The Use of a Finely-Divided Mining By-Product in RCC for Dam Construction


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Title: The Use of a Finely-Divided Mining By-Product in RCC for Dam Construction

Author(s): Richard Gagne, Danielle Martin, Francine A. Blais, Alain Prezeau and Salsutio Guzman

Publication: Special Publication

Volume: 172


Appears on pages(s): 103-118

Keywords: Compressive strength; heat of hydration; modulus of elasticity; permeability; roller compacted concrete; vebe tests

Date: 12/1/1999

The ore enrichment process used by QIT Fer et Titane of Sorel, Quebec, Canada generates a mining by-product referred to as OPP fmes (Ore Pretreatment Plant Fines). It is a fine dark powder, composed mainly of ilmenite, hematite, magnetite, and quartz, with a particle-size distribution similar to ASTM Type I I cement. The aim of this research project was to assess the potential use of OPP fines as a filler material in RCC for dam construction. A three-variable factorial plan of experiment was used to analyze the effects of the total dosage of fine particles (cement + OPP fines), the OPP fines replacement ratio (OPP fines/[ OPP fmes+cement]) and the water/fines (W/[OPP fines+cement]) on the fresh and hardened properties of RCC. The properties evaluated were: Vebe time, compressive strength, modulus of elasticity, water permeability, and heat of hydration. The research program also included a full-scale field test where approximately 140 m3 of RCC were produced to build an 8 m x 8 m x 2 m slab to evaluate the in situ properties of an RCC containing the OPP fines. This RCC was designed to meet Hydro-Quebec’s typical specifications for dams. The results show that OPP fines is a very effective filler in RCC because its particle-size distribution is very similar to that of the cement. Therefore, a large proportion of the total fines content (cement or fly ash) can be replaced by OPP fines without significantly changing the workability of the RCC. A simple mathematical model, based on the results of the factorial analysis, is proposed to select the total fines content, the OPP fines replacement ratio, and the water/fines ratio of an RCC mixture as a function of the required Vebe time (5 s to 60 s) and 91-d compressive strength (5 to 25 MPa). The results of the in situ testing program show that it is possible to produce an optimized RCC with a 91-d compressive strength of 23 MPa and very low heat generation, when using 120 kg/m3 of cement (ASTM Type II) and 80 kg/m3 of OPP fines (40% OPP fines and 60% cement).