Effect of Supplementary Cementitious Materials on Rheological Properties, Bleeding, and Strength of Structural Grout by ProQuest

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									 ACI MATERIALS JOURNAL                                                                                   TECHNICAL PAPER
Title no. 105-M66


Effect of Supplementary Cementitious Materials on
Rheological Properties, Bleeding, and Strength of
Structural Grout
by K. H. Khayat, A. Yahia, and M. Sayed

Cement grouts used for crack injection, anchorage sealing, and             combinations of HRWRs and VMAs can be used to enhance
post-tensioning applications are proportioned to exhibit high              the resistance of specialty grouts to forced bleeding.8-10
flowability to facilitate casting and adequate cohesion to prevent            The effectiveness of incorporating SCMs to enhance
phase separation and bleeding. An experimental investigation was           rheological and mechanical properties is affected by the type
carried out to evaluate the effect of different types of supplementary
                                                                           and content of the SCM. It can also be affected by the state
cementitious materials (SCMs) on rheological properties, stability,
and compressive strength of structural grout. Substitutions of cement by   of dispersion of all solid particles in the matrix. The dispersion
3% silica fume, 10 to 30% Class F fly ash, and 40% granulated blast-       of solid particles is, on the other hand, dependent on the degree
furnace slag were considered. Various binary systems that resulted in      of adsorption of chemical admixtures onto the solid particles.
good performance were also combined to investigate the effect of           The adsorption of HRWR depends on the composition of the
ternary cement blends on grout performance.                                aqueous solution, alkali content, type of sulfate, and presence
   The use of SCMs in structural grouts is shown to increase water         and dosage of chemical admixtures in use.11 The impact of the
demand in mixtures made with portland cement. When incorporated            degree of adsorption of HRWR on fluidity of cement-based
in well-dispersed systems, the use of binary and ternary cements           material has been thoroughly investigated.12-16 The fluidity of
led to higher fluidity, lower yield stress, higher plastic viscosity,      cement paste made with a given content of polynaphtalene
and greater resistance to forced bleeding compared with reference          sulfonate (PNS) based HRWR is reported to decrease with
mixtures made with portland cement. This paper discusses the               the increase in the degree of adsorption of the HRWR; this
performance of various grout mixtures prepared with binary and             reflects a lower content of the polymer remaining in the solution
ternary binders and different concentrations of high-range water-
reducing admixture.
                                                                           to disperse cement particles. In general, PNS-based HRWR can
                                                                           more strongly be adsorbed onto the aluminates hydration
                                                                           products (in particular, ettringite) than those of the hydration
Keywords: admixtures; adsorption; bleeding; grout; rheology.
                                                                           products of the silicate phase.16-18 The degree of PNS adsorption
                                                                           is typically higher in cements of low alkali content than in those
                        INTRODUCTION                                       with high alkali content.11 Furthermore, the type of calcium
   In addition to enhancing mechanical properties and durability,          sulfate has an effect on HRWR adsorption in low-alkali cement;
the partial substitution of cement by supplementary cementitious           however, this factor is less apparent in high-alkali cement.16 The
materials (SCMs) can enhance rheological properties and                    use of hemihydrates and proper content of alkali can
stability of the cement paste.1,2 Proper substitution of cement            result in lowering the HRWR adsorption and, therefore,
with SCMs can lead to greater packing density of the fine                  enhancing initial fluidity.
powder, hence reducing interparticle friction. Given the                      Some thickening agents, or VMAs, are used in conjunction
spherical shape of fly ash (FA) particles, the partial replacement         with HRWRs to design a highly-deformable mixture with
of cement by FA can further enhance flow properties. The partial           low yield stress and relatively high plastic viscosity to
substitution of cement by silica fume in cement grout can                  control bleeding and sedimentation. The interaction between
improve the washout loss resistance of the grout, hence                    VMA and HRWR and its effect on flow characteristics,
enhancing in-place compressive strength and bond strength.3                rheology, and stability of highly-flowable cement-based
Furthermore, the use of silica fum (SF) in cement grout used for           materials, such as those used for underwater anchorage
post-tension applications can enhance rheological properties,              sealing and protection of post-tensioning ducts against
eliminate bleeding, reduce temperature rise and risk of thermal            corrosion as well as self-consolidating concrete, have been
cracking, enhance long-term strength and impermeability, and               investigated.8,19-21 Limited information exists, however, on
enhance the electrical resistivity of the grout.4-7 This can               the HRWR adsorption in cement-based systems containing
therefore improve the service life of post-tensioned                       VMA. The effect of incorporating some combinations of
concrete structures exposed to adverse conditions.                         SCM in highly flowable systems needs to be further
   Highly flowable grout and concrete systems are often                    investigated to identify the advantages and limitations of
proportioned with high-range water-reducers (HRWRs) and,                   using binary and ternary cementitious materials to design
in some cases, with viscosity-modifying admixtures                         structural grout containing VMA.
(VMAs) to ensure high deformability and stability. The
incorporation of HRWRs can lower the yield stress of                         ACI Materials Journal, V. 105, No. 6, November-December 2008.
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