Rheology Of Cement Paste Research Articles

Particle packing and rheology of cement pastes at different replacement levels of cement by α-Al2O3 submicron particles

The aim of this study was to clarify the micro-scale processes which control the fresh and hardened properties of hydrating cement pastes containing up to 10wt% of α-Al2O3 submicron particles and a polycarboxylate-type superplasticizer. The main factor controlling the changes in the microstructure and properties of the fresh pastes with increasing α-Al2O3 cement replacement levels was found to be the increase in the total specific surface area, whereas particle packing played only a minor role. However, in the case of the hardened pastes much more complex and somewhat counteracting effects were observed. Depending on the cement replacement level of the pastes, the sum of these effects was either a hardly noticeable improvement in their mechanical properties, compared to those of the reference paste, or even a reduction in them. These differences decreased with increasing curing time.

Rheology of cement paste under high pressure

The objective of this study was to investigate whether cementitious materials undergo changes during pumping processes due to pressure variation. The influence of pressure on the rheological properties of cement pastes, which assumably represented the lubricating layer that forms along the profile of concrete during pumping, was evaluated using a rotational rheometer with a high-pressure cell. Cement pastes with water-to-cement ratios ranging from 0.35 to 0.6 were tested according to a protocol designed to simulate the conditions of an actual pumping process based on field tests. The shear rates, shearing durations, and pressure levels from 0 to 30 MPa were experimentally simulated. The test results indicated that below a certain water-to-cement ratio (0.40) elevated pressures lead to changes in the rheological properties, while changes were negligible when the ratio was above this threshold. Further, at low water-to-cement ratios the thixotropy of the cement paste can reverse into rheopexy after pressurization.

The role and interaction of superplasticizer and emulsifier in fresh cement asphalt emulsion paste through rheology study

The workability and mechanical properties of cement asphalt emulsion (CA) mortar are unstable due to the complex interaction between cement and asphalt emulsion. To reveal the interaction between cement and asphalt emulsion, the effect of emulsifier and superplasticizer on the rheology of cement paste and asphalt emulsion is investigated, respectively, and the effect of the interaction between emulsifier and superplasticizer on the rheology of cement paste is studied in this paper as well. Results show that the apparent viscosity and yield stress of asphalt emulsion increase with superplasticizer and emulsifier dosage. Emulsifier can change the yield stress and apparent viscosity of cement paste, and its effect on cement paste differs greatly with the type and dosage of emulsifier. Some emulsifiers can increase the yield stress of cement paste, but some emulsifiers can decrease the yield stress of cement paste. Emulsifier has interaction with superplasticizer, thus affecting the reducing water effect of superplasticizer on cement paste. There is a competition relationship between emulsifier and superplasticizer when they are adsorbed by cement particles. The mixing method, in which superplasticizer is mixed with cement before emulsifier added, is beneficial to obtain a lower apparent viscosity of cement paste for all tested emulsifiers.

Which parameters, other than the water content, influence the robustness of cement paste with SCC consistency?

Robustness is the capacity of cement-based mixtures to tolerate small variations in constituent elements, mixing parameters or temperature. It is an important reason slowing down the practical implementation of self-consolidating concrete (SCC). Especially the sensitivity of fresh SCC properties to a small variation in water content can be found in literature. The influence of the mixing sequence and mixing procedure on the robustness of SCC mixtures is not extensively reported.The present paper evaluates the effect of mixing time, mixing speed and the addition time of superplasticizer on the rheological properties of cement pastes with SCC consistency, which can be related to SCC mixtures. By means of rheology, the changes induced by the variations in mixing procedure are compared to the changes induced by the variations in water and superplasticizer content. The results indicate that changing the water content is the main factor influencing rheology of cement pastes with low water-to-powder ratio (w/p). However, with increased water content in the paste mix design, other factors, such as adding time of the superplasticizer and mixing speed have equal or even superior importance as changing the water content. Dependent on the mix design, it may thus be necessary to use variables other than the water content to study robustness.

Influence of high mixing intensity on rheology, hydration, and microstructure of fresh state cement paste

From both the fundamental and applied points of view, there is a growing interest in characterizing the rheological properties of concentrated suspensions, such as cement paste. When a cement paste is sheared, its intrinsic network structure will respond to the shear induced stresses. The influence of mixing intensity on the rheological properties of fresh state cement paste is studied. The results showed that contrary to what is popularly believed, when subjected to a high mixing intensity, the rheological properties of cement paste can increase once a certain threshold mixing intensity is achieved. This increase in rheological properties was associated with changes in the chemical nature and physical nature of the cement pastes.

