Outdoor freeze-thaw cycling of dry-press bricks

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Outdoor freeze-thaw cycling of dry-press bricks

NATIONAL m S @ M G H COUNCIL CAYABA

OUTDOOR FREEZE -THAW @ YCLING

OF

DRY-PRESS BRICKS

by

J, I. D ~ v i s o n

Internal Report No, 308 of the

Further studies sf a d r y-press brick showing ansmalous performance between laboratory tests and field performance have been carried out a n d are W O W reported. The author, a research officer on the etaff of the Atlantic Regional Station sf the Division, in Halifax, has a special interest i n the performance sf m a s o n r y materials and csnstrkctlans exposed to the climatic conditisns of the Atlantic Region.

Ottawa

D e c e m b e r 1964

N.

B,

Rutckeon

OUTDOOR FREE

ZE

-THAW CYCLING

OF

P r e v i o u s l a b o r a t o r y f r e e z e -thaw t e s t s om a p a r t i c u l a r d r y - p r e s s bricke r esulted in t h e i r deterioration a f t e r r e l a t i v e l y few

cycles. In a t e s t made on % k of t h e s e bricks t h e y all failed between

1 % and 32 cycles, t h e a v e r a g e being 28 c y c l e s ( I ) , Quite t h e opposite r e p o r t s have c a m e f r o m f i e l d studies w h e r e s a t i s f a c t o r y d u r a b i l i t y is indicated in an a r e a subjected t5 s e v e r e driving r a i n s and a n above a v e r a g e n u m b e r of freeze-thaw cycles d a r i n g the winter season. This contradiction r a i s e s a question concerning the c o r r e l a t i o n between l a b o r a t o r y t e s t s and n a t u r a l freeze-thaw actiora.

In o r d e r t o study t h e r e l a t i o n between the two, a simple

Bsnatura3p' f r e e z e - t h a w t e s t w a s conducted. Specimens of the d r y - p r e s s b r i c k w e r e placed on edge in a metal t r a y located on the roof

of the NRC Atlantic Regional Laboratory Building, In the fall of the

year w a t e r was added t o t h e t r a y until t h e b r i c k s w e r e i m m e r s e d to a depth of l / 2 in, At the end s f the freezing s e a s o n in the spring, t h e water was r e m o v e d f r o m the tray and the bricks w a r e bedded in

sand for t h e s u m m e r months.

Thus, the b r i c k s w e r e subjected t o freezing and thawing,

as t h e t e m p e r a t u r e fluctuated during the winter, in a fairly s a t u r a t e d conditioan. They would not be a s completely s a t u r a t e d as in the

l a b o r a t o r y t e s t , a modification of Method B i n M T M

C67

-60,

i n which t h e b r i c k s a r e soaked i n water for 4 hr between Breezing, r e m o v e d and s e t in water t o a depth of J ; / Z in. En a t r a y a n d then put into a

f r e e z e r e The s p e c i m e n s on exposure, even a f t e r heavy rain, would n o r m a l l y have s o m e ti m e in which w a t e r could d r a i n f r o m the upper p a r t before f r e e z i n g o c c u r r e d . The r a t e of f r e e z i n g an n a t u r a l

e x p o s u r e would a l s o be lower than i n t h e l a b o r a t o r y t e s t which r e

-

quires that the t e m p e r a t u r e of the a i r in the freezing chamber must

not be above %

6 " F

witkin an hour a f t e r t h e b r i c k s a r e p l a c e d in t h e chamber.

The outdoor t e s t is, however, s t i l l much m o r e s e v e r &

than that o c c u r r i n g in a m a s o n r y wall w h e r e the d e g r e e of saturation. i s undoubtedly much lower even in the most e x t r e m e c a s e s , and t h e r a t e and extent of f r e e z i n g are r e t a r d e d by (a) the i n t e r i o r t e m p e r a t u r e

Am outdoor freezing t e a t s i m i l a r t o the one above, except that no water w a s initially added t o the t r a y s , was conducted at the British Building R e s e a r c h Station (2). By way sf casmparison, the B r i t i s h r e s e a r c h w o r k e r s suggest that as much decay occurs in five

years in this type of t e s t ae would occur in twenty or m o r e y e a r s in a

brick-ow-edge coping on a parapet

-

owe of the s e v e r e s t conditions in

which bricks a r e normally exposed in the field.

