This work determines the replacement ratio of fly ash of 25% in SBR-modified cement mortars based on the past research, including SBR emulsion (SBR-E) and SBR powder (SBR-P). In addition to the Japanese guidelines for the repair material, the past researches related to polymer-modified cement mortars are also used to determine an appropriate mix proportion of the patch repair material for deteriorated RC building structures. According to the experimental results in this work, it can be observed that increasing the S/W ratio of SBR is useful to improve the flexural bonding strength effectively; however, the compressive, flexural and tensile strength of cement mortars decreases. Besides of the mechanical strength, the workability and economy are considered to determine the S/W ratio of 10% of SBR-P for cement mortars with fly ash. Additionally, according to the regression results, its corresponding compressive, flexural, tensile and flexural bonding strengths are 36.5, 9.68, 3.35 and 2.8 MPa, respectively. For most of RC buildings with an age of over 30 years in Taiwan, since their average testing compressive strength is around 20 MPa, the suggested mix proportion of SBR-modified cement mortars with fly ash can provide enough performances for the patch repair.
Considering the durability of fly ash concrete against the chloride attack, a quantitative evaluation of the rebar corrosion rate in concrete is necessary. In this study, reinforced concrete specimens containing premixed chlorides were prepared, using concrete with cement or fine aggregate partly substituted by fly ash. The corrosion rate of rebar in the specimen was evaluated by the polarization resistance which is an electrochemical corrosion index. The specimens were stored in the wet or dry condition at the temperature of 20 or 40 ºC. As a result, the corrosion rate of rebar was greatly suppressed by admixing fly ash with the increase of the concrete resistivity at the temperature of 20 ºC, while such suppression effect decreased with the rise in temperature to 40 ºC. The suppression effect was remarkable in the cases of fly ash addition as the substitution of fine aggregates. Moreover, the influence of a variation of the chloride content in concrete on the steel corrosion rate was significant when the specimens were stored in the dry condition. The influence of the environment temperature and the chloride content in concrete on the steel corrosion rate measured in this study could be generally evaluated by using an existing equation.
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