Structural Features of Nanomodified Cement Stone

The article reviews the effect of mixing water pre-modified with fulleroid nanomaterial on cement paste rheology and cement stone structure. Also pH value of modified mixing water is determined and its variation under the effect of nanomaterial is shown. Typical acidulation of obtained slurry is noted and time of its activity (aggregative stability) beneficial to formation of cement stone structure is determined. Analysis of the obtained results is evidencing changes in properties of cement systems prepared with the use of nanostructured water, namely increase in cement paste setting time and improvement of its fluidity with rheological properties maintained; enhancement of pore structure with improved uniformity of distribution throughout the volume, leading to increase in strength properties of cement stone.

Effect of hydrophobic units of polycarboxylate superplasticizer on the flow behavior of cement paste

ABSTRACTFor the tuning of conformation of polycarboxylate (PCE) superplasticizers, hydrophobic groups of different stiffness were incorporated, including styrene (St), methyl methacrylate (MMA), ethyl acrylate (EA), and n-butyl acrylate (n-BA) units. The effect of these hydrophobic groups on the dispersing performance, adsorption process and, rheology of cement paste were investigated. Investigation on the solution conformation and adsorption layer thickness indicated the action mechanism of these groups. High backbone stiffness resulted in a lower extent of conformation condensation from pure aqueous solution to pore solution, and therefore more carboxylic groups could be accessible for adsorption. However, the conformation change after adsorption might also be limited and the size of single molecule after adsorption should be small. Hydrophobic groups always resulted in a coiled PCE conformation in salt solution, which indicated a lower adsorption affinity and thinner adsorption layer for these PCE molecules.

Influence of GGBS on Rheology of Cement Paste and Concrete with SNF and PCE based Superplasticizers

Limestone and clay which are the major ingredients of the cement production are non-renewable resources. Therefore, it is essential to identify a sustainable material to replace cement. The by-product from the steel plant is subsequently granulated to desired fineness and is termed as Ground Granulated Blast furnace Slag (GGBS). Superplasticizers (SP) are used to improve the workability of concrete at low water-cement ratios and increase the compressive strength by reducing it. But, this workability is sometimes lost rapidly as time progresses after contact between the cement and water. Therefore, it is necessary to understand the mechanisms that influence the cement-super plasticizer interaction for selecting an appropriate type of admixture at an optimum dosage. In this present research the compatibility study, between six combinations of cement using different percentages of GGBS with two different SPs were investigated. The optimum dosage was found using marsh cone test. The cement mortar flow test was conducted to find out the setting time and compressive strength of the mortar. It is found that the increase in addition of GGBS decreases the dosage of Superplasticizers to achieve the desired workability. The target mean strength of the M40 concrete was achieved with replacement of 50% GGBS using PCE based SP.

Rheology and Setting Time of Cement Paste

Experimental results about effect of superplasticizer dosage, fly ash content and water to cement ratio on rheology and setting time are presented. 16 samples are evaluated using a Brookfield laboratory rheometer and a standard vicat needle apparatus. Spread of the samples is also measured using mini slump cone (d1=60mm, d2=35, h=60mm) and an empirical relationship between spread and yield stress is put forward.

Steady state flows of fresh cement pastes and concretes: simplified underlying physics

From rational and micromechanical arguments on energy levels of particle/particle and particle/ fluid interactions, we first provide here a conceptual diagram of predominant interactions within flowing cement pastes under simple shear in steady state as a function of shear rate and solid volume fraction. We focus then on what is universal and common to all polymers used in the cement construction industry and describe at first order the main changes in the underlying physics occurring when such molecules are added to a cement suspension. We finally discuss the upscaling between cement paste rheology and concrete fresh properties.

Effect of mixing method on microstructure and rheology of cement paste

Mixing is one of the most important processes for producing concrete. The influence of different mixing methods on the rheological properties and fresh state microstructure of cement pastes were evaluated. In this work, the mixing process of cement paste was based on two different sample preparation methods: ASTM C305 and ASTM C1738. ASTM C1738 uses a high shear mixer, whereas ASTM C305 uses a planetary mixer to homogenize cement paste. A considerable increase in the rheological properties was seen in pastes prepared using the ASTM C1738 protocol versus those prepared according to ASTM C305, especially when a superplasticizer was incorporated. Not only were the rheological properties affected, but differences in hydration kinetics and fresh state microstructure were also observed, with mixtures prepared with ASTM C1738 generally displaying more flocculated microstructural features and accelerated hydration kinetics than mixtures prepared with ASTM C305.

