ferro-cement for canadian fishing vesselsdfo-mpo.gc.ca/library/26424.pdf · ferro-cement during a...

Ferro-Cement for Canadian

Fishing Vessels

Compiled and Edited by W.G. Scott, C. Eng., P. Eng.

for

Industrial Development Branch, Fi sheries Service,

Department of the Environment

Ottawa

August 1971

This Report includes work contracted by

the Industrial Development Branch of the

Fisheries Service,

Department of the Environment,

and other related information

the originators of which have

kindly allowed us to reproduce.

Industrial Development Branch, Fisheries Servic~, Department of the Environment, Ottawa, Canada

I N D E X

SECTION A - Foreword by W.G. Scott

SECTION B - Reports of the Work Undertaken by the British Columbia Research Council:

Part I - Project 1968-69

Part II - Project 1969-70

Part III - Technical Supplement

SECTION C - Illustrations of Reinforcing Materials Studied

SECTION D - Regulatory Aspects of Ferro-Cement Vessel Construction:

Part I - W.E. Bonn, Ministry of Transport, Ottawa.

Part II - Lloyds Register of Shipping

SECTION E - Papemand Discussions on Ferro-Cement from the Conference on Fishing Vessel Construction Materials, Montreal, 1968.

SECTION F - Special Bibliographies:

Part I - Bigg, Delaney, Wood.

Part II - British Columbia Research Council

,.

"

FOREWORD

Early in 1966 the rapid upsurge of interest in ferro-cement

for fishing vessel construction prompted the Industrial Development

Branch of the then Department of Fisheries of Canada to begin examination

of this newer medium in some depth.

Our basic objectives were to produce quantitative data on the

physical and mechanical characteristics of ferro-cement which could lead

to the boats of that material being certified by the Board of Steamship

Inspection of Canada's Ministry of Transport.

important for vessels exceeding 15 gross tons.

This was especially

The other significant objective was ~o provide usable and

practical information on acceptable construction techniques. Many

fish boat owners provide their own labour in constructing vessels to

defray actual construction cost in dollar ter~s to them and many

smaller boatyards require guidance on acceptable engineering and

production steps.

Ferro-cement was considered as an excellent contender in the

smaller boat construction field which usually does not have the

engineering and production support inherent in larger vessel building

concerns. It uses a construction technique which can be carried out with

little training; it is economic in material costs, in the sense that there

is little or no scrap; it has important possibilities for these areas

where good boat ·-building woods (until now the traditional material for

hulls) are hard to come by; and above all vessels, once designed, can

be quickly constructed thus allowing them and their owners to pursue their

intended purpose - fishing.

This particular project was conducted in a way typical of our

usual method of working, whereby we contacted a group who were interested

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in initiating our studies. In this instance, the British Columbia

Research Council was chosen, and a program, as outlined in this

publication, was commenced.

Throughout the project we invited and obtained, very close

co-operation from the Headquarters and Regional staffs of the Marine

Regulations Branch of the Ministry of Transport.

As the project progressed, close attention was paid to any

published material on ferro-cement and a detailed bibliography has

been developed.

There were also many national and international authorities,

who provided useful comment to assist us, and to them we extend our

thanks.

Mention should also be made of the many provincial authorities

who helped us in this activity, in particular the Federal Provincial

Atlantic Fisheries Committee which sponsored the "Conference on Fishing

Vessel Construction Materials" in Montreal in October, 1968. All of

the pertinent papers (or comments) on ferro-cement from that conference

have been included in this report.

In Canada, interest and know~how in ferro-cement exists in

greater strength in British Columbia than elsewhere. Various companies

(and individuals) are engaged in ferro-cement construction not only for

high displacement-length vessels such as fishing vessels, but for other

marine uses.

These groups, being commercial enterprises, have every right

to safeguard their construction processes as they have borne development

costs ..

Our initial aim was to find out what this new medium offered

in strength values, and how it could be economically worked to reproduce

•

•

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lab test figures consistently, by people working by themselves, remote

from engineering consultation.

The construction style itself is appealing, certainly in so

far as support equipment is concerned. Much of the equipment is only

used for a short period; rental can well overcome the cash outlays and

problems of ownership. John Samson's and Geoff Wellens', "How to build

a Ferro-Cement Boat" is one piece of literature which lists everything

in detail required to construct a boat of ferro-cement.

To the best of the writer's knowledge, scantling lists "per se"

have not yet been developed for the various hull parts of a ferro-cement

boat. Lloyd's Register of Shipping, appearing in print as the most

frequently mentioned authority, does not have rules such as are published

for steel, glass or wooden vessels. We understand, however, that Lloyd's

is prepared to assess plans of proposed vesseLs and outline corrections

and alternatives.

Lloyd's has a set of tentative requirements which recommend

on the type of facility required; what steps must be taken during

construction; what basics it believes advisable in quality control of

materials and techniques. Of most importance in the Lloyd's measures

is the listing of various tests required and how these should be done.

The Canadian Ministry of Transport have adopted a considerate

position which is well explained in the paper read by Mr. W.E. Bonn at

the "Conference on Fishing Vessel Construction Materials" held in Montreal

in 1968. Basically, Canadian Steamship Inspection will certify on an

"experimental hull" basis, any unit exceeding 15 gross tons. The procedure

from design through delivery to the owner is similar to Lloyd's, however,

once a vessel enters service the surveys are more frequent than occur with

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other materials.

It should be emphasized that anyone contemplating a

construction in ferro-cement, if it is of a tonnage certifiable under

the Canada Shipping Act or if it is ·intended that it be built to a class

survey, should contact the respective authorities before any commitments

are made. In essence, don't ask for approval after it's done, find out

about it before you start. All Regulations change, often in a direction

which is less onerous and therefore cheaper.

In ferro-cement, there are several claims to "magic potions"

which enhance the material's possibilities and there are alternative

construction styles offered, each one claiming a particular advantage.

However, ferro-cement is a matter of developing a structural material

by human efforts, i.e. it has to be made as you go, comprising of mortar

and reinforcement to produce (if properly mixed and cured) a medium the

characteristics of which under test show tendencies approaching a

homogeneous material such as steel or aluminum.

It should not be confused or equated to reinforced concrete,

as many people would think, since it is not oriented the same way and

is therefore dissimilar.

We have to recognize that some reinforced concrete technology

is applicable to ferro-cement and with general construction forming a

field for continuing progress in our society, on should look forward to

gleaning new technical information from that environment.

The actual theories are more akin to thin shells of reinforced

concrete and not to the massive structures we see as pillars, girders,

floors', etc., in buildings.

,

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The writer's first experience in the material was when he

was privileged to see a variety of marine craft constructed of

ferro-cement during a visit to Vancouver. During that trip the

writer met numerous people from the ' local ferro-cement industry,

and was given a three day "immersion" course in ferro-cement boat

construction.

This visit really initiated the project report which

follows and which we believe has established factual information

and performance data on ferro-cement. The project is continuing

and additional reports will become available as progress is made

In our approach we purposely insisted that the methods

and materials should represent the style one could obtain from a

limited facility, low quality control operation using commercially

available, cheap and common material.

We did not look for excellent lab results with which

to "boost" the medium, and which could never be produced in reality

without considerable plant, specialist labour and other cost

escalators. Our view was to quantify the expected standards which

a modest production venture could achieve.

A number of people have helped put this publication together;

Professor G. Bigg of Carleton University, Ottawa, together with some of

his students prepared the bibliography; the mesh photographs are

by H. Schade of the Department's photographic unit; Lloyd's Register

of Shipping, Montreal, has kindly allowed us to incorporate its list of

tentative requirements.

Last, but not least we gratefully acknowledge the effort,

interest and enthusiasm of the British Columbia Research Council.

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In the beginning Art Kelly and Tom Mouat and more recently Bill English

and A.W. Greenius, put a lot of effort into this project and it is hoped that

the pages which follow will be helpful to readers.

W.G. Scott

30/4/71

Reports of the Work

Undertaken by the British Columbia

Research Council

Part I - Project 1968-1969

Part II - Project 1969-1970

Part III - Technical Supplement

I N D E X

CONTENTS OF THIS REPORT:

The present report consists of the following parts:

Part 1. A summary of the information derived from the literature survey and from the limited testing program, and its significance to fishin~ vessel construction.

Part 3. Recommendations for action to ensure orderly progress in the utilization of ferro-cement in fishing vessel construction.

Appendix 1. The scope of the project initiated in March, 1968, of which this report constitutes the Final Report.

Appendix 2. The paper "Ferro-cement as a Fishing Vessel Construction Material" by A.M. Kelly and T.W. Mouat, which contains most of the results of this project.

Appendix 3. Results of the freeze-thaw tests, carried out under Bub-contract at the University of Alberta and a discussion of the effect of 1/4" reinforcing rods and of 1114 gauge 1" square mesh hardware cloth. '

Appendix 4. Bibliography.

