- Will it be more expensive to use stainless steel reinforcing in place of carbon steel reinforcing or galvanised reinforcing in my structure?
- What are life-cycle costs (LCC)?
- What is spalling?
- Other methods are available that can delay the onset of concrete cancer/spalling, like cathodic protection, special coatings and special concrete blends. Why should I use stainless steel reinforcing?
- Why is dedicated stainless equipment so important?
- Hot dipped galvanised reinforcing has been suggested as an alternative to stainless steel reinforcing; will it prevent concrete cancer in my structure?
- Why are there different grades of stainless steel reinforcing and which one is best for my application?
Will it be more expensive to use stainless steel reinforcing in place of carbon steel reinforcing or galvanised reinforcing in my structure?
Only if life cycle costs are not factored in. There are predictive models available that can help assess areas at risk of early deterioration. The true value from using stainless steel reinforcing in these areas may take several years. Traditional carbon steel reinforcing will corrode over time, especially in the presence of chlorides and carbonation — so will galvanised. This deterioration will cause spalling which will need to be repaired, and sometimes the structure may require demolition; this will be expensive. Stainless steel members will not expand and rust as mild steel, and reports suggest your stainless steel reinforcing should last 300+ years, even in a high chloride environment. Additionally, when compared with total contract costs, the outlay on stainless steel reinforcing in the known critical areas is usually only a small percentage.
What are life-cycle costs (LCC)?
These are all of the costs involved for the total duration of the design life of your structure, not just initial costs. Life cycle costing enables potential long-term benefits to be assessed against short-term expenditure — e.g. material costs plus installation costs are your initial costs, however life cycle costing also recognises and factors in inspection costs, maintenance costs (multiplied by frequency), repair costs, lost production costs and disruption costs. It also includes estimated inflation costs (on material and labour), giving an idea of the future outlay required to preserve, repair or rebuild your asset. These are the true costs associated with the lifespan of your structure.
What is spalling?
Spalling (often referred to as “concrete cancer”) is essentially a result of traditional carbon steel reinforcing within a concrete section rusting. Due to the porous nature of concrete, chlorides can permeate and seep through to cause corrosion. The rusted steel expands up to seven times its original size, causing the surrounding concrete to delaminate, crack and bulge out. This can drastically reduce the strength of the structural member as well as being a major eye-sore to the public. Spalling concrete should be repaired as soon as possible, before the steel bars corrode further and damage larger areas — hence the term ‘concrete cancer’.
Other methods are available that can delay the onset of concrete cancer/spalling, like cathodic protection, special coatings and special concrete blends. Why should I use stainless steel reinforcing?
Stainless steel reinforcing will prevent concrete cancer, not just delay it. Painting your concrete with special coatings requires constant inspections and regular reapplications. Cathodic protection also needs to be checked regularly to ensure the system is working, and power supply can be difficult to connect to in remote areas. Special concrete blends can and often do crack, opening up pathways for corrosion directly to the reinforcing. Only stainless steel reinforcing will give you peace of mind in achieving a 300+ year design life for your concrete structure, virtually maintenance free.
Why is dedicated stainless equipment so important?
When carbon steel filings get embedded in the chromium oxide layer of stainless steel, this passive layer — which is usually self-healing — is unable to repair itself due to the lack of oxygen available once this fragment starts to rust. This area will begin to pit, and the rust will eat deeper and deeper into the stainless steel. Durinox equipment has never been used to process carbon steel.
Hot dipped galvanised reinforcing has been suggested as an alternative to stainless steel reinforcing; will it prevent concrete cancer in my structure?
No, it will only delay the onset. It may outlast ordinary mild steel, however it will never give the same corrosion-free protection that stainless steel provides. Just how much protection galvanising can offer is arguable, considering concrete is a high-pH environment and zinc does not perform well at certain pH levels.
Why are there different grades of stainless steel reinforcing and which one is best for my application?
Studies on the different grades of stainless and their performance in the high pH of concrete are ongoing. Initial results suggest that even the cheaper grades of stainless steel will perform as well as some of the more well-known grades when complemented by the high pH nature of concrete. Durinox stocks Austenitic grade 316 due to its non-magnetic properties and industry acceptance by specifiers. 316 has a higher percentage of nickel compared to the duplex grades (LDX2101, 2304 and 2205), which can mean the pricing is higher and more volatile. The duplex grades help bring down initial outlay costs and keep pricing more stable while offering the same durability as 316. In short, if Durinox can keep the price of stainless steel reinforcing down, it will be more attractive to asset owners restricted by budget constraints, or who are not willing to factor in life cycle cost benefits.