Effect of polyacrylamide on rheology of fresh cement pastes

In this paper, we study the effects of polyacrylamide (PAM) on both aqueous solutions and fresh cement pastes. Our solution viscosity and hydrodynamic radii measurements in various solutions suggest that calcium ions lead to a cross-linking of anionic PAM and to the formation of PAM micro-gels. Our adsorption measurements show that the majority of these micro-gels adsorb on cement grains whereas our rheological measurements on cement pastes suggest that these micro-gels are able to adsorb simultaneously on several cement grains and bridge them increasing therefore the macroscopic yield stress of the suspension. Finally, we show that the contribution of PAM to yield stress is very sensitive to shear history, as the paste structure seems to progressively lose its ability to rebuild with each shearing or re-mixing cycle. We suggest that this feature could find its origin in the progressive flattening of the micro-gels at the surface of the cement grains.

Measuring Cement Paste Rheology Using a Modified Dynamic Shear Rheometer: An Approach to Detect Cement-Admixtures Incompatibilities

Abstract The objective of this research is (1) to develop an easy-to-use Superpave dynamic shear rheometer (DSR)–based device that could measure cement paste rheology with permissible repeatability and sensitivity, and (2) to investigate whether potential cement-admixtures (mineral and chemical) incompatibilities can clearly be identified through direct measurement of cement paste rheology. The DSR was modified to make it suitable for measuring cement paste rheology and a DSR-based rheology test procedure with optimum parameters and test conditions was subsequently developed. An extensive laboratory investigation using the modified and optimized DSR-based rheology test procedure with varieties of cements, supplementary cementitious materials, and different types and dosages of commonly used chemical admixtures under different temperature conditions was conducted. The heat of hydration (HOH) and setting time tests were also performed for all of the studied mixtures as supporting tools. The rheology tests were conducted using both static and dynamic mode of operations. The rate of change of plastic viscosity and yield stress was found to be the most sensitive parameter to identify the studied incompatible mixtures in the static mode and used to develop acceptance criteria. Similarly, monitoring storage modulus over time followed by determining ultimate storage modulus was used to detect the same incompatible mixtures in the dynamic mode. The rheology-based test results are strongly supported by the HOH and setting time results. The test results show that DSR in modified form is capable of measuring cement paste rheology with permissible reproducibility and sensitivity and detecting incompatible mixtures. The modified DSR-based procedure has a great potential to detect problematic combinations of concrete ingredients during the mixture-design process and thereby avoid concrete cracking and other durability issues resulting from incompatibilities.

Effects of Nanomaterials on the Hydration Kinetics and Rheology of Portland Cement Pastes

Abstract In this paper, effects of nanomaterials on the hydration kinetics and rheology of ordinary Portland cement pastes were investigated. Three nanomaterials, nano-limestone, nano-silica, and nano-clay (a highly purified magnesium aluminosilicate), were added to a cement paste at the levels of 0.0 %, 0.5 %, 1.0 %, and 1.5 % (by mass) of cement. The heat of cement hydration of the paste was measured using isothermal calorimetry. Rheological behavior of the paste was characterized using a rotational rheometer. The rheology measurements were performed at 10, 30, 60, 90, and 120 min after the cement was mixed with water. Set times of the paste were measured according to ASTM C191 [Standard Test Methods for Time of Setting of Hydraulic Cement by Vicat Needle, Annual Book of ASTM Standards, ASTM International, West Conshohocken, PA]. The experimental results indicate that the addition of nano-limestone and nano-silica accelerated cement early hydration, the maximum heat flow increased, whereas the time to reach the heat-flow peaks decreased. The initial and final set times were also reduced. These effects were enhanced with increased nano-addition level. The addition of nano-clay also significantly increased the intensity of the heat flow peaks, and, especially, the peak corresponding to the renewed reaction of the aluminate phase. Addition of these nanomaterials generally increased yield stress and viscosity of the cement paste, especially after 60 min when cement hydration started to accelerate. Nano-clay considerably influenced the rheological behavior of the cement paste. Significantly higher shear stresses were required to initiate the flow.

Influence of lignosulfonate on the early age rheology and hydration characteristics of cement pastes

Four different cements made from gypsum mixed with clinkers possessing varying amounts of clinker phases were employed to investigate the influence of lignosulfonate on the early age rheological and hydration properties of cement pastes. Two test methods were employed; the parallel plate rheometry and isothermal calorimetry. Here, lignosulfonate was quantitatively shown to impact the early age hydration of cement pastes depending on the C3A and C3S compositions, in the respective order. A threshold amount of ~4.6% C3A is needed to sufficiently impair the performance of lignosulfonate at normal working dosages (0.4% bwoc). When high amounts of C3A was present (~10%), flash set of the cement paste occurred even at the low dosage of 0.2% bwoc of lignosulfonate. When cement possessed low amount of C3A, lignosulfonate mainly retarded the hydration of C3S, but this effect decreased when the C3S was doped with Al.