I

FERRO-CEMENT AS A FISHING VESSEL CONSTRUCTION MATERIAL

INTRODUCTION:

4

REPORT - PART I

To

Industrial Development Service Department of Fisheries of Canada

In March, 1968, the British Columbia Research Council contracted with the Department of Fisheries of Canada, Industrial Development Service, to carry out a study of ferro-cement as a fishing vessel construction material. The scope of the study is indicated in Appendix 1. Its objectives were:

1. To collect and collate as much as possible of currently available information on the properties of ferro-cement and on its use as a boat-building material.

2. To carry out a limited program of testing to determine the physical and mechanical properties of ferro-cement, as fabricated by conventional techniques.

The main results of the study were presented to the Conference on Fishing Vessel Construction Materials held in Montreal October 1 - 3, 1968, in the paper "Ferro-cement as a Fishing Vessel Construction Material" by A.M. Kelly and T. W. Mouat (Appendix 2). The freeze-thaw • tests, which were sub-contracted to the University of Alberta, were not completed in time for the above paper, and are now included as Appendix 3, along with a short discussion of the effect of reinforcing rods or heavy mesh.

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PART 1. SUMMARY OF INFORMATION DERIVED FROM LITERATURE SURVEY AND LIMITED TEST PROGRAM AND ITS SIGNIFICANCE TO FISHING VESSEL CONSTRUCTION.

Ferro-cement is an old boat-building material - its history goes back a hundred years. Its modern impetus started with Professor P.L. Nervi during World War II, with the encouragement of the Italian Navy. Construction of four vessels of 150 tons and over was started but not completed. After the war, Professor Nervi built a l65-ton motor sailer, and a 38-foot ketch, which appear to have been very successful.

In the 1960's ferro-cement construction of motorboats and yachts was taken up in England and New Zealand, and since then the popularity of ferro-cement has been growing at an ever increasing rate. The main centers of commercial activity at the present time are England, New Zealand, Florida, California and British Columbia. There is also evidence of substantial activity in the Communist world.

A striking feature of the present ferro-cement boat-building industry is its emphasis on "trade secrets". There is very little published information on the relationship bet,-1een the final properties of the ferro-cement and such factors as cement mix, type and disposition of reinforcing, and lay-up and curing procedures. There has been a brisk trade in licenses involving the transt'er of "secrets", in which Sea crete Ltd., Norfolk, U.K., and Ferro-Cement Ltd., Auckland, New Zealand, have been particularly active. There is very meagre information on quality control, the effect of stress concentrations, vibration and fatigue, or on the effect of adverse environmental conditions. This lack of reliable information poses a serious obstacle to the rational application of ferro-cement construction to vessels over 15 tons.

It was the lack of basic information on ferro-cement which led to the modest series of tests which have been done by the B.C. Research Council in parallel with the literature survey. It is significant that, despite their limited scope, they are already being quoted by boat-builders - mainly in the sense that the builders' (secret) method gives a better result - but factual data in support of such statements is virtually non-existent.

It should be made clear samples made and tested under the the best that could be produced. standard of "amateur" production, Marine Design Enterprises Limited with this in mind. There were no vision of panel fabrication. The made are described in Appendix 2.

at this point that the ferro-cement BCRC program were never intended to be Rather they were to represent a minimum and the contractor who made them, of Vancouver, was chosen and instructed engineering controls or on-site super-different types of samples which were

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The test program on the samples comprised tension, compression and shear (sample size 1 3/4" x 12") transverse'bending (5 3/4" x 12") membrane tests, both compressive and impact (12" x 12") and freeze-thaw cycling (4" x 16"). All samples were 3/4" thick. Mesh content was 1 to 12 layers of 1/2" hexagonal galvanized aviary wire and some samples contained 1/4" mild steel reinforcing bars on 2" centers, or one layer of 1114 gauge 1" square mesh hardware cloth.

Detailed results of the tests are given in Appendix 2 and Appendix 3. Briefly, they are as follows:

Tension:

Tensile strength increased almost linearly with the number of meshes. There was no evidence of levelling off, so presumably an even higher ratio of steel to cement would have been advantageous. There was little difference between panel directions. The maximum tensile strength (12 mesh layers) was 950 p.s.i., which is about twice the value for unreinforced concrete but below the values quoted by others for ferro-cement. Some commercial producers -e.g. Seacrete Ltd. - quote "ultimate tensile strength" in the{ 5000 p.s.i. range. This is believed to be derived tensile strength, from bending measurements, but no firm information is available.

Compression:

Compressive strength varied from 5000 to 9500 p.s.i. with little dependence on number of meshes. The value for unreinforced concrete is about 7000 p.s.i. The type of failure observed (splitting between meshes) indicates that cross-bonding of meshes is desirable, and good penetration is essential. Seacrete Ltd. quotes values from 7200 to 12,200 p.s.i., depending on time since fabrication.

Shear (across panel):

Shear strength varied roughly linearly with number of meshes from a mean of 50 p.s.i. to a mean of 100 p.s.i.

Transverse Bending:

Tests were in accordance with ASTM Designations A438-62 and C293-64, with allowances for sample thickness (3/4" instead of the 3" - 5" in the ASlM Specification). The modulus of rupture derived from these tests varied nearly linearly with number of mesh layers from a reean of 700 p.s.i. to a mean of 2500 p.s.i. In one panel, trowelled from both sides and not vibrated, the deleterious eff~ct of incomplete penetration was illustrated by shearing along the middle, neutral, axis.

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Membrane Test (compressive):

In this test a 12" x 12" panel was loaded cyclically by a 1" diameter piston, until failure occurred. The maximwn load borne varied from about 500 lbs (1 mesh layer) to as much as 2000 lbs (10 or 12 mesh layers). The panels were consistently more resistant to loads applied to the front, trowelled face.

Membrane Test (impact):

This was similar to the compressive test, with a falling weight substituted for the piston. The results of this test are more qualitative than quantitative, since the point of "failure" is difficult to define. Impact resistance was less than expected. Failure for panels with 2 - 4 layers of mesh was typically by cracking at from 27 to 200 inch-lbs. Failure for panels with six layers or more was typically by punching shear at from 36 to 300 inch-lbs. The high values of resistance were nearly all for impact on the front, trowelled face.

Freeze-tha'-T :

Eight samples from each of three panels containing one, six and twelve layers of mesh respectively.,,,ere cycled as far as possible in accordance with ASTM C 291-67. Electronic vibration equipment could not be used to determine mechanical condition because the thickness of the samples (3/4") was below the range of the equipment (3" - 5"). Instead, weight loss was determined 12 times for each sample during the passage from 0 to 309 freeze-thaw cycles. Weight loss in this kind of cycling is known to be correlated to resistance to natural weathering under freeze-thaw conditions. Loss of weight varied linearly with the number of cycles. The six-layer and twelve-layer samples proved satisfactorily resistant, with average weight losses after 309 cycles of 20% and 4% respectively. The only one-layer sample which survived to 309 cycles without disintegrating had lost 44% of its weight.

Although these tests must be considered preliminalY, it looks as if the resistance of good ferro-cement to natural freeze-thaw cycling should be very high.

Reinforcing Bars and Heavy Mesh:

The effect of 1/4" mild steel reinforcing bars on 2" centers at the median plane was explored in three panels, and the effect of a median layer of #14 gauge square mesh hardware cloth in one panel. With 1/4" rods t,,,o panels were made in the horizontal position, one trowelled on both sides, the other plywood-backed and trowelled on the top face, and one panel was made in the

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vertical position, trowelled on both sides. The panel with hardware cloth was made horizontally on a plywood backing, and trowelled on the top face. The last three panels were roughly twice as strong as a horizontally made. plywood-backed panel containing the same number of fine mesh layers, but no heavy reinforcing. It would be wrong, in our opinion, to attribute this increase in strength directly to the heavy reinforcing. Rather, we believe it is due to a better distribution of the fine mesh, which is held away from the median plane by the rods or heavy mesh, and is thus more effective. These test panels, and also the previous ones without heavy reinforcing~ show the importance and the difficulty of ensuring that the fine mesh aviary wire reinforcing is in the right place in the panel to do its job.

General Comments on Tests:

The variability of the test results, and the low strength values from some samples - samples from flat panels which might be thought easier to make well than a boat hull - illustrate a vital point with ferro-cement.

It has been widely stated that ferro-cement lends itself to non-professional construction, and that relatively unskilled labour can be employed. This is essentially true, but nevertheless some phases of the operation - for example the securing of ·the mesh, the cement mix, and the plastering - are very critical, and adequate craftsmanship is vital to success. As hull sizes increase, good quality control, with sound design and good construction techniques, will become more and more important.

Ferro-cement for Fishing Vessels:

The praises of ferro-cement have been sung so widely in recent months that we will limit ourselves here to a brief recapitulation.

1. The raw materials are widely available and cheaper than other boat-building materials. (A ferro-cement hull is estimated to cost in the order of 15% to 30% less than one in steel or

·wood, depending on size and construction method.) Of course, the hull is only part (on the average, about 60%) of the cost of the vessel.

2. Very little highly skilled labour is involved - although as noted earlier there are some critical steps that require care and experience.

3. Ferro-cement is well suited to "one-off" construction, since no expensive building, fixtures, or tools are required. The total capital investment can be very low.

