Sandcastle worm-inspired phytic acid and magnesium oxychloride cement copolymerization for performance enhancement

Mechanical performance and water resistance of biochar admixture lightweight magnesium oxychloride cement

The applications of magnesium oxychloride cement (MOC) have been extensively studied recently due to its eco-friendly and high-strength nature. However, one of the significant limitations of MOC is its poor water resistance. To address this limitation, this study explored the prospect of incorporating biochar particles (up to 25 % of the dry mass of MgO) to form lightweight MOC with improved water resistance. The compressive (fc) and flexural (ff) strengths were investigated after 28-day curing and under 56-day water attack. The fc of MOC after immersion was determined under both wet (directly after immersion) and dry (air-dried to constant weights) conditions. The results indicated that the inclusion of 5 % and 10 % biochar increased the 28-day fc, while the addition of biochar decreased ff regardless of its dosage. Microscopic examination uncovered that the increase in strength resulted from the promoted production of phase 5 (5 Mg(OH)2·MgCl2·8H2O) and the reduction in unreacted MgO. The inclusion of 5 % and 10 % biochar increased the compressive and flexural strength retention ratios after 56-day immersion. The ff with 5 % biochar inclusion after immersion was higher compared to that of pure MOC. Moreover, the inclusion of biochar had minimal effects on the thermal degradation of MOC. The above results suggest that biochar can be a potential additive to enhance the mechanical behaviour and water resistance of MOC. As fc of immersed MOC increased during air-drying, a new equation was developed to describe variations in fc of MOC subject to different degrees of saturation during drying.

Improvement mechanism of water resistance and volume stability of magnesium oxychloride cement: A comparison study on the influences of various gypsum

The development of magnesium oxychloride cement can effectively utilize the waste of potash industry and reduce its harm to the environment. Although magnesium oxychloride cement paste (MOCP) has excellent performance in dry environment, its performance is greatly deteriorated in water or humid environment, which severely limits its practical application. In order to improve the water resistance of MOCP, MOCP was modified by various gypsum in this study, and the intrinsic mechanism was explored. Results showed that replacing MgO with gypsum delayed the setting time of MOCP and effectively improved its volume stability. Although the incorporation of gypsum reduced the 14-d air-cured compressive strength of MOCP, waste gypsum was able to significantly improve the water resistance of MOCP compared to natural gypsum. When 80% flue gas desulfurization gypsum and phosphogypsum (weight of magnesium oxide) were incorporated into MOCP, the 14-d air-cured compressive strength of MOCP was only decreased by 14.49% and 15.94% compared with the control group, but its 28-d water immersion strength retention coefficient (SRC) could still reach 61.02% and 46.55%, respectively. However, for the control group and MOCP with 80% natural gypsum, the 28-d SRC were only 28.99% and 8.41%. The incorporation of high-volume waste gypsum to MOCP not only reduced the relative content of MgO, but also improved the stability of the 5-phase in water, which was beneficial to improve the water resistance of MOCP. In addition, high-volume waste gypsum-modified MOCP had lower cost and carbon emissions, and exhibited superior water resistance and sustainability compared to existing MOCP compositions.