Increase In Plastic Viscosity Research Articles

Effect of silica fume type on rheology and compressive strength of geopolymer mortar

Silica fume (SF) is widely used in the developing of high-performance geopolymer systems. Previous studies have shown that using different types of SF may have different influences on the performance of geopolymers. What are the key factors (affecting the properties of geopolymers) still need to be clarified? This paper investigated the effects of three types of silica fume (SF1− SF3) with various silica contents (98.0%, 94.7% and 53.1%) and particle sizes (D50: 3.3 μm, 3.1 μm and 11.8 μm) on the rheology and compressive strength of alkali-activated calcium alumina cement (CAC)/fly ash mortar. The incorporation of SF can significantly increase the plastic viscosity. The increase in plastic viscosity was due to the ball-bearing action of the spherical SF particles, which reduced the friction between the particles under shearing. Replacing 20% of the fly ash with SF1 and SF2 improved the compressive strength of geopolymer mortars while the incorporation of SF3 decreased the compressive strength at the same replacement ratio. Inductively coupled plasma (ICP) spectrometry results indicated that the amorphous silica in the SFs was dissolved in an alkali solution. Activators with high concentrations of monomer and dimmer silicon groups may promote the reaction between precursors and activators. The formation of additional aluminosilicate gels reduced the amount of large capillary pores (500 nm to 1000 nm), leading to improved strength. The incorporation of coarse SF3 introduced extra voids in the mixture, as suggested by calculations of packing density, leading to reduced strength.

Bentonite-Based Drilling Boyolali Mud Fabrication with Additive Carboxymethyl Cellulose, Na2CO3 and KOH

This study aimed to examine the effect of adding KOH, Na2CO3, and Carboxymethyl Cellulose additives on the physical properties of the mud, as well as the optimal additive for sludge production. The preparation of the basal sludge involved the addition of 22.5 grams of bentonite, 350 millilitres of distilled water, and 10 grams of Barite as a constant variable. Then it stated 0.5 variations of the Na2CO3 additive; 1.5; 3 grams, KOH 0.5; 1.5; and 3 grams, and Carboxymethyl Cellulose 3; 6; and 9 grams. A physical property measurement involving density was conducted. Samples were evaluated for Plastic Viscosity and Yield Point at 300 and 600 rpm dial speeds. After 30 minutes of filter press compression, the filtration loss, mud cake, and pH were measured. The results indicate that the KOH additive decreases Yield Point by 8.6 lb/100ft2 and increases Filtrate Loss by 5.8 mL and sediment pH by 11.12 points. The additive Na2CO3 then causes a reduction in Filtrate Loss of 10.4, 8.8, 7.6 mL and an increase in Plastic Viscosity. While Carboxymethyl Cellulose can increase Plastic Viscosity by 7; 13; 55 cP, Gel strength by 4; 6; 40 Lb/100 ft2, and Filtrate Loss by 10; 8; 7.6mL. Carboxymethyl Cellulose is the additive that has the most significant effect on the physical properties of the mud because it can affect Plastic Viscosity, Gel Strength, Yield Point, and Filtrate Loss so that the soil can approach API 13A Standards. The optimal amount of Carboxymethyl Cellulose should be added at a mass of 6 grams, or 13 cP.

RHEOLOGICAL PARAMETERS OPTIMIZATION OF HYDROCARBON-BASED DRILLING FLUID DEPENDING ON THE MINING AND GEOLOGICAL CONDITIONS OF THEIR APPLICATION

