during production. Many that were developed in east Europe generally suffer from low
strength-gain characteristics. Thus, they are not expected to be good candidates for low-
However, other fast-setting and very high early strength portland-cement-based binders
have been manufactured that have very good potential for low-temperature applications.
The basic matrix of these modified cements are portland cements that contain additional
phases which can react with water very rapidly, causing an early onset of setting and hard-
ening. These cements are usually manufactured from a single homogeneous clinker or can
be produced by intergrinding and/or blending special clinkers and additives with regular
portland cement clinkers. Since they are special cements and are not used routinely, they
are generally two to three times more expensive than regular portland cement. Important
physicochemical properties of these cements are described below.
Regulated-set or Jet cements
Regulated-set cement, also called Jet cement in Japan, is manufactured under patents
issued to the U.S. Portland Cement Association. A modified portland cement clinker con-
taining mainly alite (tricalcium silicate, C3S) and a calcium fluoroaluminate (11 CaO7
Al2O3CaF2) is made. A suitable proportion of the fluoroaluminate clinker is blended with
normal portland cement clinker and calcium sulfate so that the final cement contains about
20 to 25 percent of the fluoroaluminate compound and about 10 to 15 percent calcium
sulfate. The cement is generally very fast setting at room temperature, but can be retarded
to the desired set time by using citric acid, sodium sulfate, calcium hydroxide, boric acid,
and other retarders. A chloride analog of this cement was also made in the Soviet Union.
However, since the presence of chloride ions was found to induce corrosion in the steel
reinforcements, this cement has not enjoyed much popularity.
The basic hydration reactions of the silicates present in this cement are the same as for
regular portland cement. However, the hydration of the fluoroaluminate, which is respon-
sible for the rapid-setting characteristics of Jet cement, is extremely complex, and is further
complicated by the presence of other set-regulating compounds that are added to achieve
reasonable working time. The early strength development of regulated-set cement is due to
the rapid reaction of the haloaluminate phase with calcium sulfate forming ettringite. The
ultimate strength and other physical properties of this cement are comparable to those of
the portland cement except that, because of the high content of the reactive aluminate phase,
the sulfate resistance of structures made with these cements will be poor.
Regulated-set cement is very popular in Japan and is quite frequently used for winter
constructions and repairs at ambient temperatures of 3 to 5C (27 to 23F), although
the curing operation is facilitated by covering the constructed surfaces with canvas sheets.
The formation of large quantities of ettringite is responsible for the properties of
sulfoaluminate-phase-containing cement, also known as the very high early (VHE) strength
cement. The VHE or the sulfoaluminate cement is commercially available (manufactured)
in the United States. In contrast to the expansive Type K cements, the formation of ettringite
when these cements come in contact with water gives rise to rapid strength development.
The processing science of these cements has improved quite rapidly in recent years. Minor
expansions that were often experienced earlier with these cements have been controlled to
the point that these cements are sold as zero-shrinkage cements. In these cements, like the
haloaluminate cement, the ettringite formation is very rapid, occurring largely before the
paste has gained strength and well before hydration of the calcium silicates. The ettringite
formation reaction for this cement can be written as
4CaO3Al2O3 SO3 + 8CaSO4 + 6Ca(OH)2 + H2O = 3(6CaOAl2O33SO332H2O).
This cement is being marketed for special use and has limited use at low temperatures.