Eine Plattform für die Wissenschaft: Bauingenieurwesen, Architektur und Urbanistik
Eine Plattform für die Wissenschaft: Bauingenieurwesen, Architektur und Urbanistik
Rheological approach for recycling returned concrete
According to a recent survey, 10 billion m3 of concrete is produced every year around the world. A non-negligible portion of produced concrete is not completely used and consumed in job-sites: it is sent to concrete production in mixer truck and it is called returned concrete. The main reason for concrete to be returned to the plant is that contractors prefer buying a bigger quantity of concrete compared to the estimated amount required, to avoid the risk of interrupting casting due to shortage of material. The rate of returned concrete is about of 0.5% of the amount produced at the plant. Estimates say that more than 50 million m3 of concrete is produced every year all around the world. The correct and efficient recovery of the 250,000 m3 of returned concrete is therefore a problem of great interest, both from an environmental and economic point of view. This study will present an additive that acts on the viscosity of the concrete by making this returned concrete easier to recycle. By increasing the viscosity of the cement it is possible to facilitate mixer truck cleaning operations. Rheological experiments on cement paste and proper additive allowed us to optimize the formulation of the additive. In this way we could identify the correct amount of admixture and maximize the viscosity increase effect. Stress controlled rheometer is not able to characterize a concrete system with its aggregates, for this reason the cement paste has been studied as a simplified system. With different measurement protocols by a continuous procedure or with an oscillatory one, we were able to define the window-time at which it is necessary to use the additive to optimize the release of the mixer truck. In the second part of this work we will show the results of the effect on the final behaviour of the additive in relation to the different cement classes and job site temperatures.
Rheological approach for recycling returned concrete
According to a recent survey, 10 billion m3 of concrete is produced every year around the world. A non-negligible portion of produced concrete is not completely used and consumed in job-sites: it is sent to concrete production in mixer truck and it is called returned concrete. The main reason for concrete to be returned to the plant is that contractors prefer buying a bigger quantity of concrete compared to the estimated amount required, to avoid the risk of interrupting casting due to shortage of material. The rate of returned concrete is about of 0.5% of the amount produced at the plant. Estimates say that more than 50 million m3 of concrete is produced every year all around the world. The correct and efficient recovery of the 250,000 m3 of returned concrete is therefore a problem of great interest, both from an environmental and economic point of view. This study will present an additive that acts on the viscosity of the concrete by making this returned concrete easier to recycle. By increasing the viscosity of the cement it is possible to facilitate mixer truck cleaning operations. Rheological experiments on cement paste and proper additive allowed us to optimize the formulation of the additive. In this way we could identify the correct amount of admixture and maximize the viscosity increase effect. Stress controlled rheometer is not able to characterize a concrete system with its aggregates, for this reason the cement paste has been studied as a simplified system. With different measurement protocols by a continuous procedure or with an oscillatory one, we were able to define the window-time at which it is necessary to use the additive to optimize the release of the mixer truck. In the second part of this work we will show the results of the effect on the final behaviour of the additive in relation to the different cement classes and job site temperatures.
Rheological approach for recycling returned concrete
Curto, Fabio (Autor:in) / Ferrari, Giorgio (Autor:in) / Carra, Stefano (Autor:in)
2013
6 Seiten, 5 Bilder, 4 Tabellen, 6 Quellen
Aufsatz (Konferenz)
Englisch
Beton , Zementpaste , Beimengung , Rheometer , Recycling , Rheologie
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