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Rheologische Messungen an Baustoffen 2020

Herausgeber: Markus Greim, Wolfgang Kusterle und Oliver Teubert

Rheologische Messungen an Baustoffen 2020

Tagungsband zum 29. Workshop und Kolloquium, 11. und 12. März an der OTH Regensburg

Publisher: Markus Greim, Wolgang Kusterle and Oliver Teubert

Rheological Measurement of Building Materials 2020

Proceedings of the 29th Conferences and Laboratory Workshops, 11th and 12th March at OTH Regensburg

ISBN:

978-3-347-02886-9 (Paperback)

978-3-347-02887-6 (Hardcover)

978-3-347-02888-3 (e-Book)

1. Edition 2020

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: Christian Greim

Typesetting: Dr. Helena Keller, Christian Greim

Published and Printed by: tredition GmbH; Halenreie 40-44; 22359 Hamburg; www.tredition.de

Preface

Rheological properties of calcium-sulfoaluminate cement mortars

Jacek Gołaszewski, Małgorzata Gołaszewska

Are Alkali Activated binder behaviors intermediate between cement and mineral suspensions?

Teresa Liberto, Maurizio Bellotto, Agathe Robisson

Oszillatorische Rheometrie zur Identifizierung von Strukturabbauprozessen an mineralischen Baustoffen

Marcel Ramler, Prof. Jürgen Quarg-Vonscheidt

Investigations on maximum fibre content for injecting highperformance mortars

Ludwig Hertwig, Klaus Holschemacher

Effect of Rheological Properties of Concrete Foundation on the Implementation of CFA-Piles

Yannick Vanhove, Chafika Djelal

Experimental setup to determine rheological properties of frazil ice

Felix Paul, Tommy Mielke, Doru C. Lupascu

Rheology - suitable measurement methods for building materials

Helena Keller, Markus Greim

Preface

The art of rheological measurements for construction materials was until 50 years ago a totally unknown territory. Even today it is often hard to understand, unless you are an expert in the field. There are many people who buy the costly equipment for rheological measurements. However, they often find after some time that the test set up, numerous influencing factors and the proper interpretation of the results is not that easy to work out. As a consequence this expensive equipment ends up lying in the corners of the labs gathering dust.

This conference and workshop on the “Rheology of Building Materials” in Regensburg cannot solve all these problems. It, however, supplies a platform for excellent presentations of recent research work as well as demonstrations of useful equipment and exchange of ideas.

The proper workability of materials bound by mineral binders is essential for an economic production and for a perfect performance in hardened state. The papers in these proceedings show examples of enhanced testing and applications.

These proceedings address important rheological topics:

• Inline control of ready mix concrete

• Tests on concrete and mortar for different purposes (e.g. rheology of calcium-sulfoaluminate mortars, of alkali activated binders, of mortars for 3D-printing)

• The influence of fibres on injecting mortars

• Oscillatory measurements.

The papers on mineral materials are enhanced with a special contribution on the behaviour of granular frazil ice. Hopefully, the reader will enjoy these papers and get a lot of inspiration as well as some new ideas for her/his own work.

Personally, due to my retirement this summer, this conference is the last I chair. In the future I will join you as an ordinary delegate. I wish Markus Greim, Oliver Teubert, Helena Keller from Schleibinger Testing Systems and my still unknown successor as chair a lot of success for the future. I would like to also thank them all for their engagement in this Conference, which is indeed the 29th.

Furthermore, I would like to thank all the authors and conference delegates for their contributions. I hope to meet you next year at the 30th anniversary at the OTH Regensburg.

Wolfgang Kusterle

Regensburg, March 2020

Rheological properties of calcium-sulfoaluminate cement mortars

Jacek Gołaszewski, Małgorzata Gołaszewska
Silesian University of Technology, Gliwice, Poland

