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Kamal H. Khayat - One of the best experts on this subject based on the ideXlab platform.
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rheology control of ultra high performance concrete made with different fiber contents
Cement and Concrete Research, 2020Co-Authors: Le Teng, Weina Meng, Kamal H. KhayatAbstract:Abstract The study aims to improve flexural properties of ultra-high-performance concrete (UHPC) prepared with different steel fiber volumes by controlling the rheological properties of the suspending mortar. Welan gum and High-Range Water Reducer were incorporated to control rheology. Optimum rheological properties led to enhanced fiber distribution. Fiber distribution coefficient was proposed and considered to characterize fiber dispersion and orientation. For UHPC with 1%, 2%, and 3% fiber volumes, the highest flexural performance was obtained with mortars having plastic viscosities of 36, 52, and 66 Pa·s, respectively. Beyond these values, further increase in viscosity resulted in greater air entrapment and lower mechanical properties. Prediction model for flexural strength that considers a correlation between fiber dispersion and flexural-to-tensile strength ratio of the UHPC was developed. Viscosity of UHPC mortar was shown to be a reliable indicator to determine flexural-to-tensile strength ratio, and hence predict flexural strength of UHPC.
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Effect of supplementary cementitious material content and binder dispersion on packing density and compressive strength of sustainable cement paste
ACI Materials Journal, 2016Co-Authors: Iman Mehdipour, Kamal H. KhayatAbstract:© 2016, American Concrete.The reduction of cement content and incorporation of high volume of supplementary cementitious materials (SCMs) are key factors for the design of environmentally friendly concrete (Eco-Crete). The effectiveness of incorporating an SCM to enhance rheological and mechanical properties and durability of concrete depends on the type and content of SCM, as well as the degree of dispersion of the binder resulting from the use of High-Range Water Reducer (HRWR). An experimental investigation was undertaken to evaluate the effect of binary and ternary cementitious materials on the packing density of the binder and compressive strength at 7 and 56 days of cement paste. The influence of the dispersion state of the binder on packing density was evaluated using the wet packing density approach to determine the optimum Water demand (OWD) needed to achieve maximum wet density. The effectiveness of incorporating a high volume of SCM to enhance packing density is shown to increase with an increase of HRWR dosage, resulting from a greater degree of dispersion of the binder. The incorporation of sufficient dosage of HRWR led to lower OWD needed to achieve maximum density and higher packing density. The coupled effect of these changes results in higher compressive strength. Compared to the packing density of 0.58 for binder with 100% cement, the use of SCMs in a well-dispersed system is shown to secure packing density of 0.60 to 0.73. The ternary binders containing 40 or 50% slag and 5 or 10% silica fume, by volume of total binder, can ensure lower OWD, greater packing density, lower CO2 emission, and higher compressive strength. Such binder systems can be adopted for use in sustainable cement-based materials.
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viscosity enhancing admixtures and the rheology of concrete
Understanding the Rheology of Concrete, 2012Co-Authors: Kamal H. Khayat, N MikanovicAbstract:Abstract: Viscosity-enhancing admixtures (VEAs) are Water-soluble polymers that increase viscosity and cohesion of cement-based materials. Such enhancement is essential in highly flowable concrete, including self-consolidating concrete (SCC), to control the risk of segregation and to maintain a homogenous suspension in the plastic stage until the onset of hardening. For a given mixture composition, the VEA’s ability to enhance stability can vary widely with the type and dosage rate of the admixture as well as that of the High-Range Water Reducer often needed to maintain the targeted fluidity. This chapter discusses the mode of action of various types of VEAs and their effect on the rheological properties and workability of various types of cement-based materials.
