BACILLUS SUBTILIS - AND THERMUS THERMOPHILUS DERIVED BIOCONCRETE IN ENHANCING CONCRETE COMPRESSIVE STRENGTH

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1 BACILLUS SUBTILIS - AND THERMUS THERMOPHILUS DERIVED BIOCONCRETE IN ENHANCING CONCRETE COMPRESSIVE STRENGTH Muhammad Isha, I. 1 Afifudin, H. 2 and Mohd Saman, H. 3 1 Faculty of Civil Engineering, Universiti Teknologi MARA, Jengka Campus, Pahang, MALAYSIA. 2 Faculty of Civil Engineering, Universiti Teknologi MARA, Permatang Pauh Campus, Pulau Pinang, MALAYSIA. 3 Institute of Infrastructure Engineering and Sustainable Management (IIESM), Faculty of Civil Engineering, Universiti Teknologi MARA,40450 Shah Alam,,MALAYSIA. Corresponding author: isha@pahang.uitm.edu.my ABSTRACT Bacteria can precipitate mineral through biomineralisation which can be exploited to increase the strength of concrete. In this study, two types of bacteria, namely Bacillus subtilis and Thermus thermophilus, were used to produce bioconcrete. These bacteria are able to precipitate silica minerals when incubated in silicic acid solution. The silica minerals subsequently react with calcium hydroxide in the secondary hydration process, thus increasing the density of concrete. These bacteria were prepared in different cell concentrations and were incorporated in the concrete mix. Compressive strength tests were performed at the age of 3, 7, 28 and 60 day of curing. The effect of different cell concentrations of Bacillus subtilis and Thermus thermophilus on concrete strength was studied. Microstructure examination was also performed to substantiate the findings. The results show that Bacillus subtilis bacteria enhanced compressive strength significantly in early age while Thermus thermophilus contributes considerably in later age. The optimum concentration was found to be 10 6 cell/ml for both bacteria. The microstructure examination confirmed that there are conspicuous crystal growth within the concrete matrix that contain either Bacillus subtilis or Thermus thermophilus. Keywords: Bacillus subtilis, bioconcrete, compressive strength, microstructure examination, Thermus thermophilus 1. INTRODUCTION Many researchers opt to find alternative material that can be incorporated inside the concrete in the hope to reduce the usage of cement and at the same time to enhance its properties. Typically, supplemantary cementatious material (SCM) such as fly ash, silica fume and ground granulated blast furnace slag (GGBS) are commonly used to replace a portion of cement inside concrete (Mehta, 1999). Although it is proven that SCMs enhance the properties of concrete, these materials are relatively expensive and its availability is limited. Recently, a novel concrete technology has been introduced, that is by incorporating biological approach in concrete (Henk, 2007). This crossbreed between biology and engineering study of concrete is called bioconcrete, which involves the utilisation of bacteria mineral precipitation to increase the strength and durability of concrete (Ghosh and Mandal, 2006). The mineral precipitation occupies the voids between cement matrix and therefore leads to denser concrete. The approach does not deplete any natural resources since the bacteria used can be easily reproduced by cultivation process. The use of biological approach in concrete is also considered as a green technology as its production does not involve greenhouse gas emission. Typically, bacterial mineral precipitation can be classified into two categories; calcium carbonate (calcite) precipitation (Bang et al., 2001; Bachmeier et al., 2002; Muynck et al., 2008) and silica mineral precipitation (Mera and Beveridge, 1993; Inagaki et al., 1998). Many researchers focus on calcite precipitation bacteria which include Baccilus species (Muynck et al.,2008; Achal et al., 48

2 2009; Henk and Erik, 2009), Sporosarcina species (Park et al., 2010; Chahal et al., 2012) and Shewanella species. (Ghosh and Mandal, 2006). Bacillus species is soil-based bacteria and it is a ureolytic type. The ureolytic type bacteria produce urease which catalyses urea to produce CO 2 and ammonia, resulting in an increase of ph in the surroundings where ions Ca 2+ and CO 3 precipitate as calcium carbonate. Meanwhile, a thermophilic type of bacteria such as Thermus species have been experimented by Inagaki et al. (1998) in precipitating silica in alkaline solution. However, to date, there is no report use of silica precipitating bacteria into concrete mix. Hence, this research paper focuses on using Thermus species. It is hypothesised that thermophilic bacteria could withstand high temperature due to cement hydration reaction. Bacillus subtilis was also adopted for comparison. 2. MATERIALS AND METHODS 2.1 Cultivation of Bacteria The Bacillus subtilis and Thermus thermophilus bacteria were cultivated until they are mature. Both types of bacteria were obtained from American Type Culture Collection (ATCC). Bacillus subtilis was cultured inside the tryptic soy broth with 0.5% yeast extract and the mix was kept at 30 C for one day. Thermus thermophilus was cultured by incubating it directly in Castenholz Tye media containing silicic acid at 74 C for two days. The duration and temperature for incubating both bacteria were adopted to ensure the optimum growth of both bacteria based on previous literature (Mera and Beveridge, 1993; Inagaki et al., 1998). Figure 1 reveals the cultivation of Bacillus subtilis and Thermus thermophilus inside their respective solution. These bacteria were then diluted to produce desired cell concentrations. For this study, both bacteria were diluted in 10 3, 10 4, 10 5, 10 6 and 10 7 cell/ml concentration using serial dilution method. The counting for bacteria cell concentration was made by using Haemacytometer and it is viewed as in Figure 2. All these tasks were done at the Biological Laboratory, Faculty of Applied Science, UiTM. Figure 1: Bacillus Subtilis and Thermus thermophilus cultivated with their respective solution 49

