Nemkumar Banthia

Professor

Relevant Degree Programs

 

Graduate Student Supervision

Doctoral Student Supervision (2008-2018)
A novel functionalized composite coating for controlling bio-corrosion in wastewater concrete pipes (2018)

Bio-corrosion in sewage pipes is mainly caused by the diffusion of aggressive solutions and in-situ production of sulfuric acid by sulphur-oxidizing microorganisms which affect the physicochemical properties of concrete pipes. In this study an accelerated pilot-scale experimental setup is designed and built to replicate conditions in sewage transport systems as well as the bacterial induced corrosion processes in pipes. The reliability of the accelerated set-up is evaluated by conducting different tests on corroded samples over a 6 months period. In addition to the parameters such as weight loss and pH measurements that have been investigated by previous authors, variations in corrosion depth, flexural strength and absorption were also studied. Prevention of concrete bio-corrosion usually requires modification of concrete mix or application of antimicrobial coatings on the inner surface of the pipe. The composition of the coating is a key factor in controlling resistance to bio-corrosion which is dependent on the neutralization capacity of the material or its ability to prevent the growth of bacteria. The most common method for controlling the growth of bacteria is using bioactive chemicals (biocides) which are essentially toxic compounds. Undesired leaching of biocides to the surrounding environment as well as their short bio-resistance lifetime have increased the need for more efficient, environmental friendly and long-lasting alternatives. In this study, multiphase composite coatings are developed and tested. Controled-release mechanism was implemented inside the coating by mixing the binder matrix with functionalized sodium bentonite clay impregnated with zinc oxide and solidifying the antibacterial agent in 3D framework of coating material. Tensile strength, chemical resistance, leaching stability, microstructure and resistance to bio-corrosion in the accelerated chamber were investigated. Results show that the developed antibacterial coating can create a corrosion-resistant and effective physical/chemical barrier on concrete wastewater pipes and protects the concrete from bio-acid. Moreover, coatings successfully immobilized antibacterial agents inside the matrix and increased bio-resistant lifespan and durability of the repair material. This would likely lead to an increase in the service life of aged/corroded concrete pipelines.

https://open.library.ubc.ca/collections/24/items/1.0365537

Non-destructive detection of corrosion of epoxy coated rebar (2018)

Deteriorating infrastructure is an acute and dangerous problem, which is often caused by the corrosion of concrete reinforcement. Marine structures and bridge decks, where sea water and de-icing salts lead to chloride ion diffusion into the concrete are particularly at risk. Epoxy coated rebar (ECR) is a popular choice for the latter structures. However, corrosion of ECR, which occurs due to coating damage, poses a challenge to non-destructive corrosion detection. This study investigated the corrosion behaviour, accelerated corrosion and non-destructive corrosion detection of ECR. The electrochemical corrosion behaviour of ECR in simulated concrete pore solutions was studied and compared to uncoated rebar (UCR). The polarized area of ECR was related but not proportional to the sodium ion concentration of the test solution. Furthermore, ECR was more susceptible to corrosion than UCR, particularly in the presence of NaCl and in NaHCO₃ solution. A test solution of Na2CO₃ and NaHCO₃ led to the formation of a very fragile passive layer, that grew slowly but continuously. However, the protective layer was sensitive to even small amounts of NaCl. Corrosion of ECR was accelerated in neutral and alkaline NaCl solutions as well as in concrete. Neutral and alkaline environments promoted coating holiday and undercoating corrosion, respectively. Part of the undercoating corrosion process was cathodic delamination, whose acceleration prior to corrosion acceleration slowed down the lateral corrosion expansion. Once corrosion had expanded across the entire surface, the subsequent corrosion rate was not affected by the initial cathodic disbondment. Successful ECR corrosion detection was limited with the linear polarization resistance and ground penetrating radar method. However, concrete properties such as maturity, moisture and chloride content had a significant effect on the measurements. Corroded bars affected the Hall effect (HE) voltage to a lesser extent than intact rebar. Furthermore, corrosion of ECR led to higher concrete surface and lower bar temperatures during active infrared thermography (IRT) tests. The thermal results of ECR opposed those of UCR. The HE and IRT tests showed that the effects of corrosion on the thermal and magnetic behaviour during induction thermography would complement and oppose each other for UCR and ECR respectively.

