水中重法和表干法测量密级配压实沥青混合料密度的统计分析

Statistical Analyses of Density Measured by Submerged Weight in Water and Saturated Surface Dry for Compacted Hot-Mix Asphalt(HMA) Specimens

压实沥青混合料试件的密度测量一直受到道路工作者的关注。由于水中重法简单、方便,在I型密级配沥青混合料的设计、施工和质量控制中允许采用。采用水中重法和表干法对我国沥青混凝土路面上常用的3种密级配沥青混合料,共计38个试件测量其视密度和表干毛体积密度。利用统计工具SPSS对两种方法测量的密度进行了统计分析。统计结果表明:水中重法和表干法测量的密度变异性,统计学上没有差异,但两种方法测量的密度值有显著差异。38个试件的平均视密度比平均表干密度大0.028 89 g/cm3,由此计算的沥青混合料试件空隙率相差达1.1%。两种方法计算的密度差或空隙率差值与试件的吸水率成正比例关系。建议在沥青混合料配合比设计中,不再使用水中重法测量的视密度代替表干法的毛体积密度。在工程施工过程和质量检测中,只有当试件或芯样吸水率极小时或不吸水时,水中重法方能代替表干法测量试件或芯样的毛体积密度。

There has been much attention given to the determination of the specific gravity （Gmb） of compacted hot-mix asphalt （HMA） specimens. Due to simple and convience, submerged weight in water method is allowed to use for I type mix in design, construction and quality control in China. In order to evaluate the efficacy of the method, a total of 38 compacted HMA specimens are tested by using two test methods： （1） saturated surface dry （SSD）; （2） submerged weight in water（SWW）. Each specimen is tested two times in each of the two methods. The specimens represented field-sampled and lab-prepared mixtures, three nominal maximum aggregate sizes, and a variety of aggregates typically used in China. Test results indicate that statistically significant differences exist between mean Grab values generated by the two testing methods. In general, the SWW method yielded the greater Grab values than SSD. Significant differences in the variability of test results are not observed between test methods. The average Gmb of SWW is 0. 028 89 g/cm3greater than that of SSD, which results to the more the error of air void 1.1%. The more the mixture absorbs water, the error of air void has greater differences computed by the two methods. It is suggested that the impact of test results on existing volumetric property specifications should be considered and that the SSW method should not be used in the design of proportion of mixtures.