Investigating mechanical properties and biocement application of CaCO3 precipitated by a newly-isolated Lysinibacillus sp. WH using artificial neural networks

Jindarat Ekprasert,Ittipon Fongkaew,Rungtiwa Kamngam,Wachiraya Boonsuan,Poemwai Chainakun

doi:10.1038/s41598-020-73217-7

Jindarat Ekprasert, Ittipon Fongkaew + Show 3 more

Open Access

https://doi.org/10.1038/s41598-020-73217-7

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Abstract

A newly-isolated Lysinibacillus sp. strain WH could precipitate CaCO3 using calcium acetate (Ca(C2H3O2)2), calcium chloride (CaCl2) and calcium nitrate (Ca(NO3)2) via non-ureolytic processes. We developed an algorithm to determine CaCO3 crystal structures by fitting the simulated XRD spectra to the experimental data using the artificial neural networks (ANNs). The biogenic CaCO3 crystals when using CaCl2 and Ca(NO3)2 are trigonal calcites with space group R3c, while those when using Ca(C2H3O2)2 are hexagonal vaterites with space group P6522. Their elastic properties are derived from the Voigt–Reuss–Hill (VRH) approximation. The bulk, Young's, and shear moduli of biogenic calcite are 77.812, 88.197, and 33.645 GPa, respectively, while those of vaterite are 67.082, 68.644, 25.818 GPa, respectively. Their Poisson’s ratios are ~ 0.3–0.33, suggesting the ductility behavior of our crystals. These elastic values are comparable to those found in limestone cement, but are significantly larger than those of Portland cement. Based on the biocement experiment, the maximum increase in the compressive strength of Portland cement (27.4%) was found when Ca(NO3)2 was used. An increased strength of 26.1% was also found when Ca(C2H3O2)2 was used, implying the transformation of less-durable vaterite to higher-durable calcite. CaCO3 produced by strain WH has a potential to strengthen Portland cement-based materials.

Highlights

A newly-isolated Lysinibacillus sp. strain WH could precipitate CaCO3 using calcium acetate (Ca(C2H3O2)2), calcium chloride (CaCl2) and calcium nitrate (Ca(NO3)2) via non-ureolytic processes
The results showed that strain WH grown with calcium chloride and calcium nitrate could produce calcite, suggesting its potential to be used for accelerating the hydration process that produces C–S–H which is the main source of cement strength
A calcifying bacterium Lysinibacillus sp. strain WH was isolated from saline soil

Summary

Introduction

A newly-isolated Lysinibacillus sp. strain WH could precipitate CaCO3 using calcium acetate (Ca(C2H3O2)2), calcium chloride (CaCl2) and calcium nitrate (Ca(NO3)2) via non-ureolytic processes. The inevitable consequences of long-term usage of the cement-based materials are the formation of microcracks within the infrastructure due to exposure to environmental factors such as temperature changes, corrosive substances, and external loads. These factors affect mechanical properties of the materials including compressive strength, tensile strength and p ermeability[2]. Bacterial cells act as nucleation sites for CaCO3 crystal formation[9] Among these metabolic processes, urea hydrolysis is less complex and its pathway is the most widely s tudied[10]. We focus on the growth and potential application of calcifying bacteria which can produce C aCO3 in the absence of urea

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