time and higher strength, which makes them suitable as scour resistance materials. At the w/c of 1.0, OPCSS with a volume ratio of 3:1 and SACPU with 6% PU were selected for scour resistance tests. It showed that maximum scour depths and sediment transports were 7.0–12.2 and 1.1–1.2% as those without reinforcing conditions. The critical shear stress on the seabed under reinforcement is ∼103 times greater than the bed shear stress. This inhibits the occurrence of scouring. The study evaluated the applicability of cementitious reinforcement for scour resistance. This study analyzed material and mechanical properties, hydrated minerals, and microstructures, and conducted scour tests to optimize grouting material ratios for seabed scour protection, providing references for soil reinforcement and grouting protection.

Effect of using nano-silica on the rheological, fresh and strength characteristics of cement-based grout for grouting columns

For ground improvement via grouting, the rheological abilities of nano-silica (NS) added to Portland cement (PC) based-grouts have been investigated at a wide range of NS replacements (0%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%) and water/binder (w/b) ratios (0.5, 0.75, 1, 1.25, 1.5) by conducting the rheometer tests. Using proper grouts from the rheology, then, the fresh and unconfined compressive strength (UCS) tests were performed to criticize the adequacy of NS replacements. From the rheology, the shear stress, apparent viscosity, yield stress and plastic viscosity of PC grout with NS demonstrated that using low to moderate dosages (<2.5%NS) particularly at the consistency of w/b = 1 yielded more favorable flow required high attention at high shear rates. From the fresh tests (w/b = 1), the favorite NS dosages of rheology (<2.5%NS) were also obtained from the workability of mini-slump, flow time and setting time, while the bleeding tests ensured the stability of grouts (<5%) for moderate to high NS rates. Hence, for both the rheology and fresh effects (w/b = 1), the moderate replacements (1.5%NS-2%NS) appeared better for flow issues. From the strength tests (w/b = 1, 28-day) with increasing NS, UCS of PC grout (1.26 MPa) proportionally increased up to 2%NS as an optimal dosage of peak strength (6.92 MPa), then gradually decreased to 4.82 MPa from the peak. The UCS efficiency of moderate NS rates corroborated their flow abilities. All NS dosages sufficiently provided the limit of bearing strength (>0.4 MPa) in ground enhancement. For the optimal rate (2%NS), increasing the curing times (3-day to 28-day) increased the UCS markedly as evidence of NS on the strength quality, and offered the 7-day for the early age of strength development. The failure patterns and SEM images also promoted the effects of NS. The research from the flow and strength findings not only demonstrated the promising effects of NS for grouting, but also offered some insights into designs and applications of foundation works.

Effect of glass powder on the rheological and mechanical properties of slag-based mechanochemical activation geopolymer grout

This article discusses the effects of glass powder (GP) replacements and sodium hydroxide (NaOH) molarity on the rheological, fresh, mechanical and microstructure characteristics of slag-based mechanochemical geopolymer (MG) grout. A conventionally activated geopolymer grout and an ordinary Portland cement (OPC) grout were also investigated for comparison. Four glass powder replacement ratios were used (0%, 10%, 20% and 30% by the total precursor weight) to prepare slag-based mechanochemical geopolymer at three NaOH concentrations (1.25, 2.5 and 3.75 molars). The experimental results showed that the rheological behaviour of MG grouts was considerably reduced, whereas the setting time and the bleeding capacity value increased when slag was substituted with 0%–30% GP. However, after 28 days, the unconfined compressive strength (UCS) improved by 2%–13% when 10%–20% GP was used as a slag replacement, then dropped by 4% when 30% GP was substituted. The results confirmed that both geopolymer grouts irrespective of the activation method had shorter setting time and more stable bleeding capacity than OPC grout. The results also revealed that the UCS of geopolymer grout is enhanced by 18% when the source materials are activated by the mechanochemical method compared to the conventional activation of geopolymer grout. The microstructure results revealed that the activation method had a considerable effect on the microstructure of geopolymer grout because the ball milling process increased the surface area and reduced the particle size of slag compared to conventionally activated geopolymer grout.

