Influence of mixing sequence and superplasticiser dosage on the rheological response of cement pastes at different temperatures

An experimental methodology to study the rheological response of superplasticised cement pastes subjected to temperatures ranging from 5 to 45 °C is presented. The content of a polycarboxylate-based superplasticiser (PC) and moment of its addition to the mix (direct or delayed) are investigated. A loop of shear rate ramps is applied to each sample in order to obtain information about apparent viscosities and yield stresses, as well as a measure of their thixotropic behaviour. Results from the experimental campaigns indicate PC saturation dosages depend only slightly on temperature. The evolution of yield stress and thixotropy with temperature shows inverted trends under some conditions.     

Influence of cement and superplasticizers type and dosage on the fluidity of cement mortars—Part I

Concrete quality is controlled by the flow behavior of cement paste, which is related to the dispersion of cement particles. Superplasticizers (SPs) provide the possibility of a better dispersion of cement particles, thereby producing paste of higher fluidity. With the development of high strength, high performance concrete, SPs are becoming indispensable. SPs are adsorbed on the cement particles. This adsorption is uneven and depends upon the clinker composition of cement and the type of SP used. This work is focused on the study of the influence of lignosulfonic acid (LS)- and melamine sulfonic acid (SMF)-based SPs on the fluidity of mortars made with ordinary Portland (OPC), low alkali (LAC) and white cement (WC) at different water to cement ratio. It is shown that LS are more effective than SMF in providing better fluidity. Further WC has given the highest fluidity among the cements used. It is attributed to the lower C₃A+C₄AF and alkali content, and higher SO₃ content.     

Influence of temperature on yield value of highly flowable micromortars made with sulfonate-based superplasticizers

Self-consolidating concretes (SCC) were proved to be very dependant on concreting temperature and the elapsed time. To enhance the concreting conditions of these flowable concretes, it is important to have a better knowledge of their rheological behavior, depending on the kind of superplasticizer used. The variation of the plastic viscosity and the yield value with the elapsed time and temperature must be accurately quantified. However, the methods of measuring these parameters are expensive and unsuitable with a good forecast of the material behavior due to numerous parameters that interact with each other. A simplest method to study the variation of these rheological parameters, depending on the mixture design, is proposed, using the micromortar, which derivates from the studied SCC. Moreover, to forecast the concrete behavior on the site, a simple thermodynamical approach of the cementitious matrix behavior through the study of the hydration kinetics is described.     

Shear-thickening behavior of high-performance cement grouts — Influencing mix-design parameters

Rheology of concrete is of great importance to its flow performance, placement and consolidation. A full understanding of fresh concrete flow behavior can be achieved through a good understanding of paste rheology. Cement pastes exhibit a complex rheological behavior affected by several physical and chemical factors, including water-to-cement ratio (w/c), high-range water-reducer (HRWR) type and dosage, and cement characteristics. An experimental investigation was carried out to evaluate the effect of w/c, HRWR–cement combinations, and supplementary cementitious materials (SCM) on the pseudoplastic behavior of high-performance cement grouts. Grout mixtures proportioned with w/c of 0.30, 0.33, 0.36, and 0.40, various cement–HRWR combinations, and cement substitutions by 8% silica fume were investigated. The incorporation of HRWR can lower the yield stress of mixtures, thus enhancing deformability, while silica fume improves mechanical and durability performances.High-performance structural grouts are shown to exhibit shear-thickening behavior at low w/c and shear-thinning behavior at relatively higher w/c. Mixtures made with polycarboxylate HRWR acting by steric effect exhibited greater shear-thickening behavior compared to those made with polynaphthalene sulfonate-based HRWR acting by electrostatic effect. The paper discusses the effect of mixture parameters on non–linear rheological behavior of various grout mixtures prepared with different w/c, HRWR–cement combinations, and silica fume.     

Influence of superplasticizers on rheological behaviour of fresh cement mortars

To assure required workability of high performance concrete (HPC), various superplasticizers are used. Only by using superplasticizers can rheological properties of HPC mix be adequately adjusted to the methods and conditions of concrete processing. Thus, the key element in efficient workability shaping is the complex knowledge how superplasticizers influence the rheological properties of fresh concrete in different technological circumstances.In the paper, the methodology and test results of an investigation into the influence of chemically different superplasticizers on the rheological properties of standard mortars are presented and discussed. The rheological parameters of mortars yield value g, and plastic viscosity h were determined using VISCOMAT PC rotational rheometer. In the research, the influence of the performance of superplasticizers was investigated taking into account following factors: chemical origin of superplasticizers (SNF/naphthalene sulfonic acid/, AP/polycarboxylate acid, PC/policarboxylate ester/), superplasticizer dosage, W/C ratio, cement type (CEM I, CEM II and CEM III), cement physical and chemical properties and temperature.The results presented in the paper show that by testing rheological parameters of mortars with rotational viscometer, it is possible to complex and precisely determine the performance of superplasticizers. On the ground of obtained results, it is possible to optimise the composition of mortars and concretes from workability point of view.     

