Civil Engineering Reference
In-Depth Information
cement, by strength category. In the research discussed here, mechanical
trials were conducted with mortars prepared with a CEM I 42.5N Portland
cement (defined in standard EN 196-1, 2005), blended with a series of
natural pozzolans: pumice from Ciudad Real, volcanic tuff from the Canary
Islands and almería and opaline from Salamanca. Two replacement ratios
were used: 20 and 35%.
The mechanical findings (Fig. 4.5) showed that the mortars containing 20%
pumice from Ciudad Real had a 28-day mean strength of 45 MPa, or 90%
of the strength found for Portland cement alone (100/0). When 35% of the
cement was replaced, however, compressive strength was 19% lower than in
the control. Similarly, Hossain (2003, 2005) and Siddique (2011), studying
volcanic ash and pumice powder, reported that the compressive strength
of mortar containing blended cement declined with rising percentages of
pozzolan. Mehta (1981), in a study with blended Portland cements containing
10, 20 and 30% Santorin earth, found that the 7-day strength was proportional
to the cement content in the blend. In the 28-day specimens, however, the
cement containing 10% pozzolan was 6% stronger than the control, while
strength in the 20 and 30% pozzolan blends was only 7 and 18% lower than
in pure Portland cement.
Canary Island tuff raised mortar mechanical strength. When the ratio was
80/20, the 28-day values were similar to the findings for cement (98.8%).
When the ratio was 65/35, strength in the samples was 90% of the value
for the unblended cement. By contrast, the Almería tuff exhibited deficient
behaviour, with 28-day values for the 65/35 blend of 24 MPa or 50% of
Portland cement strength. By contrast, other authors reported good results
for cements with a high with tuff content. Uzal and Tutanli (2003, 2012)
60
7 days
28 days
50
40
30
20
10
0
100/0 80/20 CR 65/35 CR 80/20 Ca 65/35 Ca 80/20 Al 65/35 Al 80/20 Sa 65/20 Sa
Cement/addition
4.5
Compressive strength in mortars with different cement : addition
ratios.
