TY - JOUR
AU - Reddy, M Sudhakara
AB - Abstract Microbial-induced carbonate precipitation (MICP) has a potential to improve the durability properties and remediate cracks in concrete. In the present study, the main emphasis is placed upon replacing the expensive laboratory nutrient broth (NB) with corn steep liquor (CSL), an industrial by-product, as an alternate nutrient medium during biocementation. The influence of organic nutrients (carbon and nitrogen content) of CSL and NB on the chemical and structural properties of concrete structures is studied. It has been observed that cement-setting properties were unaffected by CSL organic content, while NB medium influenced it. Carbon and nitrogen content in concrete structures was significantly lower in CSL-treated specimens than in NB-treated specimens. Decreased permeability and increased compressive strength were reported when NB is replaced with CSL in bacteria-treated specimens. The present study results suggest that CSL can be used as a replacement growth medium for MICP technology at commercial scale. Electronic supplementary material The online version of this article (10.1007/s10295-018-2050-4) contains supplementary material, which is available to authorized users. Introduction Concrete is one of the most widely used structural building materials in the world. The incomparable and excellent properties of concrete, such as strength and durability, have made it an attractive construction material. An escalating demand for urban infrastructure has become a great challenge with the increasing world population. Annually, 10 billion tons of concrete production was estimated to meet the increasing demands of all urban infrastructures like residential buildings, transport connectivity and industrial units [7]. With growing dependence, sustainable design of concrete structures is also a prime concern in the world. Studies conducted by the Organization for Economic Cooperation and Development (OECD) have reported that approximately 30% of greenhouse gases are emitted from the residential and commercial building sectors [45]. Energy requirements, water resources, natural resources consumption and demolition waste have left an enormous environmental footprint on earth [36]. Factors like climate change, temperature variations and external chemical attacks affect the lifecycle performance of concrete leading to its durability problems [28]. Ingress of aggressive agents like CO2, SO42− and Cl− ions into the matrix of concrete leads to premature deterioration causing irreversible changes in its serviceability. Permeation due to the interconnected pore system in the near surface concrete matrix directly influences the rate of deterioration [10]. Early deterioration of infrastructures around the globe is a matter of concern. Intensive research has been done to protect the concrete structures suffering from the penetration of aggressive agents. Use of different organic and inorganic surface pore-blocking agents has been reported by researchers to protect the concrete structures from the ingress of aggressive substances. Varity of concrete surface treatments with silanes, siloxanes sodium silicate, polyurethane, ethyl silicate and nano-SiO2 has been investigated [28, 38]. Drawbacks like detachment with aging in outdoor exposure are also associated with the surface coaters, which did not promise the long-term performance. Recently, application of biotechnology in concrete research led to a bio-inspired treatment method to enhance the durability properties of concrete. Microbial-induced calcium carbonate precipitation (MICP) by using calcifying bacteria in construction material via biomineralization process has become substantially popular. MICP technology has become an innovative and promising technique for improving the durability properties of concrete structures [5, 21, 23, 30, 32, 37]. Improved mechanical strength and effective reduction in porosity of concrete with MICP are positive attributes. The challenges associated with the use of MICP for improving concrete durability include the potential negative impacts of the organic substrates in the growth medium on the concrete setting process and the cost associated with supplying the bacterial growth medium. Disadvantages in the use of organic matter (i.e., yeast extract) on the retardation of setting process of cement paste have been reported by many researchers [20, 42, 44]. The operating cost of this technology at the commercial scale might have economic limitations [22, 30]. The use of laboratory grade nutrient broth, i.e., yeast extract cost is as high as 60% of the total operating cost [33]. Implementation of MICP technique in newly constructed concrete structures at field scale would not be possible because of its expensive cost. Hence, it is essential to use an inexpensive, high-protein-containing alternative nutrient source to reduce the overall production cost of this technology. Previously, we reported the use of lactose mother liquor, collected from the dairy industry, as a nutrient source for biomineralization [1]. Later, we used