Variable forming
Euroform, a company in the Herrenknecht group, has developed a new system of tunnel formwork or shuttering that is versatile for different tunnel dimensions. The EP Shutter has a modular design can therefore be used several times, and is easier to handle. According to managing director Allesandro Polla the easier handling allows faster assembly times and reduces transport costs compared to conventional shuttering. Euroform also claims a high buyback value with only reassembly necessary rather than full refurbishment. The example of EP in the Euroform catalogue demonstrates the use of a hinged structure, anchors and struts, or other support frame, to cover a range of radii from 4.4 to 8.9m with the same components.

Euroform also supplies vibrating systems (for concrete settlement), reinforcement carriages and concrete distribution systems. Special formwork caters for vaults, inverts, niches, enlargements and circular sections.

Another variable arch form, supplied by Ceresola, has been used by the Thiess- John Holland contracting JV for large-width stretches of the Airport Link motorway. This is claimed to be the first time that an arch form has been designed to line tunnels with multiple-lane configurations. Four sets have been used for concrete forming over 3-lane (17m wide) stretches of the road and a major cavern up to 30m wide on the Airport Link, and another in the associated Northern Busway tunnel. Thiess John Holland project director Gordon Ralph said that the relative speed of the variable-arch form is significant on this project as it is being completed within such tight time frames. Original assembly of a formwork set takes but reassembly between set-ups is not necessary. The recent flooding in Brisbane will, of course, have caused further scheduling problems. One arch form can be used to line about 60m of tunnel a week.

Putting it there
Placing concrete where required in the tunnel can be a very tricky task especially when this has to be done at a high level, behind formwork and around any steel reinforcement used. These obstacles can usually be overcome with the use of concrete pumps of sufficient capacity, distributing pipework and accessories, vibrators, and appropriate concrete additives to improve flow and workability.

Another simpler and possibly cheaper approach in suitable circumstances is to use a belt conveyor. Putzmeister’s Telebelt is a dedicated extending conveyor system that can be used to place concrete at substantial distance from the source, but generally at similar levels or in the invert. In addition to its major use on dam construction, Putzmeister Telebelt is being used for tunnel concreting on the Xiluodu hydroelectric project in China, the third largest in the world. The first Telebelt TB 105 unit on site had already been se on the Thee Gorges Dam project further down the Yangtze River, accumulating 20 000 working hours. To more newer type 110G Telebelts were ordered for the SinoHydro Bureau 7. The concrete used carries aggregate particles up to 60mm in size, which would prevent the use of concrete pumps.

SinoHydro Bureau 7 is responsible for the overflow tunnel and surface structures, but the Telebelt also helps work by Hydro Bureau 6, Hydro Bureau 14 and others constructing the surge tank, underwater outlet and main transformer building.

Great attention has been paid to manoeuvrability in the design of the Telebelt, which is carried on a highway semi-trailer, which is versatile to meet local road weight restrictions. One Telebelt may be used at several construction sites on the project. A tandem dolly is also available to move the semi-trailer with a dozer. Performance is also highly rated, with a Telebelt TB 110G emptying a 6m3 in 2.5 minutes at normal speed, or in 1.8 minutes at a higher speed.

Accelerated hardening
If concrete can be made sufficiently strong for removal of formwork at an earlier stage of the process then it follows that the quicker hardening, or curing, should produce an equivalent increase in productivity. This can be achieved by shortening the time that formwork or shuttering has to be kept in position in order for the concrete to cure, or reducing the number of sets of formwork required on a particular project.

The advantages of using accelerating and hardening additives in shotcrete mixes is now widely known, and is practically regarded as essential to achieve early support and maximise the efficiency of mix usage by reducing rebound.

Now a development from BASF Construction Chemicals promises to allow users to achieve substantial increases in the efficiency of concrete casting, both for precast products and for cast in situ linings and other structures.

