Effect of Bacterial Bio-Calcination on the Strength and Durability of Cement Mortar

Abstract

This work investigated the effect of growth media on the strength
development and microstructure of cement mortar. The bacterium
called Bacillus Coagulans was incorporated at different cell
concentrations of 1.5x108
, 6.0x108 and 1.2x109 suspension density
with varying percentage replacement of Nutrient Broth Medium
(NBM) at 30%, 40% and 50% and mixing water to the dry mix of
cement and sand (fine aggregate). Mix ratio of 1:3 was used with
water cement (w/c) ratio of 0.5. To establish the objective of gain
in strength, mortar cubes were tested at 3, 7, 14 and 28 curing
duration and the results compared with controlled cement mortar.
Compressive strength obtained for control cement mortar was
24.08N/mm2 and optimal bio-cement mortar was 28.02N/mm2 at
28days curing age was achieved with the addition of 1.5x108B.
Coagulans suspension density with 50% NBM. The strength
improvement is due to the growth of calcite crystals within the
pores of the cement sand matrix as indicated from the
microstructure obtained from Scanning Electron Microscopy
(SEM) examination. It also indicates 3.46% improvement of water
absorption at 28days for 1.5x108 B. Coagulans suspension density
with 50% NBM as against 5.98% water absorption at 28days
curing age for control.