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"If these ions are floating around, if they're moving through honey instead of water, they'll be significantly slowed down," says Bentz. "The trick is to find the right chemical that will change the viscosity of the solution."
The researchers took a cue from the food industry, which uses additives as thickeners in everything from salad dressings to carbonated drinks. Bentz searched for similar additives that would both increase the viscosity of the water solution found in concrete and slow ion diffusion; he even tried using food thickeners, including xanthum gum, which is used in sauces and ice cream.
After screening multiple additives in water solution in order to model the behavior of ions in concrete, the team found that those with a smaller molecular size were more successful at slowing the rate of ion diffusion. Additives that occur in small molecular chains, with branches of hydrogen and oxygen, were particularly good at increasing a solution's viscosity. Bentz says this might be due to the fact that such hydrogen and oxygen branches can interact with water molecules to form a barrier against infiltrating ions, making it harder for them to penetrate.
The team also tested various additives within small cylinders of cement mortars--essentially, concrete without the aggregates. Bentz mixed the additives with cement, let the mortars dry, and placed each mortar into a chloride solution for up to one year. After removing the mortars from the solution, he and his team broke apart each mortar and analyzed how far chloride ions were able to penetrate. Compared with mortars without any additives, those with additives showed significant reduction in chloride diffusion.
However, the technique may not be quite ready for industry-scale application, mainly due to potential costs. Bentz says to get such results he had to make the additive as much as 10 percent of the cement solution. "The industry is comfortable with one percent, so there's a cost factor, in that it'll cost 10 percent more," says Bentz. "We've demonstrated proof of concept, and now we would like to find an additive that works at 3 to 5 percent concentration."
Jason Weiss, professor of civil engineering at Purdue University, works on improving concrete mixtures and increasing the material's long-term performance. He says that such a technique may one day make bridges and roads less susceptible to corrosion. "This has an enormous potential," says Weiss. "This would imply that a bridge that could last 30 years would now last 40 to 45 years under the same type of chemical attack."
Researchers aim to cut carbon-dioxide emissions by shedding light on the nanostructure of cement.
The Romans used volcanic ash to make concrete that would last 2000 years. We can make a similar concrete by utilizing the fly ash from coal fired power plants. The ratio of ash to portland cement is varied to get differing strengths. The ash is a substitute for some of the portland cement. This results in much slower set times. These particles (pozzolons) fill in the matrix of the concrete thus increasing density so salts cannot penetrate. My assumption is that because of the slower set times contractors are not willing to use pozzolons.
The verbage used in this article says that the viscosity is increased in concrete to make it more durable? This must be some kind of public relations speak as scientist have for years been steadily reducing the viscosity & lowering the water cement ratio in order to enable concrete to be less permeable & more durable.
I do know that by utilizing nana sized materials in your mix designs will enable a more durable concrete as personal testing has revealed. Stopping the ionic exchange of H2O & Chloride ion has been studied on many fronts for years with good empircal results already demonstrated.
What I would like to study is the patent that they claim they have, & find out how this particular government funded entity was granted a patent, & how they plan to transfer to technology with minimal red tape to those who need it now.
If their hypothesis that increasing the viscosity of the water solution works, I think the glutinous rice flour would be a good choice. Ancient Chinese used it to enhance concrete in thousand years ago.
Alkali-silica reaction (ASR) is a significant durability problem that has resulted in premature deterioration of various types of concrete structures in the United States and throughout the world.
Although several viable methods exist to prevent ASR-induced damage in new concrete structures, very few methods mitigate further damage in structures already affected by ASR-induced expansion and cracking.
Lithium compounds have been recognized for more than 50 years as effectively preventing expansion due to ASR, and there has been renewed interest in recent years in using lithium compounds as either an admixture in new concrete or as a treatment of existing structures.
This report is intended to provide practitioners with the necessary information and guidance to test, specify, and use lithium compounds in new concrete construction, as well as in repair and service life extension applications.
Federal Highway Administration
Guidelines for the Use of Lithium to Mitigate or Prevent Alkali-Silica Reaction (ASR)
http://www.tfhrc.gov/pavement/pccp/pubs/03047/
Regarding enhancer's comment above... I too have heard that the rice flour mixed into the Great Wall has allowed the grout to out last some of the stones themselves. Is it great grout or poor stones? :-) Nonetheless, concrete longevity is sure an area needing more research.
In considering rapidly national debts and deficits, it's sad to think that in the potentially poorer budgetary future there may be many forced expenditures to repair needed infrastructure rather than say build new hospitals. Or worse, there may occur closure and abandonment of core infrastructure assets for lack of financial resources. Something as simple as crumbling concrete could dramatically erode a nation's ability to sustain and grow its economy.
Manufacturing in the United States is in trouble. That's bad news not just for the country's economy but for the future of innovation.
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jmaximus9
86 Comments
Bad by Design?
There are roads in Europe, built by the Romans, that are still in use today. Yet somehow we can't build a road today that lasts 20 years. Gee I wonder why?
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