Behavior of Bacterial Concrete under Freezing and Thawing Cycles

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1 Research Article Open Access JOURNAL OF ADVANCES IN CIVIL ENGINEERING AND CONSTRUCTION MATERIALS Journal Home Page: Behavior of Bacterial Concrete under Freezing and Thawing Cycles Mohamed Fadhel Suliman 1, Saad Issa Sarsam 2* 1 MSc. Student, Department of Highways and Transportation, University of Al-Mustansiria Baghdad, Iraq. 2 Professor, Department of Civil Engineering, College of Engineering, University of Baghdad, Iraq. Abstract Cracking exhibit a durability problem since the ingress of moisture and harmful chemicals such as sulphates and chlorides into the concrete through the cracks can cause premature matrix degradation and corrosion of embedded steel reinforcement, which may result in the decrement of strength and life. In this work, assessment of the durability of control and bacterial concrete was adopted by subjected the casted cubes, prisms and cylinder specimens to cycles of freezing and thawing. Concrete specimens of various type (cube of 100x100x100 mm, cylinder of 100mm diameter and 200 mm height, and prism of 100x100x500 mm) sizes have been prepared in the laboratory, then separated to two sets (with and without bacteria). A soil bacterium named Bacillus subtilis was cultured in the laboratory, the concentration of bacteria cell of B. subtilits in normal saline (NaCl, 9 g/l) suspension was 10 6 cell/ml. Data was analyzed to assess its impact on the strength properties (compression, tensile and flexural strength). It was noticed that the precipitation of calcite by continuous hydration of cement helps in production of calcium carbonate precipitation with the help of bacteria. It was observed that the bacterial concrete at end of cycles of freezing and thawing (60cycles) exhibits higher compressive, splitting tensile and flexural strength of 25.8%, 22.7% and 22% respectively than that of control concrete. It was concluded that implementation of the bacteria in the concrete mixture is beneficial to overcome the impact of freezing-thawing cracking and can be considered as sustainable and environment friendly solution for durability and resistance to frost weather. Key words: Bacteria, Durability, Concrete, Freezing and Thawing, Strength properties. Copyright: 2018 Unique Pub International (UPI). This is an open access article under the CC-BY-NC-ND License ( Correspondence to: Sarsam SI. Department of Civil Engineering, College of Engineering, University of Baghdad, Iraq. saadisasarsam@coeng.uobaghdad.edu.iq Funding Source(s): NA How to Cite: Suliman MF, Saleem MC. Behavior of bacterial concrete under freezing and thawing cycles. Journal of Advances in Civil Engineering and Construction Materials 2018; 1(1): Editorial History: Received : , Accepted: , Published:

2 1. Introduction Concrete is commonly used for the construction of rigid pavement for airport and major arterials in Iraq. Microcracks usually occur due to various mechanisms such as temperature gradient of thick pavement, repeated loading, shrinkage after casting, and Freeze-thaw cycles. Maintenance of cracks of macro size is a routine work, but the problem arises when micro cracks exists [1]. Cracks tend to expand further and eventually require costly repair. If micro cracks grow and reach the reinforcement, the reinforcement may corrode when it is exposed to water and oxygen and possibly carbon dioxide and chlorides (indirect degradation) [2-3]. There are a numbers of environment issues that aggressively attack concrete [4], these include the Sulfate environment, Alkali-silica or alkali-carbonate environment (alkali-aggregate reactions) freezing and thawing environment, acid environment, and chloride (corrosion) environment. Freeze-thaw cycles create a serious problem in the concrete structures. In sub-freezing temperature, residual moisture in pores freezes and expands producing cracks. Subsequent freeze/thaw cycles result in the propagation of these cracks. Therefore, alternating freeze-thaw cycles has the potential to deteriorate concrete lacking inadequate freezing and thawing resistance [5]. Deterioration of concrete exposed to freezing conditions can occur when there is enough internal moisture present that can freeze at the given exposure conditions. The source of moisture can be either internal (water already in the pores of concrete that is redistributed by thermodynamic conditions to provide a high enough degree of saturation at the point of freezing to cause damage) or external (water entering the concrete from an external source, such as rainfall) [6]. The determination of the resistance of concrete specimens to rapidly repeated cycles of freezing and thawing in the laboratory is covered by ASTM C-666 [7] in two different procedures: procedure A, rapid freezing and thawing in water, and procedure B, rapid freezing in air and thawing in water. Both procedures are intended for use in determining the effects of variations in the properties of concrete on the resistance of the concrete to the freezing-and-thawing cycles specified in the procedure. The frost resistance of concrete can be evaluated through the analysis of the variations of strength, elastic modulus and deformations as well as visual feature such as scaling and cracks [8]. The influence of freezing rate on freeze-thaw durability of concrete was studied by [9], specimens have been subjected to 300 freeze-thaw cycles at freezing rates of 4 to 6 c/h. Pulse velocity variation were used as indicators of concrete deterioration. It was concluded that the freezing rate has a significant influence on freeze-thaw durability, deterioration was always in the form of internal cracking, and no scaling was observed. [10] Stated that Bacterial concrete helps in increase the strength of concrete by the action of calcium precipitation of bacteria and it proves to be cost effective. Bacterial concrete increases compressive strength up to 20% as reported by [11]. The economical dose found by analysis is 10 ml that helped to make bacterial concrete quite economical. The cost of bacterial concrete is higher by 7-15% than conventional concrete [12-13]. It was stated by [14] that the use of bacterial concrete is one of the ecofriendly techniques for crack healing. This technique uses the calcium precipitate produced by bacterial metabolic activities to heal cracks. Bacterial concrete shows greater strength and durability than normal concrete. The addition of Bacillus Subtilis bacteria showed significant improvement in the compressive, split tensile and flexural strength than the conventional concrete. Another research [15] have investigated whether the cement mortar beams supplemented with bacteria performed better, when subjected to freeze-thaw attacks, 41

