Stress sensitivity of permeability in high-permeability sandstone sealed with microbially-induced calcium carbonate precipitation

Microbially induced carbonate precipitation(MICP)catalyzed by S.pasteurii has attracted considerable attention as a bio-cement that can both strengthen and seal geomaterials.We investigate the stress sensitivity of permeability reduction for the initially high-permeability Berea sandstone(initial permeability∼110 mD)under various durations of MICP-grouting treatment.The results indicate that after 2,4,6,8 and 10 cycles of MICP-grouting,the permeabilities decrease incrementally by 87.9%,60.9%,38.8%,17.3%,and then 5.4%compared to the pre-grouting condition.With increasing the duration of MICP-grouting,the sensitivity of permeability to changes in stress gradually decreases and becomes less hysteretic.This stress sensitivity of permeability is well represented by a power-law relationship with the coefficients representing three contrasting phases:an initial slow reduction,followed by a rapid drop,culminating in an asymptotic response.This variation behavior is closely related to the movement and dislocation of the quartz framework,which is controlled by the intergranular bio-cementation strength.Imaging by scanning electron microscopy(SEM)reveals the evolution of the stress sensitivity to permeability associated with the evolving microstructures after MICP-grouting.The initial precipitates of CaCO3 are dispersed on the surfaces of the quartz framework and occupy the pore space,which is initially limited in controlling and reducing the displacement between particles.As the precipitates continuously accumulate,the intergranular slot-shaped pore spaces are initially bonded by bio-CaCO3,with the bonding strength progressively enhanced with the expanding volume of bio-cementation.At this stage,the intergranular movement and dislocation caused by compaction are reduced,and the stress sensitivity of the permeability is significantly reduced.As these slot-shaped pore spaces are progressively filled by the bio-cement,the movement and dislocation caused by compaction become negligible and thus the stress sensitivity of permeability is minimized.

Experimental study on permeability and strength characteristics of MICP-treated calcareous sand

Calcareous sand is the main fill material for island reclamation projects,but untreated calcareous sand might not be used as a reclamation fill due to its poor mechanical properties.Microbial induced calcite precipitation(MICP)was directly used to consolidate calcareous sands.One-dimensional sand column tests were conducted to identify the optimized solutions and to investigate the effects of cement solution concentration,relative density,and consolidation frequencies on the permeability and mechanical properties of MICP-treated calcareous sands.Finally,three-dimensional model tests were carried out to investigate the effective consolidation range of microbially treated calcareous sands.The results show that the MICP-treated calcareous sand shows a reduction in the permeability of the sample,while the calcium carbonate cementation and its filling effect improves the mechanical properties of the soil.The one-dimentional test results show that the effective values for cement solution concentration,relative density,and consolidation frequencies range from 0.5 mol/L to 1.5 mol/L,30%-70%,and 5-15 times.The consolidation frequencies have the greatest influence on the permeability and strength properties of the treated calcareous sand.A quadratic polynomial regression model for permeability and strength was established through response surface analysis,and the regression model proved to be highly accurate and reliable through testing.In three-dimentional tests,the consolidation range tends to move downwards in a trapezoidal shape,showing a"big bottom and small top"pattern,with a consolidation range of approximately 34 times the diameter of the pipe.This study serves as a reference for selecting consolidation parameters for subsequent tests and applications of MICP-treated calcareous sands.

Environmental investigation of bio-modification of steel slag through microbially induced carbonate precipitation

Steel slag(SS)is one of byproduct of steel manufacture industry.The environmental concerns of SS may limit their re-use in different applications.The goal of this study was to investigate the leaching behavior of metals from SS before and after treated by microbially induced carbonate precipitation(MICP).Toxicity characteristic leaching procedure,synthetic precipitation leaching procedure and water leaching tests were performed to evaluate the leaching behavior of major elements(Fe,Mg and Ca)and trace elements(Ba,Cu and Mn)in three scenarios.The concentrations of leaching metals increased with the content of SS.After it reached the peak concentration,the leaching concentration decreased with the content of SS.The leachability of all elements concerned in this study was below 0.5%.The carbonate generated from the MICP process contributed to the low leachability of metals.After bio-modified by MICP process,the leaching concentrations of Ba from TCLP,SPLP and WLT tests were below 2.0 mg/L,which was the limit in drinking water regulated by U.S.EPA.The concentrations of Cu leached out from MICP-treated SS-sand samples were below 1.3 mg/L which is the limit regulated by national secondary drinking water.Compared with the regulations of U.S.EPA and Mississippi Department of Environment Quality(MDEQ),MICP-treated samples were classified as non-hazardous materials with respects to the leaching of metals.Meanwhile,maximum contaminant limits regulated by U.S.EPA states that MICP-treated SS are eco-friendly materials that can be reused as construction materials.