Bacteria for Concrete Surface Treatment - Biotechnologies and Biomimetics for Civil Engineering - page 341

porosity at 28 days of curing. Assay for CaCO3 precipitation in vitro indicated that
bacterial cell walls, but not dead cells, accelerated carbonation of Ca2 + ions in
Ca(OH)2 solution. Since CaCO3 formed can fill up the void, decrease the porosity
and increase the compressive strength in concrete, bacterial cell walls could act as
a promising concrete admixture with benefits in enhancing mechanical perfor-
mance and improving other carbonation-related properties (Pei et al. 2013 ).
15.3.4 Improvement in the Durability of Concrete or Mortar
Surface Treatment by Biodeposition
Nowadays, performance-based durability criteria have drawn the attention in
specifications for building materials. A major goal of any performance-based
specification is to ensure the durability of building materials and structures.
Durability is regarded as the ability of the materials and structure to perform
satisfactorily with minimum maintenance over the anticipated service life. The
quality of any building material depends on three major parameters, such as (i)
compressive strength, (ii) permeability, and (iii) corrosion. For an efficient bac-
terial concrete, it should produce more compressive strength, less permeability and
should not cause corrosion of any reinforcement. To improve the durability of
concrete structures, engineers started using mineral additives in the form of waste
materials from industries such as fly ash, ground granulated blast furnace slag. In
spite of so much development in the ingredients of concrete final product, concrete
was not adapt well to environment and has the ability of self-healing. Most of these
additives were passive in nature. More research and development is required to
take some measures to enhance the resistance of permeability, ingress of chloride
and carbonation to protect the reinforcing material added in concrete from dete-
rioration. Several tests are available to the engineer for diagnosing the condition of
the concrete. The alkalinity of the concrete at the surface and at various depths
down to the position of the reinforcement will give an indication of how much and
how soon the reinforcement may be at risk. This is known as the depth of the
carbonation front. The presence of chlorides can be determined, again at varying
depths. The permeability of the concrete will give an indication of its susceptibility
to absorption of air and water. Particularly cracking of the surface layer of concrete
reduces material durability as ingress water and detrimental chemicals cause a
range of matrix degradation processes as well as corrosion of the embedded steel
reinforcement (Neville 1996). Durability problems such as crack formation are
typically tackled by manual inspection and repair, i.e., by impregnation of cracks
with cement or epoxy-based or other synthetic fillers (Neville 1996). There are so
many synthetic agents or latex binding agents (such as acrylic, polyvinyl acetate,
butadiene styrene) which are used to avoid any kind of fractures and fissures in the
concrete structures or used in repair applications such as the bonding of fresh
concrete, sprayed concrete, or sand/cement repair mortar to hardened concrete.