One-part geopolymer (OPG) grout offers advantages over two-part geopolymer grout in the handling and storage of feedstocks, mainly because of the large quantities of caustic solutions that must be handled for producing two-part geopolymer. However, OPG often suffers from a low degree of reaction, a high number of crystalline by-products and, as a result, low strength. Here, one-part geopolymer was assisted by mechanochemical activation (MC-OPG) to produce grout. The precursor materials (slag and fly ash) and sodium silicate were mechanochemically activated utilising co-grinding to produce a geopolymeric precursor, after which water is the only additive required to initiate the geopolymerisation reaction. The effects of slag/fly ash ratios on grout mixtures were also investigated. A series of tests was examined, including rheological characteristics, setting time, bleeding, unconfined compressive strength (UCS), ultrasonic pulse velocity, scanning electron microscopy and X-ray diffraction. The results showed that the mechanochemical activation technique increased the rheological characteristics and reduced the fresh properties (setting time and bleeding) of geopolymer grout compared to the one-part geopolymer. Considering mechanical properties, the UCS of MC-OPG grout was higher (41–73%) than that of OPG grout. Furthermore, slag content significantly affected the rheological, fresh and mechanical properties of all the geopolymer grouts regardless of the activation method.

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This article discusses the effects of glass powder (GP) replacements and sodium hydroxide (NaOH) molarity on the rheological, fresh, mechanical and microstructure characteristics of slag-based mechanochemical geopolymer (MG) grout. A conventionally activated geopolymer grout and an ordinary Portland cement (OPC) grout were also investigated for comparison. Four glass powder replacement ratios were used (0%, 10%, 20% and 30% by the total precursor weight) to prepare slag-based mechanochemical geopolymer at three NaOH concentrations (1.25, 2.5 and 3.75 molars). The experimental results showed that the rheological behaviour of MG grouts was considerably reduced, whereas the setting time and the bleeding capacity value increased when slag was substituted with 0%-30% GP. However, after 28 days, the unconfined compressive strength (UCS) improved by 2%-13% when 10%-20% GP was used as a slag replacement, then dropped by 4% when 30% GP was substituted. The results confirmed that both geopolymer grouts irrespective of the activation method had shorter setting time and more stable bleeding capacity than OPC grout. The results also revealed that the UCS of geopolymer grout is enhanced by 18% when the source materials are activated by the mechanochemical method compared to the conventional activation of geopolymer grout. The microstructure results revealed that the activation method had a considerable effect on the microstructure of geopolymer grout because the ball milling process increased the surface area and reduced the particle size of slag compared to conventionally activated geopolymer grout.