## 5 Conclusions  
In this paper, indoor tests were conducted on the compressive strength, flexural strength, bonding strength of slag-based geopolymer grouting material used in homogenized micro-crack crushing technology, and the morphology and polymerization reactants of the geopolymer were observed. Moreover, on-site grouting tests were conducted to study the grouting effect of the geopolymer on the local weak road base. The main conclusions are presented below.  
As the age increased, the compressive and flexural strength of the slag-based geopolymer gradually increased. The maximum compressive strength and the flexural strength of  
Figure 21: Deflection of the concrete pavement before and after grouting. (**a**) Deflection of monitoring line I; (**b**) Deflection of monitoring line II; (**c**) Deflection of monitoring line III.  
Figure 22: Grouting layer at the bottom of concrete pavement slab. (**a**) Solidified layer of geopolymer; (**b**) Layer thickness.  
the geopolymer at 28 d were 18.88 MPa and 6.50 MPa, respectively. The maximum flexural bonding strength at 14 d was 4.58 MPa. However, the compressive and flexural strength gradually decreased with the increase in the ratio of water to slag powder. The early strength of the geopolymer with a ratio of water to slag powder of 0.26 to 0.28 increased rapidly, among which the compressive and the flexural strengths of geopolymer materials with a ratio of water to slag powder of 0.28 were both better.  
The flexural strength test of new and old bonding beams and the compressive shear bonding strength test methods were proposed. As the age increased, the bonding strength of the geopolymer gradually increased. However, as the ratio of water to slag powder increased, the bonding strength first increased and then decreased. The bonding performance of the geopolymer in the range of ratio of water to slag powder of 0.26-0.28 was good; secifocallythe geopolymer with a ratio of water to slag powder of 0.28 had the highest compressive shear bonding strength.  
Blast furnace slag powder was rich in CaO and SiO\({}_{2}\), which could produce the C-S-H gel in geopolymer materials under the action of an alkali activator. As the ratio of water to slag powder increased, the shrinkage of the geopolymer slurry increased, the porosity increased, and the compactness decreased after consolidation. When the ratio of water to slag powder was small, a variety of crystal phase substances and gel phase substances coexisted. When the ratio of water to slag powder was 0.28, the reactants were mainly gel phase substances, and the shrinkage cracks were relatively small.  
The slag-based geopolymer grouting material could effectively fill the voids at the bottom of the concrete pavement slab and also consolidate the loose material of the local road base. The average deflection of monitoring lines I, II, III decreased by 49%, 41%, and 54%, respectively, after grouting, and the coefficient of variation of deflection values decreased by an average of 16%. After the solidification of the geopolymer slurry, it was distributed in a layered manner, which further compacted the road structure layer and improved the overall bearing capacity of the road structure layer.  
Conceptualization, W.L. and J.Y.; methodology, J.Y.; software, W.L.; validation, W.L. and J.Y.; formal analysis, W.L.; investigation, J.Y.; resources, B.L.; data curation, W.L.; writing--original draft preparation, W.L.; writing--review and editing, J.Y.; visualization, W.L.; supervision, W.L.; project administration, B.L.; funding acquisition, B.L. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the Project of Science and Technology of Henan Transportation Department (Grant numbers 2018J4 and 2019J1).  
Not applicable.  
The authors declare no conflict of interest.