The influence of supplementary cementing materials (SCMs) on the hydration and durability of blended cement has been evaluated using chemical and physical principles. Similarities and differences between various SCMs has been considered while they have been grouped into categories as latent hydraulic or pozzolanic and sub-divided into siliceous, aluminous, carbonaceous etc. For instance has the important synergy between SCMs producing calcium aluminate hydrate and calcium carbonate been elucidated showing how maximizing water binding leads to reduced porosity and thereby increased strength by forming calcium monocarboaluminate hydrate. Similarly would any magnesium content in the carbonate lead to hydrotalcite formation in the presence of aluminates.The interaction of admixtures with SCMs, like plasticizers, and the use of accelerators to speed up hydration are also treated.The influence of SCMs on durability issues like chloride ingress, carbonation, alkali aggregate reactions, sulphate resistance and freeze-thaw resistance is discussed as well. The importance of not accelerating the durability exposure too much is stressed in order avoid creation of products from the SCMs that will not occur in practice. Generally speaking SCMs improve the resistance of blended cements to most degradation mechanisms at equal w/c, with the exception of carbonation that can be improved by reducing w/c.
The binding of CO2 by concrete carbonation is an ongoing natural process. Many estimates have been given over the past decades and the last 5-10 year the knowledge has increased significantly regarding the capability to estimate the binding of CO2 by concrete carbonation. This included better insight of the carbonation mechanisms, increased quantity of field data, and developments of models that calculate the CO2-binding by concrete in service life and in the recovery phase. It was found that the Norwegian concrete stock in 2011 will bind around 165 000 tonnes assuming a service life and a recovery phase of 100 years each. Most of the CO2 will be bound in service life, as the model calculated the binding to be 140 000 tonnes in this phase. Furthermore, it was found that the specific CO2binding to cement was 111 kg CO2/ton of cement consumed, for which 94 kg CO2/ton of cement was bound in the service life of concrete. The model calculations were considered to be conservative to avoid overestimations. Model prediction by further variation of the demolition rate demonstrated the strong influence of this parameter on the total CO2-binding in the recovery phase. If single products are demolished at 100% rate and at 90% crushing rate after service life, they may carbonate in the range of 69-93% by volume depending and the concrete quality.
The aim of the study was to investigate the effect of the type of surface on the chloride ingress resistance of concrete. Concrete cylinders with both cut and cast surfaces were exposed to sea water in the tidal zone at Østmarkneset in the Trondheim Fjord in Norway after approx. 1 months of curing. Chloride profiles were determined after 35, 200 days, 1, 2 and 5 years of exposure. Three concretes with water-to-binder ratio 0.45 and with different cements were examined. One concrete was prepared with a coarse Portland cement, the second was prepared with a finely ground Portland cement, and in the third concrete 20% of the Portland cement was replaced by siliceous fly ash.
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