Development of a performance-based methodology for assessing concrete durability

Lead Research Organisation: Heriot-Watt University
Department Name: Sch of the Built Environment

Abstract

A lack of reliable, consistent and standardised test procedures for evaluating concrete performance is frequently cited as a major barrier to the adoption of performance specifications and that the appropriate testing technology has not been sufficiently developed to satisfy performance-based philosophy. Indeed, performance-related design methods now permitted under EN 206-1: 2000 Annex J which states that 'such a method may be based on satisfactory experience with local practices in local environments, on data from an established performance test method for the relevant mechanism or on the use of proven predictive model'. Central to the concept of performance-based specifications include the availability of reliable, repeatable test methods which can evaluate the required performance characteristic(s) along with performance compliance limits which should take into account the inherent variability of the test method. It is evident that test procedures and predictive models are required such that those properties of concrete which ensure long-term durability can be determined very early on in the life of a structure and that it will meet specified requirements. The situation is made more complex by the range of cements now available under BS EN 197 which defines a total of 27 products in the family of common cements. There is thus a need for quick, reliable performance tests for concrete durability which have to go far beyond current reliance on the 28-day compressive strength. The lack of adequate performance-related test methods is one of the main factors inhibiting the move from prescriptive to performance-based specifications and forms the focus of this proposal. Furthermore, since it is the cover which protects the steel from the external environment, attention is directed towards assessing the performance of this zone. It is set against this background that the programme of work aims to develop predictive models and exploit novel testing techniques which can then be used in a performance-based testing protocol in the assessment of concrete durability. The techniques will utilise both electrical property measurements and permeation characteristics of concrete as a means of quantifying durability and hence long term performance.

Publications

10 25 50
publication icon
McCarter W (2012) Developments in Performance Monitoring of Concrete Exposed to Extreme Environments in Journal of Infrastructure Systems

publication icon
McCarter W (2009) Real-time monitoring of covercrete response to environmental action in International Journal of Modelling, Identification and Control

publication icon
McCarter W (2015) A durability performance-index for concrete: developments in a novel test method in International Journal of Structural Engineering

publication icon
N Holmes (Author) (2010) Development of a New Marine Exposure Site on the Atlantic North-West Coast of Ireland in Proc. of the Bridge and Concrete Research in Ireland Conference

publication icon
N. Holmes (Author) (2010) The influence of different European cements on the transport and early age properties of concrete in the cover-zone in Proc. 2nd International Conference on Durability of Concrete Structures (ICDCS 2010), ISBN 978-4-8329-0360-9.

publication icon
S. V. Nanukuttan (Author) (2010) Guidelines for selecting concrete mixes based on performance testing and long-term performance in Proc. 13th Int. Conf. on Structural Faults and Repair Conference (Theme 2, Concrete and Composites - Concrete and Structural Behaviour), ISBN 0-947664-67-9 (CD),

publication icon
S. V. Naukuttan (Author) (2010) Use of performance specification and predictive model for concretes exposed to a marine environment in Proc. 13th Int. Conf. on Structural Faults and Repair Conference (Theme 2, Concrete and Composites - Concrete and Structural Behaviour), ISBN 0-947664-67-9 (CD),

publication icon
W. John McCarter (Author) (2012) Developments in performance-based testing of concrete in Proceedings 3rd International Conference on the Durability of Concrete Structures, ISBN 978-1-909131-04-0.

publication icon
W. John McCarter (Author) (2009) Performance monitoring of cover-zone concrete in Proc. 'Concrete in aggressive Aqueous Environments' Conference, Eds. M. Alexander and A. Bertron, ISBN 978-2-35158-070-7

publication icon
W. John McCarter (Author) (2010) 'Developments in monitoring techniques for durability assessment of cover-zone concrete in Proc. 2nd International Conference on Durability of Concrete Structures (ICDCS 2010), Sapporo, Japan, ISBN 978-4-8329-0360-9

 
Description Implementation of both design for durability and performance-based standards and specifications are limited by the lack of rapid, simple, science-based test methods for characterizing the transport properties and deterioration resistance of concrete. Indeed, the lack of adequate performance-related test methods is one of the main factors inhibiting the move from prescriptive to performance-based specifications. The situation is made more complex by the range of cements now available under BS EN 197 which defines a total of 27 products in the family of common cements.



This project focused on the use of both surface-permeation and discretised electrical property measurements to study cover-zone concrete. Since the durability of reinforced concrete structures depends, in the main, on the performance of the cover-zone - as it the cover-zone which protects the steel from the external environment - then such measurenents could be exploited in monitoring the long-term concrete peformance exposed to natural environments. In this work, use is made of a small, multi-electrode array embedded within the surface 75mm of concrete specimens thereby allowing an integrated assessment of the protective properties of the cover region. Concretes were manufactured with different European cements (CEM) and water/binder ratios representing mixes which satisfied the requirements for a range of environmental exposure classes including exposure to chlorides. Electrical property measurements were taken over the curing and post-curing periods; in this extended test-period, there was evidence of on-going hydration, pozzolanic reaction and pore-structure refinement. In addition, in the post-curing period, when exposed to a cyclic chloride ponding regime, measurements could be used to study the convective zone and ionic enrichment of the surface layer.