corn steep liquor (CSL), a by-product from the starch industry, as a low-cost nutrient medium for the MICP technology [3]. We have extended these studies further to study the durability properties of building materials, such as compressive strength, permeability and prevention of corrosion and compared the results with the commercially available nutrient medium [2, 4]. Eryuruk et al. [27] demonstrated that the hydraulic conductivity of a paddy field decreased through a biocalcification process using CSL as a source of nutrients. Recently, Amiri and Bundur [6] used CSL as an alternative carbon source for biomineralization in cement-based materials and studied its impact on initial setting of cement paste and mortar mixes and compressive strength. Though CSL served as an alternative to nutrient medium or yeast extract medium in biomineralization and improved the permeability, compressive strength and initial setting of cement-based materials, no reports are available about the nutrient components, such as carbon and nitrogen content, bacterial cells and change in pH on the chemical and structural properties of concrete. The present study was aimed to test the efficacy of nutrient components present in the CSL on the structural properties of concrete. To evaluate the presence of organic matter in concrete specimens, carbon and nitrogen content was determined at different depths of the concrete specimens. The change in pH at different depths of the concrete specimens was also monitored. A comparative study was conducted to figure out the influence of nutrient broth and CSL on setting property of cement and compressive strength of concrete. Further, the CSL-treated concrete specimens were analyzed for sorptivity test, water permeability test, rapid chloride permeability test (RCPT), scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM–EDX), and X-ray diffraction (XRD). Materials and methods Microbial strains and culture conditions The bacterial strain, Bacillus sp. CT5, isolated by us from the cement sample [1] was used in this study. Corn steep liquor was collected from Sukhjit Starch & Chemicals Limited, Phagwara, Punjab, India. The chemical composition of the CSL is as follows: pH 4.0; total carbohydrates 5.8%; proteins 24%; fats 1.0%; minerals 8. 2%. For the growth and experimental purposes, 1.5% CSL was used throughout the study. Nutrient broth (NB) (Peptone 10 g/L, yeast extract 10 g/L, sodium chloride 5 g/L) procured from Himedia (Himedia, India) was also used to grow the bacteria. To carry out microbial calcium carbonate precipitation in concrete specimens, the culture was grown in autoclaved CSL medium (1.5% v/v) and nutrient broth supplemented with filter-sterilized 2% urea (w/v) and 25 mM CaCl2 solution at 37 °C under shaking condition (120 rpm). The pH of the CSL and NB media was adjusted to 7.5 with 1 N NaOH prior to autoclave without urea and CaCl2. Materials Ordinary Portland cement (43 Grade) conforming to IS 8112-2013 standards [14] was used in the present study. Locally available, clean, dry and well-graded natural river sand conforming to Zone II was used as fine aggregate. The specific gravity of fine aggregates was 2.70. The coarse aggregate used was crushed gravel with nominal particle size of 20 and 10 mm. The specific gravity for 20 mm aggregates and 10 mm aggregates was 2.63 and 2.65, respectively. Both fine aggregate and coarse aggregate conform to IS: 383-1970 standards [15]. Preparation of cement paste This experimental program was conducted to study the influence of addition of the bacterial culture and plain nutrient ingredients on the initial and final setting properties of cement. The change in initial setting characteristic of cement paste upon incorporation of bacterial cells and the associated nutrients at the casting stage was investigated by using Vicat Apparatus as per IS 4031: 1988 (Part 5) [17]. Briefly, for conducting setting time test, water required to produce standard cement paste, i.e., standard consistency was first determined by IS 4031: 1988 (Part 4) [16]. Then the paste for measuring setting time was prepared by using 0.85 times the water required to give a paste of standard consistency. In the present study, the standard consistency was determined to be 29.5%. Accordingly, 25.1% water was added for measuring setting time of cement. Five types of cement pastes were prepared. The composition and nomenclature of the pastes is presented in Table 1. Control paste was made by mixing cement and water. Corn steep liquor paste was prepared by adding 1.5% of corn steep liquor, 2% urea and 25 mM CaCl2 to cement, while NB paste was made by adding 1.3% of nutrient broth, 2% urea and 25 mM CaCl2 to cement. CSL-CT5 paste and NB-CT5 paste were prepared by mixing cement with bacterial cells grown in CSL medium and NB medium supplemented with 2% urea and 25 mM CaCl2, respectively. The consistency of all the mixes was kept the same. Mixing ingredients of cement paste mixes Cement mixes . Cement (g) . Water (g) . NB media (g) . CSL media (g) . Bacterial culture (g) . Control 400 100.3 – – – CSL 400 – – 100.3 – NB 400 – 100.3 – – CSL-CT5 400 – – – 100.3 NB-CT5 400 – – – 100.3 Cement mixes . Cement (g) . Water (g) . NB media (g) . CSL media (g) . Bacterial culture (g) . Control 400 100.3 – – – CSL 400 – – 100.3 – NB 400 – 100.3 – – CSL-CT5 400 – – – 100.3 NB-CT5 400 – – – 100.3 CSL corn steep liquor medium, NB nutrient broth medium, CSL-CT5 bacterial paste in CSL, NB-CT5 bacterial paste in NB Open in new tab Mixing ingredients of cement paste mixes Cement mixes . Cement (g) . Water (g) . NB media (g) . CSL media (g) . Bacterial culture (g) . Control 400 100.3 – – – CSL 400 – – 100.3 – NB 400 – 100.3 – – CSL-CT5 400 – – – 100.3 NB-CT5 400 – – – 100.3 Cement mixes . Cement (g) . Water (g) . NB media (g) . CSL media (g) . Bacterial culture (g) . Control 400 100.3 – – – CSL 400 – – 100.3 – NB 400 – 100.3 – – CSL-CT5 400 – – – 100.3 NB-CT5 400 – – – 100.3 CSL corn steep liquor medium, NB nutrient broth medium, CSL-CT5 bacterial paste in CSL, NB-CT5 bacterial paste in NB Open in new tab Preparation of concrete specimens Concrete mix was prepared by using cement: sand: coarse aggregate in the ratio 1: 1.82: 3.24 (by weight) and water to cement ratio (w/c) of 0.5. For casting of bacterial-treated specimens, CSL medium and NB medium with bacterial culture (4 × 108 cells/ml) supplemented with 2% urea (w/v) and 25 mM calcium chloride solution (w/v) were used instead of water. The bacterial culture was prepared by growing the cells in CSL and NB medium till it attained the O.D600, of 0.5 (exponential phase). Then this culture was admixed with the concrete. The bacterial culture to cement ratio was also maintained at 0.5. For the bacterial spray treatment, the culture was grown in CSL as well as in NB medium till it reached the O.D600, of 0.5 (4 × 108 cells/ml). Cement, sand and aggregates were thoroughly mixed for 2 min in the concrete mixture before adding water, CSL medium and NB medium. The ingredients were mixed properly and the fresh mix in the plastic stage was immediately transferred to iron moulds (150 mm × 150 mm × 150 mm). After casting, all the specimens were allowed to remain in the iron moulds and kept in a casting room at room temperature of 27 ± 2 °C for 24 h. Thereafter, the specimens were demoulded and cured till the testing age. Four different curing regimes as specified in Table 2 were adopted in this study. Outline of different sets of concrete specimens and method of curing treatments Specimens . Material used . Method of curing . Control Cement: sand: coarse aggregate water/cement = 0.5 Water curing for 28 days CSL treated (CT) Cement: sand: coarse aggregate CSL media/cement = 0.5 Submersion in CSL media with urea and CaCl2 without bacteria for 28 days NB treated (NT) Cement: sand: coarse aggregate NB media/cement = 0.5 Submersion in NB media with urea and CaCl2 without bacteria for 28 days CSL-bacterial admixed treatment (CBAT) Cement: sand: coarse aggregate bacterial culture/cement = 0.5 Submersion in CSL media, urea, CaCl2 and bacterial culture for 28 days NB-bacterial admixed treatment (NBAT) Cement: sand: coarse aggregate bacterial culture/cement = 0.5 Submersion in NB media, urea, CaCl2 and bacterial culture for 28 days CSL-bacterial spray treatment (CBST) Cement: sand: coarse aggregate bacterial culture/cement = 0.5 Bacterial spray on specimens twice a day till 28 days NB-bacterial spray treatment (NBST) Cement: sand: coarse aggregate bacterial culture/cement = 0.5 Bacterial spray on specimens twice a day till 28 days Specimens . Material used . Method of curing . Control Cement: sand: coarse aggregate water/cement = 0.5 Water curing for 28 days CSL treated (CT) Cement: sand: coarse aggregate CSL media/cement = 0.5 Submersion in CSL media with urea and CaCl2 without bacteria for 28 days NB treated (NT) Cement: sand: coarse aggregate NB media/cement = 0.5 Submersion in NB media with urea and CaCl2 without bacteria for 28 days CSL-bacterial admixed treatment (CBAT) Cement: sand: coarse aggregate bacterial culture/cement = 0.5 Submersion in CSL media, urea, CaCl2 and bacterial culture for 28 days NB-bacterial admixed treatment (NBAT) Cement: sand: coarse aggregate bacterial culture/cement = 0.5 Submersion in NB media, urea, CaCl2 and bacterial culture for 28 days CSL-bacterial spray treatment (CBST) Cement: sand: coarse aggregate bacterial culture/cement = 0.5 Bacterial spray on specimens twice a day till 28 days NB-bacterial spray treatment (NBST) Cement: sand: coarse aggregate bacterial culture/cement = 0.5 Bacterial spray on specimens twice a day till 28 days CSL media, NB media, urea and calcium chloride had the following concentrations: CSL (1.5% v/v), NB media (1.3% w/v), 2% urea (w/v) and 25 mM calcium chloride (w/v). All specimens were prepared in triplicate Open in new tab Outline of different sets of concrete specimens and method of curing treatments Specimens . Material used . Method of curing . Control Cement: sand: coarse aggregate water/cement = 0.5 Water curing for 28 days CSL treated (CT) Cement: sand: coarse aggregate CSL media/cement = 0.5 Submersion in CSL media with urea and CaCl2 without bacteria for 28 days