Hyperalkaline seepage water and the accompanying carbonate deposits from the grouted foundation rock of a rock-fill dam

The inspection gallery of a dam is leached by reservoir water that has infiltrated through the rock-fill dam body from the high-pressure water area upstream (leakage), and groundwater seeping through the foundation bed which has been injected with ordinary Portland cement (OPC) grout. Seepage waters with a pH greater than 12 are characterized by the major components of Ca(OH)2 and alkali hydroxides, lower Mg2+ concentration and higher K+/Na+ molar ratio than those for river and spring waters and groundwater near the dam site, and the extensive carbonate deposits precipitated from the waters. During a low discharge period, NaOH was the major component because Ca2+ was removed as carbonate deposits. Based on the stable isotope ratios of hydrogen and oxygen in the water, which reflect the altitude effect, it was inferred that the seepage waters are supplied from the shallow groundwater near the dam site and that the leakage is a mixture of the seepage water and reservoir water. Alkali hydroxides and Ca(OH)2 cement porewaters formed during the early stages of hydration of OPC are still present in the cement mass after 46 years, and that the OPC still remains partially unhydrated. These highly alkaline porewaters have seeped through gaps of the concrete joint surfaces to discharge into the inspection gallery. The Ca(OH)2 concentration in the seepage was below the portlandite saturation, therefore, the grout-derived solutes are considered to have been diluted as they diffused into the shallow groundwater before being discharged with the groundwater seeping into the gallery due to the hydraulic head difference and mixed with the groundwater. Ca(OH)2 in the seepage reacted with atmospheric CO2 in the inspection gallery, and the carbon stable isotope ratio of the carbonate deposits produced in this way was unusually low, about −25‰ VPDB, due to the large disequilibrium isotope fractionation during the direct reaction of CO2 with OH− in the solution. In addition to the change in its discharge, the hyperalkaline seepage and the resulting carbonate deposits with unusually low δ13C values can be measures of the durability of the grout-treated foundation rock of the rock-fill dam, because the decrease in pH in the future is related to the instability of the grout hydration products by carbonation.

Development and characterization of eco- and user-friendly grout production via mechanochemical activation of slag/rice husk ash geopolymer

In this study, mechanochemical activation was used both to increase the reactivity of a one-part geopolymer during ambient curing and as an alternative activation technique to overcome the difficulties associated with conventional two-part geopolymers. The mechanochemical grinding of raw materials of varied compositions in a solid-state resulted in the synthesis of ready-to-use geopolymeric precursors, which with just the addition of water, resulted in the development of eco- and user-friendly geopolymer grout. In addition, conventionally activated geopolymer grout and ordinary Portland cement (OPC) grout were investigated for comparative purposes. Four rice husk ash (RHA) replacement ratios were used (0%, 10%, 20%, and 30% by the total precursor weight) to investigate the feasibility of using RHA as a partial precursor in slag-based mechanochemically activated geopolymer (MSG) grout. A series of tests were examined, such as rheological behavior (flow curve response, yield stress, and plastic viscosity), fresh properties (setting time and bleeding capacity), mechanical characteristics (unconfined compressive strength, ultrasonic pulse velocity), and microstructure analysis (scanning electronic microscopy, X-ray Diffraction). The experimental results showed that the rheological characteristics and fresh properties of MSG grouts were considerably enhanced in terms of groutability when slag was replaced with 0–30% RHA. In addition, the mechanical characteristics increased with the increased partial replacement of slag with RHA up to 20% and decreased beyond that. In terms of activation mechanism, the mechanochemical activation technique reduced the rheological characteristics and fresh properties while the strength increased by 18% compared to the conventional activation method. Microstructural analysis revealed the existence of more unreactive particles in both conventionally activated geopolymer and MSG grout containing 30% RHA. The results also confirmed that MSG grouts had a shorter setting time and more stable bleeding capacity than OPC grout.

