THE EFFECT OF POLYPROPYLENE GLYCOLS ON THE PROPERTIES OF FE-RICH ALKALI ACTIVATED MATERIALS

The use of non-traditional binders has increased over the last decades and alkaliactivated materials (AAM) are considered viable candidates for several industrial applications. However, AAM high susceptibility to shrinkage can hinder their wider use and several admixtures/additives have been tested attempting to reduce such phenomena. This work is focused on testing the efficiency of different polypropylene glycols (PPG) as shrinkage-reducing agents in Fe-rich alkali activated materials. The effects of the PPG molecular weight and dosage on the drying shrinkage, porosity, and mechanical properties of the resulting AAM are described herein. The obtained results showed that PPG-containing systems present enhanced volumetric stability relative to pure inorganic matrices. AAMs volumetric stability is favoured by the addition of organic oligomers with shorter polymeric chains, but mainly controlled by PPG content rather than its molar weight. Mercury intrusion porosimetry (MIP) data confirm that PPG-containing AAMs have a higher porosity and a broader pore size distribution than reference samples. A maximum drying shrinkage reduction of 58% has been achieved. The beneficial effect that PPG exerts on pastes’ volumetric stability is however accompanied by a consistent deleterious impact on strength development. Pure inorganic polymers achieved a highest flexural and compressive strength of 7±1 and 100±12 MPa after 28 days of curing at room conditions (20°C and 65RH). An abrupt decay of the AAM’s mechanical properties was observed when PPG dosages above 3.0 wt% were introduced into the inorganic matrix. A 5.0 wt% addition decreased flexural and compressive strength after 28 days of curing to a minimum of 2±0 and 52±2 MPa, respectively. Notwithstanding, all the produced alkali activated materials presented reduced shrinkage and interesting mechanical features.