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Abstract:
The paper represents a synthesis of the aspects concerning the decorative concrete. It deals with three of the most important problems of the decorative concrete, i.e. the change of the colour, surface treatment and degradation caused by dirtiness. The following factors, which determine the change of the colour of the concrete, are analyzed: the W/C ratio; type of casing; the porosity of the casing, inadequate vibration, striking time, the hardening and using conditions. The treatments by which there can be obtained the decorative concrete, having the aspect of sandstone or marble, are presented, as follows: washing, acid treating, mechanical treatment (polishing, buffing, sanding, stone granulating, milling). The paper ends with the analysis of the factors which determine the colouring (dirtiness) of decorative concrete, the ways of preventing and remedyng them.
Keywords: Decorative concrete, the composition of the concrete, the shade, the sandstone.
1. Introduction
Concerning the decorative concrete, the shade of the concrete is very important. If, after hydration the white cement remains white, the grey cement could be of different shades sometimes very diverse and often unforseeable.
The homogeneity of the "grey" shade is influenced by the following factors:
a) the shade variation of the dry cement; the cements of the same class and resulted from the same source are not always uniform and homogeneous from the point of view of the gray shade;
b) the variation of W/C ratio - a defference of 0.05 is enough to make the shade of gray lighter (when W/C increases) or to make darker the shade of gray (when W/C decreases);
c) the variation of the casing porosity could influence the darkening of the colour of the cement - because of the decrease of W/C ratio at the contact surface between the casing and concrete;
d) the inadequate vibration determines the phenomenon of deposit of the grains depending on the diameter, on the surfaces, remaining only the cement paste;
e) the time - interval at which the striking is made; if the interval is short, the shade is light gray, if the interval is long the shade is dark gray;
f) consequently, the drying conditions after striking influence the dry and warm air determines a light colour concrete and the very dry air but very...