Hydrocarbon-based solutions (HCBS) today are capable ofperforming tasks that water-based muds cannot do. First of all — theability to keep the well walls at a lower density, their insensitivity to clayand salt deposits, the similar nature of the hydrocarbon base and reservoirfluids. These advantages make it possible to use HCBS in the constructionof wells characterized by intensive caving, with high zenithangles and extended horizontal sections. HCBS is successfully appliedat the fields located beyond the Arctic Circle when opening, for example,Devonian deposits. But in addition to the indisputable positive aspects,HCBS also have disadvantages. Among their main disadvantages, highcost is distinguished, which increases the requirements for the quality ofthe solution for trouble-free and fast well drilling, the impossibility ofusing HCBS in absorbing horizons. In addition to the high cost, hydrocarbon-based fluids, due to their nature, are characterized by compressibilityand a non-linear dependence of viscosity on temperature. Simplyput, under the influence of high temperatures, the rheological parametersof the solution decrease, and under the influence of low temperatures,they increase. And if solutions are constantly being found for the firstproblem, improving and developing new viscosity modifiers, emulsifiersand additives, then the second problem has long gone unnoticed. But forthe deposits of the Arctic, characterized by vast zones of permafrost, thesolution of this problem is more relevant than ever. An increase in plasticviscosity when the solution is cooled (for example, in permafrost zones)is possible during long-term circulation stops: during tripping operationsor running casing, etc. This increase in rheology can cause circulationloss, fluid loss, increased timewell construction, and hydraulic fracturing.In this work, we decided to investigate the dependence of the HCBSrheology on temperature and to choose the concentration of reagents thatwill allow leveling this dependence, since, due to the nature of theHCBS, it is impossible to eliminate it completely.

Investigation on the rheology, self-shrinkage, pore structure, and fractal dimension of coral powder-cement slurry

There is a significant amount of coral powder in coral aggregates, which has a negative impact on the operational performance, mechanical characteristics, and durability of coral reef sand concrete. The present study investigates the effect of coral powder with varying fineness and content on rheological and self-shrinkage properties using an Anton Paar MCR102 rotational rheometer and YC-BWS bellows self-shrinkage apparatus, respectively. The dynamic yield stress, rheological index, and plastic viscosity are obtained according to the Bingham model, Modified Bingham model, and Herschel-Bulkley model. The pore structures of coral powder-cement slurry are studied using a combination of MIP and SEM tests. Fractal theory is used to characterize the pore size distribution. The results demonstrate that the coral powder-cement slurry exhibits a shear thinning phenomenon. The Herschel-Bulkley model is successful in simulating the rheological behavior of cement slurry. The dynamic yield stress and plastic viscosity increase gradually as the fine coral powder content increases. With the increase in the coarse coral powder content, the dynamic yield stress decreases gradually while the plastic viscosity increases. The self-shrinking value of the coral powder-cement slurry increases rapidly within 1d but gradually stabilize with age. The self-shrinkage value increases with the increase in the coral powder admixture. The self-shrinkage value of the fine coral powder-cement slurry is less than that of the coarse coral powder-cement slurry. It is found that increase in the coral powder reduces the compressive strength of the cement paste, however, cement replacement with 10% coral powder is acceptable. Pore surface fractal dimension and capillary pore volume is able to effectively characterize pore size distribution and pore volume, respectively. Furthermore, the strength has a positive and negative linear relationship with the pore surface fractal dimension and capillary pore volume, respectively. The ratio of pore surface fractal dimension to capillary pore volume can be used as a parameter of the strength model. A linear relationship between the strength and the ratio of pore surface fractal dimension to capillary pore volume is proposed, and the model exhibits high accuracy.

Cementitious nanocomposites engineered with high-oxidized graphene oxide: Spotting the nano to macro correlation

