Title: IMPROVED SHOTCRETE MIXES FOR BRIDGE REPAIR IN ONTARIO
Abstract: An investigation, sponsored by the Ontario Ministry of Transportation has been carried out to evaluate current shotcrete repair methods for bridges and to compare the physical performance of a range of shotcrete mixes. Current shotcrete mixes specified in Ontario use full strength latex modified mixes. A review of shotcrete repair work completed over recent years, indicates that while some repairs exhibit satisfactory performance, others show significant on-going deterioration, mainly in the form of delamination. Based on the results of a literature review and laboratory bench testing programme, 11 mixes were chosen for field trials. The mixes were chosen to evaluate the effect of fine and coarse aggregate on the mix as well as several admixtures including silica fume, latex, steel fibres, and polypropylene fibres. Based on the field observations and the results of the laboratory testing, the following conclusions can be drawn regarding the mixes tested in this study: 1) Accelerators: should not be used for dry mix applications, except under extremely difficult application conditions, due to too rapid a setting time and caustic composition; 2) Fibres: steel or polypropylene fibres are not recommended for structural repairs where there is a congestion of reinforcement because of the potential of voids forming behind the reinforcing steel; 3) latex: not recommended for the following reasons: low strength when used at standard dilutions, and unacceptably thin application thicknesses due to long initial set time resulting in more cold joints in the patch; 4) Silica fume: provides an 'easy to shoot' mix with good properties at a silica fume content of 8%, and likely to be less expensive than latex shotcrete mixed on site; 5) gradation: the finer gradation is preferable due to better surface appearance; 6) welded wire fabric reinforcement: the use of welded wire fabric for reinforcement of the patched surface may disguise the delamination of the applied shotcrete while in the plastic state; and 7) surface preparation: the current MTO specification for surface preparation is sufficient, and the application of cement slurry has no effect on the bond strength. The results of the field and laboratory testing programme indicate that a fine aggregate mix modified with 8% silica fume offers the best option for durable bridge repairs. It is recommended that this mix be evaluated in full scale field trials. (A) For the covering abstract of the conference see IRRD Abstract no. 807788.
Publication Year: 1991
Publication Date: 1991-01-01
Language: en
Type: article
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