粉煤灰和矿渣对自密实混凝土早龄期抗裂性的影响

Early-age Cracking Behavior of Self-compacting Concrete Mixed with Fly Ash and Slag

目的 揭示粉煤灰和矿渣对自密实混凝土(SCC)早龄期抗裂性影响的作用机理。方法 在矿物掺和料掺量占胶凝材料总质量分别为30%和50%下,结合同步砂浆的水化放热特性、SCC的抗压和劈拉强度及SCC水分蒸发量试验,开展了不同粉煤灰与矿渣复掺掺量的SCC早龄期抗裂性能试验研究。结果 粉煤灰复掺矿渣后会延迟胶结体系水化,并影响SCC在龄期1 d时的抗压和劈拉强度;同时会延迟SCC开裂时间,但会增大SCC龄期12 h时的水分蒸发量,增加SCC龄期24 h时的开裂面积;在矿物掺和料掺量占胶凝材料总质量30%、且粉煤灰与矿渣复掺质量比为7∶3时,SCC龄期1 d时的抗压和劈拉强度最大,龄期24 h时的开裂面积最小,仅为对比组的64%;此外,粉煤灰复掺矿渣后可提高SCC龄期3 d后的抗压和劈拉强度。结论 粉煤灰复掺矿渣后会增加受约束结构混凝土的开裂风险,矿物掺和料掺量占胶凝材料总质量需控制在30%以内,且矿渣复掺掺量不宜超过粉煤灰掺量。

The early-age cracking behavior of self-compacting concrete(denoted as SCC) with different ratios of fly ash and slag at 30% and 50% total mineral admixtures was carried out;meanwhile, combined with the simultaneous mortar hydration heat test, compressive strength and splitting tensile strength of SCC and concrete moisture evaporation test, the mechanism and influence law of concrete were revealed.The results show that delay the hydration of the cementitious system is delayed and the formation of compressive and splitting strength of SCC at 1 d age are affected by mixing with slag.In addition, mixing with slag delays the cracking time of SCC,but increases the water evaporation capacity of SCC at 12 h and the cracking area of SCC at 24 h.It has the highest compressive strength and splitting tensile strength, and the least cracking area of SCC at 24 h age when the mineral admixtures content is 30% and the mixture ratio of fly ash and slag is 7∶3,its cracking area within 24 h age is only 64% of the comparison group.Furthermore, the mechanical strength of SCC after 3 d age is enhanced.It can be seen that mixing with slag will increase the cracking risk of concrete of the constrained structural members, so the mineral admixtures content should be controlled within 30% and the proportion of slag should not exceed the proportion of the fly ash when fly ash is mixed with slag.