THE TRUTH ABOUT FIBRES: PART THREE

THE TRUTH ABOUT FIBRES: PART THREE

In this series of articles we have touched on synthetic fibres being a viable alternative to traditional reinforcing for concrete (PART ONE); and the fact that not all fibres are created equal and what Stratmore offers as credible, certified options (PART TWO). In this article we will get to grips with a slightly more controversial subject: how do polypropylene fibres stack up against cellulose fibres?

BACKGROUND

Here in New Zealand we have been a little slower in the uptake of fibres for concrete reinforcement. Our Northern Hemisphere industry cousins have embraced fibre a lot more willingly for over 40 years and it is being used in more applications than ever.  It is only natural, then, that other materials will attempt to contest the place of the fibres used most often i.e. polypropylene fibres.  One such material is cellulose; and in New Zealand we have already seen these fibres being offered as alternative. 

For most the decision as to whether to embrace synthetic fibres for reinforcing is not an easy one.  Can fibre deal with plastic shrinkage crack reduction, is it tough enough, how does it perform when the concrete is exposed to impact or shattering, is it resistant to abrasion, how does it cope with freeze thaw and fire spalling?  And then cellulose fibres are introduced into the formula and further ‘muddy the water’.  Particularly when these cellulose fibres claim to provide the same secondary reinforcement in concrete.

Polypropylene has been the ‘go-to’ material, but does cellulose perform as well?  This is the question that Dr. Nemkumar (Nemy) Banthia, PhD, PEng, FRSC set out to answer.  Dr. Banthia is a Professor of Civil Engineering at the University of British Columbia and the CEO of IC-IMPACTS (a Canada-India Research Centre of Excellence which aims to solve challenges facing both nations in relation to water, health, and infrastructure).  He is best known for his research in the fields of cement-based and polymer-based fibre reinforced composites, particularly on testing and standardisation, fracture behaviour, strain-rate effects, durability and development of sustainable materials.

A COMPARISON BETWEEN POLYPROPYLENE AND CELLULOSE

Dr. Banthia researched cellulose and polypropylene fibres as secondary reinforcement in concrete using industry standard performance test methods.  A summary of his findings are as follows:

  1. PROPERTIES– cellulose (being a plant extract) has a high permeability to moisture and its moisture content varies greatly with their environment.  This can affect the water demand of fresh concrete.  Polypropylene fibres on the other hand are hydrophobic and do not absorb water.  Furthermore, polypropylene fibres are 100% resistance to the highly alkaline environment of the concrete and will last for the life of the concrete once incorporated.

  2. VOLUME – fibre’s effectiveness in controlling plastic shrinkage is largely dependent on the fibres’ surface area and volume.  If cellulose fibres are used, more of the fibre will be required to reach a given level of fibre volume, when compared to polypropylene.

  3. PLASTIC SHRINKAGE – One of the industry standard tests for plastic shrinkage is found in the International Code Council’s (ICC) acceptance criterion.  It is acknowledged that some cellulose fibres have an ICC evaluation report.  But the criterion does not cover cellulose fibres used in concrete over steel deck construction, in fire-resistive construction and when used in concrete slabs exposed to abrasive and impact conditions (e.g. forklifts).  Only quality polypropylene fibres meet these criteria.

  4. CRACK HOLDING – in tests cellulose fibres performed quite well but quality polypropylene fibres outshone them as to the ability of the fibres to carry a load after the concrete cracks.

  5. COMPRESSIVE STRENGTH– the tests revealed that there is no statistical difference in the compressive strength of concrete between cellulose and quality polypropylene fibres. 

  6. FREEZE THAW – the freeze-thaw tests also revealed that the performance between the different types of fibre was negligible.

  7. IMPACT RESISTANCE– fibre certainly comes into its own in respect of impact resistance.  Fibres absorb the stresses and spread them to other areas of the concrete, resulting in a tougher, more durable surface.  And if the concrete does crack the fibres bridge that crack, resisting further crack growth.  Cellulose fibres do perform reasonably well in energy absorption.  However, fibres with larger denier and inter-connected fibre weave perform better than, say, monofilament fibres such as cellulose – they absorb a greater amount of energy.

IN SUMMARY

While cellulose fibres do perform reasonably well across some performance areas (e.g. reduction of plastic shrinkage cracking and compressive strength) only polypropylene fibres can offer true peace of mind across all performance measures.

TALK TO US

As mentioned in THE TRUTH ABOUT FIBRES: PART TWO Stratmore has the sole distributorship for both Fibermesh and FORTA-FERRO polypropylene fibres.  These fibres have been designed specifically for use in concrete – they are not a by-product of the plastic rope industry or made from recycled plastic.  These fibres are the best of the best – why would you compromise your project?

We are happy to share information and our knowledge about fibres.  After over 20 years of importing and supply of these fibres in New Zealand we do know a thing or two!  Call us on 0800 835 699 or visit our web site for more data on fibres for reinforced concrete: http://fbsltd.co.nz/product-catalogue/fibre-reinforcement-systems

Product Catalogue: 
Product Catalogue: 

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