One of the most important component in hydraulic cements is calcium di and tri-silicates-based cement, which is widely used as building and construction material. There are three main compounds in the cement: dicalcium silicate (C2S), tricalcium silicate (C3S), and calcium aluminate (C3A). Highly crystalline calcium hydroxide (Ca(OH)2) and amorphous calcium-silicate-hydrate (C—S—H) are the principal phases formed in crystallinity and the hydration of calcium silicates (C2S and C3S). The paste form of hydrated cement slurry mostly consists of C—S—H and calcium hydroxide (CH). Additional phases including sulfoaluminate and secondary phases are formed. Since calcium hydroxide component (CH) is soluble in water may cause low strength. It has been reported that mechanical properties of cement are improved by reduction of CH and addition of SiO2 (S). Biocementation is a process to produce binding biomaterials to act as cement. Such phenomena is created by a mixture of calcium-silicate-hydrate gel mixed with hydroxyapatite. In biocement composition, calcium silicate hydrate has been reinforced with co-precipitated particles of hydroxyapatite. Biocompatibility of such biomaterial is also enhanced due to absence of aluminum and magnesium in the composition of biocement. The biocement is suitable for variety of applications including dental implants, bone fixation, and bone repair. In fact, biocement is a mixture of mineral oxides once it hydrated crystals are formed. Such biomaterial are originated from living organism calcinates and silicates are as by-product of living organism or even biopolymeric materials are produced. Biocement production has extensively progressed as it is considered as green biomaterial. Environmental demand and use of biocement for stabilization of soil is in an extensive recent research growth of waste conversion to desired biomaterial.
Urease enzyme plays important role in biocementation. During the hydrolysis of Urea this enzyme acts as a catalyst and acclerates the reaction. Due to change in pH, in presence of some form of calcium biocalcification takes place. This biocalcification products are usually calcite form of calcium carbonate. They get deposited in the pores, voids and micro cracks in concrete. This results in the densification and seals the microvoids resulting in impermeability to water and chlorides. Potential microorganism for biocementation can be identified by studying their urease activity. You can see the paper written by myseld D D Sarode (ICT, Mumbai, India), Abhijit Mukherjee (Curtin University, Austrelia), Achal Shanghai, China or Dr Reddy, Thapar University, Punjab, India.
Diane Gardner at Cardiff University (UK) has done work on this that might be useful:
http://repository.tudelft.nl/assets/uuid:a10ad3ec-d3ea-4c05-a48d-26ae734442dc/Harbottle.pdf
Dear Ghasem Najafpour,
I hope my papers can help you on how to screen and select desired strains for biocement applications.
Thanks Dr. Armstrong, we shall utilize your supportive literature in our current work.
Which halophilic bacteria and iron reduction bacteria are suitable for biocementation and bioaggregation of soil particles?
Thanks Seyed
Our target is to produce EPS bio-polymers; in fact we did; we need to identify the potential organisms using PCR!
Regards
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