https://open.library.ubc.ca/collections/24/items/1.0362873

Seismic strengthening of unreinforced masonry walls using sprayable Ecofriendly Ductile Cementitious Composite (EDCC) (2018)

Due to their good sound and thermal insulation properties, unreinforced masonry (URM) walls are widely used in partitioning many of the commercial and residential buildings worldwide, either as in-fill or stand-alone. URM is considered one of the most common types of partition wall systems in many of the mid-age, low-rise to mid-rise, school and hospital buildings in North America. URM is still a very common and major building material, in many of the developing countries, being used in many residential and commercial buildings.URM partition walls are known to have very low drift capacity in seismic events and the failure mechanisms are known to be mostly brittle and of catastrophic nature, during earthquake ground motion. Compared to other partitioning systems, URM walls tend to perform poorly during earthquake events, leaving many injuries, casualties, and fatalities behind.This dissertation elaborates on development of a novel, effective, and practical methodology for a robust out-of-plane seismic strengthening technique toward seismically upgrading URM partition walls, using a thin plaster layer of sprayable Ecofriendly Ductile Cementitious Composite (EDCC). The EDCC layer is devoted to secure such walls, which exist in most parts of the world; specially, in developing countries, where world’s most population density is concentrated. In many of these countries, retrofit is the only option, since building replacement is not practical nor an economically feasible solution. The EDCC material can be applied in three different methods: hand troweled, hopper sprayed, or pump sprayed. The thickness of the layer can vary between 10mm to 20mm, depending on the design variables.Full-scale URM walls are built, strengthened, and tested on a shake table, using the strongest real historical earthquake records. The EDCC layer is providing nearly full out-of-plane detention for the wall’s building blocks, as well as minor but uniform shear capacity enhancements for the in-plane action; therefore, holding the masonry units together from falling apart and being thrown during an earthquake generated ground motion. The newly developed high performance material is sprayable, ductile, and resilient, while being affordable, and easy to apply, with much less carbon footprint compared to other similar repair materials.

https://open.library.ubc.ca/collections/24/items/1.0365816

The effects of global climate change on carbonation induced corrosion of reinforced concrete structures (2013)

There is nearly unanimous consensus amongst scientists that increasing greenhouse gas emissions, including CO₂ generated by human activity, are affecting the Earth‘s climate. Climate change has the potential to overwhelm existing capacities, as well as durability of concrete infrastructure. Carbonation of concrete occurs due to a reaction between atmospheric CO₂ and the hydrated phases of concrete, leading to a drop in its pH and the depassivation of embedded rebar. Therefore, increases in carbonation rates of reinforced concrete structures are expected as a result of increased temperatures and CO₂ concentrations, with the enhanced risk of carbonation induced corrosion likely affecting the longevity of our concrete infrastructure.This thesis considered the potential consiquences of global climate change on our concrete infrastructure, with the objective being to determine if there is an increased risk of deterioration due to carbonation induced corrosion. A unique numerical model was developed to determine carbonation rates in structures, and verified through experimental tests. The model was applied to a number of cities in locations throughout the world to determine where structures were most vulnerable. Additionally, a number of other laboratory experiments were carried out to supplement the numerical model and provide insights as to how carbonation progress can be monitored within a structure. Using the model developed, and inputting forecasts for increases in future atmospheric CO₂ concentrations and weather conditions, it was shown that for medium quality, non-pozzolonic concrete in geographic areas where carbonation induced corrosion is a concern, global climate change will affect its progress in our concrete infrastructure. We will see much higher ultimate carbonation depths in the long term. The use of non-destructive testing (NDT) methods, and structural health monitoring (SHM) techniques could be invaluable in monitoring the progress of carbonation in a structure, but the data generated by the methods and techniques used must be analyzed carefully before making any conclusions. For the NDT methods and carbonation pH sensors which were evaluated in this study, it was found that ambient test conditions had a major impact on results.

