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New fire-resistant coating to prevent failure in steel building fires

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NTU Assistant Professor Aravind Dasari putting his finger on a piece of plastic that is cool enough to touch, which was placed behind a steel plate coated with FiroShield and exposed to a flame over 900 degrees Celsius. Credit: Nanyang Technological University

A few extra coats of ‘paint’ could be all that the steel in a building needs to prevent itself from buckling and failing in a fire.

Scientists from Nanyang Technological University, Singapore (NTU Singapore) and Singapore’s industrial developer JTC have developed an affordable 3-in-1 coating that offers enhanced  and corrosion protection.

Existing  in buildings are usually coated with a fire-retardant layer to shield the bare metal from damage by fire and meet the fire protection standard of two hours – aimed at giving occupants enough time to evacuate the building. Today’s conventional intumescent coatings are thick, more expensive and laborious to apply.

In contrast, this made-in-Singapore coating can be applied to bare steel without the need for sandblasting to prepare the surface, reducing coating time by half, and will protect the material against fire for two hours without falling off.

Named FiroShield, the new coating is cheaper and less laborious to apply, and can function aesthetically like normal paint.

FiroShield has also been tested on other construction materials, such as reinforced concrete and laminated timber, and has the same excellent performance.

Leading the research team is Assistant Professor Aravind Dasari from the School of Materials Science and Engineering and Professor Tan Kang Hai from the School of Civil and Environmental Engineering.

The team leaders said the knowledge that they have obtained over the years of research on the different aspects of polymers and combustion, combined with civil and structural engineering experience, helped to streamline their approach.

The strength of their coating comes from a balanced mix of additives, which work well together to give off simultaneous chemical reactions when faced with extremely high temperatures. They knew that they had found the right formula when they were able to coat steel samples evenly with a spray gun.

“In a fire, our coating forms a compact charred layer that acts as a protective barrier against the heat,” added Prof Dasari, who is also a Principal Investigator at the NTU-JTC Industrial Infrastructure Innovation Centre (I3 Centre).

“While typical fire coatings will also form a charred layer, those are thick and foam-like, which can fall off easily and leave the steel exposed to the fire. What we aimed at was an innovative coat that works differently from conventional intumescent coatings and can stick to the steel surface for as long as possible under high temperatures, and yet has durability and weather resistance under normal conditions without a need for a top coat of paint.”

Mr Koh Chwee, Director, Technical Services Division of JTC and Co-Director of the I3 Centre, said that through collaboration with academic institutions like NTU, JTC aims to develop new and innovative solutions to enhance safety and construction productivity for its industrial infrastructure projects.

“The ease of application of this new fire and corrosion resistant coating on steel structures will help reduce labour-intensive work, thus improving productivity and enabling faster coating of prefabricated steel components. More importantly, the new coating’s ability to maintain superior adhesion under  leads to increased building safety for occupants. We are confident that the new coating will be able to reduce both paint material and labour costs, and become a new alternative to other fire protection products,” said Mr Koh.

Combination of materials used for coating

The base material of the new coating is made of synthetic resins, which are polymers commonly used to make paints. To give it fire and corrosion-resistant properties, Prof Dasari’s team added a combination of common chemicals, including one that is endothermic – absorbing heat to start a chemical reaction that causes the coating to adhere firmly to the steel.

The team went further to develop a coating that is able to have assorted colours; pigments can be added to the mixture so it achieves the aesthetic function of normal paint. Paint manufacturers looking to add the benefits of FiroShield to their products should find that commercialisation is straightforward, as the innovation relies simply on the addition of key chemicals into their paint manufacturing process.

To achieve a two-hour fire rating, FiroShield requires just five layers of coating, compared to conventional coatings, which requires up to 15 layers or more. It is thus two times faster to apply and is cheaper by about 50 percent due to its lower materials cost and manpower requirements.

In addition to its fire-resistant properties and easy application, FiroShield can also protect the steel surface from corrosion, which no other fire coatings in the market can do at the moment. FiroShield is expected to last longer when exposed to weathering elements such as moisture and UV rays. Its performance barely dipped by two percent, as compared to the drop of up to 75 percent for conventional coatings when subjected to weathering tests in the lab. This will reduce the maintenance cost and frequency of inspections over the lifespan of a building.

For the next phase of development, FiroShield will be sent to the UK for an industry certification, which includes a load-bearing fire test that no facilities in Singapore can do currently.

Its proprietary formulation has been filed with NTU’s innovation and enterprise arm, NTUitive, and upon the completion of the certification, NTUitive will work with JTC to explore commercialisation options.

After the certification, which is expected to be completed by April 2018, the new coating will be applied on  structures within the upcoming JTC Logistics Hub. The joint research team will also work with the relevant agencies to roll out this technology on a larger scale.

Building on this technology, Asst Prof Dasari will also work with JTC at the I3 Centre to develop another type of innovative  for the construction and building industry, which addresses more properties beyond fire and corrosion resistance





NIST method sees through concrete to detect early-stage corrosion

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When you suffer a fall, an on-the-field collision or some other traumatic blow, the first thing the doctor will do is take an X-ray, CT scan or MRI to determine if anything has been damaged internally. Researchers at the National Institute of Standards and Technology (NIST) are using the same principle, but in a more powerful form, to detect corrosion, the primary danger threatening the health of the steel framework within the nation’s bridges, roads and other aging physical infrastructure.