Abstract

The paper presents research into the rheological properties of calciumsulfoaluminate (CSA) cement mortars. CSA cements may prove to be an alternative to Portland cement, due to its lower carbon footprint. High cost of CSA cement is, however, one of detriments to its more widespread use. To mitigate this issue, it may be possible to mix CSA cement with other cements or nonclinker main constituents of cements. Presented research dealt with the issue of rheological properties of mortars with cement which are a mix of CSA cements with 10, 20 and 30% of Portland cement CEM I 42.5R NA and 10, 20 and 30 % of limestone. Tested was early shrinkage of the mortars, the yield stress and plastic viscosity, and an increase of torque in the first 1,5h of hydration. The results indicated that there is no negative interaction between CSA cement and limestone in terms of rheological properties, achieving slightly higher shrinkage than CSA cement, while the effect on yield stress and torque was small, but dependant on the amount of limestone. Addition of CEM I 42.5R NA to CSA cement indicated a negative interaction between two binders in terms of yield stress and torque changes in time, however the effect on shrinkage was small, but not inherently negative as the shrinkage was significantly lower than in case of Portland cement CEM I 42.5R NA.

Introduction

Calcium sulfoaluminate (CSA) cements have been gathering more interest in the last few years, due to the lesser impact of their production on environment in comparison to ordinary Portland cement (OPC) [1,2] In case of OPC, for each ton of clinker produced, on average 0.85 tons of CO2 is produced, mostly due to the chemical process of calcination of limestone and high heat needed to obtain required clinker phases (~1450oC) [3,4]. In case of CSA, the emissions of CO2 are lower, due to lower temperature in kiln (~1250oC), lower amount of limestone calcinated during production, as well as less energy needed to grind the obtained CSA clinker [1,5,6]. This translates into lower emission of CO2 in comparison to OPC; research of Li et al [7]indicated that the decrease in emission of CO2 is in range of 20-30%, while Ellis [8] estimated, that there can be up to 35% of reduction in CO2 emissions.

CSA cement is a mineral hydraulic binder, which clinker is obtained by burning limestone, bauxite (or other aluminum-rich rocks) and gypsum, however there is research being conducted on using waste materials for CSA production [9–11]. Main mineral phases of sulfoaluminate (SA) cement is ye’elemite (C4A3Ŝ) and belite (C2S) with secondary phases of calcium sulphate (CŜ), and small amounts of aluminoferrite (C4AF). Completely different phase composition is responsible for different hydration of CSA cements. The main product of the reaction of hydration of CSA cement is ettringite C63H32, C2AŜH8 (stratlingite) and monosulphate, with CSH phases appearing after 14-30 days of the hydration start [12,13]. This leads to many beneficial characteristics of CSA cement: it has a short initial setting time, fast strength development and low shrinkage.

CSA cements have been introduced by A. Klein in the 1960sin the USA, and decade later developed mostly by Chinese enterprises [14]. Due to its short setting time, high early strength and low shrinkage, they found use in production of prefabricated elements, bridges, and shotcrete. [15] The scope of using CSA cements is limited, mostly due to the high production cost connected to the rarity of raw materials (especially bauxite), therefore the research in the field is often directed to mixing CSA cement with other materials to obtain binders of similar characteristics but of a lower cost.

American Guide for the Use of Shrinkage-Compensating Concrete [16] has even included the mixture of Portland cement and CSA cement in amount of 10-30% as a cement type “K” of expansive cements. Chaunsali and Mondal [17] had found that mixing OPC with 15% CSA cement caused a significant expansion of cement paste, however Le Saoût et al. [18] had shown, that the chemical shrinkage was higher in case of pastes with 90% OPC and 10% of CSA as a binder than in OPC. There was also research conducted by Huang et al. [19] into the rheological properties of fresh mortars with CSA and OPC blends, which had shown that the addition of CSA to OPC may increase the yield stress and viscosity of the mortar, depending on the anhydrate content. It must be noted, however, that the topic of rheology of CSA – OPC blends was not well developed in existing literature.

Similarly, there is very little information concerning the rheology of the CSA blends with mineral fillers, such as limestone. There are studies available that show the positive effect of limestone of hydration of CSa, mostly due to the stabilization of ettringite in the presence of hemicarboaluminate and monocarboaluminate which can appear in the presence of limestone. [10,20–22]

Thus, the aim of the presented study was to investigate the rheological properties of mortars with CSA blends with CEM I 42,5R and limestone in amount 10, 20, and 30% of binder mass. Also tested was early shrinkage measured by the cone method. Rheological parameters of yield stress and plastic viscosity were also tested, as well as the change of torque in first 1h of hydration.

