【作者】 游有鲲；

【导师】 钱春香； 缪昌文；

【作者基本信息】 东南大学 ， 材料工程， 2004， 硕士

【摘要】 一、研究目的在火灾高温作用下,高强混凝土(High-Strength Concrete,HSC)往往易于发生爆裂破坏,使混凝土中钢筋直接暴露于高温中,而导致建筑构件失去耐火能力,同时高温后HSC剩余强度与渗透性能将发生很大程度劣化。本文着重研究HSC受火高温下的爆裂性能及其抑制措施,采取再养护、掺加矿物掺合料等方式改善HSC高温后剩余强度与渗透性能,对HSC受火后损伤程度的评价方法提出建议。二、研究内容与方法本文主要研究HSC抗火灾能力改善措施,具体研究内容分为HSC抗高温爆裂措施、高温后HSC剩余强度的改善与恢复措施以及高温后HSC抗渗性能改善措施等三个方面。在此基础上,提出HSC火灾后性能评价方法。本文主要研究以硅灰和粉煤灰为掺合料、水灰比0.25的HSC,采用燃油炉按照标准升温曲线加热,以爆裂度评价高温后HSC的爆裂性能。研究有机纤维、聚合物乳液、防火涂层等措施对HSC爆裂度的影响。本文同时研究了偏高岭土、赤泥、矿渣等掺合料对高温后HSC剩余强度的影响,并采取不同再养护溶液对高温后HSC进行了再养护,研究了再养护溶液对HSC高温后剩余强度的恢复性能的影响。本文研究了高温后HSC渗透性能的影响因素。其中渗透性能采用高温后HSC试件吸水系数、氯离子渗透系数以及空气渗透系数分别表征。本文研究了不同爆裂抑制措施对HSC试件渗透性能的影响,以及再养护溶液、有机硅涂层等对高温后HSC氯离子渗透性能的影响。研究比较了三种渗透性能测试方法之间的对应关系以及其与爆裂性能的关系,并采用MIP、SEM等方法研究了HSC高温前后浆体的微观结构。最后,对受火后HSC性能的无损测试与损伤程度评价方法进行了研究,提出了HSC高温损伤程度的分级评价指标。三、研究结论在HSC中掺加PP纤维可以抑制爆裂。不同的纤维,抑制爆裂效果不同。同掺量下,掺加长度为19mm的单丝PL纤维与长度为5mm的单丝PS纤维,抑制HSC爆裂效果最为显著。掺加粒状植物纤维或聚合物乳液,由于不能在HSC中形成连贯的释放水蒸气通道,因而其抑制HSC爆裂效果并不显著。掺加聚合物乳液的HSC高温下更易于发生断裂破坏。采用防火涂料具有一定抑制爆裂作用。浆体孔结构测试表明,掺加单丝PP纤维的HSC高温后形成了具有连通性的孔隙,对抑制HSC的爆裂具有积极作用。爆裂临界棱柱体模型计算表明,掺加单丝PL纤维的HSC中,爆裂临界棱柱体直径Dc(mm)最大,HSC内部水蒸气迁移直径较大,抑制HSC爆裂所需的同直径纤维掺量最小,抑制HSC爆裂效果越好。不同矿物掺合料配制的HSC具有不同密实度,SFHSC高温爆裂性高于FAHSC。HSC强度损失率随受火温度升高而逐渐加大,其中抗折强度损失率高于抗压强度损失率。有机纤维对HSC高温前后强度影响较小。在HSC中,以偏高岭土M作为混凝土第二掺合料,可以提高高温后抗压强度剩余率,其提高幅度高于赤泥。HSC中掺加适量CaF2对800℃后剩余抗压强度率有一定提高。采用水溶液、硫酸铝溶液、氟硅酸镁/硅酸钠等溶液再养护可以显著恢复混凝土的残余强度。采用盐溶液再养护的HSC具有较好的抗折强度恢复值。MIP试验表明,采用盐溶液对纤维熔化后的孔径有多重细化作用,其中对大孔道的细<WP=6>化有较显著作用。采用有机硅乳液再养护的浆体孔径的变化同时受到水溶液再水化作用与有机硅对孔道的密封作用。采用水溶液再养护对浆体细微孔径有较大的细化作用。采用SEM观察到,高温后HSC浆体经过再养护后,在浆体孔道中重新生成了不同数量与形状的针状结晶体。采用有机硅乳液再养护的浆体孔道中则看到有机硅材料对孔道密封形成的絮状物。本文采用PCK方法测试HSC高温后吸水系数。高温后HSC吸水系数、氯离子渗透系数与空气渗透系数显著上升。三种渗透系数之间有较好的对应关系,高温后HSC吸水系数低于0.139kg/(m2.s1/2)或氯离子渗透系数小于5.55×10-13 m2/s,则高温下发生爆裂的可能性较大。不同爆裂抑制措施对应着高温后HSC不同的渗透性能。经过再养护后,高温后HSC的抗渗性能得到部分恢复。高温后HSC强度性能、渗透性能的损伤程度的评估可以采用超声脉冲方法、空气渗透性能等无损测试方法;高温后HSC超声声速比VT/V0与火灾温度T有关系T=958-781VT/V0;超声声速与HSC火灾温度T关系为VT =4.78446-9.62553×10-4T-4.69172×10-6T2;高温后HSC抗压强度与超声声速关系为R=32.87453-0.64728 VT+3.213 VT 2,据此实现对HSC的抗压强度无损测试。对高温后HSC材料性能的损伤程度评价可按承载力、爆裂性能以及渗透性能等子项进行分项分级评估。更多还原

