Concrete technology

13 May 2014

A new world record has been set for the largest continuous concrete pour in history – a feat achieve

A new world record has been set for the largest continuous concrete pour in history – a feat achieved during foundation construction of the 335 m Wilshire Grand hotel in downtown Los Angeles, US. Conc

As pressure mounts on contractors to work efficiently and cost-effectively, concrete equipment manufacturers and other suppliers are upping their game to help meet these demands.

This can start at the design stage and could include anything from models of the exact amounts of concrete that will be needed and where, to co-ordinating just-in-time jobsite delivery of equipment, and automatic calculations of concrete setting times.

US-based concrete contractor Adjustable Forms, for instance, tackles large-scale cast in-situ concrete projects using technology such as 3D modelling and building information modelling (BIM). The company uses Tekla Structures Design BIM software to help streamline many of its business operations, from preparing bids, to design and co-ordinating workflow once the project starts.

Working from 2D CAD drawings, a PDF or a 3D model supplied by the design engineer, the company creates a preconstruction 3D model in the BIM software and extracts material quantity information. Adjustable Forms project manager Eric Lindquist said the technology helped the company to produce more accurate bids.

“We do all of our quantity takeoff/extraction from the preconstruction model to ensure the scope is correct,” he said. “We extract the quantities and import them into an estimating tool, which allows us to develop accurate estimates for bidding jobs, minimising the risk of blowing an estimate based on miscalculated quantities.

The company also used a preconstruction model for drawing co-ordination. This helps them identify issues with the design and bring it to the attention of the owner, general contractor and design team.
During construction, the technology can be used to establish a workflow for different processes – from drawing co-ordination, schedule loading, pour management, rebar detailing, shoring and formwork layouts, as well as modelling safety systems.

3D modelling

Meanwhile, 3D modelling was central to Norwegian contractor Hæhre’s design for the twin-deck Labbdalen Bridge. This will be a key new structure in the country’s 3,140 km E6 Highway improvement programme – the main north-south road linking Norway to Sweden.
Falsework & formwork specialist RMD Kwikform worked together with Hæhre’s to supply formwork and shoring to support construction of the 73 m East Labbdalen Bridge and 78 m West Labbdalen Bridge.

Hæhre used RMD Kwikform’s 3D Locus programme to create a steel shoring model for the project’s 28.4 m central span. The software calculated the exact positioning and quantity requirements for the Rapidshor support system.

RMD Kwikform engineer Adam Fixter said, “By taking the 3D model of the bridge and putting it into our customised suite of computer-aided design software, we were able to create our own 3D model of the shoring solution.

“This allowed us to work with our distributor Teknikk and Hæhre to create a workable solution for the site, eliminating clashes, while creating plans, sections and elevations for the site team. This process gave them all the information they needed to correctly erect the equipment.”

The precise adjustment of formwork was also a key demand on a project to construct a new cooling tower for a coal-fired power plant in Krishnapatnam, Andhra Pradesh, India. Contractor Tata Projects was tasked with constructing the 172.5 m tall tower with a tapering diameter – the maximum diameter is 132 m at the base, reducing to 76.4 m at the centre and increasing again at the top ring to 77.4 m.

Tata Projects used Doka cooling tower formwork SK175, which is designed for precise adjustment, for the job. Andreas Guttenbrunner, head of the Doka Power Plants Competence Centre said, “SK175 allows radii of up to 70 m to be navigated without any adjustments and all commonly occurring geometries during cooling tower construction are covered.”

In total, the project used 128 Doka SK175 units – a climbing scaffold that serves as a carrier for the steel formwork, which is transported by electromechanically-driven lifting systems from one concreted section to the next.

Construction is also progressing in one-day cycles, thanks to strict workflow plans created by Doka engineers. The working platforms and scaffolding were delivered to the site in accordance with an agreed schedule drawn up in conjunction with the construction management team, and assembly takes place under the supervision of a Doka formwork instructor.

Formwork manufacturer Pilosio, meanwhile, said 70% of the formwork it supplied to support construction of a motorway junction north of the city of Durban, South Africa, was tailor-made for the job.

Contractor CMC is building the N2-M41 Mount Edgecombe Interchange – a project which includes two of the longest viaducts in the country. The first measures 947 m long and 26 m high, and the second is 18 m high and 443 m long.

Pilosio is supplying 200 m2 of P300 formwork for foundations and trusses, 500 m2 of steel formwork for the construction of the viaducts’ pile shafts, 350 m2 of steel formwork for the construction of the pier caps, and two sets of Maximix model formwork and custom-made products totalling 940 m2.

In addition, it is supplying its Omnimode shoring system with customised to carry suspended work platforms which will be used in the installation of the roadway ashlars (masonry).

The manufacturer said its technical proposal, including the substantial volume of customised formwork, had been decisive in it winning the order. Pilosio also emphasised rapid supply times and co-ordination with the various organisations involved in the project as crucial to its success.

