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B. Physical tests in the laboratory.—The laboratory tests are to include the examinations and determinations indicated below:

1. Mineralogical examination.

2. Specific gravity.

3. Weight per cubic foot.

4. Sifting (granulometric composition).

5. Percentage of silt and character of

same.

6. Percentage of voids.

7. Character of stone as to percentage of absorption, porosity, permeability, compressive strength, and behavior under treatment.

C. Chemical analysis.—Analyses are to be made to determine the composition and character of the stone, silt, etc., used in tests.

II. TESTS AND CLASSIFICATION OF MORTARS MADE WITH TYPICAL PORTLAND CEMENT AND

SAND, GRAVEL, AND STONE SCREENINGS (-INCH SCREEN).

A. Proportions and conditions.-Proportions to be stated by weight and volume. The unit of volume for cement is 100 pounds per cubic foot. The typical Portland cement is to be prepared by thoroughly mixing a number of brands, each of which must meet the following requirements:

Specific gravity, not less than 3.10.

Fineness, residue not more than 8 per cent on No. 100 nor 25 per cent on No. 200 sieve.

Time of setting: Initial set, not less than 30 minutes; hard set, not less than 1 hour nor more than 10 hours.

[blocks in formation]

Constancy of volume: Pats of neat cement 3 inches in diameter, one-half inch thick at center, tapering to a thin edge, shall be kept in moist air for a period of 24 hours. A pat is kept in air at normal temperature and observed at intervals for at least 28 days. Another pat is kept in water maintained as near 70° F. as practicable and observed at intervals for at least 28 days. A third pat is exposed in an atmosphere of steam above boiling water in a loosely closed vessel for 5 hours. These pats must remain firm and hard and show no signs of distortion, checking, cracking, or disfiguration.

The cement shall not contain more than 1.75 per cent anhydrous sulphuric acid nor more than 4 per cent magnesium oxide.

A test of the neat cement must be made with each mortar series for comparison of the quality of the typical Portland cement.

B. Physical tests in laboratory.—The laboratory tests include the following determinations, those designated as items 1 to 10 being each made at the ages of 7, 28, 90, 180, and 360 days:

1. Tensile strength with one part cement to varying percentages of material.

2. Compressive strength with one part cement to varying percentages of material. 3. Transverse strength with one part cement to varying percentages of material. 4. Shearing strength with one part cement to varying percentages of material.

5. Tensile strength with cement, material sifted to one size.

6. Compressive strength with cement, material sifted to one size.

7. Transverse strength with cement, material sifted to one size.

8. Shearing strength with cement, material sifted to one size.

9. Modulus of elasticity in compression of different mixtures as to proportion and size of aggregate.

10. Modulus of elasticity in tension of different mixtures as to proportion and size of aggregate.

11. Yield in mortar.

12. Porosity.

13. Permeability.

14. Volumetric changes in setting.

15. Absorption.

16. Methods of waterproofing.

17. Freezing tests.

18. Coefficient of expansion.

19. Effect of oil: (a) On hardening mortar; (b) on hardened mortar. 20. Effect of sea water.

III. TESTS AND CLASSIFICATION OF CONCRETE MADE WITH TYPICAL PORTLAND CEMENT AND STONE, STONE AND GRAVEL SCREENINGS, GRAVEL, SAND, CINDER, SLAG, ETC. A. Proportions and conditions.-Proportions to be stated by weight and volume. Unit of volume for cement, 100 pounds per cubic foot.

B. Physical tests in laboratory.—The laboratory tests include the following determinations, those designated as items 1 to 6 being each made at the ages of 30, 90, 180, and 360 days:

1. Tensile strength with different mixtures as to proportion and size of the aggregate.

2. Compressive strength of different mixtures as to proportion and size of aggregate.

3. Transverse strength of different mixtures as to proportion and size of aggregate.

4. Shearing strength with different mixtures as to proportion and size of aggregate.

5. Modulus of elasticity in compression of different mixtures as to proportion and size of aggregate.

6. Modulus of elasticity in tension of different mixtures as to proportion and size of aggregate.

7. Character of crushed stone used: (a) Weight per cubic foot; (b) size;

(c) percentage of voids; (d) percentage of silt.

8. Weight per cubic foot, uncrushed.

9. Yield.

10. Absorption.

11. Porosity.

12. Permeability.

13. Methods of waterproofing.

14. Protective influence against corrosion of metal.

15. Fire-resisting qualities: (a) Effect of heat on hardening concrete; (b) eîfect of heat on hardened concrete; (c) thickness necessary for proper insulation.

16. Freezing tests.

17. Volumetric changes.

18. Effect of vibration and of applied stress (impact): (a) On hardening of plain and reinforced concrete; (b) on hardened plain and reinforced concrete.

