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Study: Thermocol Composites in Reinforced Concrete

Tuesday, September 21, 2021

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According to researchers from the Department of Science and Technology at the Indian Institute of Technology, Roorkee, the use of thermocol or expanded polystyrene (EPS) as a composite material in reinforced concrete could help buildings resist earthquake forces.

Testing of the composite material proved to be beneficial for buildings up to four stories high.

About the Research

In sandwiching the thermocol or EPS between two layers of concrete, in addition to reinforcements in the form of welded wire mesh, researchers found that in testing a full-scale building and several wall elements that the material better withstood earthquake forces.

The team reported that because thermocol resists earthquakes by reducing the mass of the building, it was able to better prevent collapse typically initiated by the inertia effect of forces being applied to a structure in the event of an earthquake. In these specific instances, the chances of a building collapsing depends on the mass of the structure as a whole.

Produced in a factory, the new material utilizes an expanded polystyrene core and wire mesh reinforcements to create the core and reinforcement panels. Concrete is then sprayed onto the resulting core material. The team reports that production does not require any shuttering and can be constructed quickly.

Professor Yogendra Singh, who supervised the research, reported that an analysis of the study revealed that a four-story building constructed with this technique was capable of resisting earthquake forces, even in the highest seismic zone (Zone 5) of the country, without any additional structural support.

In addition to resisting earthquakes, the use of expanded polystyrene core in the concrete walls also showed thermal comfort, as the core better achieved the necessary insulation against heat transfer between building interiors and exterior environment. The result makes it easier to keep building interiors cool in hot environments and warm during cold conditions.

The technology also has the potential of saving construction material and energy, with an overall reduction in the carbon footprint of buildings. It replaces a large portion of concrete volume from the walls and floor/roof.

Test for the study were conducted by research scholar Adil Ahmad, who also evaluated the behavior of the constructions under lateral forces, as earthquakes tend to cause a force predominantly in a lateral direction. Ahmad’s investigation was supplemented with detailed computer simulation of a realistic four-story building.

The tests were conducted at the National Seismic Test Facility of the Department of Earthquake Engineering, IIT Roorkee and were developed under the Fund for Improvement of S&T Infrastructure program of Department of Science & Technology, Government of India.

Recent Concrete Research

In August, Swedish multinational power company Vattenfall announced that it had recently developed what it’s calling a “climate-smart hydropower concrete” that can reportedly use less cement, reducing its overall carbon dioxide emissions by about a quarter.

The company reports by reducing its cement content in structural concrete, there is a direct reduction in the strain on what otherwise would be inputted to the environment. To achieve this reduction in cement quantity and heat development, Vattenfall is using by-products that react with cement in combination with lessons learned from the company’s major periods of expansion in the 1950s and '60s to develop a modern, climate-smart concrete concept.

In wake of the development, Vattenfall is planning to utilize the climate-smart hydropower concrete to replace parts of an existing dam at its Lilla Edet power station in Göta älv near Gothenburg, Sweden. The company plans to complete the dam replacement project by 2024.

Some time earlier, in June, researchers out of the Worcester Polytechnic Institute published findings that use an enzyme found in red blood cells that could develop a new take on “self-healing” concrete. They say that the material could lengthen structures’ lifespans and slash carbon emissions in the process.

The work, published in the journal Applied Materials Today, uses an enzyme that automatically reacts with atmospheric carbon dioxide to create calcium carbonate crystals, which mimic concrete in structure, strength and other properties, and can fill cracks before they cause structural problems.

Research was led by Nima Rahbar, associate professor of Civil and Environmental Engineering and lead author of the paper.

According to WPI, Rahbar’s research, which previously received funding from the Massachusetts Clean Energy Center, uses carbonic anhydrase (CA), an enzyme found in red blood cells that transfers CO2 from the cells to the blood stream.

For concrete, the CA enzyme, which is added to the concrete powder before it is mixed and poured, acts as a catalyst that causes atmospheric CO2 to create the calcium carbonate crystals, whose matrix is similar to that of concrete. Reportedly, when a small crack forms in the enzymatic concrete, the enzyme inside the concrete connects with CO2 in the air, triggering the growth of a new matrix that fills in the crack.

The process, which Rahbar has patented, can reportedly heal millimeter-scale cracks within 24 hours.

The approach includes three facets: a concrete mix that, when used to build a structure, will autonomously mend small cracks that form; a mixture that can induce self-healing in larger cracks or holes; and a process that can be applied to traditional concrete to mend cracks.

In April, researchers at Rice University were reported to continue their work on graphene, saying that they optimized a process to convert waste from rubber tires into graphene that can then be used to strengthen concrete.

While it is acknowledged that recycled tire waste is already used in Portland cement, the Rice researchers note that graphene itself has been proven to strengthen cementitious materials at the molecular level.

To recover the graphene from the tires, the researchers used a “flash” process that they introduced in 2020. The process exposes material to a jolt of electricity that removes everything but the carbon atoms. Those atoms then reassemble into turbostratic graphene, which is more soluble than graphene produced from graphite and therefore easier to use in composite materials.

According to Rice, the lab flashed tire-derived carbon black and found about 70% of the material converted to graphene. When flashing shredded rubber tires mixed with plain carbon black to add conductivity, about 47% converted to graphene. (Elements besides carbon were vented out for other uses.)

For the actual process, the electrical pulses lasted between 300 milliseconds and one second. The lab calculated that the electricity used in the conversion process costs about $100 per ton of starting carbon.

The researchers then blended minute amounts of tire-derived graphene—0.1 weight/percent (wt%) for tire carbon black and 0.05 wt% for carbon black and shredded tires—with Portland cement and used it to produce concrete cylinders.

After curing for seven days, the cylinders showed gains of 30% or more in compressive strength. After 28 days, 0.1 wt% of graphene sufficed to give both products a strength gain of at least 30%.

Rice graduate student Paul Advincula is lead author of the paper on this research that recently appeared in Carbon. Co-authors are Rice postdoctoral researcher Duy Luong and graduate student Weiyin Chen, and Shivaranjan Raghuraman of C-Crete. Chemist James Tour is the T.T. and W.F. Chao Chair in Chemistry as well as a professor of computer science and of materials science and nanoengineering at Rice.

The Air Force Office of Scientific Research and the Department of Energy’s National Energy Technology Laboratory supported the research.

   

Tagged categories: AS; Building materials; Colleges and Universities; concrete; Good Technical Practice; India; Quality Control; Research; Research and development

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