Civil Engineering Reference
In-Depth Information
15.10
BORATE CEMENT
Solutions of some alkaline borates such as potassium tetraborate (K
2
B
4
O
7
.4H
2
O) or
sodium octaborate (Na
2
B
8
O
13
.4H
2
O) in combination with calcium chloride exhibit
cementing properties based on the formation of crystalline calcium borates. The bonding
of these systems is based on the development of a three-dimensional structure held
together by hydrogen bonds.
Combinations of boric oxide with polyacrylic and polyphosphonic acid exhibit quick
setting and hardening based on the formation of hydrogen-bonded complexes.
15.11
HYDRAULICALLY REACTIVE CALCIUM GERMANATES,
STANNATES, AND PLUMBATES
Dicalcium and tricalcium germanate have evoked scientific interest as their structure is
isotypic with that of dicalcium and tricalcium silicate. Both compounds possess a distinct
hydraulic reactivity. Tricalcium germanate exhibits a very fast initial hydration without
any induction period, yielding, besides calcium hydroxide, three or more crystalline
hydrate phases as products of hydration.
The hydration rate of dicalcium germanate is significantly slower, but the hydration
products are similar to those formed in the hydration of tricalcium germanate. The
bonding characteristics of the formed C-G-H phases are better than those of the C-S-H
phase formed in calcium silicate hydration. Calcium germanates have no practical use as
inorganic cements, because of their prohibitive costs.
Calcium stannates and plumbates also exhibit hydraulic reactivity, but are of no
practical interest. Calcium titanates are not hydraulically reactive.
15.12
BLENDS OF BASIC CEMENTS
Blends of two or more binders may yield products whose chemistry of hydration and
cementing characteristics may or may not differ significantly from those of pure cements
constituting the blend. The properties of the new binder will depend both on the quality
of the original binders being blended together, and on their mutual ratio in the blend. The
properties of the resulting combination of binders may be either beneficial or unwelcome.
Table 15.4 shows the properties of blends of selected cements as published by Heble
et
al.
(1997).