Comprehensive Effect of the Time and Water-Cement Ratio on the Rheological Properties of Power-Law Cement Grouts

The rheological properties of cement grouts are significantly affected by the changes of the time and the water-cement ratio, which determine the diffusion state of grouts in rocks and soils and influence the outcome of projects. In this study, Portland cement grouts with water-cement ratios of 0.50, 0.55, 0.60, 0.65, 0.70, and 0.75 at six moments, including 0 minutes, 5 minutes, 10 minutes, 20 minutes, 30 minutes, and 60 minutes, were evaluated to figure out the comprehensive effect of the time and the water-cement ratio on the rheological properties of power-law cement grouts. The results showed that the water-cement ratio had a great influence on both the consistency coefficient and the rheological index of the power-law cement grouts. The former appeared to have a downward trend with the increase of the water-cement ratio, and the latter appeared to have an upward trend. There was a rising tendency between the time and the consistency coefficient, while the rheological index was less affected by time. The difference between its maximum and minimum values was within 5%. Combined with the perspectives of statistical theory, practical applicability, and accuracy, the exponential model was the optimal model for showing the relationship between the comprehensive effects of the time, water-cement ratio, and consistency coefficient of the power-law cement grouts. The linear model was the optimal model of the rheological index based on the comprehensive effect of time and the water-cement ratio. Based on this, a power-law rheological equation with consideration of the comprehensive effect of time and water-cement ratio was established. The research results could not only improve the rheological theory of power-law cement grouts but also provide technical support for engineering practice.

Heat of hydration, bleeding, viscosity, setting of Ca(OH)2-GGBS and MgO-GGBS grouts

Hydrated lime (Ca(OH)2)- and reactive magnesia (MgO)-activated ground granulated blast-furnace slag (GGBS) have shown advantages in geotechnical applications compared with Portland cement (PC). To apply these two novel binders in slurry form to field applications, the properties of their grouts need to be investigated, which is the objective of this study. The heat of hydration, bleeding, viscosity, and setting behavior of Ca(OH)2-GGBS and MgO-GGBS grouts were investigated and compared with PC and pure GGBS grouts in this study. All grouts indicated a decrease in bleeding and setting time, but an increase in viscosity with decreasing the water/cementitious material (W/C) ratio. Compared with the PC grout, the pure GGBS grout with the same W/C ratio demonstrated higher bleeding and setting time, and lower heat rate and viscosity. Bleeding and setting time decreased and peak heat rate and viscosity increased with an increase in the activator (Ca(OH)2 or MgO)/GGBS ratio within GGBS-based grouts. The peak heat rate in Ca(OH)2-GGBS grouts was higher than that of pure GGBS or Ca(OH)2 grout, indicating that Ca(OH)2 was effective on activating hydration of GGBS. The peak heat rate in MgO-GGBS grouts was significantly lower than MgO grout and the heat rate was limited after 8 h. The bleeding and setting times of MgO-GGBS grouts were significantly lower than those of Ca(OH)2-GGBS grouts, which was primarily attributed to the hydration of MgO.

Vipulanandan Constitutive Models to Predict the Rheological Properties and Stress–Strain Behavior of Cement Grouts Modified with Metakaolin

Abstract In this study, the effects of metakaolin clay (MK) on the rheological properties, setting time, compressive strength, and toughness of cement grouts with water-cement ratios (w/c) of 0.6 and 1.0 were investigated. Based on the information in the literature, the amount of MK used in various mix designs varied up to 10 % by the weight of cement. The compressive stress–strain behavior of cement grout modified with MK was investigated up to 90 days of curing. The addition of 10 % of MK increased the apparent viscosity of the cement grout from 20 cP to 62 cP and from 13 cP to 44 cP with w/c ratios of 0.6 and 1, respectively. Setting time of cement grout mixes with a w/c ratio of 1.0 had longer initial and final setting times than the grout mixes with a w/c ratio of 0.6. The addition of 10 % MK increased the compressive strength of the cement grouts with w/c ratios of 0.6 and 1 from 8 MPa (1,175 psi) to 30.1 MPa (4,366 psi) and from 2.4 MPa (348 psi) to 17.8 MPa (2,582 psi) after 90 days of curing, respectively. The addition of 10 % MK increased the toughness of the cement grouts with w/c ratios of 0.6 and 1 from 1.42 J·m−3 to 2.27 J·m−3 and from 0.94 J·m−3 to 1.38 J·m−3 after 90 days of curing, respectively. The Vipulanandan p–q model was used to predict the changes in stress-stain behavior with curing time. The Vipulanandan rheological model also has a limit on the shear stress were as the other model did not have a limit. Based on the Vipulanandan rheological model, the maximum shear stresses produced by the portland cement grouts with w/c ratios of 0.6 and 1 with 0 MK were 58 Pa and 33 Pa, respectively. The addition of 10 % MK to the Portland cement (PC) grouts increased the maximum shear stresses by 155 % and 136 % for w/c ratios of 0.6 and 1, respectively.

