MIOl:IIGAl:l STATE !i"LG!WlA1 DEPAB.T',,i\ENT

Qb8.r1.eS lll[. Ziegler State Higlwm.y Commissioner

OO!.IPRESSED if!OOD FOR F~PANSJ.Oil JOINT FILLER

B. Yi. Pocock

Research Project l1o. '3() G-1 (7) B

Research Laboratory 'res·Ung and I\eBearch Di'lrision

Heport :f-98 May 28, 1947

IN'rRODUC'fiON •

EXPANSION IN AIR AND IN WATEIJ.

Expansion in Air

Expansion in Water

PRESSURE OF EXPANSION IN ViATER AND IN MORTAIJ. •

Presrmre of Expansion in Water

Pressure of Expansj.on in ilffortar •

EFFE:CT OF SURE'ACE THEllTl\IE.\'lT

Stacking Treated Samples

FIELD INSTALLATIONS

Location and Installation

. .

BRhavior of Wood J'oints After Installa.tion

CONCLUSIONS . .

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COMPRESSED WOOD FOR EXPANSION JOINT FILLER

INTRODUCTION

Michigan is one of several States now permitting the use of compressed

wood as a filler material for expansion joints in concrete pavemen<b, It

was deemed therefore of considerable importance to augment the Department's

knowledge of compressed wood behavior, which had been partially confined to

knowledge obtained from other sources/by instituting its own program of

study desig:ned to procure certain original and fundamental data.

The laboratory study was set up in order to obtain first-hand infor-

mat:Lon concerning certain specific and fundamental physical properties of

different species of wood when compressed before imr~allation in the joint.

These properties included (1) the extent to which wood, when compressed to

half its original thickness, will expand when the load is released (a) in

air an<d (b) in water; (2) the pressures developed when such precompressed

wood is allowed to expand (a) in water and (b) lll mortar; and (3) relation-

ships which might be established between the rates of expansion and conse-

quent development of pressure, and the application of certain surface

treatments designed to retard the entrance of moisture during shipment and

handling.

Species of wood included in this study were Cal:Lfoi'aia redwood,

cypress, Douglas fir and wes<bern cedar. Samples were purchased kiln-dried

and dressed to seven-quarters thickness. Ji'rom these, laboratory specimens

were cut, measuring four inches square,

"' Self -Expanding ,Toint Filler for Concrete Pavement VI. J. Van London, Houston, Texas Chapter A.S.C.E., li'ebrua:ry 15, 1945

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EXPJ\NSION:_IN AIR AND IN WATER

In order to study the comparative expansion properties of the four

speciec: of wood and the effect of varying moisture contents thereon,

laboratory specimens were prepared having different ranges of moisture con-

tent, With thFJ exception of moistures in the "as received" condition, the

ranges of moisture content were established by soaking in water to constant

weight, then allowing to air dry for predetermined intervals. The actual

moisture contentr; were determined by drying specimens prepared simul-

taneously for this purpose at 105 degrees C. to constant weight.,

All specimens were compresr;ed to 0. 75 inch thickness at. the rate of

0,065 inch per ndnute,

Expansion in Air

Af'ter con:pression to 0, 75 inch, specimens were placed on a drying

rack Hll.d tl:>.icknesses were recorded at intervals for seve;n. deys. Reference

to Figure 1 shows the relative expansion properties of the four species of

wood when allowed to expand to constant thickness in air at room tempera-

ture. In general, the greater the original moisture content, the greater

was the ultimate expansion in air. Drying rack and associate equipment

are shown in Figure 2.

After seven days' expansion in air, specimens had come to constant

thickness in all cases. They were then stood upon end, grain vertical, in

1/4 inch depth of water, each specimen being sandwiched individually between

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TO 3/4 INCHES ORIGINALLY

EXPANSION IN AIR 7 TO 14 HOURS EXPANSION IN WATER

MOISTURE TIME 1 COMPRESSION

SUBSEQUENT EXPANSION

Figure 1

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Figure 2. Center shows drying rack used for concH­tioning wood blocks at different stages of investiga­tion. At left can be seen water bath for immersion of blocks. At right is one of a series of identical instrumentf1 incorporating dynamometer ring and dial indicator for measuring pressures developed in vrood in contact wlth water or mortar.

I1'igure 3. Wood blocks after compression to half thickness shovvn standing in 1/4 inch depth of v1ater with grain vertical. Blocks held in con·lJEtct with blotting paper by rubber bands.

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two sheets of blotting paper held in intimate contact with the wood by

rubber bands. This was to simulate position in an actual expam1ion join·!;

in concrete pavement. (See Figure 3)

Swelling of all specimens began immediately after contact with water.

Thiclmesees were averaged and recorded, at first at fifteen minute inter­

vals, then at hourly, then daily intervals for seven days. The 1/4 inch

depth of water was maintained by additions, Here again, constant thick­

ness was reached at the end of seven days.

