Long-Term Mechanical and Durability Behaviour of Two Alkali-Activated Types of Concrete

Abstract

A promising solution for reducing the carbon footprint of concrete is
the use of alkali-activated concretes (AAC). Before this material can be
widely applied, its long-term behaviour needs to be understood,
especially since some studies reported a decrease of mechanical
properties over time. Similarly, Prinsse et al. reported decreasing
mechanical properties, especially elastic modulus and flexural and
splitting tensile strength for the studied slag-based AAC (S100) and the
blended slag- and fly-ash-based AAC (S50) up to the tested age of
2 years. They hypothesized that these decreases could be only
temporarily. To test that hypothesis, this study continued to monitor
the mechanical properties of both AACs up to the age of 5 years. As a
reference, two OPC-based concretes (OPCC), with different strength
classes, are monitored up to the age of 3.5 years. In addition, the
internal structures of the concretes are assessed for carbonation and
internal micro cracking. S100 shows stabilization of the elastic modulus
and the compressive strength, whereas the tensile splitting strength
continued to decrease up to 5 years. This is attributed to a combination
of carbonation and drying, since the microscopic analysis showed
increased porosity around the ITZ and in the carbonated region. In
addition, S50 shows an ongoing decrease of all tested mechanical
properties, which is attributed to carbonation. No decreases in
mechanical properties are found for OPCC.