不同粗骨料取代率下粉煤灰再生混凝土的力学性能研究

Mechanical properties of fly ash recycled concrete at different replacement ratio of recycled coarse aggregate

为探讨不同再生粗骨料取代率下粉煤灰对再生混凝土力学性能的影响,以及再生混凝土抗折强度与再生粗骨料取代率、水胶比之间的关系,以RC30设计强度等级为基础设计了16组配合比,制作了96块再生混凝土试块,主要进行了再生混凝土的抗压强度试验和抗折强度试验。得出如下结论:随粉煤灰掺量的增加,不同再生粗骨料取代率,抗压强度变化规律有所不同;再生粗骨料取代率为0、30%和40%时,抗压强度随粉煤灰掺量的增加整体呈下降趋势;而当再生粗骨料取代率为50%时,随粉煤灰掺量的增加,抗压强度先减小后增大。粉煤灰掺量大于20%时,天然骨料混凝土的抗压强度急剧下降,而再生骨料混凝土的抗压强度降低幅度均较小,大掺量粉煤灰在再生混凝土中或将有更大的应用空间。通过观察抗折强度试件破坏断面,分析再生混凝土变形破坏特征。粉煤灰的掺入提高了天然骨料混凝土的抗折强度,且掺量为20%强度最高。再生粗骨料取代率为30%时,随粉煤灰掺量变化抗折强度整体呈下降趋势,但下降幅度很小;再生粗骨料取代率为40%和50%时,呈先减后增再减的趋势。天然骨料混凝土的折压比随粉煤灰掺量的增加而提高;再生混凝土折压比随粉煤灰掺量的变化趋势与抗折强度一致,但变化幅度略小。粉煤灰对再生混凝土抗折强度的影响大于抗压强度;再生粗骨料取代率为30%,粉煤灰掺量为10%为较优掺量。提出再生混凝土抗折强度预测式。

In order to discussthe influence of fly ash onmechanical property of recycled concreteat different replacement ratio of recycled coarse aggregate(RCA),and the relationship between flexural strength of recycled concrete and replacement ratio of RCA and water-binder ratio.16 groups of proportion were designed and 96 specimens were made based on the same strength RC30.The experimental studies for the compressive strength and flexural strength of recycled aggregate concrete(RAC)were conducted.The results indicate that the compressive strength is different with the increase of fly ash content,when replacement ratio of RCA is different.When the replacement ratio of RCA is 0、30% and 40%,the compressive strength decreases with the increase of fly ash content.When the replacement ratio of RCA is50%,the compressive strength reduces first and then increases with the increase of fly ash content.The compressive strength of natural aggregate concrete(NAC)decreases sharply,while the compressive strength of recycled aggregate concrete decreases slightly,when the fly ash content exceeds 20%.Large amount of fly ash in recycled concrete may have greater application space.The deformation and failure characteristics of recycled concrete were analyzed by observing the failure section of the flexural strength specimen.The incorporation of fly ash improves the flexural strength of natural aggregate concrete,and the strength is the highest when the content is 20%.When the replacement ratio of RCA is 30%,the flexural tensile strength decreases with the change of fly ash content,but the decline is very small.When the replacement ratio of RCA is 40% and 50%,it decreases first and then increases and then decreases.The flexural compression ratio of NAC increases with the increase of the fly ash content.The variation trend of flexural compression ratio with the fly ash is agreed with flexural tensile strength,while the variation amplitude is slightly small.The effect of fly ash on the flexural strength of recycled concrete is bigger than the compressive strength.When the replacement ratio of RCA is 30% and the fly ash content is 10%,it is the preferable content.A prediction formula for the flexural tensile strength of recycled concrete is proposed.