Characterization of Soil Treated With Alkali-Activated Cement in Large-Scale Specimens

Abstract

Soil improvement with hydraulic binders is currently used in practice because of the advantages of using the local soil enhancing its geotechnical properties. However, environmental issues related to quicklime applications and carbon-dioxide emissions associated to Portland cement production encouraged the development of new binders. In this work, alkaline-activated cement (AAC) synthetized by fly ash and an alkaline solution was used to stabilize silty sand. The behavior of the treated soil was evaluated performing tests on a physical model and the results were compared to laboratory data to define its compaction, strength, and stiffness properties. Those tests include nuclear density gauge measurements, light falling weight deflectometer tests, and plate load tests, whereas unconfined compression tests with unload-reload cycles and seismic wave measurements were performed at the laboratory. These tests, very common in current geotechnical practice, have proved to be also adequate to quality control and to evaluate the geomechanical properties of this material. The results at 28 days show a significant improvement given by the AAC, but still show some sensitivity to water when flooded. The comparison of results from different tests provided the evolution of stiffness with strain level.

Evaluating Shear Strength of Sand- GGBFS Based Geopolymer Composite Material

“…After 90 days of curing, the strength of the soil mixed with an activator and 15, 20 and 25 % fly ash increased by 16, 31 and 77 times respectively compared with non-stabilized samples [5]. Similar results were found recently by Cruz et al [6], who found that the unconfined compression strength of soil improved approximately 32 times when Alkali-Activated binder was added. In contrast to the OPC and lime, clayey soil, improved with alkaline activated low calcium fly ash, exhibited a slow increase in the unconfined compressive strength UCS until the 28th day, and then it showed similar or larger UCS than the conventional stabilizers [7].…”

“…From an early stage of curing, the geopolymer-soil composite exhibited a deformation modulus two times higher than the untreated samples [6]. After 14 days of curing, the deformation modulus of the geopolymersoil composite increased to 183.1 MPa compared with 20.0 MPa for the untreated samples [6]. It was found that the compression index (Cc) and swelling index (Cs) decreased from 2.3 and 0.66 for untreated low strength clay and high swelling clay respectively to about 0.5 and 0.2 for treated samples respectively [15].…”

“…The addition of alkali activated stabilizer resulted in reduced volume strains and an overall decrease of compressibility of the treated soil [20]. From an early stage of curing, the geopolymer-soil composite exhibited a deformation modulus two times higher than the untreated samples [6]. After 14 days of curing, the deformation modulus of the geopolymersoil composite increased to 183.1 MPa compared with 20.0 MPa for the untreated samples [6].…”

Mechanical Behaviour of Steel Slag–Rubber Mixtures: Laboratory Assessment

“…On the three models, the dynamic stiffness modulus was measured with a light weight deflectometer (LWD) with a plate 200 mm in diameter (Figure 4c, d) to avoid the influence of the foundation material, considering that the depth of the stress bulb was twice the diameter of the plate. The test was performed on the centre of the model to avoid boundary effects and the geophone where the deflections were measured was located in the centre of the plate, as done previously by [45]. Compaction was performed using a vibrating hammer adapted for this specific purpose with a rod coupled with a 148 mm diameter disc.…”