CEMENT-BASED MATERIALS IMPROVED BY SURFACE-TREATED ADMIXTURES

Cement-based materials containing solid admixtures such as silica fume and short carbon fibers were improved by surface treatment prior to using the admixtures. Mortar with high consistency, even without a water-reducing agent, was obtained by using silica fume that had been surface treated with silane. The tensile strength was increased by 31% and the compressive strength was increased by 27%. Moreover, flexural storage modulus (stiffness), loss tangent (damping capacity), and density were increased. The tensile strength of cement paste was increased by 56%, and the modulus and ductility were increased by 39% by using silane treated carbon fibers and silane treated silica fume, relative to the values for cement paste with as-received carbon fibers and as-received silica fume. Silane treatment of fibers and silica fume contributed approximately equally to the strengthening effect. Silane treatment of fibers and silica fume also decreased the air void content. The effects on strengthening and air void content reduction were less when the fiber treatment involved potassium dichromate instead of silane, and even less when the treatment involved ozone. The addition of short carbon fibers to cement paste containing silica fume and methylcellulose caused the loss tangent under flexure to decrease by up to 26% and the storage modulus to increase by up to 67%, such that both effects increased in the following order. The addition of methylcellulose to cement paste containing silica fume caused the loss tangent to increase by up to 50% and the storage modulus to decrease by up to 14%. Silane treatment of silica fume had little effect on the loss tangent, but increased the storage modulus by up to 38%. The specific heat of cement paste was increased by 12% and the thermal conductivity was decreased by 40% by using silane-treated silica fume and silane-treated carbon fibers. The specific heat was increased by the carbon fiber addition because of fiber-matrix interface slippage. The specific heat was increased by the silica fume addition because of slippage at the interface between silica fume and cement. The increase was enhanced by silane treatment of the silica fume. Silane treatment of carbon fibers decreased the thermal conductivity. Silica fume and silane treatment of carbon fibers increased the effectiveness of these admixtures for reducing the drying shrinkage of cement paste.

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  • English

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Filing Info

  • Accession Number: 00795750
  • Record Type: Publication
  • Contract Numbers: NSF/GER-9023496-02, CMS-9632407, NSC 84-2211-E-009-14
  • Files: TRIS
  • Created Date: Jul 27 2000 12:00AM