STUDYING THE EFFECT OF FREEZE AND THAW CYCLES ON BOND STRENGTH OF CONCRETE REPEIR MATERIALS

The mechanisms of damage to concrete from repeated cycles of freezing and thawing are not well understood and continue to be intensively studied. Original research was based on the fact that water expands 9 percent when it freezes. Further researches proposed more mechanisms. Hydraulic pressure theory proposes that destructive stresses can develop if water is displaced to accommodate the advancing ice front in concrete. If the pores are critically saturated, water will begin to flow to make room for the increased ice volume. The concrete will rupture if the hydraulic pressure exceeds its tensile strength. In this paper the results of an experimental study of the effect of freeze & thaw cycles on the bond between repair materials and concrete substrate is presented. The work was aimed at studying the effect of various factors such as initial curing periods and surface preparation method on bond strength. Old concrete samples were made based on BS6319, Part 4 standard. Smooth as-sawn and acid etching methods were used for preparation of concrete substrate surface. Ordinary concrete with cement type II and concrete containing microsilica were used as repair materials. Repaired samples were subjected to 10 to 100 freeze and thaw cycles based on ASTM C666. The bond between repair materials and concrete substrate was evaluated based on slant shear test method (BS, 1984). The obtained results are tabulated and presented in this paper.