Rheologische Messungen an Baustoffen 2016

Tagungsband zum 25. Workshop und Kolloquium, 2. und 3. März an der OTH Regensburg

Bearbeitet vonWolfgang Kusterle, Oliver Teubert, Markus Greim

1. Auflage 2016. Buch. 368 S. HardcoverISBN 978 3 7345 1314 5

Format (B x L): 14 x 21 cmGewicht: 666 g

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Herausgeber: Markus Greim, Wolfgang Kusterle und Oliver Teubert

Rheologische Messungen an Baustoffen 2016

Tagungsband zum 25. Workshop und Kolloquium, 2. und 3. März an der OTH Regensburg

ISBN: siehe Umschlag

1. Auflage 2016

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

Alle Rechte vorbehalten.

Das Werk ist in allen Teilen urheberrechtlich geschützt. Jede Ver­wertung außerhalb der engen Grenzen des Urheberrechtsgesetzes ist ohne Zustimmung der Autoren unzulässig und strafbar. Das gilt ins­besondere für Vervielfältigungen, Übersetzungen, Mikroverfilmun­gen und die Einspeicherung und Verarbeitung in elektronischen Systemen.

Layout: Benedikt Hoffmann

Satz: Benedikt Hoffmann, Tan Trung Le, Heide Seemann, Lisa Mundt, Benjamin Härtwig, Nancy Tripke, Sarah Pfennig, Nathalie Welle, Christian Greim

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

Printed in Germany

1

Publishers: Markus Greim, Wolfgang Kusterle and Oliver Teubert

Rheological Measurement of Building Materi-als 2016

Proceedings of the 25th Conferences and Laboratory Workshops, 2nd and 3rd March at OTH Regensburg

ISBN: printed on the cover

1. Edition 2016

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: Benedikt Hoffmann, Tan Trung Le, Heide Seemann, Lisa Mundt, Benjamin Härtwig, Nancy Tripke, Sarah Pfennig, Nath­alie Welle, Christian Greim

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

Printed in Germany

2

ContentsPreface 6Wolfgang Kusterle

Application of Rheology to Characterize the Stability of Mortar Compositions under Vibration 8Yared Assefa Abebe (M.Sc.) and Prof. Dr.-Ing. Ludger Lohaus

Experimental investigation of the effect of silica fume on geopolymer mortar cured under ambient temperature 20Mohammed Al-Majidi, Andreas Lampropoulos, Andrew Cundy

Experimental investigation of the effect of superplasticiz-er/surfactant aided aqueous dispersion of multi-walled Carbon nanotubes on workability and mechanical proper-ties of cementitious composites 37S. Alrekabi, A.B. Cundy, A. Lampropoulos, I. N. Savina

Influence of Flow Ability on Early Vertical & Horizontal Length Changes in Cementitious Materials 54Adrian Bajrami, Thomas A. Bier

Development of a lab-intensive mixer with integrated ab-solute value rheometer and tribometer: KNIELE KKM-RT 15/22.5 72Christian Baumert, Harald Garrecht IWB Stuttgart, Harald Kniele, Alexander Kniele

Structure-effect relationship between modern superplasti-cizers and the rheological properties of fresh cement pastes 80Dipl.-Ing. Raphael Breiner, Dr.-Ing. Michael Haist, Prof. Dr.-Ing. Harald S. Müller

Rheological behavior of mortars: comparison between rotational and squeeze-flow techniques 100Fábio A. Cardoso, Vanderley M. John, Rafael G. Pileggi, Phillip F.G. Banfill

Zusammenhang von plastischer Viskosität, Strukturab-baurate und Mischungsstabilität von Bindemittelsuspensionen 120Dario Cotardo, Ludger Lohaus

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A new empirical test method for evaluating sag/slip con-trol and workability in mortars containing mineral rheo-logical additives 139Alberto Fernández-Ibarburu, Pedro Díaz del Castillo, David González

Admixtures and rheological properties of Self-Compacting Concrete 151Jacek Gołaszewski

Rheology of Constructing Materials: 25 Years Ago - The Next 25 Years 169Markus Greim

Messungen an Polymerbetonmischungen zur Prozessoptimierung 183Klaus Hock, Eva-Maria Szargan-Hock

