Tímarit Verkfræðingafélags Íslands - 01.10.1959, Blaðsíða 21

TlMARIT VFl 1959
71
MOBERG P0Z20LANS
by
Hörður Jónsson' and Haraldur Ásgeirsson*.
Móberg is a rock formation which is found in abun-
dance in Iceland. This volcanic glass substance of dif-
ferent morphological stages has in earlier tests exhibited
decisive pozzolanic activities (1).
As the use of pozzolans may be of considerable im-
portance (2) in future constructions in this country it
was decided to conduct some research on pozzolans at
this laboratory.
This interim report is prepared in order to present the
data already obtained and to contemplate what further
studies should be carried out.
Natural pozzolans are not used intentionally in Ice-
land, in spite of numerous possible advantages. One
reason being perhaps the inability to judge pozzolans
except by long time performance tests (3,4). Pozzolans,
however, often enter unintentionally into concretes as
silty impurities in basaltic aggregates.
In the fall of 1956 fifteen samples were collected for
pozzolanic testing. These samples were gathered from
the neighbourhood of power plants already planned, in
the vicinity of Hvítá and Thjórsá rivers and from
locations near Reykjavik. Of these samples, twelve were
of moberg, one of rhyolitic pumice, one of pumice and
volcanic ash and one of olivine rich sand.
Table I lists more precisely localities where these
samples were taken. They were selected in a
close collaboration with the geologist of the Institute,
Mr. Tomas Tryggvason, who has prepared the petro-
graphic descriptions included in table I.
From the numerous methods adapted for pozzolans,
the following physical and chemical tests were performed:
1. Chemical analysis (5).
2. Surface area determinations (6).
3. Dissolved silica and reductions in alkalinity (7).
4. Ability to combine with lime (8).
5. Solubility in boiling 5% HCl (9).
6. Mortar specimens were made in accordance with
1 Chemical Engineer at the University Reseai’ch
Institute.
- in charge of the Material Testing Division of the
University Research Institute.
DIN 1164 (German specification) except that in
these 15 and 30 per sent of the cement was re-
placed with pozzolans. The mortars were cured
in a saturated lime solution for 3, 7, 28, 90, 180
and some for 360 days. (10).
7. Free lime in 180 day mortars (11).
8. Lime mortar strength determinations (12).
For preparation of mortars two grades of standard
sand were used, marked sample 16 and sample 17. No.
16 is a quax-tz sand (German cement spec.) and 17 is
Ottowa silica sand (A.S.T.M. cement spec.). These sands
were used as reference samples in a number of tests.
The cement used was type I Danish Portland cement.
Additional test under way is the pyrex glass aggregate
expansion test (13).
,,A pozzolan is a silicous or silicous and alumineous
material, which in itself possesses little or no cementi-
tious value, but will in finely divided form and in the
presence of moisture, chemically react with calcium
hydroxide at ordinary temperature to form compounds
possessing cementitious properties“ (A.S.T.M. standards
1958, Part 4, page 195).
It can be seen frorn this defination that pozzolans can
be complex materials. It is therefore to be anticipated
that these do respond diffei'ently to different tests. It is
also well known that both chemical and physical met-
hods of testing pozzolans have a large number of re-
coginzed limitations (13). Some of these test are
arbitrary ones obtained from experience with one or
moi-e types of pozzolans, (13, 14). Others are designed
to reveal a more genei'al character (15, 23.).
The data already obtained in this investigation and
the trends seen are presented in the following graphs,
tables and discussions.
1. Results of chemical analysis are shown in table
II. These analysis do not indicate any well defined re-
lation to pozzolanic activity as exhibited by other tests.
The Chemical composition of the mobei'g is a basaltic
one and resembles some Italian pozzolans as shown in
Chemistry of Cement and Concrete by Lee and Desch
(16), p. 359. Free and ci'ystalline water (13) does not
seem to influence to any noticeable extent the pozzo-
lanic activity.