Building Design and Construction Handbook - Merritt - Ventech!

9.8 SECTION NINE
ping the cone, occur; the cone is not lifted up smoothly in one movement; the cone
tips over because of filling from one side or pulling the cone to one side; or if the
measurement of slump is not made to the center vertical axis of the cone.
Various penetration tests are quicker and more suitable for untrained personnel
than the standard slump test. In each case, the penetration of an object into a flat
surface of fresh concrete is measured and related to slump. These tests include use
of the patented ‘‘Kelley ball’’ (ASTM C360, ‘‘Ball Penetration in Freshly Mixed
Hydraulic Cement Concrete’’) and a simple, standard tamping rod with a bullet
nose marked with equivalent inches of slump.
Air Content. A field test frequently required measures the air entrapped and entrained
in fresh concrete. Various devices (air meters) that are available give quick,
convenient results. In the basic methods, the volume of a sample is measured, then
the air content is removed or reduced under pressure, and finally the remaining
volume is measured. The difference between initial and final volume is the air
content. (See ASTM C138, C173, and C231.)
Cement Content. Tests on fresh concrete sometimes are employed to determine
the amount of cement present in a batch. Although performed more easily than
tests on hardened concrete, tests on fresh concrete nevertheless are too difficult for
routine use and usually require mobile laboratory equipment.
9.7 PROPERTIES AND TESTS OF HARDENED
CONCRETE
The principal properties of concrete with which designers are concerned and symbols
commonly used for some of these properties are:
ƒ� c
� specified compressive strength, psi, determined in accordance with ASTM
C39 from standard 6- � 12-in cylinders under standard laboratory curing;
unless otherwise specified, is based on tests on cylinders 28 days old
ƒ�c Ec � modulus of elasticity, psi, determined in accordance with ASTM C469; usually
assumed as Ec � w1.5 (33)�ƒ�c , or for normal-weight concrete (about 145
lb/ft 3 ), E c � 57,000�ƒ� c
w � weight, lb/ft 3 , determined in accordance with ASTM C138 or C567
ƒ t � direct tensile strength, psi
ƒ ct � average splitting tensile strength, psi, of lightweight-aggregate concretes determined
by the split cylinder test (ASTM C496)
ƒ r � modulus of rupture, psi, the tensile strength at the extreme fiber in bending
(commonly used for pavement design) determined in accordance with ASTM
C78
Other properties, frequently important for particular conditions are: durability to
resist freezing and thawing when wet and with deicers, color, surface hardness,
impact hardness, abrasion resistance, shrinkage, behavior at high temperatures
(about 500�F), insulation value at ordinary ambient temperatures, insulation at the
high temperatures of a standard fire test, fatigue resistance, and for arctic construction,
behavior at cold temperatures (�60 to �75�F). For most of the research on
these properties, specially devised tests were employed, usually to duplicate or
simulate the conditions of service anticipated. (See ‘‘Index to Proceedings of the
American Concrete Institute.’’)