Cement freezing–thawing resistance of hardened cement paste with synthetic zeolite

This research article analyzes the synthetic zeolite is produced from the waste of AIF3 (amorphous SiO2), NaOH and Al(OH)3 by low-temperature (105 °C) synthesis and modified with CaCl2. The modified zeolite influence on freeze–thaw and de-icing salt resistance of the hardened cement paste was tested with the replacement of 5% and 10% of the cement mass in the concrete by the zeolite additive. The specimens with 3% NaCl solution on the top surface were tested by one-sided freeze–thaw cycles. The scaled material content, the elongation of specimens and the ultrasonic pulse velocity were tested after every 7 cycles of freeze–thaw. Internal and surface X-ray diffraction patterns were obtained and analysed. The results of the investigation indicated significant improvement of freeze–thaw and de-icing salt resistance of the hardened cement paste. High freeze–thaw with de-icing salt resistance was obtained by changes in the microstructure of the modified cement paste and cement hydration products. The capillary porosity was reduced and the content of calcium silicate and aluminate hydrates was increased with reduction of Ca(OH)3 content in the hardened cement paste. As a result a denser structure with different morphology of hydration products was obtained in the hardened cement paste with synthetic zeolite additive from SEM images. The synthetic zeolite can be used as an additive for high freeze–thaw and de-icing salt resistance cement products (concretes, mortars).