コンクリートの中性化と鉄筋のさびについて

Abstract

Experimental studies on the neutralization of concrete specimens and the rusting of reinforcement embeded have been conducted throught 20 years.Kinds of cement used in this test were normal portland cement, blust furnace slag cement and portland pozzolan cement. The proportions of concrete of each kind of cements were as follows:Proportion Slump(cm) W/C(%) Compacted by1:2:4 {0 41-42 vibration5 50-51 rodding20 61-63 _??_1:3:6 {0 48-50 vibration5 68-69 rodding20 89-90 _??_Standard specimens of φ15cm×30cm with φ16mm steel bars, embedded were made in July, 1937, cured in moisture for 28 days, and then stored outdoors until the tests were mrde.The neutralization depth was measured by the use of phenol-phtalene alcohol solution on the splitted section of each specimen at the ages of 6 month, 1, 3, 5, 10 and 20 years, and at the same time, the rusting conditions of embedded steel bars were observed.The results of tests are summarized as follows:1) When concrete has not defects and the water cement ratio is smaller than 70%, the neutralization depth is less than 10mm and the neutralization scarcely pregresses further after it has advanced to certain depth. There results are same irrespective of kinds of cement.But, if concrete has some defects such as air voids, cracks and water film under aggregates, the neutralization develops mostly through the defects. Particularly when the water cement ratio is larger than 70%, for instance 89%, the neutralization progresses gradnally as the develops with age increases, and the neutralziation depth reaches 3-5 times as deep as that found in the concrete of smaller water cement ratio. In this case, the degree of neutralization varies depending upon the kind of cement; that is to say, concrete made with blended cement is neutralized much faster than concrete with portland cement.2) It is considered that the rusting of reinforcing steel occurs not by neutralization of concrete. Almost of the rusting of embedded steel bar develops due to the defects of the concrete, and movement of air or water through the defects.