NB treated (NT) Cement: sand: coarse aggregate NB media/cement = 0.5 Submersion in NB media with urea and CaCl2 without bacteria for 28 days CSL-bacterial admixed treatment (CBAT) Cement: sand: coarse aggregate bacterial culture/cement = 0.5 Submersion in CSL media, urea, CaCl2 and bacterial culture for 28 days NB-bacterial admixed treatment (NBAT) Cement: sand: coarse aggregate bacterial culture/cement = 0.5 Submersion in NB media, urea, CaCl2 and bacterial culture for 28 days CSL-bacterial spray treatment (CBST) Cement: sand: coarse aggregate bacterial culture/cement = 0.5 Bacterial spray on specimens twice a day till 28 days NB-bacterial spray treatment (NBST) Cement: sand: coarse aggregate bacterial culture/cement = 0.5 Bacterial spray on specimens twice a day till 28 days Specimens . Material used . Method of curing . Control Cement: sand: coarse aggregate water/cement = 0.5 Water curing for 28 days CSL treated (CT) Cement: sand: coarse aggregate CSL media/cement = 0.5 Submersion in CSL media with urea and CaCl2 without bacteria for 28 days NB treated (NT) Cement: sand: coarse aggregate NB media/cement = 0.5 Submersion in NB media with urea and CaCl2 without bacteria for 28 days CSL-bacterial admixed treatment (CBAT) Cement: sand: coarse aggregate bacterial culture/cement = 0.5 Submersion in CSL media, urea, CaCl2 and bacterial culture for 28 days NB-bacterial admixed treatment (NBAT) Cement: sand: coarse aggregate bacterial culture/cement = 0.5 Submersion in NB media, urea, CaCl2 and bacterial culture for 28 days CSL-bacterial spray treatment (CBST) Cement: sand: coarse aggregate bacterial culture/cement = 0.5 Bacterial spray on specimens twice a day till 28 days NB-bacterial spray treatment (NBST) Cement: sand: coarse aggregate bacterial culture/cement = 0.5 Bacterial spray on specimens twice a day till 28 days CSL media, NB media, urea and calcium chloride had the following concentrations: CSL (1.5% v/v), NB media (1.3% w/v), 2% urea (w/v) and 25 mM calcium chloride (w/v). All specimens were prepared in triplicate Open in new tab Compressive strength, carbon and nitrogen and pH profile To study the compressive strength, concrete cubes of 150 mm dimension were casted. The specimens were cured in bacterial culture grown in CSL and NB medium along with their respective controls. After 28 days of curing, the compressive strength was measured as per IS 516: 1959 standards [13] using an automatic compression testing machine, COMPTEST 3000. Concrete cubes after respective curing were drilled using a rotary hammer drilling machine to collect the concrete powder for analyses. Concrete cubes were drilled up to the depth of 50 mm from two opposite sides as reported earlier by us [31]. Concrete powder was separately collected from each depth. Different points were drilled from each side of the cube to get a homogenous sample of concrete powder. The powder samples obtained were analyzed to calculate carbon and nitrogen content at various depths. To calculate the amount of organic carbon in concrete powder, Walkley–Black procedure was followed [43]. Kjeldahl method was used to determine the ammonia producing nitrogen in the concrete powder as per IS: 5194-1969 standards [18]. For the quantitative determination of carbohydrate content in NB and CSL media, anthrone method was used [34]. Briefly, 4 ml of anthrone reagent (200 mg anthrone in 100 ml of 95% H2SO4) was added in 1 ml of NB/CSL media and the test tube was heated in boiling water bath for 10 min. After cooling, absorbance was measured at 620 nm by the UV–Vis spectrophotometer. Concentration of the sugar in the sample was calculated from the glucose calibration curve. The pH variations at various depths were investigated potentiometrically in concrete specimens treated microbially with CSL media. The pH glass electrode was immersed in the suspension of a 1:5 concrete powder: water after stirring for 1 h. Permeation properties The efficiency in resistance towards water penetration was investigated for the different mixes as described in Table 2 at the age of 28 days. Sorptivity was determined according to ASTM C1585 [9]. The cylindrical test specimen of diameter 100 mm and thickness 50 mm was prepared to conduct the sorptivity test. Before conducting the test, a side surface of the specimen was sealed by sealing material (i.e., epoxy) and the initial mass was noted. One surface of the specimen was exposed to water and the mass increase of the specimen by absorption was monitored by weighing it at different time intervals. The mass change was recorded at the intervals of 60 s, 5, 10, 20, 30, 60 min and every hour up to 6 h. From the value of mass change, the volume of water absorbed per unit of cross-sectional area was evaluated at each time interval. A plot between the square root of time and volume of water absorbed was plotted. The slope of the graph is taken as the value of sorptivity for that specimen. To determine the penetration of chloride ions in concrete through electrical conductance, a rapid chloride penetration test (RCPT) was conducted as per ASTM C1202-97 [8]. Cylindrical