Rheologische Messungen an Baustoffen 2018 E-Book

Markus Greim

• Herausgeber: tredition
• Kategorie: Bildung
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Seitenzahl: 197

Veröffentlichungsjahr: 2018

Beschreibung

Tagungsband zum 27. Workshop und Kolloquium, "Rheologische Messungen an Baustoffen 2018" 7. und 8. März an der OTH Regensburg Einige Beiträge sind in Englischer Sprache verfasst.

Leseprobe

Herausgeber: Markus Greim, Wolfgang Kusterle und Oliver Teubert

Rheologische Messungen an Baustoffen 2018

Tagungsband zum 27. Workshop und Kolloquium, 7. und 8. März an der OTH Regensburg

ISBN: siehe Umschlag

1. Auflage 2018

Copyright: die jeweiligen Autoren, gegebenenfalls Schleibinger Geräte Teubert u. Greim, http://www.schleibinger.com

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Layout: Benedikt Hoffmann

Satz: Christian Greim, Ines Kreter

Verlag: tredition GmbH; Grindelallee 188; 20144 Hamburg; www.tredition.de

Publisher: Markus Greim, Wolgang Kusterle and Oliver Teubert

Rheological Measurement of Building Materials 2018

Proceedings of the 27th Conferences and Laboratory Workshops, 7th and 8th March at OTH Regensburg

ISBN: printed on the cover

1. Edition 2018

Copyright: by the particular authors, else by Schleibinger Geräte Teubert u. Greim GmbH, www.schleibinger.com

All rights reserved.

The content and works published in this book are governed by the copyright laws of Germany. Any duplication, processing, distribution or any form of utilisation beyond the scope of copyright law shall require the prior written consent of the author or authors in question.

Layout: Benedikt Hoffmann

Typesetting: Christian Greim, Ines Kreter

Published: by tredition GmbH; Grindelallee 188; 20144 Hamburg; www.tredition.de

Contents

Preface

Effect of Chemical Admixtures on Rheological Properties of Oil Well Cement and Prediction of Cement Rheology Using a Mathematical Model

Ghada Bassioni

Estrichzusatzmittel-Wirkungsweise und Anwendung

Dr. Roland Augustin

Gel formation capacity in mortars using mineral rheological additives under shear stress and the influence of dispersion.

Alberto Fernández-lbarburu, Pedro Díaz del Castillo, David González.

Advance Rheology Modifying Admixture (ARMA) for Concrete Applications

Paloma Cristina Frías de León, David González Amago, José Manuel Gómez Gómez

Repeatability and reproducibility of measurement of rheological parameters of fresh mortars and concretes

Jacek Gołaszewski, Grzegorz Cygan, Małgorzata Gołaszewska

Contribution of the coarse aggregates to rheology - effects of flow coefficient, particle size distribution, and volume fraction

Wolfram Schmidt, Alejandra Ramírez Caro, Regine Sojref, Berta Mota

Assessment of rheological effects in the binder on the rheology of mortar and concrete

Sarah Leinitz, Wolfram Schmidt, Hans-Carsten Kühne

Mischungsstabilität von fließfähigen Betonen – rheologische Messungen zur Bestimmung des Einflusses von Leim, Mörtel und Gesteinskörnung

Dipl.-Ing. Christoph Begemann, Dipl.-Ing. Dario Cotardo, M. Sc. Tobias Schack, Univ.-Prof. Dr.-Ing. Ludger Lohaus

Ein Vorschlag zur einfachen Bestimmung der Fließgrenze nicht- newtonscher Fluide als physikalischer Parameter zur Charakterisierung fließfähiger Baustoffe

Prof. Dr.-Ing. Jürgen Quarg-Vonscheidt, Dipl.-Ing. Katharina Sosinka

Squeeze flow of cement-based mortars: assessment of pressure distribution by dynamic mapping

Fábio A. Cardoso, Franco A. Grandes, Victor K. Sakano, Andressa C.A. Rego, Rafael G. Pileggi

Untersuchung, Beurteilung und zeitnahe Aussteuerung der rheologischen Frischbetoneigenschaften von SVB

Ivan Parić1, Markus Greim2, Markus Erhardt3, Horst Weißmann4, Wolfgang Kusterle1

Pumping behaviour of modern concretes

Egor Secrieru, Viktor Mechtcherine

Hochleistungs-Feinkornbetone im Injektionsverfahren

B.Eng. Ludwig Hertwig, M.Sc. Philipp Ulbricht, Prof. Dr.-Ing. Klaus Holschemacher

Priority Program Opus Fluidum Futurum – Rheology of reactive, multiscale, multiphase construction materials

Viktor Mechtcherine

Preface

Views on rheology measurements of mineral materials changed during the last 27 years. This is documented by the papers presented in the 27 Conferences on the Rheology of Building Materials at the OTH. However, the basic problems are still the same. Rheology is more in the focus nowadays due to urgent need for processing new materials in new applications in a robust way. But we are still searching for repeatable and reproduceable test methods, which should be simple and straight forward in their use. On one hand many applications tell us, that rheology may be quite complicated, and no simple test ever will give reliable results. On the other hand, civil engineers are used to simple test methods. They must rely on them, even if they know their limitations.