Materials and methods

Two types of commercially available cements were used in the research: CSA cement and CEM I 42,5R NA cement, which chemical and phase composition are shown in Table 1 and Table 2 respectively. One type of limestone was used in the research – commercially available ground limestone, which complies with the requirements set by standard EN 197-1 [23] and EN 197-2 [24] for limestone used for as a main constituent of cements The chemical composition of limestone is shown in Table 1.

The specific surface area of CSA cement was 4500 cm2/g, CEM I 42,5R NA cement had SSA of 3950 cm2/g and limestone - 4800 cm2/g. The initial setting time determined according to standard EN 196-3: 2016 [25] of used CSA cement to was 20 minutes, while CEM I 42.5R NA was 260 min.

Table 1: Chemical composition of materials used in the research

Table 2: Phase composition of cements used in the research

All tests were conducted on mortars, which composition was based on standard mortar according to EN-197 – 1 [23], namely: 450 g of cement, 1350 g of standard sand, and water-cement ratio of 0.5. Due to technical aspects, w/c ratio was raised to 0.6 in case of rheometric tests in anticipation of high yield stress of mortars with CSA cement. Mixing procedure was assumed also according to EN-197 – 1 [23], however in case of CSA cements with 20% and 30% of CEM I 42.5R NA addition, the procedure was shortened due to a rapid workability loss of the fresh mortar, and lasted just 90 s instead of 240 s.

Mortars have been subjected to rheological tests in a rheometer Viskomat NT after 5 minutes from mixing, and then underwent a 1.5 h measurement cycle, shown in Figure 1, which aim was to check the changes in the torque in time. The first five minutes of the cycle was devoted to measuring the yield stress and plastic viscosity of the mortars and thus the rotational speed increased rapidly, and then gradually decreased, while the rest of the measurement cycle had a constant rotational speed.

Figure 1: Measurement cycle for rheometric tests.

To calculate the yield stress and plastic viscosity of the mortar, simplified Bingham model was adopted.

Where: M – torque, N – rotational speed of measuring cylinder, g – shear resistance, h – plastic flow resistance. In this equation, the shear resistance g corresponds to the yield stress τ0 and the plastic flow resistance h - plastic viscosity ηp, and they will be referred as such further.

In the research, early shrinkage was measured in Shrinkage Cone deltaEL, as shown in Figure 2. System allows for continuous measurement of fresh mortar, by laser measurement of changes in height of conical sample. The linear change in sample height corresponds to the volumetric shrinkage of the sample. Standard mortars were prepared and placed in the cone immediately after mixing. The measurement itself lasted 24 h. The apparatus was kept in a climatic chamber, in set temperature 20oC and humidity of 65%, for the duration of the tests, to minimize the effects of environmental conditions on the sample.

Figure 2: Shrinkage measurement equipment - Shrinkage Cone deltaEL setup.

Results and discussion

3.1 Rheology of fresh mortar

The results of continuous measurement of torque of CSA cement with CEM I 42.5R NA addition are shown in figure 3.

As it can be seen, CSA cement is characterized by the lowest torque, which changed very little in time, rising from around 14 Nmm to 20 Nmm during the first 90 minutes. The torque of Portland cement CEM I 42.5R NA underwent more visible change, increasing from 25 Nmm to over 40 Nmm. However, the mortars with a mix of CSA cement with 10, 20 and 30% of CEM I 42.5R NA had exhibited unusual behavior. The torque of those cements substantially increased, and quickly reached 100 Nmm. The tests have been stopped after the torque reached 100 Nmm, due to the fact, that for the high torque values, mortar can be so stiff, that it does not let the probe pass. This leads to the mortar skidding on the walls of measuring container, and yields wring test results. The increase in torque, caused by rapid loss of workability, made it impossible to accurately measure yield stress and plastic viscosity, thus for mortars with cements with 20% and 30% of CEM I 42.5R NA addition, the measuring process shown in figure 1 was changed to constant rotational speed of 60 rpm. Still, the loss of workability was extremely swift, and the measurement had to be stopped after 10 minutes in case of 30% addition of CEM I 42.5R NA to CSA cement, and was practically impossible for mortars with cement with 20% of CEM I 42.5R NA mass.

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