Rheologische Messungen an Baustoffen 2017 E-Book

Markus Greim

• Herausgeber: tredition
• Kategorie: Wissenschaft und neue Technologien
• Sprache: Deutsch

Seitenzahl: 144

Veröffentlichungsjahr: 2017

Beschreibung

Tagungsband zum 26. Workshop und Kolloquium "Rheologische Messungen an Baustoffen", 21. und 22. Februar 2017 an der Ostbayerischen Technischen Hochschule Regensburg

Leseprobe

Rheologische Messungen an Baustoffen 2017

Tagungsband zum 26. Workshop und Kolloquium, 21. und 22. Februar an der OTH Regensburg

Herausgeber: Markus Greim, Wolfgang Kusterle und Oliver Teubert

Rheologische Messungen an Baustoffen 2017

Tagungsband zum 26. Workshop und Kolloquium, 21. und 22. Februar an der OTH Regensburg

1. Auflage 2017

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 2017

Proceedings of the 26th Conferences and Laboratory Workshops, 21st and 22nd Februrary at OTH Regensburg

ISBN: printed on the cover

1. Edition 2017

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

Development of green self-compacting concrete containing low clinker cement and calcerous fly ash.

Jacek Gołąszewski, Grzegorz Cygan

A Particle Distance Model for Self-Compacting Mortars and Concretes

Dr.-Ing. Stephan Uebachs, BUI Brameshuber + Uebachs Consulting Engineers, Aachen, Germany

Einfluss der Granulometrie der feinen Gesteinskörnung auf die Rheologischen Eigenschaften Selbstverdichtender Mörtel

Dipl.-Ing. Eduard Schwab, Dr.-Ing. Stephan Uebachs, Brameshuber + Uebachs INGENIEURE GmbH, Aachen

Interfacial rheology: measurement technique for adhesive mortar-air interface

Alessandra Lie Fujii1, Fábio Alonso Cardoso2, Anne Daubresse3, Evelyne Prat3, Mohend Chaouche1

Why nonionic starch ethers act as anionic flocculants in cementitious systems

Andrea Glatthor, Crespel & Deiters GmbH & Co. KG

The modification brought by a polymer powder on mortars at their early age

Ines Tchetgnia Ngassam University of Cape Town

Rheological properties of viscosity modifying admixtures in aqueous solution and their performance on macroscopic rheology of cementitious mortars

Oliver Mazanec, Simone Klapdohr, Christoph Hofheinz

Natural rheology modifying admixtures for concrete

Wolfram Schmidt, Inès L. Tchetgnia Ngassam, Rose Mbugua and Kolawole A. Olonade

Einfluss der Mischintensität bei zweistufigen Mischverfahren auf die Verfestigung von Zementsuspensionen

Landmann, Mirko; Palzer, Ulrich

Concepts for assuring printability of concrete using rheology as a tool for additive construction

V.N. Nerella1*, V. Mechtcherine1, M. Krause2, M. Näther3,

eBT-V - A new rheometer for fresh concrete

Markus Greim, Helena Keller Schleibinger Geräte Teubert u. Greim GmbH, Buchbach, Germany

Preface

For decades little attention was given to the rheology of construction materials by civil engineers. Simple one point methods seemed to be sufficient for evaluating this “unimportant” phenomenon. The focus was on the properties of the final product.

When new constitutive materials entered the market, new construction materials and new production processes were developed. But even mixing technology changed. Mortar and concrete are stiff or soft suspensions with a yield point, thixotropy and grain sizes up to 32 mm, and are not that easy to evaluate as Newtonian liquids. Suddenly rheological data got more important. Self-compacting concrete and 3D-printing are examples for these developments.

