Conservation Project – Ruben Paul Borg

Industrial Heritage in Use

The Reinforced Concrete Water Tower Conservation project

by Ruben Paul Borg

The Reinforced Concrete Water Tower conservation project presents a key development in the recovery of industrial heritage in Malta.

This Water Tower was constructed in the 1930s to serve the needs of the Public Abattoir and is the only structure of its type and size in the Maltese Islands.1 The Water Tower consists of a reinforced concrete structure c.15 m high with a c.10 m diameter tank having a capacity of 400 cubic m. The tank consists of a shell structure with a cylindrical drum resting on a truncated conical structure with a dome at the base and ring beams, supported on 12 slender reinforced concrete columns.

The structure continued to serve the needs of the Abattoir for several decades; there were attempts at repair during the 1970s, including the installation of reinforced concrete jackets to the slender columns. The age of the structure, its location in the Grand Harbour, the storage of water with high salinity and other factors, contributed to its degradation, with extensive corrosion of reinforcement and loss of section.

As a result of severe degradation and significant loss of section particularly of the shell structure of the tank, the Water Tower was set for demolition in 2010. The case for the conservation of this unique water tower was presented to the government by the University of Malta, Construction Materials Engineering research group, to reverse plans for its demolition leading to a strategic conservation programme.2

The Reinforced Concrete Water Tower before (left) and after (above) restoration.

However, due to the extreme degradation of the structure, the project required the development of new materials, technologies, methodologies and engineering solutions in the emerging field of reinforced concrete conservation, which had to be designed specifically for the complex structure. The new technologies had to be designed to respect the original materials and structure, whilst ensuring long term performance of the restored Water Tower.

Plan and section of the water tower. The Water Tower Durability and Structural Health Monitoring System Control Room.

The project was developed with respect to fundamental principles in conservation including: • Documentation and detailed appraisal of the structure; • Materials authenticity with the development of advanced materials, optimised for application in the water tower structure; • Structural optimisation with reference to the original structure and its performance; • Reinstatement of original details and form, for the integrity of the structure; • Advanced restoration techniques to provide solutions to specific challenges in degradation; • Strengthening of the structure using advanced materials: UHPC applied in thin jackets to columns and thin Textile

Reinforced Concrete applied to the tank; • Re-treatability in view of future interventions, whilst reinstating lost sections and ensuring stability; • Legibility of interventions, achieved through the newly developed and optimised materials exploiting innovation in materials engineering, whilst respecting the authenticity of the cement-based materials; • Structure in service, brought back in operation as an asset, promoting long term use and maintenance; • Structural health monitoring system supporting longer term performance of the structure. The complexity of the conservation project and the innovative solutions which had to be developed, required a comprehensive management framework that could ensure the recovery of the industrial heritage monument.

The scientific restoration methodology included the investigation of the existing structure through key strategic steps.3 The comprehensive data gathered was required to inform the Water Tower conservation: • Archival research and documentation of historical records; • Appraisal of the industrial heritage structure, including the creation of a catalogue of defects and mapping of defects, and the scanning of the structure.

The mapping of defects was conducted in four stages to assess the performance over time, between 2009–2019.

The 400 cub.m. water tank consists of thin reinforced concrete cylindrical and conical elements with a dome at the base, resting on twelve slender columns.

Extensive research campaigns were conducted on the materials and structure. These included: • Non-destructive tests on the structure using advanced techniques. Seventeen different advanced methods were applied, including Ground Penetrating Radar on the structure, ultrasound, eco-impact flaw detection, half-cell corrosion potential, thermal imaging, resistivity; • Advanced material testing; sampling and extraction of concrete cores and reinforcement and their characterisation.

Eleven different advanced methods were applied including compressive strength, depth of carbonation, chloride migration, petrography; • Testing of steel reinforcement; • Microtremor investigation before, during, and after restoration, and with the tank empty and full of water.

Numerical structural modelling and scenario testing were exploited to optimise repair and strengthening interventions.4 Finite Element analysis was conducted with respect to the original structure, damaged structure, and the repair and strengthened structure under different actions including wind and seismic action.

The methodologies for restoration were planned depending on specific needs of the structure and its components. New complex techniques for restoration were developed and applied in the restoration project including the reversal of past repair interventions, electrochemical chloride extraction, re-alkalisation of reinforced concrete, epoxy injection and polymer concrete patch repair and the use of corrosion inhibitors, re-integration of the structure using replica materials, strengthening with new ultra-high performance concrete and textile reinforced concrete and improvement of bond between materials using specialist techniques.

The recovery of the structure could only be made possible through specific solutions which had to be developed by the University of Malta, including new advanced materials. Ultrahigh-performance concrete (UHPC) with self-healing and self-compacting properties, based on nano-additives, fibre-reinforced with increased ductility, was developed and tested at the University of Malta.5

The Ultra-high performance concrete was designed with exceptionally high-strength for long term durability performance, based on self-healing additives and nano-additive

Validation of the restoration project and structural performance using different monitoring strategies. materials (nano-alumina, nano-cellulose and nano-cellulose fibres) through an optimised mix design. The UHPC was then applied and tested on replica columns and eventually applied for the construction of jackets to the columns. Carbon-textile composite reinforced high-performance concrete with self-healing properties was similarly developed and tested on replica tank shell elements for the effective strengthening of the tank.