3 the test was done as per the specifications of ASTM C 666 [7], the results at the end of 180 cycles showed the rate of damage for the beams that contain bacteria is lower for the control beams. The presence of bacteria in different mediums increased the resistance of concrete towards freeze-thaw attack. From the above it can be concluded that bacteria can be easily cultured and safely used in improving the strength characteristics of concrete [16]. The inclusion of these bacteria in concrete will result in high strength, crack free and durable concrete structures in the future [17]. Based on the above introduction, the present investigation will consider implementation of Bacillus subtilis in the concrete to study its influence on the durability of concrete after it is subjected to freezing and thawing cycles. 2. Experimental 2.1. Material Characteristics Cement The Iraqi Ordinary Portland cement (Type 1) with a commercial name of (Tasluga) was implemented throughout the present work. Table 1 exhibit the chemical composition of cement, while Table 2 presents the physical properties of cement. Table 1. Chemical composition of cement. Oxide % by Weight Limit of Iraqi Specification No.5/ 1984 [18] CaO SiO Al2O Fe2O MgO 1.39 < 5.0 SO < 2.80 C3A Loss on ignition Insoluble residue 1.07 < 1.5 Lime saturated Factor C3S C2S C3A C4AF Table 2. Physical properties of cement. Physical Properties Test Result Limits of Iraqi Specification [18] Specific surface area, Blain s method m²/kg Soundness, Autoclave s Method, % 0.03 < 0.8 Setting time, Vicat s method Initial setting hour: min Final setting hour: min Compressive strength 3 days N/mm² 7 days N/mm² Coarse Aggregate 2:15 3: min 10 hours Crushed gravel with a nominal size of (19 mm) brought from Nibaee region was used in this work. The gravel was separated into different sizes by sieve analysis then recombined to match the grading requirements 42