In addition to efficiency, BASF’s new development also addresses the key requirements of a sustainable construction industry of energy demand reduction (lower carbon dioxide emissions), material optimisation, and meeting high quality specifications, chiefly by achieving high early strength development, whilst balancing the requirement for an optimum mix to achieve the concrete specification with the aims of using more binding material and reduced clinker content.

Crystal speed hardening
BASF’s development is trade-named as ‘Crystal Speed Hardening’ (CSH) using the new `X-Seed’ hardening accelerator. The product is said to boost development of early strength in a way that was never achieved before by modifying the kinetics of cement hydration. Already primarily developed for precast production efficiency, it also offers distinct advantages in cast in situ operations also. (See figure 1.)

The abbreviation ‘CSH’ also refers to calcium silicate hydrates; the products of cement hydration that are responsible for the compressive strength of concrete. The hydration speed depends on the chemical composition of clinker and other cementitious materials. In an induction period, in which there is nucleation and growth of hydrated cement crystals, there is slow dissolution of cement particles and formation of clusters, and their aggregation into small nuclei. This provides strength as the system is able to overcome an energy barrier allowing C-S-H growth to proceed.

Temperature increase can help accelerate strength development, albeit with some disadvantages, but this is impractical in most cast in situ circumstances.

BASF’s X-Seed 100 is a liquid suspension of crystal seeds containing synthetic nanoparticles designed to boost the hydration process of early-age cement (6-12h old), strongly accelerating the growth of calcium silicate hydrate crystals. It works at a wide range of temperatures, with crystals between cement grains growing quickly and promoting improved properties in the final microstructure through natural hardening, without the typical effect on durability of common accelerators, BASF claims. The crystals can grow with virtually any energy barrier as in standard conditions, with preferential growth in between the cement particles rather than layering on the particles as normal, thus slowing down growth. It is also claimed that surface layer can be of higher density, and slow down the diffusion of products and reactants. The accelerated formation of hydrates occurring in the presence of X-Seed is presented schematically in figure 2.

BASF has conducted three series of tests corresponding to different approaches to the use of the product, with concrete batches with different dosages of X-Seed 100 compared to plain concrete (with no accelerator) as well as concrete treated with traditional accelerator such as concentrated solutions of nitrates, thiocyanates and formats. Traditional accelerators, for comparison, were used in the dosages that have previously resulted in the best performance. Two different dosages of X-Seed 100, 2.5 and 4.0 per cent, were used in the tests. (See figure 3).

The CSH concept, of which X-Seed is a key component, is compatible with all BASF admixture technologies such as the ‘Zero Energy System’ and ‘Smart Dynamic Concrete’, says BASF.

Spanish application
One application of X-Seed in the formation of a tunnel concrete lining is the UTE Legutiano Tunnel on the high-speed railway between Madrid, Bilbao and Donosti in the Basque Country, northern Spain. The concrete specification required a final strength of 80 MPa, with an early strength requirement of 12-15 MPa to reach 12 MPa as soon as possible (see figure 4).

X-Seed 100 additive has been used in a mix design of:
• CEM I 52.5R 520 kg/m3
• Sand 0-5 780 kg/m3
• Aggregate 5-10 150 kg/m3
• Water 155 kg/m3
• W/C 0.3 kg/m3
• Glenium TC1323 1.3 per cent
• Meycom 685 1.5 per cent

The results are shown in the graph of figure 4, demonstrating a 20 per cent increase in productivity and better workability.

Sprayed concrete
The advantages of spraying rather than casting concrete are widely appreciated, for permanent (secondary) as well as temporary lining, not least removing the need for formwork and the efficiencies that produces. However, just because sprayed concrete can be applied relatively easily, and can be adapted to site conditions, it does not mean that it can be applied without care and attention to specification. The SCL (sprayed concrete lining) design approach, and structured NATM, still demand careful attention to the efficacy of the mix and the means of application in order to ensure proper coverage, and both short- and long-term properties.

