This research aims to experimentally investigate the potential use of a geopolymer made from various stabilizers or byproducts (fly ash (FA-F, FA-C), slag (SL), glass powder (GP), metakaolin (MK), marble powder (MP), bottom ash (BA), rice husk ash (RHA), silica fume (SF)) to enhance the mechanical performance of soil (clay) via a deep mixing technique. Strengths of geopolymer soilcrete specimens were determined by unconfined compressive strength (UCS) tests regarding curing times (7 to 365 days) by comparing with Portland cement (PC). In addition, ultrasonic pulse velocity (UPV) tests, the effect of molarity (8–16 M), stress-strain behavior, failure modes, and microstructure (SEM, EDX) of geopolymer specimens were examined. Compared to PC, UCS responses of geopolymer specimens yielded: (i) a decreasing trend for FA-F, GP, MK, BA, and MP + FA-F, (ii) an increasing trend for FA-C, SL, and combinations of SL (BA + SL, RHA + SL, SF + SL, MK + SL) favorable with fewer proportions of stabilizers, and (iii) higher increments due to long-term curing (90, 365 days). Despite some decrements, most UCS values were found acceptable (>0.2 MPa) for sufficient enhancement of soft clay. The UCS results were mostly confirmed by UPV performances. The geopolymer specimens were also found to present: (i) strength development for alkaline concentrations from 10 to 14 M, (ii) brittle behavior of stress–strain curves that failed in axial splitting and near axial directions, and (iii) intensity of the silica peak for strength responsibility of the dense microstructure. The findings relatively support the usage of stabilizers or byproducts in the production of geopolymers for potential use in deep mixing. Thus, this research could be a basis for further efforts in this area.

Optimization of the stabilization materials in terms of their dosage rates specifically used for stabilization applications have become a great interest by the experimenters due to the concerns of strength performance, time and economy for the construction projects. Using a relatively recent optimization technique, Response Surface Methodology (RSM), this paper is mainly focused on investigation of the optimum amounts of stabilizers (Sewage Sludge Ash (SSA) and Polypropylene Fiber (PF)) and Curing Time (CT) that yield to maximum unconfined compressive strength (UCS) for stabilization of a marginal sand (poorly-graded sand). For this purpose, an experimental study has been carried out conducting UCS tests, where the stabilizer proportions are 0-30% for SSA and 0-1% for PF, by total dry weight of sand+SSA. Also, the curing times considered prior to testing are 0, 7 and 14 days. All UCS tests have been performed following the experimental program by central composite design that used the ranges of stabilizer proportions and curing times. On the basis of experimental data, a full quadratic model with natural log transformation and backward analysis has been built through RSM considering the factors of SSA, PF, CT, and the response of UCS. The results indicate that the mathematical model built in this study is statistically significant (p ≤ 0.05) through the analysis of variance (ANOVA), thus it is applicable for optimization process. The findings from the optimization effort demonstrate that the most potential values for SSA, PF and CT are 19.95%, 0.57% and 12.15-day, respectively. The proposed values could be beneficial for the experimenters in practice specifically for preliminary evaluations prior testings of stabilizations.

Non-traditional soil stabilisers for stabilising marginal soils could be a viable and alternative solution to traditional stabilisers in terms of cost prohibitive as well as enhancement of engineering characteristics. In this preliminary attempt of the study, an applicability of the superplasticiser, which is quite common in concrete production but not so in soil stabilisation, has been investigated for stabilisation of a fine-grained soil (low-plasticity clay) compared with the combinations of traditional stabilisers of bottom ash and lime, as an alternative non-traditional soil stabiliser. An extensive experimental programme including unconfined compressive strength (UCS) tests has been conducted for this aim. Based on the testing results, the engineering characteristics (i) the stress–strain curves, (ii) failure modes of specimens, (iii) UCS, (iv) elasticity modulus (Es) and (v) energy absorption capacity (Ed) [Consoli, N. C., Montardo, J. P., Prietto, P. D. M., & Pasa, G. S. (2002). Engineering behavior of a sand reinforced with plastic waste. Journal of Geotechnical and Geoenvironmental Engineering, 128(6), 462–472] of stabilised clay with superplasticiser, bottom ash and lime have been figured out for pre- and post-freezing and thawing conditions, with the discussion in detail. The results indicate that the superplasticisers separately or in combination with bottom ash and lime produce satisfactory engineering characteristics for stabilisation of clay for pre- and post-freezing and thawing conditions. The influences in the stabiliser combinations are statistically significant for the entire results of UCS (p-value < .05), which is moderately correlated with the Es and Ed. On the basis of the UCS values due to the requirements of the standard guide, the compositions including superplasticiser, lime, lime+superplasticiser, lime+bottom ash for non-freeze–thaw, lime+superplasticiser for freeze–thaw are found to effectively improve the native clay. The understanding from the findings with the discussions through the study is relatively promising for the use of superplasticiser in the soil stabilisation.