New measuring tools and even very sophisticated and expensive rheometers are available now. For investigating the rheological parameters of cement bound materials, rheometers of different scale are used. Binder paste may be tested with rheometers intended for liquids, but for testing concrete with coarse aggregates special rheometers with no standard geometries have to be used. But how shall we use them? There are different types on the market, but it is difficult to compare their relative results. All will print nice graphs and precise numbers. But how reliable are this data? Moreover, absolute values are difficult to achieve. The main problems are particle migration, plug flow, wall slippage and often a geometry far from the classical plate-plate model. No certified calibration material for mortar and concrete is available at the time.

The problem from the material side is the time shear history and temperature dependent behaviour of all lime/gypsum/cement bound materials and the inhomogeneity of concrete with coarse aggregates. Shall we focus on optimised particle distribution or is it sufficient to use rheological admixtures for any mix? Portland cement is a robust binder in concrete, but in future the percentage in the ecological binders will be reduced.

The 26thConference 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. The papers are collected in this proceedings. Beside the conference an interesting workshop took place in the new lab facilities of the faculty of civil engineering at the OTH Regensburg campus Galgenbergstrasse. After 25 years of rheological workshops the facilities in Prüfeninger Strasse are history now.

I would like to thank all lecturers and visitors as well as all members of the organizing committee for their support.

I am looking forward to meet you in Regensburg again.

Wolfgang Kusterle

Development of green self-compacting concrete containing low clinker cement and calcerous fly ash.

Jacek Gołąszewski, Grzegorz Cygan

Silesian University of Technology, Faculty of Civil Enginering, Department of Building Materials and Processes Engineering

Phone: [phone], e-mail: [email protected]

Abstract

The paper presents a concept of shaping the properties of green self-compacting concrete (SCC), emphasizing mostly the minimization of the amount of clinker in concrete and obtainment of their low hardening temperature. The main purpose of this SCC concrete are massive and semi-massive constructions, as well as the constructions build during summer. Designed according to the proposed concept SCC are characterised by the low content of clinker, amounting from 60 to 77 kg/m3and good strength properties. It was proven that by optimizing materials and mix design one can obtain green SCC, characterized by low hardening heat and good mechanical properties in longer periods of hardening. Ground high-calcium fly ash can be used for self-compacting concrete, without negatively affecting its properties after hardening.

1 Introduction

The purpose of sustainable construction is to create and responsibly manage a healthy environment following the principles of environmental protection and efficient means. The responsible, sustainable production and use of construction materials represents one of the most important modern problems. Concrete, with its exceptional combination of functional and visual characteristics, is nowadays the primary construction material. Consequently, implementation sustainable development and sustainable construction principles into concrete designing, production and usage practice (into concrete construction live cycle) is particularly important.

One of the courses for such an action is to implement in practice the idea of green concrete. Green Concrete is defined as a concrete which uses waste material as at least one of its components, its production process does not lead to environmental destruction, and it has high performance and life cycle sustainability [1], [2]. In other way, Green Concrete is a term given to a concrete that has had extra steps taken in the mix design and placement to insure a sustainable structure and a long life cycle with a low maintenance surface. e.g. energy saving, CO2emissions, waste water. The key factors that are used to identify whether the concrete is green are: amount of Portland cement replacement materials (amount of clinker in concrete), manufacturing process and methods, performance and life cycle sustainability impacts.

The paper presents a concept of shaping the properties of green self-compacting concrete (SCC), emphasizing mostly the minimization of the amount of clinker in concrete and obtainment of their low hardening temperature. The main purpose of this SCC concrete are massive and semi-massive constructions, as well as the constructions build during summer.