Performance of new viscosity modifying admixtures in enhancing the rheological properties of cement paste

The use of viscosity modifying admixtures (VMA) has proved to be very effective in stabilizing the rheological properties and consistency of self-compacting concrete (SCC). SCC is known for its excellent deformability, high resistance to segregation and use, without applying vibration, in congested reinforced concrete structures characterized by difficult casting conditions. Most of the commercial VMAs currently available in the market are costly and increase the price of such a concrete. Identification or production of new low-cost VMA is then essential. This paper presents the performance of four new polysaccharide-based VMAs in enhancing the rheological and consistency properties of cement paste. The study of the rheological properties and consistency of cement paste to screen the dosage and type of new VMA to be used in SCC is a promising approach. Investigation was carried out on cement pastes with combinations of various dosages of new VMAs and of a superplasticizer (SP) to study the influence on rheology, consistency and washout mass loss. A commercial VMA designated in this paper as “COM” was tested for comparison. The study on new VMAs is encouraging and confirms that pastes with satisfactory rheological and consistency properties comparable with or even better than commercial VMA can be developed. The combined use of proper dosages of VMA and SP is shown to clearly contribute to securing high-performance cement pastes that is highly fluid yet cohesive enough to reduce water dilution and enhance water retention. Attempt has also been made to correlate rheological properties (yield stress) to consistency (slump) of pastes.     

Influence of superplasticizer type and dosage on the slump loss of Portland cement mortars—Part II

Fluidity and slump loss are cardinal features responsible for the quality of concrete. These are related to the dispersion of cement particles and the hydration process, which are greatly influenced by superplasticizers (SPs). A variety of SPs are commercially available. Their influence on the fluidity and slump loss differs considerably. In this work, SPs based on lignosulfonic acid (LS), melamine formaldehyde sulfonic acid (SMF), naphthalene formaldehyde sulfonic acid (SNF), and polyacrylic acid polymer (CE) are tested with ordinary Portland cement (OPC) at different water-to-cement ratio. The results reveal that not only SPs of different base groups behave differently but even the SP of the same base group SMF behave differently. Fluidity increased with increase in the dosage of SP. CE was most effective followed by LS, SNF, and SMF SP.     

An investigation on the rheological and sulfur-retention characteristics of desulfurizing coal water slurry with calcium-based additives

Desulphurizing coal water slurry is a kind of new clean coal water slurry(CWS), which has good performance on SO₂ emission during combustion and gasification process. But, the addition of sulfur-retention agents have some effects on the stability and fluid characters of the coal water slurry. In this paper, the viscosity, stability and rheology of Xinwen coal water slurry have been studied by adding different kinds of calcium-based sulfur-retention agents and different dosage. The results show that the sulfur-retention agents have little effect on rheological nature of CWS, which still presents pseudoplastic fluid. The addition of sulfur-retention agents will increase the viscosity of CWS, but the stability will decrease a little. The results also show that inorganic calcium has less negative effect on the performance of CWS than the organic calcium. The viscosity of the CWS with organic calcium agent keeps 1000–1200 mPa s when Ca/S molar ratio is 2. Sulfur release of the CWS with CaCO₃ reduces to 52% at Ca/S = 2 compared to original of 98%.     

Coupled effect of time and temperature on variations of plastic viscosity of highly flowable mortar

Self-consolidating concrete (SCC) is being increasingly used as construction material for its workability. However, the rheological properties of such concrete, which is made with significant concentration of high-range water-reducing admixture (HRWRA), depend in most cases on the casting temperature of the material. The study presented herein aimed at evaluating the coupled influence of time and temperature on the variations of plastic viscosity (µ) of micro mortar made with polymelamine (PMS), polynaphtalene (PNS) and polycarboxylate (PCP) polymer. In total, seven micro mortar mixtures proportioned with various binder compositions and water-to-binder ratios of 0.42 and 0.53 were prepared at 10 to 33 °C. Test results show that the plastic viscosity varies linearly with the coupled effect of time and temperature for mixtures made with PNS or PMS HRWRA. However, for mixtures made with PCP-HRWRA, both temperature and mixture proportioning have influence on the variation of viscosity with time.     

Experimental study of cement grout: Rheological behavior and sedimentation

Three basic elements (cement, water and admixture) usually make up injectable cement grouts used for prestressed cable coating, repair and consolidation of masonry, soil grouting, etc. The present study was divided into two parts. First, in order to characterize rheologically fresh cement paste with water/cement ratios (W/C) varying between 0.35 and 1, an experimental study was carried out and has revealed that the cement past behaves like a shear-thinning material, whatever is the W/C ratio. Second, to study the time evolution of their density, a γ-densitometer bench was used. Relying on the water content and the density measured, we demonstrate that the computation of the degree of hydration of cement is possible.The cement/geotechnics interdisciplinary approach proposed here has made it possible to obtain a large range of original results useful to improve our understanding of the sedimentation processes for cement pastes with different W/C ratios.     

