HCSFA concretes have equal compressive strength fc values with
the reference concrete, both at early (7 days) and late (28 days)
age; afterwards, the composite concretes exhibit higher values
of strength than the OPC concrete. This is related with the low
porosity of HCSFA concrete observed. In contrast, the HCFA
addition has the opposite results, due to the presence of clays
which lead to higher porosity at early ages, following swelling
and cracking.