MEASUREMENT OF WET COLOR CHANGE OF BRICKS DURING DRYING

Abstract

 Japan is located in the warm and wet climate zone. Therefore, from the standpoint of visual assessment of landscape design, it is important to take care of the color changes of building and civil engineering materials in the rain. It is well known that hygroscopic solids, such as concrete, show wet colors; Their lightness values become lower and their chroma values become higher when they get wet. A lot of results of wet color measurements were reported in the past. However, these previous reports measured only two states, dry and wet. There are no detailed reports of color changes during wetting or drying process.

 Suppose that there is a material that shows wet color. It is expected that its color change during wetting or drying process will depend on the degree of its wettability. This means that, two materials showing the same wet colors in the rain may show different colors after the rain stopped, i.e., during drying. This information will be necessary and useful in the landscape design under changing weathers.

 In this paper, we measured the color change during drying of beige-, red- and brown-colored garden bricks. In the experiment, we soaked the bricks in distilled water for 30 minutes to wet them completely. Then, after taking them out from water, we measured their color changes during drying within 1 minute, at five-minute interval to 60 minutes, at ten-minute interval to 90 minutes, and at 120 minutes. In the experiment, we let bricks dry naturally at room temperature 23±1 ℃ and relative humidity 50±5 %.

 The results are as follows: The drastic color change arose at 5 minutes for red brick, and between 15 and 20 minutes for beige brick. For brown one, the gradual color changes occurred until 40 minutes. These color change differences during drying can be possibly explained by their differences of water content ratio.