The admixture or application of crystalline powders to either new or pre-existing concrete structures can dramatically improve their sustainability by enhancing their performance and extending their effective service life.
Farhad Nabavi, expert on the sustainability of concrete structures with Xypex Australia, points out that the sustainability of a concrete structure is inextricably related to its strength and durability.
“The sustainability of concrete structure can be defined as lifetime performance over environmental impact,” said Nabavi to Sourceable. “By decreasing environmental impact and/or increasing the performance and or service life of a concrete structure, its sustainability can be increased.”
Nabavi takes the example of the maintenance and repair work required for a standard structure made from concrete and the improvements to sustainability that can be achieved via enhanced durability.
“Let’s say a normal structure needs to be repaired about to ten to fifteen years in a marine environment due to different forms of deterioration. For repairs you need materials, for repair we need cement, we need water, we need aggregate. These are all environmental resources, which means the actual repair of deterioration already has environmental impacts.
“The production of these materials needs energy, and which in turn generates carbon dioxide emissions, and against has an impact on the environment. So when we increase the service life of the structure actually we have reduced the environmental impact of the structure.”
According to Nabavi one of the most effective means of improving the durability and extending the service life of concrete is to prevent the intrusion of corrosive substances into the concrete itself that either cause or spur the deterioration process.
“Aggressive substances that cause deterioration, such as chloride ions, carbon dioxide in the air or various other chemicals found in the soil, like sulphides, can diffuse into concrete via two main defects – interconnected pores, which are normally called capillary pores, and surface cracks,” Nabavi said.
“Because cement is a chemical compound, there are many different chemicals inside the concrete that are ready to react with these intruding liquids and gases. These chemical reactions can then cause deterioration of the concrete structure.”
The chemical reactions that transpire within concrete structures following the intrusion of aggressive substances can have a devastating impact on the their resilience and strength.
“Some of those chemicals attack the steel reinforcement – for example carbon dioxide can reduce the Ph of the concrete to 9 – 9.5, initiating the process of corrosion. Chloride ions can then reach the surface of the steel reinforcement via the interconnected pores and cracks, and when the concentration of chloride ions reaches a critical level the corrosion of the steel reinforcement can initiate.
“This corrosion of the steel produces rust, or what we call corrosion products,that can occupy around five times more volume than the original reinforcement. The expansion inside the concrete causes cracks and spalling of the concrete, so the result is we have reduction of the strength of the reinforcement, because the steel has been converted into rust, reduction in the strength of the concrete itself as well.”
Given that the precondition for these corrosive chemical reactions to take place is their intrusion via cracks or pores, Nabavi points to simply blocking the conduits of entry as the best means of preventing concrete deterioration and spalling.
“All [forms of deterioration] need these paths and passages in order to diffuse into the concrete – these interconnected pores and cracks. If we can block those pores, and heal those cracks, then we can definitely reduce the rate of diffusion of these liquids and gases significantly.”
A highly effective means of producing such barriers is crystalline technology, which can be added to concrete structures multiple stages of their lifecycle.
“Crystalline technology is essentially generates a barrier inside the pores and cracks by means of non-soluble, permanent crystals,” Nabavi said.
“The crystal materials are like a dried powder that can be introduced to new structures as a concrete admixture which is added at the time of batching, or applied to existing concrete structures as a coating on the top of their surfaces.
“Scanning electron microscope images show that the crystals bridging and healing the pore and cracks, and by doing this we can reduce the diffusion of these aggressive substances into the concrete. Because we have reduced the diffusion rate of those substances into those concrete the service life of the structure can be extended significantly.”
According to Nabavi in addition to visual evidence of the effect of the crystals in the form of electron microscope images, independent studies attest to the ability of crystalline technology to extend concrete structure service life by as much as a century.
The upshot of this increased durability and longevity is less maintenance and repair work, and dramatically improved sustainability.
“When we increase the service life of the structure we have actually reduced the environmental impact of the structure,” said Nabavi. “Then, as per the definition of sustainability for concrete structures, we can conclude that increasing their service life also raises their sustainability.”