Sumio Horiuchi

Effective use of fly ash slurry as fill material

A lot of effort has been put into increasing coal ash utilization; however, 50% of total amount is disposed of on land and in the sea. Several attempts have been reported recently concerning slurried coal fly ash use for civil engineering materials, such as for structural fill and backfill. The authors have studied this issue for more than 15 years and reported its potential for (1) underwater fills, (2) light weight backfills, and (3) light weight structural fills, through both laboratory tests and construction works. This paper is an overview of the results obtained for slurry, focusing on the following. (1) Coal fly ash reclaimed by slurry placement shows lower compressibility, higher ground density, and higher strength than by the other methods. This higher strength increases stability against liquefaction during earthquake. (2) Higher stability of the fly ash ground formed by slurry placement is caused by higher density and its self-hardening property. (3) Stability of fly ash reclaimed ground can be increased by increasing density and also by strength enhancement by cement addition. (4) Technical data obtained through a man-made island construction project shows the advantages of fly ash slurry in terms of mechanical properties such as higher stability against sliding failure, sufficient ground strength, and also in terms of cost saving. (5) Concentration in leachates from the placed slurry is lower than the Japanese environmental law. (6) In order to enlarge the fly ash slurry application toward a lightweight fill, mixtures of air foam, cement and fly ash were examined. Test results shows sufficient durability of this material against creep failure. This material was then used as lightweight structural fill around a high-rise building, and showed sufficient quality. From the above data, it can be concluded that coal fly ash slurry can be effectively utilized in civil engineering projects.

Field Test of Ethanol/Bentonite Slurry Grouting into Rock Fracture

Crystalline rocks have fractures which may cause unexpected routes of groundwater seepage. Cement grouting is one of the most effective methods to minimize seepage; however, cement materials may not be suitable for the purpose of extra-long durability, because cement is neutralized or degraded by chemical and physical influence of chemical reaction. Natural clay like bentonite is one of the most promising materials for seepage barrier; however, water/bentonite grout is so viscous that enough amount of bentonite can not be grouted into rock fractures. To increase bentonite content in grout with low viscosity, the utilization of ethanol as a mixing liquid was studied. Ethanol suppresses bentonite swelling, and more bentonite can be injected more than that of water/bentonite slurry. In this paper, grouting into in-situ rock mass fracture from the ground surface was tested to investigate the barrier performance and workability of ethanol/bentonite slurry as a grouting material.

Coal Fly ASH Slurries for Back-Filling

Publisher Summary This chapter discusses the coal fly ash slurries for back-filling. In Japan, more than 4 million tons of coal ashes are annually discharged from power plants, and 60% of the total coal ash is disposed. Its use as a construction material is the main focus of such investigations. Tunneling and shielding are used for excavation, and back-filling is an important technology for minimizing environmental impact, such as settlement of ground or leakage of ground water. As a conventional back-filling grout of shields and tunnels, cement/water slurry and sodium silicate solution are injected together by the 1.5 shot method. Because coal fly ash has a high pozzolanic activity and good fluidity, it has been used as a component of a variety of grouts. It seems well-suited for being a major component of the primary slurry for back-filling grout. The chapter discusses the applicability of coal fly ash as the main component of back-filling grout, based on results obtained in a series of laboratory tests. Two types of fly ashes from Australian coals are discussed in the chapter. Since strength development of the slurry can be easily controlled by the amount of sodium silicate added, the grout can be used for back-filling and for a variety of construction works.

In-situ Utilization of Waste Bentonite Slurry

Abstract The increase in waste bentonite slurry, being discharged through substructural constructions, has become a serious problem because of its negative environmental effects and the decrease in the capacity of disposal sites. This paper describes two methods to utilize the waste slurry: in-situ slurry solidification and cast in place slurry-cement material. Therein the effectiveness of sodium carbonate with respect to viscosity decrease of the mixtures, and higher compressive strength of the solidified slurry are confirmed through laboratory tests and field application. Also, the additions of a retarder and a dispersant make long-distance transportation possible by preventing segregation. This procedure will help in the development of low-cost recycling systems involving collection, processing, transport and utilization.