Process for using sludge from geothermal brine to make concrete and

Abstract

A process is provided for using silicious sludge (filter cake), obtained by precipitation of silica from silica-rich geothermal brine, to make a concrete material (geocrete). The process includes combining the sludge with a cementing material, such as portland cement and/or flyash and activating the cementing material with an activating media. When portland cement is used as the cementing material, the activating media is water. In such case, the sludge is preferably dewatered and the residual water content is determined, the entrapped brine adding to the water content of the mixture. Preferably, the dry weight ratio of sludge to cementing material is about 2:1 to about 3:1; although, ratios as high as 9:1 can be used when high strength of the geocrete is not required. The preferred amount of water used is about 40 weight percent, including water content of the sludge, which may typically be between about 10 and about 30 weight percent. The sludge may contain hazardous or toxic materials which precipitate from the brine with the silica and which are present in the entrapped brine; therefore, the sludge may be water washed before use to flush out residual brine and some contaminants contained in the sludge or may be otherwise treated. Chlorides present in the brine, which may undesirably accelerate setting time, are also removed by the water wash. Slurry mixability of the geocrete is enhanced by the addition of coarse aggregate to the mix, the preferred amount of aggregate added being less than about 50 weight percent of the dry mixture. A cement having a 60 day cure compression strength of at least about 3000 psig is thereby provided. A corresponding composition of concrete is provided.