A.L.A. Fraaij

Study on the development of the microstructure in cement-based materials by means of numerical simulation and ultrasonic pulse velocity measurement

The formation of microstructure in cementitious materials was simulated with a numerical model. Simulation results have been verified by measuring the evolution of the ultrasonic pulse velocity (UPV). In this contribution, the applied computer-based cement hydration model is presented. The UPV measurements are also presented and evaluated. Experiments were performed on concrete mixtures with water/cement ratio 0.40, 0.45 and 0.55. The concrete was cured isothermally at 10, 20, 30 and 40 °C. Correlations between the development of the microstructure and the evolution of UPV were found. Two critical processes were individuated. The first is the percolation threshold of the solid phase. The second is the full connectivity of the solid phase. Both in the experiments and in the numerical simulations it was possible to distinguish these critical stages. These stages are discussed and conclusions are drawn regarding the potential of numerical simulation models in the study of early age cementitious materials for quantitative analysis of hydration processes.

THREE-DIMENSIONAL MICROSTRUCTURE ANALYSIS OF NUMERICALLY SIMULATED CEMENTITIOUS MATERIALS

In order to predict the transport properties of porous media, such as permeability and electrical conductivity of cementitious materials, a better understanding of the microstructural characteristics, including the geometrical and topological properties, is required. In this contribution, the microstructure of cementitious materials is simulated by using the cement hydration model HYMOSTRUC. In this computer-based numerical model, the hydrating cement grains are modeled as gradually growing spheres, which become in contact while growing. The simulated porous medium can be described as a series of sections taken from three orthogonal directions, in which each unit (pixel) is filled either with a solid or a fluid phase (pores). Various algorithms based on a random walk process are utilized to determine the local geometrical information, such as gravity centers coordinate, perimeter and area of each individual pore. The percolating path of the fluid in three dimensions is traced by using an overlap algorithm. Both three-dimensional (3D) geometrical information and topological space characterization including branch node network and genus of the pores are derived. Calculation results of these algorithms are compared with results obtained by other microstructural models at various degree of hydration.

EXPERIMENTAL STUDY AND NUMERICAL SIMULATION ON THE FORMATION OF MICROSTRUCTURE IN CEMENTITIOUS MATERIALS AT EARLY AGE

Abstract The formation of microstructure in early age cement paste and concrete was examined with an ultrasonic experimental set-up. Research parameters included the influence of curing temperature (isothermal curing at 20, 30 and 40 °C), water/cement ratio (0.40, 0.45 and 0.55) and amount of aggregate. In parallel with the experiments, the cement hydration model HYMOSTRUC was utilized to simulate the formation of the microstructure. In this study, the cement paste was considered as a four-phase system consisting of water, unhydrated cement, hydration products and that part of the hydration product that causes the contact between the hydrating cement grains (so called “bridge volume”). A correlation has been found between the growth of bridge volume calculated with the model and the changes in the pulse velocity. It is believed that ultrasonic pulse velocity (UPV) measurements can represent a valuable tool to investigate the development of the microstructure at early age.

Electrochemical Behavior, Microstructural Analysis, and Morphological Observations in Reinforced Mortar Subjected to Chloride Ingress

The behavior of steel reinforcement was studied using electrochemical impedance spectroscopy (EIS) and polarization resistance (PR) techniques in conditions of chloride-induced corrosion in ordinary Portland cement-mortar specimens immersed in 7% NaCl for a test period of 120 days and compared to specimens immersed in demineralized water for the same period as reference specimens. This study was an initial phase of ongoing research on electrochemical methods for corrosion protection in reinforced concrete structures and aimed at investigating the applicability of widely accepted techniques as EIS and PR and their possible correlation with structural observations of the bulk matrix, relevant to cement-based materials science and product-layers distribution, to corrosion and further protection. The results indicate that the concept of EIS modeling and the components used in the latter correspond well to alterations in structural properties of the bulk matrix, while the electrochemical behavior can be additionally supported by morphological observations of the steel/cement paste interface.

The Quality Improvement of Stony Construction and Demolition Waste (CDW)

Worldwide construction and demolition waste (CDW) is currently dumped. To close the building cycle and the building materials cycle by recycling CDW in high technical applications, the technical quality of stony materials must be improved. For this purpose, concrete rubbles and brick rubbles, the two major stony constituents of CDW, should be separated from each other. Based on the differences in density and content of Fe2O3 between the two materials, a wet method of jigging and a dry method of magnetic separation are effective, tested.

Quality improvement of granular wastess—The effective way to recycle secondary raw building materials

Granular wastes have negative effects on the environment due to contamination. On the other hand, stony components in granular wastes have a potential good perspectives for utilization in civil engineering works as secondary raw building materials. To reuse such materials without environmental risks, all contaminants must be removed or reduced to an acceptable level. Therefore liberation of materials is an important step in waste treatment. For this purpose, separation and cleansing techniques are suitable. Based on the analysis of contaminants in wastes, it is discussed how to select suitable techniques. The rules for technique selection and processes for quality improvement are set up. To evaluate the environmental quality and technical quality of output products, it is necessary to check leaching behaviours and physical properties.

Clay-brick recovery from masonry debris by means of a thermal process

Publisher Summary Clay-bricks from masonry constructions are reused on a very small scale in the Netherlands. The mortar is chipped from the bricks, which is a very labor-intensive job. This chapter proposes a thermal process used for the clay-brick recovery from masonry debris. A thermal process might be a suitable technology to recycle clay-bricks. Clay-brick mortar separation can be achieved by heating to a temperature of 850°C. At this temperature cement mortar decomposes and lime decomposes at a temperature of 400°C. The recovered clay-brick must be checked on internal cracking. Internal cracking will influence the mechanical properties of the clay-brick, which can be checked by measuring the tensile and compressive strength. The difference in linear expansion coefficient between mortar and clay-brick causes shear stresses on the clay-brick mortar interface. The mortar is compressed and in the clay-brick there are tensile stresses, if there is still a bond between the two components. The mortar clay-brick interface is the weakest part of masonry and therefore might break by shear stresses. The temperature for collapsing of the interface depends on the properties of the clay-brick related to the properties of the mortar and the resistance of the interface for shear stresses.

The development of an ESEM based counting method for fine dust particles and a philosophy behind the background of particle adsorption on leaves

The multi scale benefits of urban greenery (green facades and green roofs) have attracted more and more interest of recent research work. The multi scale benefits of vegetation vary from; mitigation of the urban heat island effect, stimulation of the ecological value and biodiversity, aesthetical reasons and for example air pollution reduction. Air pollution control is at the moment mainly focussed on the reduction of fine particle concentrations. Particulate air pollution is damaging for the human health, it causes cardiovascular and lung diseases. Especially dust particles smaller than 2.5 micrometers are of great interest because they can be deeply inhaled into the respiratory system. To determine the effect of leaves on particle adsorption, micrographs are taken of ivy (Hedera helix) leaves using an Environmental Scanning Electron Microscope (ESEM). The examined leaves are exposed to a simulated rainfall in order to determine a method for particle counting on leaves and to determine the self cleaning effect of adsorbed particles on ivy leaves. The self cleaning effect is considered to be an important factor in the effectiveness of particle adsorption by leaves and the potential for resuspension of particles. Particles on pre- and post-rain leaves were counted via the ESEM micrographs using an image analyzer. Results showed that there is no significant effect on particle loss due to rain in the performed experiment. Our findings suggest that a strong Van der Waals bonding between