19. Adhesion of concrete to metal under varying conditions, for varying periods, up to at least three years: (a) Effect of shape; (b) effect of embedded length; (c) effect of various kinds of loading; (d) effect of chemical action; (e) relative value of surface adhesive resistance and grip. 20. Effect of oils: (a) On hardening concrete; (b) on hardened concrete.

21. Coefficient of expansion.

22. Effect of sea water.

C. Full-size tesis. The laboratory tests of full-size beams, building blocks, and bricks include the following:

1. Beams of various spans, sections, and compositions.

2. Building blocks and bricks, as to (a) compressive strength, wet and dry mixtures; (b) transverse strength, wet and dry mixtures; (c) shearing strength, wet and dry mixtures; (d) absorption, wet and dry mixtures; (e) permeability; (ƒ) methods of waterproofing; (g) effect of accelerating the hardening of concrete blocks by means of live steam, etc.; (h) fire-resisting qualities; (i) efflorescence.

IV. TESTS OF REINFORCED CONCRETE.

A. Beams. Tests of beams to include determinations of

1. Effect of amount of reinforcement.
2. Effect of character of reinforcement.

3. Effect of form, size, and position of
reinforcing bars.

4. Effect of initial stress in reinforcement.

5. Effect of different manners of loading. 6. Methods of providing for diagonal

stresses.

7. Effect of variation in section, such as trapezoidal, T-shaped, etc.

8. Effect of variation in length and depth.

9. Effect of restraining the ends. 10. Effect of repetitive loading.

B. Columns.-Tests of columns to include determinations of

1. Effect of amount of reinforcement.

2. Effect of disposition of reinforcement:

4. Effect of character and eccentricity of

loading.

(a) Longitudinal; (b) hooped; (c) 5. Effect of variation in section, such as combination of (a) and (b).

square, round, and rectangular.

3. Effect of form, size, and position of 6. Effect of fixing the ends. reinforcement.

C. Slabs.-Tests to be made of slabs1. Supported at two or four edges. 2. Fixed at two or four edges.

4. Effect of concentration of load.

5. Variation in per cent of reinforcement. 6. Variation in span and thickness.

3. Use of expanded metal, wires, etc.
D. Arches.-Tests to be made of forms and features of arches as follows:
1. Continuous ring.

2. Hinged.

4. Shape.

5. Span and rise.

3. Voussoirs.

WORK AT TECHNOLOGICAL INSTITUTIONS.

In connection with the work at the laboratories it has been deemed desirable by the national advisory board and the joint committee on concrete and reinforced concrete to invite the cooperation of those technological institutions possessing proper facilities for carrying on investigations comprising, in part, tests in which the methods of execution are still open to formulation and which involve general phenomena. In addition to this, it was thought desirable for this laboratory to act in an advisory capacity to any laboratory desiring to conduct investigations along these lines. Among the topics which are available for such investigations may be mentioned—

.

1. Shearing: Comparison of methods.

2. Modulus of elasticity: Comparison of methods.

3. Protective influence of concrete against corrosion.

4. Fire-resisting qualities of concrete.

5. Methods of waterproofing.

6. Coefficient of expansion.

7. Effect of vibration and applied stress.

8. Adhesion of concrete to metal.

9. Reinforced-concrete beams: (a) Effect of different manners of loading; (b) methods of providing for diagonal stresses; (c) effect of variation in section; (d) effect of restraining ends; (e) amount and character of reinforcement.

10. Reinforced-concrete columns: Method of testing.

SEQUENCE OF TESTS.

It is evident that the investigations embraced in the foregoing programme will cover a number of years, and it is therefore the aim of the United States Geological Survey to investigate first those questions which will yield information most urgently needed in constructive work by the different branches of the Government, the policy being to work continuously upon as many of the problems as the facilities and appropriation will permit.

As the investigation progresses it may be found necessary to do considerable experimental work in determining the proper methods to be followed, the sources of error to be guarded against, and the probable causes of given phenomena, and the programme may therefore be varied according to conditions.

SUMMARY.

In the following pages the character of the investigations being conducted at the laboratories is presented, together with a description of the apparatus and methods of testing, methods of computing, and forms used for recording the results, the work of each section being separately described.

The methods of testing are given in some detail without, however, any reference to the investigations which led up to their adoption. These investigations often entailed a series of comparative tests between a number of different methods. No change of method is made without a thorough series of tests on identical material by both the old and the proposed method, not only to determine the relative advantages and disadvantages of the two methods, but also to have an equation between the results obtained by both methods by which, should the new method be adopted, the results obtained by the old method would be comparable with those obtained by the new.

The theories underlying the methods of testing are not touched upon except in one instance. The methods used in testing beams are somewhat different from those used by other investigators, hence the theories underlying the methods used at these laboratories are explained.

The methods used in transforming the data obtained at the testing machines into form for publication are not treated in detail, an outline only being given.

a See Form B (p. 24) and footnote relating thereto (p. 23).

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