Undissolved Ilmenite Mud from TiO2 Production—Waste or a Valuable Addition to Portland Cement Composites?

This paper presents a method of utilising ilmenite MUD created during the production of titanium dioxide (TiO2) according to the sulphate method as an additive for Portland cement composites. After the production process, undissolved MUD was additionally rinsed with water and filtrated in the factory to make it more useful (R-MUD) for implementation and also to turn back some of the by-products of the production of TiO2. R-MUD is less hazardous waste than MUD. It has a lower concentration of sulphuric acid and some heavy metals. The rinsing process raised the concentration of SiO2, which is a valuable part of R-MUD because of its potential pozzolanic activity. This means that the R-MUD might be a reactive substitute of part of Portland cement in building composites. The article presents the results of research on the pozzolanic activity of R-MUD and other materials with proved pozzolanic activity, such as silica fume, fly ash and natural pozzolana (trass). Tests were performed using thermal analysis techniques. The tests showed that the pozzolanic activity or R-MUD after three days is at the same level as silica fume and after 28 days it is twice as high as the activity of fly ash. Beyond the 180th day of curing, R-MUD had the same level of activity as fly ash. The summary is supplemented by calorimetric tests, which confirm the high reactivity of R-MUD compared to other commonly used concrete additives, already in the initial hydration period. In summary, heat of hydration after 72 h of Portland cement with R-MUD is at the same level as the heat of hydration of Portland cement with silica fume and also pure Portland cement grout. The results confirm that the process of formation of micro-silica contained in R-MUD react with calcium hydroxide to form the C-S-H phase, which is responsible for the microstructure of cement composites.

Ultrasonically Enhanced Physical Properties of Milky Cement for Ground Improvement

This study investigated the change created in physical properties by irradiating ultrasonic waves in Portland cement grout. In previous research, the grout equipment was scaled-up and a grout circulation system was used for the experiment. The physical properties of ordinary grout materials were compared with those irradiated by ultrasonic waves to observe its effects. This was done by analyzing and comparing the viscosity, strength and granularity. The results indicate that grout irradiated by ultrasonic waves outperformed the non-irradiated grout in all categories of physical properties.

The effect of blast-furnace slag particle size on the hydration of slag–Portland cement grouts at elevated temperatures

The UK nuclear industry has historically used a unique specification of cement powder that differs from construction industry requirements. However, the slags that complied with this specification have become unavailable. The material now used to meet the requirements of the specification is a blend of standard construction industry ground granulated blast-furnace slag (GGBS), which has high fineness, with Calumite which is a coarser slag powder. Both materials have very similar chemical compositions, and the main reason for blending is to control the particle size distribution (PSD) to replicate the performance of the previous supply. The effect of changing the PSD on the performance properties of the cement paste was investigated. Isothermal conduction calorimetry at elevated temperatures was carried out to monitor the heat of hydration; it was found that the peak heat and total heat evolution increased with an increase in GGBS content. It was also found that Calumite contributes very little to the hydration reaction and thus behaves similarly to an inert filler. As the GGBS content was decreased, the fluidity of the pastes increased up to a certain point, but decreased again for systems dominated by very coarse particles, indicating that there is an optimum balance between the finer and coarser slag particles within this cementing system.

