Civil Engineering Reference
In-Depth Information
2.0
MAGNESIUM OXYCHLORIDE CEMENT
2.1
Description
The first oxychloride cement was reported by Sorel.
[1]
Magnesium
oxychloride cement (MOC), referred to as Sorel cement can be formed by
mixing fine particles of calcined magnesite with magnesium chloride
solution (specific gravity 1.18-1.20). Many of its properties are superior to
those of portland cement. Most are dependent on the chemical composition
and the reactivity of calcined magnesite with magnesium chloride solu-
tion.
[2]
For example, coarse-grained magnesite compressed of grains coated
with iron minerals results in reduced strength compared to magnesite
consisting of primarily microcrystalline material.
MOC has excellent fire resistance, low thermal conductivity, good
abrasion resistance, and high values of compressive and flexural strength.
The cement has a high rate of early strength development, is lightweight,
and resistant to attack by alkalis, organic solvents, common salts, and
sultates. Its excellent binding capability enables the formation of suitable
composites containing a variety of fillers and by-product materials includ-
ing: wood flour, sawdust, asbestos fines, and stone chips.
[3]
MOC is also
commonly used as a flooring material, for heat and sound insulation
purposes, and for making artificial stone, dental cement, tiles, refractory
bricks, and foam concrete walls.
The high water solubility of MOC has limited the extent of its use
as a construction material for structural (exterior) applications. The excel-
lent engineering characteristics, however, have encouraged researchers to
seek methods to improve the water resistance of MOC.
2.2
Hydration Reactions
The reaction products in the system MgO-MgCl
2
-H
2
O are prima-
rily Mg
3
(OH)
5
Cl•4H
2
O (5 form), Mg
2
(OH)
3
Cl•4H
2
O (3 form), and
Mg
10
(OH)
18
Cl•5H
2
O.
[4]-[6]
The 5 and 3 form are present at room tempera-
ture. A molar ratio of MgO:MgCl
2
:H
2
O of 5:1:13 with some excess MgO
is recommended to form essentially the 5 form and some Mg(OH)
2
. The
activity of MgO depends on the temperature of calcination (800-1000°C)
and influences the speed of reaction and strength development. Variability
of MgO due to the source of magnesite may require adjustments to the
MgO:MgCl
2
•H
2
O ratio to achieve maximum strength.
