title: Observation and characterization of colloids derived from leached cement hydrates.
abstract: The possibility of colloid generation from cement hydrates in a cementitious repository environment has been investigated through leaching experiments. Pulverized samples of High Flyash and Silica fume-content Cement (HFSC) and 1:9 ordinary portland cement/blast furnace slag (1:9 OPC/BFS) hydrate were leached in low-salinity groundwater at three solid-to-liquid (S/L) mass ratios (1:5, 1:50 and 1:100), and two temperatures (20 and 60 degrees C) for durations of nearly 2 and 8 months. Detailed characterization of colloid populations has been undertaken by TEM coupled with X-ray analysis. In addition, the surface charge and stability behavior of colloids have been investigated. The colloid concentrations in HFSC hydrate leachates generated at 20 and 60 degrees C show similar trends with S/L ratio. The colloid concentrations of leachates with the lower S/L ratio (1:50 and 1:100) are in the range of 10(11)-10(12) particles per liter. The majority of these particles are composed predominantly of Si, Ca, and Al; the mean particle size is less than 100 nm. The lowest colloid concentrations are found in the leachates with the highest S/L ratios, and the colloid populations tend to be dominated by larger particles. HFSC-derived colloid stability is due to a high negative zeta potential at alkaline pH values, combined with a calcium concentration that is below the critical coagulation concentration (CCC) for the colloids. A preliminary interpretation of HFSC-derived colloid stability based on classical DLVO theory provides a semi-quantitative explanation of the dependence of colloid populations on the S/L ratio in the leaching experiments.
authors.affiliation: Central Research Institute of Electric Power Industry, 2-11-1 Iwado-kita, Komae, Tokyo 201-8511, Japan. tujita@criepi.denken.or.jp
authors.forename: T
authors.initials: T
authors.lastname: Fujita
authors.forename: D
authors.initials: D
authors.lastname: Sugiyama
authors.forename: S W
authors.initials: SW
authors.lastname: Swanton
authors.forename: B J
authors.initials: BJ
authors.lastname: Myatt
mesh_terms: D003102:Colloids / Q000737:chemistry*; D003252:Construction Materials; D006863:Hydrogen-Ion Concentration; D010316:Particle Size; D012989:Soil Pollutants / Q000032:analysis; D014867:Water; D014873:Water Pollutants / Q000032:analysis
chemical_list: D003102:Colloids; D012989:Soil Pollutants; D014873:Water Pollutants; D014867:Water