某服役32年立交桥顶板混凝土芯样碱骨料反应鉴别研究

Identification of AAR in the panel of an overpass after 32 years of service

某立交桥面板混凝土所用骨料具有碱活性且未采取碱活性抑制措施,服役32年后发现桥面板混凝土强度明显降低并存在开裂现象。为确定桥面板混凝土碱骨料反应状态,对典型部位的混凝土芯样开展了抗压强度测试、80℃残余膨胀试验、产物分析及微观分析等研究。结果显示:芯样混凝土抗压强度均低于设计值,部分已低至50%以下;在80℃加速养护的80 d内,芯样膨胀趋势明显,且径向膨胀率和轴向膨胀率均超过0.10%;弹性波波速呈下降的趋势,体积电阻率逐渐增大。染色分析表明部分骨料周围被染为棕黄色,疑似碱骨料反应产物;微裂纹分析显示芯样切片内部存在具有典型碱骨料反应特征的微裂纹。综合已有分析表明:该立交桥顶板混凝土存在典型的碱骨料反应损伤特征,未来发生较大残余膨胀并破坏的可能性较大。

Alkali-silica reactive aggregates were used in the panels of one overpass and no prevention measures were taken during the construction process.After 32 years of service,many sign of serious ageing in the panel are found such as cracking and declination in strength,which might be caused by alkali-aggregate reaction(AAR).Accordingly,a number of cores extracted from the panels and compressive tests,expansion test under 80℃as well as microscopic analysis were tested.[Results]show that the compressive strength of the cores are all lower than the design value and some are even lower than 50%.During 80 days of curing at 80℃,both the axial and radial expansion ratios increase and the 80 d expansion ratio could reach as high as 0.10%.Also during the 80 d curing at 80℃,the elastic wave velocity in the cores decreases and the volume electrical resistivity increases gradually.The staining analysis showed that AAR gel was found around some coarse aggregates for the rims of the aggregates were stained brownish yellow.Microcrack analysis showed that typical AAR network microcracks were found in the core slices.To sum up,typical damaging signs caused by AAR in the panel concrete of the overpass are identified by microscopic analysis,suffered and it’s probable that concrete will be expanding continuously and cause more damage in the panels in the future.