https://open.library.ubc.ca/collections/24/items/1.0073691

Towards comprehensive interpretation of the state parameter from cone penetration testing in cohesionless soils (2011)

The Cone Penetration Test (CPT) is widely used for determining in-situ properties of soil because of its continuous data measurement and repeatability at relatively low cost. The test is even more attractive in cohesionless soils such as sands, silts and most tailings due to difficulties associated with retrieving undisturbed samples in such soils. Behaviour of soils is highly dependent on both density and stress level. The state parameter is widely accepted to represent the soil behaviour encompassing both density and stress effects. Hence, determining the in-situ state parameter from CPT is of great practical interest.The CPT was analysed using a large strain spherical cavity expansion finite element code using a critical state soil model (NorSand) capable of accounting for both elasticity and plastic compressibility. The constitutive model was calibrated through triaxial tests on reconstituted samples. The state parameter was then interpreted from CPT tip resistance, and the results were verified against an extensive database of calibration chamber tests. The efficiency of the method was further investigated by analysing two well documented case histories confirming that consistent results could be obtained from different in-situ testing methods using the proposed framework. Consequently, cumbersome and expensive testing methods can be substituted by a combination of triaxial testing and finite element analysis producing soil specific correlations.One of the difficulties in analysing the cone penetration problem is the less researched effect of high stresses developing around the cone on the behaviour of the soil. A hypothesis was put forward on the particle breakage process at the particle level and its implications for the behaviour of sands at higher stress levels were discussed. A series of triaxial tests were performed, focusing on the effects of particle breakage on the location of the critical state line. The hypothesis was used to explain the observed behaviour. Particle breakage was shown to cause additional compression and a parallel downward shift in the critical state line. The magnitude of the shift was linked to the amount of breakage and it was argued that significant breakage starts after the capacity for compression due to sliding and rolling is exhausted.

https://open.library.ubc.ca/collections/24/items/1.0063028

Microstructural refinements of concrete due to fiber reinforcement and its influence on corrosion initiation of reinforcing steel (2010)

Permeability plays an important role in governing the durability of concrete in deleterious environments. Earlier studies indicated that the addition of cellulose fiber is effective in reducing water permeability and thereby making concrete more durable. In this thesis, microstructural refinement and corrosion resistivity performance of fiber reinforced concrete (FRC) were studied. Two fiber types, cellulose and polypropylene, at various dosages, were examined. Microstructural refinement was studied using thermoporometry (TP) and mercury intrusion porosimetry (MIP) methods. After that, a two-part experiment was performed to investigate corrosion of steel in concrete in the presence of fiber reinforcement. First, diffusion of chloride in concrete was investigated using the bulk diffusion test as well as a silver nitrate spray test. A rapid chloride permeability test was also performed. Secondly, FRC beams were subjected to flexural stress while exposed to a simulated tidal zone of marine environment. Corrosion activity in reinforcing steels was monitored for 56 weeks using three electrochemical methods: half-cell potential, galvanic current and linear polarization resistance.Results demonstrated that fibers did bring about a refinement in the pore structure by converting part of the permeable porosity to non-permeability porosity. Diffusion results clearly show that while the presence of fibers increased the coefficient of chloride diffusion based on total chlorides, there was a decrease in the coefficient related to free chlorides. Fibers therefore appear to bind the chlorides and inhibit their transport. Corrosion tests indicated that fibers delayed corrosion in specimens with no load or a lighter load, but were not as effective in specimens carrying a heavier load.Finally, a long-time performance of fiber reinforcement was illustrated through a service life modeling. Corrosion initiation period was analyzed using a model called LIGHTCON. Empirically based on the test results, it was modified to take the effects of fiber reinforcement and load intensity into consideration. The modified model was then verified in two case studies. In each of the cases, a critical impact of load induced cracks on a service life of structures was emphasized and a promising benefit of fiber reinforcement was demonstrated.

