玄武岩纤维桥梁混凝土韧性特征及衰减规律

Toughness characteristics and attenuation law of basalt fiber bridge concrete

为研究玄武岩纤维对桥梁混凝土的增韧阻裂效果,设计了弯曲韧性试验、断裂韧性试验,分析不同玄武岩纤维掺量(体积分数,0%、0.07%、0.08%、0.09%,下同)对桥梁混凝土抗裂性能的影响规律,从中选出最优纤维掺量。利用动态疲劳加载试验,研究普通混凝土和最优纤维掺量组在不同荷载应力水平下(0.5、0.7)弯曲韧性系数和断裂能的劣化衰减规律,并基于扫描电镜(SEM)试验,从微观角度剖析玄武岩纤维对桥梁混凝土的增韧阻裂机理。试验结果表明:玄武岩纤维能够增加混凝土的弯曲韧性,起到增韧阻裂作用,有利于避免在荷载作用下混凝土过早开裂,玄武岩纤维掺量为0.08%时,改善效果最明显,28 d弯曲韧性系数较普通混凝土提高了235%,玄武岩纤维显著提升了桥梁混凝土的断裂能,当纤维掺量为0.08%时,提升效果最明显,较普通混凝土提高了247%,在不同荷载应力水平下,桥梁混凝土的弯曲韧性系数和断裂能都随着疲劳加载次数的增加而逐渐衰退,且初期降低幅度小,后期降低幅度较大。但掺入玄武岩纤维可以减缓桥梁混凝土衰减速率,提高其抵抗疲劳开裂的能力,进而延长桥梁混凝土疲劳寿命,纤维与水泥基体之间良好的黏结性能,使得玄武岩纤维在混凝土内部形成稳定的乱向三维网状结构,起到“二次微加筋”作用,并且通过玄武岩纤维与水泥基体的摩擦和纤维的拉拔作用,消耗了桥梁混凝土裂缝扩展所需要的能量,起到增韧阻裂的作用。

In order to study the toughening and crack resistance effect of basalt fiber on bridge concrete,bending toughness test and fracture toughness test were designed,the influence law of different of basalt fiber(volume percentage,0,0.07%,0.08%,0.09%,the same below)on the crack resistance of bridge concrete,and the optimal fiber content were selected.The degradation and attenuation laws of flexural toughness coefficient and fracture energy of ordinary concrete and optimal fiber content group under different load stress levels(0.5 and 0.7)were studied by using dynamic fatigue loading test.Based on the scanning electron microscope(SEM)test,the toughening and crack resistance mechanism of basalt fiber on bridge concrete was analyzed from the micro scopic of view.The results show that basalt fiber can increase the flexural toughness of concrete,play the role of toughening and crack resistance,and help to avoid premature cracking of concrete under load.When the content of basalt fiber is 0.08%,the improvement effect is the most obvious.The flexural toughness coefficient of 28 d is 235%higher than that of ordinary concrete.Basalt fiber significantly improves the fracture energy of concrete,when the fiber content is 0.08%,the lifting effect is the most obvious,which is 247%higher than that of ordinary concrete.Under different load stress levels,the flexural toughness coefficient and fracture energy of bridge concrete gradually decline with the increase of fatigue loading times,and the decrease range is small in the initial stage and large in the later stage.However,adding basalt fiber can slow down the attenuation rate of bridge concrete,improve its ability to resist fatigue cracking,and then prolong the fatigue life of bridge concrete.The good bonding performance between the fiber and the cement matrix makes the basalt fiber form a stable disordered three-dimensional network structure in the concrete,which plays the role of secondary micro reinforcement.Through the friction between the basalt fiber and the cement matrix and the pulling effect of the fiber,the energy required for the crack propagation of the bridge concrete is consumed,which plays the role of toughening and crack resistance.4 tabs,11 figs,28 refs.