Bewertungsverfahren für die rheologischen Eigen-schaften von Mörtel – Assessment procedures for the rheological properties of mortars 192M.Sc. Hakan Kilinc, Univ.-Prof. Dr.-Ing. Rolf Breitenbücher

Rheology Testing of Deep FoundationConcrete 211Thomas Kränkel, Dirk Lowke, Christoph Gehlen

The Water Demand of Cement – Is There Any True Appli-cation-Relevant Parameter Existing? 224Peter KruspanJulian Link

Entwicklung eines faserbewehrten, selbstverdichtenden Schwerbetons unter Berücksichtigung der Werksbedingungen 227M. Sc. Klemens Laub, Dipl.-Ing. (FH) Markus Tenwinkel, Dr.-Ing. Barbara Leydolph, Dr.-Ing. Ulrich Palzer

Studying printability of fresh concrete for formwork free Concrete on-site 3D Printing technology (CONPrint3D) 236V.N. Nerella, M. Krause, M. Näther, Viktor Mechtcherine,Ivan Parić, Florian Fleischmann, Markus Greim, Wolfgang Kusterle

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The Determination of Rheological Properties of “High Slump Concrete” and SCC - the Advantages of a Modified Online Ball Measuring System 247Ivan Parić, Florian Fleischmann, Markus Greim, Wolfgang Kusterle1

X-ray computed tomography of porosity in fibre rein-forced self-compacting concrete 265Tomasz Ponikiewski,

Test Evaluations of a Fully Automatic Mortar Mixer with Torque Measurement for Determining Water Demand 281Garrecht, H.; Schließer, A.; Baumert, C.; Özogul, M.,

Influence of effects on nano and micro scale on the rheo-logical performance of cement paste, mortar and concrete 294Wolfram Schmidt, Berta Mota Gassó, Heinz Sturm, Jutta Pauli

Optimierung der Verarbeitbarkeit von Sichtbetonsorten 308Rolf-D. Schulz,

Study of mix design parameters for self-compacting con-crete based on the rheological characterization of cement based mortars 329José Roberto Tenório Filho, Everton Luiz da Silva Mendes, Profa. Dra. Karo-line Alves de Melo Moraes

Bibliography of All Papers: Rheology of Building Materials 1992 - 2016 339Markus Greim (ed.)

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PrefaceIn 1981 Prof. Juergen Teubert published his fundamental model for reaching sufficient workability of fresh concrete in Betonwerk+Fer­tigteiltechnik. Some years later he initiated a small conference on the rheology of building materials. With about 20 participating experts this event took place in 1992 at the University of Applied Sciences Regensburg. This was the starting point for a series of annual con­ferences and laboratory workshops in Regensburg. This year we are proud to celebrate the 25th anniversary.

This anniversary has been possible only due to the dedication of Prof. Teubert, the close cooperation with Markus Greim and Oliver Teubert, Schleibinger Testing Systems and the staff of the OTH Re­gensburg. Beside the professors, especially Johann Stolz has been responsible for all the little organisational details during these con­ferences. Personally, I took part in the conference in 1996 and have been chairing it since 2002. In 2011 we had to organize two sessions in order to accommodate 180 delegates. The following year the ven­ue therefore moved from the campus at Pruefeninger Strasse to Galgenbergstrasse in Regensburg where it has been ever since. The language also changed from German to English (or bilingual). This event is organized as a low cost conference without any attendance fee. This is only possible by numerous hours of work put in by the organizing committee, Schleibinger Testing Systems and by the hos­pitality of the OTH.

Rheology has not been a core science within civil engineering, rather within food and cosmetic industry. Civil engineers used for many years quite rudimental one point methods for assessing the work­ability of mortars and concrete. These methods provide sufficient reliable results as long as comparing similar well known materials during conformity testing. However, when using new constituent materials, new mix design and new building materials, the one point methods reach its limitation. PCE’s and self­compacting concrete are examples for that. Therefore, rheometers like the historic VIS­COCORDER or the Viscomat NT are used for the testing of cement paste. But the application of the same principles on concrete is more

6

difficult due to the large aggregates. Finding a compromise between “pure“ rheological theory and practical application was the topic of these conferences. Beside the classic application of the rheology on cement bound materials, other building applications have been pre­sented as well. However, Ditmar Hornung summed it up correctly in 2012: Cement – nothing works without rheology.

