Design of self compacting concrete by particle packing optimization

Civil Engineering and Geoscience

Measuring water demand or packing density of micro powders: Comparison of methods

Civil Engineering and Geoscience

Design of ecological concrete by particle packing optimization

The goal of this research project on Ecological Concrete was to reduce the CO2-emission of concrete and to reuse secondary materials form concrete production and other industries simultaneously. This also minimizes the use of natural resources and the production costs. To replace cement in concrete in a safe way, the main question answered in this thesis was how particle packing models can be used to predict the mechanical properties of ecological concrete from its basic components. To optimize ecological concrete on packing density the Compaction-Interaction Packing Model was developed, in which particle interaction of fillers is taken into account. The developed cyclic design method for ecological concrete, which is based on the packing density, water demand and strength, enables concrete mixture optimization based on performance. Demo projects and laboratory experiments showed that more than 50% cement could be saved and the CO2-emission could be reduced with 25%, while at the same time the concrete mixtures still satisfied the demands for appropriate use.Design and ConstructionCivil Engineering and Geoscience

Using particle packing technology for sustainable concrete mixture design

The annual production of Portland cement, estimated at 3.4 billion tons in 2011, is responsible for about 7% of the total worldwide CO2-emission. To reduce this environmental impact it is important to use innovative technologies for the design of concrete structures and mixtures. In this paper, it is shown how particle packing technology can be used to reduce the amount of cement in concrete by concrete mixture optimization, resulting in more sustainable concrete. First, three different methods to determine the particle distribution of a mixture are presented; optimization curves, particle packing models and discrete element modelling. The advantage of using analytical particle packing models is presented based on relations between packing density, water demand and strength. Experiments on ecological concrete demonstrate how effective particle packing technology can be used to reduce the cement content in concrete. Three concrete mixtures with low cement content were developed and the compressive strength, tensile strength, modulus of elasticity, shrinkage, creep and electrical resistance was determined. By using particle packing technology in concrete mixture optimization, it is possible to design concrete in which the cement content is reduced by more than 50% and the CO2-emission of concrete is reduced by 25%.Structural EngineeringCivil Engineering and Geoscience

Impact of cracks on chloride-induced corrosion and durability of reinforced concrete structures - a literature review

Structural EngineeringCivil Engineering and Geoscience

Application of acoustic emission measurements in the evaluation of prestressed cast in-between decks

A large number of concrete structures, that is built in the sixties and seventies of the twentieth century, need to be re-evaluated. It should be judged whether their capacity is still sufficient for the increased traffic loads. Acoustic emission (AE) is a non-destructive technique that can possibly be used to get a better insight in the structural state of these concrete structures. However, interpretation the AE measurements is challenging and is even more difficult when the concrete is cracked by for example alkali–silica reaction. Due to the existing cracks the wave attenuation affects the acoustic emission measurements. For an investigation into the capacity of pre-stressed cast in-between decks a 1:2 scale bridge was loaded in the Stevin laboratory of Delft University of Technology under two-way shear. In this preliminary research it was investigated whether AE-measurements can be used to get an idea about the structural condition of a structure, or more precise, to what extent the ultimate capacity is reached. For testing the concrete in-between decks a cyclic loading procedure is applied. It appeared that cyclic loading resulted in a lower capacity in comparison with the previously performed static loading experiments. There was no AE indication of early failure due to cyclic loading. Usually applied parameters, like ‘Kaiser Effect’ and ‘Calm Ratio’ are investigated. Furthermore, it was investigated whether the location of cracks could be determined by the emitted sound during the fracture process and applying a relatively large numbers of AE-sensors (so-called source location). In this article the performed AE measurements are reported and results discussed.Structural EngineeringCivil Engineering and Geoscience

The use of particle packing models to design ecological concrete

Ecological concrete can be designed by replacing cement with fillers. With low amounts of cement it becomes increasingly important to control the water demand of concrete mixtures. In this paper a cyclic design method based on particle packing is presented and evaluated on the basis of experiments on cement pastes combined with quartz powder. The packing density of sixteen pastes is measured using the mixing energy test. Furthermore, the cement pastes were tested on compressive strength at 7 and 28 days. Adding quartz powder M600 can increase the packing density by more than 10%. This means that fine quartz powders can improve the packing density to such extent that the cement content can be decreased while simultaneously the water cement ratio is decreased. This occurs for pastes with a packing density higher than the completely saturated packing density of cement. Additional strength tests were performed on two mixtures with constant water cement ratio and showed a 15% strength increase when 20% of the cement was replaced by quartz powder M600. In the design procedure for ecological concrete, increased strength efficiency can be balanced by lowering the amount of cement.Design and ConstructionCivil Engineering and Geoscience

Reliability assessment of existing reinforced concrete bridges and viaducts through proof load testing

In the assessment of existing infrastructure performing only a desk study is often not sufficient to determine the structural reliability of a bridge or viaduct. For concrete structures gathering field data by performing a proof load test offers detailed information about the structural performance. However, the relation between the magnitude of the load and the structural reliability is not immediately clear. In the present study the challenges in determining the target load and the uncertainties that require attention are described. An approach is presented that addresses the time-dependent character of the structural reliability, the need for accurate stop-criteria, the knowledge level and spatial uncertainty. It is shown how both past traffic loads and a proof load test may contribute to the proven strength of a structure. The described methodology provides a starting point towards a flexible approach for proof load testing in which structure-specific information and requirements are considered.Concrete Structure

Influence of particle packing density on the rheology of low cement content concrete

Optimizing concrete mixtures with regard to cement content is one of the most important solutions in sustainable concrete design. Workability o f these low cement content or ecological mixtures is very important. Eleven mortar mixtures are presented, which show how a higher packing density can be used to obtain mixtures that require less water. Higher packuig densities reduce the void volume between the particles and therefore decrease the amount of water necessary to fill this void volume. The reduced amount of water and lower water/cement ratio can be used to save a certain amount o f cement when concrete is designed for a fixed strength class.Structural EngineeringCivil Engineering and Geoscience