Experimental Investigation of Unconfined Compression Strength and Microstructure Characteristics of Slag and Fly Ash-Based Geopolymer Stabilized Riverside Soft Soil

Abstract

To solve the issues of insufficient early strength of cement stabilized soil and high resource cost, high reduction cost, and high environmental cost induced by the application of cement, the slag and fly ash-based geopolymer was adopted as the stabilizer to treat riverside soft soil. This study mainly investigated the effects of stabilizer content, slag-to-fly ash ratio, and alkaline activator content on the strength of geopolymer stabilized soils with different curing ages. Unconfined compressive strength (UCS), scanning electron microscope (SEM), and X-ray energy spectrum analysis (EDS) tests were carried out. The results show that the stabilizer content, slag–fly ash ratio, and alkaline activator content have a decisive influence on the UCS of geopolymer-stabilized soil. The mix-proportions scheme of geopolymer stabilized riverside soft soil, with a geopolymer content of 15%, a slag–fly ash ratio of 80:20, and an alkaline activator content of 30%, is considered optimum. It is proven by SEM that the uniformly distributed gelatinous products formed in the geopolymer-stabilized soil bind the soil particles tightly. Moreover, the EDS analysis confirms that the gelatinous products are mainly composed of C-S-H gel and sodium-based aluminosilicate (N-A-S-H).

Experimental Study on Durability Degradation of Geopolymer-Stabilized Soil under Sulfate Erosion

“…Moreover, stable network structure products were uniformly distributed on the surface of the stabilized soil particles. When combined with the XRD results, they were determined to be N-A-S-H gels (typical polymerization products) [ 31 , 32 ]. The N-A-S-H gel contributes to enhancing the bonding strength between soil particles and preventing the intrusion of free sulfate ions into the stabilized soil [ 26 ].…”

“…A cube mold with a side length of 70.7 mm was used for all immersion tests. According to the literature [ 31 ], after the fresh, stabilized soil mixture was molded, it was covered with plastic wrap until demolding after 24 h. The demolded specimens were cured under standard curing conditions for 28 days.…”

“…The loading rate of the UCS test was set to 1 mm/min, and the average strength of three parallel specimens was taken as the measured strength value [ 31 ]. The strength retention coefficient ( δ n ) is used to evaluate the degree of sulfate erosion, and the specific calculation is as shown in Equation (2).…”

Influence of Multiple Factors on the Workability and Early Strength Development of Alkali-Activated Fly Ash and Slag-Based Geopolymer-Stabilized Soil

“…According to the experimental method in [ 39 ], the 3, 7, and 28 d UCS values of the stabilized soil specimens were tested by a universal testing machine, as shown in Figure 1 .…”

“…Further studies found that lower moisture content and composite geopolymer materials were helpful in reducing poor bonding between the geopolymer and soil particles [ 35 , 36 , 37 , 38 ]. Luo et al [ 39 ] proposed using slag/fly ash composite as a stabilizer for soft soil; the measured 28-day UCS of stabilized soil was higher than that of undisturbed soil (56.0 times higher) and cement-stabilized soil (1.39 times higher). Singhi et al [ 31 ] found that Si/Al and Na/Al ratios were important factors affecting the soil–geopolymer system (the main raw materials of which were fly ash and slag), and different mixing ratio schemes corresponded to different stabilization effects.…”