4 according to Iraqi specification (IQS 45/1984) [19]. The aggregate was flushed and cleaned by water. Later, it was air dried. The physical properties of coarse aggregate are shown in Table 3. Table 3. Physical properties of coarse aggregate. Properties Results Limits of Specification Specification Bulk Specific gravity ASTM C127-01, [20] Absorption,% ASTM C127-0, [20] Clay content 0.06 <0.25 IQS No , [19] Fine Aggregate Fine aggregate (passing sieve No.4) was brought from Al-Ukhaider region and used in this work. The physical properties of fine aggregate are shown in Table 4. The combined aggregate gradation is presented in Table 5. Table 4. Physical properties of fine aggregate. Properties Results Fineness modulus 2.5 Specific gravity 2.6 Absorption, % 0.85 Table 5. Combined aggregate gradation implemented. Sieve size mm Percentage finer by weight Water The water used in mixes was drinking water of Baghdad area. This water was also used for curing Methodology The methodology implemented in this investigation consists of three steps, in the first step, Culture and growth of bacteria (Bacillus subtilis) in the laboratory was conducted. In the second step, preparation of concrete specimens (cubes, cylinder and beams) was conducted. In the third step, after curing of the specimens for 28 days, specimens were subjected to 30 and 60 freezing-thawing cycles then the strength properties of concrete specimens were evaluated Preparation, Isolation and Culture of Bacteria Bacillus subtilis The isolation and culture of bacteria Bacillus subtilis starts by collection of soil samples from Agricultural areas in Baghdad city and evacuation in glass bottles. As demonstrated in Figure 1, the soil sample was then mixed with distilled water and shacked vigorously to ensure thorough mixing. Serial dilution was made by transfer of 1 ml of soil suspension to 9 ml of distilled water in test tube, this soil suspension is of 10-1 dilution. 43

5 Figure 1. The Serial dilutions process of soil suspensions. After mixing this solution in vortex mixer, one ml of 10-1 dilution was transfer to 9 ml of distilled water, then the concentration of solution becomes 10-2 dilutions. This process was repeated until 10-6 dilution is obtained. After all these steps, petri-dishes plates with nutrient agar media according to the bacteria requirement have been prepared. The solution of concentration 10-4 to 10-6 was spread by cotton swab on the petri-dishes plate with nutrient agar media in it and incubated in 37 C to 24 hours in the incubator. After 24 hours, the plates are taken out from incubator, the type of colony formation in the Petri dish plate was checked. Some more petri-dishes plates with the same media and soil sample with different concentration have also been prepared. After this, the different types of colonies on different plates were observed and the growth after 24 hours incubation was checked as shown in Figure 2. The morphology of different colonies was checked by gram staining method. Similar preparation procedures have been reported by [15, 21]. Figure 2. Growth of different type of colonies Bacillus on different plates. The urease test method and vitek 2E compact system have been implemented for identification of Bacillus subtilis. Afterword, preparation of the concentration 10 6 of bacterial cell (Bacillus subtilis) starts by Transfer of loop full of single colonies of Bacillus subtilis that form urease enzyme from nutrient agar to brain heart broth 44

6 media and incubation at 37 C on shaker at 150 rpm for 24 hours as exhibited in Figure 3. The harvest of bacterial cell was done by centrifuge the 24 hour s old grown culture (5000 rpm, 5 minutes). The sediments (bacterial cell) were form after centrifuge and were re-suspended in normal saline (NaCl, 9 g/l). The concentration of bacteria cell of Bacillus subtilits in suspension was 10 6 cell/ml. Figure 3. Centrifuge device and the sediments (bacterial cell) Preparation of Concrete Mixture Normal Concrete Materials Normal concrete mixture was designed as per (ACI ) method [22], such mixture is usually used for rigid pavement in order to get the suitable compressive strength of 30Mpa at 28 days. The design mixture and proportions of concrete are given in detail in Table 6. Table 6. Materials and proportions for mixture concrete. Material Weight Cement 373kg/m 3 Water 178 kg/m 3 Coarse aggregate 1080 kg/m 3 Fine aggregate 644 kg/m Bacterial Concrete Materials In the mixing process of bacterial concrete, the bacterial concentration of 10 6 cell/ml of water was added to the water during the process of mixing, nutrients (calcium lactate of 2% of cement mass) were firstly dissolved in part of the mixing water and part of the mixing water was replaced by bacterial suspension, as shown in Figure 4. 45

7 Figure 4. Preparation of the bacterial solution with mixing water Freezing and Thawing Test The specimens that will be subjected to cycles of freezing and thawing are cubes, cylinder and prisms prepared and tested in triplicate for each type of mixture (normal, and bacterial concrete). The prepared specimens were subjected to 28 days curing period in a water bath before the cyclic freezing and thawing. The freezing and thawing test was carried out according to ASTM C-666 [7] procedure B, (rapid freezing in air and thawing in water). Freezing and thawing tests are started by placing the specimens in the thawing water at the beginning of the thawing phase of the cycle at temperature 30±2 C for 2½ hour to ensure that the specimens are completely thawed then, the specimens are taken out of water and are placed in deep freezer at temperature (- 11±1 C) for 4±½ hour as the beginning of the freezing phase of the cycle. This procedure is repeated for 60 cycles of freezing and thawing. Specimens were subjected to visual examination after each cycle to detect scaling, cracking or any other expected defects. Figure 5 shows part of the tested specimens and freezing apparatus. Figure 5. Part of the prepared Specimens and the freezing apparatus. 46