There has been increasing interest in using nanosized fillers in cement-based construction materials to upgrade mechanical properties, durability, and multi-functionality. In this context, graphene oxide (GO) is proved to be an effective candidate, and its interaction with cement can lead to remarkable enhancement in its macro-properties. To guarantee reproducibility and to maximize environmental and health safety, a GO water suspension ( GONan, Nanesa, Italy ) was selected from the market-available products. A complete morphological, microstructural and chemical characterization was performed by Atomic Force Microscopy (AFM), X-ray Photoelectron Spectroscopy (XPS), Raman Spectroscopy, Infra-Red Spectroscopy (FTIR-ATR), X-ray Diffraction (XRD), and Thermogravimetric Analysis. The aggregation test of GONan in saturated Ca(OH) 2 water solution was also performed, and results were obtained by UV-VIS spectroscopy and Scanning Electron Microscopy (SEM). Different dosages (0.01%, 0.1%, and 0.2% by weight of cement) of GONan were added to a commercial M5 mortar. Fresh properties were determined by rheology measurements and flowability and workability tests. Samples were hardened in water at room temperature (RT) for 7, 14, and 28 days. The compressive and bending strength of all samples were evaluated following the standards. The microstructural features of nanocomposites hardened at 28 days were investigated by SEM. Results clearly evidenced that the extra-low GONan dosage (0.01%) was the most promising formulation. Despite the worsening of fresh properties (i.e., increase of plastic viscosity and decrease of flowability and workability by 150%, 50%, and 100%, respectively, compared to the control sample), the mechanical properties of such an extra-low dosage nanocomposite at 14 days showed a notable increase of 20% and 40% for bending and compressive strength, respectively.

Experimental and Numerical Studies on Flowing Properties of Grouting Mortar Based on the Modified MPS Method

Grouting mortar has widespread application in engineering because of the advantages of good durability, low cost, and environmental friendliness. To study the flowing properties of grouting mortar, laboratory minislump tests taking different rheological parameters of grouting mortar into consideration were conducted to obtain the flow time and flow pattern of grouting mortar. A modified MPS method (moving-particle semi-implicit method) introduced two sections of Bingham rheological, and segregation was proposed. The effects of the plastic viscosity on the flow state of mortar were studied, and the relationship between the plastic viscosity and the flowing time was established. The numerical results show that the modified MPS method can be used to predict the flow time and flow pattern of mortar in the template, and plastic viscosity has a great influence on the flow time of concrete, and with the increase of plastic viscosity, the time to flow to the specified area also increases. Moreover, the analysis of the rheological parameters can provide the basis for the design of mix ratio in the construction practice.

Development of a hydrocarbon completion system for wells with low bottomhole temperatures for conditions of oil and gas fields in Eastern Siberia

The paper presents the results of investigations on the influence of low bottomhole temperatures in the intervals of productive formations on the technological properties of solutions used for drilling and completion of wells in order to determine the possibility of increasing gas recovery coefficient at the field of the “Sila Sibiri” gas pipeline. The analysis of technological measures determining the quality of the productive horizon drilling-in was carried out. It was found out that the dispersion of bridging agent in the composition of the hydrocarbon-based drilling mud selected from the existing methods does not have significant influence on the change in the depth of filtrate penetration into the formation in conditions of low bottomhole temperatures. The main reason for the decrease in the near-bottomhole zone permeability was found out – the increase in plastic viscosity of the dispersion medium of the hydrocarbon-based drilling mud under the influence of low bottomhole temperatures. A destructor solution for efficient wellbore cleaning from hydrocarbon-based solution components in conditions of low bottomhole temperatures was developed. The paper presents the results of laboratory investigations of hydrocarbon-based drilling mud and the developed destructor solution, as well as its pilot field tests. The mechanism of interaction between the destructor solution and the filter cake of the hydrocarbon-based drilling mud ensuring the reduction of the skin factor in the conditions of the geological and hydrodynamic structure of Botuobinsky, Khamakinsky and Talakhsky horizons of the Chayandinskoye oil and gas condensate field has been scientifically substantiated.

Influence of Lightly Burned MgO on the Mechanical Properties and Anticarbonization of Cement-Based Materials

