Rheocrete 222+, a combined waterproofer and organic corrosion inhibitor from BASF Construction Chemicals, received top honours. The trial, after stringent review, has been accepted for publication in the International Journal of Electrochemical Science. For BASF, this is industry recognition at a high level for a product that has proven itself in projects around the globe for over two decades.
Says David Bowerman of BASF Construction Chemicals’ Admixture Systems Division: “This trial by AUS puts the theory around corrosion inhibitors to the test and provides insight into the performance of different formulae. The results speak for themselves with regard to the capabilities of Rheocrete 222+, underlining the effectiveness of the product but also highlighting the advantages of organic corrosion inhibitors over inorganic solutions – which is particularly relevant to construction in the UAE region.
“Ground water and chlorides corrode the steel in reinforced concrete, weakening structures. Unless precautions are taken at design stage, structures are likely to require extensive repair to keep them in service. In the Middle East, concrete frequently fails to meet its design life in the hot, humid, salt laden atmosphere. Corrosion inhibitors can reduce the lifecycle costs of structures in aggressive environments and enhance their design life. However, the effectiveness of corrosion inhibitors can vary, so selecting the right product is vital.”
The AUS trial: Reduction of Corrosion Process in Steel Bars Using Inhibitors
Corrosion inhibitors act in a number of ways to retard or delay the corrosion mechanism: in simple terms, they form a chemical inhibition film on the steel reinforcement at either the anode or cathode, or both. Three commercial inhibitors were used in the AUS study: a Calcium Nitrate Inhibitor (CNI), an anodic corrosion inhibitor (ACI), and the RHEOCRETE 222+ corrosion inhibitor, which is a dual formulation.
A corrosion cell comprising four concrete beams was constructed. Three beams made use of different corrosion inhibitor admixtures and the forth was a control beam with no addition of admixture. Super plasticizer was added to maintain approximate 100mm slump for the four mixes.
The performance of admixtures against corrosion was highest for RHEOCRETE 222+ than others. The same findings were achieved from the corrosion mass loss which was calculated theoretically using Faraday law. Visual observation of the broken samples also confirmed these findings.
These results can be further tested using Life 365 (http://www.life-365.org), a free and independent computerised corrosion modelling program that shows the effectiveness of Rheocrete 222+ and demonstrates the reduction in life-cycle costs resulting from its use.
Organic corrosion inhibitors win hands down
Ideally, in construction, contractors want a corrosion inhibitor that is environmentally friendly, is capable of slowing down chloride penetration through the capillary pores of the concrete, will reduce permeability of concrete, and will form a protective corrosion resistant film around the steel reinforcement. Also, since dosing admixtures like these into a concrete mix can adversely affect workability, initial slump and setting time — and mitigating these effects can additionally affect strength development and concrete-steel bond strength — a product that does not produce these effects is highly desirable.
There are two key types of corrosion inhibitor to choose from: organic and inorganic. Inorganic corrosion inhibitors (typically nitrate based) act as a passivator, counteracting the damaging action of chloride ions on steel through the presence of nitrate ions. However, they also act as an accelerator when dosed into fresh concrete, increasing slump loss and reducing setting time. A big disadvantage is that, if underdosed, inorganic corrosion inhibitors can accelerate localised corrosion. Unlike organic inhibitors, which have a fixed dosage, to work efficiently calcium nitrate based admixtures require knowledge of the likely chloride content of the concrete throughout the lifespan of the structure. This is almost impossible to determine.
The advantage of dual action organic corrosion inhibitors is that they can diffuse through the concrete and form a corrosion inhibiting layer on the metal surface. They also reduce the porosity and permeability of the concrete to water and chlorides.
Rheocrete 222+ is the only product in the AUS test that combines two forms of protection: a hydrophobic pore-blocking waterproofer and an organic inhibitor which forms a corrosion-resistant protective film on the reinforcing steel. The inhibiting action is anodic, reducing the dissolution of iron, and cathodic, acting as a barrier to oxygen and moisture.
Optimising the benefits of Rheocrete 222+
Says Bowerman: “It’s the unique formula of the Rheocrete 222+ that makes it so effective. The findings of the AUS trial describe its action concisely: ‘The Rheocrete 222+ admixture is a combination of amines and esters in a water medium. The ester component acts by lining the pores of the cement matrix, slowing the rate at which chlorides and moisture enter the concrete. The amines adsorb onto the reinforcing steel to provide an additional barrier to corrosion by forming a protective film. This film slows the corrosion process once it begins by preventing chlorides from reacting with the reinforcing steel, and by depriving the corrosion process of moisture’. Dual-action inhibitors also reduce deterioration caused by ingress of sulfates as a consequence of the concrete’s reduced permeability.”
Rheocrete 222+ has a 20-year international track record – it was first widely used in the USA but is now also available in the Middle East for over 10 years. The product is also sold in Asia/Pacific and Europe. It’s been used in a number of high profile construction projects, including construction at the Khalifa Port and Industrial Zone; construction and repair of bridges, culverts and roads in Oman; at Jebel Ali Power Station K; Halul Port and Doha West Sewage Treatment projects in Qatar; the Emirates Twin Towers; and more.
But best practice goes hand in hand with quality outcomes. Notes Bowerman: “The use of fully-compacted, properly cured concrete will ensure maximum durability of concrete — putting a high-quality admixture into low-quality concrete will not get you the results you need. BASF has a full range of systems and solutions to meet specific needs.
“In addition to Rheocrete 222+ we recommend assessment of BASF’s Smart Dynamic Concrete technology which uses the RheoMATRIX viscosity-modifying admixture along with a superplasticiser from our Glenium range (formulated from polycarboxylic ether polymers produced in-house by BASF) which will assist you to achieve the specifications required for your application. Curing compounds from our Masterkure range will furthermore ensure full hydration of the concrete and minimise the risk of cracking.”
Concludes Bowerman: “When it comes to corrosion, prevention is better than cure. While corrosion inhibition solutions may initially cost more, the value in terms of greater durability, lower lifecycle costs and extended design life, more than make up for it.”
Monday, July 23- 2012 @ 13:39 UAE local time (GMT+4) Replication or redistribution in whole or in part is expressly prohibited without the prior written consent of Mediaquest FZ LLC.