Influencing factors and mechanism analysis of strength development of geopolymer stabilized sludge

To solve the problem of carbon emission and high energy consumption of traditional binder, the coal-bearing metakaolin (CMK) geopolymer was used to stabilize sludge. The unconfined compressive strength (UCS) test was conducted to determine the proportion of alkali activator firstly. On this basis, the effects of alkali-precursor ratio, precursor content, NaOH molarity, curing time, curing temperature and slag content on the mechanical properties of stabilized sludge were investigated. Finally, the SEM and XRD tests were conducted to analyse the microstructure of stabilized sludge. The results showed that the UCS of stabilized sludge first increased and then decreased with increasing Na2SiO3:NaOH ratio and the rational proportion of alkali activator of geopolymer was Na2SiO3:NaOH=75:25. The UCS increased as the alkali-precursor ratio, precursor content and NaOH molarity increased. As the curing time, curing temperature and slag content increased, the UCS of stabilized sludge improved more obviously. The microstructural analysis showed that no new minerals were formed in geopolymer stabilized sludge. With the increase of alkali-precursor ratio, precursor content, NaOH molarity, curing time, curing temperature and slag content, the amount of amorphous N-A-S-H and C-(A)-S-H gels increased, which made the soil structure denser through bonding and filling effects, thus increasing the strength of stabilized sludge.