Abstract:
Cement is widely used as a construction material in the construction industry. However, there are challenges
affecting its durability efficacy. Cement mortar/concrete is subject to degradation by aggressive ions such as
sulphates and chlorides. Sulphates can be introduced into the concrete or mortar by Sulphur producing bacteria of
the species Thiobacilli. Microbiologically induced CaCO3 precipitation (MICP) has found its application in bioremediating
cement based materials. It has been found to be environmental friendly. However, no work has been
reported on bioremediation of biodegraded cement based materials. This paper presents findings of possible
bioremediation of mortars after undergoing biodegradation. Bacillus flexus, a beneficial bacterium was used. The
control mortars were prepared using Ordinary Portland Cement (OPC). The test mortars were prepared and cured
in a solution of Thiobacillus thioparus, a Sulphur oxidizing bacteria, deleterious bacterium for 14, 28, 56 and 90
days. Compressive strength analysis was conducted on the 14
day of curing. Results showed
that the lowest compressive strength was recorded on the 90
th
th
th
th
,28
,56
and 90
day as 31.02 MPa. This was a 34.17 % loss in
compressive strength. Another category of mortar cured in Thiobacillus thioparus for 28 days was bioremediated
for 28 days using Bacillus flexus solution. Compressive strength and Scanning Electron Microscopy (SEM) analyses
were then done. The results show a compressive strength of 45.83 MPa at the 56
th
day. This represents a 99.91 %
strength recovery from biodeterioration. The SEM analysis results revealed a denser material. This was due to
massive precipitation of calcium carbonate in the mortar matrix and pores/voids for bioremediated mortars as
opposed to the biodegraded mortars. The results further revealed reduced ettringite crystals on the bioremediated
mortars. Bacillus flexus could perhaps be used in restoring lost compressive strength as well as in sealing voids in
degraded concrete in sewer lines and other cement based materials. This could improve on its efficacy with
minimal repair.
