It is also proposed to subject these test pieces, some made with water
of known purity, and others with alkaline water, to contact with
alkaline soils near the projects, and with soil of known composition
near the testing laboratories at Pittsburg. As these tests progress and
other lines of investigation are developed, the programme will be
extended, in the hope that the inquiry may develop methods of preparing
and mixing concrete and reinforced concrete which can be used in
alkaline soils without danger of disintegration.
Investigations into the effect of salt water on cement mortars and
concretes, and the effect of electrolysis, are being conducted at
Atlantic City, N.J., where the test pieces may be immersed in deep sea
water for longer or shorter periods of time.
At the Pittsburg laboratory a great amount of investigative work is done
for the purpose of determining the suitability and availability of
various structural materials submitted for use by the Government. While
primarily valuable only to the Government, the results of these tests
are of indirect value to all who are interested in the use of similar
materials. Among such investigations have been those relating to the
strength, elasticity, and chemical properties of wire rope for use in
the Canal Zone; investigations of the suitability and cementing value of
concrete, sand, stone, and pozzuolanic material found on the Isthmus;
investigations as to the relative resistance to corrosion of various
types of wire screens for use in the Canal Zone; into the suitability
for use, in concrete sea-wall construction, of sand and stone from the
vicinity of San Francisco; into the properties of reinforced concrete
floor slabs; routine tests of reinforcing metal, and of reinforced
concrete beams and columns, for the Supervising Architect of the
Treasury Department, etc. The results have been set forth in three
bulletins[9] which describe the methods of conducting these tests and
also tests on constituent materials of concrete and plain concrete
beams. In addition, there are in process of publication a number of
bulletins giving the results of tests on reinforced concrete beams,
columns, and floor slabs, concrete building blocks, etc.
The Northampton laboratory was established because it is in the center
of the Lehigh cement district, and therefore available for the mill
sampling and testing of purchases of cement made by the Isthmian Canal
Commission; it is also available for tests of cement purchased in the
Lehigh district by the Supervising Architect and others. It is in a
building, the outer walls of which are of cement plaster applied over
metal lath nailed to studding. The partitions are of the same
construction, and the floors and roof are of concrete throughout.
The inspection at the factories and the sampling of the cement are under
the immediate direction of the Commission; the testing is under the
direction of the U.S. Geological Survey. A large force of employees is
required, in view of the magnitude of the work, which includes the daily
testing of consignments ranging from 5,000 to 10,000 bbl., sampled in
lots of 100 bbl., which is equivalent to from 50 to 100 samples tested
per day.
The cement to be sampled is taken from the storage bins and kept under
seal by the chief inspector pending the results of the test. The
quantity of cement sampled is sufficient for the tests required under
the specifications of the Isthmian Canal Commission, as well as for
preliminary tests made by the cement company, and check tests made at
the Geological Survey laboratory, at Pittsburg.
The tests specified by the Commission include determination of specific
gravity, fineness of grinding, time of setting, soundness, tensile
strength (with three parts of standard quartz sand for 7 and 28 days,
respectively), and determination of sulphur anhydride (SO_{3}), and
magnesia (MgO).
The briquette-making and testing room is fitted with a mixing table,
moist closet, briquette-storage tanks, and testing machines. The mixing
table has a concrete top, in which is set plate glass, 18 in. square and
1 in. thick. Underneath the table are shelves for moulds, glass plates,
etc.
The moist closet, 5 ft. high, 3 ft. 10 in. wide, and 1 ft. 8 in. deep,
is divided into two compartments by a vertical partition, and each
compartment is fitted with cleats for supporting thirteen tiers of glass
plates. On each pair of cleats, in each compartment, can be placed four
glass plates, each plate containing a 4-gang mould, making storage for
416 briquettes. With the exception of the doors, which are of wood lined
with copper, the closet is of 1:1 cement mortar, poured monolithic, even
to the cleats for supporting the glass plates.
The immersion tanks, of the same mortar, are in tiers of three,
supported by a steel structure. They are 6¼ ft. long, 2¼ ft. wide, and 6
in. deep, and 2,000 briquettes can be stored in each tank. The overflow
from the top tank wastes into the second, which, in turn, wastes into
the third. Water is kept running constantly.
The briquette-testing machine is a Fairbanks shot machine with a
capacity of 2,000 lb., and is regulated to apply the load at the rate of
600 lb. per min. Twenty-four 4-gang moulds, of the type recommended by
the Special Committee on Uniform Tests of Cement, of the American
Society of Civil Engineers, are used.
The room for noting time of set and soundness is fitted with a mixing
table similar to that in the briquette-making room. The Vicat apparatus
is used for determining the normal consistency, and the Gilmore
apparatus for the time of setting. While setting, the soundness pats are
stored in galvanized-iron pans having about 1 in. of water in the
bottom, and covered with dampened felt or burlap. The pats rest on a
rack slightly above the water and well below the felt.
For specific gravity tests, the Le Chatelier bottles are used. A pan, in
which five bottles can be immersed at one time, is used for maintaining
the benzine at a constant temperature. The samples are weighed on a pair
of Troemner’s No. 7 scales.
The fineness room is fitted with tables, two sets of standard No. 100
and No. 200 sieves, and two Troemner’s No. 7 scales similar to those
used for the specific gravity tests.
The storage room is fitted with shelves for the storage of samples being
held for 28-day tests.
The mould-cleaning room contains tables for cleaning moulds, and racks
for air pats.