On 8 _January

_1968,

_{lour samples w e r e selected and placed}

in a copper t r a y for exposure on the Atlantic Regional Laboratory roof. Water was added to the t r a y mtih the samples, placed on edge, w e r e i m m e r s e d t o a depth of 112 in. The b r i c k s w e r e selected t o span a

range in suction from 45 to 75 gm/min/36 s q in. P r e v i o u s t e s t s of this type s f brick showed that the saturation coefficient w a s between 0, 7 1 and 0. 80 in this range of auctisn, and the compressive strength was between 6000 and 9000 psi, The saturation coefficient increased and the compressive strength decreased with i n c r e a s e in suction s f the bricks.

During the f i r s t winter the b r i c k s were frequently inspected. Longitudinal c r a c k s were f i r s t noted on the bottom s i d e s 0% a l l four b r i c k s on 2 8 March 1960. These c r a c k s continued t o develop and on

26 April, whew the bricks w e r e brought into the laboratory for

inspection, i f w a s noted that smaller cracks were Branching out from

the main cracks. Small hairline c r a c k s were also noted on the top of a11 of the bricks. The b r i c k s w e r e , however, s t i l l relatively sound. During this spring inspection the bricks w e r e dried, weighed, and photographed. They w e r e then replaced in the copper t r a y and bedded in sand for the summer months. In the fall, as noted above, the sand

was removed and replaced with 1/2 in, of water. This procedure of spring and fall inspections was repeated until 10 June 1963 when the t e s t was discsntinued because s f the advanced state of the c r a c k s in the bricks.

Loss in weight of the bricks a s a result of outdoor exposure

i s shown in Table I.

Deterioration can be followed pictorially in F i g u r e s I. to 4. F o r comparison it should be recorded that four specimens in the s e r i e s r e f e r r e d t o e a r l i e r

QT),

of comparable saction t s the specimens listed above, failed in 15 t o 24 cycles during the laboratory test. It is of

i n t e r e s t that the l o s s in weight of the bricks increased with the suction.

Freeze-thaw cycles for the four winters w e r e determined from monthly weather surnmarie a of the local meteor slogical office and a r e listed

below. F o r t h i s determination one cycle was considered t o have

occurred when the t e m p e r a t u r e dropped below 30"

F

and then r o s e above 33"

F.

Winter

1966

(from 8 January)

5

8

The alexposure't freeze-thaw testing was c a r r i e d on beyond the point where specimens were considered t o have failed in Laboratory teats. In the latter t e s t s the specimens would undoubtedly have been

removed not l a t e r than the end sf the second winter QFigur e

21,

although t e s t s conducted at different t i m e s and judged on visual observation a r e

difficult t o a s s e s s accurately. T h e pattern s f cracking that o c c u r r e d in this t e s t w a s s i m i l a r t o that which occurred in laboratory cycling.

CONCLUSIONS

1,. F a i l u r e s in a d r y - p r e s s brick, that occurred during e a r l y

cycles of laboratory freeze-thaw t e s t s , a l s o occurred in an outdoor freeze-thaw test, but required m o r e cycles.

2, The pattern of failure was similar in both laboratory and outdoor tests.

3. The brick does not p o s s e s s sufficient durability to survive freeze-thaw cycling in a n e a r l y saturated condition.

4. The satisfactory durability s f the brick in the field must r e s u l t f r o m the fact that its degree of saturation when frozen in a

REFERENCES

Q P )

Davisoan,

J.

1. Effect of Silicone Treatment on Small Panels Assembled with High Suction Dry-Press Bricks. National Research Council, Divieion of Building Research,

DBR

Internal Report

No,

241, Ottawa, Fabruar y 1962.

(2)

Building Research

1962,

Department of Scientific and Industrial Research,

He

M. S,

O.,

London,

1963,

p. 38,

L a S IN WEIGHT

OF

THE BRICKS M ,s$

RESULT

OF

OUTDOOR EXPOSURE

Final Original Weight Weight Lose Suction, Weight, W e i g h t , Loss, s f Original,

F i g u r e 4 1 9 6 3

-

T w o V i e w s of B r i c k s at E n d of T e s t , After 2 2 5 F r e e z e - t h a w C y c l e s