Raja Rizwan Hussain

Role of Manganese Sulfide Inclusions in Steel Rebar in the Formation and Breakdown of Passive Films in Concrete Pore Solutions

This study examined manganese sulfide (MnS) inclusions in steel rebar exposed to a simulated concrete pore solution to understand their role in passive film, corrosion, and pit propagation behavior. The passive film was characterized using x-ray photoelectron spectroscopy, Raman spectroscopy, scanning electron microscopy, and electrochemical techniques. The results showed that MnS inclusions adversely affected the nature of the passive film and accelerated corrosion and pit formation. A schematic model was developed to explain the deterioration of passive film formed on steel containing MnS inclusions, and was validated by Raman spectroscopy of the resulting rust formed on such steel.

Fiber-reinforced concrete incorporating locally available natural fibers in normal- and high-strength concrete and a performance analysis with steel fiber-reinforced composite concrete:

This study provides an experimental investigation on the properties of fiber-reinforced composite concrete consisting of natural fibers (coconut coir) and rounded, straight steel fibers in a comparative manner for both normal-strength concrete (NSC) and high-strength concrete (HSC). This investigation was carried out using several tests, which included workability test, compressive strength test, indirect tensile strength test, and flexural strength test. A total of 10 mix batches of NSC and HSC containing 0%, 0.5%, and 1.0% fiber volume dosage rates on coir and steel fibers were tested to determine the enhancement of mechanical properties of composite concrete. In both NSC and HSC, the workability of concrete significantly reduced as the fiber dosage rate increased. In NSC, the compressive strength test indicated that strength decreases compared to plain concrete for both types of fiber. In HSC, compressive strength decreases compared to plain concrete for coir fiber and also decreases with increasing fiber volume dosage rate and increases for steel fiber with increasing fiber volume dosage rate. In NSC, split tensile test showed that tensile strength decreased for 0.5% coir and increased for 0.5% steel compared to plain concrete. But in HSC, strength increases for 0.5% coir compared to 0.5% steel and plain concrete. In NSC, flexural strength and flexural toughness of composite concrete increased in both types of fiber. But in case of concrete with coir fiber, flexural strength for 0.5% and 1% fiber volume dosages is same and increases for steel fiber. In HSC, increase of flexural strength for 0.5% coir compared to plain concrete was observed. Flexural strength also decreases with increase of fiber volume dosage for both types of fiber. In post-cracking stage, the fibers were fully utilized when it increases the ductility and toughness of both types of concrete. This research has shown that 0.5% and 1.0% coir fibers give improved performance in flexural strength of NSC, and 0.5% coir fiber gives improved performance in flexural and tensile strengths of HSC. Also, addition of coir fibers in both types of concrete increases the ductility and toughness of concrete, whereas reduction of workability of fresh concrete and compressive strength of hardened concrete occurs using coir fibers in both types of composite concrete.

Oxygen Transport and Corrosion of Steel in Concrete under Varying Concrete Cover, w/c, and Moisture

This paper verifies the detailed experimentation and electrochemical mass balance modeling of corrosion in reinforced concrete under the effect of varying oxygen concentrations. Various concrete corrosion cells with different compositions under four different environmental conditions (air dry, submerged, 95% relative humidity [RH], and alternate wetting and drying) were investigated under controlled laboratory conditions in this paper. Using the results of these laboratory tests and a constitutive equivalent electrochemical circuit model based on mass and energy transfer through the porous media for the corrosion process, it was possible to predict the influence of oxygen concentration on the corrosion rate of the reinforcement under various defined conditions. The variation in oxygen concentration available for the corrosion reaction was taken into account, simulating the actual field conditions, such as varying the concrete cover depth, RH, and water-cement ratio (w/c). The modeling task was incorporated by the use of the concrete durability model as a finite element computational approach for the effect of oxygen on corrosion in relation to the w/c, concrete cover, chloride concentration, and various environmental humidity conditions. This comprehensive modeling and experimental investigation involving a variety of materials and environmental variables will help in the understanding of oxygen-controlled corrosion reaction in reinforced concrete structures. This comprehensive modeling will also provide significant future research prospects in the field of oxygen-limiting corrosion modeling of steel-reinforced concrete.

Incorporation of Rubber-steel Bearing Isolation in Multi-storey Building

AbstractBase isolation incorporation has moved towards a popular technology in the seismic vulnerable regions. The system mitigates lateral action of tremor hazard providing flexibility of structures. Implementing base isolation on buildings in the soil and seismic condition of medium risk seismicity is currently an important issue. A thorough investigation is of burning need for buildings to be incorporated with base isolator and to carry out dynamic analysis. The study provides incorporation of rubber-steel bearings and focuses on the structural changes. Designs of base isolation bearings are performed along with structural viability check. Lead rubber bearing (LRB) and high damping rubber bearing (HDRB) have been inserted on the corresponding structural bases. In finite-element approach, link element simulates the bearing. Bi-linear hysteretic behaviour is presented for LRB and equivalent linear model simulated HDRB. Linear static, free vibration and dynamic frequency-domain analyses are performed for ...

Multivariable Empirical Analysis of Coupled Oxygen and Moisture for Potential and Rate of Quantitative Corrosion in Concrete

AbstractQualitative as well as quantitative effect of oxygen on the corrosion of reinforced concrete structures under various environments and compositions has been successfully obtained through extensive multivariable laboratory experimentation in this research for which the previous research data is limited and has difference of opinion. The experiment results of this research showed that the diffusion of oxygen is not an influential factor for corrosion inhibition as long as the reinforced concrete is not placed completely under water even in very high humidity environmental conditions as much as 95% relative humidity. The only exception is when the diffusion path of oxygen from the surface of concrete to the depth of steel reinforcement is extended and made slender enough by using a thick concrete cover and low water/cement ratio to make the coefficient of oxygen comparable to that of submerged condition which is not a normal practice. In all cases of relative humidity less than one hundred percent, t...

