Environmental Engineering Reference
In-Depth Information
Figure 3.9.
Typical profile through margin of basalt plateau, showing conditions which lead to slope insta-
bility.
Landsliding in fissured, extremely weathered basalt in Victoria, Australia is described
by MacGregor et al. (1990).
3.2.6
Alkali-aggregate reaction
As discussed in Section 3.2 above, most volcanic rocks of Tertiary and younger ages con-
tain appreciable amounts of glass, which may react with alkalis in Portland cement if the
materials are used as aggregates in concrete. In older rocks, much or all of the glassy mate-
rials have usually developed a very fine crystalline structure and are less likely to be reac-
tive. Zeolite minerals which occur in many volcanic rocks may also react with alkalis in
cement.
Guillott (1975, 1986) and McConnell et al. (1950) describe observed effects of concrete
expansion due to alkali aggregate reaction and discuss the mechanisms involved. Stark
and De Puy (1987) describe observations and tests on affected concrete at five dams in
USA. Cole and Horswill (1988) describe the deleterious effects and remedial work carried
out at Val de la Mare dam, in Jersey, Channel Islands.
Shayan (1987) and Carse and Dux (1988) discuss some limitations of chemical and
mortar bar tests for the prediction of the actual performance of aggregates in concrete.
The deleterious effects can be largely avoided by the use of low-alkali cement or poz-
zolanic additives in the concrete.
If volcanic rock is to be used as aggregate careful checking for possible alkali-aggregate
activity is advisable, particularly if low-alkali cement is not available. Studies usually
include checking of past performance, petrographic examination (ASTM, 1974a), and
laboratory testing including the Quick Chemical Test (ASTM, 1974b or Standards
Association of Australia, 1974a), the Gel-Pat Test (Building Research Station, 1958) and
the Mortar Bar Test (ASTM, 1974c or Standards Association of Australia, 1974b).
3.2.7
Volcanic rocks (intrusive and flow) check list of questions
-Vesicular zones?
- “Clinker” or “breccia” zones?
- Lava tunnels?
-Old weathered/soil profiles?
- High mass permeability?
- Interbedded pyroclastic or sedimentary materials?