An effort is made to keep all the rooms at a temperature of 70° Fahr.,
and, with this in view, a Bristol recording thermometer is placed in the
briquette-room. Two wet-and-dry bulb hygrometers are used to determine
the moisture in the air.
Samples are taken from the conveyor which carries the cement to the
storage bins, at the approximate rate of one sample for each 100 bbl.
After each 4,000-bbl. bin has been filled, it is sealed until all tests
have been made, when, if these have been satisfactory, it is released
for shipment.
The samples are taken in cans, 9 in. high and 7½ in. in diameter. These
cans are delivered in the preparation room where the contents are mixed
and passed through a No. 20 sieve. Separate samples are then weighed out
for mortar briquettes, for soundness pats, and for the specific-gravity
and fineness tests. These are placed in smaller cans and a quantity
sufficient for a re-test is held in the storage room awaiting the
results of all the tests.
The sample for briquettes is mixed with three parts standard crushed
quartz, and then taken to the briquette-making room, where eight
briquettes are made, four for 7-day and four for 28-day tests. These are
placed in the moist closet in damp air for 24 hours, then removed from
the moulds, and placed in water for the remainder of the test period. At
the proper time they are taken from the immersion tank and broken.
From the sample for soundness, four pats are made. The time of setting
is determined on one of these pats. They are placed in the pan
previously described, for 24 hours, then one is placed in running water
and one in air for 28 days. The others are treated in the boiler, one in
boiling water for 3 hours and one in steam at atmospheric pressure for 5
hours.
The sample taken for specific gravity and fineness is dried in the oven
at 100° cent. in order to drive off moisture. Two samples are then
carefully weighed out, 50 grammes for fineness and 64 grammes for
specific gravity, and the determinations are made. As soon as anything
unsatisfactory develops, a re-test is made. If, however, the cement
satisfies all requirements, a report sheet containing all the data for a
bin, is made out, and the cement is ready for shipment. From every fifth
bin, special neat and mortar briquettes are made, which are intended for
tests at ages up to ten years.
_Salt-Water Laboratory._--The laboratory at Atlantic City, for
conducting investigations into the effects of salt water on concrete and
reinforced concrete, is situated so that water more than 25 ft. deep is
available for immersion tests of the setting and deterioration of such
materials.
Through the courtesy of the municipality of Atlantic City, Young’s
cottage, on old Young’s Pier, has been turned over, at a nominal rental,
to the Geological Survey for the conduct of these tests. The laboratory
building is about 700 ft. from the boardwalk, and occupies a space about
100 by 45 ft. It is one story high, of frame-cottage construction, and
stands on wooden piles at one side of the pier proper and about 20 ft.
above the water, which is about 19 ft. deep at this point. Fresh running
water, gas, electric light, and electric power are supplied to the
building (Fig. 6).
In this laboratory investigations will be made of the cause of the
failure and disintegration of cement and concrete subjected to the
action of sea water. Tests are conducted so as to approach, as nearly as
possible, the actual conditions found in concrete construction along the
sea coast. All sea-water tests are made in the ocean, some will probably
be paralleled by ocean-water laboratory tests and all by fresh-water
comparative tests.
Cements, in the form of pats, briquettes, cubes, cylinders, and in a
loose ground state, and also mortars and concretes in cube, cylinder,
and slab form, are subjected to sea water.
The general plan for the investigations is as follows:
1.--Determination of the failing elements and the nature of the failure;
2.--Determination of the value of the theories advanced at the present
time; and,
3.--Determination of a method of eliminating or chemically recombining
the injurious elements.
Preliminary tests are in progress, including a study of the effect of
salt water on mortars and concretes of various mixtures and ages. The
proportions of these mixtures and the methods of mixing will be varied
from time to time, as suggested by the progress of the tests.
_Fire-Proofing Tests._--Tests of the fire-proofing and fire-resistive
properties of various structural materials are carried on in the
laboratories in Building No. 10, at Pittsburg, and in co-operation with
the Board or Fire Underwriters at its Chicago laboratory (Fig. 2, Plate
XIII). These tests include three essential classes of material: (_a_),
clay products, protective coverings representative of numerous varieties
of brick and fire-proofing tiles, including those on the market and
those especially manufactured for these tests in the laboratory at
Pittsburg; (_b_), characteristic granites of New England, with
subsequent tests of the various building stones found throughout the
United States; and (_c_), cement and concrete covering material,
building blocks, and concrete reinforced by steel bars embedded at
different depths for the purpose of studying the effect of expansion on
the protective covering.
In co-operation with the physical laboratory, these tests include a
study of the relative rates of conductivity of cement mortars and
concretes. By embedding thermo-couples in cylinders composed of the
materials under test, obtaining a given temperature by an electric coil,
and noting the time required to raise the temperature at the various
embedded couples to a given degree, the rate of conductivity may be
determined. Other tests include those in muffles to determine the rate
of expansion and the effect of heat and compressive stresses combined on
the compressive strength of the various structural materials. The
methods of making the panel tests, and the equipment used, are described
and illustrated in Bulletin No. 329, and the results of the tests have
been published in detail.[10]
_Building Stones Investigations._--The field investigations of building
stones are conducted by Mr. E. F. Burchard, and include the examination
of the various deposits found throughout the United States. A study of
the granites of New England has been commenced, which includes the
collection of type specimens of fine, medium, and coarse-grained
granites, and of dark, medium, and light-gray or white granites. A
comparative series of these granites, consisting of prisms and cubes of
4 and 2 in., respectively, has been prepared.
[Illustration: Fig. 6.