3. Effective Method of Concrete Repair Using Polymer-Cement Material

      To prolong the life of structures, a technique is often used by which parts that have deteriorated are removed, and the removed parts are back-filled. However, as the back-filling material occasionally peels off, the adhesive properties of all-purpose polymer-cement material and deterioration properties due to neutralization were investigated.

      Investigation showed that, in many cases where the required adhesive strength (guideline: 1.0N/mm2) was not obtained, voids on the adhesive interface and in the back-filling material had led to peeling. Such peeling was also caused by the weakening of hardened material through moisture absorption by the base material concrete immediately after back-filling.

      It became clear that the spraying construction method (by which the spraying pressure is raised as high as the technique will allow) is useful for reducing voids on the adhesive interface and for filling the steel back surface appropriately (Fig.1). It also became clear that, to obtain an adhesive strength equal to or greater than the guideline value, surface treatment by spraying emulsion with added resin is more effective than the conventional technique of water spraying and using back-filling material with a high water retention percentage of 0.5% or more (Fig.2).

      Investigation also demonstrated the need to consider not only the water/cement ratio but also the air content in terms of the progress of deterioration due to the neutralization of polymer cement back-filling material. This is because the polymer cement tends to contain more air than normal cement. The following formula was proposed for estimating the neutralization depth by considering the factors of water/cement ratio, air content, and time. This enables forecasting of the progress of neutralization.

where, y: neutralization depth (mm), W/C: water/cement ratio (%), Air: air content (%), t: time (year)

Fig.1 Filling to the steel back surfaceFig.2 Influence of the water retention rate and surface treatment method on adhesive strength

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