Over the years we had the privilege to listen to presentations from the world leading experts on applied rheology here in Regensburg. The conference has also been the initiation for many new and fruit­ful contacts, especially in late night sessions at Gravenreuther or Dicker Mann.

The papers of this 25th conference are published in print in this pro­ceedings. They cover the influence of new and known additives on mortars and concrete as well as newly developed or improved test­ing methods. For papers from previous conferences see http://www.schleibinger.com/cmsimple/?Rheologie.

I would like to thank the Founding Fathers of this conference, all lec­turers and visitors as well as all members of the organizing commit­tee for their support. Without them this successful conference would not have been possible.

“πάντα ῥεῖ ­ Panta rhei” – this Greek expression can be applied to our conferences as well. They will never be the same, yet the important topic of rheology will always be discussed and our visitors are very faithful to attend. No doubt we will have interesting conferences in the future. Therefore, I am looking forward to our further meetings in Regensburg.

Wolfgang Kusterle

7

Application of Rheology to Characterize the Stability of Mortar Compositions under Vibra-tion

Yared Assefa Abebe (M.Sc.) and Prof. Dr.-Ing. Ludger LohausInstitute of Building Material Science, Leibniz Universität HannoverPhone: 0511- 7628966, e-mail: yared.a@baustoff.uni-hannover.de

Abstract

The fresh concrete properties including the flowability and stabili­ty are mainly dependent upon the rheological characteristics of the mix. The flowability of concrete is mainly related to the yield stress and the viscosity. It is well known that the static stability which is relevant to the stability of concrete at rest is mainly governed by the yield stress and the thixotropic behavior of the mix. However, rhe­ological explanations with regard to the dynamic stability such as the case when a concrete is being vibrated are not only rare but also incomplete. To this end, within the scope of this work, an attempt was made to find out the relevant rheological properties that play a decisive role in the stability of mortar under the influence of vi­bration. The results of the investigations have clearly indicated that the stability of mortar compositions during vibration is dependent on the viscosity and the residual interparticle structure of the paste compositions that they are made from.

1 Introduction

Today‘s modern structures, which usually feature dense reinforce­ments as well as slender and geometrically complex elements, re­quire a concrete with higher workability and stability. Among the main factors that determine these fresh concrete properties are the rheological properties of the suspending medium, namely the ce­ment paste or the mortar. While the flowability and workability of concrete is mainly related to the yield stress and the viscosity, the stability is governed by the yield stress, viscosity and thixotropy. As

8

such, the question as to which rheological property is relevant to which state of stability depends on whether the concrete is at rest or under the influence of external stresses.

The static stability is relevant to the segregation process at rest such as the sedimentation of coarse aggregates after casting of self­com­pacting concrete (SCC). It depends first and foremost on the yield stress. At rest, no segregation of coarse aggregates would take place as long as the yield stress of the suspending medium (τo) is higher than a certain critical yield stress (τo,c), i.e. τo > τo,c. In contrast, the segregation of the coarse aggregate would be inevitable when τo < τo,c. However, the extent of the segregation is dependent upon the rate at which the inter­particle structures get re­built after the destruction caused by the stress applied during casting. In other words, the thixotrop­ic behavior of SCC plays a vital role in limiting the extent or depth of sedimentation of the coarse aggregates. At rest, a concrete with a strong thixotropic behavior can rebuild its interparticle structures in a relatively short time, thereby increasing its viscosity and yield stress and its resistance against segregation [1] [2] [3].

The dynamic stability is relevant to the segregation process under the action of stress such as during casting, pumping and vibrating processes. However, the extent of segregation depends on the mag­nitude of the applied stress. For the same type of concrete, one can argue that the stress caused by standard vibration influences the rhe­ological properties and the segregation process significantly when compared to the normal casting process. Very high external stresses such as those caused by vibration, can cause a complete break­down of the interparticle structures resulting into a significant reduction of the yield stress (τo) [4] [5] which makes the sedimentation of the coarse aggregates inevitable. Under such circumstances, the viscosity of the mix provides the main resistance against the segregation pro­cess by influencing the velocity of settlement of the aggregates. To some extent, the residual interparticle structure could also contrib­ute to the overall stability during vibration. Accordingly, unlike SCC, the rheological characterization of concrete under vibration should focus on the structural breakdown phenomena rather than the struc­

9

tural build­up process [6].