This study aims to study the influence of a lightly burned magnesium oxide (LBMO) expansion agent on the rheological properties (the slump flow, plastic viscosity and variation of shear stress) of cement-based materials. Four different mass contents (i.e., 0%, 3%, 6% and 9%) of LBMO were selected. The following compressive strength and expansion value of the corresponding cement concrete were tested. Cement concrete with two strength grades of 30 MPa and 50 MPa (C30 and C50) was selected. Results indicated that the addition of LBMO can effectively decrease the fluidity and increase the plastic viscosity of fresh cement paste. An optimum dosage (3%) of LBMO is the most advantageous to the compressive strength of cement concrete. The addition of LBMO can increase the expansion rate of cement concrete, thus preventing inside cracks. Moreover, the incorporation of LBMO led to a reduction in the fluidity of the cement paste and an increase in plastic viscosity. The addition of LBMO can increase the expansion rate of cement concrete, thus preventing inside cracks. It can be found that little difference exists in the compressive strength and the expansion rate of cement concrete with strength grades of 30 MPa and 50 MPa. Finally, the increased dosage of LBMO, curing age and compressive strength led to improving the carbonization resistance of cement concrete.

Preliminary Investigation of the Mechanical and Physical Properties of Natural Hydraulic Lime Grouts with Nano-Silica

Natural hydraulic lime-based grouts are often used in the structural consolidation of old stone masonry walls, mainly to re-establish the monolithic behaviour of masonry constructions. To ensure an adequate grouting operation, it is essential to have good fresh and hardened grout properties. The motivation of the present study was to examine the fresh and hardened properties of natural hydraulic lime grouts with nano-silica (NS) and silica fume (SF). The contribution of these materials and the dosage of a high range water reducer admixture (HRWR) were investigated on the rheological properties, water capillarity, open porosity and mechanical strength of injection grouts. The effects on rheology were analysed through plastic viscosity and yield stress. The results indicated that, even for reduced NS content, an increase in plastic viscosity and yield stress occurred, which required a higher HRWR content in order to not compromise the grout’s rheological performance. The results also showed that, when NS and SF were combined, a beneficial joint effect occurred, resulting in a substantial and positive change on the mechanical strength and microstructure of the hardened injection grouts. Taguchi’s method was used to optimize the grout’s formulation and to fulfil the required performance concerning the fresh and hardened state.

Flow fields of a non-Newtonian fluid in vortex chamber pumps

Problem. Pumping different fluids by hydraulic transport is associated with fast wear of the pump contact surfaces. The fluids being pumped are often non-Newtonian. The use of jet pumps for pumping is impractical due to low efficiency. Vortex chamber pumps may have higher efficiency when pumping non-Newtonian fluids, however, their operation on such fluids has not yet been studied. The aim of this work is to study the characteristics of the flow fields of a non-Newtonian fluid using the example of a Bingham fluid in the vortex chamber pump. Methodology. Predicting pump energy performance and determining flow fields for highly viscous fluids using CFD simulations enables advanced jet pumps to handle non-Newtonian fluids. Results. Modeling was carried out based on the numerical solution of the RANS equations with the SST turbulence model. To ensure the operability of the vortex chamber pump when pumping non-Newtonian fluid, with known rheological parameters of the mixture, it is necessary to select the required supply pressure for the active flow, and also to consider the issue of diluting the liquid with water to reduce the mixture viscosity and achieve the specified values of the pumping energy parameters. Originality. The hypothesis that the vortex chamber supercharger can operate on a hypothetical ideal fluid has been confirmed. In this case, the performance indicators of such a supercharger improve and tend to ideal. With an increase in plastic viscosity, the volumetric flow rate of the pumped fluid decreases, and at high values of the viscosity, an active flow is ejected through the axial channels. Practical value. Researchers can use the theoretical results of this work to design new devices for pumping other Bingham fluids, such as oil paint, resins, varnishes, swamp soils, and many others.

Enhancing Hematite-Based Invert Emulsion Mud Stability at High-Pressure High-Temperature Wells.

