Carbonation of filler type self-compacting concrete

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Impact of air entrainment on the microstructure and mechanical performance of high performance mortar

At the Magnel Laboratory for Concrete Research an intensive vacuum mixer which can regulate the air pressure is available. As such the amount of entrapped air in cementitious materials can be varied. The effect of the reduced air content due to vacuum mixing on the rheology and workability was already investigated in previous work. Furthermore, the previous work investigated the influence of entrained air on the rheological properties. The impact of vacuum mixing on the compressive strength and the microstructure of (ultra)high performance mortar is documented elsewhere. However, the impact of air entrainment on high performance mortar has not yet been published. Therefore, this paper will focus on the evolution of the pore structure of air-entrained high performance mortar by using mercury intrusion porosimetry, fluorescence microscopy and air void analysis. This data will enable to verify the pore diameters, often used to explain the evolution of the rheology by the ratio of shear stresses and the surface tension. Furthermore it explains the evolution of the density, the compressive strength and the bending tensile strength. The air entrainment was varied between 0 % abd 2.5 % wt.cement. As a consequence the air content was systematically increased. In case of the air void analyser, the amount of air cavities was increased from 1 % to 14 %. From the cumulative air void fraction it was noticed that pores with a diameter of 80 µm were dominant in the mortar. From data of the mercury intrusion porosimetry the amount of capillary pores was increased from 7.4 % and 22.2 %. The critical diameter at lower percentage of air entrainment was 40 nm, a more continuous curve was obtained for the highest percentages. Furthermore, the amount of pores situated between 10 µm and 100 µm were limited or not existing. In conclusion, this paper highlights the underestimation of the lareger air pores by mercury intrusion porosimetry. Besides this, the decrease in compressive strength and bending tensile strength can be explained by the changes in the pore structure. Finally, it was checked whether the increase in plastic viscosity due to air entrainment was caused by the air bubbles or by the polymer itself

Structural and thermal performances of topological optimized masonry blocks

Structural topology optimization is the most fundamental form of structural optimization and receives an increasing attention from engineers and structural designers. The method enables the exploration of the general topology and shape of structural elements at an early stage of the design process and gives rise to inspiring and innovative improvements. In this paper, topology optimization as a principle is used to design new types of insulating masonry blocks. Two main objectives are addressed: maximizing the structural stiffness and minimizing the thermal transmittance. The first part of this paper uses these objectives to create new block topologies. A general problem is formulated and the influences of boundary conditions, external loading, and filter value on the resulting geometry are discussed. In general, maximizing the stiffness is in strong contrast to minimizing the thermal transmittance. This causes problems not encountered in conventional topology optimization. Nevertheless, by adjusting the interpolation schemes and adding multiple load groups, convergent solutions are found. An isotropic material model with an enforced solid-or-empty distribution is considered as the primary method. The optimized block topologies are then thoroughly analyzed to review their structural and thermal performance using the commercial finite element software Abaqus. The direct compressive strength of the block is a measure of the structural performance and the equivalent thermal conductivity gives an indication of the thermal performance. The second part then gives some thoughts on three-dimensional optimization and the incorporation of mesostructures in the design

Vibrated concrete vs. self-compacting concrete: comparison of fracture mechanics properties

This study focuses on the fracture mechanics aspect of self-compacting concrete, compared to vibrated concrete. The most commonly used experiments to investigate the toughness and cracking behaviour of concrete are the three-point bending test (3PBT) on small, notched beams, and the wedge-splitting test (WST) on cubic samples with guiding groove and starter notch. From the resulting P-CMOD curves (applied load versus crack mouth opening displacement), different fracture parameters, such as fracture energy and fracture toughness, can be extracted. Moreover, using inverse analysis, the sigma-w relationship (tensile stress versus crack width) can be derived. This paper lists the results of a series of tests on samples, made of VC, SCC of equal strength, and SCC with identical w/c factor. Subsequently, a comparison of the mechanical characteristics is made, revealing important differences regarding several fracture parameters

Verification of the bursting and spalling formulas in the FIB model code by finite element analyses of anchorage zones of pretensioned girders

In order to predict the stress and possible crack distribution in the anchorage zones of pretensioned girders several models have been developed as can be found in the fib Model Code, the ASHTOO code or Eurocode 2. In this paper, the bursting and spalling formulas from the fib Model Code are evaluated by finite element calculations since some issues could be raised when applying the proposed formulas for industrial applications, especially for beams of limited dimensions. The effect of the upper strands, the assumed stress distribution at the opposite side of the equivalent symmetric prism, the stress transfer diagram along the strands and the effects of the strand position relative to the simplified resultant forces remain unclear. Accordingly two-dimensional finite element models were developed to gain insight into the bursting and spalling formulations from the fib Model Code. The numerical models render stresses and the stress flow results, which allow a more clear coupling to well-known strut-and-tie models. The results indicate that for various strand configurations, especially for small beams, the fib formulations may be too conservative