Effects of Fly Ash Inclusion and Alkali Activation on Physical, Mechanical, and Chemical Properties of Clay

Abstract

This study investigated the improvement in the behaviour of a clay soil due to the addition of alkali-activated fly ash as a stabilising agent, and the effects of different activation factors such as alkali dosages and silica moduli. The alkali activator solution used was a mixture of sodium silicate and sodium hydroxide. Class F fly ash was used as the precursor material for the geopolymerisation process. Soil samples stabilised with non-activated class F fly ash were prepared and tested to compare the results with samples stabilised with alkali-activated fly ash. Compaction tests, unconfined compressive strength tests, X-ray diffraction analysis, and scanning electron microscopy analysis were carried out on samples cured 1, 7, and 28 days at room conditions. The results showed that the compressive strength of stabilised soil significantly increased when the fly ash was activated. The optimal activation parameters to stabilise the soil were found to be alkali dosages in the range of 12% to 16% and a silica modulus of 1.25. The highest compressive strength recorded was at 1293 kPa with an alkali dosage of 16% and a silica modulus of 1.25, while for the non-stabilised soil, it was at 204 kPa at 28 days of curing. Mineralogical analysis showed a decrease in the peak intensities of kaolinite and illite, while microstructural analysis indicated an alteration in soil texture with the addition of the alkali-activated fly ash.

Why geopolymers and alkali‐activated materials are key components of a sustainable world: A perspective contribution

“…In some cases, a mix design can be so robust that comparably large variations of the precursor properties still provide satisfactory outputs; for example, in applications with minimal requirements such as earth embankments or substrate layers. [61][62][63] Key parts of the technical requirements also refer to safety during use and after the end of the product life cycle. This aspect is usually addressed by determining the leaching of heavy metals and selected organic compounds; the latter is usually not relevant to AAMs.…”

“…Hence, performance consistency is a key concern when using waste‐based materials for alkali activation. In some cases, a mix design can be so robust that comparably large variations of the precursor properties still provide satisfactory outputs; for example, in applications with minimal requirements such as earth embankments or substrate layers 61–63 …”

Geotechnical Characteristics of Fine-Grained Soils Stabilized with Fly Ash, a Review

“…Table A4 (Appendix A) shows the UCS of fly ash-stabilized soils determined by many investigators and Figure 4 summarizes the mechanism of strength improvement in fine-grained soils stabilized with class C and class F fly ash based on the literature. It has been shown that the strength of soil stabilized with class C or class F fly ash shows an increase [3,10,16,27,33,35,88,98,101,[103][104][105][106][107][108][109][110][111][112][113][114]. However, several researchers have pointed out that there is an optimum level of fly ash addition to stabilize soil [51,60,104,115].…”

Influence of Biomass Silica Stabilizer on Unconfined Compression Strength of Sodium Silicate Stabilized Soft Clay Soils

“…The samples were completely covered by platinum under a high vacuum environment during sample preparation. Moreover, the EDAX method was used to find the major elemental composition on the surface of treated particles [8,15,[20][21][22].…”

“…Pakir et al, [14] reported that the strength of clay soils increases with the increment of TX-85 content and curing period. As a result, this product can be categorized as a stabilizer agent [15].…”