Drilling fluids have a crucial continued role in drilling a successful well; however, most of the drilling technical and operational challenges are incorporated with the drilling mud stability and properties. The solid particles settling in drilling mud that deteriorates its stability is a common issue encountered in high-pressure high-temperature (HPHT) conditions. This issue, known as solids sagging, may eventually result in stuck pipes, wellbore instability, and loss of circulation. The objective of this work is to introduce garamite to enhance the stability of hematite-based invert emulsion mud under HPHT situations. The used garamite and hematite weighting material were analyzed using X-ray fluorescence, scanning electron microscopy, and particle size distribution to identify their compositions, morphologies, and particle sizes. The effects of adding different concentrations of garamite (0.5, 1.0, 1.25, and 1.5 g) to the field formula of hematite-based invert emulsion mud were investigated. The mud density, stability, sagging tendency, rheology, viscoelasticity, and filtration properties were studied to formulate a stabilized and distinguished-performance drilling mud. The obtained results indicated that garamite did not change the mud density while enhancing the emulsion stability by increasing the electrical stability proportionally with the added garamite quantity. The sagging experiments showed that adding 1.25 g of garamite is sufficient to prevent the sagging problem in both static and dynamic conditions as it was enough to enforce the sag parameters into the safe range of sag performance indicators. This 1.25 g of garamite improved the yield point by 152% from 19 to 48 lb./100 ft2 with a slight increase in plastic viscosity from 14 cP for base mud to 18 cP and significant increase in the gelling strength and viscoelastic properties. Adding 1.25 g of garamite showed a slight enhancement in the filtration properties as the filtrate volume was reduced by 8% from 3.7 to 3.4 cm3 and the filter cake thickness has 16% reduction from 2.69 to 2.26 mm. As a result, a mud with distinguished performance, in terms of rheology, suspension, sag performance, and stability, was obtained. Hence, a basis for safely drilling the HPHT formations was delivered, which reduces the drilling cost by minimizing the nonproductive time.

Influence of Bingham fluid viscosity on energy performances of a vortex chamber pump

One of the problems in the development of coal-water technologies is the use of reliable and long-lasting pumps. To date, classic pumps, due to the use of mechanical moving parts and seals, are subject to rapid abrasive wear. The solution to this problem can lie in the creation of new vortex chamber pumps developed by the authors. They are highly reliable, simple in design and have no moving parts. The object of this paper consists in determining the range of vortex chamber pump performance when pumping Bingham fluids of different rheological parameters, as well as to determine the dependence of the pump efficiency on the Bingham viscosity and the yield stress. Study of the pump performance was conducted experimentally and with CFD simulation. It was found that an increase in the liquid viscosity reduces the vacuum value near the axis. For the first time it was found that the tenfold increase in plastic viscosity reduces the pump efficiency by about 20%. This results in the fact that the supercharger cannot pump the coal-water slurry with τ0>12 Pa and μB>1 Pa⋅s. The findings can be extended not only to coal-water slurry, but also to all Bingham fluids.

Influence of Graphene Oxide on Rheological Parameters of Cement Slurries

In recent years, graphene-based nanomaterials have been increasingly and widely used in numerous industrial sectors. In the drilling industry, graphene oxide in cement slurry has significantly improved the mechanical parameters of cement composites and is a future-proof solution. However, prior to placing it in a borehole ring space, cement slurry must feature appropriate fluidity. Graphene oxide has a significant influence on rheological parameters. Therefore, it is necessary to study graphene oxide’s influence on the rheological parameters of cement slurries. Thus, this paper presents rheological models and the results of studies on rheological parameters. A basic cement slurry and a slurry with a latex addition were used. The latex admixture was applied at concentrations of 0.1%, 0.03%, and 0.06%. In total, studies were carried out for six slurries with graphene oxide and two basic slurries. The obtained results of studies on the slurries with graphene oxide were compared with the control slurry. It was found that the smallest graphene oxide concentration increased slurry value, some rheological parameter values, plastic viscosity, and the flow limit. Surprisingly, a concentration up to 0.03% was an acceptable value, since the increase in plastic viscosity was not excessively high, which allowed the use of cement slurry to seal the hole. Once this value was exceeded, the slurry caused problems at its injection to the borehole.

