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Rheology of Cement Grouts: On the Critical Shear Rate and No-Slip Regime in the Couette Geometry
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics. Skanska Sweden AB, Sweden.
2019 (English)In: Cement and Concrete Research, ISSN 0008-8846, E-ISSN 1873-3948Article in journal (Refereed) Published
Abstract [en]

The rheological properties of cement grouts play a key role in determining the final spread in grouted rock formations. In terms of flow properties, cement grouts are known to be complex thixotropic fluids, but their steady flow behavior is often described by the simple Bingham constitutive law. Due to their time dependent nature, the flow curves of cement grouts have been known to exhibit an unstable non-monotonic region, characterized by a negative slope below a critical shear rate. Within this paper, we focus on how this unstable region that is dominated by flow localization is affected by rheometer geometry and flow sweep measurement interval. We carried out controlled shear rate (CSR) flow sweeps on typical micro-cement grouts within different Couette geometries. Lastly, we discuss the effects of geometry and measurement interval on the resulting flow curves, with a focus on the critical shear rate that separates homogenous from non-homogeneous unstable flow.

Place, publisher, year, edition, pages
Elsevier, 2019.
Keywords [en]
Rheology, Cement Paste, Critical Shear Rate, Physical Properties, Portland Cement, Cement Grouts, Yield Stress Fluid
National Category
Civil Engineering
Research subject
Civil and Architectural Engineering
Identifiers
URN: urn:nbn:se:kth:diva-251623DOI: 10.1016/j.cemconres.2019.05.014ISI: 000487173500030Scopus ID: 2-s2.0-85066289804OAI: oai:DiVA.org:kth-251623DiVA, id: diva2:1316116
Funder
Svenska Byggbranschens Utvecklingsfond (SBUF), 13225
Note

QC 20190521

Available from: 2019-05-16 Created: 2019-05-16 Last updated: 2019-10-24Bibliographically approved
In thesis
1. On the measurement and application of cement grout rheological properties
Open this publication in new window or tab >>On the measurement and application of cement grout rheological properties
2019 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The rheological properties of cement-based grouts play a key role in determining the final spread in grouted rock formations. Rheologically, cement grouts are known to be complex thixotropic fluids, but their steady flow behavior is often described by fitting the simple Bingham constitutive law to flow curve data. The resultant Bingham parameters are then used in grouting design of e.g. tunnels, to estimate the penetration length. Since cement grouts are thixotropic suspensions, the interpretation of their flow curves as obtained from flow sweeps in concentric cylinder rotational rheometers is often complicated by: the presence of wall slip, sedimentation and unstable flow at low shear rates. A systematic approach to study these effects within the constraints of the concentric cylinder geometry (Couette) and for different cement grout concentrations was carried out as part of the Licentiate research work. Of particular interest was the influence of geometry and flow sweep measurement interval on flow curves, including the characteristic unstable flow branch that appears at applied shear rates that are below the critical shear rate. The unstable flow branch observed below the critical shear rate has been described as a characteristic feature in the flow curves of thixotropic suspensions, e.g. cement grouts, laponite. From a practical standpoint, this information can then be readily used to improve rheological measurements of cement grouts. The existence of the critical shear rate below which no stable flow occurs, plus the complex wall slip phenomenon are then discussed by considering how they affect actual spread in rough and smooth rock fractures.

Another major part of the research presented in this thesis relates to the measurement of model yield stress fluid (YSF), i.e. Carbopol, velocity profiles within the radial flow geometry. Radial flow between parallel plates, is an idealized fundamental flow configuration that is often used as a basis for grout spread estimation in planar rock fractures. Compared to other flow configurations with YSFs, e.g. channels, only a limited amount of work has presented analytical solutions, numerical models and especially experimental work for radial flow. Thus, as a first step towards more systematic studies of the plug flow region of YSFs in radial flow the current work presents the design, manufacture and for the first time velocity profile measurements that were conducted by using the pulsed Ultrasound Velocity Profiling (UVP) technique. The current observations for tests carried out with different disk spacings and flow rates show a distinct plug region, coupled with wall slip effects for the Carbopol model YSF fluid that was used. The theoretically predicted velocity profiles and the measured ones agree reasonably well, and the main discrepancies are discussed. Future studies, would then be targeted at improving the current experimental setup, for detailed measurements of the plug flow region along the radial length, which remains a challenging issue for studies on YSFs and engineering applications such as rock grouting design.