The research conducted included extensive experimental campaigns in the development and assessment of the mechanical and durability properties of the new materials, their performance with respect to the applications for which these were designed and the assessment of the bond performance when applied onto the existing structure. The new materials and technology developed and optimised in the laboratory, had to be transferred to replica structures and eventually to the water tower structure.

A site production facility was set up, and replica structures were created including columns and shell wall elements to enable the testing of materials and application of technologies on these structures, prior to intervention on the Industrial heritage structure proper.

An advanced sensor network system for monitoring over time was designed, based on durability monitoring including new sensors developed by the University of Malta, structural health monitoring and environmental monitoring.

The advanced system, based on 150 sensors and the monitoring station enables the long-term monitoring of different parts of the structure when in use, ensuring maintenance and timely restoration in the future. The system contributes to conservation, in monitoring the actual restoration interventions and their effectiveness, whilst serving as an important case for the exploitation of this technology on other heritage structures.

The project presented key challenges in materials engineering and the development of novel ultra-high-performance materials; sensor network systems for advanced structural health monitoring; and advanced restoration technology for degraded concrete industrial heritage structures.

These areas are brought together to address the conservation of the Water Tower, through a new Technology Platform created as a new University of Malta Research and Training Station for the development of advanced materials and sensor systems, structural repair and the conservation of Industrial Heritage structures. To this end, the Government of Malta and the University of Malta entered into a framework agreement for the setting up of the Water Tower Research Centre.

The structure was brought back into operation as industrial heritage in use, following an intense validation exercise through the monitoring of structural behaviour during the filling of the tank. The validation exercise included an analysis of the structural modelling, compared to the actual performance through the monitoring system sensor data during the filling up and emptying operation.

The Water Tower has been reintegrated back in operation as a useful asset within the Public Abattoir facilities for water storage and water management. The project led to improved energy conservation through the use of water with lower consumption of energy in heating and water efficiency.

Embodied energy and carbon have been analysed through a life cycle assessment of ultra-high durability concrete, textile reinforced concrete and the Water Tower restoration. The life cycle inventory is based on primary data and the environmental impact assessment was conducted with respect to impact categories for different life cycle phases.

The Water Tower Conservation project was funded through the ReSHEALience Horizon 2020 project,6 the Public Abattoir, the Government of Malta and the Planning Authority. It was led by Prof. Ruben Paul Borg, Construction Materials Engineering Research Group, Faculty for the Built Environment, University of Malta.

The Water Tower stands as key representative of the industrial heritage in the Maltese Islands which, until now, has been largely ignored. The structure, which was set

for demolition in 2010, has been restored, through advanced engineering solutions, innovation in high-performance materials and sensor systems, with potential for wider applications and interventions in Buildings and Infrastructure in Malta.

The restoration project was recognised at the Malta Architecture and Spatial Planning Awards in 2021. The project was awarded the Prix d’Honneur in Restoration for ‘the outstanding contribution to Maltese Cultural Heritage and the achievement of architectural excellence in Malta’ and also the 2021 Judge Maurice Caruana Curran Award for the best project in all categories, by Din l-Art Ħelwa.

The Sustainable Industrial Heritage Restoration was further awarded the International Energy Globe national award, considered as the most important Awards for Sustainability worldwide, by Energy Globe International in 2022.

The complex restoration led to its Scheduling as a Grade 1 National Monument in 2022, marking a first important step towards a wider appreciation of industrial heritage in the Maltese Islands. n

In the Din l-Art Ħelwa Architectural Awards presented in May 2022, this project received the Prix d’Honneur in Restoration, and the Judge Maurice Caruana Curran Award for the best project in all categories.

Notes: (1) Ruben Paul Borg, 2020, Concrete Heritage: Challenges in Conservation, Symposia Melitensia, Vol. 16, 35–52; Praxis: Applying Theory in Practice, University of Malta Junior College Conference, Malta; (2) Ruben Paul Borg, 2019, Strategy for the restoration of the Reinforced Concrete Water Tower, SBE 19 Malta, Proceedings. International Conference, 21st–22nd November 2019, Proceedings, SBE Malta, ISBN 978-99957-1-612-7, ISBN 978-99957-1-613-4 (ebook); (3) Ruben Paul Borg, 2019, The Appraisal of Reinforced Concrete Heritage Structures, SBE 19 Malta, Proceedings. International Conference, 21st–22nd November 2019, Proceedings, SBE Malta, ISBN 978-99957-1-612-7, ISBN 978-99957-1-613-4 (ebook); (4) Ruben Paul Borg, Liborio Cavaleri, 2019, Structural Assessment of a Reinforced Concrete Water Tower, SBE 19 Malta, Proceedings. International Conference, 21st–22nd November 2019, Proceedings, SBE Malta, ISBN 978-999571-612-7, ISBN 978-99957-1-613-4 (ebook); (5) Ruben Paul Borg, 2019, The Mechanical and Durability Performance of Ultra High Durability Concrete, SBE 19 Malta, Proceedings. International Conference, 21st–22nd November 2019, Proceedings, SBE Malta, ISBN 978-99957-1-612-7, ISBN 978-99957-1-613-4 (ebook); (6) ReSHEALience Horizon 2020 Project Ultra High Durability Concrete, www.uhdc.eu, (accessed 1st March 2022).

The Water tower listed as a Grade 1 national monument, aligned with the nineteenth-century gate at the Abattoir

Ruben Paul Borg is associate professor at the Department of Construction and Property Management at the Faculty for the Built Environment at the University of Malta.