Mechanism of Nucleation and Growth of Passive Film on Steel Reinforcing Bar at Different Durations of its Exposure in Concrete Pore Solution at Nanoscale

The nanoscale passive film formation on steel reinforcing bars at different stages of their exposure in concrete pore solution is characterized by the application of atomic force microscopy, Raman spectroscopy, electrochemical impedance spectroscopy, electrochemical noise, and cyclic voltametry studies. Based on this, a new description of the sequence of reactions during the formation of passive film on steel reinforcing bars is suggested in this paper. The results generated during this investigation revealed that the surface of the steel reinforcing bars prior to their embedding in a concrete pore solution remain covered with a film of ferric hydroxide (Fe(OH)₃). The passive film on the reinforcing bars is formed by the dissolution of this oxide film followed by a series of chemical reactions. The nanotechnological investigations conducted in this paper indicated that a protective passive film on a reinforcing bar’s surface develops within 24 hours of its exposure to the concrete pore solution. Further exposure helps growth of the film over a period of up to 7 days. Beyond this period of exposure, no significant changes in either the structure or the protective property of the film are recorded. In solid concrete, however, the film formation and its growth is slow compared with the concrete pore solution, and a minimum period of 20 days is needed to form a complete protective film on the reinforcing bars embedded in concrete.

Efficient design in building construction with rubber bearing in medium risk seismicity: case study and assessment

AbstractEarthquakes pose tremendous threats to life, property and a countrys economy, not least due to their capability of destroying buildings and causing enormous structural damage. The hazard from ground excitations should be properly assessed to mitigate their action on building structures. This study is concerned with medium risk seismic regions. Specifically, the heavily populated capital city Dhaka in Bangladesh has been considered. Recent earthquakes that occurred inside and very close to the city have manifested the citys earthquake sources and vulnerability. Micro-seismicity data supports the existence of at least four earthquake source points in and around Dhaka. The effects of the earthquakes on buildings are studied for this region. Rubber base isolation is selected as an innovative option to lessen seismic loads on buildings. Case studies have been carried out for fixed and isolated based multi-storey buildings. Lead rubber bearing and high damping rubber bearing have been designed and inc...

Experimental investigation of time dependent non-linear 3D relationship between critical carbonation depth and corrosion of steel in carbonated concrete

Abstract This paper aims at the experimental investigation of time dependent non-linear relationship between critical carbonation depth and corrosion rate of steel in carbonated concrete by laboratory controlled experimentation under severe environmental condition. In this research, three-dimensional experimental observations are taken consecutively involving carbonation depth, half-cell potential and elapsed time as well as the gravimetric corrosion mass loss. The experimental observations revealed an interesting non-linear relationship between the above said measurements due to the varying resistivity of carbonated concrete. It is also found that the carbonation induced corrosion does not start until the carbonation depth reaches a certain critical level from the steel rebar and the half-cell potential values become constant after carbonation reaches the critical depth and then start rising again after carbonation reaches the rebar level.

Novel Approach Towards Calculation of Averaged Activation Energy Based on Arrhenius Plot for Predicting the Effect of Temperature on Chloride Induced Corrosion of Steel in Concrete

Reinforced concrete structures exposed to aggressive environments such as severe chloride attack coupled with high temperature suffer from accelerated corrosion. The objective of this paper is to model and verify the effect of temperature on chloride induced corrosion potential and corrosion rate of steel in concrete by incorporating a novel approach towards calculation of averaged activation energy based on Arrhenius plot. This paper presents a semiempirical corrosion modeling approach which obeys the basic corrosion science laws and is also verified by the experimentation involving a wide range of chloride and temperature variations (0 %–10 % total chlorides and 20–60°C temperatures). The modeling task has been incorporated by the use of a concrete durability model developed by our research group at the University of Tokyo as a computational platform on which the coupled temperature-chloride induced corrosion throughout the life of reinforced concrete structures is examined in both space and time domains.

Non-linear FEM analysis of seismic induced pounding between neighbouring multi-storey structures

Pounding of neighbouring construction of structures due to seismic excitation increases the damage of structural components or even causes collapse of structures. Among the possible building damages, earthquake induced pounding has been commonly observed in several earthquakes. Therefore it is imperative to consider pounding effect for structures. This study aims to understand the response behaviour of adjacent buildings with dissimilar heights under earthquake induced pounding. Effects of different separation distances between structures are also investigated. Nonlinear finite element analysis in time domain has been carried out for pounding of neighbouring structures having varying heights. To show the importance of avoiding pounding in structures the results obtained were compared with model having no pounding phenomena. The results were obtained in the form of storey shear, pounding force, storey drift, point displacement and acceleration. The acceleration at pounding level significantly increases during collision of building. The generated extra pounding force may cause severe damage to structural members of structures. Pounding produces shear at various story levels, which are greater than those obtained from no pounding case. Building with more height suffers greater damage than shorter building when pounding occurs. Increasing gap distance tends to reduce story shear in consistent manner. The results also show that the conventional modelling of building considering only beams and columns underestimates pounding effects. More realistic modelling such as beams, columns and slabs shall be adopted to accurately understand the pounding phenomenon.