What they have developed is a noninvasive “spectral fingerprint” technique that reveals the  of concrete-encased steel before it can cause any significant degradation of the structure it supports. The detection method is described in a new paper in the journal Applied Magnetic Resonance.

When water and oxygen corrode iron, different iron oxide products are produced, with the two most common being goethite and . “The brown rust that forms when you leave a hammer out in the rain is mostly goethite, and when a steel reinforcing bar [rebar] corrodes inside a concrete bridge deck, that is mostly hematite,” said NIST physical chemist Dave Plusquellic. “We have shown in our new study with goethite, and our previous work with hematite, that terahertz radiation—electromagnetic waves with frequencies 10 to 100 times higher than the microwaves used to cook food—can detect both corrosion products in the early stages of formation.”

Current imaging methods for uncovering corrosion use microwaves to record changes in the physical state of the affected steel, such as changes in the thickness of a rebar within the concrete of a bridge or other structure.

“Unfortunately, by the time such changes are detectable, the corrosive process is already well on its way toward causing cracks in the concrete,” said physicist and NIST Fellow Ed Garboczi.

Additionally, Garboczi said most of the microwave imaging methods rely on comparisons with baseline measurements of the steel taken at the time of construction, a practice that only goes back about 25 years.

“That’s a real problem since the average age of the 400,000 steel-reinforced concrete bridges in the United States is 50 years and there is no baseline data available for many of them,” he explained.

The NIST terahertz wave detection method works because goethite and hematite are antiferromagnetic. In other words, the pairs of electrons sitting side-by-side within the iron atoms in these materials spin in opposite directions, leaving them unaffected by . In contrast, the electrons in the iron atoms of a household magnet, which is ferromagnetic, spin in the same direction and are either attracted or repelled by external magnetic fields.

“Terahertz waves will flip the spin alignment of one of the electrons in a pair and get absorbed by hematite or goethite,” Plusquellic said. “Using a millimeter wave detector, we discovered that this antiferromagnetic absorption only occurs within narrow frequency ranges in the terahertz region of the electromagnetic spectrum—yielding ‘spectral fingerprints’ unique to goethite and hematite, and in turn, iron corrosion.”

With current advances in terahertz sources and detectors, the new NIST nondestructive evaluation technique has the potential to rapidly detect tiny amounts of iron-bearing oxides from early-stage corrosion of steel surrounded by concrete, polymer composites (such as pipe insulation in a factory), paints and other protective materials.

“In the laboratory, we have demonstrated that a 2-milliwatt terahertz source can produce waves that detect hematite through 25 millimeters of concrete,” Plusquellic said. “Using terahertz sources with powers in the hundreds of milliwatts and state-of-the-art receivers with unprecedented signal-to-noise ratios, we should be able to penetrate 50 millimeters, the thickness of the concrete covering the first layer of rebar used in most steel-reinforced concrete structures.”

Next up for the NIST team will be an attempt to find a spectral fingerprint for akageneite, an iron corrosion product formed in the presence of chloride ions, which come from sources such as seawater and road deicing salt.

“Akageneite can cause problems in steel-reinforced concrete similar to those seen with goethite and hematite,” Garboczi said.

The antiferromagnetic corrosion detection method was first conceived in 2009 by the late William Egelhoff, a NIST fellow and pioneer in the field of magnetic materi

How to pave over our cigarette butt problem

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Soon the footpath you walk on could be full of cigarette butts, instead of being littered with them.

Trillions of cigarette butts are produced every year worldwide, with most discarded into the environment. They take ages to break down while their toxic chemical load is released into creeks, rivers and the ocean.

Now a team at RMIT University in Melbourne, Australia, led by Dr Abbas Mohajerani has demonstrated that asphalt mixed with cigarette butts can handle heavy traffic and also reduce thermal conductivity.

This means the product could not only solve a huge waste problem but would also be useful in reducing the urban heat island effect common in cities.

Mohajerani, a senior lecturer in RMIT’s School of Engineering, said he was keen to find solutions to mounting cigarette butt waste.

“I have been trying for many years to find sustainable and practical methods for solving the problem of cigarette butt pollution,” Mohajerani said.

“In this research, we encapsulated the cigarette butts with bitumen and paraffin wax to lock in the chemicals and prevent any leaching from the asphalt concrete. The encapsulated cigarettes butts were mixed with hot asphalt mix for making samples,” Mohajerani said.

“Encapsulated cigarette butts developed in this research will be a new construction material which can be used in different applications and lightweight composite products.

“This research shows that you can create a new construction material while ridding the environment of a huge waste problem.”

About 6 trillion cigarettes are produced every year, leading to more than 1.2 million tonnes of cigarette butt waste. These figures are expected to increase by more than 50 per cent by 2025, mainly due to an increase in world population.

“Cigarette filters are designed to trap hundreds of toxic chemicals and the only ways to control these chemicals are either by effective encapsulation for the production of new lightweight aggregates or by the incorporation in fired clay bricks,” Mohajerani said.

The project is the result of five years of research. It has been published in the journal of Construction and Building Materials(Elsevier).