Wpływ popiołu lotnego wapiennego na właściwości reologiczne zaczynów i zapraw cementowych

The use of mineral additives allows modifying properties of concrete and results in substantial economic benefits. The research presents the influence of calcareous fly ash volume and degree of activation by grinding on the rheology of cement pastes and mortars. The rheological parameters of cement pastes and mortars were determined using a rheometer Viskomat NT. The results show that due to rheological properties of mixes calcareous fly ash (W) can be used as a cement component, however, after the activation and preferably in the multicomponent cement together with siliceous fly ash (V) or ground granulated blast furnace slag (S). Due to the workability, calcareous fly ash (as a type II additive) should be used after activation by grinding or by separation, preferably in an amount of not more than 20%.

Viscosity and water demand of limestone- and fly ash-blended cement pastes in the presence of superplasticisers

The rheological behaviour of fresh cement has a direct effect on the microstructural development of mortar and concrete. Inasmuch as the presence of mineral additions impact cement paste rheology and consequently its permanent microstructure and strength, a full understanding of blended cement behaviour should be pursued. The present study addresses the joint effect of mineral additions (limestone and fly ash) and superplasticisers admixtures on the viscosity and water demand of cement pastes.Cement pastes were prepared with 10, 30 or 50 wt% limestone or fly ash as mineral admixtures. Melamine-, naphthalene- and polycarboxylate-based superplasticisers were used. Paste rheology was studied in terms of variations in yield stress and viscosity with the solids content and amount of mineral additions added. The strength and microstructure of the blended cement pastes were determined at viscosity values of 1.5 Pa·s. in the presence of superplasticisers.The findings showed that the Krieger–Dougherty equation could be used to determine the effect of solids content on the apparent viscosity of limestone- and fly ash-blended cement suspensions, as well as the effect of superplasticisers. Adding less than 30% limestone to cement had no effect on paste rheology: i.e., the w/c ratios for minimum and optimal workability were similar to the ratios for ordinary cement. However, adding fly ash did lower the minimum water demand, and the optimal amount of water needed for suitable fluidity. The inclusion of 10% of either addition raised paste strength, while higher proportions 30 or 50%) had the opposite effect. The use of mineral additions reduced the effectiveness of cement superplasticisers.

Rheology of semi-solid fresh cement pastes and mortars in orifice extrusion

Short fiber-reinforced semi-solid fresh cement pastes and mortars, tailored for extrusion, have much lower water-to-binder ratio and higher viscosity than normal cement pastes or mortars. The rheology of these pastes or mortars cannot be characterized by traditional rheology test methods suitable for normal fresh cement pastes or mortars with much greater water-to-binder ratio and lower viscosity. In this paper, orifice extrusion is employed to calibrate rheology of the semi-solid fresh cement mortar. An analytical model is developed for orifice extrusion of semi-solid pastes and mortars obeying a rigid-viscoplastic constitutive relationship, von-Mises yield criterion and the associated flow rule. Orifice extrusion results are interpreted using the analytical model and the established experiment data interpretation method, and the associated rheological parameters are derived for the semi-solid fresh cement mortar. This study provides a simple analytical model, together with experiment and data interpretation methods, for characterizing the complex intrinsic rheological behavior of semi-solid fresh cement pastes or mortars.

Roles of Packing Density and Water Film Thickness in Rheology and Strength of Cement Paste

Roles of Packing Density and Water Film Thickness in Rheology and Strength of Cement Paste

Combined effect of expansive, shrinkage reducing and hydrophobic admixtures for durable self compacting concrete

This paper presents the results of an investigation carried out to develop white self-compacting concretes (SCCs) especially devoted to durable architectural structures. In fact, shrinkage-free SCC mixtures were studied, obtained by combining CaO-based expansive agent and shrinkage reducing admixture. Also a hydrophobic admixture was added to SCC in order to preserve the white surface from the growth of micro-organisms as well as to increase concrete durability. Rheological tests were carried out on cement pastes, as well as on fresh SCCs, containing the three admixtures in order to study their influence (alone or in combination) on cement paste and concrete rheology. Also thermogravimetric analysis was carried out on cement pastes in order to evaluate the influence of various admixtures on portlandite solubility. Hardened SCCs were characterized by means of compression tests, free dying shrinkage, and restrained expansion measurements.