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correlating rheology of self consolidating concrete to corresponding concrete equivalent mortar
Aci Materials Journal, 2009Co-Authors: Tahir Kemal Erdem, Kamal H. Khayat, Ammar YahiaAbstract:The investigation reported in this paper seeks to develop a methodology to evaluate the rheological parameters and thixotropy of self-consolidating concrete (SCC) using those of concrete-equivalent mortar (CEM). The mixture proportioning of CEMs are derived from their corresponding concrete mixtures by eliminating the coarse aggregate fraction and replacing it by a certain mass of sand of the same surface area. SCC mixtures with Water-cementitious material ratios (w/cm) of 0.35, 0.38, and 0.42 and coarse aggregate-total aggregate volume ratios (CA/A) of 0.44 to 0.53 were investigated. The mixtures with a w/cm of 0.38 and 0.42 incorporated low and moderate dosages, respectively, of a viscosity-modifying admixture to enhance stability. For each SCC, the dosage of High-Range Water-Reducer (HRWR) was varied to cover a wide range of slump flow consistencies ranging between 570 and 730 mm (22.4 and 28.7 in.). All SCC mixtures were proportioned with 450 kg/m 3 (758.5 lb/yd 3 ) of ternary silica fume-ground granulated blast-furnace slag cement. A simple method is also proposed to determine the HRWR demand of SCC from that of the corresponding CEM. Test results showed that a good correlation can be established between the yield stress, plastic viscosity, and thixotropy of SCC and their corresponding CEM mixtures. Both thixotropy and plastic viscosity of SCC mixtures and their corresponding CEM mixtures are shown to vary primarily with variations in the w/cm and relative volume of coarse aggregate.
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Performance characteristics of cement grouts made with various combinations of High-Range Water Reducer and cellulose-based viscosity modifier
Cement and Concrete Research, 2003Co-Authors: M Saric-coric, Kamal H. Khayat, Arezki Tagnit-hamouAbstract:Abstract Cellulose-based viscosity-modifying admixtures (VMA) are used to increase the viscosity of cement-based systems, hence, reducing the risk of material separation during handling and transport and thereafter until the onset of hardening. To ensure proper fluidity such admixtures are incorporated along with High-Range Water Reducers (HRWRs). The ability of the VMA to ensure the required rheological properties depends on the type and interaction with the incorporated HRWR. Good understanding of such interaction is essential to ensure adequate performance. Limited knowledge is available on the effect of cellulose-based VMA and HRWR on physico-chemical characteristics and cement hydration. The performance of grouts made with 0.40 Water/cement (w/c) ratio containing a liquid-based cellulose material was investigated for mixtures made with polynaphtalene sulfonate (PNS) and polymelamine sulfonate (PMS) HRWR. The grouts are tested for fluidity, rheological properties, stability, setting and rate of hydration. The grouts were also tested for strength and pore-size distribution, and microstructural characteristics. This paper summarizes the results of the study regarding the influence of the type and dosage of HRWR on key characteristics of grouts made with the cellulose-based VMA.
A Yahia - One of the best experts on this subject based on the ideXlab platform.
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Statistical Models to Optimize Fiber-Reinforced Dune Sand Concrete
Arabian Journal for Science and Engineering, 2014Co-Authors: Mourad Hadjoudja, M.m Khenfer, Habib Abdelhak Mesbah, A YahiaAbstract:Flexural strength and toughness of dune sand concrete (DSC) can be improved by reducing the Water-to-cement ratio, adding fillers to improve the compactness of the matrix, or incorporating steel fibers. The incorporation of fibers and fillers can increase the viscosity and yield stress and necessitates higher dosage of High-Range Water-Reducer to maintain the desired fluidity. The mixture proportioning of DSC involves tailoring several parameters to achieve adequate fresh and mechanical properties. The optimization procedure of DSC reinforced with steel fibers often necessitates several trial batches before establishing optimal balance among the various mixture parameters that affect workability and mechanical properties of concrete. DSC proportioned with 0.46-0.73 w/c ratio, 65-335 kg/m3 of limestone filler, and 0-108 kg/m3steel fiber was evaluated. The study was undertaken to model the influence of w/c, limestone filler, and fiber contents on air content, plastic viscosity, compressive and flexural strength characteristics of the DSC. Experimental test results showed that the incorporation of 94.5 kg/m3 of fiber resulted in a significant improvement in flexural strength (up to 11.5 MPa). Statistical models established using a central composite design indicate that the w/c has the greatest effect on air content, plastic viscosity, and compressive strength of DSC than limestone filler and fiber. However, the fiber is shown to have the greatest effect on flexural strength. The established models showed that the use of limestone filler can compensate for the reduction in compressive and flexural strengths due to the increase in w/c. Trade-off between w/c, limestone filler content, and fiber dosage to optimize mixture proportioning to enhance the mechanical properties of DSC without adversely affecting fluidity is discussed.