2 The concept of green self-compacting concrete

The composition and constituents of SCC are chosen on the basis of appropriate rheological properties of the fresh concrete, taking under consideration the requirements for concrete in the construction. Fresh SCC has to fulfil following requirements: fluidity, which has to guarantee swift and precise filling of the form and covering of reinforcement, self-compaction, meaning its ability to quickly remove air from the mix, and lastly the stability, meaning the mix has to be resistant to segregation [3]. The reconcilement of the requirements of fluidity and self-compaction, namely obtaining a suitable rheological properties of the fresh concrete, is the biggest difficulty during the process of concrete designing. It is assumed, that for the sake of fluidity requirement the yield value of fresh concrete should be as low as possible. At the same time its plastic viscosity should be shaped so that the concrete mix properly and quickly fills the mould and to effectively remove air with a minimum segregation. The necessity to meet the rheological criteria determines the need for a specific composition and constituents of self-compacting concrete (Fig. 1). First and foremost, assumed are: small w/(c+a) ratio (w-water, c-cement, a - mineral additives), and a large amount of finest fraction (< 0.125 mm), which also includes cement and mineral additives (stone powder, ground granulated blast furnace slag, fly ash and others). Mineral additives increase the amount of cement paste without increasing the amount of cement over the necessary minimum. Due to the fact that presence of additives helps to reduce the amount of cement in the concrete mix, the amount of heat generated during the hydration is reduced. By properly choosing the type and amount of cement and additives it is possible to regulate the technical properties of concrete. Low w/c ratio and high content of finest fractions reduce the amount of free water in the mix increasing its resistance to segregation and sedimentation. The expected fluidity is obtained by use of effective PCE superplasticizers. Moreover, in order to lower the risk of segregation of the fresh concrete and obtaining its proper ability to flow, rounded, regularly shaped gravel is used; its maximal size should not exceed 20 mm and its sand content should be 40 ÷ 50%. In order to eliminate or reduce the segregation and the leakage of cement paste from the mix, and to lower its pressure on the formworks, it is recommended to use viscosity increasing admixtures. They also allow to improve the stability of the concrete mix without the need to interfere with its basic composition.

Figure. 1: Green SCC of low hydration heat concept

Proper selection of the constituents of the concrete mix is also essential for the suitability of building process of the massive construction (Fig. 1). The concrete composition is calculated so that the amount of heat generated by cement hydration is minimized, taking under consideration, of course, the requirements for concrete in construction [4]. Due to the fact that cement is a constituent determining the amount of generated heat, it is necessary to use the cements of low hydration heat and try to limit their content to the necessary minimum. In order to further limit the amount of generated head during the hardening of the concrete, as a substitute for the part of cement used are mineral additives - the best results are obtained by using fly ashes or ground granulated blast furnace slag. It is best to assume the w/(c+a) ratio lower than 0.5 (however, to reduce of the amount of generated heat to a minimum, w/c ratio can be higher). In order to delay the setting time and to spread the heat production in time, retarding admixtures are used. Due to the minimization of the amount of cement (and cement paste) it is beneficial to use aggregate of a biggest possible grain size and the amount of sand not higher than the 30-35%. It is worth noting that because of the technological factors and the possibility of causing tension in the element, aggregate grains should not be bigger than 31.5 mm.

The general concept of composition of SCC with low hydration heat is presented in Fig. 1. It was assumed, that the amount of the cement paste in this concrete should not exceed from 280 to 300 dm3/m3, meaning it should not diverge from the amount of cement paste in mechanically compacted concrete. For this amount of cement paste, by adequately choosing the w/c ratio, type and amount of cement and type of mineral additives, it is possible to more or less freely shape the rheological properties of the concrete mix, the amount of heat generated during the hardening and properties of the hardened concrete. It is also possible to fulfil the requirements from concrete standards that apply to the amount of cement (300 – 350 kg/m3) and w/c ratio (0.45 – 0.60) which result from the exposition class dependant on the environmental conditions according to EN 206. If it is possible on the grounds of expected properties of hardened concrete, it is beneficial to set a possible high w/c ratio. The necessity of guaranteeing required stability of the SCC mix imposes the use of aggregate of maximal grain size of 16 mm. Use of gravel aggregate is an optimal choice considering the requirements for SCC and massive concrete. It was assumed, that required rheological properties of the concrete mix will be obtained by the use of carefully selected superplasticizer with retarding action, avoiding use of viscosity enhancing admixtures.

