The effect of calcined clays of the swelling type, on the strength and expansion behavior
of Portland limestone cement is studied at 5oC. Local clays were thermally activated by burning one
hour at 900 °C and were ground to a Blaine of 2842 (cm2/g). The pozzolanic reactivity of the
activated clays was defined chemically and according to ASTM C311/C311M-13. Portland
limestone cement was prepared by replacing 30% CEM I 42.5 N by limestone powder. Pozzolanic
cements were prepared by replacing 10 and 20% of the limestone powder by calcined clays, the
mixes were used to replace 30% of CEM I. Mortars specimens pre-cured for 28-day long as well as
for a short period of one day, were immersed in sulfate solutions at 5oC for time up to 90 days. The
compressive strength and length change were measured for the samples.
The results show that replacement of limestone with calcined clays improves the compressive
strength and the expansion of Portland limestone cement mortars in water and sulfate solutions.
Ettringite was detected in the expanded mortars and no thaumasite formed. The results are
interpreted in terms of the mechanism of thaumasite formation. |
