【作者】 程大伟；

【导师】 杜应吉；

【作者基本信息】 西北农林科技大学 ， 水工结构工程， 2009， 硕士

【摘要】 粉煤灰应用技术的快速发展,对提高粉煤灰的利用率水平起到很大的促进作用。在大掺量粉煤灰混凝土中粉煤灰掺量可以比普通粉煤灰混凝土明显增大,粉煤灰的效用能得到充分的发挥,经济效益显著。目前,大掺量粉煤灰混凝土断裂韧度的研究正逐步深入,但尚未发现关于异型塑钢纤维、灰胶比和水胶比对大掺量粉煤灰混凝土的强度和断裂韧度影响的研究。本文应用三元二次正交旋转组合设计安排试验,研究了异型塑钢纤维掺量、灰胶比和水胶比对异型塑钢纤维大掺量粉煤灰混凝土的强度和断裂韧度的影响规律。主要研究成果如下:(1)建立了以抗压强度、劈拉强度和断裂韧度为因变量的三元二次回归方程,对影响抗压强度、劈拉强度和断裂韧度的因素进行主效应分析、单因子效应分析及两因子间交互作用分析,得出异型塑钢纤维是提高塑钢纤维大掺量粉煤灰混凝土的抗压强度和断裂韧度的有益因子,灰胶比是提高塑钢纤维大掺量粉煤灰混凝土的抗压强度、劈拉强度和断裂韧度的有益因子,水胶比是影响异型塑钢纤维大掺量粉煤灰混凝土的抗压强度、劈拉强度和断裂韧度的显著因子。(2)对试件尺寸为100mm×100mm×400mm异型塑钢纤维大掺量粉煤灰混凝土三点弯曲梁弯曲试验的结果表明:异型塑钢纤维的掺入显著改善了大掺量粉煤灰混凝土的断裂韧度。当异型塑钢纤维体积率为1%时,断裂韧度提高了56%。在大掺量粉煤灰混凝土中,通过掺加异型塑钢纤维可以有效抑制大掺量粉煤灰混凝土早期干缩裂缝以及离析裂缝的产生及发展,极大地减少了收缩裂缝,尤其是有效抑制了连通裂缝的产生,均匀分布的纤维单丝起到了“承托”骨料的作用,降低了大掺量粉煤灰混凝土表面的析水和骨料的离析,从而使混凝土的孔隙率大大降低,提高了大掺量粉煤灰混凝土的强度和断裂韧度。(3)粉煤灰掺量的增加能够提高异型塑钢纤维大掺量粉煤灰混凝土的强度和断裂韧度。保持异型塑钢纤维体积为0.5%、水胶比为0.4不变,只有当灰胶比为0.5时,强度和断裂韧度才达到最大值。粉煤灰的三大效应——形态效应、微集料效应、活性效应能够使混凝土的微结构变得均匀、大孔消失、浆体—骨料界面区的孔隙率减小,生成致密网状的C-S-H凝胶填充了孔隙,同时粉煤灰在二次水化反应中要消耗Ca(OH)2,在很大程度上改善了浆体和界面的结构,使大掺量粉煤灰混凝土的密实性大大提高,从而提高了强度和断裂韧度。(4)水胶比增大会导致强度和断裂韧度的降低。与水胶比为0.3时相比,当水胶比增大到0.5时,塑钢纤维大掺量粉煤灰混凝土的抗压强度、劈拉强度和断裂韧度分别降低了39%、39%和22%。水胶比的增大意味在塑钢纤维大掺量粉煤灰混凝土中相对用水量的增多,大量游离水存在于大掺量粉煤灰混凝土的各晶格间和粗细毛孔中,在蒸发的条件下件下造成粉煤灰混凝土干缩及裂缝的产生。同时水胶比过大,造成混凝土的粘聚性和保水性不良。在粉煤灰混凝土振捣过程中,水泥浆体与骨料分离,造成流浆、离析现象。这些现象的不良影响是造成粉煤灰混凝土强度和断裂韧度降低重要原因。更多还原

