Slag-based Geopolymer Solidified Sludge And Its Mechanical Properties In Dry-wet Chloride Salt Cycles

As a new type of green soil curing agent,geopolymer has the advantages of high strength,good durability and low carbon emission,of which slag is a commonly used precursor of geopolymer.Therefore,it is important to study the strength and durability of sludge cured by slag-based polymers.In this study,the effects of alkali-to-solid ratio,age of maintenance and type of alkali exciter on the strength of cured sludge were first investigated.Slag-based polymer cured sludge excited with Na OH（NO）,Na₂SiO₃（NS）and calcium carbide slag（CS）as alkali excipients was then maintained to a certain age and tested in distilled water and NaCl solution in dry-wet cycles.The unconfined compressive strength and microscopic morphology of the cured sludge after dry-wet cycling were studied and the following patterns were found:（1）The best alkali-solid ratio of NO,NS and CS curing sludge is 0.2,and the strength of NO curing sludge is reduced when the alkali-solid ratio is lower or higher than 0.2;while the strength of NS curing sludge is significantly reduced when the alkali-solid ratio is lower than0.2,and when the alkali-solid ratio is higher than 0.2,the strength remains almost the same as when the alkali-solid ratio is 0.2;the strength of CS curing sludge is reduced when the alkali-solid ratio is lower than 0.2,and when the alkali-solid ratio is higher than 0.2,the strength is only reduced 0.2,the strength remains almost the same as when the alkali-solid ratio is 0.2;the strength of CS curing sludge is reduced when the alkali-solid ratio is lower than 0.2,and higher than 0.2 has only a certain effect on the initial strength improvement and has no obvious effect on the later strength improvement of the cured sludge.（2）The strength of NO,NS and CS cured sludge at 7 days increased and then decreased with the increase of dry-wet cycles,the strength of NO and CS cured sludge at 14 days increased and then decreased with the increase of dry-wet cycles,the strength of NS cured sludge at 14 days decreased with the increase of dry-wet cycles,and the strength of NO,NS and CS cured sludge at 28 days all decreased with the increase of dry-wet cycles.The strength of 28 days NO,NS and CS cured sludge decreased with the increase of dry-wet cycles;after 30 dry-wet cycles of 28days three kinds of cured sludge,it was found that the strength loss rate of NS was the largest,NO was the second and CS was the smallest.（3）Using mass loss rate,deformation modulus loss rate and strength loss rate as evaluation indicators,the durability of slag-based polymer cured sludge under the action of dry-wet cycles of chlorine salt was comprehensively evaluated using grey correlation theory,and the results of grey correlation calculation showed that the durability of cured sludge decreased with the increase of the number of dry-wet cycles,and the durability of the three types of cured sludge under the action of dry-wet cycles of erosion was ranked from largest to smallest:CS>NO>NS.（4）The damage characteristics of the three types of cured sludge after dry-wet cycles can be seen,NO cured sludge after 30 dry-wet cycles more surface intact,almost no cracks and epidermal peeling phenomenon.cycle 30 times after the NS cured sludge surface of many small cracks,and the surface cracks of the samples cycled in distilled water than in the NaCl solution cycle more surface cracks.CS cured sludge cycle 30 times the surface of the samples have epidermal peeling.（5）SEM and XRD results showed that amorphous gels C-A-S-H and N-A-S-H were produced within the slag base polymer and that the gels resulted in tighter bonds between the cured soil particles and a denser structure.the internal structure of the soil after dry-wet cycling was slightly looser and cracks and pores were produced,and Friedel was found in the cured soil cycled in NaCl solution’s salt and NaCl crystals.