This thesis provides a multifunctional design approach for sustainable concrete, particularly earth-moist concrete (EMC), with application to concrete mass products. EMC is a concrete with low water content and stiff consistency that is used for the production of concrete mass products, such as paving blocks, curbstones, and sewage pipes. The stiff consistency allows for short processing times as the product can immediately be removed from the mold. The practical design of EMC mixes is based on experience and variations that are made during production, as an in-depth scientific description of the material is limited. Within this thesis, a multifunctional design approach is proposed that is based on particle packing ideas derived from theories for geometric packings of polydisperse systems. This new approach for the mix design of EMC mixes considers the entire grading of all solid ingredients in order to compose a concrete mix that meets required performance criteria. A computer based optimization algorithm was developed that allows for the composition of a granular mix taking into account theories of continuous geometric particle packing. Using the algorithm, EMC mixes have been designed that are characterized by optimized and dense particle packing, lower cement content, and better workability in fresh state. Since the early-age behavior of EMC is one of the most relevant criteria for production, the formation of interparticle forces in the micro range has been studied, and relations to the granulometric properties of the concrete mix have been accounted for. This overall consideration of the granulometric properties and resulting effects on the concrete properties in fresh and hardened state results in EMC mixes that have higher mechanical strength compared to classical mix designs. In this way, cement is used more efficiently and cement content can be reduced. The aspect of sustainability is further addressed by the incorporation of waste materials and industrial by-products in EMC and other types of concrete. To do this, the ideas of the new mix design concept have been used to replace primary filler materials, such as limestone powder or fly ash, by fine inert stone waste materials generated in the natural stone industry. This successful replacement of conventional raw materials lowers the environmental footprint of the produced concrete to a further extent. Adopting the ideas of a closed concrete life cycle, attention was also paid to the utilization of recycled materials in concrete used for the production of concrete mass products. Recycled aggregates have been applied to replace traditional aggregates, and fines that originate during the recycling process have been used as source to replace partly reactive filler materials. Finally, photocatalytic materials have been investigated to give multifunctional properties to concrete mass products and enhance their contribution to sustainability. The photocatalytic properties of these semiconducting materials come along with air-purifying and self-cleaning abilities. The working principles of the photocatalytic oxidation (PCO) of nitrogen oxides (NOx) in EMC have been studied under experimental conditions and the reaction kinetics of the PCO have been modeled. The experimental work on photocatalytic materials revealed that the performance of already available systems differs to a large extent and that improvements are achieved when the application techniques on industrial scale account for the specific properties of the photocatalysts. Furthermore, the NO degradation performance of a photocatalytic concrete paving block has been modeled by means of the Langmuir-Hinshelwood model. The validation of the model by experimental data revealed a good agreement between experimental results and predicted values of the model. Thus, the new mix design concept allows for the performance based design of sustainable and multifunctional concrete mixes suitable for the production of concrete mass products.
|Qualification||Doctor of Philosophy|
|Award date||17 Nov 2010|
|Place of Publication||Eindhoven|
|Publication status||Published - 2010|