Figure 1 shows these results as well as those relating to expansion

in air. It would appear that wood in the "as received" condition, con­

te.ining about five to seven per cent. moisture, displays the greatest ability

to expand when inmtersed in water after being compressed; wood containing

higher percentages exhibits the lowest ability, The effect of immersion in

water after a preliminary expansion in air is greatly diminished with

increasing original moisture content. A study of l''igu.re 1 discloses

interesting comparisons among the four species investigated.

PRESSURE OF EXPANSION IN WATER liND IN lliO.IIT!fi

In o1•der to obtain as complete info!'lllation as possible with respect

to relative expansion properties of the four types of wood, it was con­

sj.dered advisable to investigate the magnitude of forces set up when com­

pre":sed wood if: restrained from expanding after immersion in water or fresh

eon crete. Accordingly, a battery of instn.urrents was set up for this pur­

pose, constructed as shown in Figure 4. Standard C-clamps were arranged to

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Figm·e 4. pressu.res wood when series of

View of apparatus used in measuring exerted by both normal and compressed E.iUrrounded by vra ter or mortar. A tlu·ee such instrmnents was used in

thif. investige:t.ion. Instrwnent consists e~lf'len­ti~:dly of a large C-clamp with suitable steel plates for sandwiching ~lpecimens, a dynamometer ring and a dial indicator registe1·ing in ten­·thousandths of an inch.

hold a compressed wood block between suitable steel plates, with a dyna­

mometer ring and dial indicator for recording total force produced. Pres­

sures were calculated in the conventional manner in pounds per square inch.

PresS}l!£ of Expansion in Water

Refel"ence to Figure 5 disclose<: that in all cases the presriUres

produced by total inunersion in v1ater of wood compressed to half its

original thickness were far greater than the pressures developed by speci­

mens which were not c,ompressed. These differences were enormously greater

in the case of cypress and western cedar, although the pressures developed

by ther;e two species in the uncompressed state were less than those pro­

duced by redwood and fir in the 1.mcompressed state.

Pressure of Ex-oansion in li!ortar

Although the pressures developed tending to produce expansion of wood

when inunersed in water are of fundamental signific~Emce, it was felt neces­

sary to obtain data concer-ning such pressures resulting from immersion in

fresh mortar. This, it was believed, would more nearly simulate the actual

case of using compressed wood as a filler material for expansion or con­

traction joints in concrete pavement.

Therefore, employing the same apparatus wh;i.ch was used in studying

the pressures developed in water, records were secured of pressm"es induced

when wood specimens were surrounded by a standard 1;2 Portland cement­

natural sand mortar. Af-ter pressures had become stabilized at approxi­

mately ninety-five hours after each experiment was started, water was

poured over the specimen to simulate rainfall, its depth being maintained

at 1/4 inch.

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EFFECT 1 PRECOMPRESSION mz EXPANSIVE FORCE oj VARIOUS WOODS m WATER

CURVES e· COMPRESSED CURVES A: NOT COMPRESSED

Figure 5

Reference to Figure 6, in which pressm·es of expansion in mortar are

plotted against time, showrJ ultimate pressm·es ranging from fifteen to

approximately fifty-five p.s.i., depending on the species of wood. At the

extreme left in each graph can be seen the curve of compressive strength

of normel concrete. At first glance it would appear that all the pressure

curves for wood lie well under the curve of compressive strength of con­

crete. The magnified portions of the curves, however, show that this is

not the case during the first few hours. For a period of from tlu·ee to

four hours depending upon the species, the pressure developed by compressed

wood is corwiderably greater than the compressive strength of concrete.

It was therefore considered advisable to investigate the possibility

of treating compressed wood in some mmmer which would dela..y the entrance

of water without sacrificing ultimate pressure, in this way postponing the

development of' pressure until the concrete is strong enough to wi·thstand

. it.

EFFECT OF SURl•'ACE TREATMENT

Treatment employed consisted of (a) one dip and (b) two dips in a

good grade of commercial (proprietary) membrane-curing compound. In case

(b) (two dips) samples were allowed to dry to touch before application of'

the second dip. In all cases, as shovm in Figure 6, two dips imparted the

deGired postponement of pressure. In three out of four species, one dip

proved insufficient, and in the fourth case (fir) it was barely sufficient.

In no case did treatment seriously retard the development of' pressure with

corresponding tendency to follow a receding concrete faoe.

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Stacking Treated Samples

Inasmuch as any of the four species of wood studied appeared to have

definite merit as a joint filler Jnateria.l, the question naturally arose

whether commercially fabricated joint filler ma.tel·ial prepared in the

manner above could be stacked and handled without sticking together. It

was fotmd that no sticking occurs provided the pieces are dusted wi"bh

powdered chalk as soon as dry to touch after the second dip.

FIELD INSTALLATIONS

Because of the promising results of the laboratory investigations,

it was decided to make certain field installations of expansion and con­

traction joints using compressed wood. The Grand Ledge-Mulliken paving

project F'-25-6 was ava.llable as a site for a limited number of experimental

joints .at ·~his particular time (Ocr~ober, 1946). Plans were therefore ma.de

to incorporate two expansion joints and two contraction joints of' one inch

and l/2 inch thickness respectively, uslng California redwood, compressed

and treated with two dips of membrane-curing compound..

