Gulf Construction Online - Preprufe membrane can extend rail life

Railway Construction

An artist’s impression of the Makkah station.

Preprufe membrane can extend rail life

01 June 2016

A high-performance waterproofing solution can provide an extended service life for the region’s major construction projects which face challenges that can compromise their below-ground concrete structures, says ILTAZ ALAM*, product manager at GCP Applied Technologies.

Basements in the Gulf region face particular challenges including groundwater, high average annual temperatures, and in coastal sites aggressive ground conditions including chlorides and sulphates which attack concrete and its steel reinforcement.

And with key projects such as railway stations requiring completely dry basements and a service life of up to 120 years, the use of high-performance waterproofing solutions that offer genuinely comprehensive protection against water ingress is essential.

A variety of major rail projects in the region have recently seen the use of high-performance Preprufe Plus, a fully bonded waterproofing membrane from GCP Applied Technologies (formerly Grace Construction Products). Preprufe was extensively used on the Haramain High Speed Railway, one of the largest infrastructure projects in the Middle East, as well as on station boxes on four out of the five contracts to construct the multi-billion-dollar Doha Metro.

Preprufe comprises an extremely durable high-density polyethylene membrane combined with a powerful adhesive. Applied to a foundation before concrete is poured, Preprufe bonds directly and aggressively to poured concrete. The patented Advanced Bond Technology and simplicity of application avoids the potential for any defects due to incorrect installation of the membrane, which can cause water to track behind it and migrate to other parts of the structure. Its unique performance also avoids problems that can occur with other membranes due to ground movements.

The continuous intimate seal formed also substantially reduces the risk of leaks. Preprufe does not require a protective layer before rebar is installed, further accelerating the construction programme. The membrane system is considerably easier and quicker to install than alternatives even in intense heat and humidity and can be trafficked immediately after installation.

For over 21 years and with more than 50 million sq m installed globally, Preprufe is proven in many challenging ground conditions including projects across the Middle East which have very high water tables.

Preprufe Plus is the second generation of Preprufe launched in 2014 with double self-adhesive zip laps to provide an even more robust seal between adjacent sheets. It provides a physical barrier that will protect structures against chloride and sulphate attack and will ensure the structure remains unaffected even if their concentration changes over time.

In rail projects, Preprufe Plus has chiefly been installed below station boxes as well as for concrete walls where they are cast onto diaphragm walls. Its simplicity and ease of installation makes it particularly useful in constrained sites such as underground rail stations. Where the outside of the walls can be accessed after striking formwork, GCP’s Bituthene 8000 HC membrane has been used, as in the case of Doha Metro.

Utilising an advanced surface coating developed by GCP, Preprufe also simplifies the installation process by removing multiple layers and complicated detailing. Protective layers of concrete or boards are eliminated, reducing the depth of excavation and spoil, accelerating the critical path of the project programme and ensuring the project remains on track.

When it comes to successfully waterproofing critical rail stations above and below grade, getting the detailing right is essential, and GCP has archived a huge library of details to draw on to suit any project. Such critical areas are the interfaces between the concrete tunnel segments and the station box itself and between the tunnel and cross passages.

Water migration

Complete protection of structural integrity means providing a membrane that not only restricts moisture or water ingress, but also stops water migration between the membrane and the building. Water migration between conventional membranes and the structure can cause considerable issues in terms of locating and repairing leaks.

Once a leak becomes visible, it is often a considerable distance from the source, making remediation haphazard and expensive. Conventional membranes are often covered with a mesh-like layer and then attached to mud slabs or blinding concrete which separates the membrane from the structure and provides paths for water to migrate.

Haramain Railway

The Haramain High Speed Railway project faced the challenge of building four new stations in four years in extreme heat and desert conditions. Designed by the joint venture team of architects Foster + Partners and Buro Happold, in collaboration with local architect Dar Al Handasah, this 450-km high-speed rail link will link Islam’s holiest cities Makkah and Madinah to the Red Sea coastal city of Jeddah, and to King Abdullah Economic City, which is currently under construction.

Faced with aggressive ground conditions and high water tables, the project team selected Preprufe 300R waterproofng membrane for its exceptional protection to all built elements and extending above the water table. To further minimise risk and ensure continuity, Bituthene 8000 HC waterproofng membrane was also specified, post-applied to provide complete protection for the substructure walls from the aggressive soils. In total, the installation saw 300,000 sq m of Preprufe 300R as well as 150,000 sq m of Bituthene 8000 HC.

Preprufe offers a solution that not only protects structures from ingress by ground water and harsh chemicals, but also provides an intimate seal preventing migration of water and contributing to a design life of more than 100 years. And with over 50 years’ experience as a leading provider of waterproofing solutions, GCP is ideally placed to provide the expertise and support to ensure a successful result in below ground constructions.

• ILTAZ ALAM is product manager at GCP Applied Technologies, which provides premier specialty construction chemicals and building materials for many of the world’s most renowned structures.