Abstract
Biostabilization is a newly proposed method to improve the strength and durability of geomaterials, and it can serve as an alternative to chemical and mechanical stabilization. The objectives of this study are to perform biostabilization treatments for selected roadway construction geomaterials and to evaluate the biostabilization effects on engineering properties of the geomaterials. Three types of geomaterials were selected, and two of them were compacted soil from unpaved road surface. Bacillus pasteurii, the biostabilization bacterium, was used to induce mineral precipitates within the geomaterial pore spaces, where the biostabilization effects were performed. Two types of liquid incubation media, containing NH4Cl or (NH4)2 SO4, were applied for bacteria culturing. Unconfined compression, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD) measurements were conducted to evaluate the biostabilization results. From unconfined compression, sample strength performance was improved by the biostabilization treatments; the benefits of biostabilization were pronounced by a relatively long culturing time and an oven-dry procedure; the liquid culturing medium containing NH4Cl performed better than the medium containing (NH4)2 SO4. After biostabilization, SEM photographs provided direct evidence for the precipitates induced by bacteria within the geomaterial pore space. The precipitates either connected the adjoined particles or partially covered the particle surface, which increased the surface roughness. EDS and XRD results indicated that calcite, dolomite, and albite were the major precipitates produced during biostabilization treatments. In conclusion, biostabilization ameliorated the microstructures of the geomaterials and improved their strength. Future research topics should include the applications of biostabilization for in situ road construction.
Highlights
Geomaterials, such as soils and aggregates, are widely applied in roadway infrastructure systems
Soils are used for embankment fills and subgrades, while aggregates are used for pavement bases and in Portland cement concrete (PCC) or asphalt concrete. e quality of geomaterials directly influences the longevity of infrastructure systems; enhancing the stability of geomaterials is a prominent issue considered during construction
Loose silica sand had no cohesion, no unconfined compressive strength, comparing with the SP-SM soil and SM soil, it was used as a reference to represent the “absolute effect” of the biostabilization. e results of unconfined compression tests are presented in Figure 2; log-scale was used in the y-axis due to the data range
Summary
Geomaterials, such as soils and aggregates, are widely applied in roadway infrastructure systems. E quality of geomaterials directly influences the longevity of infrastructure systems; enhancing the stability of geomaterials is a prominent issue considered during construction. At sites with marginal or weak soils, mechanical and chemical stabilization should be applied [1]; when aggregates with high porosity are used in PCC or asphalt concrete [2, 3], chemical treatments with sodium silicate solutions are usually. Advances in Civil Engineering performed to seal the pores, improve the strength and durability of PCC or asphalt concrete, and prevent concrete deterioration [4]. Naturally occurring or engineered bacteria are injected into the geomaterials, and precipitates of inorganic cementing materials, induced by microbe-produced polymers, serve as binding agents to bond soil particles and plug pores among coarse aggregates [7]
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