Rheological and pumping behaviour of 3D printable cementitious materials with varying aggregate content

3D printing with cementitious materials is an emerging technology and provides an active area of research. Despite this, there are only limited studies that examine the pumping behaviour of high yield stress fluids such as printable concrete. We present a study on the rheological behaviour of 3D printable cementitious materials with different aggregate-to-binder ratios (a/b) and analyse the pumping and printing characteristics with the measured rheological parameters. We observed that an increase in a/b resulted in a significant increase of plastic viscosity, and a nominal increase in yield stress and storage modulus. The variation in plastic viscosity and yield stress with increasing aggregate content was analysed with the Krieger-Dougherty and Chateau-Ovarlez-Trung model, respectively. Also, the rheological properties of the paste rich lubrication layer during pumping were determined with the help of a tribometer. The yield stress and viscous constant of the lubrication layer increase with the increase in a/b. The pumping pressure predictions were carried out by a suitable theoretical model by considering appropriate flow conditions for different mixtures. The variation in critical height of printed elements with an increase in a/b was correlated with the observed rheological parameters.

Influence of Rheological Behavior of Mortar Matrix on Fresh Concrete Segregation and Bleeding

In this paper, the effect of water-binder ratio, sand ratio and high-range water reducer (HRWR) content on the rheological behavior of mortar formulated from concrete mixture was investigated by using a RheoCAD rheometer. The segregation of fresh concrete and hardened concrete was, respectively, measured by two different modified methods, coarse aggregate sieving-washing method and image processing method. The bleeding of fresh concrete was measured by two laser displacement sensors. The experimental results show that sand ratio and HRWR content have significant influences on yield stress whereas have little contribution to plastic viscosity. The segregation of concrete increases with the decrease of yield stress and is affected by plastic viscosity meanwhile. There is a weak relationship between bleeding rate and yield stress, but the bleeding rate decreases with the increase of plastic viscosity. Furthermore, it is convenient to analyze the degree of segregation and the distribution of coarse aggregate particles by image processing method and to real-timely monitor the bleeding and settlement of fresh concrete by laser displacement sensors.

Effect and Mechanism of Coral Powder on the Rheological Properties of Cementitious Materials

To study the effect and mechanism of micro coral powder on the flow behavior of fresh cement paste, the fluidity and rheological parameters of cement paste with fine coral powder of different dosages were investigated. The influence mechanism of coral powder on rheological properties was investigated by testing the water demand, the adsorption behavior and the zeta potential. Results show that with the increasing dosage of coral powder, the fluidity of the cement paste decreases and the torque of cement paste increases at the same rotation speed. The derived yield stress and plastic viscosity increase with the increasing dosage of coral powder. Because micro coral powder has higher volume and area than cement with the same mass, the water demand ratio of coral powder is very high, which is one of the reasons for the fluidity drop with the coral powder content. With the same dosage of polycarboxylate superplasticizer (PCE), the adsorption amount and the adsorption ratio of PCE by blended micro coral powder are much higher than that of cement particles. Therefore, compared to cement paste without PCE, the fluidity of cement paste with PCE decreased more significantly at the same coral powder content. In addition, competitive adsorption of Ca2+ between coral and cement particles reduces the positive charge density on the surface of cement particles, causing the decrease of the adsorption capacity of cement particles for PCE, thus affecting its rheological properties.

A comparative study on performance evaluation of hybrid GNPs/CNTs in conventional and self-compacting mortar

In this paper performance of graphite nano platelets and carbon nanotubes was investigated in both conventional as well as self-compacting mortar. Workability, linear-shrinkage, rheological properties, flexural and compressive strength, air content and water absorption tests were conducted. Results reveal that by addition of nano media in cement matrix workability, shrinkage, air content, and water absorption adamantly reduces as compared to control mixtures. On the other hand yield stress, plastic viscosity, compressive and flexural strength enhances significantly. The shrinkage response of SCM-3 and CCM-3 depicts reduction of 66% and 61% respectively. Furthermore, yield stress and plastic viscosity increase 53% and 12% respectively. By addition of nano media deviation in crack propagation, more nucleation sites, capturing the micro voids, filling the pores and dense packing of the hydrated products were found. Increase in compressive strength and flexural strength was observed. Hence hybrid nano media can be intruded as a potential candidate in cement matrix for enhancing the structural properties.

