Biocementation of Calcareous Beach Sand Using Enzymatic Calcium Carbonate Precipitation

Ahmed Miftah,Huriye Bilsel,Hamed Khodadadi Tirkolaei

doi:10.3390/cryst10100888

Ahmed Miftah, Huriye Bilsel + Show 1 more

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https://doi.org/10.3390/cryst10100888

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Abstract

Beach sands are composed of a variety of minerals including quartz and different carbonate minerals. Seawater in beach sand contains several ions such as sodium, magnesium, calcium, chloride, sulfate, and potassium. These variations in mineralogy and the presence of salts in beach sand may affect the treatment via enzyme-induced carbonate precipitation (EICP). In this study, set test tube experiments were conducted to evaluate the precipitation kinetics and mineral phase of the precipitates in the presence of zero, five, and ten percent seawater (v/v). The kinetics were studied by measuring electrical conductivity (EC), pH, ammonium concentration, and carbonate precipitation mass in EICP solution at different time intervals. A beach sand was also treated using EICP solution containing zero and ten percent seawater at one, two, and three cycles of treatment. Unconfined compressive strength (UCS), carbonate content, and mineralogy of the precipitates in the treated specimens were evaluated. The kinetics study showed that the rate of urea hydrolysis and the rate of precipitation for zero, five, and ten percent seawater were similar within the first 16 h of the reaction. After 16 h, it was observed that the rates dropped in the solution containing seawater, which might be attributed to the faster decay rate of urease enzyme when seawater is present. All the precipitates from the test tube experiments contained calcite and vaterite, with an increase in vaterite content by increasing the amount of seawater. The presence of ten percent seawater was found to not significantly affect the UCS, carbonate content, and mineralogy of the precipitates of the treated beach sand.

Highlights

Enzyme-induced carbonate precipitation (EICP) is an emerging biologically-based ground improvement technique that precipitates calcium carbonate within the pores of a granular soil via hydrolysis of urea catalyzed by free urease enzyme
Due to the scarcity of previous studies considering the applicability of using enzyme-induced carbonate precipitation (EICP) in the marine environment, the current study aimed to evaluate applying this technique to the strengthening of calcareous beach sand and exploring the effects of seawater on the efficiency and mineralogy of the enzymatic calcium carbonate precipitations
Enzyme concentration of 10 mL/L, which is equivalent to 4650 U/L, was selected for EICP solution preparation in the aqueous medium and beach sand treatment experiments in this study

Summary

Introduction

Enzyme-induced carbonate precipitation (EICP) is an emerging biologically-based ground improvement technique that precipitates calcium carbonate within the pores of a granular soil via hydrolysis of urea catalyzed by free urease enzyme. Despite many studies on using microbially induced calcite precipitation MICP and EICP for soil improvement, there are only a few MICP studies using this technique for the treatment of beach sand [16,17,18,19,20,21,22,23]. Shanahan and Montoya [16] created a bench model simulating a coastal sand dune using a clean fine sand, typical of coastal dune deposits. They applied MICP treatment to the sand dune model and assessed the resistance of the model to erosion under simulated wave actions. They reported that the samples treated with MICP had high resistance to erosion as compared to untreated

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