ICE - Institution of Civil Engineers - Virtual Library

Although it has been postulated for many years that it is excess water rather than whole water that lubricates the cementitious materials and governs flowability of paste (excess water is water in excess of that needed to fill up voids), there has been no detailed investigations to study the actual effects of excess water. This was due to the lack of a suitable method for measuring the packing density and voids content of cementitious materials. To resolve the problem, the authors have recently developed a new wet packing method that was applied herein to measure the packing densities and voids contents of cementitious materials containing different amounts of cement, pulverised fuel ash and condensed silica fume. The flowability properties of the paste formed of the cementitious materials with different water contents were also measured and correlated to the excess water contents, each determined as water content minus voids content. The results revealed that whereas an improvement in packing density would increase excess water content, flowability is governed mainly by excess water to solid volume and excess water to solid surface area ratios.

The aim of this study was to examine usability of diatomite, a natural amorphous and porous raw material, as an additional blend in an effort to improve the performances of natural pozzolan-blended cements. To this aim, varying proportions of pozzolan, diatomite and pozzolandiatomite-blended cements were prepared and chemical, physical, mechanical, mineralogical and microstructural tests were applied to the resulting cements. The test results indicated that diatomite blend may be effective in improving pozzolanic properties, reducing setting time, reducing alkali content and increasing early-ultimate strengths of pozzolan-blended cements.

The correct assessment of industrial by-products and waste materials requires an in-depth knowledge of their characteristics. In thermally activated products, the calcining conditions have an important influence on the properties and later behaviour of cementitious matrices. The present study was carried out to determine the effect of calcining conditions (2–5 h at 700–800°C) on the properties of treated paper sludge. Various chemical, physical, morphological, mineralogical and pozzolanic characteristics were evaluated in order to provide a complete understanding of the properties of the calcined sludge and the possibility of using them in the manufacture of blended cements. The results showed that the thermal conditions have a major influence on the properties of the calcined sludge, primarily the mineralogical and morphological properties, as well as the pozzolanic behaviour.

The mechanical properties of Portland cement are closely related to the chemical composition of the clinker, and particularly to the concentration of tricalcium silicate, C₃S. In the industrial production process, the clinker must be rapidly quenched, to avoid its decomposition into dicalcium silicate and lime and also to avoid the transformation from higher temperature phases to lower temperature phases. This study investigated the kinetics of thermal decomposition of the C₃S. Samples of laboratory-made C₃S were thermally treated under specific conditions to determine the continuous cooling transformation (CCT) diagram of the material. The CCT diagram of the C₃S showed decomposition rates with values that were much higher than the values traditionally accepted in the literature.

This paper deals with the pozzolanic reactivity of pyrogene oxides (represented by Aerosil) that belong to the colloidal silicas. Pyrogene oxides are highly reactive pozzolanic nanoscale additives. They react much faster pozzolanically than other commonly used pozzolans and in this way they consume the available calcium hydroxide in a much shorter time. It is shown by using in situ X-ray transmission microscopy, pH-change measurements and the strength property results that Aerosil begins to react as early as the first hour of contact with both the added calcium hydroxide in solution and with the products of the tricalcium silicate (C₃S) hydration reaction. In comparison with the other commonly used pozzolans, that is, silica fume, pyrogene oxides contribute by developing a better early and final strength. The concrete specimens that were cast by combining silica fume with small quantities of Aerosil were considered to belong to the ultra high performance class and were additionally characterised by finer pores and reduced total porosity.