Cool pavement / Water-retentive blocks take the heat off urban areas

(Japan) It was blazing hot this summer, especially in urban areas where temperatures did not fall below 25 C even at night. The cities were hit especially hard because concrete and asphalt retain solar heat, giving rise to higher air temperatures in a process known as the heat island phenomenon, a growing problem across the nation. To help solve the problem, Matsuo Corp. in Ibaraki has developed a water-retentive pavement named Eco-Pavers: Tamochi-mannen (We’ll keep it!). The blocks of pavements are equal in strength to ordinary pavement blocks but they absorb and retain rainwater and groundwater. When the retained water evaporates, it reduces the heat on the surface of roads through vaporization, resulting in lower temperatures in the area. This mechanism works much like a sprinkler system to reduce temperatures. The product is also environmentally friendly: It uses recycled waste materials such as concrete, asphalt and the incinerated ash of urban garbage; it saves energy by reducing the need for air-conditioning; and it contributes to the development of a recycling-oriented society. In July, the blocks were designated as “This Year’s Product” under the Osaka prefectural government’s “Model Program for Promoting the Active Order Placement of New Technologies of Venture Companies,” which aims to use new technologies developed by venture firms for public works projects. According to Hitoshi Nishiwake, 46, the firm’s third president, the company leads the block manufacturing industry in the use of industrial waste materials. In the past, the firm had used sand from beaches and rivers to make the cement for its concrete products, mixing in sandstone as an aggregate. Its use, however, was limited out of concern for the environment. More than 30 years ago, the firm began using iron and steel slag generated from blast furnaces at a steel plant. For the past 10 years, it has used slag (sandy incineration ash) generated from a solid waste incineration and melting process at the Ibaraki City Environment and Hygiene Center and also slag generated from sewage sludge melting facilities in Kyoto, Osaka and Hyogo prefectures. Five years ago, Matsuo began using recycled crushed stones from concrete and asphalt generated from construction sites as an aggregate. Nishiwake said: “We’ve tried used and recycled materials, and the three types of paving blocks we made were officially designated by the Osaka prefectural government as ‘recycled products’ last year.” Matsuo, which will mark its 70th anniversary next year, began developing water-retentive blocks in June 2002 as the heat island phenomenon became a growing public concern. “Unpaved roads can be cooled by sprinkling water on them in the hot summer,” Nishiwake said. “But since roads are usually paved with concrete and asphalt, I thought we could do something about it.” To manufacture ordinary concrete products, cement is mixed with various materials, then water is added. The mixture is then poured into molds, where it solidifies in less than a day. “Our firm works differently,” Nishiwake said. “We knead a thick concrete in a mixer, put it into molds, press and vibrate it into shape and then remove it from the molds quickly. The entire process–called vibration concrete molding–is done automatically by machine. “As our concrete is thick, water-retaining voids remain in the finished product,” he said. He added that the conventional method of using a lot of water to make concrete would not work because it makes the concrete denser and eliminates the voids. According to the size of voids, the blocks become either water-permeable or water-retentive. Water-permeable blocks do not retain rainwater as it runs through the voids. However, water-retentive blocks not only retain rainwater, but they are helped by the capillary phenomenon to absorb and store rainwater and groundwater. The paving blocks thus always retain water for evaporation. Nishiwake said: “The voids must be micron-size. So we use materials with a density that allows them to fill with water very slowly, and water-permeable blocks have a rougher texture than that of denser ordinary blocks.” One of the challenges, however, is to maintain the strength of products that have many voids. “In a process of trial and error we used various materials and changed their mixtures,” Nishiwake said. “We mixed incinerated ash with recycled aggregates, such as used concrete and asphalt.” In October 2003, the first water-retentive blocks were completed. The firm then tested water-retentive blocks, water-permeable blocks and ordinary blocks to gauge their water absorption and retention. The three types of blocks were left to soak in water for 24 hours, then weighed to see how much water had been retained. The test showed that water-retentive blocks are superior to ordinary blocks in both water absorption and retention. Forty-eight hours after the blocks were removed from the water, they still retained 60 percent or more of the water they had absorbed. “The strength of water-permeable blocks is about 60 percent of that of ordinary blocks,” Nishiwake said. “Water-retentive blocks are as strong as ordinary blocks and strong enough to bear the weight of vehicles. They can be used anywhere. And with their capacity for retaining water, they can be used as vegetation blocks, too.” The firm first tested the water-retentive blocks on the lots of privately owned houses. The surface temperature of the blocks was lower than the air temperature by 2-3 C and lower than the surface temperature of ordinary blocks by 10 C or more. After confirming that the product reduced temperatures, the firm jumped into the market in April last year. “We paved a square at a housing complex on Port Island in Kobe and the square in front of JR Himeji-Bessho Station,” Nishiwake said. “We’ve made [the blocks] in various colors to blend in with the surrounding landscapes.” When the prefectural government announced this year’s model program for new technologies, called “Measures for Heat Island Phenomenon and the Promotion of a Recycling-Oriented Society,” the firm applied, and in July, the product was chosen from six applicants. The firm will lay the pavement blocks for sidewalks on National Route No. 308 in Higashi-Osaka, Osaka Prefecture, and other places. The firm has received many inquiries from across the Kansai region, and Nishiwake hopes the blocks will be used more widely. He said: “We’ve worked with used and recycled materials for a long time. I personally inherited the spirit of “mottainai” [literally: “It’s a shame to waste things.”] from my ancestors. As global warming progresses, we’ll take a natural approach to conserve the global environment and continue contributing to it company-wide in the future.” According to Yasuhiro Onaha, assistant director of the prefectural government’s waste and recycling division, Eco-Pavers were chosen for the government’s new technology initiative model project. The product was also one of the first recycled products officially acknowledged by the government in a program launched last fiscal year. In the program, the government examines products that were manufactured with used and recycled materials generated in the prefecture. As a result, the government has acknowledged 176 products that promote the use of recycled materials. Onaha said: “We believe products made from recycled materials will be used more often to contribute to an environmentally friendly society. I hope Matsuo and other firms involved in the eco-business will succeed.” Yuzuru Kato / Yomiuri Shimbun Senior Writer

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