Porosity, gas permeability, carbonation and their interaction in high-volume fly ash concrete

This paper describes the results of research into porosity, gas permeability and carbonation of high-volume fly ash (FA) concrete, including a literature review and comparison between models and experimental results. Four mixtures were made, each with a different FA replacement level-0, 35, 50 and 67 %-but with the same water-to-cementitious materials ratio. A vacuum saturation technique and a gas permeation experiment indicate that both porosity and gas permeability increase with increasing FA content. A reduction is noticed between 1 and 3 months for the FA mixtures owing to the pozzolanic reaction. No existing models seem to predict the porosity and gas permeability correctly for all mixtures. Carbonation tests show that the carbonation depth is considerably higher for the 50 and 67% FA mixtures at all ages compared to the ordinary Portland cement concrete. The Jiang model overestimates the carbonation depth for high-volume FA concrete significantly, while the Atis, models predict the depth rather well. Carbonation seems to have a negative effect on gas permeability, especially for the 50 and 67% mixtures

Gas transport and carbonation in high-volume fly ash concrete versus age at testing

The consumption of energy and emission of CO2 related to the production of cement can be reduced by partially replacing cement by fly ash. When 50 % or more of the cement in a concrete mix is replaced by fly ash, the name "high-volume fly ash concrete" can be used. In this paper the effect of the cement by fly ash replacement level (0, 35, 50 or 67 %) on gas permeability and carbonation is described. The water-to-cementitious materials ratio (W/CM) for the different mixes was kept constant. Both permeability to oxygen and carbonation increased significantly with increasing fly ash content. When accelerated carbonation testing is carried out at later age (6 or 3 months, compared to 1 month), the resulting carbonation depth is reduced. Carbonation in itself seems to have a negative effect on gas permeability, especially for the 50 and 67 % fly ash mixtures. The obtained experimental results were compared with models described in literature. The model of Atis, which includes the parameters compressive strength and porosity, predicts the carbonation depth for concrete with high volumes of fly ash rather well

Effect of curing age on the durability of high-volume fly ash concrete

High volume fly ash (HVFA) concrete is one of the "green" alternatives developed to reduce the energy consumption and CO2 emission related to the cement production. The pozzolanic reaction of fly ash is a retarded process compared to the cement hydration. As a result, the strength, microstructure development and consequently also the durability behavior of fly ash mixtures will be strongly influenced by age. After all, durability is, to a large extent, determined by the possibility for aggressive substances to penetrate into the concrete, and the latter is in turn determined by the porosity and transport properties of the concrete. This paper describes the results of tests on 4 fly ash mixtures, each with different fly ash replacement level namely 0, 35, 50 and 67 %, but with the same water-to-cementitious materials ratio. The experiments were executed at the age of 1, 3 and 6 months. Permeable porosity and gas permeability increased with increasing fly ash content. A reduction in porosity was noticed between 1 and 3 months for the fly ash mixtures due to the pozzolanic reaction. The carbonation depth was considerably higher for the 50 and 67 % fly ash mixtures at all ages compared to the ordinary Portland cement concrete. Carbonation appeared to have a negative effect on gas permeability, especially for the 50 and 67 % mixtures

Relapsing infiltrates after Pneumocystis pneumonia in stem cell transplant patients: think about BOOP!

Bronchiolitis Obliterans Organizing Pneumonia (BOOP) can complicate allogeneic haematopoietic stem cell transplantation. It is associated with prior grant-versus-host disease (GVHD) and the case fatality is 21%. In 22%, diagnosis is preceded by tapering the corticosteroids given as a treatment for GVHD. We report a fatal case of BOOP after tapering the corticosteroids that the patient received for a Pneumocystis jirovecii pneumonia after stem cell transplantation

Opvattingen van directieleden van revalidatiecentra, over het management in hun centra /

Diss. lic. pedagogische wetenschappen: orthopedagogie