https://open.library.ubc.ca/collections/24/items/1.0062800

A study of bond between fibre reinforced polymer and concrete under quasi static and impact loading (2009)

This thesis examines the typical behavior of the interface bond between a selection of FRP treatments and various types of surface preparation on reinforced concrete beams under loading. It also describes an innovative specimen that enables examination of bond properties using a notched beam under a four-point bending test. The thesis also studies the bond between FRP and concrete under impact loading and discusses the strain rate sensitivity of the FRP–concrete bond. Three surface treatment methods (water jetting, sandblasting, and jackhammering), two bonding agents (aromatic isocyanate (ATPRIME®) and vinyl ester), and three FRP systems (sprayed glass fiber reinforced polymer, sprayed carbon fiber reinforced polymer, and glass fiber reinforced polymer wrap) were investigated. The influences of FRP bond length, specimen notch depth, and a wide range of loading rates (creep, quasi-static loading, and impact loading) on bond behavior were also investigated. The notched beam specimen was also used to understand the debonding mechanism under impact loading. An impact setup was successfully developed to measure the bond stress and fracture energy of the FRP–concrete bond. Bond strength values and toughness values were calculated for different surface treatments, FRP application methods, and bonding agents used. The FRP–concrete bond strength was found to be a strain rate sensitive parameter that increases as the strain rate increases. A dynamic improvement factor (DIF) was defined to characterise the influence of different material and strain rate parameters on bond strength. A correlation was found to relate dynamic improvement factor to strain rate for different surface preparation types. An attempt was made to calibrate the energy and traction parameters of the cohesive element in ABAQUS to reproduce the same load displacement behavior as observed in the test from a modeled beam. Using different ABAQUS cohesive zone parameters, the load displacement behavior of the beam was modeled. Even though the load displacement did not completely match the tests, similar magnitudes of displacement and stress were achieved and the debonding mechanism was similar to the reality.

https://open.library.ubc.ca/collections/24/items/1.0063162

Master's Student Supervision (2010-2017)
Development and testing of a weatherometer to accelerate the surface checking of wood (2009)

A new version of a weathering device (Accelerated Check Tester, ACT) was built, and weathering cycles for accelerating the surface checking of decking board samples exposed in the device were developed. The device permits the testing of realistic-sized decking board samples that are oriented horizontally and restrained in the device by screws. Two experiments were carried out to validate the device and associated test cycles. In the first experiment, southern pine (Pinus sp.) and western red cedar (Thuja plicata) samples were exposed to 6 different cycles in the ACT to determine which elements of weathering cycles (moisture, heat, freezing and UV radiation) were critical to the ACT’s function of accelerating checking. Large number of checks developed on the surface of samples subjected to wetting and drying cycles. Samples subjected to a cycle that also involved UV exposure developed significantly more and larger checks than samples subjected to any of the others cycles. Checking was much more pronounced in southern pine than in western red cedar samples. The second experiment examined the checking and distortion that developed in artificially weathered boards compared to those that developed in naturally weathered boards. Matched pairs of kerfed and unkerfed southern pine boards were subjected to accelerated weathering in the ACT or natural weathering. The number and length of checks that developed in boards exposed in the ACT were similar but not identical to those in boards subjected to natural weathering. The width of checks was greater in boards subjected to accelerated weathering. Kerfing had no significant effect on checking or distortion of boards. Exposure of boards in the ACT accelerates checking approximately 16 times compared to natural weathering. The Accelerated Check Tester should be a very useful tool for obtaining information on factors that affect the checking of wood.

