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Kamal H. Khayat - One of the best experts on this subject based on the ideXlab platform.
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experiment design to evaluate interaction of high range water reducer and antiwashout admixture in high performance Cement Grout
Cement and Concrete Research, 2001Co-Authors: A Yahia, Kamal H. KhayatAbstract:The injection of Cement Grout in water-saturated medium and the sealing of anchorages require the use of Grout with high resistance to water dilution to enhance in-situ performance. This can be achieved by reducing the W/C and incorporating an antiwashout admixture (AWA) to enhance the stability. Such admixture can increase the viscosity and yield stress and necessitate higher dosage of high-range water-reducer (HRWR) to maintain the desired fluidity. Cement-based Grouts with 0.30 to 0.50 W/C and different combinations of AWA and HRWR were evaluated. The study was undertaken to highlight the influence of W/C and dosage of chemical admixtures on fluidity, washout resistance, and residual compressive strength (RCS) of the underwater-cast Grout. Statistical models established using a statistical design of experiments indicate that the W/C has greater effect on changes in minislump flow, washout, and RCS than the concentrations of HRWR and AWA. On the other hand, for mixtures prepared with a fixed W/C of 0.40, the models show that measured responses are highly affected by the dosages and interaction of both admixtures. Trade-off between fluidity and washout resistance and means to optimize mixture proportioning to enhance the resistance to water dilution without adversely affecting fluidity are discussed.
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analytical models for estimating yield stress of high performance pseudoplastic Grout
Cement and Concrete Research, 2001Co-Authors: A Yahia, Kamal H. KhayatAbstract:Abstract The yield stress of Cement Grout is commonly determined by extrapolating the shear stress–shear rate flow curve to a zero shear rate using an analytical model. High-performance structural Cement Grouts, made with relatively low water-to-Cementitious materials ratio (W/CM) incorporating various supplementary CMs and rheology-modifying admixtures (RMAs), can exhibit rheological behavior different than that of conventional Grout. Such mixtures can exhibit high pseudoplastic shear thinning characteristics. Therefore, the degree of error in estimating the yield value of high-performance Grouts can be greater than for conventional ones. In this paper, yield stresses of Cement Grouts made with 0%, 0.03%, 0.05%, and 0.075% of welan gum RMA, by mass of binder, and various high-range water-reducer (HRWR) concentrations were evaluated. Mixtures with different replaCement values of silica fume and blast furnace slag were also investigated. All Grouts had a constant W/CM of 0.40. Yield stress values obtained using various rheological models are compared. The results showed that, depending on the adopted analytical model, the deducted yield stress can be quite different. A new method to estimate yield stress of high-performance, pseudoplastic Grout is proposed and shown to result in lower yield stress estimates than the other models. For mixtures made with 100% Cement, the estimated values of yield stress given by the proposed model are found to be close to those estimated using the De Kee model.
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Effect of Welan Gum-High-Range Water Reducer Combinations on Rheology of Cement Grout
ACI Materials Journal, 1997Co-Authors: Kamal H. Khayat, A YahiaAbstract:The effects of combined additions of welan gum, a commonly used rheology modifier, and naphthalene-based high-range water reducer on the rheological properties of Cement Grouts are investigated for mixtures made with 0.40 water-to-Cement ratios. Grouts with dosages of rheology-modifying admixture varying from 0 to 0.075 percent by mass of Cement were prepared. For each group of Grout, the concentration of high-range water reducer was varied to obtain four mixtures of various fluidity levels. Measured properties included apparent viscosities at different shear rates, and estimates of plastic viscosity and yield value. Other measurements of consistency included the ease of spread and flow of Grout evaluated using the mini-slump and Marsh cone tests, respectively. The Grout stability was evaluated by measuring its resistance to water dilution when cast in water as well as its ability to retain water when subjected to sustained pressure (forced bleeding). Initial setting times were determined for selected mixtures. In all, a total of 27 Grout mixtures were evaluated. Test results show that the increase in the dosage of rheology-modifying admixture increases significantly the yield value and plastic and apparent viscosities of Cement Grouts. Combined with an adequate dosage of high-range water reducer, losses in fluidity are regained without significant reduction in stability. With the increase in high-range water reducer dosage, the apparent viscosity at low rates of shear decreases more dramatically than that at high rates of shear due to the pseudo-plastic behavior of such Grouts. The combined use of proper dosages of rheology-modifying admixture and high-range water reducer is shown to clearly contribute to securing high-performance Cement Grout that is highly fluid, yet cohesive enough to reduce water dilution and enhance water retention. For equal fluidity level, greater stability is obtained with mixtures containing high contents of viscosity modifying admixture. The initial setting time is shown to be delayed by the incorporation of high-range water reducer and rheology-modifying admixture with the latter additive exhibiting greater influence on retardation of setting.