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4. Ferro-cement should require very little maintenance. It is immune to rot and marine-borer attack. It becooles stronger with age, and shmvs no evidence of corrosion in sea water. As stated elsewhere it appears, from the limited data avail-able, to be very resistant to freeze-thaw cycling. It is resistant to abrasion.

5. The material is fire-proof, and is substantially more resistant to heat from a fire on board than fibreglass or aluminum or, under some conditions, even steel.

6. Ferro-cement boats are claimed to give some 10% more useful inside space (due to the absence of frames) than a wooden hull of the same overall dimensions. In some small vessel designs of about 40' overall length this is doubtless true. It is also claimed that condensation does not occur with ferro-cement. This is definitely not true under all typical conditions, and the lining necessary to prevent it will then encroach on the 10% extra space.

7. The acoustic properties of a ferro-cement hull, because of extra mass and panel stiffness, should be superior to other materials. tVhile this aspect has not been documented, it could lead to improved fish location and perhaps to more effective catching.

Some "question marks" in ferro-cement vessel construction are the following:

1. It is claimed that ferro-cement suffers less damage in a severe impact than wood or fibreglass, and that repair of the damage is quicker and cheaper. No quantitative data is available on the strength of such a repair, or on the long-term integrity of the bond between the patch and the undamaged ferro-cement. A similar situation occurs when the plastering of a hull, normally done in one continuous operation, is unavoidably interrupted. There are "recipes" for assuring a good bond of th"e new cement to the old, but no published measurements on the short- or long-term characteristics of the joint.

2. How strong is ferro-cement? One finds phrases in the liter-ature such as "innnensely strong", "comparable to wood", "as strong as steel". Comparison with other materials is difficult and misleading, because "strength" in the ship-building sense is a combination of a number of physical properties such as resistance to tension, shear and bending, ability to distribute localized stresses without failing,

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resistance to vibration and fatigue, etc. The strength required is also a function of the design, and the optimum design for ferro-cement is certainly different from that for wood or steel, and in fact has probably not yet been evolved.

An important factor in the subjective estimation of the strength of ferro-cement stems from the fact that the material cannot be produced much thinner than 3/4". For vessels up to about 40' long this gives a very strong, rather heavy hull, and because of the shell strength a minimum of internal support is required. The vast majority of the ferro-cement vessels built so far have been far under the 100' size for which longitudinal bending moments start to become appreciable. For this class of vessel ferro-cement is certainly adequately "strong". The real question is what happens in vessels large enough so that racking and bending moments are significant. Here the properties of the material will have -a major influence on the design of the vessel - and it is just these properties which at present are mysterious and ill-defined.

3. Quantitative information is needed on the effect of stress concentrations in ferro-cement, and the best method of distri-buting stress by additional stiffening, which usually would also be of ferro-cement.

4. There is no published data on the resistance of ferro-cement to vibration and fatigue. While it is not suggested that ferro-cement is deficient in this respect, the necessary data for design purposes must be available if over- and under-design of engine and machinery supports are to be avoided. With the continually increasing horsepower of main engines, and the increasing use of auxiliary pm.,er machinery, this factor will grow in importance as time goes on.

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PART l.. ACTION NEEDED.

To ensure orderly progress in the utilization of ferro-cement in fishing vessel construction, research is needed to establish the properties available in the material, and how to get and to use these properties to best advantage. This vital information must be made available to commercial shipbuilders and to individual fisherman-builders in a form which will meet their needs and will encourage sound economical construction.

Research on Ferro-cement:

The aspects of ferro-cement on which present information is inadequate and on which we believe research is needed are summarized below. Each item must be approached in two ways -one for the "shipyard", where a fair amount of soph~stication and specialization may pay dividends; the other for the "back-yard", i. e. the individual fisherman-builder who wants to use common materials and straightforward techniques.

1. Material:

2. Design:

3. Construction:

4. Operation:

To minimize cost for a specified strength Cement additives or substitutes Better sand sizing and control of mix Improved reinforcing, amount, type, treatment

(galvanized or ~ot?) Placing of reinforcing, cross tying Material specification

Most economical design for necessary strength Scantling tables and other design information Stiffening of edges and openings Engine and machinery bearers Installation of tanks in ferro-cement

Control of cost and quality Lay-up methods, curing Obtaining and testing of material samples Effect of joints and interrupted plastering Check points during construction Inspection and non-destructive testing of

critical elements of hull, e.g. keel, engine bearers, deck fittings (some development or adaptation of existing non-destructive testing methods will be required)

Efficiency and economy Noise, vibration, condensation, water-tightness Low maintenance construction and finish

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5. Studies on stress concentration J vibration and fatigue effects and other accelerated environmental testing, e.g. freeze-thaw, concentrated brine

6. Laboratory testing of hull sections and components

7. Strain-gauging of new or existing hulls

It is clear that a very worthwhile research program, extending over several years, could be set up to provide the basic information on the properties and use of ferro-cement which is now lacking. We are convinced that such a program would make a major contribution to the effective and safe utilization of ferro-cement in fishing vessel con-struction.

Certification of Ferro-cement Vessels:

For the would-be builder of a vessel over 15 tons, the burning question is how to obtain certification by the Canadian Department of Transport, without excessive expenditure or risk. In a paper, "Regulatory Aspects of Traditional and New Construction Materials", given at the Montreal Conference on Fishing Vessel Construction Materials, . October 1968, W.E. Bonn, Superintendent, Hulls and Equipment Division, Marine Regulations Branch, outlined the requirements which would lead to provis;i.onal certification for Home Trade "class III (not more than 20 miles offshore and not more than 100 miles from a port of refuge).

In addition to the economic penalty imposed by this limitation on operations, there are other serious problems which arise from lack of knowledge of the capabilities of the material, and from lack of experience in quality control. Appropriate scantling tables, such as are available for wood, steel, aluminum and fibreglass, do not exist. Suitable testing and inspection procedures have still to be evolved, and better guidelines for design and construction are urgently needed, especially by the individual fisherman-builder.

Until these needs are met, and full certification can be reasonably assured before construction is undertaken, ferro-cement will suffer a major disadvantage in relation to established materi.als. Many builders feel this is unfair, because of the extensive experience with ferro-cement going back to World \-Jar II. But in view of the lack of quantitative data and documentation on this experience, it is hard to see how the Department of Transport, in discharging its responsibilities to ensure safety at sea, could proceed otherwise at the present time.

The problem of certification must be resolved as quickly as possible, and this can only be done through the cooperation of all concerned. The leadership and initiative of the Department of Fisheries

- ,,-Industrial Development Service is playing, and will play, a . vital role in providing the mechanism for this cooperation. We feel that the time is ripe for a significant joint effort by the commercial ferro-cement shipbuilders towards the optimizat~on of design, construction and quality control in ferro-cement. Needless to say a corresponding effort by the public agencies is also required, and this must safeguard the interests of the fisherman-builder, whose means and needs are different, though not always radically different, from those of the commercial builder.

WNE/cz

. .~

ff/~~~ W.N. English, Head Division of Applied Physics

APPENDI.X 1.

BRITISH COLUMnl/.\ l1ESf:ARCH COUNCIL UNIVERSITY OF BRITISH COLUMBIA VANCOUVER 8, B. C.

J

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Department of 1o'18heries February 9, 1968

water immersion.) The skills required to build.boats from this material are rather less than required when using more conventional materials, so savings in labour costs should also be attainable.

At a recent meeting in Ottawa bet"Teen Messrs. L. S. Bradbury, J. Frechet and VT. ~. Scott of the Department of Fisheries and A. M. · Kelly of the Council, the Department expressed interest in the subject. Suboequently, Messrs. Frechet and Scott" during a visit to Vancouver, inspected tim ferro-cement boats, one completed, one incomplete. They also met with Mr. John Samson, of Marine· Design Enterprises, who was instrumental in introducing the material to Canada. This proposal is a result of these meetings.

C. PROCEDURE

The project will be carried out in two phases: data collection and testing.

Phase I

A literature search will be conducted, covering the period 194tl- to the present, to determine what has been publlshed in the professional journals relating to ferro-cement. Particular attention will be paid to the Marine and Civil Engineering journals.

Concurrently, ive will enter into correspondence "dth all known Naval Architects, Marine EngIneers and professional builders who are engaged in the desie;n and/or constructlon of ferro-cement boats and other structures and as 11'any an19.teur builders as pOGsible within time and bu.dgetary constraints. It is hoped·that a good deal of useful information can be obtained economically in this rna,nner. In addition, those designers and builders "Tho are in or reasonably near the Vancouver area (including those in the North-ilestern U.S.A.) will be visited and interviewed at length.

The inforJ~~tion gathered in this phase will be collated and written up as a "state-of-the-art" revie",.