2017 DFG started funding a Priority Program called SPP 2005 Opus Fluidum Futurum, which involves projects at eleven German universities. Results from this basic research will help us in the near future for a better understanding of rheological phenomena. It will also highlight rheology as an important research topic.

Beside concrete and mortar, highly flowable materials as injection mortars or Oil Well Cement products are addressed in the papers of the 2018 conference. Which role plays the rheology of the paste and its content in the mix, which role have mortar and coarse aggregates? How do they arrange or segregate, when being pumped through a pipe? Which requirements must be met by admixtures for screeds?

The papers of the 27th Conference on the Rheology of Building Materials will give some answers to the mentioned questions regarding applied rheology and its application for different building and construction materials. Beside the conference an interesting workshop for rheological measurements took place in the laboratory.

I would like to thank all speakers and conference delegates as well as all members of the organizing committee for their support.

We are looking forward meeting you in Regensburg again.

Wolfgang Kusterle

Effect of Chemical Admixtures on Rheological Properties of Oil Well Cement and Prediction of Cement Rheology Using a Mathematical Model

Ghada Bassioni

Chemistry Department, Faculty of Engineering, Ain Shams University,

P. O. Box 11517, Cairo, Egypt; Phone: [phone]; Fax: [phone]

E-Mail: [email protected]

Abstract

The fluidity of cement slurry is of significant importance in oil well cementing operations. Controlling its rheology is key for proper displacement at extreme well conditions. Different superplasticizers, classical as well as of the newer generations, are tested for their rheological performance in oil well cement paste. The structure of the used polymers varies in their functional groups and consequently on their charge densities. The rheological properties are measured using a FANN viscometer and results are discussed against zeta potential measurements. The relation between shear stress and superplasticizer dosages are plotted and the results show the differences in the superplasticizers’ activities: polymers with short side chain and low charge density reduce the viscosity and make them more reliable in drilling operations. The investigations clearly show that the chemical characteristics of cement can change the previous beliefs towards polymers’ reactivity and consequent performance. Furthermore, mathematical equations are used to predict the viscosities of modern polycarboxylate based superplasticizers without having to deal with many different and time-consuming experiments prior being able to judge on used admixtures and slurries.

1 Introduction

In oil and gas wells construction, the primary cementing procedure consists of placing cement slurries into the annular space between the drilled rock formation and steel casing. The cement slurry hardens to form a hydraulic seal avoiding migration of formation fluids through the annulus. Controlling the fluidity of cement slurry will ease its displacement at extreme well conditions. There are other reasons that make studying the rheological behavior of oil well cement of particular importance. For example, proper cement flow regime must be maintained in order to achieve complete mud removal [1, 2] which is considered as a critical objective in well cementing. The appropriate cement slurry design is a function of many parameters, including the formation integrity, drilling mud characteristics, casing hardware, wellbore geometry, presence of spacers and washes and mixing conditions.

The cement slurry has to be maintained fluid and pump-able until it is properly placed, then it is allowed to set immediately after placement [3]. Any delay in the development of compressive strength will increase the "waiting on cement" time (WOC) necessary before continuing the next step in the operation, which is drilling.

Neat cement slurries have typically a fluid loss which varies from 700 to 2500 mL over a thirty minute period. This rate will lead to fast setting, incorrect placement of the slurry and consequently will result in failure of the complete cementing job. In order to control the fluid loss from the cement slurry to the surrounding rock formation, the permeability of the cement matrix must be minimized. This is managed by addition of chemicals that supply excellent fluid loss control and simultaneously do not adversely affect other properties of the slurry, such as rheology, free water, thickening times and compressive strength [4].

The choice of the type and concentration of the oil well cement additives, especially superplasticizers, are key for the technological application. In literature, the adsorption capacity of superplasticizers and thus their effect in relation to their molecular structure are well described [5]. Numerous studies of the rheological properties of cement pastes have proven that these properties depend on many factors among which the following are cited: water/ cement ratio (w/c), specific surface area, mineral composition, conditions during measurements and their duration [6].

