Browsing by Author "Paul, Suvash Chandra"

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    Corrosion deterioration of steel in cracked SHCC
    (SpringerOpen, 2017) Paul, Suvash Chandra; Van Zijl, Gideon Pieter Adriaan Greeff
    The presence of cracks is unavoidable in reinforced concrete structures and also a gateway for chloride into concrete, leading to corrosion of steel reinforcing bars. So, crack control, crack width limitation and chloride threshold levels are well-established concepts in durability of reinforced concrete structures. This paper reports on accelerated chloride-induced corrosion in cracked reinforced strain-hardening cement-based composites and reinforced mortar beams, both in loaded and unloaded states. Corrosion rates are monitored and loss of mass and yield force, as well as corrosion pitting depth in steel bars are reported. The chloride content at different depths in specimens is also determined through XRF, and through chemical testing of acid and water soluble chloride content by titration. Finally, different relationships are drawn between crack properties, mass loss, yield force, corroded depth and chloride levels at the steel surface for different cover depths. It is found that the crack spacing and free chloride at the steel surface level are best correlated to the corrosion damage in the specimens.
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    Impact of chemically treated waste rubber tire aggregates on mechanical, durability and thermal properties of concrete
    (Frontiers, 2020-04-15) Khern, Yih Chen; Paul, Suvash Chandra; Kong, Sih Ying; Babafemi, Adewumi John; Anggraini, Vivi; Miah, Md Jihad; Savija, Branko
    ENGLISH ABSTRACT: Studies have shown that the incorporation of waste tire rubber aggregates reduces the strength, increases permeability and decrease thermal conductivity of concrete. However, only a few studies have investigated the effect of surface-modified rubber aggregates on the properties of concrete. This study investigates the effect of the surface treatment of waste tire rubber as coarse aggregates with different oxidizing solutions and different treatment durations on the mechanical, durability and thermal properties of concrete. The properties of concrete incorporated with 8% rubber coarse aggregates (by volume of natural aggregates) which were treated with three different solutions: water (H2O), 20% sodium hydroxide (NaOH) and 5% calcium hypochlorite [Ca(ClO)2] (both as% weight of water) for durations of 2, 24, and 72 h, respectively. The effect of these treatments on the compressive strength, splitting tensile strength, water permeability, thermal conductivity and diffusivity of concrete was investigated. Results show that Ca(ClO)2 has a more positive effect on the strength and permeability compared to NaOH solution and water. Experimental results were statistically analyzed using ANOVA and Post Hoc tests. The analyses showed that the improvement of concrete strength is only significant when the treatment with NaOH and Ca(ClO)2 is prolonged to 72 h. Furthermore, the microstructural analysis of concrete showed that the improvement in the strength is due to the improved bonding between cement paste and rubber aggregates as a result of surface treatment. This microstructural improvement also resulted in lower water permeability of concrete. However, the thermal conductivity and diffusivity increased when the surface treatment duration increases as there are less air voids in the samples. This study shows that, with appropriate pretreatment, a certain percentage of natural aggregates can be safely replaced with waste tire rubber aggregates while maintaining sufficient quality of the resulting concrete.
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    Impact of induction furnace steel slag as replacement for fired clay brick aggregate on flexural and durability performances of RC beams
    (MDPI, 2021-10-21) Miah, Md Jihad; Ali, Md Kawsar; Babafemi, Adewumi John; Paul, Suvash Chandra
    ENGLISH ABSTRACT: This research investigates the flexural and durability performances of reinforced concrete (RC) beams made with induction furnace steel slag aggregate (IFSSA) as a replacement for fired clay brick aggregate (FCBA). To achieve this, 27 RC beams (length: 750 mm, width: 125 mm, height: 200 mm) were made with FCBA replaced by IFSSA at nine replacement levels of 0%, 10%, 20%, 30%, 40%, 50%, 60%, 80%, and 100% (by volume). Flexural tests of RC beams were conducted by a four-point loading test, where the deflection behavior of the beams was monitored through three linear variable displacement transducers (LVDT). The compressive strength and durability properties (i.e., porosity, resistance to chloride ion penetration, and capillary water absorption) were assessed using the same batch of concrete mix used to cast RC beams. The experimental results have shown that the flexural load of RC beams made with IFSSA was significantly higher than the control beam (100% FCBA). The increment of the flexural load was proportional to the content of IFSSA, with an increase of 27% for the beam made with 80% IFSSA than the control beam. The compressive strength of concrete increased by 56% and 61% for the concrete made with 80% and 100% IFSSA, respectively, than the control concrete, which is in good agreement with the flexural load of RC beams. Furthermore, the porosity, resistance to chloride ion penetration, and capillary water absorption were inversely proportional to the increase in the content of IFSSA. For instance, porosity, chloride penetration, and water absorption decreased by 43%, 54%, and 68%, respectively, when IFSSA entirely replaced FCBA. This decreasing percentage of durability properties is in agreement with the flexural load of RC beams. A good linear relationship of porosity with chloride penetration resistance and capillary water absorption was observed.