3 Figure 2: Bacteria viewed at 400X in a Haemacytometer counting chamber 2.2 Preparation of concrete specimens In this experiment, five different concentrations of cell (10 3, 10 4, 10 5, 10 6 and 10 7 cell/ml) were made for both Bacillus subtilis and Thermus thermophilus. A total of eleven series of grade 30 concrete specimens of size 100mm x 100mm x 100mm were cast. Five series are designated as B3, B4, B5, B6 and B7 corresponding to concentration of 10 3, 10 4, 10 5, 10 6 and 10 7 cell/ml of Bacillus subtilis respectively. Another five series, T3, T4, T5, T6 and T7 represents Thermus thermophilus concrete corresponding to concentration of 10 3, 10 4, 10 5, 10 6 and 10 7 cell/ml respectively. Finally, one series of control specimens without bacteria is prepared. The mix proportion for the grade 30 concrete is shown in Table 1. The materials used for the concrete were Ordinary Portland Cement (OPC), mining sand, aggregate and distilled water. Table 1: Mix Proportion for 1 m 3 Concrete Grade 30 Cement (kg) Water (kg) Mining Sand (kg) Aggregate (kg) Slump (mm) ± Tests Conducted Compressive Strength Test - The compressive strength test was conducted to determine the strength development of concrete specimens at 3, 7, 28 and 60 days. For each age, three (3) specimens were prepared. The compressive strength was determined following BS EN :2009 and EN :2000. The specimens were compressed at a rate of 3 kn/sec until failure and the results were recorded. Microstructure examination - Microstructure examinations on control and mirobed concrete specimens were performed at early age using Scanning Electron Microscope (SEM). The micrograph of Bacillus subtilis, Thermus thermophilus and silica precipitation from literature were also presented to validate the findings. 3. RESULTS AND DISCUSSION 3.1 Compressive strength 50

4 Figure 3 illustrates the compressive strength for eleven series of concrete specimens. It is apparent that the integration of Bacillus subtilis at 10 6 cell/ml concentration gives the maximum improvement in compressive strength. It can be observed that the optimum concentration of Thermus thermophilus concrete is also 10 6 cell/ml. The compressive strength for Thermus thermophilus poses similar trends like Bacillus subtilis with the highest enhancement of strength is made from those of 10 6 cell/ml concentration. Although 10 7 cell/ml is the highest concentration of Bacillus subtilis adopted, it only charts the second highest of compressive strength in the series. 3.2 Percentage improvement Figure 4 presents the percentage improvement of compressive strength attributed to the bacteria. Obviously, the contribution of 10 3 cell/ml Bacillus subtilis was found to be insignificant to the strength of concrete. Again, the lowest strength development for compressive strength is reflected by the Thermus thermophilus concrete with concentration of 10 3 cell/ml. control Figure 3: Compressive strength for eleven series of concrete specimens Unfortunately, the blending of 10 7 cell/ml pose negative effects on the strength development at the age of 3 days but gain the strength in later days. The Bacillus subtilis concentration of 10 6 cell/ml was high in early strength but decreases steadily in later days compared to those of other concentration. On the other hand, the percentage increase recorded for Thermus thermophilus concrete made of 10 6 cell/ml concentration is considered insignificant in early strength but the marked increase is shown in later strength. It is suggested that the enhancement in strength was due to the effect of silica precipitated form the bacteria that fill up the cement matrix. 51

