Improvement of a clayey soil with alkali activated low-calcium fly ash for transport infrastructures applications

Abstract

19The improvement of geotechnical properties is often achieved by the addition of traditional 20 binders, such as cement or lime. However, the use of such binders implies a considerable 21 financial and environmental cost that needs to be mitigated. An unconventional solution, similar 22 to cement in terms of performance but more environmentally friendly, consists in the use of 23 binders made from alkaline activated industrial residues. The technique consists on the 24 activation of raw materials (such as fly ash or blast furnace slag) rich in Si, Al, or even Ca, with 25 high pH alkaline solutions. The present work was developed aiming the possible stabilization, 26 using different fly ash contents, of a clayey soil with sand. The activator solution was composed 27 of sodium hydroxide and sodium silicate. The extended experimental campaign included 28 unconfined compressive strength (UCS), California Bearing Ratio (CBR), pulse velocity tests 29 and triaxial tests to assess the geomechanical improvement induced by the new binder. As a 30 mean of comparison, the experimental campaign included also the stabilization of the same soil 31 with either cement or lime. The obtained data indicates that the use of alkaline activation as a 32 soil stabilization technique provides competitive geomechanical results, when compared with 33 those obtained with traditional binders.34 35

Compressed earth blocks stabilized with glass waste and fly ash activated with a recycled alkaline cleaning solution

“…The commercially available software Minitab 17 was used which, based on the number of independent variables assumed, established a total of 13 random runs. The soil/precursor range was defined based on previous experience by the research team (Corrêa- Silva et al, 2019;Cristelo et al, 2018;Miranda et al, 2017;Rios et al, 2016); while the activator/solid range was defined after the maximum and minimum CS content in the paste that presented the most adequate workability. This range was on the 'dry side' of the Proctor curve, thus below the 17% humidity threshold that produced the expansion of the paste.…”

Strength Development and Microstructural Behavior of Soils Stabilized with Palm Oil Fuel Ash (POFA)-Based Geopolymer

“…The sudden increase in the percentage of Na indicates the possibility of geopolymer gel formation (NASH) [49]. It was proved that low calcium fly ash-based geopolymer results in N-A-S-H formation as a dominant gel, and very low and slower development of calcium silicate hydrate (C-S-H) gel [50]. The decline in the percentages of Si and Al (from point 1 to 3) was mainly a result of the geopolymer reaction with the time elapsed via dissolving alumina and silica, confirming the significant growth in strength [49].…”

Unsaturated Response of Clayey Soils Stabilised with Alkaline Cements

“…The latter reaches very significant increases after only 28 days (90 to 95% of its ultimate compressive strength), while alkaline cements based on low-calcium precursors, like the FA used in the present study, have shown significant strength gains even after 90 days [1,14]. The soil used during this research work was already submitted to previous studies that primarily focused on stabilisation with cement and lime, but also with alkaline cements based on FA, aiming at increasing its uniaxial compressive strength (UCS) [2,16]. In short, these studies found that conventional binders reached higher UCS values after 28 days, while the alkaline cements were able to produce higher UCS for longer curing periods, up to 90 days.…”

“…However, the rising and ever more acute concerns with the environment have shifted the most important paradigm in the construction industry-the Portland cement dependency-towards the need for more environmentally friendly binders. Alkaline activation is a strong example which, by allowing the introduction of industrial wastes and residues into the fabrication of such alternative binders, represents a twofold advantage, by mitigating the need for OPC and by reducing the volume of wastes that are landfilled [1][2][3][4][5][6][7][8][9].…”

“…From a mechanical performance perspective, the first studies focusing on the use as a soil stabiliser have demonstrated clear and significant increases in compressive strength [2,3,14] and split tensile strength [15], as well as increases in stiffness [16,17], relatively to the original soils. The effectiveness of the technique is also a function of the intrinsic properties of the soil, but especially of the quality of the precursor (unburned rate, original composition, amorphisation degree), of the type of activator (alkali concentration, hydroxide/silicate ratio) and of the activator/precursor ratio (including the total water content and the alkali/precursor ratio) [1,16,18].…”