THE EFFECT OF CaO-RICH ADMIXTURES ON CONTROLLING DRYING SHRINKAGE OF ALKALI ACTIVATED MATERIALS

Alkali-activated materials (AAM) are emerging in the construction sector by providing an opportunity to up-stream several industrial by-products. One of the main technical challenges regarding these by-product-based innovative materials is to overcome their tendency to suffer severe drying shrinkage. In this work, the feasibility of using CaO-based admixtures to mitigate drying shrinkage phenomena was investigated and its effects on fresh pastes and hardened specimens’ properties are described. The obtained results showed that increasing CaO-rich admixtures dosage up to 3.0 wt% has a beneficial impact on AAMs volumetric stability. A maximum drying shrinkage reduction of 62.1% was achieved and samples with low open porosity and considerable flexural (up to 7 MPa) and compressive strength (up to 116 MPa) were produced. Notwithstanding, elevated CaO dosages induced detrimental modifications on pastes workability suggesting a dosage threshold of 2.0 wt%. At this dosage, strength development and a reasonable setting time were maintained while linear deformation reduced up to 40%. Reducing alkali-activated materials susceptibility to shrinkage is expected to increase their attractiveness for large-scale applications, and by doing so, will contribute to the valorisation of industrial by-products, facilitating the transition towards a circular economy, while suppressing the usage of virgin raw materials.