8 3. Results and Discussion 3.1. Effect of Freezing and Thawing Cycles on Mechanical Properties The relationship between strength and number of cycles are summarized in Table 7 for cubes and cylinders and prisms with and without bacteria, respectively. It is clear from the results that the mechanical strength (compressive, splitting tensile, flexural strength) for bacterial concrete performed better than the control concrete (without bacteria) before and after subjecting to freezing and thawing cycles. The results have shown that the mix of bacterial concrete at 60 cycles of freezing and thawing shows higher in compressive strength, splitting tensile strength, and flexural strength by (25.8, 22.7 and 22) % respectively than that of the control mix. Table 7. Test results of compressive, tensile, and flexural strength after freezing and thawing cycles. Mixture Type Compressive Strength (MPa) Splitting Tensile Strength (MPa) Flexural Strength (MPa) Number of cycles after 28 days curing Number of cycles after 28 days curing Number of cycles after 28 days curing Zero 30 days 60 days Zero 30 days 60 days Zero 30 days 60 days Control Bacterial This may be attributed to that the calcite layer improves the impermeability of the specimen, thus increasing its resistance to freeze-thaw attack. Table 8 show percentage of decrease in strength for cubes and cylinders and prisms with and without bacteria subjected to alternate freezing and thawing cycles. Figure 6 show strength devices test setup. It can be seen from the result that the mechanical strength decreases gradually as the cycles of freezing and thawing increase. The reduction in the strength properties after cyclic freezing and thawing for both types of concrete may be attributed to the fact that the water in the capillary pores of the hardened cement paste freezes which leads to increase in the volume of water and leads to dilating pressure which causes disintegration to the concrete when it exceeded the strength of concrete. Mixture Type Table 8. Percentage of decrease in compressive strength after freezing and thawing cycles. Control Bacterial Compressive Strength % reduction % reduction after 30 after 60 cycles cycles Splitting Tensile Strength % reduction % reduction after 30 after 60 cycles cycles Flexural Strength % reduction after 30 cycles % reduction after 60 cycles Based on the test results obtained, it can be noticed that the reduction in strength properties in bacterial concrete specimens due to freezing and thawing cycles is lower than that in the control concrete specimens.such reduction was in the range of (40-50) %. This may be attributed to the continuous crack healing process occurred due to the precipitation of calcium carbonate by the bacteria due to Microbial-Induced Calcite Precipitation MICP which provides an option to improve the durability of concrete structures by controlling the porosity through calcite deposition and therefore reduction of the effect of frost water in pores and a new created cracked deterioration and leads to decreasing reductions in strength [15-16, 21]. 47

9 Figure 6. Strength devices test setup. 4. Conclusion Based on the testing program, the following conclusions can be drawn. 1. Implementation of bacteria (Bacillus subtilis) in the mixing water of concrete exhibit a positive influence on the durability and strength properties of concrete. 2. Bacterial concrete at end of cycles of freezing and thawing exhibits higher in compressive, splitting tensile and flexural strength by 25.8%, 22.7% and 22% respectively than that of control concrete. 3. The reduction in compressive strength at end of cycles of freezing and thawing was 4% and 2.27% for control and bacterial concrete. 4. The reduction in splitting tensile strength at end of cycles of freezing and thawing was 4.49% and 3.27% for control and bacterial concrete. 5. The reduction in flexural strength at end of cycles of freezing and thawing was 5% and 3.65% for control and bacterial concrete. 6. The reduction in strength properties in bacterial concrete specimens due to freezing and thawing cycles is lower than that in the control concrete specimens. Such reduction was in the range of (40-50) %. 7. Bacteria provides an option to improve the durability of concrete structures and reducing the effect of frost-thaw cycles impact on concrete pores and a new created cracked deterioration and leads to controlling the reductions in strength. 5. Conflicts of Interest The author(s) report(s) no conflict(s) of interest(s). The author along are responsible for the content and writing of the paper. 6. Acknowledgments NA 48

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