In this paper, measurement methods and evaluation techniques that make it possible to determine all three rheological parameters ­ yield stress, viscosity and thixotropy – are introduced. The rheological in­vestigations were carried out using a rotational viscometer (Viskomat NT from Schleibinger). The Herschel­Bulkley and Bingham mod­els were applied in order to determine the yield stress and viscosity of the pastes. The thixotropy was determined by making use of the breakdown area between the static yield stress (τo,s) and the dynam­ic yield stress (τo,d) depicted at different shear rates [7]. The stability properties of different mortars made from different paste composi­tions were then investigated using a combined sedimentation­sieve test, a wash­out test and penetration test.

2 Rheological Measurement and Evaluation Tech-niques

The measurement profile applied for determining the rheologi­cal properties of the paste compositions was formulated in such a way that the time and loading dependency behaviors could also be reflected. The advantage with this profile is that in addition to the relative yield stress and relative viscosity, which are determined at a steady state condition, the thixotropic behav­ior could also be de­termined by quantifying the magnitude of applied stress required to breakdown the interparticle structure and to bring the system to a steady state. The first shear rate of 150 U/min is applied for ca. 3 minutes in order to homogenize the mixtures and start the measure­ments under the same condition.

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Figure 1: Measurement profile for rheological investi­gation of paste and mortar

The relative yield stress and relative viscosity are determined using the dynamic yield stress (τo,d) curves – the Y­intercept (b) and the gra­dient (tan α) representing the yield stress (τo) and dynamic viscosity (η).The Herschel­Bulkley model was applied in order to determine the relative yield stress, since the classic Bingham model has at times led to negative values. The relative yield stress values so determined are then integrated in the Bingham model in order to determine the relative viscosity. The thixotropic behavior is determined by delin­eating the area (Athix) between the curves formed by the points of the static yield stress (τo,s) and the dynamic yield stress (τo,d) at different shear rates.

τod,150

τos,50

τos,75

τos,100 τos,125

τos,150

τod,125 τod,100

τod,75

τod,50

Measured Shear resistance

Mea

sure

d Sh

ear r

esis

tanc

e [N

.mm

]

Time [min]

11

Shea

r res

ista

nce 𝑻 𝑴

~ 𝝉

[N.m

m]

Rotation speed v ~ �̇� [U/Min]

𝒃 ~ 𝝉𝟎

𝑨𝑻𝒉𝒊𝒙 = � 𝑻𝑴𝒎𝒂𝒙

𝟏𝟓𝟎

𝟓𝟎𝒅𝒗 − � 𝑻𝑴𝒎𝒊𝒏

𝟏𝟓𝟎

𝟓𝟎𝒅𝒗

𝑨𝑻𝒉𝒊𝒙

TMmax = f(τo,s)

TMmin = f(τo,d)

Rotation speed v50 𝟏𝟓𝟎

𝒕𝒂𝒏 𝜶 ~ 𝜼

Figure 2: Measured data and evaluation method

3 Experimental investigations and Materials

The rheological investigations on diff erent paste and mortar compo­sitions were carried out using a rotational viscometer (Viskomat NT from Schleibinger). Diff erent paddles were used for the paste and mortar investi­gations, see fi gure 3.

12

5

Figure 4: Vibrated mortar, Sieve test, Wash-out test and Penetration test

The paste compositions have all the same water-cement ratio (w/c) of 0.6 and superplasticizer (SP) content of 5.41 % of the amount of water. But they differ in the water – fines ratio (VW/VF) ranging from 0.8 – 1.2.

Material type Sp. gr. (kg/dm3)

w/c = 0.6 VW/VF = 0.8 VW/VF = 0.9 VW/VF = 1.0 VW/VF = 1.2

CEM I 42.5 N [ml] 3.13 232.2 247.5 261.2 285 Fly ash [ml] 2.31 315 270.9 231.3 162.7 Water [ml] 1.0 437.8 466.6 492.5 537.3 Air voids [ml] - 15 15 15 15 SP [% of water] 1.05 5.41 5.41 5.41 5.41

Table 1: Paste compositions for a total volume of 1000 ml

The mortar compositions for the stability tests were produced by combining these paste compositions with sand (0/2 mm) at a constant volume of 456.6 ml/1000 ml.

