摘要:通过改变再生粗骨料取代率,并考虑引气剂的影响,对再生混凝土长龄期下的立方体抗压强度和收缩性能进行试验;采用不同的加载龄期,对再生粗骨料取代率为50%的再生混凝土徐变性能进行试验研究;建立了再生混凝土长龄期强度推算公式。结果表明:长龄期下再生混凝土的立方体抗压强度变化规律与普通混凝土基本一致,28 d龄期再生混凝土的立方体抗压强度随再生粗骨料取代率的增加而降低;再生混凝土的收缩随再生粗骨料取代率的增加而增加,添加粉煤灰、矿粉等矿物外掺料可以使再生混凝土收缩降低;加载龄期对于再生混凝土徐变值有影响,加载龄期越早,再生混凝土徐变值越大;利用所建立的强度推算公式计算得到的强度值与试验结果比较吻合,并且优于欧洲CEBFIP Model Code 1990规范建议公式的计算结果。
关键词:再生混凝土;引气剂;矿物外掺料;长龄期强度;收缩徐变;拟合曲线
中图分类号:TU528.79文献标志码:A
Abstract: The effects of the recycled coarse aggregate(RCA)replacement ratio and airentraining agent on cube compressive strength and shrinkage of recycled aggregate concrete(RAC) were experimentally investigated. The creep of RAC with 50% RCA replacement ratio was also studied by varying the loading time. Meanwhile, the calculation formula for the compressive strength of RAC at various ages was established. The experimental results reveal that the longterm strength increasing rule of RAC is similar to that of natural aggregate concrete. The cube compressive strength of RAC at 28 d reduces whereas the shrinkage increases with the increase of RCA replacement ratio. In addition, adding reasonable amount of slag and fly ash can reduce the shrinkage of RAC. The loading time has an effect on the creep of RAC as the creep is greater when the specimens are loaded at an earlier age. The compressive strength values calculated by the proposed formula are in good agreement with the experiment results and more accurate than the outcomes deprived from the suggested formula in CEBFIP Model Code 1990.
Key words: recycled aggregate concrete; airentraining agent; mineral admixture; longterm strength; shrinkage and creep; fitted curve
0引言
1试验设计
再生粗骨料取代率为50%时的再生混凝土收缩率略小于文献[6]的研究结果;再生粗骨料取代率为100%时的再生混凝土收缩率与文献[6]的研究结果比较接近,但是明显小于文献[7]的研究结果。对于本次收缩率试验结果小于文献[6],[7]的研究结果,可以解释为此次试验的再生混凝土中掺入了粉煤灰,由于粉煤灰颗粒的弹性模量明显高于水泥颗粒[89],故能通过微集料效应抑制再生混凝土的收缩。同时,矿粉和粉煤灰的掺入会显著改善再生混凝土的微观结构,使水泥浆体的空隙率明显下降,强化了集料界面,提高了混凝土密实度,使得再生混凝土的收缩减小。
2.3加引气剂再生混凝土徐变试验
(2)根据试验结果,考虑再生粗骨料取代率的影响,给出了再生混凝土长龄期下抗压强度的推算公式。该推算公式计算的强度值与试验结果吻合较好且优于欧洲CEBFIP Model Code 1990规范的建议公式。
(3)再生混凝土收缩变形随再生粗骨料取代率的增加而增加,且随着再生粗骨料取代率的提高,收缩发展加快;再生混凝土的收缩变形在28 d内发展较快。与文献[6],[7]试验结果对比分析表明,本文收缩试验结果较小,说明拌合物中加入粉煤灰、矿粉的再生混凝土的工作性能得到有效改善,收缩减小。
(4)在加载早期,再生混凝土徐变发展较快,随后增长较慢;在持荷时间相同条件下,加载龄期较早时,再生混凝土徐变值偏大。
参考文献:
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