The ‘comb-type’ molecule of polycarboxylate superplasticizer consists of one main linear chain with lateral carboxylate and ether groups (PCE) as seen in Figure 1. According to the literature, the carboxylate groups are instrumental in the adsorption of these additives to the cement particles [7]. In classical plasticizers dispersion is due to electrostatic repulsion (as in melamine and naphthalene based admixtures, MFS and NSF, respectively) while in polycarboxylates dispersion is owing to the carboxylate groups. It is primarily due to the steric repulsion associated with the long lateral ether chains [8]. The high degree and duration of the fluidity that these admixtures afford are related to structural factors; hence, the shorter the main chain and the longer and more numerous the lateral chains, the greater and more long-lasting is the fluidity induced.

Furthermore, polymers with similar anionic charge densities are adsorbed concurrently and develop their full potential. Therefore, the anionic charge densities as well as the steric position of anchor groups along with the main chain and adsorbed conformation of macromolecules are studied. Theses parameters may play an important role on polymers' adsorption behavior in cement/admixtures slurries. Furthermore, a relationship between rheological properties of the cement paste and the chemical components is established. Moreover, this physical property can be used for comparison purposes between different chemical additives to evaluate their performances [9].

This study also demonstrates the consistency in findings with computational methods in comparison to the structure function behavior of polycarboxylates.

2 Experimental

Six different polymers are used in this study. The influence of polymer dosage (plasticizers) on cement rheology is examined. In that framework, an API standard protocol is followed [10]. The impact of polymer dosage on present chemical interactions after complete hydration is evaluated.

2.1 Characterization of the superplasticizers

The superplasticizers are characterized by using Gelpermeation Chromatography coupled with a refractive index detector. Polymeric solution of 10 mg/mL superplasticizer are studied using 0.1 mol/L NaNO3 solution as mobile phase. The static phase entails three columns positioned in series: ultrahydrogel 120, ultrahydrogel 250 and ultrahydrogel 500 (Waters) that allow a separation of 5000- 400000 Dalton. GPC- software Astra 4.908 (Wyatt Technologies) is further applied to define the molecular weight.

The anionic charge density is identified using a Particle charge detector PCD 03 pH (Mütek). Polymeric solutions of a concentration of 200 mg/L are prepared. Pore solutions of the cement suspensions are filtered prior use. 10 mL of the polymeric solutions are titrated vs. the cationic polymer poly-dadmac (0.001 N) in pure water and in the cement pore solution.

Figure. 1: Chemical structures of polycarboxylates of the first (a), second (b) and third (c) generations.

2.2 Characterization of the class G cement

X-ray diffraction (XRD) measurements for oil well cement class G under investigation are obtained using (Bruker D8 powder diffractometer, BRUKER, Germany) using EVA software.

The particle size of the cement grains (D50) is determined using a laser granulometer (Cilas 1064). The density of the cement particles is determined using a Helium pycnometer.

The optimum dosages of the plasticizers under investigation are determined using a mini-slump test. The blank water/cement ratio is obtained by starting with a cement cake that spreads a diameter of 18 ± 0.5 cm on a glass plate and becomes 26 ± 0.5 cm upon polymer addition.

In order to measure the free chemical additives concentration in the pore solution, the organic carbon content is determined using a total organic carbon (TOC) analyzer (Elementar, Vario TOC cube, Germany). For each system 9 different additive dosages (0.1%-2% by weight of cement (bwoc)) are prepared and measured. The amount of chemical additives adsorbed on cement has been calculated from the difference in the concentration of chemical additives in the liquid phase before and after contact with cement (depletion method).

The zeta potential approach is used in order to determine the surface charge on the cement particles and the electrostatic stabilization of the cement/additive system. The electro-acoustic instrument (DT 1200, Dispersion Technology, USA) is used. Cement/additives solutions have been prepared such that 550 g of oil well cement class G is mixed with 220 g of distilled water according to ASTM C305 standard at 25 °C. The additive solution is then added with an increment of 1 mL until a plateau is reached.

2.3 Rheology

A rotational viscometer as shown in Figure 2 is employed to measure the viscosities of cement/additives systems [11]. The cement slurry is filled into the gap between the outer cylinder (rotor) and the inner cylinder (bob) [12]. The rotor is driven at a constant rotational velocity. The rotation of the outer cylinder in presence of the cement slurry generates a torque on the bob. A torsion spring restrains the movement of the bob and a dial is attached to it indicating the displacement of the bob [11]. The rheology test is conducted according to API RP 10-B2 specification using (OFITE 800 Viscometer, OFI testing equipment, USA). The initial dial reading is taken 10 seconds after continues rotation at lowest speed (3 rpm). The remaining readings are recorded in ascending order, and then in descending order, after continuous rotation of 10 seconds. The shear stress is measured at shear rates of 3, 6, 30, 60, 100, 200, 300 rpm. The shear rate is measured in s-1 and the viscosity is measured in (mPa.s).