4. Results and Discussions

The results of the rheological investigations of the different paste compositions are shown in figure 5. Despite the different VW/VF ratios, the relative yield stress values lie more or less in the same range. This could be attributed to the highly flowable nature of the pastes compositions as can be witnessed by the mini slump-flow test results exceeding the 40 cm mark. At such high level of flowability, it could be assumed that the chosen Water – SP combinations are enough to exceed the saturation point after which a further increase in fluid con-tent do not necessarily lead to an increased flowability but increase the risk of segregation. Hence, no significant differences could be detected with regard to

Figure 3: Paste paddle (left ), Viskomat NT (middle) and Mortar paddle (right)

In addition to the standard mini slump­fl ow and funnel fl ow­time tests, the stability properties of diff erent mortars made from diff er­ent paste compositions were also investigated using combined sed­imentation­sieve test, wash­out test and penetration test. The com­bined sedimentation­sieve test was conducted fi rst by vibrating the mortar for 30 seconds in a segmented tube. Then, the mortar from the upper and lower sections was sieved on a 0.25 mm sieve in order to determine the separation / segregation properties of the mix. Af­terwards, the particles with sizes < 0.25 mm were washed out and the remaining sand mass (0.25 – 2 mm) was dried and weighed in order to analyze the sedimentation stability of the mixes.

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Figure 4: Vibrated mortar, Sieve test, Wash­out test and Penetration testThe paste compositions have all the same water­cement ratio (w/c) of 0.6 and superplasticizer (SP) content of 5.41 % of the amount of water. But they differ in the water – fines ratio (VW/VF) ranging from 0.8 – 1.2.

Material type

Sp. gr.(kg/dm3)

w/c = 0.6

VW/VF = 0.8 VW/VF = 0.9 VW/VF = 1.0 VW/VF = 1.2

CEM I 42.5 N [ml]

3.13 232.2 247.5 261.2 285

Fly ash [ml] 2.31 315 270.9 231.3 162.7

Water [ml] 1.0 437.8 466.6 492.5 537.3

Air voids [ml]

­ 15 15 15 15

SP [% of water]

1.05 5.41 5.41 5.41 5.41

Table 1: Paste compositions for a total volume of 1000 ml

The mortar compositions for the stability tests were produced by combining these paste compositions with sand (0/2 mm) at a con­

80

70

20

10

0 25 50

0,8

Rheological lnvesitigations

75 100 125 Shear rate [U/min]

Yield stress

0,9 1,0 1,2 VwNf-Werte

y = 0,47x + 0,85 �0,99

y = 0,28lt + 0,86 R2 = 0,99

y=0,16x+0,78 R' = 0,99

y = 0,06x + 1,04 R' = 0,9

]

150 175

•Vwtvf=0,8

•VwNf=0,9

•VwNf=1,0

•VwNf:1,2

60

50 J .2 40

§ 30 'iii '.E 20 ::;;

10

0

Viscosity 0,50 .;;�::�]�Ge o,35 i 0,30

:;o,26 ; -;; 0,20 o �0, 115 �- 1S: 0,10 _ o

0,06 dm . 0,00 .� .. 0,8 0,9 1,0

VwM-Werte

0,8

t +-

Mini slump-flow

0,9 1,0 VwNf-Werte

Thixotropy 350

i�u·.�,··· J100 . : �

50 � .,.

0 . ·• 0,8 0,9 1,0

VwNf-Wene

1,2

1,2

14

stant volume of 456.6 ml/1000 ml.

4. Results and Discussions

The results of the rheological investigations of the different paste compositions are shown in figure 5. Despite the different VW/VF ra­tios, the relative yield stress values lie more or less in the same range. This could be attributed to the highly flowable nature of the pastes compositions as can be witnessed by the mini slump­flow test results exceeding the 40 cm mark. At such high level of flowability, it could be assumed that the chosen Water – SP combinations are enough to exceed the saturation point after which a further increase in fluid content do not necessarily lead to an increased flowability but in­crease the risk of segregation. Hence, no significant differences could be detected with regard to the yield stress. The relative viscosity val­ues and the thixotropic behavior, on the other hand, decrease with increasing VW/VF ratios. This is to be expected since an increase in the VW/VF ratios implies an increased water film thickness and great­er distance between the individual fine particles, thereby reducing the potential for the formation of colloidal flocculants as well as CSH bridges which are the results of early nucleation processes. Conse­quently, the resistance to flow (viscosity) as well as the applied shear force required to break down the interparticle structure (thixotropy) decreases.