Phase II

A scheclule of tests, ou.tlined in the follmring sections, will be carried out. The test schedule should be consldered to be flexible and subject to modificat.ion as test results are accumulated. The procedures are based on assumed charact~ristics and practical strength valu::!s that have been estimated from verbal reports of actual service pcrfOrJi}':lOc8 of the materj.al. The proposed tests are intended to produce prt~liminary data as a basis for the desic;n of useful structures and of more sophisticated tests. In ~cncral,

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Dep3rtment of Fisheries February 9, 1968

tests 1, 2, 3 and !j. are intended to roake dlrect compo.risons betvTeen ferro-cement and steel in such a 'my that formulas appl:i.cable to steel constructi.on can be acl:::\pted for use ld.th ferro-cement through substHution of appropriate factors. 'l'csts 5 and 6 are desie;ned to produce us~ful dnta for general structural desi.c;n and the determj.nation of conditions under ,·rhich ferro-cement methods may reasonably be used.

For these preliminary tests, the selection of materials will be limited to at most three cement mixes and three confj.8Ul'ations of "\-Tire m~sh and reinforcing, makinc; a total of nine possible combinations.

He '-Till arrange to have a number of p~ne1s of about 4 feet by 8 feet constructed to our spccificatjons by Mr. John Samson. These panels \·,ill then be cut. into test sections of the requir3d sizes. This procedure ,·Till ensure that each set of test sections has essentj.ally uniform characteristics. Before testing, the Height and volume of each section ,·rill be determined. 'l'he follmring tests \vill then be performed, for each confic;uration of mIx/reinforcinG.

1. Tensile

Two adjoinint; sCJ..uare samples of 12-inch edge length, cut at leAst 6 inches from the side of the original panel shall each b~ cut into 6 strips approxhilately 1-3/1+ inches in '

Department of Fisheries February 9) 1968

Each specimen is to :be tested in bending, t'\vo longitudinal and tvTO cross sp~cimcns, face up, the remaining four specimens face dmTn. All tests are to be in accordance with the procedures of A.S.T.l~. DesiGnation A~-38-62 and Designation C293-64 insofar as applicable.

l~. Diaphragm or Flat Plate Bending

Four sql~re samples the same as required in 3. above are each to be .simply supported on a square fixture having cylindrical contact surfaces of 1/4 inch radius, and initial contact lene;ths of 10 inches for each side of the square. Two specimens' are to be tested face up and two face down. Each is to be loaded centrally on an area 1 inch in diameter.

Load is to start at 100 pounds, and is to be increased in 100-palmd incr~ments to 600 pounds, then in 200-pound increments to 1600 pounds, then in 400-pound increments to ultimate. The lea d is to be removed after each increase. Deflections loaded and unloaded for each step are to be observed and recorded.

5. Impact

Four square samples, similar to those of 3. above are to be tested for impact resistance while resting on the fixture of 4. above by dropping onto each a 'chilled-iron grinder-ball approxiwately 4 inches in diameter and of spherical shape, so as to strike the specimen ,\fith an energy of 150 foot-pounds. If no evidence of failure appears, successive impacts each 50 foot-pounds greater than its predecessor shall be applied until evidence of failure appears.

6. Freeze -Tha'\-T

Eight specimens 4 inches by 16 inches shall be cut and tested in accordance with A.S.T.M. Designation C29l-61T and Designation C215-60.

APPENDIX 2

Reprinted from: Proceedings of the Conference on Fishing Vessel Construction Materials, Montreal, Canada, October 1 - 3, 1968.

Ferro-Cement as a Fishing Vessel

Construction

Material

by

A. M. Kelly and T. W. Mouat British Columbia Research Council,

Vancouver, B.C. Mr. Kelly Mr. Mouat

Mr. Kelly was born in St. John's, Newfoundland, in 1930. He earned his diploma in engineering and his B.Sc. in mathematics at St. Francis Xavier University, Antigonish, N.s., in 1957. He obtained his M.Sc. in geology and geophysics at the Massachusetts Institute of Technology, Cambridge, Mass., in 1963. He did further post-graduate study at McGill University, Montreal, from 1964 to 1966. From 1951 to 1956 Mr. Kelly served in the Canadian Army. Between 1957 and 1964 he was Lecturer and Assistant Professor at St. Francis Xavier University ; in 1966 and 1967 he was with the Unica Research Company, Montreal, and from 1967 to date he has been Assistant Head of Operations Research at the British Columbia Research Council. He has had a lifelong interest in boats and naval architecture is his hobby.

Mr. Mouat was born in Nelson, B.C, in 1912. He obtained his B.Sc. degree in mechanical engineering from the University of British Columbia in 1934, and his M.Sc. degree in electrical engineering from the California Institute of Technology in 1939. From 1934 to 1938·he was employed by Cemco Manufacturing Company; from 1940 to 1946 he was with the Electrical Engineering Section of the National Research Council, heading the section before he left to become Project Engineer at the University oJ British Columbia, a position he held until 1949, when he assumed his present duties with the Division of Engineering of the British Columbia Research Council. Since 1949 Mr. Mouat has done a considerable amount of materials research and testing, including work on wood, metals, soils and concrete.

ABSTRACT

The material is described and a brief history of its usage given, including the results of some of the research which has been performed in the past. The current "state of the art" is then surveyed, with emphasis on three points: Costs of Construction; Strength and durability, and Design considerations. Finally, the results of a series of strength tests, made on flat panels of various confIgurations, are presented.

INTRODUCTION

"Ferro-Cement" is the name given by Dr. P. L. Nervi, of Italy, to a material consisting essentially of a number of layers of wire mesh impregnated with a mortar made of frne sand and Portland cement. Nervi (I956) showed that the resulting material did not behave like ordinary reinforced concrete but, in his words, "exhibited all the mechanical properties of a new material". The reasons for this behaviour appear to depend fundamentally on two things:

136

1. TIle ratio of reinforcement to mortar, by weight,

2. The dissemination of the reinforcement through-out the matrix of mortar.

\ The material is easy to fabricate into complex shapes without the use of fonns or moulds; it has good strength to weight and stiffness to weight ratios; it is waterproof; it is corrosion resistant, and it is relatively inexpensive. These properties lead to the conclusion that it ought to be a useful material for marine applications; indeed, many such applications have been made. The increasing interest in the material on the Pacific Coast reached a level some months ago such that the Industrial Development Service of the Department of Fisheries of Canada commissioned the British Columbia Research Council to carry out a study of ferro-cement as a boatbuilding material. This report is the outcome of that study.

The stated aims of the project were:

1) To collect and collate as much as possible of currently available infonnation on the properties of ferro-cement and its use as a boatbuilding material, and

2) To carry out a limited program of testing to detennine the physical and mechanical properties of ferro-cement, as fabricated by conventional techniques.

HISTORY OF FERRO-CEMENT

The invention of ferro-cement, as defmed above, is generally credited to Nervi and dates from the work he did in the years 1942-43. It is of interest to note, however, that similar methods were in use by Lambot, in France, as early as 1849 (Cassie, 1967). In fact, Lambot took out French and Belgian Patents, on what he called "Fen;:iment" in 1856. He caused several rowing boats to be built of the material. One of these was apparently still afloat in 1949, nearly 1 00 years later. In 1955, this and another were found in the mud on the bottom of the pond where the first had been kept; the older one is currently on display in a museum in Brignoles, France. Cassie reports that it is still in surprisingly good condition.

In 1887, the year of Lambot's death, a similar boat was constructed in Holland. This vessel, now 81 years old, is still afloat on the Pelican Pond at Amsterdam Zoo (Morgan,

CONFERENCE ON FISHING VESSEL CONSTRUCTION MATERIALS

1968a). Gabellini, in Rome, also built boats by this method, around the turn of the century.

No evidence of true ferro-cement construction in the period 1888 to 1942 was found, although many reinforced ' concrete vessels were built in this period. In the United States alone, during World War II, 104 vessels, ranging in displacement from 4,000 tons to 12,750 tons were con-structed (Tuthill, 1945).

One of the first sea-going reinforced concrete :;hips was the 356 ton "Namsenfjord", launched in Norway in August 1917. In March 1919, the SS "Armistice", 1,150 tons, was launched in Great Britain (Taylor, 1961). Morgan (1968) reports that this vessel is still in active service, 49 years later. Nine old concrete vessels have been converted for use as a floating breakwater at Powell River, B.C. The oldest of these is the "Peralta", 6,065 gross tons, built in 1916. The first of these were installed in 1947 and 1948 and all are still in good condition.

In 1941-1943, Dr. P. L. Nervi, the noted Italian architect and engineer, began a series of experiments on what he christened "Ferro-cement". His work led to the acceptance of tlle material by the Italian Naval Registry and the Department of Marine Engineering of the Italian Navy. As a result, in 1943, construction was started on a 40().ton freighter and three 150-ton naval vessels, all of ferro-cement. The work was abandoned in September 1943 because of the exigencies of war. In 1945, a 165-ton motor sailer, "Irene", was built by the fmn of Nervi and Bartoli for their own use. Nervi reports that the total weight of this vessel was approximately 5% less than an equivalent wooden ship; its cost was 40% less (Nervi, 1951). This vessel was subsequently wrecked in 1957. However, Nervi (1951) stated "After five years of hard and regular use in the Mediterranean, the boat is as good as the day it was launched and has never required any maintenance what-ever". In the same paper, he reports that the vessel had two serious accidents during that period, but sustained only minor damage. In 1948, he had built for his own use a 38-foot ketch, the "Nennele". The vessel has a skin composed of seven layers of mesh with one layer in 1/4-inch reinforcing bars on 2-inch centers. The total skin thickness is only I/2-inch (Nervi, 1956). Morgan (1968) reports that this vessel is still in regular service and is in excellent condition.