One property that is usually vital to a successful sprayed concrete lining is earlyage strength development, through the use of accelerators and other additives. In tunnel situations the accelerator, invariably now non-alkaline, (such as Sika Sigunit, Mapei’s Mapequick, BASF Meyco SA series, Shotcrete Technologies’ ST-Alkali Free) has to be added at the nozzle, or just before. Controlled dosing is necessary to achieve the right mix. Other additives, such as water reducers (e.g. Sika ViscoCrete-SC, BASF Meyco Delvocrete, Mapei Mapeplast) and retarders for extended workability and slump-life (e.g. Sika Tard, BASF Meyco Glenium, Mapei Mapetard) may be added to the mix earlier, to balance the effects of transport and storage procedures.

It may be that early-age strength development is more important in temporary/primary lining; especially to control possible ground movement. However it can have an important part to play in permanent support, even if it is not part of the overall lining specification. In the deep Sedrun section of the Gotthard Tunnel four Sika- Putzmeister 500 rigs, with a 17m reach, and two smaller Sika Aliva 500 concrete spraying systems were used to apply layers of steel fibre reinforced sprayed concrete to achieve a final thickness of 150-290mmfor primary lining. This was followed by a waterproofing layer and cast in situ concrete using formwork to produce permanent lining of 300-1200mm. The sprayed and cast concrete employed Sika additives such as superplasticisers to ensure long ‘open’ times and early age strength. On the Sedrun spray systems, an automatic plc is used to achieve synchronisation of additive dosing in coordination with the concrete pump.

Putzmeister has introduced a new Sika- PM4207 concrete spraying system to replace the Sika-PM 407 model, but it is five units of the later that are being used on the Pahang-Selangor Raw Water Transfer project in Malaysia. Most of the 44.6km-long main tunnel is being driven by hard-rock gripper TBM in granite, but there is 8.5km of NATM main tunnelling (in metamorphic rock and portal zones, and four access adits totalling 2.5km in length. The non-TBM drives are all horseshoe shape in section with typical NATM-type support patterns including reinforced sprayed concrete to around 50mm thickness in NATM drives (rock class B), and 100mm in the adits (poorer rock class CII). The contractor, a joint venture of Shimizu, Nishimatsu, UEMB and IJM, is employing the five Sika-PM 407 concrete-spraying systems fed with material by highway-type truck mixers. Typical sections are 4.60m wide x 4.70m high in the NATM main tunnel stretches and 6.6m wide and 5.40m high in the adits. Work began n June 2009 for completion in May 2014.

The new model Sika-PM 4207 spraying rig is based on the 407, retaining its compact form and versatility despite the inclusion of new features, as requested by customers. The basic frame is designed to be very robust for tunnel work, and the carry customer-specified options. Special features of the 4207 include an additive management system to save material costs, computerised control interface and colour display showing performance data, mix composition, error diagnostics, warnings, a standard rops/fops cab, xenon working lights, protected support legs, and an optional turbocharger for use on diesel engines at high altitude. Various options include power cable drum, a catalytic converter and diesel particle filter, fire protection and a water pump.

The Linthal 2015 hydroelectric refurbishment project in Switzerland, part of the Linth-Limmern network of power stations, makes considerable use of advanced sprayed concrete equipment to line caverns and tunnels. The plant list includes four Meyco Potenza Robojets with contractor Marti, a Meyco Spraymobile and Suprema with Rothpletz, a Meyco Rama 6 spraying manipulator and Meyco GM drymix spraying unit used with a Herrenknecht hard-rock gripper TBM, and wet-process spraying equipment with the Aker Wirth TBM driving an access incline.

Two Potenza units provided immediate support of the control cavern, and it was one of these machines that had to be carried by aerial cableway over several hundred metres to get to the work area. Another Potenza is being used to secure a drill-and-blast access drive, using Meyco SA 166 accelerator and Rheobuild T3 plasticiser in the concrete mix. BASF Construction Chemicals also supplies to local concrete batching plant with Glenium Ace 30 hyperplasticiser and Micro Air 302 air entraining agent for pre-cast segment production.

