Materials

Cement-free sewerage concrete combats fatbergs and corrosion

Cement-free sewerage concrete ...
The team's new cement-free concrete (right) alongside conventional but corroded Portland cement concrete
The team's new cement-free concrete (right) alongside conventional but corroded Portland cement concrete
View 1 Image
The team's new cement-free concrete (right) alongside conventional but corroded Portland cement concrete
1/1
The team's new cement-free concrete (right) alongside conventional but corroded Portland cement concrete

The cement used to construct concrete sewerage systems around the world does a mighty job of helping wash away our waste, but does have its shortcomings. Scientists in Australia have developed a new cement-free solution they say is better equipped to handle the corrosive nature of these environments, while also helping avoid the buildup of troublesome and costly fatbergs.

The new cement-free concrete was developed by scientists at Australia’s RMIT University, where we have seen a number of innovative approaches to producing enhanced forms of concrete. These include re-using steel slag as a concrete aggregate and working building rubble into new types of road materials, and now RMIT scientists are turning their attention to the free lime.

This chemical compound is used in large amounts in the production of common Portland cement, but also makes it vulnerable to corrosion in the highly acidic environments of sewerage systems. Furthermore, residual lime can bleed out of the concrete and contribute to fatbergs, the greasy masses of oil, fat and non-biodegradable matter that can grow to weigh several tonnes and clog up pipes.

“The world’s concrete sewage pipes have suffered durability issues for too long,” says Dr Rajeev Roychand, who led the research. “Until now, there was a large research gap in developing eco-friendly material to protect sewers from corrosion and fatbergs. But we’ve created concrete that’s protective, strong and environmental – the perfect trio.”

Roychand and his team produced their new cement-free concrete largely using by-products of the manufacturing industry, combining nano-silica with fly ash, slag and hydrated lime. In testing, the team found its concrete surpassed the strength standards required of sewage pipes, with the unique blend significantly improving longevity.

“Our zero-cement concrete achieves multiple benefits: it’s environmentally friendly, reduces concrete corrosion by 96 percent and totally eliminates residual lime that is instrumental in the formation of fatbergs,” Roychand says. “With further development, our zero-cement concrete could be made totally resistant to acid corrosion.”

The research was published in the journal Resources, Conservation & Recycling.

Source: RMIT

4 comments
Username
Is it less energy consuming to produce? Can it replace concrete in all applications? So many unanswered questions.
Johannes
Would be interesting to know how this new concrete interacts with steel reinforcing elements, particularly regarding the corrosion potential.
piperTom
Sometimes, it is what's omitted that tells the tale. Cost? Cost is not mentioned, though the referenced article does mention the cost... of the current methods. The main ingredients of this new tech don't seem expensive, but the total absence of any discussion of that has to mean something.
Gregg Eshelman
If it can be coated smoothly onto the inside of existing pipes and adhere firmly to them, it could improve the flow capacity of existing infrastructure despite reducing the diameter some. With joints smoothed over and a smoother surface, turbulence would be reduced and flow speed increased a bit.

One possible method would be to develop a fast setting version of this concrete then use a 'bell' to pull through a pipe while the concrete is injected ahead of it. Pull the bell through the pipe and it pushes the new concrete into a smooth layer on the interior of the pipe. It would stay centered despite the pull of gravity due to managing the concrete flow to be slightly higher at the bottom to counteract the weight of the bell. Another method would be an inflatable tube put into the pipe while concrete is injected around it then allowed to cure. This has been done for many years to line and reinforce old brick chimneys. Care must be taken and sometimes temporary reinforcements installed to avoid blowing the old brick chimney apart and making a huge mess.

But there's already a technology for this. Resin impregnated felt. A resin soaked felt tube is inverted into the pipe then really hot water is circulated through the pipe to harden the resin. A cutting device is then put into the pipe to cut holes where other pipes join. If the pipe is large enough, a person (who isn't claustrophobic) can go in to do the cutting. The result is a smooth, seamless pipe that flows more liquid than the old pipe. A big benefit of this process is many applications (for sewers and storm drains) require no digging. Another benefit is it can accommodate odd shaped drains so a really old one made of brick in an egg shape, or flat bottom with an arched top, or metal banded wood that's partially rotten pose no problems. The liner will push out tightly to the inner surface and the resin will bond. Spiral wound riveted iron or rolled and seamed 'tin' sheet steel that's next thing to rust being held in place by long undisturbed soil can be lined with this process.

Another process is called pipe bursting. A heavy plastic pipe of the same internal diameter as the old is forced into old concrete, terracotta, pottery, metal, wood pipe so fast the old decayed pipe bursts apart. The broken old pipe stays in-situ. For this to work the old pipe must be weakened enough to break up and the soil around it must be able to compact some as the old pipe is pushed outwards.

For metal pipe that's still strong but has internal corrosion and perhaps some small holes, there's a process that shoves in new plastic lining. The machine slightly compresses and lubricates the plastic liner as it's being forced in rapidly. Once a length of pipe is started *it must not stop* or the liner will expand and become unable to slide. This process can have problems with joints that have protrusions into the pipe or gaps wider than the pipe into which the liner can expand then jam against the end of the next section. This is often used in aboveground gas and liquid pipes where individual sections of the metal pipe are easy to access.

For these and other relining processes the benefits are saving time and cost of replacing the old pipe, especially with underground pipes due to avoiding all or nearly all excavation - especially when pipes run below buildings.