Mixing Reservoir Sediment with Fly Ash to Make Bricks and Other Products

Taiwan (the Republic of China) relies heavily on reservoirs for water supply, flood control, irrigation, hydropower, and recreation. The sedimentation of such reservoirs over the years has caused large capacity losses of the reservoirs, threatening the wellbeing of the island nation. Dredging (including excavation of exposed reservoir bank and bottom during low flows) has been used to remove the deposited sediments. How to best dispose of or utilize the dredged sediment remains an important challenge to Taiwan and many other nations. The purpose of this paper is to describe an ongoing research project seeking to utilize the dredged reservoir sediments for making bricks and other construction or gardening products (blocks). Fly ash is used as a cementing agent to facilitate the making of such bricks and blocks. The project is exploring two alternative methods to make bricks from reservoir sediment: a high-temperature and a room-temperature process. The high-temperature process is similar to the use of clay to make fired-bricks in conventional brick manufacturing; a temperature of the order of 1000 o C is required for the clay to vitrify. This process does not require the use of fly ash, though adding fly ash to the sediment may be desirable in situations such as when there is a need to find a beneficial use of the fly ash, or when it is difficult to form and maintain good brick shapes without fly ash prior to firing/vitrification. The room-temperature process for making sediment bricks uses fly ash. In this process, reservoir sediment is mixed with fly ash and a small amount of water. The mixture is then compacted in a mold (die) to form an agglomerate of brick shape or other desired shapes -- depending on the mold shape. Because the fly ash in the mixture contains cementitious materials such as CaO, upon setting and curing, hard and strong bricks, similar to concrete bricks, can be produced. The preliminary study shows that for bricks of good strength, either type C fly ash must be used, or some CaO must be added to the type F fly ash. Even though this study is still ongoing and inconclusive, it does show that strong bricks can be made at room temperature by using fine sediment mixed with fly ash, with or without the addition of lime (CaO), depending on the CaO content in the fly ash used.