Mapei admixtures and Technical Services for the construction of the new San Giorgio bridge in Genoa

Mapei is one of the Italian manufacturers that contributed with their own-brand products to the construction of the New Bridge in Genoa, designed by the architect Renzo Piano and built by Webuild and Fincantieri Infrastructure.

For this particular project, Mapei supplied admixtures for the ready-mixed concrete used to make the piers and the floor slab, and supplied a team of technicians and specialists, working round the clock, from when work first started up until the placing of the last cubic metres of concrete.

Mapei also supplied solutions for the repair, strengthening and waterproofing of the access ramp that connects the San Giorgio Bridge to the A7 Motorway on the eastern side.

“We are pleased to have played a part in the construction of the New San Giorgio Bridge in Genoa”, commented Veronica Squinzi, Mapei CEO, “And supplying solutions which are certified and durable has always been our mission”.

The technologies and systems proposed by Mapei, along with the Technical Services team supplied by the Company and the constant discussions and feedback with the designers, the manufacturer of the concrete and the main contractor’s engineers, all played an important part in completing the most important infrastructure in Italy for decades, a true symbol of reconstruction, commitment and the desire to recover.

“Less than two years following the collapse of the Morandi Bridge, and especially today when the memory of this tragedy is more alive than ever, the inauguration of the New Bridge is a clear demonstration of how the dedication, commitment and passion people have for their work can help create something exceptional and sustainable”, added Marco Squinzi, Mapei CEO.

Design of the bridge

The bridge is made up of a steel and concrete deck and a 1,067 metre truss divided into 19 spans (14 spans of 50 metres, 3 spans of 100 metres, 1 of 40.9 metres and 1 of 26.27 metres), with the whole structure supported by 18 reinforced concrete piers with an elliptical section.

The gentle forms of the bridge, from its elliptical piers to the deck similar to the hull of a ship, and the light tones of its elements, help the structure blend in with the surrounding landscape.

Construction of the piers

The 18 reinforced concrete, elliptical piers were made by placing the concrete in a continuous cycle using climbing formwork, special formwork that is attached to the actual structure using the concrete placed earlier as a support base. When the new concrete is poured, the previous concrete must already have certain mechanical properties in order to bear the weight not only of the formwork, but also of the new concrete.

The piers were constructed between June, 2019 and January, 2020 and the various operations were carried out in different weather conditions and at different temperatures, which had an influence on the type admixtures employed, leading Mapei to proposing a combination of various different products.

The combination of cutting-edge admixtures, which are used to modify hydration reactions and the hardening rate of cementitious materials, meant that the results expected were achieved in complete safety and guaranteed that the mechanical properties between the various concrete pours remained constant.

DYNAMON XTEND W400 N is a super-plasticising, liquid admixture that reduces the amount of water required in the mix by 20%, while having a neutral effect on the setting time of concrete.

DYNAMON LZ 551 is an admixture that extends the workability time of concrete, without provoking any delay in setting and hardening times.

MAPEFAST ULTRA is a nanostructured, inorganic polymer-based admixture that is used to improve the mechanical properties of concrete in cold weather and is based on new, innovative “seeding catalysis” technology.

The final requirement, and one that was particularly important to the client, was that the exposed surfaces should have an excellent finish once the formwork had been removed, with no defects and a uniform colour, and that it should enhance the materic effect of the perfection of the element. The result was achieved brilliantly, thanks not only to the correct mix-design, but also to the use of a special form-release agent with the ability to guarantee such a high-quality and attractive finish. After a series of mock-ups on site, it was decided to use: MAPEFORM W60, a from-release solution in water dispersion for concrete with a high quality finish.

Making the floor slab

Once assembly of the metal framework for the deck had been completed, Mapei was involved in the second phase with products for the concrete pour for the floor slab, which was made using compensated-shrinkage concrete to prevent the formation of shrinkage cracks.

This operation was carried out in June, 2020 and, in this case too, various design factors had to be taken into consideration, such as the particularly high mechanical properties required, the rate of compensated-shrinkage which had to be maintained to within specified limits and, an aspect particularly important for the actual placing and finishing operations of the concrete, it had to have extended workability in hot weather and be able to achieve high mechanical properties after a short curing cycle to facilitate levelling and surface-finishing operations.

As in the case of the piers mentioned previously, achieving the required results was made possible by using a combination of specific products:

DYNAMON XTEND W202 N acrylic admixture, which significantly reduces the amount of mixing water required and helps mechanical properties develop more quickly after short curing cycles.

DYNAMON LZ 551, an admixture that extends the workability of concrete without provoking any delay in setting and hardening.

EXPANCRETE PLUS expansive admixture for controlled-shrinkage concrete.

To minimise the evaporation of water, which could lead to the onset of crazing, the following was used for the kerbstones along the sides of the slab:

MAPECURE WG, a water-based, film-forming curing agent that stops evaporation and protects surfaces against the effects of the sun and wind.

Repair work on the access ramp

Repair and strengthening work was carried out on the foundations, the piers and the deck of the viaduct.

The products used for the piers and vertical features were:

MAPEFER 1K, cementitious mortar to protect the rebar against corrosion.

MAPEGROUT EASY FLOW, fibre-reinforced, thixotropic cementitious mortar for the repair of concrete structures; applied using a spray-rendering machine.

MAPEGROUT EASY FLOW GF, fibre-reinforced, thixotropic cementitious mortar for the repair of concrete structures where a higher level of ductility is required.

MAPELASTIC GUARD, elastic cementitious mortar for the protection of concrete structures and elements against aggressive atmospheric agents.

MAPEGROUT HI-FLOW B2, hi-flowing, fibre-reinforced, compensated-shrinkage mortar for the repair of concrete structures.

MAPEGROUT GF BETONCINO B1, hi-flowing, fibre-reinforced concrete for the repair of concrete structures where hi-flowing, pre-dosed concrete is required to reintegrate particular thicknesses and conformations.

MAPEFIX EP 585, pure epoxy resin-based chemical anchor for structural loads.

The following products were used for the intrados and extrados of the bridge deck:

MAPEFER 1K, cementitious mortar to protect the rebar against corrosion.

MAPEGROUT EASY FLOW, fibre-reinforced, thixotropic cementitious mortar for the repair of concrete structures; applied using a spray-rendering machine.

MAPEGROUT LM2K, thixotropic cementitious mortar for the repair of concrete, applied in layers 3 to 20 mm thick in a single application.

ADESILEX PG1, thixotropic epoxy adhesive for structural bonds.

EPOJET, super-plastic epoxy resin for injecting and anchoring purposes.

MAPECOAT E23, epoxy primer to protect concrete before applying polyurethane coating and paint.

MAPECOAT PU33, two-component, polyurethane resin-based, elastic coating to protect concrete.

MALECH, water-based acrylic primer and adhesion promoter with good defect-filling properties.

ELASTOCOLOR PAINT, elastomeric, crack-resistant, protective interior and exterior paint with permanent elasticity and high resistance to chemicals.

The slab for the access ramp was waterproofed with the following products:

PRIMER SN, two-component, fillerized epoxy primer.

PURTOP 400 M, solvent-free, hybrid polyurea membrane, applied in-situ to create a waterproofing membrane on decks, walls and flat roofs.

PURTOP PRIMER BLACK, specific, solvent-based primer to improve adhesion of asphalt to surfaces waterproofed with products from the PURTOP line.