Stack upon stack of old tires fill one corner of Fenglin Junior High in Talinpu. "A hundred thou sand of them altogether," says section chief Shiau Jia-sheng of the Kaohsiung Dept. of Environmental Protection. Three years ago environmental departments around Taiwan began collecting used tires in an effort to counter the spread of dengue fever, by depriving mosquitoes of a common breeding ground. It was probably in Kaohsiung that the most tires were collected. The department planned to create a fishery by using them for an artificial fish hatchery on the sea bed, having first ascertained that the tires could not pollute the sea.

But the recyclability of used tires is nothing in comparison to that of furnace slag and fly ash.

In building the new sea barrier at Talinpu, the traditional concrete blocks of poured cement have been replaced by blocks cast from a compound of water, gravel and cement, mixed with at least 64% furnace slag and fly ash. "In terms of rock costs it is 50% more economical," says Shiau, although on this occasion extra research and testing to allow for this being the first such use of the mixture meant that it only cut costs by about one third.

Chen Chen-chuan, professor of civil engineering at National Taiwan University and a national authority in concrete research, elaborates: "Concrete with furnace slag and fly ash added lacks initial period strength in construction, but initial period strength is not always necessary, especially in precast and large area structures like dams, dykes, roads and large-scale foundations. The addition of furnace slag and fly ash to cement is therefore very widespread overseas."

In fact a 35% mix of fly ash as a cement substitute was used in construction of the Feitsui Dam four years ago, to avoid the cracking that can occur in concrete due to the fast release of heat from cement.

Chen, who is in charge of concrete research on the sea reclamation project, says that he has yet to see foreign research reports into the general uses of furnace slag cement and fly ash cement, although neither are considered new in other countries.

More of a problem for him is that the quality of Taipower coal is not uniform, and that furnace slag from China Steel is produced through different methods, some by air-cooling and some by water-cooling. These and other factors meant that it took a year of testing before the new composition was successfully arrived at.

The first four months were spent in the laboratory finding the best ratio of constituents, after which research shifted to Talinpu for exposure to the on-site atmospheric conditions and cooperation with the mixing plant. After the best part of a year the finished product emerged.

More than just lowering costs, this engineering project also has environmental benefits according to Chen, by conserving energy and natural resources. Kilogram for kilogram it takes half the energy to produce furnace slag cement that is needed for regular cement. Additionally, the cement industry at present relies on limestone and clay for its raw materials, turning whole hillsides into vast eyesores and using up natural resources that future generations may never see.

For this reason regular cement is required to be at least 5% furnace slag in Japan, while in Holland the concrete dykes that keep the sea at bay contain cement of up to 70% furnace slag. The low use that is made of furnace slag and fly ash here at home has a lot to do with unwillingness on the part of the domestic cement industry, and the building industry is not interested because construction is usually carried out at great pace, which could be hampered by cement that lacks initial period strength. Another problem is that in the past unscrupulous operators, greedy for the savings to be made from using furnace slag and fly ash, have mixed the cement without regard for the correct ratios, and jeopardized safety, which naturally deters large companies anxious to protect their reputations.

But as Chen Chen-chuan points out, "resources are limited in Taiwan and should be cherished." His hope is that "in the not too distant future, and under conditions of the strictest quality control, we shall see furnace slag used on a large scale in the current national six-year plan."

[Picture Caption]

The sea reclamation project has meant a place to "settle down" for furnace slag from China Steel.

The piled concrete jacks are made from furnace slag, fly ash and a lesser proportion of cement.

The piled concrete jacks are made from furnace slag, fly ash and a lesser proportion of cement.