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    The role of cracks and chlorides in corrosion of reinforced strain hardening cement-based composite (R/SHCC)
    (Stellenbosch : Stellenbosch University, 2015-12) Paul, Suvash Chandra; Van Zijl, Gideon P. A. G.; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.
    ENGLISH ABSTRACT: By using various kinds of fibre-reinforced concrete (FRC), new dimensions of structural performance have been developed. Strain-hardening cement-based composite (SHCC) is a branch of these FRCs and show remarkably improved mechanical and durability performance. FRCs provide ductility and through fibre-bridging show remarkable strain hardening behaviour of up to 3% and in some cases, beyond 5% tensile strain for SHCC with especially-graded fine sand (particle size less than 0.3 mm). SHCC forms multiple fine cracks that are closely spaced together when subjected to tensile or flexural loads. This behaviour is a key feature of the material’s ability to potentially reduce the ingress rates of harmful substances such as water, oxygen and chlorides which are the key ingredients that cause corrosion of steel in reinforced SHCC (R/SHCC). This dissertation reports on a research study where the fibre-controlled crack widths and spacings are investigated to determine if these fine cracks delay or prevent chloride-induced corrosion in R/SHCC. Therefore, the main aim of this research was to determine a relationship between the crack width distribution, cover depth, chloride level and corrosion. The mechanical characteristics of the SHCC and reference mortar specimens are reported on where the material’s behaviour in compression, direct tension and flexural load are discussed. For the purpose of this research work, quite a large number of different types of SHCC and mortar specimens such as cubes, cylinders, small prisms and beams were tested to determine the mechanical properties. The crack widths and crack distribution under uni-axial tension and flexural testing were measured on the surfaces of the specimens made with both reinforced and un-reinforced SHCC. In the case of corrosion testing, a total of about 100 beam specimens of R/SHCC having two different sand types, two different reinforcing bar layouts and three different cover depths, were cracked and exposed to a 3.5% NaCl solution (by wt of water) representing sea water. The copper/copper-sulphate half-cell was used to record the corrosion potential in the specimens periodically in order to indicate changes in the corrosion process. The Coulostatic method (as part of the polarization resistance technique) was also used to measure the corrosion rate of steel bars inside SHCC. Little corrosion damage was seen in the specimens after about 2 years of testing. A relationship between the cracks, cover depths, chloride content and corrosion rate was then documented for the SHCC material used in this research work. The chloride ion content in SHCC and mortar specimens was determined by means of X-ray fluorescence (XRF) and chemical analysis. The presence of chloride in concrete can be in the form of free chloride and bound chloride. Therefore, XRF was mainly used to determine the total chloride (free plus bound) content at different depths of the specimens while chemical testing was performed for both total and free chloride. A link was established between these recorded values and the rate of corrosion of the steel reinforcement. The chloride diffusion coefficient of un-reinforced SHCC and mortar was also determined by doing rapid chloride migration testing. Steady-state chloride penetration profiling by means of capillary and ponding suction was also done in finely-cracked SHCC specimens. It was found that the ingress of chloride ions in an average crack width of about 50 μm occurred up to full crack height of 60 to 80 mm in under an hour of exposure. Some other durability tests such as freeze-thaw attack, capillary water absorption and electrical resistivity of SHCC and mortar were also investigated. Finally, it was found that in cracked R/SHCC specimens in the early stage of testing, a higher change (from passive to active) in corrosion potential reading could be observed due to the electro-chemical reaction. Nevertheless for this higher potential value, no major corrosion damage can be seen in the specimen in the early stage of testing. A 25 mm cover depth was found to be an approximate threshold for chloride penetration in this specific mix of SHCC material. In addition to corrosion potential and rate readings, actual corrosion-induced pitting depth and area, mass loss and loss of tensile resistance were measured after removal of the steel from the specimens at the end of the tests. Based on the detailed experimental results obtained from this research work, empirical formulas are proposed to predict the corroded depths and loss of steel force due to pitting and mass loss. A number of recommendations are made for the corrosion rate measurement methodology used here of how to improve the variations in experimental and actual results. Some observations and suggestions are also proposed based on the mechanical and durability tests performed in SHCC. In the final conclusions, some approaches are suggested for future studies on durability of SHCC, which could help researchers in increasing their knowledge of SHCC properties and which may lead to the optimal use of SHCC in a sustainable way. The use of SHCC may be feasible in the protection of concrete structures from severe chlorideinduced corrosion or in delaying such corrosion.