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Hydraulic grouts have been used for a long time for injecting sufficiently large cracks or ducts in prestressed concrete structures. However, they cannot penetrate into narrow spaces, such as millimetric cracks, because of clogging. For some grading curves of cement, it is possible to obtain grouts injectable into narrow cracks. A thorough study of optimum gradings and penetrability characteristics of grouts obtained through the combination of cement and ultrafines (such as silica fume) has enabled the formation of hydraulic grouts for injection. Possessing properties similar to the original materials and being relatively economical to use, such grouts would be particularly useful for repairing masonry structures and concrete. Materials so developed can be used under certain conditions for prestressing steel ducts.

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.

A feasibility study on the performance of silica-fume modified cement grouts for corrosion protection of post-tensioning tendons was conducted. It began with laboratory tests on flow behavior and strength development. Subsequently, the proven mixtures were mixed and grouted under site conditions using a turbo mixer. The results and experiences were compared with results obtained with conventional neat cement grouts tested parallel. Additionally, corrosion protection behavior was studied with grouted tensioned prestressing steel samples, and grouting of post-tensioning tendons of a prestressed cast-iron pressure-vessel 1:5 scale model were performed. Because the tendons of the PCIV during service are exposed to 130 C, the investigation of the various hardened grouts relevant for corrosion protection and their alteration due to long-term exposure to elevated temperatures and high humidity were included. The results showed that silica-fume modified grouts exceed the conventional neat cement grouts in view of flow behavior, bleeding, density, processing time, etc. The dosing, mixing, and injection of silica fume grouts under site conditions caused no specific problems. Even some advantages may be reported. However, silica fume grouts require more care in mix proportioning and selection of appropriate superplasticizers.

Supplementary materials have similar effects on concrete but differ in many respects including composition, geographical distribution, amount of processing required, properties, economics, method of use, and specification requirements. Blast furnace slag is a cementitious material that reacts directly with water in the presence of an activator. In the absence of a chemical activator, calcium hydroxide produced in the hydration of portland cement serves as the activator. The other common supplementary materials, fly ash and condensed silica fume, are pozzolans, which require calcium hydroxide a necessary reactant in the pozzolanic reaction. High-calcium fly ash is cementitious and pozzolanic. Natural pozzolans and rice husk ash are acceptable materials not in widespread use. Condensed silica fume is a premium product for uses such as high strength, low permeability, and high electrical resistivity. Fly ash and blast-furnace slag have the potential to reduce the cost of concrete and to provide such benefits as reduced heat of hydration, resistance to sulfate attack, and inhibition of the alkali-aggregate reaction. Blast-furnace slag provides the greatest energy savings in that it may be used with little or no portland cement. Alkali-activated slag can also be made to hydrate at low temperatures.

Quality and performance of site-stored concrete blocks and structural-quality concretes from actual structures, where concretes contained different levels of ground granulated blast furnace slag as cement replacement material, have been assessed in terms of carbonation and gas or water permeability. First, 100 and 150 mm concrete cores were cut from site-stored concrete blocks and tested to assess the coring techniques and methods of measuring properties. These provided data on depths of carbonation and nitrogen, oxygen, and water permeability of ordinary portland cement and blast furnace slag cement concretes. Second, concrete cores were taken from actual structures. The two main factors influencing the depth of carbonation were the level of slag replacement for portland cement and the environmental conditions in which the concretes were situated. Carbonation was greater in the higher slag content cements especially if associated with a sheltered or drying microclimate. However, in general, gas and water permeability decreased with increased portland cement content and as slag replacement levels were reduced from 70 to 50 percent. Based upon these observations, appropriate slag contents are recommended for future use in various types of in situ concrete element.