July 27, 2000 Coal Ash for Coloring Development of high-strength, low-absorption "coloring aggregates for colored pavement" that utilize coal ash from electric power plants Takenaka Corporation Shikoku Electric Power Company, Techno-Resource, Takenaka Corporation, Takenaka Civil Engineering & Construction Co., Ltd., and Takenaka Road Construction Co., Ltd. teamed up to develop "coloring aggregates for colored pavement" (patent pending) that utilizes the coal ash produced at coal-burning power plants. This is the first time that coloring aggregates composed primarily of coal ash have been developed to meet the need for strength and low water absorption in coloring aggregates * for asphalt pavement. * Coloring aggregates for asphalt pavement To enhance the strength of asphalt, concrete, etc., gravel, crushed stone and other such materials are usually added. Coloring aggregates, which are divided by color (browns, yellows, etc.), are used for bus lanes, crosswalks, and to separate pedestrian lanes from vehicle lanes, among other uses. Current coloring aggregates include natural stone, and man-made materials such as ceramics that have been colored and heat treated. In 1998, the latest year for which figures are available, coal-burning power plants in Japan produced 6.79 million metric tons of coal ash, of which 75 percent was recycled and the remaining 25 percent was buried in the ground as earth filling. A breakdown of the uses of recycled ash shows that 71 percent was used in cement, seven percent was used in civil engineering for roadbed materials, etc., six percent was used in the construction industry for boards, etc., two percent was used in agriculture as fertilizer, and the remaining 14 percent was used for other purposes. (Source: Center for Coal Utilization, Japan). Given that coal is being considered as a stable and economic fuel source should there be another oil crisis, and that oil-burning power plants are being converted to coal and more coal-burning plants are being constructed, the production of coal ash will surely increase in the coming years. However, due to declining demand in the construction industry, and the expectation that there will be no major growth in demand for coal ash for use with cement, new techniques and technologies must be developed to find other ways to recycle coal ash. Brief description of "coloring aggregates for colored pavement" Coal ash with a very tiny particle diameter of 20 microns or less made it possible to produce fine and dense coloring aggregates of high strength and low absorption, which was difficult with conventional materials. Absolutely no additional coloring agents are used; the natural coloring tendencies of the coal ash itself produce subdued browns.

"Coloring aggregates for colored pavement"

The coloring aggregates are produced as follows: 1) Particles having diameters of more than 20 microns are filtered out. 2) Clay is added to provide cohesion. 3) Water is added to knead the clay and ash together. 4) The material is rolled out into sheets and heated at high temperature in a kiln. 5) The finished produced is broken into pieces, which are sorted by size. This is roughly the same process by which earthenware is made, meaning that existing facilities of ordinary tile makers can be used. If the materials are heated at too high a temperature, they turn black, and if the temperature is too low, they become whitish in color. In either case, the strength of the materials cannot be guaranteed, so it is necessary to keep the temperature at the proper level.

The five companies involved in the joint development project are working to expand the recycling of coal ash by promoting its use in areas where demand is growing, such as accents for roads, parks, plazas and parking areas, as well as for road indicators. If demand expands and the amount produced increases, the resulting large cost reductions alone would be enough to create new markets for coal ash.

Finished water-permeable colored asphalt

General information about the five companies Shikoku Electric Power Co., Inc. Head Office: Takamatsu City; President: Atsuhi Ohnishi; Capital: 145.5 billion yen Techno-Resource Head Offfice: Takamatsu City; President: Tateki Nagaoka; Capital: 50 million yen Takenaka Corporation Head Office: Osaka City; President: Toichi Takenaka; Capital: 50 billion yen Takenaka Civil Engineering & Construction Co., Ltd. Head Office: Tokyo; President: Koichi Takenaka; Capital: 7 billion yen Takenaka Road Construction Co., Ltd. Head Office: Tokyo; President: Yukichi Atarashi; Capital: 300 million yen