specimens were subjected to a potential difference of 60 V for 6 h by placing them inside the test cell. The solution of sodium chloride 3% (by mass) was kept in one side of the test cell connected to the negative terminal of power supply, and the sodium hydroxide solution (0.3 N) was kept in the other side of the test cell connected to the positive terminal of power supply. Total charge passed (in terms of coulombs) is a measure of the electrical conductance of the concrete and directly proportional to the chloride penetrability. The water permeability test was carried out as per DIN 1048 standards [25] at the age of 28 days. The concrete specimens were exposed to a water pressure of 0.5 N/mm2 for 72 h and the vertical penetration depth of water into concrete was then measured after breaking the concrete specimen. Micro-structural analysis For analyzing the calcium carbonate crystals in concrete specimens at the age of 28 days, scanning electron microscopy (SEM) (ZEISS EVO 50) was done. The elemental composition of micro-structural crystals was identified with energy-dispersive X-ray spectroscopy (EDX). For conducting SEM and EDX analyses, small pieces of concrete samples were collected. Samples were finely polished and gold-coated with a sputter coating. To disperse excess charge from the sample, a thin coating of carbon was applied on the polished surface. X-ray diffraction (XRD) was done on the powdered samples, obtained while drilling and sieved through 90 µm sieve. XRD spectrum was obtained using Bruker D8 X-ray diffractometer with a Cu anode (40 kV and 30 mA) and scanning from 10° to 80° 2θ. Statistical analysis All the experiments were performed in triplicates. One-way analysis of variance was performed and the means were compared with Tukey’s test at P < 0.05. Results of compressive strength were analysed by using unpaired t test. All the analyses were performed by using Graph Pad Prism 5.1 software. Results and discussion Initial setting time cement mixes The initial and final setting time of control paste mix was 120 and 240 min, respectively. On comparison with control paste mix, no delay in initial and final setting was observed in CSL paste mix. However, a significant delay in both initial and final setting time was observed in NB paste mix. Initial setting time increased by 100 min and the final setting time by 250 min in NB paste mix when compared to control paste mix (Fig. 1). In CSL-CT5 paste mix, an increase of 20 min in initial setting and 30 min in final setting time was recorded as compared to control paste. The initial setting time was increased by 40 min and final setting time by 50 min when compared to control paste in the case of NB-CT5 paste mix (Fig. 1). All these observations indicate that the addition of plain CSL medium had no influence on the setting characteristics of cement. Whereas the addition of plain NB medium severely influenced the setting characteristics of cement. Incorporation of bacterial cells with CSL medium showed inconsequential effect on the setting characteristics. However, addition of bacterial cells grown in NB media causes not as much of delay in setting of cement as it was observed in NB paste. Fig. 1 Open in new tabDownload slide Initial and final setting times of different cement paste mixes. Bars sharing a common letter within the treatment are not significant at P < 0.05. Error bars represent standard deviation (n = 3) The presence of organic admixtures has been reported to have an adverse effect on the chemical properties of cement resulting in retardation of initial hydration of cement [46]. In NB cement paste, nutrient media contains yeast extract, and it has been reported that yeast extract acts as a retardation substance and influences the degree of hydration of cement [44]. The presence of different fractions of carbohydrates in the yeast extract acts as an effective chemical retardant [20, 41]. It was reported that carbohydrate strongly affects the silicate component and retards the hardening of Portland cement [19]. Amiri and Bundur [6] also reported the delay in initial setting in urea yeast extract medium as compared to CSL and control samples. Higher carbohydrate content in NB medium (fourfold) as compared to CSL medium might have affected the retarding characteristics in cement hardening. Compressive strength Addition of Bacillus sp. (CT-5) along with CSL/NB media and urea-CaCl2 in concrete specimen and curing with respective medium for 28 days significantly increased the compressive strength as compared to control specimen (Fig. 2). The CBAT specimens showed an increase of 25% in compressive strength as compared to the control specimens. The CBST specimens in which bacteria were introduced into concrete after casting in the form of spray during curing also increased 16% in compressive strength as compared to the control specimens. The concrete specimens with bacterial admixture in NB medium supplemented with urea-CaCl2 during casting and spraying with respective medium showed an increase of 29 and 8% in compressive strength, respectively. However, the compressive