NATIONAL BUREAU OF STANDARDS REPORT

6682

Freezing and Thawing Tests of Grout Pocket Assemblies

as Used at Welded Joints of Precast Concrete Panels

by

Leopold F, Skoda

Report to

Bureau of Yards and Docks

Department of the Navy

<NB^

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NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT NBS REPORT

1001-12-10411 March 4, 1960 6682

Freezing and Thawing Tests of Grout Pocket Assemblies

as Used at Welded Joints of Precast Concrete Panels

by

Leopold F. Skoda

To

Bureau of Yards and Docks

Department of the Navy

IMPORTANT NOTICE

NATIONAL BUREAU OF STAr

, Intended for use within the G' to additional evaluation and re' listing of this Report) either In the Office of the Director, Natl however, by the Government aj to reproduce additional copies

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST)

on October 9, 2015.

gress accounting .documents

ally published It Is subjected

production, or open-literature

n Is obtained In writing from

jch permission Is not needed,

epared If that agency wishes

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
4 ’
FREEZING AND THAWING TESTS OF GROUT POCKET ASSEMBLIES

AS USED AT WELDED JOINTS OF PRECAST CONCRETE PANELS

Leopold F. Skoda

Five specimens representing grout pocket assemblies used to

protect welded joints in precast concrete panels were subjected

to 250 cycles of freezing and thawing in order to determine the

effectiveness of epoxy/Thiokol adhesives when applied to the sur- faces of grout pockets prior to grouting. The specimens of plain

concrete were cast in two halves and were 14- by 14- by 2 5/8 in.

in size when placed together. The resulting grout pocket was

8 1/4 in. square at the top surface and 1 5/8 in. deep. The sides

of the pockets were cast at an angle of 45° with the horizontal so that the bottom of the pocket was a 5 in. square. The sides and

bottom of four of the specimens were coated with various epoxy/

Thiokol adhesive compounds just prior to grouting. The fifth specimen was used as a control specimen and was not coated. The speci- mens were frozen in air at a temperature of 2 ± 1°F, and were thawed

in a water bath at a temperature of 77 ± 1°F. The control specimen

failed after 96 cycles of freezing and thawing while no visible

damage was apparent in the coated specimens after 250 cycles. These

results clearly indicate that the use of epoxy/Thiokol adhesive mixtures significantly increases the durability of grout pocket assem- blies by improving the bond between the grout and the hardened concrete.

1. INTRODUCTION

The object of these tests was to observe the effect of adhesive coatings on the freezing and thawing properties of grout pocket assemblies as used in the 16- by 30-ft panel frame structure. The grout pockets that en- closed the welded knee joint connections did not provide adequate protection

against water penetration when subjected to weathering. It was felt that

the application of adhesive coatings to the grout pockets just prior to filling them with grout would increase their resistance to freezing and thawing

thereby improving the watertightness of the assembly. A number of simulated

grout pockets were cast of concrete and coated with various adhesives prior

to grouting. These specimens were then subjected to 250 cycles of freezing

and thawing in order to determine the effectiveness of the various adhesive

coatings

.

2 .

2. DESCRIPTION OF TEST SPECIMENS AND PROCEDURES

The simulated grout pocket assemblies were cast of plain concrete in

two pieces. When placed together the dimensions of the grout pocket

duplicated precisely those used in the panel frame structure. A recess

was also cast into each half so that upon assembly, a 1/2- by 1/2-in.

calking joint was formed at the mid-plane of each specimen, as shown in

figure 1. Five such specimens were prepared for the test. Four were

used to evaluate the adhfesive coatings and the fifth was used as a control

specimen.

The adhesives chosen for this test were epoxy/Thiokol formulations.

Past experience and knowledge of the mechanical and physical properties of

epoxy/Thiokol adhesives indicated that desirable results could be obtained.

The four major ingredients used in the epoxy/Thiokol adhesive compounds were:

(a) liquid epoxy resin (Epon 828, Shell Chemical Company), (b) liquid polymer

'.(Thiokol LP-3, Thiokol Chemical Company), (c) amine catalyst (diethylenetriamine, Carbide & Carbon Chemical Company), and (d) an inert filler (Cab-0-

Sil, Godfrey L. Cabot, Inc.). The proportions of epoxy to Thiokol used were

1:1, 1.5:1, 2:1, and 1:0, by weight. The inert filler was proportioned

1:20, by weight, of epoxy and the amine catalyst was proportioned to 8 percent by weight of epoxy. These particular ratios of epoxy to Thiokol were

used because the workability and pot life of each was suitable for this kind

of application.