【Abstract】 Research PurposesIt is known that High Strength Concrete (HSC in short) may spall when it is in a fire accident or under a high temperature. The reinforcing steel bars in the explosive spall concrete are exposed in the fire accident and attacked by the heat, which damages the residual strength and the permeability of concrete. The paper studies the performance of concrete bust-up and the treatment methods of resistance to concrete bust-up in a fire accident or under a high temperature. And the solutions were found in the research that the damaged residual strength and the permeability of spall concrete could be improved by the way of re-curing or addition of mineral admixtures. The evaluation method of concrete damage degree is also suggested in the paper. Research Contents and MethodsThe treatment methods of resistance to concrete bust-up in a fire accident or under a high temperature concludes the performance of HSC bust-up and the improvement measures of the residual strength and permeability of HSC after being attacked by heat. And based on the above investigations, the evaluation method of concrete damage degree is brought out. The research object is HSC of water-binder ratio 0.25 with the addition of silica fume and fly ash. The HSC specimens are heated in an oilstove according to a temperature ascent curve of ISO834. The spalling degree is used to value the concrete performance of explosive resistance. It studies the effect of organic fibers, polymer latex and fireproof coating on the HSC performance of resistance spalling. It also studies the effect of metakaolin, red mud, slag and other mineral admixtures on the residual strength of HSC after being heated. The concrete specimens were re-cured in solutions after being heated. So it studies the effect of the solutions on the residual strength reconversion. It studies the permeability of HSC after being heated through the test of water absorption coefficient and permeable coefficients of chlorine ion and air. It discusses the difference of the above three permeability tests and their relationship with the HSC performance of resistance to bust-up. The microstructures of HSC after being heated are studied by mercury intrusion porosimetry (MIP in short) and SEM. Conclusively, graded indexes of damage degree of HSC after fire are suggested through the research of safety tests and evaluation methods of damage degree of the performance of HSC after being heated. Research ConclusionsIt is found that polypropylene fibers (PP fibers in short) help HSC resist to bust-up under high temperature. At the same volume fraction of fibers, 19mm long PL fibers and 5mm long PS fibers are most significantly effective in improving the HSC performance of resistance to bust-up. The grainy vegetable fibers and polymer latex are considerably less evidently effective in improving the HSC performance of resistance to bust-up because with the addition of these fibers less continuous moisture accesses form in HSC. But fireproof coating helps HSC resist to bust-up in some manner. By the test of pore structure, it presents that with the addition of PP fibers continuous pores form in HSC after being attacked by heat, which improve the HSC performance of resistance to spalling. In the paper, it shows silica fume is more effective than fly ash in improving HSC performance of resistance to spalling under high temperature. The loss ratio of HSC strength increases with the rise of temperature. And the loss ratio of flexural strength is higher than the one of compressive strength. HSC strength before and after being attacked by the heat is less affected by organic fibers. The loss ratio of HSC compressive strength is enhanced by the addition of metakaolin. And the improving extent of metakaolin is large than the one of red mud. It is proved that the addition of CaF2 at a appropriate fraction improves the residual compressive strength of HSC after being attacked under the temperature of <WP=8>800℃. The residual strength is recovered by the way of re-curing in various saline solu更多还原