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KIM gets to the root of the problem

ALIREZA BIPARVA* elaborates on a long-term study on reinforced concrete exposed to aggressive marine environment that identified crystalline concrete waterproofing admixture as a protective solution.

Tiny hairline cracks are inevitable when creating a new concrete structure. It’s the nature of the environment: the earth, and therefore the foundation, will probably move a little. For the most part, these hairline cracks are not a cause for concern. Many structures will shift and settle for decades, and with proper planning, still be just as structurally sound as the day they were built.

But what about tiny salt molecules carried through the hairline cracks? They can follow the path (or easy path) and end up right where nobody wants them: the steel rebar. Salt, water and steel do not play well together – and the steel will always lose in the end. By the time anyone has noticed that the steel has been silently eroded, it is often too late for repairs and partial or complete replacement of the structure is necessary. The corrosion of metals, especially including that of reinforcing steel, has been a growing concern for structures due to the increase in occurrences and the costs of repairs.

 The best way to prevent water penetration is to block water pathways with a crystalline concrete waterproofing admixture. Crystalline admixtures form chemical crystals throughout the concrete mass, maximizing waterproofness, and are able to protect both the concrete and reinforcing steel against aggressive damaging agents, while still allowing passage of air. But not all crystalline admixtures are created equal. So how can you know which product is best to do the job of protecting your steel from corroding?

To answer this question, a long-term independent field exposure study was conducted to evaluate the durability of reinforced concrete specimens exposed to an aggressive marine environment. The study was initiated by Dr. Craig Newtson as part of a larger study of durability of concrete made with Hawaiian aggregates and exposed to such an environment. Twenty five test panels made of concrete and reinforced with steel were exposed to the aggressive, warm salt waters in the tidal zone at Pier 38 in Honolulu Harbor for a period of 9-10 years from 2002 to 2012. This study represents the longest continual test period ever carried out in the world for corrosion of reinforced concrete.

In addition to control specimens, these panels including various corrosion inhibiting admixtures and pozzolans intended to reduce the chloride penetration rates through the concrete and delay the onset of chloride induced corrosion of the reinforcing steel. During exposure, the panels were monitored for half-cell potential, chloride concentrations, cracking and visible signs of corrosion.

The key findings in the reports are as follows:

• The panel using 2% Kryton’s Krystol Internal Membrane (KIM) outperformed all other chemical admixtures used in the test. A panel containing Kryton KIM showed significantl reduced half-cell reading when compared with the control specimen. In addition, after 10 years exposure, KIM panel does not have any signs of corrosion. Panels using the remaining admixtures, Rheocrete 222+, FerroGard 901, Xypex Admix C-2000 and a latex modifier exhibited inconsistent to poor results.
• Calcium nitrite based corrosion inhibitors delayed the onset of corrosion at a dose of 20 L/m³, but did not provide reliable protection at a lower dose of 10 L/m³. These admixtures were not effective at reducing the ingress of chlorides.
• Pozzolans (15% fly ash and 5% silica fume) combined with a reduced water-cement ratio (0.36 compared to other samples batched at 0.40) performed well, although poor dispersion of the silica fume compromised the performance of at least one panel.
• Control panels (no admixture or Pozzolan) with a water-cement ratio of 0.40 experienced corrosion-induced cracking and rust residue.

These findings are particularly relevant because they are based on field exposure in a harsh coastal environment. This is the best type of testing because the exposure simulates the actual service conditions of a real structure. Laboratory tests are generally short term, and are designed to provide accelerated results using conditions that do not always model real life. Many products may perform well in a short term laboratory experiment, but perform poorly over the long-term in real-world conditions.

The durability of a concrete structure is fundamentally based on the concrete’s permeability. It is well known that permeability determines the vulnerability of concrete to external agents; therefore in order to be durable, concrete must remain relatively impervious.

Krystol Internal Membrane (KIM) is a chemical admixture in dry powdered form, effective in creating waterproof concrete. Kryton products such as KIM waterproof concrete by a chemical process that develops insoluble crystals that fill the capillary voids and micro-cracks of the concrete and permanently blocking the pathways for water and waterboron contaminations. The features of KIM provide many unique benefits to concrete that enhance durability and compensate for the properties of concrete that have historically resulted in poor durability. As this study suggests, KIM admixture differs from other single-function admixtures and supplementary cementitious materials. The combination of reducing the permeability of reducing the permeability of the concrete, reducing shrinkage cracking, and improving the self-sealing properties can increase the resistance of concrete to the penetration of harmful chemical agents.It is concluded that KIM can prevent corrosion in reinforced concrete by impeding the development corrosive conditions. The result is a structure with increased durability, a longer lifespan and lower maintenance costs over the structure’s service life.

*Alireza Biparva is R&D manager – concrete specialist at Kryton International of Canada. He has published several research papers in international journals and conferences.

Source: Gulf Construction Digital Edition