摘要
再生混凝土棱柱体与立方体抗压强度之间的关系显著异于普通混凝土,而现有模型预测精度较低、离散性较高.为此,搜集并分析了文献中139组试验数据,研究了再生骨料取代率、吸水率与二者耦合效应对再生混凝土强度的显著影响,提出了再生混凝土棱柱体与立方体抗压强度关系模型,模型预测结果变异系数仅为5.4%.为方便使用,基于骨料分类,进一步简化了该模型.模型分析结果表明其不确定性服从正态分布,且与关键参数无关,采用该模型进行结构可靠度分析时可忽略其相关性.
随着中国工程建设的不断发展,建筑垃圾产量不断上升,其中废弃混凝土约占30%~40
根据GB 50010—2010《混凝土结构设计规范》,棱柱体抗压强度(fcp)是混凝土结构设计的核心参数,由立方体抗压强度(fcc)计算得到.因此,混凝土棱柱体与立方体抗压强度关系的准确性是结构安全设计的关键.现有研
因此,基于搜集的13篇参考文
目前,国内外学者已基于试验结果对再生混凝土fcp与fcc的关系模型开展了研
现有再生混凝土棱柱体与立方体抗压强度关系模型预测结果对比见

图1 现有再生混凝土棱柱体与立方体抗压强度关系模型预测结果对比
Fig.1 Comparison of predicted results from different models for the relationship between prism and cube compressive strengths
为确定影响再生混凝土棱柱体与立方体抗压强度关系的关键参数,搜集了13篇参考文
通过系统分析发现,再生骨料取代率r与吸水率wa是影响fcp/fcc的关键参数.

图2 再生骨料取代率和吸水率的影响
Fig.2 Influence of recycled aggregate replacement ratio and water absorption ratio
由
数据分析结果显示,在参数范围内,fcp/fcc与混凝土fcc无显著关系.

图3 混凝土立方体抗压强度的影响
Fig.3 Influence of cube compressive strength
为减小普通混凝土数据离散性造成的影响,通过建立再生混凝土fcp/fcc与普通混凝土fcp/fcc的关系,提出再生混凝土棱柱体与立方体抗压强度关系模型:
(1) |
式中:αc
考虑以下3点来确定kRAC:当r=0%时,kRAC=1,此为边界条件;相同wa下,fcp/fcc与r呈线性关系(见
(2) |
式中:g(wa)为再生骨料吸水率wa的函数.
为确定g(wa)的形式,以r=100%的试验结

图4 再生骨料吸水率对kRAC的影响
Fig.4 Influence of water absorption ratio of recycled aggregate on the factor kRAC
基于试验数据,采用对数形式对g(wa)进行回归分析:
(3) |
将式(
(4) |
采用搜集的13篇参考文

图5 所提模型预测结果与试验结果对比
Fig.5 Comparison between the predicted results using the proposed model and experimental results
为方便设计人员使用,将基于再生骨料分类对所提模型(
对于Ⅱ类与Ⅲ类再生骨料,简化模型采用平均吸水率(Ⅱ类wa=4%,Ⅲ类wa=6.5%)作为代表值;考虑未经强化处理的再生骨料一般吸水率较高,采用2.5%作为Ⅰ类再生骨料吸水率代表值.将各类再生骨料的吸水率代表值代入
(5) |
式中:kwa为基于吸水率的再生骨料分类系数,其取值如
Aggregate classification | Type Ⅰ | Type Ⅱ | Type Ⅲ |
---|---|---|---|
kwa | -0.23 | 0 | 0.14 |
采用搜集的试验数

图6 简化模型预测结果与试验结果对比
Fig.6 Comparison between the predicted results using the simplified model and experimental results
再生骨料来源多样、物理性质离散性高,导致再生混凝土力学性能具有较高的离散
为表征所提模型的不确定性,引入模型预测结果的偏差,作为随机变量θ.
(6) |
采用拟合优度检验与极大似然估计法,对随机变量θ 进行统计分析,结果见

图7 随机变量θ 的统计分析结果
Fig.7 Statistical analysis results of random variable θ
为提高可靠度分析结果的精确性,对随机变量θ 与关键参数的相关性进行了分

图8 θ 与关键参数的相关性
Fig.8 Correlation between θ and the key parameters
(1)基于对文献数据的系统分析,发现再生骨料取代率r、吸水率wa是影响再生混凝土棱柱体与立方体抗压强度之比fcp/fcc的关键参数,且二者之间存在显著的耦合效应,即不同wa下,r的影响趋势不同,甚至相反.当0%≤wa≤3.0%时,r=100%相对于r=0%,fcp/fcc降低19.3%;而当wa>8.0%时,r=100%相对于r=0%,fcp/fcc增大27.1%.
(2)基于试验数据,提出了考虑r、wa与二者耦合效应的再生混凝土棱柱体与立方体抗压强度关系预测模型.模型精度较高,预测结果与试验结果比值的平均值为1.011,变异系数为5.4%.为方便设计人员使用,基于再生骨料分类,进一步提出了再生混凝土棱柱体与立方体抗压强度关系简化模型.该简化模型形式简单,且精度并未显著降低,简化模型预测结果与试验结果比值的平均值为1.008,变异系数为5.8%.
(3)所提模型预测结果的不确定性服从正态分布,其平均值为1.011,标准差为0.054;且所提模型预测结果的不确定性与r、wa、fcc等参数的相关性较弱,相关系数在-0.013~0.022之间.在可靠度分析中,可忽略上述参数对所提模型不确定性的影响.
(4)在模型建立过程中,所用试验结果中再生混凝土使用的是未经强化处理的再生骨料.在未来工作中,建议针对不同再生骨料强化处理方式的影响开展试验与理论研究,以验证和修正所提模型.
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