A Yahia - One of the best experts on this subject based on the ideXlab platform.
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analytical models for estimating yield stress of high performance pseudoplastic Grout
Cement and Concrete Research, 2001Co-Authors: A Yahia, Kamal H. KhayatAbstract:Abstract The yield stress of Cement Grout is commonly determined by extrapolating the shear stress–shear rate flow curve to a zero shear rate using an analytical model. High-performance structural Cement Grouts, made with relatively low water-to-Cementitious materials ratio (W/CM) incorporating various supplementary CMs and rheology-modifying admixtures (RMAs), can exhibit rheological behavior different than that of conventional Grout. Such mixtures can exhibit high pseudoplastic shear thinning characteristics. Therefore, the degree of error in estimating the yield value of high-performance Grouts can be greater than for conventional ones. In this paper, yield stresses of Cement Grouts made with 0%, 0.03%, 0.05%, and 0.075% of welan gum RMA, by mass of binder, and various high-range water-reducer (HRWR) concentrations were evaluated. Mixtures with different replaCement values of silica fume and blast furnace slag were also investigated. All Grouts had a constant W/CM of 0.40. Yield stress values obtained using various rheological models are compared. The results showed that, depending on the adopted analytical model, the deducted yield stress can be quite different. A new method to estimate yield stress of high-performance, pseudoplastic Grout is proposed and shown to result in lower yield stress estimates than the other models. For mixtures made with 100% Cement, the estimated values of yield stress given by the proposed model are found to be close to those estimated using the De Kee model.
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experiment design to evaluate interaction of high range water reducer and antiwashout admixture in high performance Cement Grout
Cement and Concrete Research, 2001Co-Authors: A Yahia, Kamal H. KhayatAbstract:The injection of Cement Grout in water-saturated medium and the sealing of anchorages require the use of Grout with high resistance to water dilution to enhance in-situ performance. This can be achieved by reducing the W/C and incorporating an antiwashout admixture (AWA) to enhance the stability. Such admixture can increase the viscosity and yield stress and necessitate higher dosage of high-range water-reducer (HRWR) to maintain the desired fluidity. Cement-based Grouts with 0.30 to 0.50 W/C and different combinations of AWA and HRWR were evaluated. The study was undertaken to highlight the influence of W/C and dosage of chemical admixtures on fluidity, washout resistance, and residual compressive strength (RCS) of the underwater-cast Grout. Statistical models established using a statistical design of experiments indicate that the W/C has greater effect on changes in minislump flow, washout, and RCS than the concentrations of HRWR and AWA. On the other hand, for mixtures prepared with a fixed W/C of 0.40, the models show that measured responses are highly affected by the dosages and interaction of both admixtures. Trade-off between fluidity and washout resistance and means to optimize mixture proportioning to enhance the resistance to water dilution without adversely affecting fluidity are discussed.
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high performance Cement Grout for post tensioning applications
Aci Materials Journal, 1999Co-Authors: K. H. Khayat, A Yahia, P DuffyAbstract:Grout mixes used to fill posttensioning ducts to protect wire strands against corrosion are made with portland Cement, water, and some chemical admixtures to enhance rheological and hardened properties. Such Grouts should be fluid enough to facilitate pumping and spread into place, hence ensuring proper coating of the prestressing steel with minimum zones of the ducts that are imperfectly Grouted. Unstable Grouts can exhibit sedimentation of Cement particles and bleeding of some of the free water that can propagate upwards and fill upper zones of posttensioning ducts. Bleeding can also occur whenever there are variations in elevations between different Grouted areas, such as in vertical ducts where bleeding water can also result from fluid loss between the wire strands that can rise upwards by capillary action. Free water accumulated in larger voids that is not reabsorbed can freeze and lead to some delirious expansion. Cement Grout can be exposed to freeze-thaw cycles during its service life, as in the case of Grouted ducts in the surf and tidal zones of marine structures. Consequently, it is important in some cases to ensure an adequate air-void system in the hardened Grout to resist freeze-thaw actions. A laboratory investigation was undertaken to develop highly fluid yet stable Cement Grouts with adequate and stable air-void systems and good mechanical properties. This paper reports the test results leading to the recommendation of high-performance structural Grout containing 8% silica fume replaCement and balanced combinations of high-range water reducer and rheology-enhancing admixture. Such Grout can be properly air entrained to develop an adequate and stable air-void system for frost durability.
