A team of researchers has introduced a new visual indoor test system that offers a clearer, more precise way to study how slag-based geopolymer slurry spreads and solidifies, paving the way for more effective road base rehabilitation.
Study: Diffusion and Consolidation of Slag-Based Geopolymer for Concrete Pavement Rehabilitation. Image Credit: Villi-Vonki/Shutterstock.com
A recent article in Applied Sciences details this system, which enables real-time observation of the geopolymer’s chemical reactions and consolidation behavior. The study also evaluated the material’s reinforcement performance in weak road base conditions through on-site grouting and excavation of a test pit.
Background
Concrete pavements are widely used across China due to their strength, ease of construction, durability, and low maintenance. However, over time, these pavements degrade and require rehabilitation to preserve their structural integrity. Homogenized micro-crack crushing is a commonly used rehabilitation method, but it doesn’t fully address issues in the underlying road base.
Grouting with geopolymers has emerged as a promising solution for strengthening weak road bases. Still, several variables influence how effectively the geopolymer fills and diffuses through the pavement structure. Understanding these variables requires both indoor and field testing of diffusion characteristics.
This study focused on how a slag-based geopolymer behaves during grouting, particularly after concrete pavement homogenization, providing insights into its effectiveness in real-world applications.
Methods
The geopolymer slurry was formulated using blast furnace slag powder and an alkaline activator composed of sodium silicate and sodium hydroxide in a 10.1:1 ratio. A water-to-slag ratio of 0.4 was selected to balance early strength development and rapid setting.
The custom-built indoor grouting test system included an air compressor, slurry storage tank, pressure regulator, test mold, and test bench. Three types of single-graded aggregates—2.36–1.18 mm, 4.75–2.36 mm, and 9.5–4.75 mm—were used to simulate weak, loose road base materials. Due to variations in porosity across these aggregate sizes, different grouting pressures were required.
Initial tests helped identify optimal pressure ranges. For each aggregate type, three parallel tests were conducted under varying pressures. The most effective specimens from these tests were then used for outdoor evaluation.
To better understand the chemical and physical properties of the grouted material, researchers used scanning electron microscopy to examine the geopolymer’s reaction products and consolidation behavior. Both qualitative and quantitative analyses were carried out on the test specimens.
Results and Discussion
Grouting performance varied noticeably with aggregate size and applied pressure. As aggregate size decreased, the geopolymer’s diffusion depth also declined. Only under high pressure did the slurry form a cohesive specimen with finer aggregates.
For example, the 9.5–4.75 mm aggregate formed a clear cylindrical specimen at 0.4 MPa. Lower pressures led to partial diffusion and the formation of split surfaces. The 4.75–2.36 mm aggregate produced a grout bulb and visible slurry veins, while the smallest aggregate (2.36–1.18 mm) formed only a limited bulb with no veins—likely due to a pronounced pressure filtration effect.
In diffusion-consolidation tests, larger and more porous aggregates allowed greater slurry penetration, leading to better reinforcement. Specimens consolidated with the 9.5–4.75 mm aggregate met the 28-day strength requirement, and even the smaller aggregates showed increased diffusion depths.
The indoor results helped shape practical grouting strategies. When applied on-site, the geopolymer slurry effectively filled voids beneath concrete slabs and within the road base, enhancing structural stability. The slurry also solidified quickly, forming dense fillers between weak layers and significantly improving the load-bearing performance of the pavement.
The rapid consolidation was attributed to the geopolymer’s chemical composition. Rich in SiO2 and CaO, the slag powder facilitated gel formation during polymerization. The optimal water–slag ratio also supported early hydration and dissolution, ensuring the consolidated material met engineering demands despite minor porosity and shrinkage cracks.
Conclusion
The study successfully demonstrated a visual indoor test system capable of evaluating the diffusion and consolidation behavior of slag-based geopolymer slurry under various aggregate conditions. A key takeaway was the pronounced pressure filtration effect seen with finer aggregates, especially the 2.36–1.18 mm size.
In field trials, the geopolymer slurry with a 0.4 water–slag ratio effectively filled sub-slab and road base voids. After grouting, the average deflection of the driveway dropped from 104.8 to 48, highlighting a significant boost in bearing capacity. This suggests that slag-based geopolymers offer a reliable approach for reinforcing weak road bases in concrete pavement rehabilitation projects.
Journal Reference
Li, W., Yue, J., & Liang, B. (2025). Diffusion and Consolidation of Slag-Based Geopolymer for Concrete Pavement Rehabilitation. Applied Sciences, 15(8), 4373. DOI: 10.3390/app15084373, https://www.mdpi.com/2076-3417/15/8/4373
Disclaimer: The views expressed here are those of the author expressed in their private capacity and do not necessarily represent the views of AZoM.com Limited T/A AZoNetwork the owner and operator of this website. This disclaimer forms part of the Terms and conditions of use of this website.