Queensland supply company Hasabri says the specialised concrete is tougher, stronger and more efficient than regular fibre reinforced concrete.

The result of several years of scientific development in the United States, engineered cementitious composite (ECC) looks like regular concrete but is made from specially designed micro fibres that give it high performance tensile strength to withstand heavy loads and drastically minimise crack width.

By incorporating the smaller concrete fibres into the concrete mix, the aspect ratio (a measure of fibre strength) can be increased, and thus the concrete’s overall strength is also increased.

Having recently completed trials of the new concrete, Hasabri is set to supply ECC to Australian customers, including those in the resources sector. It imports the all-important micro-modelled fibres from Japan, sourcing the remaining ECC components locally.

Hasabri director Max Moore described ECC as an ultra-ductile mortar-based composite, reinforced with short micro-mechanically designed fibres. He said the new concrete had applications for any task involving the use of concrete and, despite being about 15% more expensive than standard fibre reinforced concrete, its durability and the thinner application required meant ECC offered users time savings and long-term cost benefits.

Moore’s mission for a hard-wearing, ductile concrete solution began when he found the standard products on the market did not meet the mining sector’s heavy-duty demands.

“I was up in the Bowen coal area designing and applying cementitious thin skin liners and they never performed to my satisfaction and in the way they were supposed to; mainly because of this cracking issue and the fact that there was that much polymer in them they were difficult to use,” he said.

“And I thought there’s got to be a crossover product somewhere in the world that crosses over from a high polymer concrete to a high performance concrete yet there’s going to be some flexibility in it somewhere.”

“Sheer accident” eventually led Moore to ECC developed by an American academic and, suitably impressed, he took steps to bring the product to Australia.

Hasabri has recently completed ECC trials in the underground coal sector where Moore said he enjoyed seeing the incredulous response of mining engineers who had “eyes popping out of their heads”.

The company is taking the product to a large mining company’s new copper operation, where it is trialling the tailings as the primary aggregate component. Moore said if this proved successful, it might prove cheaper than using conventional fibre reinforced concrete.

ECC boasts ductility, strength and high performance, a trio of characteristics Moore said were not easily achieved in concrete.

Typically increased flexibility in concrete is achieved with the addition of polymer components; however the trade-off comes with reduced compressive strength. But Moore said, with ECC both strength and ductility had been achieved.

He said the developers had hit on a technique of corrupting the strong but locally concentrated bond between the concrete’s small PVA fibres, allowing it to partially ‘slip’ across its whole length. This enables the strength and elasticity of the entire fibre length to be utilised, resulting in increased load-bearing capabilities.

When stressed, instead of getting large wide cracks that significantly affect the integrity of the structure, ECC responded by “microcracking”, producing multiple tiny cracks that collectively bear the load and do not jeopardise the structural integrity of the system being supported.

This aspect gave ECC significant safety advantages over conventional concrete, Moore said.

“You’re spreading the damage across a vast area as opposed to one massive structure,” he told . “It yields under load yet it’s still got load-bearing capability as opposed to reaching a certain point and just exploding.”

Moore said the microcracks were small enough to stop water from penetrating.

With a high performance compression rating of 60 megapascals (compared to 35-40MP, a rating common in underground mining ground support systems), Moore said the ECC had the capacity to take greater relative load for its mass.

However, perhaps the most curious characteristic of the product is its claimed capacity for self repair.

Moore said self healing came about when microcracks in the ECC filled with unresolved calcium carbonate over a period of wetting and drying, “re-cementing” the fibre bond. He said because of the larger crack widths involved, this process was not possible in standard fibre reinforced concrete.

Despite being new to the Australian market, Moore said the specialised concrete was already widely used overseas, particularly in Japan and the US. He told he was aware of one other group – pipe company Rocla – that had trialled the new hard-wearing concrete.

A Rocla representative told that its ECC trials had proved successful and had allowed the company to manufacture thinner pipes.

Rocla said the product had not been commercially applied and at this stage no further trials were planned.

According to Hasabri’s Moore, ECC has a host of potential applications to the mining industry including ground control in high stress areas, pumping systems, thin wall sections and as a shotcrete lining substitute.

He said he had already seen its successful application as a thin skin liner in coal seam operations and current trials were testing its potential in tailings applications.

Because ECC uses a thinner application than traditional concrete, Moore said its use could also speed up concreting operations thus saving miners time. Alternatively by using the same level of thickness, greater loading capacity could be achieved.

While trials to date had proved successful and the response from miners who had come into contact with ECC had been “fabulous”, Moore said industry was cautious about its adoption with timing proving a critical factor.

“At the moment the mining industry’s very stressed in trying to produce,” he said. “So therefore introducing something new which they require extensive testing on – time is the issue.

“Although they’re exceptionally interested and want to become educated on it, a lot of them are saying ‘Oh perhaps when we’re not quite as hurried we’d like to have a good look at it’.”

Moore said most of the inquiries for ECC had come from the larger hardrock mines, which had expressed interest in establishing onsite, in-cycle ECC batching, something Hasabri was working towards.

“What we’re now doing is offering a service where we will source the required materials, like the superfine sands, the jet ground fly ashes and stuff like that, as close to their location as possible, recommend those to them, undergo a system in their whole testing regime, so long as they buy the fibre from us,” Moore said.

Published in the November 2007 Australia’s Mining Monthly