Performance of Coal Gangue-Based Cemented Backfill Material Modified by Water-Reducing Agents

Coal gangue-based cemented backfill material (CGCBM) is developed for backfilling the goaf in coal mines. As fresh CGCBM slurry is generally transported into underground openings through a pipeline, and after hardening, it plays the role of supporting the overlying strata. The fluidity, stability, and mechanical (compressive strength) of CGCBM become the most important properties. Adding water-reducing agents (WRAs) is considered to improve the fluidity, stability, and mechanical properties of CGCBM, but there is a risk of increased bleeding. So, two types of WRA (naphthalene series (WRA1) and poly carboxylic acid (WRA2)) are used at different contents (1.0%-2% for WRA1, 0.2%–0.6% for WRA2) by mass of binder. Slump, slump flow, yield stress, and plastic viscosity test are used to evaluate the fluidity properties of CGCBM after adding WRA. Bleeding rate test is used to evaluate the stability of CGCBM after adding WRA. Compressive strength is the most important factor in measuring the mechanical properties. SEM and XRD tests are used to analyse the mechanism of strength change. Results show that the slump, slump flow, and plastic viscosity increase after adding WRA, which reduces the yield stress and improves the fluidity. The bleeding rate increases with the increase of WRA content, leading to a decrease in stability. Adding WRA increases the compressive strength, and it increases first and then decreases with the increase of the content at the later stage. Considering the effects of WRA on the fluidity, stability, and compressive strength properties of CGCBM, the reasonable content of WRA1 and WRA2 is 1.5% and 0.4%, respectively. The research results provide guidance for the design and preparation of CGCBM with favourable performance in practical production.

Rheological models for temperature and concentration dependencies of coal water slurry

ABSTRACT Rheological properties of coal water slurry (CWS) with different concentrations (45.77, 50.78, 52.13, 55.56, 57.67, and 61.06 wt%) were investigated by rotational rheometer at different temperatures (20–60°C), and shear rate with integral magnitude logarithmically increased from 1 to 200 s−1. The results show that the CWS is a pseudoplastic fluid, whose rheological characteristic follows Bingham model well. Both the yield stress and Bingham plastic viscosity increase with increasing concentration and usually decrease with the temperature. The concentration of CWS has a positive correlation with the apparent viscosity, and the relationship is described by power law model. The apparent viscosity decreases first and then increases with the temperature, there is a critical temperature. The Guzman–Andrade equation is adopted to exhibit the effect of temperature on apparent viscosity. The rheological model coupled with shear rate, concentration, and temperature is obtained, and the adjusted coefficient of determination is 0.954 that illustrates there is a goodness of fit. The results of this study put forward a new method to obtain empirical model of non-Newtonian fluid.

Effect of MWCNT and PCE plasticizer on the properties of cement pastes

Polycarboxylate ether (PCE) plasticizer possesses by high water-reduction capability of about 30-40%. Despite the superior water reduction capability, the high dosages of PCE may cause the bleeding in cement systems, which is not suitable for high workability and self-compacting concrete. The current research is devoted to the studying of multi-walled carbon nanotubes (MWCNT) suspension prepared in combination with PCE plasticizer on the rheological properties of cement pastes. The bleeding of cement pastes modified by different dosages of MWCNT was estimated as well. The increase of yield stress in 3.7 and 3.5 times was obtained for cement paste modified by MWCNT suspension in dosage of 0.12% by weight of cement (bwoc) in 5 and 120 min after cement paste mixing, respectively. The increase of plastic viscosity in 2.95 and 1.55 times was obtained for cement paste modified by MWCNT suspension in dosage of 0.12% bwoc in 5 and 120 min after cement paste mixing, respectively. Modification of cement pastes by MWCNT suspension in the dosage of 0.24 % bwoc led to the decrease of bleeding water volume by 21.7% in comparison with cement pastes modified only by PCE plasticizer.