Special keynote lecture

Prof Karen Scrivener

EPFL, Switzerland

Future Cements and performance testing

The cement and concrete industry faces two major challenges – how to supply the increasing demand for cement and how to do this with the minimal environmental impact. The underlying idea of performance tests is to facilitate the introduction of new cementitious materials.  In this context we need to consider how cements are likely to evolve and the implications for performance tests.  We can make and exhaustive evaluation of all possible cement types starting from the availability of elements on earth.  Then considering the potential of hydrate to bridge spaces between cement grainsand so contribute to strength development.  This brings us to the conclusion that the most efficient types of cement should follow the route of partial substitution Portland cement clinker with Supplementary cementitious materials. 

To ensure good durability of materials made from such cements, performance tests must take into account how these differ from pure Portland blends in terms of both their physical pore structure and the chemical phase composition.  I will discuss some of the cautions needed in performance testing drawing on examples from the fields of carbonation, chloride ingress and sulfate attack.

Prof Pierre-Claude Aïtchin

Université de Sherbrooke Canada

The sky's the limit

In 1970, a 60 MPa concrete was used for the first time in Chicago to cast the lower-level columns of the 86-story Water Tower Place building. By optimizing the use of the cements, fly ashes and admixtures commercially available at that time, John Albinger was able to produce this 60 MPa concrete with a 100mm slump. The concrete was placed using buckets, and was heavily vibrated to produce a pleasing surface finish.  Presently in Mumbai, the Samsung Corporation is building two high-rise structures using a pumped 80 MPa concrete with a 200 mm slump for the lower-level columns, and a pumped 40 MPa self-compacting concrete up to the top floor. A few years ago, concrete was pumped (using a single pump) up to 610m during the construction of the Burj Dubai Tower. Presently, the construction of a 1200m high tower is projected in Djeddah, Saudi Arabia, where different types of concrete will be pumped to the very top of the building.

Such technical achievements have been made possible only because a true science of concrete and admixtures has been developed during the last fifty years, and because performance based specifications have been implemented.

A journey through the construction of some land mark buildings will show how, step by step, it has been possible to replace steel structures in a domain that fifty years ago was reserved for them. Concrete can now be pumped up to the sky, while steel still has to be raised piece by piece by cranes (but for how long?...).

 

RILEM TC PSC keynote lectures

Prof Lars Olof Nilsson

Lund University, Sweden

Durability of reinforced concrete structures and penetrability

A brief overview will be given on the mechanisms causing reinforcement corrosion, on the concrete properties relating to the ingress of aggressive agents (penetrability and transport properties) and on the principles for service life design and deterioration models.
The lecture will include these aspects:
1 Mechanisms causing reinforcement corrosion
1.1 Carbonation
1.2 Chloride ingress  
2 Concrete properties relating to the ingress of aggressive agents (penetrability and transport properties)      
2.1 Resistance against diffusion of CO2
2.2 Moisture transport properties
2.3 Resistance against chloride diffusion and convection
3 Service life and deterioration models (principles)
3.1 Carbonation models, in principle         
3.2 Chloride ingress models, in principle
3.3 Discussion on the influence of cracks

Prof Dubravka Bjegovic

Faculty of Civil Engineering, Zagreb, Croatia

Test methods for concrete penetrability

For a certain property and certain test method to be used as a durability indicator in the performance based design procedure, it needs to be quantifiable by laboratory and on-site tests in a reproducible manner and with clearly defined test procedures. Furthermore, limiting values of the property required for a specific environmental class and required service life of a structure need to be established.

This lecture will cover a short description of the available and commonly applied in-situ and laboratory, non-destructive, semi-destructive or destructive test methods for evaluating concrete penetrability properties. Their application will be shown on examples from engineering practice.

Dr Hans Beushausen

University of Cape Town, South Africa

Principles of the performance-based approach for concrete durability

Performance-based design concepts are based on quantitative predictions for durability (or working life) from exposure conditions and measured material parameters. The resistance of the structure, measured through durability indicators of the actual concrete used, is compared against the environmental load. On this basis, deterioration of a structure during its lifetime is quantified using appropriate deterioration models. In this concept the concrete composition is of minor importance compared to the concrete properties.

André Valente Monteiro

National Laboratory for Civil Engineering (LNEC), Portugal

Compliance evaluation of concrete cover depth

It is widely recognized that the failure of compliance of the cover depth with the specifications is one of the main causes of premature deterioration of reinforced concrete structures. However, most technical standards and codes that deal with durability design and control of execution do not provide guidelines for its assessment in structures.

In this lecture it will be presented statistical bases and guidelines for assessing the minimum cover depth achieved in concrete structures on a basis of an inspection by variables, and on a basis of an inspection by attributes. These guidelines are intended to help practitioners performing a proper estimation of the minimum cover depth achieved in structures and to support decisions on the acceptance of isolated lots regarding this parameter.

Prof Doug R. Hooton

University of Toronto, Canada

Using Performance-Based Specifications to Improve Achievement of Durable Structures

While there is widespread interest in moving from prescriptive to performance-based specifications for concrete, very few true performance-based specifications exist and many engineers are more comfortable with the traditional (conservative) prescriptive approach than the performance-based one. Some of the barriers to the wide acceptance of performance based specifications include perceptions of increased costs associated with extra testing, extra time and increased quality control/quality assurance measures. A performance-based specification should provide a system for the owner/specifier, contractor and supplier/producer to assess and maintain quality concrete. To achieve this, the responsibilities of all parties need to be clearly defined in the contract document. In addition, proper communication and improved partnership (co-operation) between the parties (owner/specifier/engineer (design professional), contractor and supplier/producer) must be ensured to report and address any problems and deficiencies quickly in order to achieve the desired in-place concrete performance.