strength of specimens treated with NB only registered a drastic decrease by 19% as compared to the control mix. Fig. 2 Open in new tabDownload slide Influence of CSL media, NB media and bacterial culture on compressive strength (MPa) of concrete specimens at the age of 28 days curing. Error bars represent standard deviation (n = 3). *P < 0.05 Specimens casted with nutrient medium alone showed drastic reduction in the compressive strength. The results of setting time and compressive strength together indicate that the addition of organic matter (i.e., yeast extract) alone has a retardation effect on hydration. Ersan et al. [26] also reported a decrease in the compressive strength of a mortar specimen due to the presence of yeast extract. Contrary to this, Amiri and Bundur [6] reported that the compressive strength of mortar increased when the specimens were treated with yeast extract and CSL as compared to control specimens as well as the specimens treated with bacteria grown in yeast extract and in CSL. Addition of CSL media had not altered the chemical and mechanical properties of concrete in this study. Our previous results also showed an increase in compressive strength in specimens treated with bacteria grown in CSL as compared to control specimens [2–4]. As the CSL is a nutritional supplement, it comprised rich, free amino acids and vitamins, which act as excellent growth stimulants for bacterial cells [40]. In bacterial admixed and bacterial spray treatment of concrete specimen with NB/CSL media had shown effective compressive strength gain in both the curing regimes. However, use of CSL as growth medium had not shown any modifications in the concrete chemical properties. On comparison with NB media, CSL may serve as a carbon and nitrogen supplement and replace yeast extract nutrient medium. Carbon, nitrogen and pH profile Carbon and nitrogen content in concrete specimens with depth-wise profile was determined. It was observed that the percentage of carbon and nitrogen content remains same at all depths for the control specimen. CBAT and NBAT specimens registered maximum carbon and nitrogen content at all depths. The carbon and nitrogen content in CBST and NBST specimens was maximum in the upper depths (0–20 mm) followed by almost same at all depths (Fig. 3). However, overall carbon and nitrogen content in NBAT and NBST specimens was observed to be much higher than CBAT and CBST specimens at all depths. Similar trend of overall carbon and nitrogen content was observed to be higher in NT specimen on comparison with CT specimen at all depths (Fig. 3). The carbon content in NB medium (800 mg/L) was estimated to be fourfold higher than that in the CSL medium (200 mg/L). The pH value in all specimens was found to be in the range of 12.1–12.5 indicating no significant change due to different treatments (Fig. 4). Fig. 3 Open in new tabDownload slide Carbon and nitrogen content (% by mass) of concrete specimens at different depths in various treatments. C carbon content; N nitrogen content. a Control specimen; b NT and CT specimen; c NBAT and CBAT specimen; d NBST and CBST specimen. Error bars represents standard deviation (n = 3) Fig. 4 Open in new tabDownload slide pH profiles of concrete specimens at different depths in various treatments. Control; CT: CSL treated; CBAT: CSL-bacterial admixed treatment; CBST: CSL-bacterial spray treatment. Error bars represent standard deviation (n = 3) Carbon and nitrogen content in concrete matrix was much higher in NB-treated specimens than that in CSL-treated specimens. Addition of nutrient broth and CSL to the concrete increased the carbon and nitrogen content. This might be due to the additional accumulation of curing material and bacterial cells on the outer surface. Joshi et al. [31] also reported the increase in carbon and nitrogen content in bacteria-treated specimens as compared to control specimens. pH is one of the most influential parameters in concrete durability and the alkaline condition of concrete with pH 12–13 keeps the reinforced steel resistant to corrosion [12]. The drop of pH of concrete destabilizes the passive state of steel which results into rebar corrosion and hence leads to premature deterioration of reinforced concrete [29]. Alkaline environment of concrete was not influenced with addition of bacterial cells supplemented with either nutrient broth or CSL in this study. No significant variation in pH was observed in medium-treated specimens as compared to control specimens in this study and the pH was maintained above 12. Similar results were reported when the specimens were treated with bacteria grown in NB medium by Joshi et al. [31]. Permeation properties Sorptivity coefficient, RCPT and water impermeability of various mixes were measured after 28 days of curing. Among all the tested mixes, control mix has highest sorptivity coefficient. The specimens treated with bacterial cultures grown in CSL and either admixed (CBAT) or sprayed (CBST) registered significantly lowest sorptivity coefficient followed by the specimens treated with bacteria grown in NB (NBAT and NBST) as