What is it about?
Currently, large infrastructures (bridges, highways, etc.) are designed for more than 100 years. To achieve long service life, coated rebars (mostly, cement polymer composite (CPC) coated rebars) are being used to enhance the corrosion resistance. However, inadequately coated rebars can lead to premature corrosion. This can also affect the bond between the rebar and the concrete. To assess the effect of CPC coating on bond strength, pull-out specimens of (150×150×100) mm with 12 mm diameter rebar with 100 mm embedded length were cast and tested. For this, three replica specimens with two types of reinforcement namely, i) Uncoated steel ii) CPC coated steel were cast. To induce corrosion, additional five specimens with CPC coated steel rebars were cast with premixed chloride and cured for 28 days. During the curing period, continuous monitoring of corrosion potential and rate was done and degree of corrosion was assessed. The effect of degree of corrosion on bond of steel-concrete-coating interface was quantified. The CPC coated rebars without corrosion exhibited 10% bond reduction. CPC coated rebars with corrosion exhibited 30-70% reduction in bond strength. Also, the corrosion is found to adversely influence the stiffness of the bond.
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Why is it important?
Recently, many RC structures are built with CPC coated steel rebars. Many of them are built without adequate consideration of the quality of concrete and coating characteristics – leading to premature corrosion of reinforcement. Experimental investigation shows that the negligible corrosion can cause significant disbondment of coating from the steel surface and reduces the tb by 40-80%. Soon, many large-scale infrastructure systems will experience initiation of corrosion and so significant reduction in bond strength and structural capacity, which may also result in sudden cracking, excessive deflection, etc. of infrastructure. This paper quantitatively estimate the effect of corrosion and disbonding of CPC coating on bond strength and stiffness of S-C-C interface. This will help engineers to plan and ensure the corrosion prevention strategies.
Perspectives
Many reinforced concrete systems are built with CPC coated steel rebars in anticipation of delayed initiation of corrosion. However, inadequate practices at construction sites may lead to premature initiation of corrosion in such systems. Note that RC systems with uncoated steel are reported to be safe until the degree of corrosion is less than 1% of steel mass loss. It may take about 10 years. During this time, RC systems with uncoated steel shows signs of corrosion. Whereas, systems with CPC coated steel rebars may face significant bond reduction soon after the initiation of corrosion. This paper quantifies the effect of initiation of corrosion on bond strength of CPC coated steel and concrete systems.
Deepak Kumar Kamde
Indian Institute of Technology Madras
Read the Original
This page is a summary of: Effect of the degree of corrosion on bond performance of Cement Polymer Composite (CPC) Coated steel rebars, MATEC Web of Conferences, January 2018, EDP Sciences,
DOI: 10.1051/matecconf/201819904010.
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