2.4 Mathematical model using Support Vector Regression method [13]

where is a nonlinear mapping from the input space to the feature space, is a vector of weight coefficient and b is a bias constant.

The coefficients and b are computed by reducing the controlled risk function in equation (2) to the minimum [14].

where Lε(d,y) isε -insensitive loss function. The loss equals null if the predicted value is within the ε -tube as shown in equation (3).

Normalization of the data is first done because different variables span different ranges. In order to ensure that all the variables receive equal attention during the training process, it is recommended to rescale the data. Therefore, data are normalized into the interval [0, 1] by using equation (4).

where Xi represent data point i, XMinXMax are the minima and maxima among all the data points, respectively, and Xi,0to1 the data point i normalized between 0 and 1. Prediction techniques are applied then on the normalized data and predicted data with the error percentage are obtained.

3 Results and Discussion

3.1 Characterization of the cement and superplasticizers under investigation

The phase composition of the class G cement in this study is listed in Table 1. It is observed that the orthorhombic C3 A content is low, typically observed for class G cement. Furthermore, the C3 S content is high that ensures early hydration strength.

Table 1: Phase composition of the oil well cement class G under investigation in [wt%]

While the chemical structures of classical plasticizers like lignosulfonate, melamine and naphthalene based polycondensates is known, the structures of the polycarboxylates under investigation is shown in Figure 1. Molecular weights vary according to Table 2 using GPC.

Table 2: Physical Characteristics of the oil well cement and the plasticizers used in this study.

Polycarboxylates PCE 1 and PCE 2 differ in the length of their side chains as reflected on their molecular weights. The polycondensates MFS and NSF show high molecular weights that are linear chains according to the Burchard parameter, while the polycarboxylates are linear statistical clusters.

According to the mini-slump test, the dosages used are generally very low attributed to the low C3 A content of oil well cement. It is observed that the polycondesate dosages are 5-10 times higher than those necessary to obtain the same effect as the polycarboxylates as seen in Table 2.

Figure 2: A schematic diagram of a concentric viscometer.

Generally, the anionic charge density is responsible for the adsorption behavior. The polycondesates MFS and NSF show higher anionic charge densities than the polycarboxylates as shown in Figure 3. The polycarboxylates show a significant change in their anionic charge densities in water and cement pore water due to complexation of the carboxylate groups with cations present in the pore solution, especially Ca2+.

Figure 3: Charge densities in [10-6 eq/ g] of the different plasticizers in water (black bars) and in pore water of the oil well cement under investigation (grey bars).

The neat oil well cement shows a zeta potential of -8.3 mV. Addition of anionic superplasticizer decreases the zeta potential further until a plateau is reached. Polycondensates negative potentials are typical for this class of superplasticizers. Zeta potential measurements of the cement pastes with optimal polymer dosages are listed in Table 2. Zeta potentials of the PCE superplasticizers are typical for molecules of side chains nEO ≥ 205. The long side chains shift the shear layer at which the zeta potential is usually measured to a less negative or even positive zeta potential.

As expected, oil well cement adsorbs small amounts of the superplasticizers due to the low C3A content as listed in Table 2. The higher the anionic charge density, the better the adsorption. MFS and NSF are generally very similar in the adsorption behavior, so are PCE 1 and PCE 3rd generation.

The polycarboxylates are more economic though in terms of dosages used. The high adsorption percentage of the polycondensates MFS and NSF indicates a bad slum-loss behavior with short plasticizing lifetime. The polycarboxylates have a long range effect and can be therefore used for longer transportation periods.

3.2 Rheology and correlation to other parameters

Superplasticizers are a fundamental ingredient for lowering the shear stress of concrete, with a selective review of those aspects that are considered important in understanding superplasticizers. The fluidity of cement slurries is considered a main factor for oil well cementing operation requirements. Therefore, studying the rheological properties (mainly attributed to viscosity) of different cement/additives system is a must [15, 16]. Furthermore, many factors can complicate the rheological characterization of cement slurry such as: settling separation by difference in density between cement particles and water, coagulation due to ongoing production of cement hydrates, differences in surface charges because of the existence of different clinker phases causing a particle coagulation and the change of the rheological behavior with time due to different hydration rates attributed to different mineral compositions (time dependant) [12].

