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06 December 2018

Researchers say they are close to perfecting bendable concrete

First publishedon www.AggBusiness.com

A research team at Louisiana State University (LSU) say they are close to bringing bendable concrete to mass adoption.

Engineered Cementitious Composites (ECC), also known as ductile or bendable concrete, were first developed by Victor Li, a professor of civil and environmental engineering at the University of Michigan, in the early 1990s.

Now the LSU researchers say they have developed a cost-effective ECC that utilises readily available ingredients. They claim their research to date has shown ECC to be superior to traditional concrete.

“Compared to typical concrete, our cost-effective ECC material has about 300 times more deformation capacity, more than two times the flexural strength, and a higher compressive strength,” said Gabriel Arce, a senior research associate in LSU’s Bert S. Turner Department of Construction Management.

“The cost of our material is approximately 2.5 times that of regular concrete; typical ECC cost can be more than four times that of regular concrete," added Arce, who is principal investigator on the LSU ECC project.

“However, when you factor in the possibility of building pavements at half the thickness and the enhanced construction productivity due to the ability to construct pavements without joints, the cost of pavements with our ECC material should be comparable to that of traditional concrete. ECC has the potential to provide [Louisiana] with more durable and reliable concrete pavements that can mitigate the necessity of recurring repair, saving [the public] time and money.”

The project to develop the new type of ECC has been in development for more than a year and is funded by Trans-SET (Transportation Consortium of South-Central States).

Four different types of sand were initially tested in addition to two types of recycled crumb rubber materials, five types of fibre, and three different types of fly ash, which is a by-product of coal combustion and can be utilised to partially replace cement in concrete materials. Once the team settled on the raw ingredients, several ECC mixes were evaluated for compressive strength, tensile strength, deformation capacity, flexural performance, workability, and cracking performance. Those were refined based on testing outcomes and evaluated further.

Arce and his team finally settled on three main ingredients.

Firstly, a type of PVA fibre readily available in the US market. It doesn’t possess the oil coating typically used in PVA fibres for ECC application but it does substantially reduce the cost and increase practicality. They were also able to reduce the fibre content by 25 percent while still producing a ductile material.

Secondly, locally available fine river sand from the Mississippi River. The sand is fine enough to be implantable in ECC materials and is a replacement for the expensive and hard-to-obtain microsilica sand normally used.

The third ingredient was locally available fly ash, which replaced up to 75% of the cement utilised in the ECC mix.

“We were able to tailor the cementitious mix and the interface between the fibres and the cementitious matrix in such a way that allowed for a ductile behaviour of the concrete,” Arce said. “In more simple terms, the formula utilises the right materials in the right proportions.”

In the coming months, Arce and the team will further develop their work with a project at the Louisiana Transportation Research Center Pavement Research Facility. There, they will build a 210-foot-long section of ECC pavement and use the LTRC PRF’s 65-foot-long Accelerated Transportation Loading System (ATLas 30) to simulate truck loading for pavement testing. The ATLaS 30 equipment is capable of compressing many years of road wear into a few months of testing to obtain performance data on the ECC material.

Trans-SET is a collaborative partnership between nine major institutions and two community colleges, led by LSU, and established to address the accelerated deterioration of transportation infrastructure through “cutting-edge technologies, novel materials, and innovative construction management processes.” Its members are LSU, Arkansas State University, Baton Rouge Community College, Navajo Technical University, New Mexico State University, Oklahoma State University, Prairie View A&M University, Texas A&M University, University of New Mexico, University of Texas at Arlington, and University of Texas at San Antonio.

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