Measurement of laminations in brick

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Publisher’s version / Version de l'éditeur:

American Ceramic Society Bulletin, 54, 8, pp. 725-727, 1975-08

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Measurement of laminations in brick

Ritchie, T.

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Measurement of Laminations in Brick

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_{A ~ Y Z E D}

THOMAS RITCHIE

National Research Council of Canada. Ottawa

L A R G E PROPORTION of the clay brick made in North America

A

_{are formed by stiff-mud extrusion, in which clay or shale of a} plastic but stiff consistency is forced through a rectangular die by means of pressure exerted by a screw auger. The flow of the clay past the auger and through the die frequently produces laminar voids. Such voids, called laminations, may result from several causes, including the inability of the clay to unite after it has been separated; for example, in flowing round the yoke carrying a core. Anothercause of lamination is the tendency of the clay to rotate with the auger. This sets up stresses that may be of sufficient magnitude to form slip-planes in the clay. A third important cause of laminations is the differential rate of flow of the clay through the die; friction between the metal die and the clay retards the flow near the die surfaces so that shear stresses may be set up within the clay and produce cleavage planes in it.

Lamination is directional, occurring parallel to the direction of clay flow. In modern brickmaking practice the dimensions of the die correspond to the length and width of the brick, and the spacing of the cutting wires that slice the extruded column into brick equals the height of the brick. Thus, laminations occur in planes parallel to the faces and ends of the brick so that when the brick is placed in a wall many of its laminations are in planes parallel to the wall surface.

Laminations usually cannot be seen from the brick surface since the action of the cutting wires is to smear the clay, covering or obscuring them. By sawing through a fired brick in the plane of its bedding surface by means of a diamond saw, laminar voids can frequently be observed.' Photographs of one of the brick used in the present study (Fig. I ) show the uncut brick and the laminations revealed when the brick is cut.

Laminar voids in certain brick tested for compressive and trans- verse strength were considered by McBurney2 to have influenced the strength ratios of such brick; and weathering and freezing and thawing tests suggested to McMahon and Ambergqhat the break- down ofcertain brick is associated with laminations. The frequently obseived pattern ofspalling in brick walls-in which a thin sheet, in some cases as large as a brick's face surface, conies away from the body of the brick-niay result from laminar voids in the same plane as the brick face.

Although laminations in brick may be expected to affect their strength and durability, no study appears to have been made specifi- cally to deterniine a relation between laminations and brick perfor- niance. Indeed, as far as is known, no method has yet been developed to provide a quantitative measure of the laminations in brick and thus enable assessment of their effect on performance. It is the purpose of this paper to describe a method developed for the measurement of the linear extent of laminar voids observed on a sawn bedding surface of a brick.

Method of Measurement

Laminations appear on the cut surface of a brick as either fine or coarse lines, sometimes short but occasionally several inches long. They frequently run parallel to the face, the hack and the ends of the brick and are curved at the corners. The method adopted for deter- mining the extent of lamination wasquite simple.

he-total

length of all the lines on the bedding surface was determined by means of a map-measure (opisonieter), an instrument capable of measuring the length of irregular lines. It has a sniall wheel that is placed at one end of a line and run along its length; the wheel is geared to a scale that gives the line's length.

Received October 25, 1974.

This paper is a contribution from the Div. of Building Research, National Research Council of Canada, and is published with the approval Gf the director of the division.

Lamination cracks, a common fault in

brick formed by stiff-mud extrusion, are

believed to affect adversely the strength

and durability of brick. A method is de-

scribed for measuring the extent of

lamination in brick involving the use of a

map-measure to track and record the

length of the lamination cracks appear-

ing on a sawn brick surface.

Fig. 1. Bedding surface of a brick (top) compared with sawn surface of the same area of the same brick (bottom), revealing laminations.

The brick were prepared for nieasure~nent by cutting a slice = '/1 in. thick from their approxiniate center using a dianiond-bladed saw, the cuts being niade in the plane of the bedding surface of the brick. Although the pattern of lamination on the two surfaces of the slice appeared to be the same, with many of the laminar voids apparently extending through the thickness of the slice, nieasure- ments were made on both surfaces. For convenience, each surface was marked by lines dividing it roughly into eight 2-in.' segments. The lamination lines in each square were measured and su~nnied to give the total extent of lamination (in inches) for each side, and the average of the two surfaces was considered to be the extent of lamination of the brick, expressed in inches. While measurements were being taken the well-illuminated brick surface was viewed under a large reading glass.

Brick

Eight brick were used in the study, all from different Canadian plants; all showed laniinations when cut. The slice removed from each brick was measured for extent of lamination by three operators working independently.

Results

Table I lists for each brick the length, in inches, of lamination measured in each of the brick's eight segments. The measurements made by the three operators are shown forboths~~rfaces ofeach slice

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Table

I.

Measurements of Extent of Lamination in Brick

Segment measurement, in. Segment Measurement, in.