https://open.library.ubc.ca/collections/24/items/1.0067135

Development of FRP based composite fibre for fibre reinforced cementitious composites (2016)

This thesis describes a method of development of a novel fibre based on fibre reinforced polymers (FRP), for use fibre reinforcement in concrete. Thermosetting epoxy resin matrix were reinforced with E-glass, S-glass, and Carbon fibre to produce different types of composite fibres. The FRP panels were produced using the Vacuum Infusion technique, and then cut to different fibre sizes. The volume fractions of reinforcements within the FRP fibre were controlled by using woven and unidirectional fabrics. The number of layers of reinforcing fibres were also changed, to obtain the optimal thickness of the fibres. The FRP material was characterized by means of tensile tests and microscope image analysis. Four different compositions of FRP were produced with tensile strengths ranging from 195 MPa to 950 MPa. The different combinations in geometry broadened the total number of fibres investigated to 12. Single fibre pullout tests were performed to obtain the fundamental fibre-matrix interfacial bond parameters for the different FRP fibres. The FRP fibres, being hydrophilic, along with having a unique rough surface texture, showed a good bond with cement matrix. A bond strength superior to industrially available straight steel fibres and crimped polypropylene fibres has been observed. The 3 best fibres were then chosen to examine the flexural behaviour FRP fibre reinforced concrete beams. The optimized FRP fibres, one each of Glass FRP and Carbon FRP were then further investigated to study the effect of matrix maturity, temperature, fibre inclination, and loading rate on the fibre-matrix interfacial behaviour using single fibre pullout tests. Scanning Electron Microscope (SEM) analysis was carried out to identify the effect of above-mentioned factors on the surface characteristics of the fibre. An attempt was also made to optimize the fibre-matrix interface to achieve an optimized failure mechanism by coating the fibre with oil. The ability of the fibre to transfer stresses across a cracked section over extended periods has been investigated by means of fibre-relaxation tests. Finally, to assess durability, the fibres were conditioned at high pH and high temperature after which single fibre pullout, direct tension tests, & SEM analysis were conducted.

https://open.library.ubc.ca/collections/24/items/1.0228635

Investigation into bond strength between EDCC/masonry (2016)

In order to apply Sprayable Eco-Friendly Ductile Cementitious Composites (EDCC) as a thin overlay material for masonry building upgrade, this study aims at understanding one of the key issues of repair: bond strength between old structure and the new repair overlay. Several influencing factors on bond strength were investigated, including repair thickness, fiber addition, substrate properties, curing age and environment. Bond strength was measured by tensile pull-off and friction-transfer tests. At the conclusion of the research, EDCC was able to achieve satisfactory bond strength provided sufficient penetrability into the substrate, even under field conditions and without curing. Fibers added into EDCC impact bond strength negatively, if they are oriented parallel to the interface as a result of manual casting or if there is a low fractal dimension of the substrate surface. Further, 56 days can be used as the maturity age of bond strength with EDCC overlay. In future applications, penetrability of EDCC overlays can be ensured through sufficient amount of superplasticizer or energy of casting. For example, EDCC with 150mm slump was able to satisfy standard bond strength requirement of concrete in the field, at the age of 45 days. Penetrability of EDCC overlay is of vital importance, since EDCC with low workability (0 slump) can’t achieve requirement of structural repair even under standard curing. To mitigate the negative effect of fiber addition on bond strength, higher substrate roughness and 3D fiber orientation can be of help, through proper surface roughness preparation and the use of spray methods (e.g., shotcrete) instead of hand application. For further study, it is suggested that measures should be taken to obtain more pure bond strength values for simplification of analysis. Also surface roughness variation and long term properties of interface are worth investigation, once proper substrates are chosen for lab research.

https://open.library.ubc.ca/collections/24/items/1.0303138

Study of some parameters affecting the measured flexural toughness of fiber reinforced concrete (2012)