5 Figure 4: Percentage increase of compressive strength for both microbe concrete 3.3 Optimum concentration Figure 5 depicts the percentage of increase of strength with respect to cell concentration of both bacteria added into the concrete mix. The plots are taken from the 3 day and 60 day compressive strength. It is noted that the optimum cell concentration of both bacteria is 10 6 cell/ml. It is obvious that the incorporation of bacteria up to 10 6 cell/ml enhance the compressive strength of the resulted concrete. Figure 5 also deduces that the Bacillus subtilis contribute marked increase in strength during early age while the incorporation of Thermus thermophilus gives enhancing effect at the later age. Based on the percentage of increase at 60 day concrete strength, it infers that Thermus thermophilus offer the highest improvement level in concrete. Due to the nature of the bacteria, Thermus thermophilus can survive thermal environments ranging from 50 C 82 C which in the opinion of the authors contribute to this phenomenon (a) (b) Figure 5: Percentage increase of compressive strength with respect to cell concentration for a) 3 day microbed concrete and b) 60 day microbed concrete 3.4 Discussion 52

6 The outcome of the present study was compared with those findings reported by Park et al., (2010) that used four calcite forming precipitation bacteria towards the compressive strength of cement mortar matrix. The results indicated that the best improvement in compressive strength was found in Arthrobacter crystallopoietes bacteria concrete with the enhancement of 8.9% in 28 days when compared to normal mortar specimen. Meanwhile, Henk and Erik (2007) reported that Bacillus Pasteurii bacteria concrete increase the 28 day compressive strength of concrete specimen by 9% with the optimum cell concentration was found to be of 10 9 cm -3. On the other hand, Achal et al., (2010) found that by using Bacillus sp. CT-5, the bacteria can increase the compressive strength of 28 day cement mortar cubes by 36%. They added that the enhancement is due to the deposition of calcite on the microorganism cell surfaces and within the pore structure of cement-sand matrix. In this research, Bacillus subtilis and Thermus thermophilus enhanced the 28 day concrete compressive strength by 18% and 21.8% respectively. It is noted that the percentage enhancement for both bacteria concrete was in similar corresponding to those of previous findings. The comparison of the percentage increase in compressive strength due to the Bacillus subtilis and Thermos thermophilus investigated in the present study with those of supplementary cementitious materials (SCM) is shown in Table 2. It appears that the increase in strength due to the inclusion of microbe in concrete is comparable to some of the SCMs reported from the previous study. However, the strength enhancement made from both microbe concrete was not able to surpass the strength enhancement made by silica fume replacement. Table 2: Percentage increase in compressive strength due to the Bacillus subtilis and Thermos thermophilus with those of supplementary cementitious materials Author Type of additive Percentage increase of 28 day compressive strength Present study (2012) Bacillus subtilis (10 6 cell/ml) 18 Thermos thermophilus (10 6 cell/ml) 22 Ramezanianpour and Jovein (2012) 15% Metakaolin replacement of cement 9 Frias et al. (2011) 10% Calcined paper sludge ash replacement of cement 2 Hooton et al. (2010) 7% Silica fume replacement of cement Microstructure examination From the SEM micrograph, it appears that there is no signature of conspicuous crystal growth in concrete without bacteria (Figure 6 (a)). However, rod-shape fibulous deposition has been observed in concrete matrix incorporated with Bacillus subtilis as shown in Figure 6 (b). The rod-shape is confirmed to be Bacillus subtilis and supported by the micrograph of the Bacillus subtilis published by Satirapathkul and Leela (2011), as portrayed in Figure 6 (c). These fibres contributed towards the improvement of the concrete properties. In Figure 6 (d), SEM micrograph revealed irregular crystalline attributed to silica deposition by Thermus thermophilus. It is suggested that irregular crystalline observed are the silica deposition made by Thermus thermophilus bacteria. 53

7 International Sustainability and Civil Engineering Journal (a) Vol.1, No.1, (July 2012) (b) (c) (d) Figure 6: SEM micrograph of concrete (a) without bacteria of 3 day concrete, (b) with Bacillus subtilis and (c) Bacillus subtilis (Satirapathkul and Leela, 2011), (d) Thermus thermophilus of 1 day concrete 4. CONCLUSIONS The following conclusions can be made from this research: a) The blending of Bacillus subtilis and Thermus thermophilus bacteria inside the concrete matrix has improved the compressive strength of concrete. b) By comparing the compressive strength incorporated between Bacillus subtilis and Thermus thermophilus, the former concrete contributes the marked increase in strength during early strength, while the later contributes the strength at the later age. c) The optimum cell concentration of Bacillus subtilis and Thermus thermophilus bacteria in giving the most enhanced effect was found to be 106 cell/ml. d) The microstructure examination confirmed that there are conspicuous crystal growth within concrete matrix that contain either Bacillus subtilis or Thermus thermophilus. 54

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