Optimised equipment

Elsewhere in the concrete sector, manufacturers continue to refine their designs to make life easier for contractors. For example, because it believes that equipment used on construction sites should be mobile, light and convenient, Wacker Neuson said it had optimised its exposed concrete surface external vibrator AR 36 in terms of performance and overall size.

The result is the AR 26 external vibrator, which is about 2 kg lighter than its predecessor but with the same power output, while still claiming to retain its flexibility. The connection flange is compatible with the AR 36, so that the fixing devices for in-situ casting formwork also fit the smaller model.

Another area of application is concrete precast factories, said Wacker Neuson, adding that where a few large external vibrators were once used, several smaller models are often used nowadays. It said this was one area of application where the smaller AR 34 and AR 43 models from the new series could work well.

However, the manufacturer said continuity was a high priority and the new external vibrators can be operated on the same frequency inverters or converters as the previous models. The bore patterns for attaching the external vibrators have also been retained.

Controls, meanwhile, has developed a new setting time meter – Vicamatic 2 – to boost the efficiency of determining and monitoring the setting process for cement, motar and gypsum. The new device features both local and remote control mode, programmable test cycles and an integrated graphic printer.

Test procedures are stored in the device’s memory and immediately usable after fitting the correct needle, weight and mould. Featuring a 109 mm colour display, Controls says the meter can automatically calculate initial and final setting times at programmable penetration depth limits.

Pumping and mixing

On the concrete pumping and mixing side, meanwhile, Reed has developed the new towable MixerPump Combo machine. This is a mixer and pump combined has designed specifically for shotcrete contractors needing a powerful, high pressure shotcrete pump and a fast, robust mixer.

The 15 m³/hr pump and 1 tonne M2200 Mixer are both powered by a 119 kW Cummins engine. The hopper has a capacity of 16 ft³ (0.453 m3) with the addition of the optional hopper extension. Reed said the mixer can completely mix 998 kg of refractory material in 3 minutes.
On the higher end of the scale in terms of mixing capacity, Liebherr has installed a Betomat V 1010 mixing tower for Alfons Greten in Essen, Germany – the largest of its mixing plants, and one that had only been installed once previously.

The set up for Alfons Greten consisted of a 1,000 m³ capacity plant and five silos capable of storing 454 tonnes of cement. The contractor will use it for producing prefabricated reinforced concrete elements.

The plant can be customised with two Eirich mixer systems upon request, and features a Liebherr Litronic-MPS III mixing plant control. Additionally, exhaust air filter systems are in place to reduce dust emissions, and the plant is also equipped with heating and insulation to allow smooth operating during winter months.

Breaking the mould

It is often down to manufacturers to demonstrate the full capabilities of their machines, and to point out that they can be used for more than just run-of-the-mill jobs. For instance, when Australian firm Baldwin Civil NT was approached about constructing a storm water canal as part of the new Inpex natural gas project in the Northern Territory, it didn’t know if it was possible to slipform a 2.1 m high wall, according to Power Curbers.

It had been assumed that the only options for a wall that size were form-and-pour or pre-cast, according to Baldwin Civil founder David Baldwin. “Power Curbers was the first call we made and we got a very positive and professional response. Within a short time we had the drawings and they said ‘we can do it.’ We took a trip to North Carolina and purchased the machines,” he said.

The wall was built using a three-pass operation – first, the 3.8 m base was poured with a 5700-C-MAX using a custom paving mold. Then, each 2.1 m side wall was poured over steel reinforcements to complete the canal.

The two 5700-C-MAX slipformers were fitted with custom-engineered straddle legs to allow them to fit inside the canal to pour the side walls, while a custom-designed belt conveyor was also needed to feed the concrete to the hopper on top of the tall barrier mould.

The contractor’s record for a single day’s pours were 274 m on the wall and 251 m on the base. In total, over 15,600 m3 of concrete was used.

However, it is one thing putting concrete in place, but quite another to remove it again. In the demolition sector, too, manufacturers have been working to boost the efficiency of their tools. Aquajet Systems, for instance, has introduced a new hydrodemolition tool – the Rotolance 2500 – which it says offers faster concrete surface preparation than other, more traditional methods of concrete removal.

Designed for shallow concrete removal, the Rotolance 2500 uses ultra-high pressure water jets to remove layers of concrete. It features a 350 mm working diameter and can be guided and monitored by an on-board control system.

In addition to being faster than conventional manual methods of concrete preparation and removal, Aquajet also said the tool could lead to labour cost savings and help prevent operator injuries caused by vibrating hand-held, manually operated alternatives. Dust pollution is also said to be virtually eliminated with hydrodemolition.

The concrete sector’s manufacturers have continued to support activities on construction projects around the world, coming up with tailor-made solutions to unique sets of problems. With such a diverse set of applications, it seems certain that the industry will continue to innovate as new challenges present themselves with each new infrastructure project.

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