## 4 Practical Application
### Practical Grouting Test of Geopolymer  
Due to problems such as insufficient base bearing capacity and insufficient strength of concrete pavement in some of the rehabilitated areas, it was necessary to reinforce the road base through grouting after homogenized micro-crack crushing. The ratio of water to slag powder of the slag-based geopolymer prepared on site was 0.28. In the field grouting test, the hole was drilled manually, and the holes were arranged in a plum style. After the hole was formed, the PVC flower tube was placed in the hole so that the slurry was diffused in a directional manner and the weak road base around the hole was strengthened. During the grouting process, the amount of grouting was artificially controlled. When the adjacent grouting hole emitted slurry or the pavement slab raised, grouting was stopped. After the completion of geopolymer grouting, traffic was opened after a short period of curing, and then the hot mixed asphalt was overlaid. In order to verify the effectiveness of geopolymer grouting, the deflection of the concrete pavement slab before and after grouting was measured. Each monitoring line was 10 m long and the spacing between measuring points was 1 m. A half-width concrete pavement was selected, and three deflection monitoring lines with a spacing of 2 m were set up. The on-site deflection monitoring lines are shown in Figure 20.  
In the weak road base areas of concrete pavement, due to the void of concrete pavement slab and the weak road base, the deflection was large and some of the deflection was abnormal. The deflection of the concrete pavement slab before and after grouting is shown in Figure 21. After grouting at the diseased location of the pavement, the overall deflection significantly decreased, and the abnormal points of deflection were eliminated. The average deflection of monitoring line I, monitoring line II, and monitoring line III decreased from 88.2 (0.001 mm), 73.9 (0.001 mm), and 104.8 (0.001 mm) to 45.2 (0.001 mm), 43.9 (0.001 mm), and 48 (0.001 mm), respectively. The average deflection of monitoring line I, monitoring line II, and monitoring line III decreased by 49%, 41%, and 54%, respectively, after grouting. Moreover, the coefficient of variation of deflection values decreased by an average of 16%. After the consolidation of the geopolymer slurry, the void was filled, and the loose road base was consolidated, thereby the weak road base was reinforced and the deflection of the concrete pavement was reduced.  
In order to observe the grouting effect of the geopolymer, typical disease locations were selected for excavation within the three monitoring line areas, as shown in Figure 22. After removing the concrete pavement slab through excavation, there was a layer of 5 mm geopolymer slurry consolidation between concrete pavement slab and cement stabilized base. Through excavation, it was found that geopolymer slurry effectively filled the void at the bottom of concrete pavement slab and the interlayer gaps between various structural layers of road. For loose road structural layers, the geopolymer slurry could consolidate  
Figure 20: The deflection monitoring of pavement slab before and after grouting. (**a**) Measurement area of deflection on site; (**b**) Deflection measuring lines.  
well. After solidification, the geopolymer slurry formed a layered structure, which was further compacted into the road structure layers; therefore, the overall bearing capacity of the road structure layers were improved.