Tímarit Verkfræðingafélags Íslands - 01.10.1959, Side 24

Reduction in Alkalinity in mM/1.
74
TlMARIT VFl 1959
Dissolved Silica in mM/1.
Grapli I. Notice the hig-h reduction in alkalinity by the
moberg samples.
influences in a mortar mix. What compounds are formed
when pozzolan reacts with lime is by no means certain.
Investigators differ on the subject. Generally, how-
ever, some forms of calcium silicates, calcium aluminium
silicates, calcium aluminates, or zeolites are expected.
A pozzolan could form one set of cementitious com-
pounds at one temperature and in one system, and an-
other set in a different system at a different tempera-
ture. Minor components might also play an important
part. Italian investigators found cubic 3 CaO . ALOa • 6HaO
at 40° C but hydrogarned of approximate compostition
3 CaO . A1203.0.33 SiO, . 5.3 H,0 at 50° C (15). Such
variation in compound formation may have bearing on
the low results obtained in the lime mortar strenght
test.
If inert pulverized material is addet to a mortar
mix it may alter the gradation of the aggregates, in-
crease denseness and thus increase workability and
strength, (19, 20, 21). The strenght shown by the
cement mortar tests could thus be partly due to physical
factors (22).
As mentioned in the introduction, moberg is a rock
formation characteristic for Iceland. As pozzolan it
Grapli II. Notice the relation between strenght and the abstorption of lime for 30% re-
placement. Samples No. 2, 4 and 15 are not moberg.