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Applicability of rheological models to high-performance grouts containing supplementary cementitious materials and viscosity enhancing admixture
Materials and Structures, 2003Co-Authors: A Yahia, K. H. KhayatAbstract:Les paramètres rhéologiques, soit le seuil de rigidité et la viscosité plastique, des suspensions de ciment sont des paramètres importants pour le contrôle de la qualité de ces matériaux. Ces paramètres sont génélement estimés à partir de la courbe d'écoulement en utilisant un modèle empirique. Les mélanges contenant un agent de viscosité montrent cependant un comportement pseudo-plastique largement plus important que les mélanges sans agent de viscosité. Les modèles empiriques utilisés pour simuler le comportement rhéologique des coulis ordinaires ne sont alors pas adéquats pour reproduire les courbes d'écoulement des coulis pseudo-plastiques. Dans cet article, on se propose d'évaluer la validité de différents modèles empiriques pour décrire le comportement rhéologique des coulis pseudo-plastiques. Quarante-quatre coulis contenant 1,5%, 3% et 5%, de la masse de liant, de la fumée de silice du laitier de haut fourneau à des dosages entre 20 et 40% et différentes combinaisons de superplastifiant et d'agent de viscosité ont été évalués. Les résultats de cette étude ont montré qu'il est difficile de décrire le comportement rhéologique des coulis pseudo-plastiques en utilisant des modèles empiriques linéaires. En général, les modèles de Herschel-Bulkley, Robertson, De Kee et Casson sont adéquats pour décrire le comportement rhéologique des coulis pseudo-plastiques. En outre, un nouveau modèle non linéaire est proposé pour mieux décrire les rhéogrammes des coulis pseudo-plastiques ayant un faible seuil de rigidité. The knowledge of yield stress and plastic viscosity of cement-based materials is of special interest in various applications, including consolidation grouting, post-tensioning systems, and for numerical simulations. These rheological parameters are generally estimated from the shear stress-shear rate data using an empirical model. Highly pseudoplastic systems may not be adequately modeled using flow models typically used for conventional grouts. This paper summarizes the results of a study undertaken to evaluate the applicability of a number of analytical models to fit experimental data obtained on cement grout. In total, 44 grouts containing silica fume replacements of 1.5%, 3%, and 5% by mass of cementitious materials, blast furnace slag substitutions of 20% and 40%, and various combinations of High-Range Water-Reducer and viscosity-enhancing admixture were evaluated. All mixtures were prepared with 0.40 Water-cementitious material ratio. Test results highlight the difficulties encountered when using conventional models to fit flow data of highly pseudoplastic mixtures of low yield stress. This is true for mixtures incorporating a viscosity-enhancing admixture, especially when combined with low dosage of High-Range Water-Reducer. In general, the Herschel-Bulkley, Robertson, De Kee, and Casson models were found to be adequate for use with highly pseudoplastic grouts. A new model is proposed to provide better fitting of rheological profiles of highly flowable, yet stable, pseudoplastic mixtures that exhibit particularly low yield stress values.
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Applicability of rheological models to high-performance grouts containing supplementary cementitious materials and viscosity enhancing admixture
Materials and Structures, 2003Co-Authors: A Yahia, Kamal H. KhayatAbstract:The knowledge of yield stress and plastic viscosity of cement-based materials is of special interest in various applications, including consolidation grouting, post-tensioning systems, and for numerical simulations. These rheological parameters are generally estimated from the shear stress-shear rate data using an empirical model. Highly pseudoplastic systems may not be adequately modeled using flow models typically used for conventional grouts. This paper summarizes the results of a study undertaken to evaluate the applicability of a number of analytical models to fit experimental data obtained on cement grout. In total, 44 grouts containing silica fume replacements of 1.5%, 3%, and 5% by mass of cementitious materials, blast furnace slag substitutions of 20% and 40%, and various combinations of High-Range Water-Reducer and viscosity-enhancing admixture were evaluated. All mixtures were prepared with 0.40 Water-cementitious material ratio.
