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The susceptibility of different aggregate types used in concrete to ASR is strongly associated with their petrography. The aim of this study is to assess the influence of the aggregate size on the ASR potential, in particular applied to the sand fractions in the size range of 0.125-4 mm. The investigation concept is based on the hypothesis that at a specific particle size reactive aggregates could change their characteristic influence in mitigating ASR instead of promoting it. For the study of the size dependent behaviour mortars are prepared, considering aggregates of different reactivity, including very reactive, slow-late and quasi non-reactive types. The analysis is based on a stepwise substitution concept, in which mortars with a constant overall grain size distribution are compared, while only one size fraction of the non-reactive base aggregate is substituted by a reactive aggregate type of this specific size fraction. For the expansion experiments an accelerated mortar bar test (80°C, immersed in NaOH solution) was applied. The results show that the slow-late reactive greywacke yielded a strong reduction of the expansion below an aggregate size in the range of 0.5-1 mm. On the other side with the very reactive borosilicate glass, the expansions increased steadily with decreasing size. To validate if the acquired expansions were caused by ASR, thin sections were analysed. Mainly, higher expansion values were consistent with extensively more amounts of ASR indicators.
It is known that the spalling risk of dense, high-strength concretes (HSC) can be reduced by the addition of polypropylene (PP) fibres and, in particular, PP-fibres that have been pre-treated using electron irradiation. It is presumed that the enhanced reduction in spalling resulting from electron irradiation pre-treatment of the fibres can be attributed to enhanced penetration of the molten fibre material into the micro-cracks around the fibres, due to their significantly decreased viscosity. So far there has been no experimental evidence for this. Against this background, this paper gives a com-parative analysis of the mode of action of PP-fibres with and without pre-treatment using multi-scale test methodology.
Initially, fire tests on small-scale building components with accompanying damage monitoring veri-fied that the amount of PP-fibres can be halved by using pre-treated PP-fibres without reducing the fire performance of HSC. Detailed investigations of PP-fibres carried out in a completed research project funded by DFG (the German Research Foundation) using digital scanning calorimetry and thermogravimetry measurements (DSC/TG) as well as viscometer measurements showed that the pre-treatment has no significant influence on the melting temperature of the PP-fibres. However, a drastic reduction of the melt viscosity due to the electron irradiation was detectable. Additional dila-tation tests showed that the expansion behaviour of both fibre types and their melts do not differ significantly [1]. Rather, both fibre types generate high pressures when their thermal expansion is hindered. Further detailed investigations by means of continuous heating tests with a low heating rate were carried out on separately produced concrete cylinders. These tests showed that the pre-treatment of the PP-fibres causes earlier dehydration in conjunction with stagnation of thermal expansion of the concrete cylinders (temperature reduction from 180 °C to 170 °C). This is accompanied by in-creased acoustic emission activity during the thermal expansion tests. This leads to the assumption that the pre-treatment of PP-fibres results in earlier micro-crack development. However, it was not possible to confirm this assumption by microscopic examination of drilling cores with a diameter of 30 mm exposed to defined temperatures in the range between 150°C and 300°C. Microscopic obser-vations and additional X-ray 3D computed tomography (3D-CT) scans on miniaturised drilling cores exposed to temperature cycles showed a similar networking of fibre beds by means of micro-cracks in HSC for both fibre types. However, energy dispersive X-ray spectroscopy and wavelength disper-sive X-ray spectroscopy revealed fundamental differences in the penetration capacity of the fibre melts of the two fibre types. The increased penetration of the pre-treated PP-fibre melt revealed in these tests, confirms the initial working hypothesis.
The moisture condition of solid brick and sandstone walls of historic buildings may be examined and monitored non-destructively and effectively by means of a novel combination of test methods which provide useful information on planning and monitoring rehabilitation and maintenance measures.
Results are presented of an interdisciplinary research project of BAM on the moisture balance in the main cornice area of the Berlin Zeughaus. The main part of the investigations was carried out in 1994 and 1995. The quality of the prognosticated drying out process has been verified annually by means of measurements up to 2002. The depth-resolved local moisture determinations were accomplished with a microwave method developed by BAM. The moisture profiles revealed excessive moisture in the building element and reflected the slow drying process. Additionally, endoscopic examinations and chemical and physical analyses of miniature samples were carried out as well to help interpret the results. Hygrothermal data could be calculated from the quasi non-destructive tests and the parameters determined by the laboratory tests. Based on the 1995 measured moisture profile in the building element, the predicted simulation calculation indicated that a relatively long drying out process must be anticipated. Therefore the planned waterproofing sealing can at the earliest be applied to the surface of the building element in 2005. The good correlation of predicted and measured moisture profiles of the past years demonstrates the high quality of the new combination of test methods.