The project also undertook predictive modelling and the development of in a remote interrogation system to allow continuous, real-time monitoring of the cover-zone concrete from an office setting. On-site instrumentation, which allowed remote interrogation of concrete samples placed at a marine exposure site, was developed (and trialled), together with data handling and processing procedures.
Exploitation Route The premature deterioration of concrete structures is a world-wide problem. In most developed countries, including the UK, around 50% of the construction budget is devoted to repair and maintenance of structures with over 30% of this expenditure on concrete structures. In addition, our infrastructure has now reached an age where capital costs have decreased, but inspection and maintenance costs have grown, constituting a major part of the recurrent costs of the infrastructure. Traffic delay costs due to inspection and maintenance programmes are already estimated to be between 15%-40% of the construction costs . Demands for enhanced performance create a pressing need to be able to determine, with an acceptable degree of confidence, the anticipated service life of concrete structures. Monitoring deterioration would provide an early warning of incipient problems enabling the planning and scheduling of maintenance programmes, hence minimising traffic delays resulting from road/lane closures. The development of integrated monitoring systems for new reinforced concrete structures could also reduce costs by allowing a more rational approach to the assessment of repair options; and, co-ordination and scheduling of inspection and maintenance programmes. It is now recognised that integrated monitoring systems and procedures have an important role to play in the total management of structures, which involves both whole-life economics and life-cycle calculations, When data from monitoring systems are used with improved service-life prediction models additional savings in life cycle costs could result.



As noted above, since it is the concrete cover-zone (covercrete) which protects the steel from the external environment, the ability to continuously monitor the covercrete would allow a more informed assessment of the current and future performance of reinforced concrete structures. The development of sensors and associated monitoring systems to assess covercrete performance would thus form an important component in the inspection, assessment, maintenance and management of structures.



The work within this project addresses these key areas and thus has direct application within the construction sector. This is currently being exploited. A patent was filed for the conductivity array developed within the project (Patent Application No. 0918449.0 'A sensor apparatus and method'). This is currently being sold under license, and further marketed through the University Research and Enterprise Services.
Sectors Construction

 
Description The work provides the basis for a simple technique (electrical property measurements) to assess the permeation properties of concrete and hence its potential long-term perfromance. Additionally, a patent application has been made on aspects of the testing methodology (see also EP/I005846/1).
First Year Of Impact 2012
Sector Construction
Impact Types Societal,Economic

 
Title A SENSOR APPARATUS AND METHOD 
Description A sensor apparatus for embedding in construction material, comprises a sensor electrode array comprising at least one pair of electrodes connectable to an electrical signal source for measuring at least one electrical property representative of electrical resistivity or conductivity between the pair of electrodes, and an anode and cathode connectable to form a cell. 
IP Reference WO2011048378 
Protection Patent granted
Year Protection Granted 2011
Licensed Yes
Impact It has led to an improved understanding of cover-zone concrete permeation properties.
 
Description Electrical Based Sensors and Remote Monitoring System for Assessing the Corrosion Related Activity in Concrete at Hangzhou Bay Bridge 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Type Of Presentation poster presentation
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact A poster presented at the 4th Civil and Structural Health Monitoring Workshop (CSHM-4), Poster 31, November 6-8, 2012, Berlin.

Outlines a remote interrogation system developed with the project and used at a test site in China.
Year(s) Of Engagement Activity 2012
URL http://www.ndt.net/article/cshm2012/papers/p31.pdf
 
Description Performance monitoring of concrete using electrical property measurements 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Presentation given at the American Concrete Institute (ACI) Spring Convention held in Tampa, Florida (3rd - 7th April, 2011) under the thematic area 'Performance-Based Specification and Testing' sponsored by ACI Committees 201 (Durability of Concrete) and 236 (Materials Science of Concrete).

A presentation outlining performance-based testing of concrete.
Year(s) Of Engagement Activity 2011
 
Description Quality Control and Performance Assessment Methods for Concrete Structures (in chloride environments) 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Describes quality control of structural concrete. A presentation at the American Concrete Institute (ACI) Spring Convention held in Tampa, Florida (3rd - 7th April, 2011) under the thematic area 'Performance-Based Specification and Testing' sponsored by ACI Committees 201 (Durability of Concrete) and 236 (Materials Science of Concrete).

Making contact with practitioners and researchers.
Year(s) Of Engagement Activity 2011