Correlating cement characteristics with rheology of paste

The influence of cement characteristics such as cement fineness and clinker composition on the “flow resistance” measured as the area under the shear stress-shear rate flow curve has been investigated. Three different types of plasticizers namely naphthalene sulphonate-formaldehyde condensate, polyether grafted polyacrylate, and lignosulphonate have been tested in this context on 6 different cements. The flow resistance correlated well with the cement characteristic (Blaine·{d·cC₃A + [1 − d]·C₃S}) where the factor d represents relative reactivity of cubic C₃A and C₃S while cC₃A and C₃S represent the content of these minerals. It was found to be either a linear or exponential function of the combined cement characteristic depending on plasticizer type and dosage. The correlation was valid for a mix of pure cement and cement with fly ash, limestone filler (4%), as well as pastes with constant silica fume dosage, when the mineral contents were determined by Rietveld analysis of X-ray diffractograms.     

Rheological properties of highly flowable mortar containing limestone filler-effect of powder content and W/C ratio

The effect of a limestone filler addition in superplasticized cement mortar was investigated. The mixtures considered in this study are highly fluid, yet stable mortars that can be used to proportion self-consolidating concrete (SCC). All the mixtures were proportioned with a fixed unit water content of 250 l and various water-cement ratios varying from 0.35 to 0.45. A limestone filler with a specific surface area of 480 m²/kg was used at different addition percentages.This paper reports test results leading to the recommendation of suitable powder contents that can be used to proportion mortar mixtures containing a limestone filler and achieving adequate rheological properties. Test results show that the effect of limestone filler is mainly affected by the W/C and the limestone filler content in use. For a given W/C, the addition of a limestone filler within a certain range did not affect fluidity. However, beyond a critical dosage, the incorporation of some limestone filler resulted in a substantial increase of the viscosity of mortar. An accurate model that can be used to predict the viscosity of such mixtures is proposed and validated on various mixtures.     

Rheological properties of grouts with viscosity modifying agents as diutan gum and welan gum incorporating pulverised fly ash

This investigation was undertaken to evaluate the influence of the dosage of the second generation of viscosity modifying agent (diutan gum) on fluidity and rheological parameters of cement-based materials grout compared to welan gum. All grouts were made with 0.40 water-to-binder ratio (W/B). The fresh properties of control grouts made without any viscosity modifying agent (VMA) and with superplasticizer (SP) were compared to those of grouts made with 0.02, 0.04, 0.06 and 0.08% diutan gum by mass of binder. Similar mixes made with welan gum were compared to those containing diutan gums. The effect of admixtures on fluidity and rheological parameters are discussed in this paper. The effect of the replacement of cement by pulverised fly ash (PFA) was also investigated. Grouts with replacements of PFA of 5, 13 and 20% by mass were used with the same W/B. Similar control grouts and mixes incorporated different dosages of PFA made with welan gum were made in order to compare the fluidity and the rheological parameters to the previous grouts made with diutan gum.The results show that the increase of the dosage of diutan gum and welan gum for a given dosage of SP increases significantly the yield value, the apparent and plastic viscosity and reduces the fluidity. With an increase in dosage of SP, the apparent viscosity at low shear rate decreases dramatically than that at high rate of shear rate due to the pseudo-plastic rheology of the grouts containing VMA. Both VMAs exhibited high apparent viscosity values at low shear rates which were attributed to the entanglement and intertwining of VMA polymer chains at low shear rate and association of water between adjacent chains. For a given dosage of VMA, diutan gum showed a high apparent viscosity than welan which could be attributed to the molecular weight and to the long-side chain of diutan gum leading to greater entanglement and intertwining. For any given dosage of SP, the diutan gum exhibited higher yield value and plastic viscosity than welan gum. Diutan gum grouts demonstrate a greater yield value and apparent and plastic viscosity than welan gum for control and PFA grouts. The replacement of cement by PFA resulted in a reduction of yield value and an increase in plastic viscosity.     

On the frictional contribution to the viscosity of cement and silica pastes in the presence of adsorbing and non adsorbing polymers

This paper is devoted to the role of hydrodynamic lubrication in the flow of dense suspensions of non-Brownian cement or silica particles. The role of hydrodynamic lubrication is ambiguous since it is primarily a source of viscous dissipation but, by preventing direct contact between particles and friction, it may facilitate flow. We show that in the concentration and shear rate regimes investigated here direct contact friction between cement or silica particles is contributing to the overall energy dissipation. Addition of water-soluble polymers, either adsorbing or not adsorbing, was used as a mean to control friction. We show that, independently of the adsorption capacity of the polymer, it is the non adsorbed polymer which, thanks to hydrodynamic lubrication, prevents direct contacts and reduces the overall energy dissipation. This leads to the counterintuitive situation where by increasing the interstitial fluid viscosity, the suspension viscosity is decreased. When hydrodynamic lubrication is no longer able to avoid direct frictional contact, dilatant and shear-thickening behaviors set in.     