The procedure used for preparing and filling the grout pockets was the same for all specimens. The pockets were first wire brushed in order to re- move any loose cementitious material with no attempt being made to roughen

the surfaces. An adhesive mixture was then brushed on to each pocket. A

single batch of grout had been mixed and was used to fill the pockets just

after they were coated with adhesive. The grout used had a sand to cement

ratio of 3:1, by weight, with the cement being of Type III. The specimens were then allowed to cure under damp burlap for 7 days. The 7-day compressive strength of 2 in. control cubes that had been cast at the time of

grouting averaged 10,540 psi.

To complete the specimens a Thiokol base calking compound was applied

to the 1/2- by 1/2-in. recess that had been formed at the center section of

each specimen. The calking was allowed to cure for two weeks before the

freezing and thawing tests were initiated.

A malfunction of the automatic testing equipment necessitated the first

113 cycles of freezing and thawing to be a manual operation. The specimens

were first soaked in water at room temperature for 48 hours. They were

then placed in a refrigerated chamber maintained at 3 ± 1°F for 7 hours.

Upon removal from the freezing chamber they were carefully inspected and

3.

then placed in a water bath and allowed to thaw overnight at a temperature

of 73 ± 2°F. This procedure yielded only 5 cycles of freezing and thawing

per work week.

The remaining 137 cycles were completed in automatically controlled

equipment that was capable of subjecting the specimens to two cycles of

freezing and thawing per day. The equipment was allowed to run continuously, thus yielding 14 cycles per week.

Changing the freezing and thawing operation from a manual to an automatic method altered the procedure somewhat. In the automatic method,

both freezing and thawing was accomplished with the specimens remaining

undisturbed in the equipment. To begin a freezing cycle one hour's time was required to reach a temperature of 2 ± 1°F. This temperature was maintained for 4 hours. The thawing cycle then began with heated water being

pumped into the chamber that contained the specimens. Five hours were re- quired for the heated, circulating water to elevate the temperature to

77 ± 1°F. This temperature was maintained for 2 hours after which the

chamber was pumped dry in preparation for another freezing cycle. Under

these conditions only a weekly inspection of the specimens was practical.

The tests were terminated after the specimens had been subjected to 250

cycles of freezing and thawing.

3. RESULTS

Figure 2 is a photograph of the top and bottom of the specimens before and after testing. The Roman numerals on the specimens indicate the

epoxy/Thiokol ratios used to coat the pockets prior to grouting and are

as follows: I - 1:1, II - 1.5:1, III - 2:1, IV - 1:0, and V - control.

No visible effects can be seen in specimens I through IV with the exception of separation of the calking compound from the sides of the joints.

As the study of the behavior of the calking compound was not the main objective of these tests, this observed separation was disregarded when con- sidering the grout pocket behavior. The control specimen. No. V, which was

not coated prior to grouting failed after 96 cycles. The first indication

of failure was observed after the 92nd cycle when hairline cracks formed

about the periphery of the grout pocket. After the 96th cycle the grout was completely dislodged from the pocket. When this happened the calked

joint was the only thing that held the specimen together. The specimen

broke in two at the calked joint as a result of subsequent handling and

not as a result of freezing and thawing.

The results of these tests indicate that an adhesive coating applied

to the cast surface of a grout pocket prior to grouting increases significantly the durability of the assembly. Its resistance to freezing and thawing increases by at least 21/2 times, as measured by the number of freezethaw cycles. However, this figure cannot be projected into a prediction

4.

of service life in the field because of the lack of confirming field trial

data, and the fact that no laboratory failures of coated specimens occurred.

As none of the coated specimens failed, no conclusion can be drawn with

regard to the relative merits of any of the epoxy/Thiokol compounds used.

The selection of a particular mixture would have to be based on other factors

such as cost, workability, pot life, and mechanical properties.

A summary of the conclusions resulting from this investigation are as follows

;

1. All of the epoxy/Thiokol adhesive mixtures tested increased significantly the durability of the grouted pockets. The resistance to freezing

and thawing of the grout pocket assemblies increased by at least 2 1/2 times

as compared with an untreated grout pocket.

2. The four epoxy/Thiokol mixtures tested displayed no differences after

being subjected to 250 cycles of freezing and thawing.

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FIGURE I. FREEZING a THAWING SPECIMEN OF GROUT POCKET
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VIEW OF TOP OF SPECIMENS BEFORE TEST

VIEW OF TOP OF SPECIMENS AFTER TEST

VIEW OF BOTTOM OF SPECIMENS BEFORE TEST

VIEW OF BOTTOM OF SPECIMENS AFTER TEST

FIGURE 2. SPECIMENS SUBJECTED TO FREEZING 8 THAWING TESTS

U.S. DEPARTMENT OF COMMERCE

Frederick H. Mueller, Secretary NATIONAL BUREAU OF STANDARDS

A. V. ABtih, Director THE NATIONAL BUREAU OF STANDARDS

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