Operator I Operator 2 Operator 3 Operator I Operator 2 Operator 3 Side Side Side Side Side Side

A B A B A B

Side Side Side Side Side

A B A B A Side _B (Brich No. 1 ) I 4.6 5.4 2 6.0 4.2 3 5.0 4.8 4 3.9 3.6 5 4.5 4.2 6 10.2 7.8 7 9 . 8 10.1 8 7.1 8.4 Total 51.1 18.5 Mean 49.8 (Brick No. 2) I 5.9 3.8 2 5.5 5.6 3 7.1 5.1 4 4.2 2.1 5 4.6 4 . 7 6 5.8 5.4 7 6.3 5.3 8 5.9 5.5 Total 45.3 37.5 Mean 41.4 (Brick No. 3) I 13.1 14.8 2 13.6 16.5 (Brick No. 1 2 3 4 5 6 7 8 Total Mean 5 14.9 17.8 6 13.8 16.7 7 16.1 18.9 8 17.0 16.4 Total 1 17.7 136.9 Mean 127.3 (Brick No. 5) 1 12.2 17.2 2 17.4 18.0 3 15.2 17.8 4 16.8 17.5 5 13.1 11.8 6 14.0 16.4 7 15.6 14.3 8 11.5 13.5 Total 115.8 126.5 Mean 121.1 (Brick No. I 2 3 4 5 6 7 8 Total Mean (Brick No. 7) 1 14.1 13.8 2 15.6 14.7 3 14.2 15.3 4 17.5 14.5 5 13.6 9 . 0 6 16.8 12.9 7 18.2 13.7 8 14.6 12.6 Total 124.6 106.5 Mean 115.5 (Brick No. 8) 1 2.2 1.8 2 1.8 3.2 3 2.6 3.5 4 2.5 3.4 5 0.8 0 . 6 6 2.1 4.3 7 2.8 3.0 8 2.0 2.4 Total 16.8 22.2 Mean 19.5

(Side A and Side B). The mean value of the measurements is also given. With few exceptions the measurements made by each operator were in good agreement for the two surfaces of each sample.

Meas~~rements of some of the brick varied considerably from

operator to operator. The difference between the lowest and the highest of the three measurements of brick No. 1, expressed as a percentage of the lowest value, was 8.556, the least difference noted; the greatest, 88.8%. occurred with brick No. 8. In spite of this considerable variation, the ranking by the operators of the extent of lamination in the samples was fairly consistent, as shown in Table 11, where it may be seen that Operators 1 and 2 placed all the brick in the same order of increasing extent of lamination. The third operator differed only in reversing the positions of brick No. 1 and 2, specimens that did not differ appreciably in extent of lamina- t ion.

The time required to measure each brick for lamination was = 1 h, although one, which contained a multitude of very short laminations that made i t ditlicult to measure, required ==2 h to complete.

Table II. Comparison of Extent of Lamination and Order of Rank as Determined bv Three Operators

Extent of lamination, Order of rank of mean, in. extent of lamination Brick No. Op. I Op. 2 Op. 3 Op. l Op. 2 Op. 3

Width of Laminations

The rneasurenients took no account of the width of the laminations, although this is probably an important factor in their influence on the properties of the brick. An estimate ofthe maximum width of

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brick No. 4=0.05: brick No. 5 =0.08; brick No. 6=0.06; brick No. 7 = 0 . 0 6 and brick No. 8 = 0 . 0 6 in.

Thomas Ritchie joined the Div. of Building Research at Na-

tional Research Council of Canada, Ottawa, so,on after graduating in ceramic engineering from the University of TO- ronto in 1949. He has been concerned with problems related to masonry construction, such as efflorescence, rain penetra- tion, dimensional instability and decay, and has published several papers on the subject.

Conclusion

The structure of many stiff-mud brick is such that in cutting them in a plane parallel to the bedding surface laminar voids are revealed. The extent of the laminations may be measured by the method described, measurement usually taking = I h to perform. Acknowledgment

The useful suggestions o f H . E . Ashtonofthe BuildingMaterials Section, Div. of Building Research, concerning tabulation and presentation of test results are gratefully acknowledged. the laminations of each brick was obtained, however, by viewing

References the brick surface under a n~icroscope at 100 magnifications and

_'

J. G. Phillips, "The Physical Properties of Canadian Building Brick," Canadian

comparing the width of the widest lamination with aneyepiece grid. D~~~~~~~~ of ~i~~~ and R ~ N ~ , ~ 816, ,947, ~ ~ ~ ~ ~ ~ ,

Each square of the grid, by calibration against a rule, represented '1. W . McBumey, "TheCompressiveandTransverseStren&thofBrick."J. Amer. Cero111. Soc., 12 [4] 217-29 (1929).

0.004 in. By this means the widest laminations were estimated to 3

,.

F , McMahon a n d C , R , '6DisintegratingEffcct of ~~~~~i~~

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