Synthesis of organic layered double hydroxide from waste bischofite and its application on ageing resistance of asphalt

For the utilization of waste bischofite from salt lakes, the waste bischofite was utilized to synthesize layered double hydroxide (LDH) by hydrothermal method, and the synthesized LDH was further organically intercalated with 3,5-Di-tert-butyl-4-hydroxyphenylpropionic acid (antioxidant, DPA) by anion exchange methods. Then, the synthesized LDH and DPA intercalated LDH (DPA-LDH) were applied to improve the ageing resistance of asphalt. X-ray diffraction and Fourier transform infrared spectroscopy manifested that LDH and DPA-LDH had been successfully synthesized. After DPA intercalation, the adhesive aggregation among LDH particles was obviously ameliorated, and the contact angle of LDH increased from 31.3° to 77.9°, the hydrophilicity of LDH was significantly decreased. The effect of LDH and DPA-LDH (3 % by weight of asphalt) on rheological properties, chemical constituents and molecular weight of asphalt before and after ageing were comprehensively studied. The high-temperature performance grade of asphalt increased from PG64 to PG70 with the addition of LDH and DPA-LDH, which indicated that LDH and DPA-LDH could enhance the high-temperature performance of asphalt. After ageing, the high and low- temperature performance of asphalt worsened, the colloidal stability index (CI) decreased from 3.548 to 1.844, the gel index (GI) was 48 %, the colloidal structure tended to gel structure, the molecular weight (Mw) enlarged from 3387 to 4101 (the Mw growth rate of 21 %). LDH could restrain the destruction of ageing on rheological properties, the colloidal structure gel of asphalt (the GI of 37.4 %) and molecular weight (the Mw growth rate of 13 %) of asphalt, and strengthen the ageing resistance of asphalt. Furthermore, the enhancement of DPA-LDH (the GI of 16.7 % and the Mw growth rate of 6 %) on the ageing resistance of asphalt was more superior than LDH. The result showed that the synthesized DPA-LDH exhibited outstanding performance in improving the ageing resistance of asphalt, which was beneficial to the long-life pavement and the utilization of abandoned bischofite from salt lakes.