compared to control or media alone cured specimens (Table 3). In RCPT, resistance to chloride ion penetration by all specimens was evaluated. The charge transfer was significantly reduced in all specimens treated with bacteria and the penetration values fall in low penetration range. In CBAT specimen the total charge passed was 1228 coulombs and in CBST specimen it was 1310 coulombs. While in control and CT specimens, similar charge transfer resistance was registered and both fall in the category of moderate penetration type (Table 3). In water impermeability test, maximum vertical penetration of water was found in control specimen (30.2 mm). The water penetration depth was significantly reduced in all specimens treated with bacteria. In CBAT specimen, minimum penetration depth of 12.5 mm, while in CBST specimen 13.9 mm was recorded. CT specimen prepared by using CSL media had the water penetration depth of 28.2 mm, while for NB medium specimens it was 31.2 mm (Table 3). Permeation properties (sorptivity, RCPT and water impermeability test) of concrete specimens treated with media and bacteria cured for 28 days Specimen . Sorptivity coefficienta . RCPT . Water penetration (mm)a . Mean charge passed (coulombs)a . Penetration typeb . Control 0.020 ± 0.0a 3180 ± 127a Moderate 30.2 ± 2.1b CSL treated (CT) 0.014 ± 0.0b 2838 ± 141b Moderate 28.2 ± 3.2b NB treated (NT) 0.014 ± 0.0b 2942 ± 148b Moderate 31.2 ± 17a CSL-bacterial admixed treatment (CBAT) 0.005 ± 0.0d 1228 ± 79c Low 12.5 ± 1.5c NB-bacterial admixed treatment (NBAT) 0.008 ± 0.0c 1204 ± 95c Low 14.2 ± 2.1c CSL-bacterial spray treatment (CBST) 0.005 ± 0.0d 1310 ± 58c Low 13.9 ± 1.3c NB-bacterial spray treatment (NBST) 0.007 ± 0.0c 1340 ± 62c Low 13.6 ± 1.4c Specimen . Sorptivity coefficienta . RCPT . Water penetration (mm)a . Mean charge passed (coulombs)a . Penetration typeb . Control 0.020 ± 0.0a 3180 ± 127a Moderate 30.2 ± 2.1b CSL treated (CT) 0.014 ± 0.0b 2838 ± 141b Moderate 28.2 ± 3.2b NB treated (NT) 0.014 ± 0.0b 2942 ± 148b Moderate 31.2 ± 17a CSL-bacterial admixed treatment (CBAT) 0.005 ± 0.0d 1228 ± 79c Low 12.5 ± 1.5c NB-bacterial admixed treatment (NBAT) 0.008 ± 0.0c 1204 ± 95c Low 14.2 ± 2.1c CSL-bacterial spray treatment (CBST) 0.005 ± 0.0d 1310 ± 58c Low 13.9 ± 1.3c NB-bacterial spray treatment (NBST) 0.007 ± 0.0c 1340 ± 62c Low 13.6 ± 1.4c aMean values sharing a common letter within the column are not significant at P < 0.05 bThe range of charge for high (> 4000), moderate (2000–4000), low (1000–2000) and very low (100–1000) as per the ASTM C1202-10 standard Open in new tab Permeation properties (sorptivity, RCPT and water impermeability test) of concrete specimens treated with media and bacteria cured for 28 days Specimen . Sorptivity coefficienta . RCPT . Water penetration (mm)a . Mean charge passed (coulombs)a . Penetration typeb . Control 0.020 ± 0.0a 3180 ± 127a Moderate 30.2 ± 2.1b CSL treated (CT) 0.014 ± 0.0b 2838 ± 141b Moderate 28.2 ± 3.2b NB treated (NT) 0.014 ± 0.0b 2942 ± 148b Moderate 31.2 ± 17a CSL-bacterial admixed treatment (CBAT) 0.005 ± 0.0d 1228 ± 79c Low 12.5 ± 1.5c NB-bacterial admixed treatment (NBAT) 0.008 ± 0.0c 1204 ± 95c Low 14.2 ± 2.1c CSL-bacterial spray treatment (CBST) 0.005 ± 0.0d 1310 ± 58c Low 13.9 ± 1.3c NB-bacterial spray treatment (NBST) 0.007 ± 0.0c 1340 ± 62c Low 13.6 ± 1.4c Specimen . Sorptivity coefficienta . RCPT . Water penetration (mm)a . Mean charge passed (coulombs)a . Penetration typeb . Control 0.020 ± 0.0a 3180 ± 127a Moderate 30.2 ± 2.1b CSL treated (CT) 0.014 ± 0.0b 2838 ± 141b Moderate 28.2 ± 3.2b NB treated (NT) 0.014 ± 0.0b 2942 ± 148b Moderate 31.2 ± 17a CSL-bacterial admixed treatment (CBAT) 0.005 ± 0.0d 1228 ± 79c Low 12.5 ± 1.5c NB-bacterial admixed treatment (NBAT) 0.008 ± 0.0c 1204 ± 95c Low 14.2 ± 2.1c CSL-bacterial spray treatment (CBST) 0.005 ± 0.0d 1310 ± 58c Low 13.9 ± 1.3c NB-bacterial spray treatment (NBST) 0.007 ± 0.0c 1340 ± 62c Low 13.6 ± 1.4c aMean values sharing a common letter within the column are not significant at P < 0.05 bThe range of charge for high (> 4000), moderate (2000–4000), low (1000–2000) and very low (100–1000) as per the ASTM C1202-10 standard Open in new tab Sorptivity test shows the water ingress into an unsaturated concrete, which is dominated by capillary suction and is an important parameter that can be correlated to the ingress of deteriorating substances (chlorides or sulfates) into concrete [35]. Sorptivity is a good measure of the quality of near surface concrete, which governs durability parameters related to rebar corrosion [24]. The results obtained in sorptivity test indicated that in CBAT and CBST specimens, the transport mechanism of water through capillary rise was altered effectively. On comparison, sorptivity coefficient ‘k’ of initial absorption was almost equal in bacterial admixed and bacterial spray-treated specimens. The low ‘k’ value of surface-treated specimen indicates that the permeation properties can be significantly improved by bacterial spray. Significant reduction to chloride ion penetration was observed in both curing treatments by RCPT analysis. The