Einfluss der Granulometrie und des Wassergehaltes auf die Festigkeit und Gefügedichtigkeit von Zementstein

Teichmann, Thomas

kassel university press, ISBN: 978-3-89958-441-7, 2008, 202 Pages
(Schriftenreihe Baustoffe und Massivbau Heft 12)

URN: urn:nbn:de:0002-4410

Zugl.: Kassel, Univ., Diss. 2007

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Content: The resistance of concrete to gases und fluids is regulated predominantly by the adaption of the cement content and the water-cement ratio (w/c-ratio) to the environmental exposition of the concrete structure during the period of use. The lower the w/c-ratio will be chosen the lower the content of capillary pores in the hardened cement stone and the higher its resistance against environmental influences will be. On the other hand the development of ultra-high performance concretes (UHPC) has shown that by increasing the packing density of the fine particles and thus reducing the remaining voids between them the water demand of the fresh concrete was significantly reduced and the density and the strength of the cement stone was improved effectively.

In this PhD-thesis the effects of the packing density on the porosity, durability and strength of the cement matrix of ordinary concretes were investigated. Firstly pure cement mixes were evaluated as a reference.. Then the cement was substituted part by part by an increasing volume of fine powders of different fineness either filling the voids between the coarser particles and thus increasing the packing density or not. By the systematic increase of the packing density together with the adaption of the water content the effectiveness of inert fine powders was proven for ordinary concrete.

It was demonstrated, that the density and the strength of the cement stone and its resistance to harmful substances can be increased significantly even by inert but void filling mineralic powders together with the adaption of the water content and thus the w/c-ratio.

Based on the results of extensive laboratory test series a mathematic model based on non-linear algorithms was developed that combines the porosity and the strength at a certain packing density and w/c-ratio with the calculated water film thickness covering the surface of the particles. As a result efficiency-coefficients (k-values) for the effectiveness of inert fines compared to the equivalent amount of cement can be determined. The coefficients are depending on the w/c-ratio. As an example with a w/c-ratio of 0,25 and a substitution of 20 vol.% of a coarsely ground cement CEM I 32,5 R by a fine, packing-effective quartz powder, a k-value of 1,87 results. If the w/c-ratio increases up to 0,45 the k-value declines to 0,21. Similar results and reactions are appearing when other powders like e.g. fine limestone flours are used.

In summary, the model, which is based on extensive laboratory test series, allows to predict the compressive strength and/or the matrix density from the water-film thickness and the packing density. It is a valuable instrument to improve ordinary or high performance concretes technically and economically by the use of grain optimized inert or reactive mineralic fillers.

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