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Beat sick concrete

What is sick concrete syndrome? Every engineer’s nightmare! Hyson Cells has been developing new technologies for fast, efficient solutions to concrete problems. CEO Sally Hall discusses how to overcome sick concrete syndrome.

Now, a groundbreaking construction technique with a track record of 32 years and 4 100 projects promises lasting performance in all civil structures, from dams to reservoirs, canals, clarifiers and more.

CEO and founder of Hyson Cells Sally Hall, née Hyson, won the Cement & Concrete Institute (now The Concrete Institute) award for Concrete Person of the Year in 1995. This was in recognition of her laboratory work, which changed the way people think about mixing grouts and concrete.

Hyson’s unique way of approaching an industry problem and then solving it doesn’t stop at mixing concrete. Her experience in the plastics moulding industry led her to develop Hyson Cells BubbleLock, a proven technology, guaranteeing a superior lifespan on all large concrete slab structures.

“After about 30 years, the concrete structures that we assumed to be unbreakable may suddenly disintegrate and collapse as a result of corrosion of the reinforcing steel,” explains Hall.

“We have solutions for this problem that can be applied to water storage structures, wastewater treatment works, canals, stormwater systems and roads,” she adds. Reinforced concrete is expensive and requires specialised personnel. By contrast, Hall’s product is far more cost-effective, using cast-in- situ articulated block mats requiring no reinforcing steel.

Alternative building technologies

Alternative building technologies (ABTs) are the only answer to the growing problem of the overstretched, overworked, underfunded municipal engineer. Designed to be more affordable, quicker and easier to maintain and install (employing a low-skilled workforce), these technologies provide an answer to the problem of under-capacitated municipalities.

Yet, many municipal tender documents do not make provision for tendering on ABTs. This is a missed opportunity, which makes many of South Africa’s capital projects much more expensive than necessary.

Sick concrete is a perfect example of why engineers need to investigate ABTs.

First off, concrete work is exact and the setting and pouring techniques need to be carried out with precision. While it’s commonly known that reinforced concrete is stronger than concrete that doesn’t incorporate rebar, what is less well known is that even reinforced concrete is still prone to cracking, especially shrinkage cracking, and has its weaknesses, especially if incorrectly designed or installed.

“If the rebar is not specially treated, corrosion of the embedded steel starts taking place after some 20 years resulting from water, chlorides and oxygen penetrating the cracks and reaching the embedded steel reinforcement,” explains Hall.

“Corrosion of the steel rebar causes it to swell as rust is formed. Rust has a lower density than metal, so it expands as it forms, creating tensile stress. This tensile stress leads to cracking, spalling and the potential failure of structures,” Hall adds.

Epoxy coatings can be applied to the steel before it is embedded in the concrete to protect against corrosion, but the fact is that special coatings are expensive. Also what often happens is that cut ends and bends are not
repainted, so even in cases where the right construction steps have been taken, a lack of site maintenance will still lead to sick concrete syndrome.

“Corrosion is a fundamental key to determining structural lifespan. There are numerous examples, from dams to power stations, where corrosion is causing loss of man hours, costing millions (if not billions) in repairs and causing anger and frustration among utility clients because of service interruptions,” says Hall.

Cost and time

“Steel is expensive and, therefore, so is rebar. Not to mention that high-quality concrete is needed to create reinforced concrete, further driving up costs. Contractors will often try to cut costs by adding stone or crusher dust to the mix. This affects workability and weakens the mix. Water will then often be added to compensate for the workability issue. This further weakens the mix. The only way to determine the strength of the final product after it has cured is to take core samples. On too many projects, this is treated as an afterthought, or neglected entirely, and when this happens, you get bridge collapses and other dangerous structural failures,” explains Hall.

The solution

Hyson Cells’ cast-in-situ pavers present an alternative to reinforced concrete slab construction. This system has no steel and uses a pumpable self-levelling sand grout. “Hyson Cells BubbleLock appears in the bill of materials as a ‘geocell’ but it is really quite a different product to conventional geocells,” explains Hall.

“Geocells originated in 1979 when the US Army Corps of Engineers did research in reinforcing sandy beaches to allow them to be trafficked by wheeled vehicles. The South African Defence Force was, at that time, fighting in Angola and approached the local plastics industry to see if they could develop a similar product. Different companies came up with different suggestions, but I developed my own manufacturing method and Hyson Cells was born,” she adds.

“Our research proved that a
200 micron film would be sufficient due to the size and shape of the cells instead of the 2 mm thick sheeting that was used in the USA. This had the added benefit that it made the product affordable,” says Hall. Hyson Cells provides mats of 200 m² and larger. These are used as sacrificial formwork to cast articulated block paving with the formwork being left embedded in the paving to serve as perfectly fitted jointing.

Maintenance comparison

The maintenance cost of reinforced concrete is lower than plain concrete but very expensive to remove and replace if it does get sick concrete syndrome, as it has to be cut out with diamond or tungsten blades and jack hammers. Maintenance of Hyson Cells BubbleLock is quick, easy and inexpensive. The area to be repaired is excavated with a pick and there is no obstructing steel. A replacement patch of the formwork is pinned in position and filled with poured grout. If a quick set is required, calcium chloride can be used as an additive.

Attitude of innovation

Hyson Cells is a company dedicated to innovation. Its Wolmaransstad Sewage Treatment Plant is an example of another one of the company’s ABTs: one that uses a cone buried in the ground rather than the usual concrete cylindrical ring standing on top of it, which municipal engineers will be more familiar with.

The revolutionary design completely negates the need for expensive rebar because the sloping walls of the cone provide the necessary structural support. “Structures such as clarifiers and methane digesters at wastewater treatment plants can be constructed at about 20% of the cost of cylindrical
reinforced structures currently in use,” says Hall.

Her plant designs incorporate the use of algae for treating acid mine drainage water, as well as industry-leading biogas and bioenergy technologies, using both algae pellets and methane recovery to generate power for the national grid or internal plant use.

Holistic engineering

Many engineering firms will provide a by-the-numbers solution that meets the needs of the tender, or find an effective short-term solution.

Where Hyson Cells differs is its holistic approach. The company sees the engineering problem as the one to be solved, asking how to deliver the most affordable solution without sacrificing quality.  “Additionally, we never forget the communities where our solutions are installed, incorporating skills development and job creation opportunities as well as making community health, safety and security a key part of our attitude of innovation,” concludes Hall.

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