Hydration and microstructure of calcined hydrotalcite activated high-volume fly ash cementitious composite

This work aims to propose a novel method to treat the defects of delayed hydration and low early-age strength of cementitious composites blended with high-volume fly ash (HVFA). The influence of calcined layered double hydroxide (CLDH) on mechanical properties, hydration process and microstructure of HVFA cementitious composites have been explored. Assessed properties of HVFA cementious composites incorporated various contents of CLDH included compressive strength, flowability, pore size distribution and the alkalinity of pore solution. The hydration process and microstructure were detected by XRD, TGA, Barrett-Joyner-Halenda Analysis (BJH), and SEM-EDS. This work revealed the promising potential of using CLDH as the hardening accelerator for HVFA composites. Results indicated that 0.5-2 wt% CLDH addition can play an important role in early-age strength increment and the HVFA mixture with 0.5 % CLDH addition performed better than other contents. In addition, microstructural analyses demonstrated an acceleration in the hydration of HVFA mortars after CLDH added, thereby higher contents of hydrated products can be observed. Meanwhile, less than 1 % CLDH addition is shown to change the morphology and composition of C-(A)-S-H to be slenderer and with higher Ca/Si ratio. Increasing the pore alkalinity by hydrolysis process and the seeding effect are the main enhancement mechanisms of CLDH.

Automated summary

This study proposed a novel method to improve the performance of cementitious composites blended with high-volume fly ash by using calcined layered double hydroxide. Experimental results showed that 0.5% CLDH addition can effectively increase the early-age strength of HVFA cementitious composites and alter the microstructure.