Influence of flexible fibers on the yield stress of fresh cement pastes and mortars

doi:10.1016/j.cemconres.2020.106221

Cement and Concrete Research

Volume 138, December 2020, 106221

https://doi.org/10.1016/j.cemconres.2020.106221 Get rights and content

Abstract

In the present work, we aim at improving our understanding of the effect of synthetic flexible fibers on the rheology of fresh cement-based suspensions. We first measure the way that synthetic fibers do increase the yield stress of various fresh cement pastes and mortars. We then measure, using micro CT, the way these fibers are deformed in a fresh paste. Finally, we propose a simple physical model allowing for the prediction of the fibers conformation as a function of their geometry, their elastic properties and the rheology of the cement-based material, into which they are dispersed. We validate this model on our results and discuss its application at the scale of mortars and concretes.

Introduction

Synthetic flexible fibers such as polypropylene or polyethylene fibers are used in a number of civil engineering applications. They may, for instance, be used as reinforcements against cracks induced by plastic shrinkage [[1], [2], [3], [4]]. Coupled with steel fibers, synthetic fibers are found to be popular in shotcrete production for tunnel linings and slope stabilization [4,5]. They are also used to reinforce asphalt concretes [6] or to reduce the risk of concrete spalling due to fire exposure [[7], [8], [9], [10]].

It is however known that addition of synthetic fibers, similarly to rigid steel fibers, leads to a decrease in the workability of fresh concretes [[11], [12], [13], [14], [15]] and mortars [15,16]. However, although it is now accepted that workability of mixtures containing rigid steel fibers scales with the product of the fiber dosage and the fiber aspect ratio (i.e. the ratio between the length and the diameter) [17], the available knowledge on synthetic flexible fibers does not provide any quantitative information on the effect of geometry and dosage on workability.

In the present work, we aim at improving our understanding of the effect of synthetic flexible fibers on the rheology of fresh cement-based suspensions. We adopt here the same approach as in [17] for rigid fibers but our results underline that the physics involved in the incorporation of flexible fibers strongly differs. In order to put the present results in perspective of the ones obtained for rigid fibers, we therefore first remind the reader of the accept knowledge on rigid inclusions. We then measure the way that flexible fibers do increase the yield stress of various fresh cement pastes and mortars. We then measure, using micro CT, the way these flexible fibers are deformed in a fresh paste. Finally, we propose a model allowing for the prediction of flexible fiber conformation as a function of the fiber geometry, its elastic properties and the rheology of the cement-based material, in which the flexible fibers are dispersed. We validate this model on our results and discuss its application at the scale of mortars and concretes.

Section snippets

Background

Dispersing rigid particles such as sand and coarse aggregates into a cement paste can conceptually be considered as adding inert non-Brownian non-colloidal particles into a yield stress fluid as long as the typical size of the constitutive elements of the paste (i.e. cement grains of average size 10 μm) can be neglected in front of the typical size of the dispersed particles. Under this condition, the rheological properties of the suspension shall depend only on the rheological properties of

Materials

The cement used in this study is a commercial cement CEM I 52.5 N (Brest). Mortars were prepared with a sand 1/4 mm from the Palvadeau quarry. The maximal packing fraction of the sand was measured using the following protocol. A container with 16 cm diameter and 32 cm height was fixed on a vibration table and was submitted to a 150 Hz vibration. A mass, equivalent to 1 kPa external pressure, was applied above the sample. 7.5 kg of sand were poured into the container and, after a 60 s vibration

Effect of the soluble organic compound in synthetic fibers on yield stress

It has first to be noted that we measured, at low dosages of fibers (i.e. less than 0.5% volume), a slight decrease in yield stress whereas we were expecting the fibers to increase the yield stress of the mixture. We dispersed some of the fibers in distilled water and in calcium hydroxide solutions. Some measurements with a TOC analyzer (results not shown here) revealed some non-neglectable organic traces in the interstitial fluid retrieved by sieving from the water/fiber mixtures. We then

Analysis and discussion

The above results all suggest that the polypropylene fibers studied here do deform when dispersed in a cement paste or a mortar. It can be expected that the more they deform, the less they shall increase the yield stress of the reference paste. This is for instance the case in Fig. 2 where the amplification of the yield stress induced by the fibers decreases when the paste consistency, expected to be at the origin of the fiber deformation, increases.