Environmental considerations in spraying concrete are not restricted to the dust suppression available in using wet-process application, which is, in any case, generally preferred for large volumes. The suitability of drives for an enclosed working environment is also important and has received more consideration. The latest in the CIFA application equipment is the CSS- 3 step3 that now has a tier3-stage3 low-emission diesel drive with catalytic exhaust. Options include an anti-particulate filter, additive tank heating and fire suppression system. The carrier is a 4-wheel-drive vehicle for a maximum speed of 27km/h using hydrostatic transmission. Three steering modes available are ‘normal’, four steering wheels, and ‘grab’ steering. Concrete output is 5-30m3/h.

On the CSS-3 concrete placement is facilitated by a 3-section boom, including a 2.7-mtelescopic section, with double-axis independent movement. The boomturret also has a 3.7-mslide on the longitudinal axis. The reach coverage is up to 16mradius. There are two drives for versatility – a 55kWelectric motor and a 61kWdiesel – with power takeoff. The carrier has four stabilisers with a self levelling sensor for real-time diagnostics. A remote control console can be used for a better view of the application area.

Control and instruction
The principles of controlling correct application of sprayed concrete are well known, and can be carried out by manual manipulation by well-trained operators. However, the operation is subject to human error and fatigue, even if access platforms can get the operator into the position.

The advent of robotic spray nozzle manipulators has made it easier to control the best pattern of sprayed concrete application, and this has opened the door to fully automatic operation, later coupled with profile surveying systems, such as Amberg’s TMS, to ensure the minimum thickness specified has been applied, and any voids filled.

Importance of training
It will be clear that adequate training in sprayed concrete application is important to maximise the chances of a satisfactory concrete lining, whether by manual, robotic or automatic nozzle operation. Several national bodies have developed specialized training and ‘Nozzleman’ certificate programmes, and some have combined in international programmes or exported knowledge to other countries.

Coupled with the recent availability of robotic, and even automatic (e.g. Meyco Logica) systems, simulators have been developed to aid in training and further develop operating procedures. Putzmeister has developed such a simulation system based on ‘open-source’ software, in cooperation with the Technical University (TU) of Dresden, Germany. The system was first demonstrated at last year’s Bauma exhibition, based on the Sika-PM 500 robotic system. The software framework, Sartorius, cross-links subsystems of mobile machines in ‘virtual’ surroundings. It is provided by TU-Dresden who says that it provides improved methods for the development of more efficient, robust and flexible software systems for machine and vehicle simulation.

The simulator was developed as part of the Inprovy research project carried out by the Chair of Construction Machines and Conveying Technology of TU Dresden cooperating with various construction machinery manufacturers and supported by the German Federal Ministry of Education & Research. The systems can be used for both product development and, with adaption, training in a virtual environment.

In operation, signals from the original control unit of the Sika-PM500 are converted into CAN-Bus signals that can be interpreted by the simulation software. The user controls the simulation model, including the flow of concrete, and the results are transmitted to the visualisation model of the tunnel, applicator and spraying concrete. According to Timo Penndorf, computation and simulation specialist with Putzmeister, the distinctive feature of the simulation models is that they consist of systems of differential equations calculated in real time. Penndorf says this improves the ‘degree of realness’ considerably, for example as far as the ‘after-bounce’ of the spraying unit is concerned.


A Putzmeister Telebelt is use for concrete placing on tunnels of the Xiluodu hydroelectric project on the Yangtze River in China Figure 1 – Development of an early compressive strength of 20N/mm2 as shown by dotted arrow; Figure 2 – Schematic view of CSH crystals in cement and water pore solution Figure 3 – Development of compressive strength with various mix recipes with and without accelerators Figure 4 – Graph demonstrating a 20 per cent productivity increase, and better worability with X-Seed 100 A Meyco Potenza concrete spraying system was transported by a Garaventa cableway to excavations for the Linthal 2015 hydroelectric project refurbishment scheme