Efficacy of Acacia Gum Biopolymer in Strength Improvement of Silty and Clay Soils under Varying Curing Conditions

Abstract

Acacia gum (AG), a polysaccharide biopolymer, has been adopted to improve the strength of three cohesive soils by subjecting them to diverse environmental aging conditions. Being a polysaccharide and a potentially sustainable construction material, the AG yielded flexible film-like threads after 48 h upon hydration, and its pH value of 4.9 varied marginally with the aging of the stabilized soils. The soil samples for the geotechnical evaluation were subjected to wet mixing and were tested under their Optimum Moisture Content (OMC), as determined by the light compaction method. The addition of AG modified the consistency indices of the soils due to the presence of hydroxyl groups in AG, which also led to a rise in OMC and reduction in Maximum Dry Unit weight (MDU). The Unconfined Compressive Strength (UCS) and California Bearing Ratio (CBR) were determined under thermal curing at 333 K as well as on the same day of sample preparation. The least performing condition of the soil's CBR was evaluated under submerged conditions after allowing the AG-stabilized specimens to air-cure for a period of 1 week. The UCS specimens tested after 7 days were subjected to the initial 7 days of thermal curing at 333 K. A dosage of 1.5% of AG yielded the UCS of 2530 kN/m² and CBR of 98.3%, respectively, for the low compressible clay (LCC) after subjecting the sample to 333 K temperature for 1 week. The viscosity of the AG was found to be 214.7 cP at 2% dosage. Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR), and average particle size determination revealed the filling of pores by AG gel solution, adsorption, and hydrogen bonding, which led to improvements in macroproperties.

Keywords: California bearing ratio; geotechnical; polysaccharides; sustainable construction materials; thermal curing.

Figure 1

Workflow methodology.

Figure 2

Consistency limits of the AG-stabilized soils: (a) HCC; (b) LCC; (c) LCS.

Figure 3

OMC and MDU of the AG-stabilized soils: (a) HCC; (b) LCC; (c) LCS.

Figure 4

UCS curves of AG-stabilized soils: (a) HCC—3D at 333 K; (b) HCC—7D at 333 K; (c) HCC—28D at 333 K; (d) LCC—3D at 333 K; (e) LCC—7D at 333 K; (f) LCC—28D at 333 K; (g) LCS—3D at 333 K; (h) LCS—7D at 333 K; (i) LCS—28D at 333 K; (j) HCC—1D; (k) LCC—1D; (l) LCS—1D.

Figure 5

UCS curves of AG-stabilized soils: (a) HCC—3D at 333 K; (b) HCC—7D at 333 K; (c) HCC—28D at 333 K; (d) HCC—1D; (e) LCC—1D; (f) LCS—1D; (g) LCC—28D at 333 K; (h) LCS—28D at 333 K.

Figure 6

CBR of AG-stabilized soils.

Figure 7

Viscosity of AG.

Figure 8

FTIR spectra of unstabilized and AG-stabilized soils: (a) HCC; (b) LCC; (c) LCS.

Figure 9

SEM of AG-stabilized soils. (a) HCC; (b) LCC; (c) LCS.

Figure 10

Zetasizer results of AG-stabilized soils: (a) HCC; (b) LCC; (c) LCS.