There seems to have been little, if any, a«tivity from 1949 to 1960. In 1961, however, the renaissance of the

A. M. Kel~l' all(/ 7: HI. /IIoliat

method started in New Zealand and in England. In new Zealand, a Mr. Manning built a 24-foot yacht in that year; this started a boom ill amateur yacht building using ferro-cement, which is still going on. ]n the sallle year, Windboats Limited, of England, began producing motor .boats, 34 feet long. Tell of these were produced in the first 18 months of operation.

Shortly after this, interest spread to North America, where tlle metllod has been widely adopted. ]n British Columbia, for example, fishing vessels, work-boats, barges, yachts and otller marine structures are now being built of ferro-cement. In fact, the material has become the basis of a thriving industry in the province-there are now four firms engaged full time in the construction of ferro-cement vessels, together with a finn specializing in their design. In addition, at least threc prominent naval architects are now producing designs for this medium.

Comparable activity is taking place in the United States, mostly in California and Florida. An interesting develop-ment is the Wusih factory in China, not far from Shanghai, which has been producing ferro-cement boats since 1963. The plant employed 600 people in 1 %6, 20 per cent of whom are women. They produce six different models, although most of their output consists of 3 and 5 tonners (Anon., 1966). The article cited does not give production figures; however, one of the accompanying photographs shows a part of a production line, with more than 25 boats under construction.

THE MATERIAL

As outlined in the introduction, ferro-cement consists of a number of layers of wire mesh impregnated with a rich mortar made of of Portland cement and fine sand. As Nervi has pOinted out (1956), the principle involved is that concrete can wit hstand large strains in the neighbourhood of the reinforcement and that the magnitude of these strains is proportional to the distribution and subdivision of the reinforcement throughout the mass of concrete. Specifically, when the amout of reinforcing material ex-ceeds about 15% of the total weight of the material, the strength increases dramatically compares to unreinforced mortar. This percentage amounts to about 30 to 40 pounds of reinforcement per cubic foot.

In order to avoid having to use forms, the usual practice is to construct an armatu re of reinforcing bars to which the mesh is attached. Conventional practice is to use eight

]37

layers of 20 gauge, I/2-inch hexagonal mesh, four on each side of the reinforcing bars, which are usually 1/4-inch maid or hard-drawn steel. This will be explained in greater dctail in the next section.

The mesh covered arn13ture is then impregnated with mortar. The mortar is made with a sand-cement ratio varying from 1.5:1 to 2:1, dependiJlg on the builder. Type 5 Portland cement .. an alkali resistant type, is commonly used, although some builders prefer the so-called "high-early" cement, which requires less curing time. Five to fifteen percent of tlle cement is replaced by pozzolan, again depending on tlle builder. This substance absorbs· the free lime produced by the setting reaction of the cement and also makes the resulting mortar more dense. The sand used is a sharp, fine grade. Grading curves vary, but in general all sand passes a number 8 sieve, willi 10 to 15% passing a number 100 sieve. Between these two, the grades are uniformly distributed. The aim here is to have a dense, impenneable mortar, with the grains of aggregate well packed and evenly coated with cement. The amount of water added should, in the opinion of most builders, be just sufficient to make the mix workable. ApprOximately 4 to 4 1/2 gallons per bag of cement is often used.

After the mesh has been thoroughly impregnated the surfaces which will be left exposed can be given quite a smooth finish by trowelling. This is best done by a professional plasterer or swimming pool finisher. The trowelling has the effect of floating some of tlle filler materials to the surface, which becomes, after curing, almost as smooth as a finished plaster wall. It must be done with care, however, as too much separation of the aggregate will weaken tlle ferro-cement. This procedure also ensures that no mesh remains exposed where it could corrode.

The material is then allowed to set until it becomes hard enough for grinding and sanding; this process takes about eight to twelve hours. At the end of this time, surfaces which require finishing are ground, using carborundum stones and carborundum sandpaper. This smoothing process done, the material is then cured for 21 to 28 days. During this period, tlle structure is kept uniformly wet at all times. The temperature should be maintained well above freezing and the stmcture should not be exposed to draughts or direct sunlight, which would cause uneven evaporation or uneven temperature distribution or both.

On completion of the curing process, exposed surfaces can be etched with muriatic acid and neutralized with

138

caustic soda to provide a good key for the fmal finish. Most builders then apply several coats of epoxy based paint. The paint is used solely to improve the appearance, as the ferro-cement is waterproof and corrosion-resistant by itself.

\ The resulting material varies from 3/4" to 1 1/4" in thickness, depending on the armature, and has a density of about 1 SO Ibs/cu. ft; this is equivalent to a weight/unit area of 9.5 to IS p.s.f.

The specific gravity of 2.4 seems high when compared to 1.6 for fibre glass and 0.9 for wood (including fastenings) (James, 1967). However, the absence of heavy internal frames reduces the weight of a ferro-cement hull sufficient-ly that for boats over about 30 feet long, the weigllt is 5 to 15% less than an equivalent wooden hull. In addition a gain of 11 % in internal volume is realized (James, 1967).

Some of the foregoing figures are general and imprecise, because of the numerous lay-up methods and mortar mixes in current use. Each of the manufacturers believes his product to be superior; understandably, none would divulge their specific sand/cement or water/cement ratios or their sand grading curves. However, in a later section of this report, specific values will be given for the test panels which were made. These are representative of typical amateur construction, and specify a useful point of departure for future work.

The few strength figures which are reported in the literature are mentioned only casually. The methods of arriving at these figures are not given. However, these sources plus verbal infornlation from local builders plus the results of our own tests (given later in detail) indicate compressive strength in excess of 6000 p.s.i. and tensile strengths between 500 p.s.i. and better than 10,000 p.s.i.

We have so far been unable to explain this seemingly excessive range of tensile strengths. No informa tion was available on the type of tests perfonned other lhan our own, which gave results of 450 to 900 p.s.i. These lower figures are consistent with the reports of Nervi (1956) and Byrne and Wright (1961) but are an order of magnitude less. than those reported by James (1967) and by several British Columbia builders who prefer not to be identified. It may be that the higher figures are derived from flexure tests; calculations based on our own flexure tests indicate strengths ranging from 2000 to 3000 p.s.i. James (1967) also reports on two other interesting tests. First, test panels were subjected to temperatures of 1,700 degrees centigrade


for 1 1/2 hours, with no effect. * Second, a sample strip 21 5/8 inches x 5 inches x 5/8 inches was tested for fatigue in flexure. A stress alternating between 600 and 700 psi was applied 8 1/2 inches from one support point; the sample survived 2 million cycles without fracture.

BOA TBUILDING METHODS

There are three methods of boat construction in current use. They will be referred to as the "pipe-frame" method, the "welded armature" method and the "wooden plug" method.

1. The Pipe-Frame Method

This is the oldest method. In its basic fonn, it appears to date back to the earliest use of ferro-cement. As is usual for all boat building, it starts with the lofting of the lines. At this point, station moulds are construted of iron pipe, bent to conform to the station shapes, instead of wood. Usually, 1/2-inch i.d. pipe is used. The stem, keel, stern post, tran-som and deck beams are Similarly made of pipe. These parts are' then assembled and welded together after the usual plumbling; levelling, squaring and fairing. This structure is supported by being hung from an overhead framework. The keel is shored up - this is the only support from below.

After the pipe-frame structure has been {aired, longitu-dinal reinforcing bars, usually 1/4-inch diameter, are attached on 2 to 3 inch centers. If required, transverse reinforcing, on 3 to 6 inch centers is also installed. These members are usually tied to the pipe frame and each other, as welding is said to disturb the structure.

The wire mesh is then fastened to the framework. Eight layers of 20 gauge, 1/2 inch hexagonal mesh (four inside, four outside) is the general practice. The mesh is pulled tight and attached by wire ties or "hog-ring" type staples. Some builders also lace the mesh in such a way as to pull the outer and inner layers together in the interstices between reinforcing bars. This practice is questionable on theoretical grounds, as it tends to concentrate the mesh on the neutral axis of the section, where it is least necessary. In addition, it leads to a "quilted" surface on the finished product if the plastering technique is imperfect.

* (This is probably Ilame temperature and not panei'temperature, as 1700

0 C is above the melting point of most steels and many sands).

A . /II. KellyallCI T. W. Moltat

The resul ting structure is then plastered from the inside, with the mortar being forced through and trowelled from the outside to give a smooth finish. It is then cured as described earlier. The finished hull thickness is from % -inch to 1 ¥. -inches, with the pipe frames, covered by mesh and mortar, standing proud inside the vessel.