Abstract [sv]

Cementbaserade injekteringsmedels reologiska egenskaper har en stor påverkan på strömning och inträngningslängd i sprickigt berg. Medlens reologi är komplex, inklusive tixotropi, men strömningen beskrivs ändå oftast med den enkla linjära Bingham modellen i injekteringssammanhang. De två parametrarna från denna modell, flytgräns och viskositet, används sedan inom injekteringsdesign, för t.ex. tunnlar och dammar, för att bedöma inträngningen. Eftersom cementbaserade medel är tixoptropa suspensioner försvåras utvärderingen vid mätning med konventionella rotationsviskometrar på grund av glidning vid fasta begränsningsytor, sedimentation/separation av partiklarna och instabila flöden vid låga deformationshastigheter. En systematisk mätprocedur för att studera ovanstående problem med rotationsviskometer och koncentriska cylindrar samt olika vanliga vattencementtal, har utförts inom ramen för detta licentiatarbete. Av särskilt intresse har varit att studera effekten av olika geometrier och tidsintervallet mellan mätningarna, inklusive den instabila delen av flödeskurvan då deformationshastigheten är lägre än ett kritiskt värde. Denna del av kurvan har i litteraturen beskrivits som karakteristisk för tixotropa suspensioner, som t.ex. cementbaserade injekteringsmedel. Praktiskt kan ovanstående kunskap användas för att förbättra mätningen av de reologiska egenskaperna. Existensen av en kritisk deformationshastighet under vilken det inte finns något stabilt flöde, i kombination med glidning vid fasta begränsningsytor, diskuteras särskilt med hänsyn till dess påverkan på faktisk inträngning i släta och råa bergsprickor.

Ett annat fokus i licentiatarbetet har varit att studera icke-Newtonska modellvätskors (Carbopol) radiella strömning mellan parallella plattor. Denna typ av strömningsgeometri används ofta som en idealiserad konfiguration för strömning i bergsprickor. I jämförelse med andra enklare geometrier, finns endast en begränsad forskning utförd för denna geometri både då det gäller analytiska och numeriska beräkningar men framförallt då det gäller experiment. Som ett första steg inför en mer systematisk undersökning av icke-Newtonsk radiella strömning presenteras i detta arbete framtagandet av en fysisk laboratoriemodell där hastighetsprofilerna mellan plattorna för första gången visualiserats med hjälp av ultraljud. De utförda mätningarna med tre olika öppningar mellan plattorna sam tre olika värden på det konstanta flödet, visar på en distinkt plugg som är ett resultat av vätskans flytgräns samt glidning i gränsskiktet mellan vätskan och plattornas fasta begränsningsytor. En jämförelse mellan uppmätta hastighetsprofiler och analytiskt beräknade diskuteras där resultaten överensstämmer relativt väl, med beaktande av de långtgående förenklade antaganden som krävs för beräkningarna.

Fortsatta studier kommer att fokuseras på att förbättra laboratoriemodellen för en mer detaljerad studie av icke-Newtonska vätskors strömning och hur pluggen utvecklas under den radiella inträngningen, vilket fortsättningsvis är av betydelse för design av injektering i bergsprickor.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2019. p. iii-xvi, 48
Series
TRITA-ABE-DLT ; 1922
Keywords
Cement-based grouts, grouting, yield stress fluid (YSF), thixotropy, critical shear rate, radial flow, wall slip, Bingham model
National Category
Civil Engineering Geotechnical Engineering
Research subject
Civil and Architectural Engineering; Materials Science and Engineering
Identifiers
urn:nbn:se:kth:diva-251745 (URN)978-91-7873-240-1 (ISBN)
Presentation
2019-06-12, B26, Brinellvägen 23, Stockholm, 13:00 (English)
Opponent
Supervisors
Funder
SBUF - Sveriges Byggindustriers UtvecklingsfondRock Engineering Research Foundation (BeFo)
Note

QC 20190521

Available from: 2019-05-21 Created: 2019-05-21 Last updated: 2019-05-21Bibliographically approved

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Publisher's full textScopushttps://authors.elsevier.com/a/1ZeFU21ISaz8z

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Shamu, JohnHåkansson, Ulf

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