Corrosion of Embedded Metals in Concrete

Strengthened by different types of concrete reinforcements Sephaku Cement discusses steel concrete and the risk of corrosion caused by embedded metals in concrete fittings.

Durable, low maintenance and one of the most widely used building materials in all forms of construction, reinforced cement concrete or RCC offers both bearing strength as well as tensile strength in various concrete applications. Reinforced using steel rods or rebar (reinforcing bars), mesh, wires or cables results in steel reinforced concrete often referred to as steel concrete. Offering added resistance to tension and compression, the tightly twisted steel rebar strands help to create a rope like reinforcement that can anchor itself in cured concrete while also offering the same propensity for expansion and contraction as the concrete itself. While successfully incorporated in several civil engineering projects, domestic buildings, foundations, lintels and even underwater projects an important element to factor for when making use of steel reinforced concrete is the corrosion of embedded metals in concrete fittings.

What is Steel Corrosion?

Described as an electrochemical process that sees the flow of electrical currents between electrons and ions, together with chemical reactions between two or more metals and compounds in both steel and concrete, the corrosion of streel reinforcements and other metals embedded in concrete causes a corrosive attack on the concrete that can be dangerous and costly to repair.

Possibly one of the most common causes of damage to the otherwise stronger forms of concrete, moisture and oxygen are the leading culprits that cause the corrosive effects on steel concrete fittings.

When exposed to various environmental factors including humidity coupled with oxygen these elements act as the catalyst that sets in motion the corrosive effects on steel rebar embedded in reinforced concrete. This corrosive activity results in the rusting effect of embedded steel and other metals which is responsible in compromising the strength of steel reinforced concrete.

Avoiding the Corrosive Effects Steel in Concrete

It is no secret that concrete and water go hand in glove and given the porous structure of cured concrete, the presence of oxygen in its sponge like make up is inevitable. And while we now know the electrochemical process that causes corrosion of steel embedded in concrete can be attributed to oxygen and moisture (amongst other elements) there are various precautions that can be taken to prevent or reduce the rate of corrosion and the inevitable damaged caused to steel reinforced concrete.

• Employ the help of “crack-free” concrete making use of low permeable concrete. Preventing undue exposure to moisture and oxygen, making use of higher cement contents resulting in higher strength concrete and less porous. The cement being alkaline will afford sufficient protection to corrosion of the steel. The passivity layer as it is called actually consists of “Beta-Gamma Ferro-oxide”. Low water to cement ratios again resulting in higher strength and less permeable concrete which will help to reduce the corrosion rate of embedded metals in concrete.
• Adding a corrosion inhibiting admixture to cement mix blends will also help reduce the rate of corrosion of embedded metals.
• Contractors manually reinforcing concrete applications may also opt to coat the reinforcement rebar using a resin sealer before embedding the steel in the concrete or could opt to use a different material for the steel e.g. Stainless steel or may opt to have the re-bars galvanised.
• Sealing concrete structures with a membrane or surface sealant will also help prevent the absorption of moisture into the body of the concrete fitting at a surface level.

Placing reinforced concrete fittings under even greater tensile stress that results in spalling and often hazardous cracks, paying close attention in adhering to safety guidelines and best practices that help to prevent the corrosion of embedded metals in concrete is a function not to be overlooked by contractors, civil engineers or home improvement enthusiasts.