Grout mixes used to fill posttensioning ducts to protect wire strands against corrosion are made with portland cement, water, and some chemical admixtures to enhance rheological and hardened properties. Such grouts should be fluid enough to facilitate pumping and spread into place, hence ensuring proper coating of the prestressing steel with minimum zones of the ducts that are imperfectly grouted. Unstable grouts can exhibit sedimentation of cement particles and bleeding of some of the free water that can propagate upwards and fill upper zones of posttensioning ducts. Bleeding can also occur whenever there are variations in elevations between different grouted areas, such as in vertical ducts where bleeding water can also result from fluid loss between the wire strands that can rise upwards by capillary action. Free water accumulated in larger voids that is not reabsorbed can freeze and lead to some delirious expansion. Cement grout can be exposed to freeze-thaw cycles during its service life, as in the case of grouted ducts in the surf and tidal zones of marine structures. Consequently, it is important in some cases to ensure an adequate air-void system in the hardened grout to resist freeze-thaw actions. A laboratory investigation was undertaken to develop highly fluid yet stable cement grouts with adequate and stable air-void systems and good mechanical properties. This paper reports the test results leading to the recommendation of high-performance structural grout containing 8% silica fume replacement and balanced combinations of high-range water reducer and rheology-enhancing admixture. Such grout can be properly air entrained to develop an adequate and stable air-void system for frost durability.


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  • Accession Number: 00767856
  • Record Type: Publication
  • Contract Numbers: CMS-9796326
  • Files: TRIS
  • Created Date: Aug 29 1999 12:00AM