Basics of Construction Microbial Biotechnology - Biotechnologies and Biomimetics for Civil Engineering - page 33

addition of pure linear (xanthan, DNA), branched (amylopectin) or globular
(albumin) biopolymers to Portland cement showed that even addition of 0.1 % of
these hydrophilic biopolymers changed strength of concrete. It was higher with
addition of biopolymers than in control after 3 days but was lower than in control
after 7 days, probably because a thin layer of the hydrophilic biopolymer on the
cement grain hindered its hydration (Wang et al. 2013, not published data).
Another important application of microbial biopolymers is production of bac-
terial polysacchartides in soil to modify its geotechnical properties (Stewart and
Fogler 2001 ). The most suitable groups of microorganisms that produce insoluble
extracellular polysaccharides to bind the soil particles and fill in the soil pores are
as follows:

• oligotrophic bacteria from genus Caulobacter (Tsang et al. 2006 );
• aerobic Gram-negative bacteria from genera Acinetobacter, Agrobacterium,
Alcaligenes, Arcobacter, Cytophaga, Flavobacterium, Pseudomonas, and

Rhizobium (Portilho et al. 2006 ; Ross et al. 2001 );
• species of Gram-positive facultative anaerobic and aerobic bacteria, such as
Leuconostoc mesenteroides producing water-insoluble exopolymer dextran
(Stewart and Fogler 2001 ) and Cellulomonas flavigena producing a curdlan-
type (beta-1,3-glucan) exopolysaccharide from cellulose (Kenyon et al. 2005 ).
It is well known that almost all bacteria produce exopolysaccharides under
excess of carbohydrates or other water soluble sources of carbon over source of
nitrogen. Therefore, such food-processing wastes or sub-products as corn glucose
syrup, cassava glucose syrup and molasses with C: N ratio [ 20 are used for
industrial production of bacterial water-insoluble polysaccharides (Portilho et al.
2006 ). After growth of exopolysaccharide-producing bacteria in soil, its perme-
ability for water is greatly reduced. Growth of exopolysaccharide-producing
bacteria in soil can be used for different geotechnical applications such as selective
zonal bioremediation, harbor and dam control, erosion potential minimization,
earthquake liquefaction mitigation, construction of reactive barrier, and long-term
stabilization of contaminated soils (Yang et al. 1993 ). Organic wastes such as
organic fraction of municipal solid wastes, sewage sludge, composted poultry
manure can be used as a source of organic matter for exopolysaccharide-producing
microorganisms in large-scale applications to diminish the cost of soil clogging.

2.4 Construction Bioplastics

There is clear trend in construction industry for using of biodegradable materials
and biopolymers (Plank 2004 ; Ramesh et al. 2010 ). There is considerable interest
in the development of biodegradable bioplastics for construction industry. Its
advantages are that use of this bioplastic will reduce the land for disposal of
construction wastes and it is producing from renewable sources so their production
will increase environmental and economic sustainability of construction industry.