Environmental Engineering Reference
In-Depth Information
11.4.15
B OUND W ATER
Bound water is the percentage of water present in interlayer spaces or more firmly
bound, but not that present in pores larger than interlayer spaces. 83 The quantity
present at a given time may help indicate the degree of hydration. It is about 32%
for fully hydrated pastes of typical cements. 83 Unfortunately, the method of deter-
mination is complicated, and an approximate estimate is obtained by equilibrating
a sample, not previously dried below saturation, with an atmosphere of 11% relative
humidity. 84
11.4.16
S HRINKAGE /E XPANSION
Shrinkage or expansion 85-87 is measured as a change in length or other dimensions,
which permits assessment of the potential volumetric change. Shrinkage may be
caused by a decrease in volume of the solid phase during hydration, or be a result
of moisture loss or carbonation. Expansion may be caused by swelling of the
hydration material due to absorption of water, when freely available, by the cement
gel, or by delayed formation of high-volume hydration material such as ettringite.
Both may induce stresses in the material, which can lead to its deterioration.
11.4.17
P ENETRATION R ESISTANCE
Penetration resistance 88 is carried out to estimate the strength of a material from the
depth of penetration by a metal rod driven into the material by a given amount of
energy.
11.4.18
C ALIFORNIA B EARING R ATIO (CBR)
The CBR 89-93 is an empirical measure of the bearing capacity of a material. It attempts
to measure the resistance of the material to penetrative deformation. Unlike in other
strength tests, the CBR is reported as a percentage of the value for a standard crushed
rock material. It is widely used in pavement design for roads.
11.4.19
T ENSILE S TRENGTH
Tensile strength 35,38,94-99 is the tensile stress that leads to failure. There are three types
of strength tests: direct tensile strength, flexural strength, and splitting tensile
strength.
11.4.20
M ODULUS OF E LASTICITY
The modulus of elasticity provides an understanding of the stiffness of the material,
that is, the strain response to an applied stress. Two main test methods are available:
static modulus of elasticity and dynamic modulus of elasticity. ASTM C469-02 100
and BS 1881: Part 121 101 are for the former and ASTM C215-02 102 and BS 1881:
Part 209 103 are for the latter. The modulus of elasticity is not a constant for a material,
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