Effects of Content and Fineness of Recycled Concrete Powder on the Properties of Alkali Activated Slag Geopolymers

Recycled concrete powder, as a kind of silicoaluminate waste, has certain cementitious activity under alkali excitation. Therefore, slag and recycled concrete powder were used as precursors of alkali activated cementitious materials, and sodium hydroxide and sodium silicate were used as alkaline composite activators to prepare alkali activated geopolymer. The effects of content and fineness of recycled concrete powder on the fluidity, setting time, compressive strength and flexural strength of alkali activated slag geopolymer were studied. The test results showed that recycled concrete powder was beneficial to improving the fluidity of alkali activated slag geopolymer and prolonging the setting time, of which the particle size was less than 75 μm recycled concrete powder had a slight reduction in the fluidity of alkali activated geopolymer paste, but a significant reduction in the extension of setting time. Recycled concrete powder was conducive to improving the compressive strength and flexural strength of alkali activated slag geopolymer. The increase of mixed recycled concrete powder was conducive to the improvement of early compressive strength and flexural strength of alkali activated slag geopolymer, but not conducive to the development of late strength. In addition, when the content of recycled concrete fine powder with particle size is less than 75 μm was 50%, the compressive strengths of alkali-activated slag geopolymer at 3 d, 14 d, and 28 d increased of by 45.3%, 28.3%, and 29.4%, respectively, and its flexural strengths at 3 d, 14 d, and 28 d increased by 28.5%, 50.9%, and 39.7%, respectively, and its fluidity was 210 mm, and the initial setting time was 80 min.