The results of the stability investigations of the different mortar com­positions are shown in figure 6. With regard to the sensitivity of the test methods, the combined sieve­sedimentation test (SST) under vi­bration has shown the most reliable test results. The penetration test did also show the expected trends to a satisfactory degree. The wash­out test, however, could not clearly indicate the differences between the different degrees of stability of the mixtures. This could be due to the random distribution of the different sizes of sand particles and the corresponding discrepancies in the measured sand masses after washing out.

15

6

the yield stress. The relative viscosity values and the thixotropic behavior, on the other hand, decrease with increasing VW/VF ratios. This is to be expected since an increase in the VW/VF ratios implies an increased water film thickness and greater distance between the individual fine particles, thereby reducing the potential for the formation of colloidal flocculants as well as CSH bridges which are the results of early nucleation processes. Consequently, the resistance to flow (viscosity) as well as the applied shear force required to break down the interparticle structure (thixotropy) decreases.

Figure 5: Results of rheological investigations on paste compositions

The results of the stability investigations of the different mortar compositions are shown in figure 6. With regard to the sensitivity of the test methods, the combined sieve-sedimentation test (SST) under vibration has shown the most reliable test results. The penetration test did also show the expected trends to a satisfactory degree. The wash-out test, however, could not clearly indicate the differences between the different degrees of stability of the mixtures. This could be due to the random distribution of the different sizes of sand particles and the corresponding discrepancies in the measured sand masses after washing out.

Figure 5: Results of rheological investigations on paste compositions

7

Figure 6: Results of stability investigations on mortar compositions

The stability analysis based on the SST under the influence of vibration clearly show an increased separation or segregation of the paste from the mortar with increasing VW/VF ratios. This tendency could also be confirmed by the penetra-tion test even though it is more relevant to the investigation as to the sedimenta-tion of larger particles in the mortars at rest.

Figure 7: Correlations between rheological parameters and stability under Vibration

The results of the rheological and stability investigations clearly indicate that the stability properties of the mortar compositions under the action of vibration are directly dependent on the viscosity as well as the thixotropic behavior of the paste compositions that they are made from. The yield stress seems to have a negligible effect in this respect, at least for the paste compositions used in this investigation. But this statement could generally be applied in the context of

Figure 6: Results of stability investigations on mortar compositions

The stability analysis based on the SST under the infl uence of vibra­tion clearly show an increased separation or segregation of the paste from the mortar with increasing VW/VF ratios. This tendency could also be confi rmed by the penetration test even though it is more rel­evant to the investigation as to the sedimentation of larger particles in the mortars at rest.

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Figure 7: Correlations between rheological parameters and stability under Vibration

The results of the rheological and stability investigations clearly in­dicate that the stability properties of the mortar compositions under the action of vibration are directly dependent on the viscosity as well as the thixotropic behavior of the paste compositions that they are made from. The yield stress seems to have a negligible eff ect in this respect, at least for the paste compositions used in this investigation. But this statement could generally be applied in the context of fl ow­able mortar or concrete compositions that are exposed to vibration, since they consist of very fl owable paste compositions. As such, the mortars made of paste compositions exhibiting higher viscosity and thixotropic behavior, in this case those with lower VW/VF ratios, have shown good stability both against separation of the paste and sedi­mentation of the sand particles under vibration. At rest, these stable mortar compositions could be expected to show greater resistance against the sedimentation of coarser particles as can be inferred from the results of the penetration test.

