Properties of Cement Grouts With Silica Fume Addition For the Injection of Post-Tensioning Ducts

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Title: Properties of Cement Grouts With Silica Fume Addition For the Injection of Post-Tensioning Ducts

Author(s): E. H. Ranisch, F. S. Rostasy, and F. F. Herschelmann.

Publication: Special Publication

Volume: 114

Issue:

Appears on pages(s): 1159-1172

Keywords: ducts; grout; grouting; injection; plasticizers; porosity; post-tensioning; prestressed concrete; silica fume; viscosity; Materials Research

Date: 5/1/1989

Abstract:
Investigations of prestressed concrete structures have shown that some tendon ducts were not satisfactorily injected. Some well-known causes are unfavorable flow properties, bleeding, and sedimentation of the grout. Further problems arise in warm temperatures from early stiffening of the grout. Tests with silica fume-modified cement grouts have shown that the enormous specific surface of the fume and its high absorptivity reduces bleeding of grout. The spherical form of the particles improves flow properties, and thereby workability. This report presents results of extensive experiments with grouts consisting of OPC with addition of five brands of silica fume plus expansive and superplasticizing admixtures. The w/c + silica fume was 0.40. Mixing and testing was carried out according to DIN 4227, Part 5. In addition, the viscosity of the mixes was measured by rotation-viscosimetry. The experiments show that the grouts should incorporate expansive admixtures and superplasticizers, the latter in a high dosage; that exceeding the allowed dosage of superplasticizer caused no disadvantages; that replacement of 5 percent cement by silica fume seemed to be optimal; and that silica fume filled the fine pores, thus the porosity of the grouts was reduced.