Material for the contraction joints was supplied by Texas Foundries,

Inc., in the form of blocks of redwood measuring 6 x 9 inches. These

pieces, originally l/2 inch thick, had been compressed by the vendor to

5/8 inch, then allowed to expand freely in dry air.

Materie.l for the expansion joints was purchased in the form of :red­

wood planks 7/4 inch thick, dressed, These planks were cut into blocks

about 5-1/2 inches wide, in some cases wider, and exactly 7-5/4 inches long.

Blocks for two complete joints were compressed in the laboratory to 0.75

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inch and allowed to expand in dry air. 'l'hey were then trimmed, fitted

into the steel supporting baskets, dowel holes were drilled, and the blocks

individually dipped twice in membrane ctu·ing compound.

In the case of all four joints, the blocks were placed with the

grain vertical. Each block was fastened to the adjacent blocks by cor--

ruga ted fasteners. Fie,'Lu:es 7 through 10 show the method used in setting up

and installing the contraction and expansion joint assemblies.

Location and Installation

The experimental joints were placed at the following locations on

October 25, 1946:

Station Type of Joint Paper Under Joint

780+68 Expansion Yes 779+68 Contraction Yes 778+68 Contraction No 777+68 Expansion No

Figures 11 through 14 illustrate the various steps involved in

installing the joint assemblies. In all four cases, the joints were made

to set flush with the surface of the pavement and were left unsealed in

order to facilitate observation of subsequent behav-ior.

Behavior of Wood Joints After Installati.sm

Periodic examination of the wood joint installations over a period

of several months disclosed that the thin compressed wood filler assemblies

used in the contract1on joints were unsatisfactory in that they did not

appear to follow the increase in joint opening which was observed. Con-

siderable space dev-eloped on each side of' the wood filler, between the wood

and the concrete joint face. See Figure 15.

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Figure 7. Wooden form used in constructing precom­pressed expansion and contraction. joints. Form m<;~de to cor)form to crown of pavement. Length of form equals vd.dth of one lane.

F igur·e 8. Contraction j otnt made of 3/8 inch com-­rneJ:cially compressed. redwood, con~d;ructed in Labore.tory, surface treated, and inr,Jtalled ln Grand Ledge-Mulliken pavement.

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Figure 9. View of compressed and treated red­wood expannion and contraction joint assemblies set up for dov;•el lubrication and sleeve installation.

Jrigu.re 10. Another view of asf,emblles in f:~ame stage as in Figure 9.

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Figure 11. Stage during installation of experi­wental precompressed and treated redvmod expansion joint a8SeJnbly at Station 780 + 68. Assertlbly is being trued to form.

Figure 1:2. Stage during installation of experi­mental p:r:·ecompressed and treated redwood expansion jo:Lnt assembly at Station 780 + 68. Steel rein­forcing mesh being placed over first. layer of con­crete west of joint. Note care being taken to avoid displacement of joint assembly.

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Figure 13. Early stage during insta;llation of pre compressed and trr::lated redvmod coniir<'l.ction joint asnembly at Station 779 + 68. Joint. n0sembly being trued to fol~m and crovmo

Figure 14. Slightly later stage than that shown in Figure 15. Note steel reinforcing mesh being covered.

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Figure 15. Shows condition of redwood contraction joint at Station 778 + 68 tb~·ee weeks afte:c -installation.

The one inch expansion joints, however, still were in fairly satis­

factory condition at this writing {May, 194, 7) , See Figure 16.

CONCLU8IONS

1. Certain species of wood when compressed to half its original thickness

in a <try statE> will expand, i.n the presence of moisture, to approxi­

mately 85% of the original thickness. Thus a board 7/4 inches- thick

when compressed and installed to form a one inch expansion joint WO"Llld

always exert a preE:sm·e against the abutting slab faces to form a

tigbt joint.

2. California redwood seems to be ideal for thiE: purpose although certain

other woods may be used successf\1lly ..

B. All compressed woods must be treated with a water repellent material

after compref:;sion in order to delay expansion in sto-rage and handling

and when plHeed in the pavemsnt to postpone the development of pres­

,sure until the concrete is strong enough to withcJtand it. Labol'ator'Y

studies indicate that this ma.y be easily accontplished by various

methods,. and therefore constitutes a n!lnor manufacturing problem.

4. It is believed that compressed wood would not be successful for joint

w:i.dths less than 3/4 inch in vddth because the thin board,s v1ould pro­

duce joint fabrication difficult.ies and the lesser wood section will

not provide the desired pressure at all times to keep the joints

sealed.

5. Although compressed wood as a joint filler material is unquestionably

superior to other materials now in conunon use, it i:::: not economically

available at the present time to contractors in Michigan.

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Figure 16. Shows condition of' redwood expansion joint at Station 780 + 68 three weeks after installation.