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.

Influence of the irradiation in cement for the Brazilian radioactive waste repositories: Characterization via X-ray diffraction, X-ray tomography and quasielastic neutron scattering

Powerful characterization techniques have allowed detailing the investigation of cementitious materials that must endure for millennia as an engineered barrier in radioactive waste repositories. Cement is used in the repository, as waste immobilization matrix, structural material and an additional barrier against the contact of the waste with the biosphere. The material properties have to comply with requirements in respect to a number of parameters including homogeneity, permeability, and leachability, as well as withstand mechanical stress, heat, chemical and microbial attack, and the effects of ionizing radiation.The present study aims to investigate the behavior of cementitious materials contributing to the understanding of the processes that occur in hydrated cement under the environmental conditions of a repository and to estimate the durability of these materials. In this study was observed the changes caused by radiation, to which the material was exposed. A reference Portland cement paste and grout samples were compared with irradiated ones by X-ray diffraction and Tomography. Original and valuable results concerning the investigation of the influence of radiation on cement samples were also obtained by quasielastic scattering. These results are not accessible by others techniques.

Studded bond enhancement for steel-concrete-steel sandwich shells

A double-wall steel-concrete-steel (SCS) composite vault has been proposed for the “Singapore Cone” Arctic offshore structure. The SCS vault performs well under uniform pressure, but can fail prematurely under partial asymmetric loading. These shells will often experience a punching shear failure or flexural steel plate buckling which is exacerbated by the loss of bond between the steel wall and concrete interface. In this study, a construction friendly method using an array of welded mini studs to improve the steel–concrete interfacial bond is proposed and studied. Two workable Type I Portland cement grout mixes are tested as the bulk material: plain, and fiber reinforced. Studded concrete steel interfaces were tested under mode I interface peeling, and mixed mode shear. The small scale tests were also modeled with the nonlinear finite element analysis software ABAQUS, and the numerical results were compared against the laboratory experimental results. After qualitatively matching the computational results with experimental results, a large scale SCS prototype is modeled and designed, with working stresses limited to the elastic range. Mode I peeling ultimate strength of 0.46fc′ was used for the prototype analysis, with mixed mode shearing limited by bulk concrete away from the studded bond surface.

Microstructure and durability of fly ash cement grouts for micropiles

This paper presents a study on the possibility of using fly ash cement as grouts for micropiles. This type of special geotechnical work is commonly used for many applications. Generally, micropiles grouts are prepared using Portland cement, although the standards do not restrict the cement type to use, as long as they achieve a strength requirement. In this research, fly ash cement grouts made with w:c ratios 0.40, 0.45, 0.50 and 0.55 were studied from 2 up to 90days of age. Their microstructure was characterized using the non-destructive impedance spectroscopy technique, electrical resistivity, and mercury intrusion porosimetry. Their durability properties have been studied by determining the water penetration under pressure, and the chloride diffusion coefficient. The compressive strength was also measured and determined, and a maximum water:cement ratio, different for each cement type was obtained. All the results were compared to those obtained for Portland cement grouts. The results obtained confirm that the performance of micropiles made using fly ash cement grouts is adequate, and as it is well know the cements with mineral admixtures provide environmental benefits, so the use of cement including fly ash will contribute to the sustainability, with similar properties to those given by OPC.

Stabilisation/Solidification of soils contaminated by mining activities: Influence of barite powder and grout content on γ-radiation shielding, unconfined compressive strength and 232Th immobilisation