Fiber reinforced concrete (FRC) exhibits better performance not only under static and quasi-statically applied loads, but also under fatigue, impact, and impulsive loading. This energy-absorption attribute of FRC is usually termed “Toughness”. Experimental characterization of the toughness of FRC remains an actively debated topic. In this thesis, concerns with various available techniques were studied and better ways of characterizing the effects of fibers on the toughness of concrete were sought. For toughness characterization, beam tests which included standardized ASTM C1609 and C1399 tests were carried out both on lab-cast and site-cast specimens. In the first part of the study, the applicability of the initial loading rate described in ASTM C1609 was evaluated. Tests were conducted on specimens carrying two volume fractions of polypropylene fiber in two separate series with both the prescribed and proposed loading rates. A comparison between ASTM C1609 and C1399 was carried out later in the study. The Canadian Highway Bridge Design Code (CHDBC) technique prescribed for FRC was also studied. Based on the results of these tests, it can be concluded that the current loading rate specified in ASTM C1609-2010 is too high for normal strength concrete and it should be reduced to 0.001mm/min initially. It was also found that for calculating Residual Strength Index (Ri), ASTM C1609 procedure is more reliable than the ASTM C1399 as ASTM C1609 is performed in a feedback controlled mode (also called the closed-loop mode) which is very helpful for maintaining stability in specimens. Since energy absorption is one of the most effective criteria for characterizing FRC, a new method called Flexural Toughness Strength Method (FTSM) was proposed. Tests are carried out on beam specimens according to ASTM C1609 and load- deflection curves are analyzed using the FTSM method. The results demonstrate that the proposed FTSM leads to FRC attributes that are not susceptible to user errors and hence more reliable. The characterization of flexural toughness based on the FTSM approach is independent of the type of deflection measuring technique and no sophisticated instrumentation is required. The Flexural Toughness Factor calculated using this approach has consistently lower coefficient of variation.

https://open.library.ubc.ca/collections/24/items/1.0050904

Development and testing of a weatherometer to accelerate the surface checking of wood (2009)

A new version of a weathering device (Accelerated Check Tester, ACT) was built, and weathering cycles for accelerating the surface checking of decking board samples exposed in the device were developed. The device permits the testing of realistic-sized decking board samples that are oriented horizontally and restrained in the device by screws. Two experiments were carried out to validate the device and associated test cycles. In the first experiment, southern pine (Pinus sp.) and western red cedar (Thuja plicata) samples were exposed to 6 different cycles in the ACT to determine which elements of weathering cycles (moisture, heat, freezing and UV radiation) were critical to the ACT’s function of accelerating checking. Large number of checks developed on the surface of samples subjected to wetting and drying cycles. Samples subjected to a cycle that also involved UV exposure developed significantly more and larger checks than samples subjected to any of the others cycles. Checking was much more pronounced in southern pine than in western red cedar samples. The second experiment examined the checking and distortion that developed in artificially weathered boards compared to those that developed in naturally weathered boards. Matched pairs of kerfed and unkerfed southern pine boards were subjected to accelerated weathering in the ACT or natural weathering. The number and length of checks that developed in boards exposed in the ACT were similar but not identical to those in boards subjected to natural weathering. The width of checks was greater in boards subjected to accelerated weathering. Kerfing had no significant effect on checking or distortion of boards. Exposure of boards in the ACT accelerates checking approximately 16 times compared to natural weathering. The Accelerated Check Tester should be a very useful tool for obtaining information on factors that affect the checking of wood.

https://open.library.ubc.ca/collections/24/items/1.0067135

Recent Tri-Agency Research Grants

This list shows a selection of research grants a faculty member was part of as nominating principal investigator or co-facilitator. Currently, the list only covers Canadian Tri-Agencies from years 2013/14-2016/17 and excludes grants from any other agencies.

 

Membership Status

Member of G+PS

Program Affiliations

 

If this is your researcher profile you can log in to the Faculty & Staff portal to update your details and provide recruitment preferences.