The difficulty we are facing here is that, as

Conclusion

In a first part of this paper, we first measured the way that synthetic fibers do increase the yield stress of fresh cement pastes and mortars. We then measured, using micro CT, the way these fibers are deformed in a fresh paste. In a second part, we proposed a simple physical model allowing for the prediction of the fibers conformation and compared this model to our results obtained on cement pastes and mortars.

Our results suggest that polypropylene fibers do strongly deform in cement-based

CRediT authorship contribution statement

Fariza Sultangaliyeva: Investigation/Methodology/Writing - Original Draft.

Hélène Carré: Supervision.

Christian La Borderie: Supervision.

Wenqiang Zuo: Investigation/Methodology.

Emmanuel Keita: Investigation Methodology.

Nicolas Roussel: Writing - Original Draft/Formal analysis/Supervision.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

The authors would like to acknowledge that this work was carried out using the financial assistance from the Program of the Investments for the Future of the French Government managed by ANDRA (convention N° RTSCNADAA16-0073).

References (24)

S. Tapkin
The effect of polypropylene fibers on asphalt performance
Build. Environ.
(2008)
M. Zeiml et al.
How do polypropylene fibers improve the spalling behavior of in-situ concrete?
Cem. Concr. Res.
(2006)
P. Kalifa et al.
High-temperature behaviour of HPC with polypropylene fibres: from spalling to microstructure
Cem. Concr. Res.
(2001)
A. Bilodeau et al.
Optimization of the type and amount of polypropylene fibres for preventing the spalling of lightweight concrete subjected to hydrocarbon fire
Cem. Concr. Compos.
(2004)
Y. Ding et al.
The investigation on the workability of fibre cocktail reinforced self-compacting high performance concrete
Constr. Build. Mater.
(2008)
T. Ponikiewski et al.
The influence of selected composition factors on the rheological properties of fibre reinforced fresh mortar
L. Martinie et al.
Rheology of fiber reinforced cementitious materials: classification and prediction
Cem. Concr. Res.
(2010)
F. Mahaut et al.
Effect of coarse particle volume fraction on the yield stress and thixotropy of cementitious materials
Cem. Concr. Res.
(2008)
J. Yammine et al.
From ordinary rheology concrete to self compacting concrete: a transition between frictional and hydrodynamic interactions
Cem. Concr. Res.
(2008)
N. Roussel et al.
From mini-cone test to Abrams cone test: measurement of cement-based materials yield stress using slump tests
Cem. Concr. Res.
(2005)

M. Grzybowski et al.

Shrinkage cracking of fiber reinforced concrete

ACI Mater. J.

(1990)

P. Balaguru

Contribution of fibers to crack reduction of cement composites during initial and final setting period

ACI Mater.

(1994)

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Influence of flexible fibers on the yield stress of fresh cement pastes and mortars

Abstract

Introduction

Section snippets

Background

Materials

Effect of the soluble organic compound in synthetic fibers on yield stress

Analysis and discussion

Conclusion

CRediT authorship contribution statement

Declaration of competing interest

Acknowledgments

Build. Environ.

Cem. Concr. Res.

Cem. Concr. Res.

Cem. Concr. Compos.

Constr. Build. Mater.

Cem. Concr. Res.

Cem. Concr. Res.

Cem. Concr. Res.

Cem. Concr. Res.

Shrinkage cracking of fiber reinforced concrete

ACI Mater. J.

Contribution of fibers to crack reduction of cement composites during initial and final setting period

ACI Mater.