The shear stress at 300 rpm is demonstrated in Figure 4. While for the neat oil well cement the shear stress is 276.9 lbf/100ft2, it is significantly decreased by 52% and 58% for lignosulfonate and polycarboxylate of the third generation, respectively. It is further seen that PCE 1 and PCE 2 show a shear stress of 155 and 192, respectively, whereas the classical polycondensate MFS has a shear stress of 212 lbf/100ft2.

Figure 4: Shear stress at 300 rpm in [lbf/100ft2] of the oil well cement with and without the different plasticizers in this study according to dosages listed in Table 2.

As indicated in Figure 5 it is shown that increasing superplasticizer concentration results in decreased rheological values reflecting on its dispersion tendencies.

Figure 5: Effect of increased dosages of the different plasticizers alone and in combination (1:1 ratio) on the shear stress at 300 rpm in [lbf/100ft2] of the oil well

Doubling the dosage from 0.1% to 0.2% bwoc results in a decrease of about 10% in shear stress values. While for the classical superplasticizers further decrease in shear stress is around 20% at 0.4% bwoc, the newer generations of PCE1 and 2 show a decrease of around 40%.

In general, upon addition of a superplasticizer to the cement slurry dispersion is attributed to three fundamental mechanisms. First is the lubrication by the adsorption of hydrophilic molecules such as polyol type water reducer [12]. Second is the electrostatic repulsion which is caused due to adsorption of high anionic charge density additive to overcome the van der Waals inter-particle attractive forces and conveying a stronger repulsive force [17]. As a result, the agglomeration of cement particle is reduced as well as it frees the water captured due to cement particle flocculation [18]. The third mechanism relies on the steric hindrance by graft chains of adsorbed polycarboxylates [12]. Furthermore, the steric repulsion or hindrance can be accomplished by multilayer of organic molecules, by a layer of molecules with long chains that extend into the liquid, or by a combination of both [19]. The mechanism associated with lignosulfonates is attributed to a combination of electrostatic repulsion and steric hindrance while the dispersion mechanism of NSF is related to electrostatic repulsion [20]. Furthermore, zeta potential measurement as a complimentary technique to prove that cement particles are des-agglomerated by an electrostatic repulsion mechanism [21] show that lignosulfonate and polycarboxylate possess an electrostatic behavior in cement suspensions, while the electrostatic effectiveness is observed to favor the addition of polycarboxylates (1 and 2). The lignosulfonate steric hindrance mechanism is investigated and proved by other studies [22, 23]. Moreover, the adsorption isotherms show differences in adsorption amounts between the utilized additives [24]. As mentioned earlier, research studies report that the performance of NSF is varying with cement compositions and is related specifically to sulfate or alkali sulfate contents in cement and the amount of C3S in the cement [25-27]. The difference between PCE 1 and PCE 2 performance in cement rheology can be attributed to their variation in chemical characteristics as well as the adsorption amounts.

The effectiveness of proposed optimum dosages is tested in order to confirm compatibility between the additives under investigation by means of rheological behavior. As illustrated in Figure 5, solutions with 0.2% bwoc of each of L and PCE 1 in combination or L and PCE 2 in combination show better dispersion performance than L and PCE 2 individually at the same concentration. However, at 0.1% bwoc each of L and PCE 1 the dispersion effectiveness is drastically dropped due to some chemical incompatibility. For example, at shear rate 100 (rpm) the viscosities for 0.2% bwoc PCE1 and 0.1% bwoc each (L+PCE1) are measured to be 220.5 and 222 mPa.s, respectively. While for PCE 2 and L + PCE 2 at the same concentration and shear rate the viscosities are 288 and 243.75 mPa.s, respectively. From the results we can see that the viscosity of L + PCE 1 is affected negatively due to chemical incompatibility while this effect is observed with less magnitude in the L + PCE 2 system. However, the viscosity for L + PCE 1 is significantly better in comparison to L + PCE 2. Alternatively, the 0.2% L can be used alone for accomplishing the best performance for the whole range of shear rates in comparison to individual systems and 0.1% bwoc each of additive mixtures. However, because this additive retards the cement hydration it’s better to use 0.1% bwoc L + PCE 1 in order to achieve a reasonable hydration time as well as have good rheological behavior that comes in consistence with other analytical tests.

As depicted in Figure 5 and as reported in previous studies [26], shear stress measurements of the analyzed samples through time show inconsistent behavior compared to with and without polymer addition while varying polymer type and dosage. A monotonic decrease in shear stress curve is observed in most of the samples. The latter decrease is attributed to phase separation.