Abstract
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.
Highlights
Weak soil such as soft clay, often utilized in construction sites, needs to be enhanced in the mechanism for sufficient bearing capacity, settlement, and permeability of foundations in many civil engineering projects such as dam construction, tunnels, highway embankments, buildings, retaining walls, and so on. [1,2]
As for the geopolymers compared to Portland cement (PC), it was observed that treatments with stabilizers alone and in combination potentially appeared to produce superior Unconfined compressive strength (UCS) performances (up to 13 MPa for 28-day (SL) and 21.5 MPa for 365-day (SF + SL)) that changed with stabilizer proportions and alkaline ratios (r)
On the effect of curing time, both PC and geopolymers resulted in UCSs that increased with increasing curing time
Summary
Weak soil such as soft clay, often utilized in construction sites, needs to be enhanced in the mechanism for sufficient bearing capacity, settlement, and permeability of foundations in many civil engineering projects such as dam construction, tunnels, highway embankments, buildings, retaining walls, and so on. [1,2]. Deep soil mixing has gained its popularity worldwide since this mixing technique has been effective to increase the strength as well as lessen the compressibility of weak soil. This mixing method essentially results in a soil-binder column by mixing the unstable soil (weak soil) with cementitious and other stabilizers in wet or dry states (i.e., lime, fly ash, bentonite slurry, bottom ash, slag, glass powder, marble dust, silica fume, metakaolin, etc.) [3,4]. By the deep mixing method, it is reported that the improved soil, due to execution of soil mixing columns, could meet the adopted design requirements by providing timely, efficient, safe, and cost-effective solutions without challenging excavation and replacement of Materials 2019, 12, 2542; doi:10.3390/ma12162542 www.mdpi.com/journal/materials
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