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Evaluation of cement grouts for embedding anchors under Water
Materials and Structures, 1998Co-Authors: A Yahia, K. H. Khayat, B. BenmokraneAbstract:Des essais d’arrachement ont été réalisés en laboratoire afin d’étudier l’effet des propriétés rhéologiques et mécaniques des coulis de scellement, de la longueur de scellement, de la procédure de mise en place ainsi que de la période de mûrissement sur le comportement des ancrages installés sous l’eau et en dehors de l’eau. Des barres d’armature de 19 mm de diamètre sont utilisées comme tirants d’ancrage. La longueur de scellement est fixée à une longueur égale à cinq fois le diamètre du tirant. Les coulis de scellement ont été mis en place en utilisant deux hauteurs de chute du coulis dans l’eau de 20 et de 200 mm. Les coulis de scellement ont été formulés en utilisant un ciment Type 10 et un ciment contenant de la fumée de silice et un rapport eau/liant de 0,40. Les coulis utilisés contiennent différents ajouts. En particulier, le superplastifiant et l’agent colloïdal sont utilisés pour améliorer la fluidité et la résistance au lessivage des coulis. Cette étude a montré en particulier que l’utilisation des coulis de ciment ayant une bonne résistance au lessivage permet d’obtenir une bonne résistance à l’arrachement des ancrages mis en place sous l’eau. Une bonne résistance au lessivage est assurée par l’utilisation de l’agent colloïdal et de la fumée de silice. Approximately 110 pull-out tests were conducted on grouted anchors cast in the laboratory to investigate the effects of the rheological and mechanical properties of cement grouts, the initial free drop distance of grout, as well as the age of testing on the behavior of anchorages cast in dry and submerged conditions. The anchors consisted of 19-mm, conventional steel bars with an embedment length fixed at five times the bar diameter. Two different casting procedures corresponding to initial free drop of the grout in Water of 20 and 200 mm were investigated. The cement grouts used in this investigation incorporated either a Type 10 or a blended silica fume cement and a fixed Water-binder ratio of 0.40. The grouts incorporated various concentrations of a High-Range Water Reducer, a rheology-modifying admixture, and silica fume. The rheology-modifying admixture and High-Range Water Reducer were jointly incorporated to enhance both fluidity and washout resistance. The test results indicate that properly designed grouts can be easily cast into place, and yet be cohesive enough to resist the washout of cementitious materials. The spread in load-carrying capacity between anchor bars cast in dry versus submerged conditions can decrease when cement grouts having a greater washout resistance level are used which can be secured by incorporating a rheology-modifying admixture and silica fume. The bond strength is shown to increase when incorporating silica fume regardless of the casting condition.
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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.
Ammar Yahia - One of the best experts on this subject based on the ideXlab platform.
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effect of solid concentration and shear rate on shear thickening response of high performance cement suspensions
Construction and Building Materials, 2014Co-Authors: Ammar YahiaAbstract:Abstract Flow performance, placement, and consolidation of concrete are mainly related to its rheology. Rheology of paste plays a key role on rheology of concrete. Cement pastes exhibit complex rheological behavior affected by several physical and chemical factors, including the solid concentration, type and dosage of High-Range Water-Reducer (HRWR), cement characteristics, and shear history. An experimental investigation was carried out to investigate the effect of solid concentration, HRWR–cement combinations, and shear rate regime on pseudoplastic behavior of high-performance cement grouts. Grout mixtures proportioned with w/c of 0.30, various cement–HRWR combinations, 8% silica fume, and different limestone powder additions were investigated. Solid concentration and shear rate regime are shown to be key factors affecting shear-thickening response of concentrated cement-based suspension (i.e. low w/c). Concentrated high-performance grout mixtures are shown to exhibit shear-thickening behavior. The use of polycarboxylate HRWR acting by hindrance effect exhibited greater shear-thickening behavior compared to polynaphtalene type acting by electrostatic effect. The use of finer particles enhances the powder skeleton and ensures polydisperse systems, hence resulting in lower shear-thickening response. For concentrated cement-based suspensions, shear-thickening is due to disorder state, and at higher shear rate, hydrocluster formation is prevailing.