水泥与多种高效减水剂相容性的统计性研究

使用日本的净浆流动度检验方法——T法流动度,对10种高效减水剂与5种水泥之间的相容性进行了交叉试验,旨在考察水泥与高效减水剂的相容性结果是否具有统计学的规律。结果显示,在本试验抽取样品范围内,无论是多个高效减水剂对水泥的相容性,还是多个水泥对高效减水剂的相容性,均具有很好的一致性,即相容性较差的高效减水剂对所有水泥的相容性均相对较差;相容性较差的水泥对所有高效减水剂的相容性均相对较差。     

水泥与减水剂相容性控制方法

综合介绍了国内一家合资企业和两家国外企业的生产、工业试验数据和控制经验.实践证明,使用二水石膏并通过调整磨内喷水量控制水泥粉磨温度在120-125℃范围;减少熟料中的C3A含量;控制适宜的碱含量特别是可溶性碱含量;通过调整硫碱比控制熟料中碱的硫酸盐化程度;控制粉煤灰的质量等都是水泥厂控制水泥与减水剂相容性的有效方法.提出将水泥与减水剂相容性的稳定性作为水泥质量稳定性的控制内容之一,并提出了控制标准.介绍了水泥与减水剂相容性发生明显波动时的调整方法.     

Estimating rheological properties of cement pastes using various rheological models for different test geometry, gap and surface friction

Shear stress-shear rate flow tests were carried out on various cement pastes incorporating different mineral additions and chemical admixtures using various test geometries. Different gaps and friction capacity of shearing surfaces of the test geometries were employed in the flow tests. Rheological properties of cement pastes were calculated from the resulting flow curves using various rheological models. The Bingham, Modified Bingham, Herchel-Bulkley and Casson models were used to estimate yield stress. Plastic viscosity was estimated by the Bingham, Modified Bingham and Casson models, while the Williamson and Sisko models were used to estimate the theoretical viscosity at zero and infinite shear rates. It was observed that the rheological properties of cement pastes varied with the change of the test geometries and rheological models used for their calculation. The performance of rheological models in estimating the rheological properties of cement pastes, as expressed by a standard error, varied with the test geometries as well as with the composition of cement pastes. The paper highlights the difficulty in reconciling rheological results from different sources and the need for standardizing rheological test methods for rheological interlaboratory results to be critically analyzed and compared.     

Enhanced thermodynamic analysis coupled with temperature-dependent microstructures of cement hydrates

This paper describes a computational method for simulating concrete performance. The method is enhanced to take into account the influence of the curing temperature history on the early-age development process. In order to investigate the effect of temperature on hydration, micro-pore structure development, and moisture profile in concrete, the authors carried out systematic sensitivity analyses. These analyses were used to create a numerical model that takes into account the temperature-dependent intrinsic porosity of hydrates and the available space for hydrate precipitation. For example, at high curing temperatures, the intrinsic porosity decreases and the available space for hydration increases. Experiments verified that the proposed method accurately predicts hydration processes, microstructure formation, and relative humidity for different mix proportions under various temperatures. Compared with the conventional model, the new model offers greater overall computational accuracy for low W/C and high temperature curing.     

Solution viscosity and flocculation characteristics of linear polymeric flocculants in various media

Rheological characteristics of linear copolymers of acrylamide (AM) and acryloyloxyethyltrimethyl ammonium chloride (Q9), differing in molar mass and chemical composition, have been studied in distilled water (DW) and industrial water (IW) obtained from a paper mill. For all copolymers, the shear viscosity, μ, was much lower as the ionic strength of the water increased, with near Newtonian behaviour observed at high ionic strengths. In DW, the polymer solutions were yield pseudoplastic. Comparison of the behaviour of all flocculants at the same shear rate in the two media was accomplished by modelling the rheological data.The characteristics of the copolymers could be related with their flocculation performance in IW. The rate of flocculation in the IW was generally higher than in the DW. In general, flocculants with higher charge density were effective at lower concentrations exhibiting a lower value for the optimum PEL dosage. The flocculation data were supported with zeta potential measurements. In all cases flocs break under shear with an inability to recover the floc size with time. Overall, the polyelectrolyte behaviour in flocculation as a function of molar mass, charge density and quality of the medium could be correlated. This is of particular importance for papermaking due to the modern tendencies for water closure.