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simple field tests to characterize fluidity and washout resistance of structural Cement Grout
Cement Concrete and Aggregates, 1998Co-Authors: K. H. Khayat, A YahiaAbstract:The ability to assess rheological properties of neat Cement Grout, such as those used in structural repair and for filling post-tension ducts, is of special interest for the evaluation of the ease of pumping, spreading into place, and filling of narrow spaces. There is an increasing need to identify dependable and simple test methods that can characterize the consistency of specialty Cement Grouts and reflect variations in rheological properties during handling and plaCement. Several tests can be used to evaluate the rheological characteristics of a Cement Grout suspension, including precise methods for the determination of rheological parameters and simple procedures to assess fluidity. Rheological properties can be accurately determined by using a coaxial cylinder viscometer. However, the use of such a viscometer is mainly limited to the laboratory, and simple methods including the mini-slump spread and the modified Marsh cone tests are usually employed in the field to verify the consistency for quality control. This paper attempts to establish relationships between rheological parameters and fluidity values obtained using simple test methods. Relationships are also determined between the wash-out resistance of structural Cement Grout and various fluidity and rheological parameters. The derived relationships are based on a wide variety of Cement Grouts covering up to 210 data points. The various Grouts were prepared with W/C ranging between 0.30 and 0.50, Type I and III portland Cements, as well as various silica fume replaCement values (up to 8% by mass), blast-furnace slag contents of 20 to 60%, fly ash substitutions of 10 to 30%, and limestone filler replaCements of up to 30%. The investigated Grouts incorporated melamine- and naphthalene-based high-range water reducer, welan gum and cellulose-based viscosity-modifying admixtures, as well as set-retarding admixture. Test results highlight the difficulties of relying on a single empirical test to evaluate the fluidity of a given Grout. Correlations between various simple measurements of fluidity and wash-out mass loss and apparent viscosities determined at different shear rates indicate that the mini-slump and wash-out mass loss measurements correspond well to viscosities determined at low-shear rates (5.1 s-1). In contrast, the modified Marsh cone measurement corresponds well to viscosity determined at high-shear rates ranging between 340 and 510 s-1. Because of the pseudo-plastic behavior of structural Cement Grouts, field quality control tests should include fluidity assessment at low and high shear rates to adequately evaluate the rheological behavior of the Grouts.
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Effect of Welan Gum-High-Range Water Reducer Combinations on Rheology of Cement Grout
ACI Materials Journal, 1997Co-Authors: Kamal H. Khayat, A YahiaAbstract:The effects of combined additions of welan gum, a commonly used rheology modifier, and naphthalene-based high-range water reducer on the rheological properties of Cement Grouts are investigated for mixtures made with 0.40 water-to-Cement ratios. Grouts with dosages of rheology-modifying admixture varying from 0 to 0.075 percent by mass of Cement were prepared. For each group of Grout, the concentration of high-range water reducer was varied to obtain four mixtures of various fluidity levels. Measured properties included apparent viscosities at different shear rates, and estimates of plastic viscosity and yield value. Other measurements of consistency included the ease of spread and flow of Grout evaluated using the mini-slump and Marsh cone tests, respectively. The Grout stability was evaluated by measuring its resistance to water dilution when cast in water as well as its ability to retain water when subjected to sustained pressure (forced bleeding). Initial setting times were determined for selected mixtures. In all, a total of 27 Grout mixtures were evaluated. Test results show that the increase in the dosage of rheology-modifying admixture increases significantly the yield value and plastic and apparent viscosities of Cement Grouts. Combined with an adequate dosage of high-range water reducer, losses in fluidity are regained without significant reduction in stability. With the increase in high-range water reducer dosage, the apparent viscosity at low rates of shear decreases more dramatically than that at high rates of shear due to the pseudo-plastic behavior of such Grouts. The combined use of proper dosages of rheology-modifying admixture and high-range water reducer is shown to clearly contribute to securing high-performance Cement Grout that is highly fluid, yet cohesive enough to reduce water dilution and enhance water retention. For equal fluidity level, greater stability is obtained with mixtures containing high contents of viscosity modifying admixture. The initial setting time is shown to be delayed by the incorporation of high-range water reducer and rheology-modifying admixture with the latter additive exhibiting greater influence on retardation of setting.