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correlating rheology of self consolidating concrete to corresponding concrete equivalent mortar
Aci Materials Journal, 2009Co-Authors: Tahir Kemal Erdem, Kamal H. Khayat, Ammar YahiaAbstract:The investigation reported in this paper seeks to develop a methodology to evaluate the rheological parameters and thixotropy of self-consolidating concrete (SCC) using those of concrete-equivalent mortar (CEM). The mixture proportioning of CEMs are derived from their corresponding concrete mixtures by eliminating the coarse aggregate fraction and replacing it by a certain mass of sand of the same surface area. SCC mixtures with Water-cementitious material ratios (w/cm) of 0.35, 0.38, and 0.42 and coarse aggregate-total aggregate volume ratios (CA/A) of 0.44 to 0.53 were investigated. The mixtures with a w/cm of 0.38 and 0.42 incorporated low and moderate dosages, respectively, of a viscosity-modifying admixture to enhance stability. For each SCC, the dosage of High-Range Water-Reducer (HRWR) was varied to cover a wide range of slump flow consistencies ranging between 570 and 730 mm (22.4 and 28.7 in.). All SCC mixtures were proportioned with 450 kg/m 3 (758.5 lb/yd 3 ) of ternary silica fume-ground granulated blast-furnace slag cement. A simple method is also proposed to determine the HRWR demand of SCC from that of the corresponding CEM. Test results showed that a good correlation can be established between the yield stress, plastic viscosity, and thixotropy of SCC and their corresponding CEM mixtures. Both thixotropy and plastic viscosity of SCC mixtures and their corresponding CEM mixtures are shown to vary primarily with variations in the w/cm and relative volume of coarse aggregate.
Lukumon O Oyedele - One of the best experts on this subject based on the ideXlab platform.
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High volume fly ash concrete: The practical impact of using superabundant dose of high range Water Reducer
Journal of Building Engineering, 2016Co-Authors: Hafiz A Alaka, Lukumon O OyedeleAbstract:The practice of using extraordinarily low Water/binder ratio for high volume fly ash (HVFA) concrete mixes in order to realize adequate early strength is prevalent. Generally, superabundant dose of high range Water Reducer (i.e. superplasticizer) is required to make such mixes workable. The relationship between superabundant superplasticizer dose and various HVFA concrete properties is thus examined in this research work. Three groups of HVFA concrete mixes were designed for this purpose. Each group consisted of 3 mixes. Except for superplasticizer dose, the proportion of materials in the three group 1 mixes were the same, each mix containing 50% fly ash as replacement for cement. Of the three mixes, one contained maximum superplasticizer dose at 2% of binder by mass, the second contained superabundant dose at 3% while the third contained 4% dose. Group 2 and 3 mixes were similar to those of group 1 except that they contained 60% and 65% fly ash content respectively. Fresh concrete tests performed on the mixes included flow table and slump tests. Mechanical tests included compressive strength, splitting tensile strength, flexural strength and wear resistance tests. The outcome of the tests revealed that superabundant superplasticizer doses helped to obtain relatively lower Water/binder ratios with good workability; led to reduction in wear/abrasion resistance; and had no observable relationship, beneficial or adverse, with the compressive, splitting tensile and flexural strengths of the HVFA concrete mixes. Increase in fly ash content was also noted to beget reduction in wear/abrasion resistance. In addition, the outcome indicated that increase in compressive strength does not necessarily translate to improved abrasion or wear resistance.
Weina Meng - One of the best experts on this subject based on the ideXlab platform.
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rheology control of ultra high performance concrete made with different fiber contents
Cement and Concrete Research, 2020Co-Authors: Le Teng, Weina Meng, Kamal H. KhayatAbstract:Abstract The study aims to improve flexural properties of ultra-high-performance concrete (UHPC) prepared with different steel fiber volumes by controlling the rheological properties of the suspending mortar. Welan gum and High-Range Water Reducer were incorporated to control rheology. Optimum rheological properties led to enhanced fiber distribution. Fiber distribution coefficient was proposed and considered to characterize fiber dispersion and orientation. For UHPC with 1%, 2%, and 3% fiber volumes, the highest flexural performance was obtained with mortars having plastic viscosities of 36, 52, and 66 Pa·s, respectively. Beyond these values, further increase in viscosity resulted in greater air entrapment and lower mechanical properties. Prediction model for flexural strength that considers a correlation between fiber dispersion and flexural-to-tensile strength ratio of the UHPC was developed. Viscosity of UHPC mortar was shown to be a reliable indicator to determine flexural-to-tensile strength ratio, and hence predict flexural strength of UHPC.