Dr Luis Fernandez Luco

Facultad de ingeniería - UBA, Argentina

Application Test of RILEM TC PSC in Venlo

In April 2012 |A|S Research & Technology organized the RILEM TC 230-PSC Application Test, that was performed by international researchers in a period of 3 days, from Sunday April 15 to Tuesday April 17 although some of them returned to Venlo in July 2012 for a new series of tests. Eight walls made of reinforced concrete were exposed outside the facilities, representing different types of concrete, curing regimes and outdoor exposures (shielded and unshielded from the rain and wind).
The aim of the Application test was the application of different techniques (preferably non-destructive) at representative locations to assess whether the panels were suitable for a design service life of 100 years, under exposure corresponding to XD3 according the EN-206. Core samples were obtained in both opportunities and they were sent to H. Beushausen, to run the battery of tests included in the Service Life Assessment (SLA) criterion developed in South Africa.

This paper summarises the description of the applied non-destructive testing methods, some of the really innovative, and the overall assessment of the results obtained.

Dr Roberto Torrent

Materials Advanced Services Ltd., Argentina

The Swiss P2P Road: from Theorecrete to Labcrete to Realcrete

The presentation deals with specifications for durability, describing the relatively fast transit (2003-2013) of the Swiss Standards from purely prescriptive to include performance requirements for the concrete producer (based on tests on cast specimens), to finally include performance requirements for the end-product (based on NDT made on the structure), making them possibly the most advanced standards in this respect. The advantages and limitations of each step in the P2P (Prescriptive to Performance) road are discussed in detail.
1.  Prescriptive Specifications ("Theorecrete")
    1.1    Theorecrete: water/cement (water/binder) ratio as durability indicator
    1.2    What does w/c ratio measure?, can conformity with w/cmax be controlled?
    1.3    w/c ratio as durability indicator: its unsuitability
    1.4    Swiss Standards 2003: "Theorecrete" Prescriptive Specifications
2.  Performance Specifications based on cast specimens ("Labcrete")
    2.1    “Labcrete” Performance Durability Indicators: their Limitations
    2.2    Swiss Standards 2008: "Labcrete" Performance Specifications
             Water  Sorptivity and Chloride Migration tests on cast specimens)
3.  Difference between "Labcrete" and "Realcrete" (especially Covercrete")
4.  Performance Specifications and Control based on "Covercrete" site testing
    4.1    Swiss Standards 2013: "Covercrete" Performance Specifications
            (NDT of Air  Permeability on site)
5.  Foreseeable consequences for the Concrete Construction Industry

Prof Kei-ichi Imamoto

Tokyo University of Science, Japan

Relationship between air permeability and carbonation progress of concrete in Japan

This study deals with the air-permeability of concrete cover and its relation with carbonation progress.  In this study, two test cases were considered.  One focused on the air permeability of new concrete and the other on that of existing concrete.  In the test with new concrete, 20 concrete specimens with water-to-cement ratios ranging from 0.3 to 1.0 were prepared.  The air permeability values of these specimens were measured at the age of 2 months; then, they were subjected to exposure tests.  In the test with existing concrete buildings, the air permeability of concrete structures and carbonation progress were measured for 4 buildings and 11 concrete specimens, the ages of which were 12–45 years.  It was found that the square root theory–based carbonation velocity increases with an increase in the air permeability coefficient (kT).  Good agreement was obtained between the air permeability of new concrete and carbonation velocity.  Although the relationship between carbonation velocity and kT for existing concrete buildings had a considerably large scatter, the relationships between them for individual buildings were comparatively good.  This might provide a good perspective for evaluating carbonation progress based on the air permeability of the concrete in new and existing structures.

Prof Carmen Andrade

Eduardo Torroja Institute (IETcc-CSIC), Spain

Performance specifications and tests to verify service life

The verification of service life is started to be specified in the contracts of large infrastructures requiring life of 100 years or more, as it was the case of Great Belt or Oresund bridges. The specification is made for the fabrication of concrete by simply limiting the value of the chloride diffusion coefficient or mentioning the test method but without fixing tolerances or the limits of application of the life prediction models. This approach which is in line with requiring performance instead of prescriptions, is producing discrepancies in the interpretation between owner and builder due to the lack of a coherent set of requirements. The situation can be avoided by making the specifications more complete and easy to be evaluated. In present work are analyzed some gaps in the definitions of the prediction models for chloride ingress which need to test not only the chloride diffusion coefficient, but also the surface concentration, the aging factor and the chloride threshold.  Regarding the tests, it is very needed to take into account their precision and the tolerances and, as their results take weeks or months, also to provide solutions in the case of failure when the concrete is already placed on site,. An alternative is to foresee a time of pre-testing prior to the real starting of the work, as was made in the case of Oresund bridge.

Prof Mark Alexander

University of Cape Town, South Africa

Examples of performance-based approaches for concrete durability in South Africa

Reinforced concrete durability continues to be a pervasive problem worldwide, and this is true also in South Africa.  To address this problem, performance based approaches for durability have been developed in S.A. over the last decade or so.  These largely revolve around an approach called the ‘Durability Index Approach’, which is aimed at controlling the occurrence of corrosion in RC structures.  This approach has achieved some status with major infrastructure providers in South Africa, and actual implementation has occurred in large infrastructure projects.  The paper briefly reviews the background to the DI Approach, places it in an international context, and gives examples of some local applications in S.A., showing how it has been useful in achieving greater durability of RC construction. The paper also reviews proposals in the latest revision to the SA Concrete Code for incorporating elements of a performance-based approach to durability specifications. It is argued that until such approaches are embedded in national or international codes, they are unlikely to be universally accepted.