movement of aggressive agents like chloride ions in the concrete matrix through capillary pore structures initiates and propagates the corrosion process of steel rebar [11]. Chloride-contaminated water movement in surface layer of concrete depends upon pore diameter, distribution and pore continuity [35]. In aforementioned results of bacterial treated concretes, clearly depict the effective sealant of pore matrix with biogenic calcium carbonate precipitation. In surface treatment, bacterial spray significantly restricts the ingress of water and aggressive agents and blocks the pore with calcium carbonate precipitation. Micro-structural analysis SEM and XRD analysis of all concrete specimens was done to characterize the calcium carbonate crystals. SEM–EDX analysis of bacterial treated specimens showed the presence of dense deposition of bacterial mediated precipitation of calcium carbonate (Fig. 5). In case of CBAT specimen, presence of different crystal lattice of calcium carbonate was found. Rhombohedral calcite crystal and spheroid vaterite crystals were observed. The EDX analysis also confirmed the elemental composition of crystals with peaks showing high amount of calcium and carbon (Fig. 5a, b). In CBST specimen, presence of dense biodeposition of closely attached rhombohedral calcite crystals was observed. The high peak of calcium and carbon on EDX analysis further confirmed the presence of calcium carbonate crystals (Fig. 5c, d). However, in case of control and CT specimen, no calcium carbonate crystals were observed in SEM–EDX analysis (Fig. 6). XRD analysis of CBAT and CBST specimen showed that majority of the calcium carbonate deposits were calcite and vaterite (Fig. 7a, b). In case of CT and control specimen, XRD spectrum revealed that the major phases present are quartz, calcium aluminium silicate, coesite and vaterite (Fig. 7c, d). Fig. 5 Open in new tabDownload slide SEM-EDX images represent the CaCO3 crystals (CC) at upper depth in CBAT (CSL-bacterial admixed treatment) specimen (a, b) and CBST (CSL-bacterial spray treatment) specimen (c, d). Star shows the spots of EDX analysis Fig. 6 Open in new tabDownload slide SEM-EDX images of CSL-treated specimen (a, b) and control specimen (c, d) at upper depth. Star shows the spots of EDX analysis Fig. 7 Open in new tabDownload slide XRD patterns of CaCO3 crystals obtained: a CBAT (CSL-bacterial admixed treatment) specimen; b CBST (CSL-bacterial spray treatment) specimen; c CSL-treated specimen; and d Control specimen SEM–EDX analysis of bacterially treated specimens showed the presence of dense deposition of bacterial-mediated precipitation of calcium carbonate. Rhombohedral calcite crystal and spheroid vaterite crystals were observed in case of CBAT specimen. In CBST specimen, presence of dense biodeposition of closely attached rhombohedral calcite crystals was observed. Formation of different kinds of morphology of calcium carbonate crystals depends on composition and mineralogy of the substrate. Calcitic substrate promotes the growth of bacterial calcite, while silicate substrate promotes the formation of spherulitic vaterite [39]. XRD analysis of bacterially treated specimens also confirmed the presence of different polymorphs of calcium carbonate like calcite and vaterite. Conclusions The present study was aimed to investigate the use of CSL as a low-cost growth substrate for supporting MICP technology and the impact of the growth medium on several key properties of the concrete using the ureolytic bacterial strain, Bacillus sp.CT5. Addition of CSL medium had no adverse effect on the setting characteristics of cement paste, while severe retardation was noticed in nutrient medium due to yeast extract. Significant improvement in compressive strength and permeation properties as a result of using CSL in bacterial treatment of concrete was observed. Use of CSL in bacterial admixed and bacterial spray-treated specimen significantly improved the resistance against the ingress of water and aggressive agents. Carbon and nitrogen contents were higher in concrete specimens cured with medium and the maximum contents were observed at the upper layers of the concrete. Both bacterial admixed treatment (that can be used for new structures) and bacterial spray treatment (that can be used as a repair procedure) using CSL were found to be effective in improving the properties of concrete. Use of bacterial admixture, medium only (CSL and NB) and surface treatment with bacterial spray did not affect the alkaline nature of concrete. Bacterial spray treatment of concrete will help in future application of MICP technology at field scale. 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TI - Corn steep liquor as a nutritional source for biocementation and its impact on concrete structural properties
JF - Journal of Industrial Microbiology and Biotechnology
DO - 10.1007/s10295-018-2050-4
DA - 2018-08-01
UR - https://www.deepdyve.com/lp/oxford-university-press/corn-steep-liquor-as-a-nutritional-source-for-biocementation-and-its-kx0Mo0PRqT
SP - 657
EP - 667
VL - 45
IS - 8
DP - DeepDyve
ER -