\

2. The Welded Armatllre Method

After lofting, wooden moulds are fabricated and erected in the nomlal manner. They stand on a keel section made of channel iron. The false work is faired as usual. The next step has several variations. In one, longitudinal reinforce-ment, on 2-inch centers, is attached temporarily to the false work and welded to a prefabricated stem and transom, the fonner being of pipe or steel rod. Transverse reinforcing, appropriately spaced, is then installed by welding to the longitudinal bars, usually on the inside. Deck beams (tee-section) are welded in place, as well as floors, flanges for bulkheads, etc. The false work is then removed, leaving a strong but elastic armature. The fairness of the annature is checked; if necessary welds can be broken or individual members cut and re-welded to make the armature fair. The mesh is installed as before and the hull plastered and cured in the conventional manner.

The second approach is to fasten wooden ba ttens to the station moulds, followed by installation of the transverse reinforcing, outside the battens. The longitudinal rein-forcing is then welded on, outside the transverse. Propo-nents of this method claim that the resulting armature does not Have to be faired after assembly. The false work is then removed. Installation of mesh and plastering is carried out as before.

Although there are no data to substantiate it, it would appear that the welded annature method is superior, as the welding of the reinforcing into a monolithic structure should result in a great areal distribu tion of stresses. Oberti (1968), who has been working with ferro-cement since 1943, concurs with this opinion.

3. The Wooden Plug Method

This method also requires wooden station moulds. In this case, they are erected upside down. After fairing, the structure is sheathed with cedar or some such soft wood. A mortar barrier of plastic or tar paper is applied to the resulting plug. Four layers of mesh, transverse reinforcing, longitudinal reinforcing and fmally four more layers of

139

mesh are nailed and/or stapled to the plug. The mortar is then applied and cured. After curing, the hull must be turned over and the falsework stripped out.

The advantages claimed for this method are that the resulting hull is fairer and more quickly constructed, the latter being because the reinforcing bars and mesh can be put in place more rapidly. The first claim appears to have some validity, although proper bracing and dimensional control should ensure fairness with the welded armature method. The second appears a dubious advantage, as the tin1e and materials required to construct the plug could very easily offset any economic advantage gained by more rapid installation of mesh and reinforcement. In addition, as the reinforcing bars are not attached to each other, great stress concentrations could occur in the completed hull.

Precise measures of labour required were not available for any of the construction methods. Reliable estimates for the welded armature and wooden plug methods indicate that between 600 and 800 man hours are required to complete the hull and deck of a vessel between 40 and 45 feet overall.

In summary, the welded annature method seems superior, especially for the professional builder.

ECONOMICS

Materials lists were obtained for three different hulls constructed by different builders. The hulls were of comparable size, ranging from 42 to 45 feet overall, with displacements from 12 to 15 tons, approxima tely. The lists

Table I

Materials Lists For Three Sample Hulls, Including Decks

Hull A Hull B Hull C*

Pipe (Y.." I. D. Iron) 900 ft. 800 ft. Nil

Reinforcing Bar (¥.") 9000 ft . 12000 ft . 12000 ft.

Wire Mesh' (Y..", 20 gal 15750 sq. ft . 15000 sq. ft. 65000 sq. ft.

Cement (Portland 6500lbs (75 5100lb5 (58 (less than 7 Type 5) bags) bags) cu. yds. of

mortar) Sand 1 2000lbs (130 10200lbs (115

bags) bags) Angle or Strap

Iron 100 ft. Nil 700 ft. --*Includes bulkheads and other internal structures.

140

are generally consistent, the variations being accounted for by differences in hull design and building techniques. Some of the builders are understandably reluctant to reveal precise details of costs; accordingly, the materials lists shown in Table I do not include identification of specific vessels. ..

Specific costs for these materials are not given, due to regional variation, differences between suppliers, wholesale and retail, and economies of scale realizable by larger commercial builders. However, as an indication of costs, these material lists, evaluated at average current Canadian prices, range from $1,400 to $2,000 approxinlately.

As mentioned before, the labour involved for hulls of this size varies from 600 to 800 man hours. Furthermore, this labour, according to the builders, is mostly of a relatively low level of skill and hence less costly than a skilled shipwright would be. If one estimates the average cost of tlus labour to be $5.00 per hour, including overhead, (tius is probably a high estimate), the labour costs would range from $3,000 to $4,000. The overall cost of a hull of comparable size to those mentioned would range then from a minimum ' of $4,400 to a maximum of $6,000, the average being $5,200. Although the cost of the hull is only one-tllird or less the cost of a completed vessel, it would appear that substantial savings can still be realized with the use of ferro-cement, especially when one considers that these estimates include the deck and, in the higher ones, such interior structures as bulkheads, engine bearers, etc.

THE TESTING PROGRAM

Because of tile appeal of this material to amateur builders, the test panels were fabricated in a manner believed to be representative of what a relatively unskilled amateur would produce. No efforts were made to impose strict control on materials, mixtures or crafstmanship. The resulting strengths should then be the minimum that could be expected.

An exploratory program of tests was planned to obtain some preliminary experience with ferro-cement and to provide a firmer basis for tile planning of more comprehen-sive future tests. This program included tension, compres-sion, shear, and bending tests, membrane tests on square samples under compressive and under impact loading, and freeze-thaw tests.


In selecting these tests the intention was to produce, if possible, data wluch could be compared with corresponding known values for steel or aluntinum, and to set preliminary stress levels for use in designing willi ferro-cement. The compressive membrane tests were intended for comparison with similar tests on metals. The impact membrane tests were expected to provide qualitative insight only into the damage to be expected under accidental impact in use. The freeze-thaw tests were considered vital since Canada's eastern and western sea coasts are subjected to many cycles each winter of freezing and thawing weather which boat-building materials would have to withstand.

Description of Sample Material (Figures 1 to 4)

Panels measuring four feet in width, six feet in length and three-quarters inch in thickness (nominal dimensions) were made up following fabrication procedures that would presumably be used by amateur boat-builders. Four groups were prepared as follows:-

Group 1 Seven panels containing respectively 1,2,4,6,8, 10 and 12 layers of I/2-inch hexagonal galvanised wire mesh, each made in down-hand position on a 3/4-inch plywood backing. The mortar was trowelled on by hand and mechanically vibrated to ensure penetration. The top surface was smoothed by hand trowelling. Quantities of ingredients for each panel are detailed . in the appendix.

Group 2 One panel containing one layer of hardware cloth having No. 14 gauge wires on a one-inch by one-inch mesh overlayed on each side with four la~ers of I/2-inch hexagonal galvanised wire mesh, made in a down-hand position on a 3/4-inch plywood backing. The mortar was trowelled on by hand. A vibrator was used to ensure complete penetration. The top surface was smoothed by hand trowelling. The quantity of ingredients is detailed in tile appendix.

Group 3 One panel similar to that of Group 2 except that I/4-inch ntild steel reinforcing bars on 2-inch centers, running in the long direction of the panel only were substituted for the hardware CIOtll.

Group 4 No panel in this group was constructed. This group was intended to involve the "gunite" method of application and was deleted from the

A. M. Kelly and T. W. Mouat

\

experiment (it is a professional's method) and replaced by Group 5 which was considered more directly related to the other groups and con-sequently more meaningful for the purpose of this explora tory program.

Group 5 Two panels similar to Group 3 except made without plywood backing and consequently trowelled from both sides. One panel was plas-tered down-hand, the other in a vertical attitude. No vibrator was used. The panets were fmished on both sides by hand trowelling. Quantities of ingredients for each panel are detailed in the appendix.

All panels were kept moist by spraying for 21 days. Following the curing period the panels were surface dried, marked for identification and cut to provide test specimens according to the cutting schedule in the appendix. Each piece was numbered when cut to identify its source panel and its orientation in the structure of that panel.

In addition to the panels, from each batch of mortar used in making up Groups 1, 2, and 3, three 2-inch cubes were made for compressive tests.

Tension Tests

From each panel in Group 1, twelve sample pieces were tested in tension. Wedge grips were applied directly to the specimen in a way sinnlar to that used for testing of metals. A tensile load was applied and gradually increased. First indications of cracking were noted and the loading was continued until it appeared that further straining would not produce additional useful data.

Results

The specimens first developed a simple crack through the mortar, followed by elongation of the wires of the reinforcing mesh, followed by a second crack more or less parallel to the first, separated from it by a small distance, typically one-half inch. Further straining produced additional cracks. Four specin1ens showing tIns cracking appear in the photographs Al and A2 in the appendix. A chart giving the range of tensile strength values, as determined from these tests, appears in the appendix. It can be seen from the chart that tensile strength increases almost linearly with the number of layers of mesh.

14J

Compression Tests

From each panel in Group 1, twelve sample pieces were tested in compression. The end surfaces as cut were flat and reasonably smooth so they were not capped prior to testing. A self-aligning head was used in the testing machine to accommodate any lack of parallelism in the specimen ends. A compressive load was applied and increased gradually until either maximum load was reached and passed or it appeared that further crushlng would not produce additional useful data.

Results

Typical compressive failures occurred in nearly all cases. As can be seen from the photographs A3 and A4 in the appendix, one or two shear planes developed; if two, the resulting wedge then penetrated the opposing part of the specimen splitting it more or less cen trally. The presence of the wire mesh appears to have guided these splits but otherwise had little effect on the results of tl1e tests. A chart showing the range of compressive strengths as determined from these tests appears in the appendix.