5 Conclusion

The fl owability and stability of cement based mixtures depend on the rheological properties, which in turn depend on their composi­tion. To this end, the infl uence of diff erent paste compositions and their rheological properties on the stability properties of mortars under the infl uence of vibration were investigated. The rheological investigations were conducted using a rotational viscometer by ap­plying a test method and evaluation technique which makes it possi­ble to determine the yield stress, viscosity and thixotropic behavior of the mixes. The stability investigations on the mortar compositions were conducted using a combined sedimentation­sieve test, a wash­out test and penetration test. The results of the investigations have clearly indicated that the stability of the mortars during vibration depend mainly on the viscosity and to some extent on the residual interparticle structure of the system. As such, the paste compositions with lesser water – fi nes VW/VF ratios exhibited a higher viscosity and

17

stronger thixotropic behavior, which have led to a good resistance against segregation and sedimentation under vibra­tion. Even in very flowable pastes, lower VW/VF ratios improve the chances for the formation of colloidal flocculants and early CSH nucleation phases which enhance the overall interparticle structure, which is manifest­ed by the increased viscosity and thixotropic behavior.

6 Acknowledgement

The investigation methods, evaluation techniques and test programs were devised by the authors and executed within the scope of a mas­ter thesis by Yana Bott and Zhanna Massold.

References[1] Roussel, N.: A theoretical frame to study stability of fresh con­

crete, Materials and Structures, Vol. 39, pp. 81­91, 2006

[2] Lowke, D.: Sedimentationsverhalten und Robustheit Selbst­veredichten­der Betone ­ Optimierung auf Basis der Model­lierung der interpartikulä­ren Wechselwirkungen in zement­basierten Suspensionen, Dissertation, TU München, 2013

[3] Roussel N., Ovarlez, G., Garrault, S. and Brumaud, C.: The or­igins of thixotropy of fresh cement pastes, Cement and Con­crete Research, Vol. 42, pp. 148­157, 2012

[4] Tattersall G.H. and Baker, P.H.: The effect of vibration on the rheologi­cal properties of fresh concrete, Magazine of Con­crete Research, Vol. 40, No. 143, pp. 79­89, 1988

[5] Banfill P.F.G., Yongmo, X. and Domone, P.L.J.: Relationship be­tween the rheology of unvibrated fresh concrete and its flow under vibration in a fresh concrete and its flow under vibration in a vertical pipe appa­ratus, Magazine of Concrete Research, Vol. 51, No. 3, pp. 181­190, 1999

[6] Lohaus, L., Cotardo, D., Abebe, Y.A.: Methoden zur Quantifi­zierung last­ und zeitabhängiger rheologischer Eigenschaften

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von Leimen mittels Rotationsviskosimeter, Tagungsband der 19. Internationale Baustoffta­gung (ibausil), Weimar, Germany (2015) Band 1, pp. 1223­1230, ISBN: 978­3­00­050225­5

[7] Assaad J. and Khayat, K.H. Assessment of thixotropy of self­con­solidating concrete and concrete­equivalent­mortar: Effect of binder composition and content. ACI Materials Journal, Vol. 101, No 5, pp. 400­408, 2004

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Experimental investigation of the effect of sil-ica fume on geopolymer mortar cured under ambient temperature

Mohammed Al-Majidi, Andreas Lampropoulos, Andrew CundySchool of Environment and Technology, University of Brighton, Moulsecoomb, Brighton BN2 4GJ, UKPhone: +44 (0) 746-2671928, e-mail: m.almajidi@brighton.ac.uk

Abstract

Geopolymer mortar is an environment friendly alternative to con­ventional cementitious concrete made from by­product aluminosil­icate materials with alkaline activator. Silica fume is a by­product of the smelting process in the silicon and ferrosilicon industry which can considerably improve the strength development of high per­formance concrete [1]. Most of the previous work on geopolymer mortar has focused on the properties of single or binary materials hardened under heat curing conditions, which is considered as a lim­itation for the production and utilisation of geopolymer concrete at a large scale. In addition, there are no published studies on the effect of silica fume on the generation of geopolymer mortar cured under ambient temperature.

This paper investigates the effect of partial replacement of fly ash with densified, undensified and slurry silica fume (SF) on the setting time, workability and compressive strength of geopolymer mortar cured under ambient temperature. The geopolymer mortar was pro­duced by mixing fly ash and slag (with potassium silicate as alkaline activator) with silica fume in varying proportions. Experimental re­sults indicate that the inclusion of silica fume impacts setting time, workability and strength performance, Key­parameters were found to be the average silica fume particle size and the degree of agglom­eration of silica fume particles.

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