Journal Apr 2021

Hydrophobic treatment for control of deterioration in reinforced concrete structures Joanitta Ndawula, Hans Beushausen, Mark Alexander

The durability of a reinforced concrete structure or structural element relates to its capacity to withstand its exposure environment, without the need for major repair over its service life. Realising concrete durability may be achieved using service life design. Service life design methods are used to ensure sufficient resistance of concrete structures to the exposure environmental actions. Avoidance of deterioration is a highly favourable option for the service life design of new structures. Surface treatment of reinforced concrete using hydrophobic impregnation (e.g. using silanes) may effectively be used for both corrosion control and avoidance of deterioration of reinforced concrete structures susceptible to chloride-induced corrosion. However, further studies are required to generate the statistical data and input variables required for the calibration and validation of service life prediction models for silane-treated structures.

Optimal dosage of Fe2O3 nanoparticles to enhance chloride resistance and microstructural properties of concrete - A comprehensive study Raghava Kumar Vanama, Harinee Addepalli, Balaji Ramakrishnan

Majority of reinforced concrete port structures in India are experiencing premature failures due to chloride-induced corrosion. The use of concrete that possesses higher chloride penetration resistance and better compact microstructure can potentially increase the corrosion initiation period and thereby, the service life of the structure. The present study investigates the influence of Fe2O3 nanoparticles in improving the durability and microstructural characteristics of concrete. Hematite nanoparticles were synthesised and comprehensively characterised. The characteristics of nano hematite blended concrete have been widely studied by rapid chloride migration, electrical resistivity against chloride migration, mercury intrusion porosimetry and XRD tests. FEG-SEM micrographs of hardened nano blended concrete indicated the strengthening of the Interfacial Transition Zone. Based on the comprehensive study, cement replaced by 0.5 weight percentage of hematite nanoparticles found to be an optimum dosage for a durable concrete in the marine environment.

Performance of organic and inorganic functional groups as corrosion inhibitors in concrete experiencing extreme corrosive environment Himanshu Guleria, Purnima, Ashish Kumar Tiwari, Shweta Goyal

Reinforcement corrosion is the major durability issue causing premature failure of reinforced concrete structures. Ingress of chloride and atmospheric CO2 are two important phenomena promoting the corrosion, but combined effect of these two causes even more severe damage than individual environment. The corrosion inhibition mechanism of various compounds depends upon the presence of functional group in their molecular structure. The present study deals with determination of the inhibition efficiency of organic and inorganic based compounds in combined chloride and carbonated environment. The aggressive environment was achieved by subjecting specimen to alternate wetting-drying-carbonation cycles. Specimen was wetted by ponding in 5% NaCl solution followed by air drying and exposed to carbonation by using environment chamber. The results show that compound containing organic functional group was able to reduce corrosion rate in combined environment, while inorganic inhibitor was unable to perform in aggressive conditions. Chloride and carbonation profile also shows that organic functional group-based inhibitor blocks the pores and resists the movement of aggressive chloride ions and carbonation front.

Corrosion inhibiting admixture for corrosion prevention in small scale reinforced concrete structures S. Shafeer Ahamed, J. Sherin Mariya, V. Roopa, M.S. Haji Sheik Mohammed

This study analyses the influence of commercially available mixed inhibitor [sodium nitrite based water reducing and corrosion inhibiting admixture (WSNI)] and bipolar inhibitor [dual mechanism corrosion inhibiting admixture (BPI)] on the strength and durability performance of Portland Pozzolana Cement (PPC) and Portland Slag Cement (PSC) mortar. The strength (compressive, split tensile, flexural, and shear) and durability (water absorption, water sorptivity, chloride ion penetration and accelerated corrosion) tests were conducted on Portland Pozzolana Cement Mortar (PCM) and Portland Slag Cement Mortar (SLCM) with and without inhibitor as per the relevant standards. The mortar mix of 1:3 with workability 75 - 90% in flow test with inhibitor admixing at 1, 2 and 5% by weight of cement were adopted in all the tests. It is found to be that inhibitor incorporation did not influence the fresh mortar properties but had resulted in appreciable reduction of the water cement ratio. The addition of WSNI and BPI significantly increases the compressive strength at early ages but marginal improvement at 28 day. There is a significant improvement in flexural and shear strength (up to 30%) for inhibitor admixed mortar in certain dosages. Appreciable reduction in water absorption and chloride ion penetration; and improved tolerable limit for chlorides were also noticed for inhibitor admixed PCM and SLCM specimens. The addition of mixed inhibitor and bipolar inhibitor at 2% is recommended for use in small sector construction projects for enhanced corrosion prevention in Reinforced Concrete (RC) structures.

Mechanical and electrochemical aspects of microalloyed steel B. Bhuvaneshwari, P. Prabha, S. Sandhiya, G. S. Palani

Microalloyed steel is widely used in the automobile sector and recently finding its place in the construction of buildings, bridges and pipelines. It is a special category of low carbon steel with high yield to tensile strength ratio due to the addition of alloying elements, which boost the microstructural and strength related properties of the steel. Tensile tests, chemical analysis, corrosion tests and the morphological studies have been conducted on Titanium microalloyed steel samples to study the mechanical and electrochemical aspects. From these studies, it is understood that the Titanium microalloyed steel has the potential in structural composites applications as the steel stabilities against corrosion is relatively good under chloride contaminated simulated concrete pore solution environment.

Cathodic protection of steel reinforcement: Past experience, performance and future opportunities George Sergi

Impressed current cathodic protection (ICCP), following on from its early success in buried pipelines and submerged structures, was trialled on atmospherically exposed steel reinforced structures in the 1970’s, first in the USA on bridge decks and then more extensively in the UK as new and better performing inert anodes were developed. Cathodic Protection (CP) of steel reinforced concrete soon became a well-established technique for controlling reinforcement corrosion of structural elements. Long-term maintenance of ICCP systems, however, started to be seen as a burden to most structure owners and managers as it involves additional and continual costs. A requirement arose, therefore, for simpler CP systems to be made available which will involve less maintenance and monitoring requirements. As a first stage to simpler systems, galvanic cathodic protection anodes were developed in the 1990’s, first, only to protect steel reinforcement immediately around patch repairs but subsequently to control reinforcement corrosion over wider areas where corrosion risk was found to be high. It was the combination of ICCP and galvanic anode systems, however, that set the benchmark for a simpler alternative long-term method for corrosion control of steel reinforcement. This paper attempts to follow the development of all CP systems utilized for atmospherically exposed steel reinforced structural elements and looks at recently developed simpler systems and methodologies that would likely form the future of the CP industry.

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