3 Experimental

During the research the possibility of obtaining the self-compacting concrete of low hydration heat according to the above mention requirements was verified. When selecting the amount and type of binder, it was sought to minimize the use of clinker in the concrete. Therefore, cement with low content of clinker CEM III was used (Table1). The amount of cement was also minimized by substituting it with calcareous fly ash (CFA) and/or limestone powder and/or silica powder. About 5 million tons of CFA is produced annually in Poland, as a result of brown coal combustion in conventional boilers. The results of studies [5] ad [6] show no negative influence of CFA on properties of hardened concrete. The main problem in practical use of CFS is, that its implementation significantly worsens workability of fresh concrete, especially in the aspect of workability loss. However, it was shown that the negative influence of CFA on the workability of fresh concrete may be reduced by processing it by grinding and even obtaining SCC with CFA is possible [4,5]. In the composition of concrete included were sand and gravel aggregate with the fraction grading shown in Fig. 2. SCC were designed using method presented in [7]. Properties of materials and concrete proportioning are shown in Tables 1 – 3.

Property

CEM I 52,5R

CEM III/B 42,5LLH/SR/NA

Initial setting, min

144

204

Water for normal consistency, %

33

31.9

Volume stability, mm

0.7

0.7

Specific surface,cm

2

/g

5032

5290

Hydration heat, J/g

225

LOI, %

1.28

0.86

SO

3

, %

2.66

1.95

Na

2

O

eq

, %

0.66

0.70

Compressive 7 days

41.6

26.9

strength, MPa 28 days

66.5

55.3

Table 1:Cement properties

Table 2:CFA properties

Table 3:Concrete proportioning

Table 4:Test results – cement + additive hydration heat [J/g]

Table 5:Concrete properties

Concretes were tested for:

•Properties of fresh SCC - measurements were performed at a temperature 20°C at 5 and 60 min after the end of mixing using the slump-flow test according EN 12350-8. The stability of each mixture was evaluated with the Visual Stability Index (VSI; according to ACI 237 R-07; 2007). Additionally, the air content in the mixture at 5 min after the end of mixing was determined according to EN 12350-7.

•Setting time of concrete - measurements were performed using ultrasonic method by means of modified Schleibinger Vikasonik system. Transmitter and receiver were placed on the sides of beams 10x10x50 cm and tested for early shrinkage. Method is presented in details in [8].

•Development of concrete hardening temperature – measurements were performer on cubic samples 250 mm on a side insulated using styrofoam coating of thickness 100 mm and thermal conduction coefficient 0.044 W/mK. Temperature measurement was performed in the middle of cube. External temperature during the measurement was 20°C.

•Early shrinkage – measurements were performed using modified Schleibinger TLS apparatus on samples 10x10x50 cm during 24 hours from the moment of placement. During the test apparatus and samples were kept in climate chamber at a temperature 20°C and humidity of 60%. Method is presented in details in [8]. It is worth to note, that after 24 hours may be further tested for shrinkage using Amsler method.

•Compressive strength after 2, 7 and 28 days - measurement were performed according to PN-EN 12390-3. The samples were cured according to PN-EN 12390-2.

•Hydration heat - for binders and admixtures used in tested concretes hydration head and hydration kinetics were measured using isomeric calorimeter TamAir produced by TA Instruments. Measurement was held during 72 hours on binder paste with w/b and SP content analogous as in concrete at a temperature 20°C.

4 Test results and discussion

Obtained results are compiled in Tables 4 and 5.

The highest amount of generated heat during the hydration process obviously characterized B0 binder (Portland cement CEM I and SP). The other binders are characterized by significantly lower hydration heat and kinetics of its generation. The amount of generated heat is mainly dependent on the amount of cement clinker and specific surface. The smallest amount of heat was generated during the hydration of ground granulated blast-furnace slag cement CEM III/B 42.5 L-LH binders.