【Abstract】 The development of fly ash application technology plays a significant role in promoting the utilization of fly ash . The volume of fly ash in concrete with large percent fly ash is higher than the the volume of fly ash in concrete with fly ash . The effectiveness of fly ash can play the role fully. And it’s economic benefits is significant. Found by searching, the research about KIC of concrete with large percent fly ash is creasing, but the research of Shaped PP Fiber volume rate how to play the role in concrete with large percent fly ash is not found. At the same time, fly ash/cement ratio and water/cement ratio , how play their roles. We still do not know. Based on previous research , this thesis using the second-degree polynomial regression Analysis and orthogonal rotation design to arrange the experiment research the law of the strengthening and KIC of concrete with large percentage fly ash. Main results as follows:(1) The thesis returns separately to the compressive strength, splitting tensile strength and KIC as the dependent variable of the ternary quadratic regression equation, and to the compressive strength, divides pulls the intensity and the KIC carries on the main effect Analysis, the single factorial effect Analysis and during two factors the correlation. The result indicated Shaped PP Fiber can enhance the compressive strength and KIC of concrete with large percent fly ash; fly ash can enhance the compressive strength, splitting tensile strength and KIC of concrete with large percent fly ash; and water/cement ratio is the remarkable factor.(2) The test of three-point bending beam on concrete with large percentage fly ash ,with the size of 100mm×100mm×400mm, indicated that the addition of Shaped PP Fiber is helpful in improving the KIC.When Shaped PP Fiber volume is 1% , the KIC increase 56%. In Shaped PP Fiber mixing to concrete with large percent fly ash, Shaped PP Fiber can suppress effectively concrete with large percent fly ash early time desiccation fissure as well as the segregation crack production and the development greatly; reduces the shrinkage fracture greatly.Especially Shaped PP Fiber has suppressed the connection crack production effectively. Uniform distribution’s textile fiber monofilament played“has supported”the aggregate role and reduced concrete with large percent fly ash the surface bleeding and the aggregate segregation greatly. Thus the concretes percentage of voids reduces greatly and enhanced the intensity and the KIC of concrete with large percent fly ash greatly. (3) The test indicated that the addition of fly ash is helpful in improving the compressive strength, splitting tensile strength and KIC。When fly ash/cement ratio is 0.5 ,the Shaped PP Fiber volume fraction is 0.5% and water/cement ratio is 0.4,the strethening and KIC is maximizing. The fly ash three big effect - - shape effect, the micro aggregate effect, the active effect can cause the concretes the microstructure become even, pocket vanishing, the hydromass - aggregate frontal zone factor of porosity reduce,produced compact netted the C-S-H gelatin to fill the hole . Simultaneously the fly ash must consume Ca(OH)2 in second hydrated responses, to a great extent improved the hydromass and the contact surface structure, Causes to mix the quantity pulverized coal ash concretes dense enhance greatly ,and enhanced the intensity and the KIC of concrete with large percent fly ash .(4) Increasing the water/cement ratio will reduce strengthening and KIC. Camparing to water/cement ratio is 0.3, when water/cement ratio is 0.5, the compressive strength, splitting tensile strength and KIC of concrete with large percent fly ash reduce separately 39%,39% and 22%. Water/cement ratio compared to increases meaning, in concrete with large percent fly ash and Shaped PP Fiber relative water consumption increase, The massive free water exist greatly in between various crystal lattices and the thick thin pore in oncrete with large percent fly ash.under the evaporation condition , creates the concrete with fly ash air shrinkage and the crack production . Simultaneously water/cement ratio compared to oversized, creates the concretes the cohesive properties coherency and the water retention property bad.In the process of vibration, hydromass and aggregate separation , creates the class thick liquid and the segregation phenomenon. Those will reduce the intensity and the KIC of concrete with large percent fly ash .更多还原