Shear Tests

Twelve sample pieces from each panel in Group 1 were tested in double shear, six with the trowelled face upward, six with the trowelled face downward. Tests were made using the natural panel surfaces in contact with the anvils of the test apparatus. The shearing force was applied and continuously increased until shearing occurred. Overtravel was restricted to the minimum practicable amount.

Results

Photographs A5 and A6 in the appendix show the results of the shear test on specimens from panels with 2 layers of mesh and 10 layers respectively. In the testing of specimens having one layer of mesh, complete separation of parts occurred in some cases. For panels with two or more layers of mesh the photographs are typical of the appearance after testing. The shear strengths as calculated from the test results show increasing strength approximately linearly related to the number of layers of mesh.

Transverse Bending Tests

Eight samples from each panel were tested in transverse bending, four with trowelled face upward, four with

142

trowelled face downward. Tests were in accordance with ASTM Designations A438-62 and C293-64 insofar as applicable.

Results

\ In each case cracks fonned on the tension face near mid-length. Following formation of an initial crack a small decrease of load occurred, then the load built up to a greater value than that at which the crack formed. Next a second crack fonned with a decrease in load followed by a further increase, then by further cracking. In no case did the test result in breaking of a specimen into major components. Some crumbling occurred along the edges of the cracks. Some samples from Group 5 (trowelled from both sides - not vibrated) which showed incomplete penetration, particularly around the 1/4-inch diameter reinforcing rods, failed by shearing along the neutral axis.

The photographs A 7 and A8 in the appendix show typical results of the bending tests. The photograph A9 shows one of the test pieces which sheared longitudinally. A chart giving the range of values of modulus of rupture, as determined from the results of these tests appears in the appendix.

Panel Tests (Compression)

Four samples from each panel in Group I were tested as point loaded flat plates. Each panel was placed on a test fIXture in the fonn of a square of half-round bars of 1/2-inch diameter with a mean side length of ten inches. A one-inch diameter anvil was placed on top of the panel at its center and load was applied to the anvil by a testing machine.

Each panel was loaded and released repeatedly, with increasing values of load until a sudden increase in deflection was noted, when the panel was considered to have failed.

Results

Each panel reacted elastically to its initial loading, then as loads increased developed cracks and pennanent deflec-tion which increased with load. Finally a load was reached that caused a disproportionate increase in deflection which was taken as indication of failure.

Failure resulted in a type of punching shear beginning at the perimeter of the I-inch anvil and spreading as a shallow

CONfERENCE ON rISJIING VESSEL CONSTRUCTION MATERIALS

cone to 3 or 4 inches diameter on the underside of the panel. The material within the cone showed considerable fracturing, but was retained by the mesh. The photographs AIO, All, A12 and Al3, in the appendix show the front and rear appearance after testing of panels with eight and ten layers of mesh. A table of values of maximum applied load for each panel appears in the appendix.

Panel Tests (Impact)

Four samples from each panel in Group 1 were subjected to impact tests. Two of these four samples were impacted on the trowelled face, the other two on the reverse side. Each panel was supported on the square fIxture described under Panel Tests (Compression) and subjected to impact by a falling weight dropped through progressively increasing distances. Variability in resistance to impact and in the nature and extent of the resulting damage made recognition of the point of failure uncertain.

Results

Impact resistance was less than expected. As a result the frrst two specimens tested were completely shattered by their initia,! impacts of 30 ft. pounds and 8 ft. pounds respectively. The photographs A14 and AIS show typical cracking type failure that occurred in panels with four layers of mesh or less. Photographs A 16 and A 17 show the type of punching shear that occurred in panels having six or more layers of mesh. A tabulation in the appendix details the maximum impact applied to each panel. .

Freeze- Thaw Tests

Owing to the complex special equipment needed for freeze-thaw testing, arrangements have been made with University of Alberta, where test facilities were available. The test results are not yet available.

CONCLUSIONS

The variability in the test results demonstrates the importance of craftsmanship in working with ferro-cement. Ostensibly symmetrical samples produced widely differing results when tested in flexure face up and face down because the distribution of reinforcing mesh was non-unifonn.

The failure to reach and pass maximum strength to weight ratios as reported by Oberti (1949), even with use of


twelve layers of mesh, indicates that a heavier gauge mesh should be used. Multiple fractures of the matrix in tensile tests and on the tension face in flexure tests showed that bond strength between wire and mortar was adequate, indicating that larger diameter wire could be used without 4isadvantage. Compression tests showed very little con-tribution to the strength of the composite material by the steel. Larger diameter wires would be expected to be more effective in compression. On the other hand if the wire diameter is increased too much, the mesh would be difficult to handle and the area available for adhesion is diminished to the point of inadequacy.

Many of the compressive strength tests resulted in splitting of the specimen between the layers of mesh. This suggests that more attention should be given to cross-bonding of the meshes and possibly to development of another type of mesh having some inherent cross-bonding characteristic. Some type of expanded metal lath would serve this purpose.

It is. evident that each aspect of the materials, mixing, and application could be improved and that ferro-cement would become more attractive as a boat-building product as each improvement is made. .

RECOMMENDATIONS

There is considerable scope for improvement in ferro-cement as a boat construction material and in fabrication procedures in the use of ferro-cement for the building of boats. Both these fields need intensive development so that reasonable levels are reached before the reputation of ferro-cement is damaged.

In the field of amateur boat building, comprehensive instruction manuals are needed which will contain step-by-step operating procedures, suggestions for optimizing the results, and thorough background discussions explaining the

143

properties of ferro-cement, suitable methods of use, sources of difficul ty and ways to avoid them.

In conducting future development work and tests more attention should be given to:-

1) Craftsmanship - to ensure that products and test specimens will be as specified.

2) Control of Ingredients - sand particularly' should be of suitable grading and grading should be uniform throughout each test series.

3) Control of Mixture - the real water-cement, and cement-sand ratios must be maintened at the specified values.

4) Control of Testing - efforts must be made to avoid or at least explain all inconsistencies in tests. Methods of measurement, both for specimen dimensions and for deflection or distortion result-ing from testing, depend largely on the surface texture of samples. Excessive roughness and pro-jecting or loose particles must be given very special attention to minimize their influence on the test results.

5) Control of Mixing - considerable variation of final properties can result Jrom slight variations of mixing procedure, timing, ingredient condition, particularly water temperature, mixing time, and hold time between mixing and emplacement.

Finally, development work in the short term should be aimed at gaining appropriate government certification of this material for use in offshore fishing vessels of small and medium sizes. This is the major step required to give encouragement to professional builders who can then be depended upon to press forward with improvements to the material and the fabrication methods.

144

Figure 1

Figure 2


PanelS

PanelS Detail


Figure 3

" "."'.

Figure 4

Panel 9 Ready for Mortar

• • 4, (, ~ • • l'': .: !~ . " .

Panel 9 Detail

145

146

REFERENCES


Morgan, R.G. (1968a) Letter to the Editor, Concrete, March, p. 128.

NOTE: The following list contains only those references cited in Nervi, P.L. (1951) "Ferro-Cement: Its Characteristics and Potentialities", Translated from the Italian; L 'Ingignere, No. I, S.L.A. Translation Center.

, this paper. An expanded bibliography, containing approx-imately 100 references, is in preparation and will be available to interested persons within a month.

Anon., (1966) "Chinese Build Concrete Boats", Concrete Products, vol. 69, No. 12, pp 36-37.

Nervi, P.L. (1956)

Oberti, G. (1949),

"Structures", F.W. Dodge Corpo-ration, New York, pp 50-62.

Byrne, J.G. & W. Wright (1961) "Reinforced Cement Mortar Con-struction - An Investigation of Ferro-


Table of Ingredients

Panel Numbers 1 2 3 4 5 6 7 8 9 10 11

I Weight of Material in Pounds Sand 184 200 210 211 195 190 204 199 189 195 195 Cement 92 92 92 92 92 92 92 92 92 92 92 Pozzolan 13% 15 15 15 15 15 15 15 15 15 15 Water 40 49% 49 56 64 36 52% 53 52 56 56

Reinforcement, Nature and Quantity Number of Layers V ... in. galv. No. 22 ga 1 2 4 6 8 10 12 8 8 8 8 Hexagon mesh I-in. pitch No. 14 ga Hardware Goth. See x Note (a) ~-in. dia. mild steel rods on 2-in. centers. x x x See Note (b)

NOTES: (a) (b)

1 layer of hardware cloth, I-inch square mesh, No. 14 ga wires with 4 layers of galv. mesh on each side. In central plane, lengthwise of panel, mild steel rods ~-in. dia. on 2-in. centers, 4 layers of galv. mesh on each side.

