The reinforced concrete water tower, constructed in the 1930s to serve the needs of the Public Abattoir, is the only structure of its type and size in the Maltese Islands. The water tower consists of a reinforced concrete structure consisting of a drum resting on a truncated conical structure with a dome at the base and ring beams, supported on 12 slender reinforced concrete columns.

It was set for demolition in 2009 because of severe degradation. The University of Malta (UM) made the case for its conservation based on new methods in the emerging field of reinforced concrete conservation. The complex restoration was based on new advanced techniques in restoration of reinforced concrete, research and development of innovative high-performance materials together with their application, and the development of a smart sensor network system for the durability and structural health monitoring of the structure.

The assessment of the structure included key strategic steps in archival research and documentation; appraisal and mapping of deterioration; characterisation of materials and assessment of the reinforced concrete including non-destructive assessment testing of materials; structural microtremor analysis; numerical structural modelling; and scenario testing to define and optimise repair and strengthen­ing interventions.

An advanced sensor network system for monitoring over time was designed and installed, based on 150 sensors for durability, structural health and environmental monitoring

New techniques for restoration were developed and applied including electro-chemical chloride extraction to remove harmful salts; re-alkalisation of reinforced concrete to prevent steel reinforcement corrosion; epoxy injection in cracks; polymer-concrete patch repair to damaged concrete; the use of corrosion inhibitors to prevent corrosion of rebar and reinstatement of the structure. New advanced materials were developed at the UM.

These include Ultra-High Performance Concrete (UHPC), a concrete increasing ductility, self-healing and self-compacting properties based on nano-additives, applied to strengthen the columns and carbon-textile composite, high-performance concrete for the strengthening of the tank. An advanced sensor network system for monitoring over time was designed and installed, based on 150 sensors for durability, structural health and environmental monitoring.

The project, completed in 2021, was led by the Construction Materials Engineering Research Group at the Faculty for the Built Environment, UM. The project was funded through the ReSHEALience Horizon 2020 Project in Ultra High Durability Concrete, the Public Abattoir, and the Planning Authority. This project was awarded the Energy Globe International Award in 2022, the Prix d’Honneur in Restoration for “the outstanding contribution to Maltese Cultural Heritage and the achievement of architectural excellence in Malta”, and the 2021 Judge Maurice Caruana Curran Award for the best project in all categories, by Din l-Art Ħelwa.     

Ruben Paul Borg is an academic, an architect and civil engineer. ruben.p.borg@um.edu.mt

Sound Bites

•        Ultra-High Performance Concrete (UHPC) is a new class of concrete with exceptional strength and durability properties. UHPC has a projected long lifespan with exceptional strength, durability and flexibility. It has a compressive strength around 10 times that of traditional concrete. UHPC can be utilised in structural applications and rehabilitation and repair. It was developed at the UM and successfully applied in the repair and strengthening of the water tower.

https://www.youtube.com/watch?v=HdjBMU4m3wQ

•        Sensors have wide applications in buildings, enabling monitoring of structures supporting Smart buildings and infrastructure. An advanced sensor network system for monitoring over time was designed for the water tower, based on durability monitoring including new sensors developed by the University of Malta, Structural Health Monitoring and Environmental Monitoring. The c150 sensors installed enable the long-term monitoring of different parts of the structure when in use, ensuring maintenance and timely restoration in the future.

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DID YOU KNOW?

•        The water tower consists of a reinforced concrete structure,15 metres high (equivalent to a five-storey block) with a 10 metre diameter tank.

•        Following restoration, the water tank was listed as a Grade 1 national monument. It stands as representative of the rich industrial heritage of the Maltese Islands.

•        Sensors were installed in different parts of the structure to monitor in real time the durability performance and structural health of the water tank in use.

•        The water tower, with a storage capacity of 400 cubic metres of water, was reintegrated as a useful asset at the Public Abattoir.

For more trivia, see: www.um.edu.mt/think.