我国现行规范中混凝土气泡参数计算方法的问题与建议

Problems and Suggestions on Computing Methods of Air-Void Characteristics of Concrete in Current Domestic Codes

根据各气泡参数的几何意义,推导了基于直线导线法的混凝土气泡分布密度与气泡间距系数计算公式,复核了欧美与我国各现行规范中对气泡参数计算的规定,并对我国现行规范在该方面存在的问题提出了修正建议。复核发现,我国铁路、公路、水运与部分电力规范中对临界浆气比的取值为4.33,应改为4.34。公路规范所给出的气泡间距系数计算公式中部分系数存在错误,不符合气泡间距系数的几何意义。我国公路与水运规范中都没有注意到当含气量或含浆量取“%”为单位时,其值为以体积比比值表示时的100倍,若要保持计算公式中各项系数不变,应规定含气量与含浆量本身就是体积比比值。除铁路规范外,我国现行规范中还普遍存在计算气泡空间密度时误将1 mm 3混凝土中气泡个数定义为1000 mm 3混凝土中的气泡个数以及在计算气泡间距系数(单位mm)时误将平均10 mm导线切割的气泡个数(单位cm-1)作为气泡频率(单位mm-1)代入计算公式的问题。以上问题都需要在各规范的下一次修编工作中重视与更正。

Computing formulas of air-void spatial distribution density and air-void spacing factor of hardened concrete based on linear traverse method were derived according to geometric interpretations of the two parameters.By the comparison between derived formulas and regulations about air-void characteristics in foreign and domestic codes,current domestic codes were reviewed and revised.In the review,it is found that the critical ratio of cement paste content to air content is 4.33 in domestic codes of railway,highway,waterway and partial power industries.However,it is not as accurate as 4.34.Some coefficients in formula provided by domestic highway code are not in accordance with geometric interpretations.Both codes of highway and waterway industries do not realize that if the air content or paste content is presented as"%"by volume,it would be 100 times of the value of volume ratio and require formula coefficients changes.To keep formula coefficients unchanged,both the air content and paste content are suggested to be presented as values of volume ratio instead of"%"by volume.Except for railway codes,domestic codes of various industries mistakenly define the air-void number in 1 mm 3 as air-void number in 1000 mm 3 in the calculation of spatial distribution density.These codes also mistakenly substitute the air-void number(unit:cm-1)intersected by 10 mm traverse for air-void frequency(unit:mm-1)in the calculation formula of spacing factor,the unit of which is millimeter.All the errors mentioned above need to be taken seriously and revised in future editions.