Derived Data

Panel Number 1 2 3 4 5 6 7 8 9 10 11

Water/Cement Ratio 0.38 0.46 0.46 0.52 0.60 0.34 0.49 0.50 0.49 0.52 0.52 Cement/Sand Ratio 0.57 0.54 0.51 0.51 0.55 0.56 0.52 0.54 0.57 0.55 0.55 Average Compressive Strength 'Of 28 days

6910 7140 7300 6250 7210 7650 7560 7260 7690 - -from 2-in. cubes, pounds per sq. inch Weight in pounds of reinforcement per sq. 0.11 0.22 0.43 0.64 0.85 1.07 1.28 1.85 1.85 1.85 1.85 ft. of panel Average Density of panel material, pounds 131 145 147 145 148 154 165 152 151 - 140 per cubic foot

NOTES: 1) In calculating ratios above pozzo!an was included as cement. 2) Sand was reputed to be oven dry but moisture content was not tested. 3) A sand analysis from a sieve test of a 100-gram sample showed:-

Screen size 3/16" No.7 No. 14 No. 25 No. 50 No. 100 in Pan Percentage Retained 0 2 3 10 55 22 8

4) Compressive strength tests were made by Warnock-Hersey International Limited, Coast Eldridge Professional Services Division.

147

148 CONFFRF.NCE ON FISHING VESSEL CONSTRUCTION MATERIALS

o ~ RA~JGE OF TEST VALUES

Speclrra0ns cui ICfD@iht':1ise of pan~I---o Sp~CimGH'S cut crosswise of panGI-aaCDD-o co

o o I'-

o o ~

o o I I

i

I I ~ I ,~

D

I I

I J . ) ~ .2 l

o ·· .. -~i--i---i--=~t" -§ ---r6= - T2 NUMBER OF MESHES

A. M. Kelly and T W. Mouat

5 A-I

A-2

Tensile Specimens After Test

Tensile Specimens After Test

149

150

0 0 0 m

0 0 0 OJ

_0 .- 0 u;0 0..1'--J:o I- 0_ (!)o ZW W 0::0 1-0 -(f)o WLO

::::0 (f)o (f)o w¢ Q: a.. ~8 0 0 of/)

0 0 0 N

0 0 0

I I ,I I I ,g ,~

:1 ·1 I


- 36 -

I I I I ! I ~ ·a

I ,I I m ~ 'I it I , ~ is 9 I I i ·1 I I ~ ,i

~ .~ ~

~ 3 0 a ~ I I a D I

I I I •

RANGE OF TEST VALUES Specimens cut lengi;'t'Jise of panel ~ Specimens cut crosswise 01 panel--~-

~ . I ~ .~

~ B I Q

I I I I

'I

1." .... __ • .1.. Ai .. _._.J-.......-J ____ L.. ,..,...,t_. _J I 2 4 6 8 10 12

NUMBER OF MESHES


a

A-3

A-4

Compression Specimens After Test

Compression Specimens After Test

151

152

---

rio' ,,-

o w

o ~

o N

. ;3 ,9 la


RANGE OF l-ES1' VALUES Spccimentl cut Icngiht"Jiso 01 panel-""''"'"' S~:){~Ci~1ens cut crosst"Jise or ponol C::~0'3_OD

lQ

I I a G I

I .~ a I Q i ~ I ~ ::~ .~

··G a .~ I 'J ~ ,3 8 .', .~

~ I , . ;1 I .J D J

a .8 '~ ~ I I

•


A·S

A·6

Shear Specimens After Test

Shear Specimens After Test

153

154

o o o V

0 0

~o ott)

fI) . 0. -....

LtJ 0:: :l f-Cl..O =>0 0::0 I.!..(\J

0 en ::> ..J ::::> 0 00 ~o

0 I I I I

I


RANGE OF TEST VALUES Specimens cut lengtht"ise of panel- -Specimens cut crosst1ise of panel----

• I I I

I I I e

13 .J

• ,~ ) , .~~ 1 I ! '8 I ;]

r

I I I I , .~

;1 I~

·l l

....-..--s._-'-__ --'-__ -J ___ ..!-___ ..L__ •. .J o 2 4 6 8 10 12

NUMBER OF MESHES


A-7

A-8

Flexure Specimen After Test

Tension Side


Tension Side

155

156

A-9



Sheared Longitudinally

A. M. Kelly and T. W. Mouat 157

Panel Tests - Compression

Layers Specimen Maximum Point Load Applied on

of Mesh Code Load Trowelled Face Back

164 630 x

1 165 563 x 166 570 x 167 300 x

264 1400 x

2 265 1080 x 266 765 x 267 567 x

364 1870 x

4 365 1850 x 366 650 x 367 490 x

464 1600 x

6 465 1410 x 466 1000 x 467 765 x

564 2050 x

8 565 1960 x 566 1000 x 567 1090 x

664 2240 x 10 665 1850 x • 666 1110 x

667 1100 x

764 1500 x

12 765 1750 x 766 1150 x 767 1260 x

158

A-lO

A-ll


Panel Specimen Compression

After Test


Mter Test


A-12

A-13


After Test


After Test

159

160 CONFERENCE ON FISHING VESSEL CONSTRUCTION MATERIALS

Panel Tests - Impact

Specimen Layers Impact on Max. Impact Remarks Code of Mesh Trowelled Face Back Inch - Pounds

160 1 x - Completely shattered by 30 ft.-lb. 161 x - Completely shattered by 8 ft.-lb. 162 x 20 Quartered; mesh intact 163 x 14 Halved; mesh intact 260 2 x 45 Halved; mesh intact 261 x 45 Quartered; mesh intact 262 x 36 Cracked in quarters to mesh 263 x 27 Cracked in quarters to mesh 360 4 x 205 Cracked in half to mesh 361 x 108 Quartered; mesh intact 362 x 27 Quartered; mesh intact 363 x 36 Quartered; mesh intact 460 6 x 73 Quartered; cracks follow mesh 461 x 215 Center punched through; cracks 462 x 143 Punching shear-type failure 463 x 63 Halved; crack opened progressively 560 8 x 215 Punching shear; quartered 561 x 54 Quartered; cracks opened progressively 562 x 215 Cracks follow mesh 563 x 45 Quartered; parallel cracks showed 660 10 x 332 Cracks follow mesh; opened slowly 661 x 89 Quartered 662 x 322 Center punched through; spalled 663 x 90 Cracks center to 3 edges 760 12 x 36 Cracks opened somewha~; spal\ed 761 x 322 Center punched; mesh bulged; spaJled 762 x 143 Cracks; center to 3 edges 763 x 322 Center punched; mesh bulged; spalled

NOTES: Tensile, Compressive, Shear, Flexure and Panel tests were performed by Golder, Brawner and Associates


A-14

A-I5

Panel Specimen Impact

After Test


After Test

161

162

A-16

A-1?



After Test


After Test

APPENDIX 3.

FREEZE-THAt-l TESTS ON FERRO-CEMENT SAHPLES: EFFECT OF REINFORCING RODS OR HEAVY MESH. (The method of making the samples is discussed in Appendix 2)

Freeze-Thaw Tests

Winter weather likely to affect the durability of concrete will be experienced along the entire length of Canada's sea coasts and on its inland waterways. A review of the literature reveals that the temperature at which destructive freezing of concrete begins may be assumed to be 15°F. It should be considered then that an exposed structure would experience a number of freeze-thaw cycles roughly equal to the number of times that a temperature of 15°F or colder is followed by a temperature of 32° or warmer. Only rarely will this exceed ten times a year. A reasonable average for design purposes would be half this number, or five cycles per year.

The United States Bureau of Reclamation in its Concrete Manual terminates the freeze-thaw test when 25 per cent of original weight has been lost from a specimen or when one thousand cycles of freezing and tha\o1ing have occurred. Material which survives five hundred cycles is considered acceptable.

The American Concrete Institute sets a limit of three hundred cycles for the test, but uses loss of physical properties as indicated by a vibration measurement, or by substantial disintegration, as criteria of failure. The Institute's Manual states that the test is more severe than is natural exposure. The three-hundred-cyc1e limit is basic also to the ASTM tests.

Specimens and Procedure

Eight samples from each panel in Group 1 were prepared for freeze-thaw tests. Because of equipment limitation and costs of testing, only the specimens from panels 1, 4 and 7 were tested. Tests were in accordance with ASTM C29l-67 as far as possible but the dimension of the specimen in the direction of the panel thickness was approximately 3/4 inch while the test equipment was intended for a test specimen dimension in the range of 3 to 5 inches. Consequently the electronic vibration equipment could not be used. The tests were conducted on the basis of weight loss. Measurements were taken at intervals of approx-imately 25 freeze-thaw cycles for a total of 309 cycles except for those specimens whose condition had deteriorated excessively before 300 cycles had been completed.

Results

The weight loss from each specimen was recorded on completion of 22, 44, 73, 103, 125, 156, 176, 205, 227, 257, 279, and 309 cycles of freezing and thawing except for samples numbered 170, 171, 172, 174, 175,

- 2 -

l76~ and 177 which did not survive to the end of the planned 300 cycles. The average weight loss as a percentage of initial weight was computed for surviving specimens and is shmvn in Fig. 1. The percentage weight loss is shown in Fig. 2 on a base of number of freeze-thaw cycles for the averages of the samples from each panel. A strong inverse relation-ship is evident between the number of reinforcing meshes and the loss of weight.

Significance of Test Results

Repeated freezing and t

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