Hangseok Choi - One of the best experts on this subject based on the ideXlab platform.
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performance evaluation of closed loop vertical ground heat exchangers by conducting in situ thermal response tests
Renewable Energy, 2012Co-Authors: Chulho Lee, Jong Min Choi, Moonseo Park, Thebao Nguyen, Byonghu Sohn, Hangseok ChoiAbstract:The effective thermal conductivity of six vertical closed-loop ground heat exchangers (GHEXs), which were installed in a test bed located in Wonju, South Korea, has been experimentally evaluated by performing in-situ thermal response tests (TRTs). To compare the thermal efficiency of the GHEXs in field, various installation conditions are considered such as different Grouting materials (Cement vs. bentonite), different additives (silica sand vs. graphite) and shapes of the circulating pipe-section (conventional U-loop type vs. 3-pipe type). From the test results, it can be concluded that the Cement Grout has higher effective thermal conductivity than the bentonite Grout by 7.4–10.1%, and the graphite outperforms the silica sand by 6.7–9.1% as a thermally-enhancing additive. In addition, the new 3-pipe type heat exchange pipe that yields less thermal interference between the inlet and outlet pipes shows better thermal performance over the conventional U-loop type heat exchange pipe by 14.1–14.5%. Based on the results from the in-situ thermal response tests, a series of cost analyses has been carried out to show the applicability of the Cement Grouting, the graphite additive, and the new 3-pipe type of heat exchange pipe section. For the same condition, the Cement Grouting can reduce the construction cost of GHEXs by around 40% in the given cost analysis scenario. In addition, an addition of graphite and use the new 3-pipe heat exchange pipe lead to about 8% and 6% cost reduction, respectively.
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Applicability of Cement-based Grout for ground heat exchanger considering heating-cooling cycles
Science China Technological Sciences, 2011Co-Authors: Moonseo Park, Jong Min Choi, Hangseok ChoiAbstract:The applicability of Cement Grout (or Cement-based Grout) has been considered as an alternative to bentonite Grout commonly used to backfill closed-loop vertical ground heat exchangers. In a geothermal heat pump system, repeated heating-cooling cycles may cause adverse effects on the integrity of Cement Grout in the ground heat exchanger. To account for the temperature cycling effect, the strength degradation of Cement Grout due to temperature cycling has been examined by measuring the unconfined compression strength of cured specimens in a humidity-temperature controlling chamber with applying temperature cycles between −5°C and 50°C. There is a tendency that the unconfined compression strength decreases with an increase in the number of temperature cycles. On the other hand, an equivalent hydraulic conductivity of a pipe-embedded Cement Grout specimen was evaluated by carrying out a modified flexible wall permeameter test equipped with a water circulating system to control temperature inside the pipe section. The applied operating temperature range was from 5 to 35°C. After three cycles of heating-cooling circulation, the equivalent hydraulic conductivity becomes asymptotic to a constant value, which implies there is no severe detachment of the pipe from the Cement Grout.
Md Akhtar Hossain - One of the best experts on this subject based on the ideXlab platform.
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dilatancy and strength of an unsaturated soil Cement interface in direct shear tests
International Journal of Geomechanics, 2015Co-Authors: Md Akhtar HossainAbstract:AbstractThe dilatancy of a soil is significantly influenced by matric suction, and it affects the apparent friction angle and shear strength of the soil. To examine the influence of dilatancy on interface behavior, a series of direct shear box tests are conducted on a compacted completely decomposed granite (CDG) soil–Grout interface in a cast in situ condition under different matric suctions and net normal stresses. The test results indicate that matric suction and net normal stress have significant influence on the hardening-softening and dilatancy of the soil–Cement Grout interface. The failure envelopes for different matric suctions are observed as linear. The apparent interface friction angle and adhesion intercept increase with matric suction. The suction envelope is found to be nonlinear as the δb-angle decreases with matric suction. A modified model is proposed to consider the influence of dilatancy on the apparent interface friction angle and hence on the interface shear strength. Experimental sh...