In this work, γ-ray shielding, unconfined compressive strength (UCS) and contaminant immobilisation performances of barite (Ba)-Portland cement (PC) grouts in Stabilisation/Solidification (S/S) treatment of 232Th-contaminated soils were studied. This is with the view to investigating the influence of the Ba and grout (G) content used in S/S mixes. Results show that the replacement of PC with Ba (up to 50%) leads to a significant increase, up about 2-fold, of the γ-ray shielding performance, but a higher Ba content in Ba-PC mixture decreases the S/S shielding performance due to the reduction of the final density of the S/S products, caused by the inhibition of cement hydration process. The highest γRS index of ~37% was found in the case of the maximum G to soil content of 50%. Ba and G content significantly influences the UCS performance of the S/S products. A marked UCS increase up to ~20% was found replacing PC with Ba with a Ba content of 50%. All the investigated S/S samples have UCS values that fulfil the quality criteria requirements. The use of Ba in PC grout allows the achievement of the almost total 232Th-immobilisation, even in extreme-acidic environment conditions (pH: 3, 1), also due to the Ba fine texture and high surface area able to reduce the final porosity of S/S products. Overall, the γRS index, observed jointly with the excellent immobilisation performances, reveals the mixture PC:Ba=1:1 with S:G=2:1 as the optimal choice in order to achieve the remediation targets and, at the same time, limit the costs, highlighting the possibility to successfully treat real 232Th-contaminated soils. However, a S:G=1:1 can be considered if a higher γ-ray shielding of 37% is required.

Corrosion Performance of Prestressing Strands in Contact with Dissimilar Grouts

To improve the corrosion protection provided to prestressing strands, anti-bleed grouts are used to fill voids in post-tensioning ducts that result from bleeding and shrinkage of older Portland Cement grouts. Environmental differences caused by exposing the strands to dissimilar grouts, however, have the potential to cause rapid corrosion. Portland Cement grout, gypsum grout, and four commercially available prepackaged grouts were analyzed to determine the chemical composition of the resulting pore solutions and tested to determine if using a second grout will provide improved corrosion protection for prestressing strands or result in accelerated corrosion. The potential consequences of leaving the voids unfilled were also evaluated. Pore solutions were analyzed for pH and sodium, potassium, fluoride, chloride, nitrite, sulfate, carbonate, nitrate, and phosphate ion content. The analyses were used to develop simulated pore solutions. Selected grouts and simulated pore solutions were paired to evaluate their potential to cause corrosion of, respectively, grout-wrapped and bare stress-relieved seven-wire prestressing strands using the rapid macrocell test. Strands were also evaluated in simulated pore solutions containing chlorides and in deionized water. Because exposure of strands to water or chlorides has the potential to cause rapid corrosion, filling voids in post-tensioning ducts with an anti-bleed grout is recommended. Gypsum grout, with its low pH and high sulfate content, will cause accelerated corrosion of strands when used in conjunction with Portland Cement grout or any of the commercially prepackaged grouts tested. When paired with Portland Cement grout, the prepackaged anti-bleed grouts evaluated in this study resulted in corrosion losses significantly below those observed for strands exposed to salt or water. The highest corrosion measured for a prepackaged grout occurred for the grout with the highest pore solution sulfate content.

Ultrasonic Testing of a Grouted Steel Tank for Debonding Conditions

The non-invasive detection of debonding conditions and cavities beneath the wall of a steel tank are common applications in a variety of engineering and construction fields. Compressional ultrasonic waves have been used for the evaluation of steel plate thicknesses; however, they lack energy for penetrating a Portland cement grout in contact with a steel wall to detect debonding conditions. In this work, a joint analysis of surface waves and Lamb waves (high and low frequency) is used for the detection of debonding conditions in a scale model grouting steel tank. The propagation of high frequency ultrasonic waves generated by a 50-kHz transmitter along the side of the tank model is analyzed in the time domain and the frequency domain. In addition, using instrumented hammers with plastic or aluminum tips (low frequency sources) and a 50-kHz transmitter, three different configurations are used for the analysis of surface waves. The low-frequency Rayleigh waves generated by the hammer are used for void detection. Fourier spectra of the measured signals indicate that the effect of a void on the waves propagating through the medium is reduced when there is debonding. The comparisons of theoretical (high frequency) dispersion curves with experimental ones, computed from frequency wavenumber (FK) spectra, show that Lamb waves dominate the surface response in the wall of the steel tank. High frequency Lamb waves are successfully used in the detection of debonding between the tank wall and the grout because of the lower attenuation measured on top of the void.