Effect of silica fume and steel slag coarse aggregate on the corrosion resistance of steel bars
Introduction
The materials of reinforced concrete require exact controls, due to reinforced concrete as the most widely used a structural material in construction. The concrete is required to be under control to reduce the deterioration of concrete under severe conditions. The main factor effect on corrosion is chloride-ions which have destroyed the natural passivity of the surface of reinforcing steel.
The durability of concrete is a key concern in civil structures because it depends strongly on the interactions of the material with the environment. There is also a little knowledge about the long-term performance of fly ash concrete, and this is one of the main limitations which facing the adoption of this technology on a large industrial scale [1]. Not only the reduction of pH of the concrete due to carbonation causes corrosion but also the chloride penetration [2]. The chloride diffusivity depends on the concrete pore structure and all the factors that determine it such as mixing the design parameters (W/C ratio, type, and proportion of mineral admixtures and cement, etc.), compaction, curing, placing and a presence of cracks [3]. The crack width promotes the corrosion of steel reinforcement due to concrete permeability [4].
Marine environments and the extensive use of de-icing salts can cause rupture of the passive layer, which allows the steel surface to act as a coupled anodic and cathodic reaction cell, where corrosion processes can take place [5], [6]. Corrosion of bars reinforcement in concrete has been studied in the last decades under severe conditions, mostly in relation to chloride threshold value (CTV) or critical chloride content [7], [8]. A number of electrochemical techniques have been used, such as open circuit potential, electrochemical impedance spectroscopy, and cyclic polarization. A wide range of reported CTVs is mainly due to the variability of pH values of the porous network solution of cement-based materials, the chloride binding capacity, and an environmental interaction [8], [9].
A Prior detection and monitoring corrosion of steel in reinforced concrete structures have paved the way to evaluate the lifespan of civil structures and have taken appropriate rehabilitation aspect. The nondestructive electrochemical corrosion monitoring methods such as galvanic potential measurement [10], [11], open circuit potential measurements, linear polarization measurements and electrochemical impedance provide effective information on corrosion status [12], [13] of the rebar in concrete. The continuous increase in the steel production since the 19th century has led to an imbalance between waste products generated in steel production processes and their subsequent usage. As a consequence, the mass dumping at the waste disposal sites has caused a significant environmental problem over the years [14], [15].
Section snippets
Materials and mix proportions
In the current experimental program, a mixture was produced by using an ordinary Portland cement (CEM I 42.5 N), which was employed for the preparation of the concrete test specimens. With contents equal to 350 kg/m3, 450 kg/m3, and 550 kg/m3 according to 4756/1-2007 of the Egyptian standards [16], Two types of coarse aggregates were used dolomite and electric arc furnace steel slag EAFSS as a partial replacement of 0%, 20%, 40%, 60%, 80% and 100% of dolomite, with a maximum nominal size of 10 mm,
Corrosion resistance
This study investigates the concrete, which is exposed to sulfates environments in order to provide an experimental data for a subsequent specification of the concrete performance. The values of corrosion potential (Ecorr) of steel reinforcement bars obtained in an open circuit potential measurement (OCP) tests and it also showed the values of corrosion current density (Icorr), the corrosion rate (C.R) and the corrosion resistivity obtained in linear polarization tests, were exposed to solution
Conclusions
Based on the results obtained from the compressive strength and the electrochemical tests, the following observations can be pointed out:
- 1)
Utilization EAFSS as a full replacement of traditional coarse aggregate (dolomite) has reduced the corrosion rate from 40 (mm/year) ×10−6 to 3.5 (mm/year) ×10−6, when silica fume was used by 20% as a replacement of cement, whereas and without the silica fume the corrosion rate has recorded 20 (mm/year) ×10−6;
- 2)
Based on an open circuit potential measurement (OCP), the
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Corrosion in Reinforced Concrete Structures
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