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influence of Grouting pressure on the behavior of an unsaturated soil Cement interface
Journal of Geotechnical and Geoenvironmental Engineering, 2012Co-Authors: Md Akhtar HossainAbstract:The strength of soil-nails depends on the behavior of the soil-Cement Grout interface at saturated and unsaturated conditions. Nowadays, pressure Grouted soil-nails are considered to provide better interface strength than gravity Grouted soil-nails. Soil-nail pullout tests have limitations to control some boundary conditions. To overcome these limitations, direct shear tests can be used to determine the actual soil-Cement Grout interface behavior. In the present study, a series of interface direct shear tests are performed between compacted completely decomposed granite (CDG) soil and Cement Grout at both saturated and unsaturated conditions under different Grouting pressures. The inter- face shear stress increases with matric suction for different Grouting pressures, and a strain softening behavior is observed for different suctions except at saturated conditions. A dilative behavior is obvious for interface as the suctionvalue is increased from a saturated condition. However, the dilation values of soil-Cement interface for different Grouting pressures are less than that of CDG soil under different suctions. The interface shear strength increases with Grouting pressure at saturated conditions, whereas, a downward trend is obvious as the suction value is increased from saturated conditions. The rate of increase of shear strength with matric suction is greater for CDG soil compared to soil-Cement interface. Interface shear strengths for different Grouting pressures are greater than CDG soil at a lower suction range but become less than CDG soil at a higher suction range. DOI: 10.1061/(ASCE)GT.1943-5606.0000585. © 2012 American Society of Civil Engineers. CE Database subject headings: Grouting; Suction; Cement; Soil nailing; Unsaturated soils. Author keywords: Grouting pressure; Matric suction; CDG soil; Cement Grout; Interface; Direct shear.
G. Ballivy - One of the best experts on this subject based on the ideXlab platform.
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the effect of degree of saturation of sand on Groutability experimental simulation
Proceedings of the Institution of Civil Engineers - Ground Improvement, 2000Co-Authors: S. Perret, K. H. Khayat, G. BallivyAbstract:Several criteria for the injectability of Cement-based Grout in soil have been documented in the literature. Some of these criteria consider the geometric characteristics of the soil, while others rely simply on the rheological parameters of the Grout mixture to estimate its potential propagation into the soil. However, the couple characteristics of intermixing of the Grout and pore water of the injection medium are seldom considered. In order to study the effect of degree of saturation of the soil on the water dilution (washout) of the Cement Grout that can alter the characteristics of the injection, a model addressing differences in propagation of Cement Grout in a saturated and partially saturated soil is proposed in this paper. The model is supported by experimental results obtained from the injection of 200 litre sand samples prepared with various degrees of saturation and fineness. The first phase of the programme consisted of injecting a microfineCement Grout made with 1·2 W/C through 22-mm diamete...
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high performance Cement Grout for underwater crack injection
Canadian Journal of Civil Engineering, 1997Co-Authors: K. H. Khayat, G. Ballivy, M GaudreaultAbstract:An investigation was carried out to compare the performance of Cement and epoxy resin Grouts used for the underwater crack injection of four damaged concrete bridge pier shafts and footings. A blended silica fume Cement and microfine Cement and a welan gum and a cellulose-based antiwashout admixtures were considered in the Grout optimization study. The mixtures were tested for fluidity, viscosity, stability, penetrability, rate of setting, and strength. This paper presents the results of the laboratory evaluation and field repair, including provisions adopted for surface preparation, crack sealing and injection, and quality control. Test results showed that the use of a microfine Cement Grout with water-to-Cement ratio of 0.6 and a high-range water reducer dosage of 2% can produce a balance between critical rheological and mechanical properties. Such Grout was found to be tolerant to changes in water-to-Cement ratio, high-range water reducer content, and temperature. The Grout developed bond strength to submerged concrete similar to that of a high-quality epoxy resin. Despite the lower injection pressure used for the less viscous Cement-based Grout, the Grout intake was 2.8 times greater per linear meter of surface crack than that observed for the epoxy resin Grout. The use of sonic tomography to reconstitute the spatial distribution of stress wave velocities within the massive pier footings indicated that the quality of concrete was significantly improved following injection with Cement-based Grout. This was attributed to the high penetrability of the microfine Cement Grout. Such quality improvement was less pronounced in the case of injection Grouting with epoxy resin. Resume : Une Otude a OtO entreprise afin de comparer la performance des coulis ‡ base de ciment et ‡ base de rOsine-Opoxie utilisOs pour liinjection sous lieau des fissures dans le fst et liempattement de quatre piliers de pont. Un ciment avec fumOe de silice, un ciment microfin, une gomme welan et un autre agent anti-lessivage ‡ base de cellulose ont OtO considOrOs dans lioptimisation du coulis. Les mOlanges ont OtO testOs pour leur fluiditO, viscositO, stabilitO, pOnOtrabilitO, taux de prise, et