Civil Engineering Reference
In-Depth Information
respects similar to comparable concretes made with port-
land cement.
sions of a concrete element, resulting in increased paste
porosity and decreased compressive strength. At low
water-cement ratios, there is insufficient space for all the
calcium aluminate to react and form CAH
10
. The released
water from conversion reacts with more calcium alumi-
nate, partially compensating for the effects of conversion.
Concrete design strength must therefore be based on the
converted strength. Because of eventual conversion,
calcium aluminate cement is often used in nonstructural
applications and used with caution (or not at all) in struc-
tural applications (
Taylor 1997
).
Geopolymer Cements
Geopolymer cements are inorganic hydraulic cements that
are based on the polymerization of minerals (
Davidovits,
Davidovits, and James 1999
). The term more specifically
refers to alkali-activated alumino-silicate cements, also
called zeolitic or polysialate cements. They have been used
in general construction, high-early strength applications,
and waste stabilization. These cements do not contain
organic polymers or plastics.
Magnesium Phosphate Cements
Magnesium phosphate cement is a rapid setting, early
strength gain cement. It is usually used for special applica-
tions, such as repair of pavements and concrete structures,
or for resistance to certain aggressive chemicals. It does not
contain portland cement.
Ettringite Cements
Ettringite cements are calcium sulfoaluminate cements that
are specially formulated for particular uses, such as the
stabilization of waste materials (
Klemm 1998
). They can be
formulated to form large amounts of ettringite to stabilize
particular metallic ions within the ettringite structure.
Ettringite cements have also been used in rapid setting
applications, including use in coal mines. Also see
“Expansive Cements” above.
Sulfur Cements
Sulfur cement is used with conventional aggregates to make
sulfur cement concrete for repairs and chemically resistant
applications. Sulfur cement melts at temperatures between
113°C and 121°C (235°F and 250°F). Sulfur concrete is main-
tained at temperatures around 130°C (270°F) during mixing
and placing. The material gains strength quickly as it cools
and is resistant to acids and aggressive chemicals. Sulfur
cement does not contain portland or hydraulic cement.
Rapid Hardening Cements
Rapid hardening, high-early strength, hydraulic cement is
used in construction applications, such as fast-track
paving, where fast strength development is needed (design
or load carrying strength in about four hours). These
cements often use calcium sulfoaluminate to obtain early
strength. They are classified as Types VH (very high-early
strength), MR (middle range high-early strength), and GC
(general construction).
SELECTING AND SPECIFYING CEMENTS
When specifying cements for a project, be sure to check the
availability of cement types as discussed below; specifica-
tions should allow flexibility in cement selection. Limiting
a project to only one cement type, one brand, or one stan-
dard cement specification can result in project delays and it
may not allow for the best use of local materials. Cements
with special properties should not be required unless
special characteristics are necessary. In addition, the use of
supplementary cementing materials should not inhibit the
use of any particular portland or blended cement. The proj-
ect specifications should focus on the needs of the concrete
structure and allow use of a variety of materials to accom-
plish those needs. A typical specification may call for port-
land cements meeting ASTM C 150 (AASHTO M 85) or C
1157, or for blended cements meeting ASTM C 595
(AASHTO M 240) or C 1157.
If no special properties, (such as low-heat generation
or sulfate resistance) are required, all general use cements
should be allowed, such as Types I, GU, IS, IP, I(SM), or
I(PM). Also, it should be noted that some cement types
meet the requirements of other types as well; for example,
all Type II cements meet the requirements of Type I, but not
all Type I cements meet the requirements of Type II. See
Tables 2-3 and 2-4 for guidance on using different cements.
Calcium Aluminate Cements
Calcium aluminate cement is not portland cement based.
It is used in special applications for early strength gain
(design strength in one day), resistance to high tempera-
tures, and resistance to sulfates, weak acids, and seawater.
Portland cement and calcium aluminate cement combina-
tions have been used to make rapid setting concretes and
mortars. Typical applications for calcium aluminate
cement concrete include: chemically resistant, heat resist-
ant, and corrosion resistant industrial floors; refractory
castables; and repair applications. Standards addressing
these cements, include British Standard BS 915-2 or French
Standard NF P15-315.
Calcium aluminate cement concrete must be used at
low water-cement ratios (less than 0.40); this minimizes the
conversion of less stable hexagonal calcium aluminate hy-
drate (CAH
10
) to the stable cubic tricalcium aluminate
hydrate (C
3
AH
6
), hydrous alumina (AH
3
), and water. With
time and particular moisture conditions and temperatures,
this conversion causes a 53% decrease in volume of hyd-
rated material. However, this internal volume change
occurs without a dramatic alteration of the overall dimen-
