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Carbonation of concrete at ambient CO2 concentration is a slow process. This makes the testing of the resistance of concrete against carbonation often too slow to be applicable for service life assessments of new structures. Raising the CO2-concentration will accelerate the test but the validity of an increase CO2-level is debated. If not valid, the service life can be seriously underestimated. In this paper, the effects of accelerating on the carbonation process are discussed. It is shown that a change in CO2 concentration will not change the carbonation process. Since carbonation occurs instantly, a zero CO2 concentration at the carbonation front is maintained. Moreover, it has been concluded that all hydrated and unhydrated cement ultimately carbonates. This implies that the amount of material that can carbonate can be determined on the basis of the amount of calcium in the unreacted cement. © 2013 Elsevier Ltd. All rights reserved.

In Nederland wordt er vanuit gegaan dat beton, gemaakt volgens de VBT 1995 in milieuklasse 3, vorstdooizoutbestand is. Niettemin moet bij nieuwe cementsoorten de vorstdooizoutbestandheid worden bewezen (CURAanbeveling 48). Ook bij het beoordelen van nieuwe betonsamenstellingen, toeslagmaterialen, vulstoffen of hulpstoffen wordt vaak de vorstdooizoutbestandheid onderzocht. Bij onderzoek naar een cementsoort of betonsamenstelling met de beste vorstdooizoutbestandheid zal hiertoe in het laboratorium een vergelijkend onderzoek worden uitgevoerd. Gebleken is echter dat de laboratoriumproeven de Nederlandse praktijk niet goed weergeven

Met de huidige bouwvoorschriften worden betonconstructies ontworpen op basis van prestaties, waarbij prestaties zijn gedefinieerd als de taken die de constructie moet verrichten met een bepaald minimum resultaat, de prestatie-eis. Bij het ontwerpen wordt meestal uitgegaan dat als het ontwerp voldoet aan al zijn prestatie-eisen, het gerealiseerde bouwwerk ook voldoet en dit bovendien zal blijven doen. Uit de praktijk blijkt vaak genoeg dat dit niet klopt. Betonconstructies verouderen zodat de prestaties afnemen. Wanneer een prestatie beneden zijn grenswaarde komt, is de levensduur van de constructie ten einde tenzij er (onderhouds-)maatregelen worden genomen waardoor de prestatie weer boven zijn grenswaarde komt.

On January 1st 2012, the European project SUS-CON has been started: “SUStainable, innovative and energy efficient CONcrete, based on the integration of all waste materials” (grant agreement no: 285463). The SUS-CON project aims at developing new technology routes to integrate waste materials in the production cycle of concrete. It should result in an innovative light-weight, eco-compatible and cost-effective construction material, made by all-waste raw materials and characterized by low embodied energy and CO2 and by improved thermal insulation performances. The focus of the SUS-CON project will be on waste materials that, for quantity, distribution and characteristics are also a social problem but, on the other hand, are available in quantities enough for feeding the concrete industry. Identifying the waste materials is the objective of WP 1. The innovative all-waste material consists of light weight recycled aggregates in a binder matrix, in equivalence to concrete. The LW aggregates consist of various waste streams, among which waste plastics not suitable for recycling into new products, bound by waste gypsum, shredded and processed waste tyre, geopolymer aggregates and so on. The use of lightweight recycled aggregates will make the target material not only lightweight but also heat-insulating. The LW aggregates have been investigated and tested in WP 2. The binder consists of waste pozzolanes or latent hydraulic materials that are activated by waste activators. Upon mixing with water, they form geopolymers, serving as binder of the all-waste concrete. The geopolymers have been investigated in WP 3.

On January 1st 2012, the European project SUS-CON has been started: “SUStainable, innovative and energy efficient CONcrete, based on the integration of all waste materials” (grant agreement no: 285463). The SUS-CON project aims at developing new technology routes to integrate waste materials in the production cycle of concrete. It should result in an innovative light-weight, eco-compatible and cost-effective construction material, made by all-waste raw materials and characterized by low embodied energy and CO2 and by improved thermal insulation performances. The focus of the SUS-CON project will be on waste materials that, for quantity, distribution and characteristics are also a social problem but, on the other hand, are available in quantities enough for feeding the concrete industry. Identifying the waste materials is the objective of WP 1. The innovative all-waste material will consists of light weight recycled aggregates in a binder matrix, in equivalence to concrete. The LW aggregates consist of various waste streams, among which waste plastics not suitable for recycling into new products and melted and bound by waste gypsum, shredded and processed waste tyre, geopolymer aggregates and so on. The use of lightweight recycled aggregates will allow making the target material not only lightweight but also heat-insulating. The LW aggregates have been investigated and tested in WP 2. The binder consist of waste pozzolanes or latent hydraulic materials that are activated by waste activators. Upon mixing with water, they form a reaction product, serving as binder of the all-waste concrete. The binders have been investigated in WP 3.

In the design stage of a concrete structure, decisions have to be made on how to fulfil the required service life and consequently, what concrete composition to use. Concrete compositions can be chosen on account of known performances but this will limit the choice of compositions and materials to those that have already been in use. Other methods may give a wider choice in concrete compositions, but mostly require proof which is generally obtained by means of testing. When limited time is available for testing, accelerated tests often are performed. If there is no good insight in the underlying principles of the effect of the acceleration, some serious mistakes in the service life designs will be made. In this paper, an example of accelerated testing is shown for carbonation. Accelerated carbonation tests at 2% CO2 and natural carbonation tests at ambient CO2-level have been executed. Based on the results, the resistance against carbonation has been calculated. Since this resistance is a material property, it should be similar in both tests. For two of the tested concrete compositions this proved to be the case, a third type of concrete made with fine cement it did, however, not. It was speculated that in the accelerated test, a different mechanism was becoming dominant for this concrete. Instead of the transport of CO2, now drying out was thought to be dominant. The drying out is a necessary step in the carbonation process as during the carbonation a relatively large amount of water is generated that, when saturating the pore space, prohibits CO2 to be transported to the carbonation front. A new simple model was derived for this case. The modelling gave a similar resistance against carbonation for the fine OPC as determined in the natural carbonation case where transport of CO2 was the dominant step in the carbonation process. If this change in dominant step had not been made, a far too high resistance in carbonation would have been calculated, seriously overestimating the service life of this fine OPC concrete in structural applications

Carbonation of concrete at ambient CO2 concentration is a slow process. This makes the testing of the resistance of concrete against carbonation often too slow to be applicable for service life assessments of new structures. Raising the CO2-concentration will accelerate the test but the validity of an increase CO2 -level is debated. If not valid, the service life can be seriously underestimated. In this paper, the effects of accelerating on the carbonation process are discussed. It is shown that a change in CO2 concentration will not change the carbonation process. Since carbonation occurs instantly, a zero CO2 concentration at the carbonation front is maintained. Moreover, it has been concluded that all hydrated and unhydrated cement ultimately carbonate. This implies that the amount of carbonatable matter can be determined on the basis of the amount of calcium in the unreacted cement.