Cement-made materials face durability and sustainability challenges. This is majorly caused by the presence of cracks. Cracking affects the mechanical strength of cement-based materials. Microbiologically induced calcite precipitation (MICP) has been found to enhance compressive strength, thus enhancing on the mechanical and durability properties of these materials. This paper presents the findings of a study conducted to investigate the effect of
There is an increasing need to enhance the durability and sustainability of cement-made materials. These materials are expected to have a long service life of more than fifty years [
To a great extent, durability aspects of mortar/concrete are possibly connected with its pore structure characteristics [
Ordinary Portland cement (OPC) exhibits shorter setting times and achieves high compressive strength earlier (at 28 days of curing) compared to blended cements [
Measures aimed at crack remediation in cement-based materials are therefore being undertaken to ensure serviceability of the structures [
Long-term durability and sustainability of cement-based materials is important in order to avert economic losses and safety considerations [
MICP mainly depends upon pH as well as presence of growth site among other factors [
In this investigation, standard sand and OPC (42.5 N/mm2) cement were used manufactured in compliance with ISO 679:1989, EN 196-1 [
Triplicate samples of test cement were analyzed for loss on ignition (LOI). Gravimetric method described in KS EAS 18:1-2017 [
Chemical composition of test cement is given in Table
Chemical composition of test cement.
Oxide (%) | OPC |
---|---|
SiO2 | 22.15 ± 0.41 |
Al2O3 | 3.89 ± 0.08 |
Fe2O3 | 3.31 ± 0.13 |
CaO | 65.89 ± 0.07 |
MgO | 1.25 ± 0.44 |
SO3 | 2.21 ± 0.16 |
K2O | 0.60 ± 0.07 |
Na2O | 0.27 ± 0.04 |
LOI | 1.64 ± 0.15 |
From the results, the test cement met the stipulated requirement by Kenya Bureau of Standards [
Analytical grade (AR) chemicals were used in this work. They were acquired from Highway Laboratory Chemical Equipment, Nairobi, Kenya. These included peptone from casein, calcium lactate, sodium hydrogen carbonate, distilled water, meat extract, and anhydrous sodium carbonate.
Microbial solution of
Test prisms were prepared using 40 mm × 40 mm × 160 mm moulds according to KS EAS 18-1:2017 [
The test was performed according to KS EAS 148–3:2017 [
Compressive strength analysis was conducted according to KS EAS 148-3:2017 [
SEM was performed on control and microbial samples after 28th day of curing. This was done using the SEM model Zeiss Ultra Plug FEG-SEM according to Scrivener et al. [
Table
Setting time and soundness for the control and microbial samples.
Test cement | Setting time (minutes) | Soundness (mm) | |
---|---|---|---|
Initial | Final | ||
OPC (H2O) | 97.0 ± 5.0 | 179.0 ± 5.0 | 1.0 ± 0.05 |
OPC (BC) | 78.0 ± 5.0 | 165.0 ± 5.0 | 1.0 ± 0.05 |
From the results, the initial and final setting times of the control were observed as 78 and 165 minutes, respectively. The initial setting time was accelerated by 15 minutes when compared with the control. The findings indicated that both initial and final setting times were significantly accelerated by
Figures
Test results for compressive strength for varied curing period.
Results for percentage gain in compressive strength for different curing periods.
OPC-H2O-H2O.
Table
Results of comparison of compressive strength development of mortar with curing age.
Curing age (days) | Compressive strength (mean ± SE) MPa | |||
---|---|---|---|---|
OPC-H2O-H2O | OPC-H2O-BC | OPC-BC-H2O | OPC-BC-BC | |
14 | 44.50 ± 1.40a | 45.00 ± 1.00a | 46.01 ± 1.15a | 47.00 ± 0.74a |
28 | 50.33 ± 0.66b | 53.06 ± 0.86b | 55.10 ± 0.48b | 56.81 ± 0.58b |
56 | 50.94 ± 0.28b | 55.04 ± 0.83b | 57.01 ± 0.07b | 58.61 ± 0.68b |
90 | 51.25 ± 0.65b | 61.63 ± 0.14c | 63.80 ± 1.04c | 65.75 ± 0.70c |
0.001 | <0.001 | <0.001 | <0.001 |
Mean values followed by the same small letter within the same column do not differ significantly from one another (one-way ANOVA,
The control mortars, labeled as OPC-H2O-H2O, met the recommended strength at 28 days of 42.5 MPa as depicted in Figure
Table
Results for
Curing age (days) | Percent compressive strength gain (mean ± SE) % | ||
---|---|---|---|
OPC-H2O-BC | OPC-BC-H2O | OPC-BC-BC | |
14 | 1.13 ± 0.22a | 3.39 ± 0.26a | 5.61 ± 0.17a |
28 | 5.42 ± 0.17b | 9.47 ± 0.10b | 12.88 ± 0.12b |
56 | 8.05 ± 0.16b | 11.92 ± 0.01b | 15.06 ± 0.13b |
90 | 20.25 ± 0.03c | 24.49 ± 0.20c | 28.29 ± 0.14c |
<0.001 | <0.001 | <0.001 |
Mean values followed by same small letters within the same column do not differ significantly from one another (one-way ANOVA,
Percentage gain in compressive strength was exhibited across all mortar categories in the range of 1.1% to 28.3%. This was found to increase as curing period increased [
OPC-H2O-BC.
OPC-BC-H2O.
OPC-BC-BC.
Figures
The images show the presence of calcium silicate hydrate, C3S2H3, (CSH), calcium carbonate, (CaCO3), ettringite (
The ettringite is shown in Figures
During microbial cultivation, calcium acetate present in the feed brought in extra Ca2+ ions into the cement matrix. This enhanced the formation of more calcium silicate hydrate (CSH) and precipitation of more calcium carbonate. The cell wall of the bacteria acted as a nucleation site and in the presence of Ca2+ ions availed by calcium acetate from the bacterial feed, crystallized out as CSH when they combined with precipitated
Generally, integrating bacterium in the cement matrix had a beneficial effect on the compressive strength development. This, in long run, is expected to enhance other physical and mechanical aspects of microbial cement-made materials. Flexural strength, resistivity to chloride, and sulphate ingress would be improved due to reduced permeability [
The data used to support the findings of this study are available from the corresponding author upon request.
The authors declare no conflicts of interest.
The authors recognize the immense support offered by East Africa Portland Cement Limited, Kenya, where the preparation of mortar prisms, compressive strength, setting time, and soundness tests analyses were carried out. Our appreciation is extended to Departments of Microbiology and Biochemistry, Agriculture, Chemistry all of Kenyatta University where cultivation of