矿物掺合料对超高性能混凝土的水化及微结构形成的影响

发布时间：2018-05-04 14:34

本文选题：超高性能混凝土 + 矿物掺合料　；参考：《东南大学》2017年博士论文

【摘要】：超高性能混凝土(Ultra-High Performance Concrete, UHPC)是一种新型的土木工程材料,与普通混凝土相比,具有极其优异的力学性能和耐久性能,不仅可作为新型的特殊构件,也可以应用于基础设施的维护与加固工程。然而传统的UHPC在实际工程中并未得到广泛应用,其中主要原因之一是该配合比中只含有大量的水泥(1100-1300 kg/m3) 和硅灰 (200-350 kg/m3) , 使得其生产成本极其昂贵; 并且水泥和硅灰的有效利用率仅为30-40%,这极大地浪费了资源和能源。因此利用矿物掺合料取代传统UHPC配合比中的部分水泥或硅灰,是解决UHPC高成本和高能耗的有效方法之一。然而目前缺乏不同矿物掺合料对UHPC宏观性能与微观机理的系统性研究,这严重制约了生态型UHPC的研究与应用进展。本文针对上述问题,应用多种现代测试技术,系统性地研究了石灰石粉、F级与C级粉煤灰、粒化高炉矿渣、偏高岭土与煅烧粘土对UHPC的宏观性能、水泥水化和微结构演变的影响。试验研究揭示了:(1)石灰石粉和C级粉煤灰能够改善UHPC基体的工作性,降低混凝土的粘度,F级粉煤灰在超过一定掺量下会降低混凝土的流动性。粒化高炉矿渣和煅烧粘土的应用增加了混凝土的粘稠性,降低混凝土的工作性。(2)矿物掺合料的应用会降低单位体积内水泥的含量,改变UHPC体系内有效水灰比w/c值的大小。过高掺量的矿物掺合料会显著提高w/c,使得体系中缺乏足够的水泥参与水化反应,混凝土在后期水化中缺乏足够的C-S-H凝胶;矿物掺合料取代量过低时,仍然有大量的水泥未得到有效利用。UHPC体系中水泥含量与总水量需要保持合适的平衡关系,满足“完全水化理论”有效w/c值,即0.4左右。满足该平衡关系且拌合物工作性较好的UHPC基体,在常温密封养护条件下,56天的抗压强度均能达到150 MPa左右,例如掺加石灰石粉、F级粉煤灰和C级粉煤灰的UHPC抗压强度值分别为 169.6 MPa、167.4 MPa 和 142.9 MPa。(3) F级粉煤灰的火山灰反应和粒化高炉矿渣的水硬性反应对水泥水化的影响较小,然而C级粉煤灰和锻烧粘土(特别是偏高岭土)中可以溶解出大量的铝离子,在孔溶液中形成大量的钙矾石AFt和单碳型碳铝酸盐AFm-Mc,消耗了体系中大量的自由水。该化学反应与水泥水化产生了对自由水的竞争关系,水泥的水化受到严重的抑制,这也影响了体系中Ca(OH)2的生成与消耗。石灰石粉的化学活性取决于UHPC体系中可溶解性铝离子的含量,CaC03与铝离子反应生成AFm-Mc。钙矾石和单碳型碳铝酸盐相的大量形成能够显著降低UHPC的孔隙率,然而对于掺加C级粉煤灰的UHPC,由于生成的钙矾石尺寸较大,与硅灰和水泥水化产物相互混合,对孔结构的细化作用并不明显,但是对于掺加煅烧粘土的UHPC,由于颗粒堆积体系不同,孔结构一定程度上得到细化。(4)选择合适的矿物掺合料取代水泥或硅灰,不仅能够维持UHPC极其优异的力学性能,提高材料的使用效率,还能改善混凝土的流变性能,降低高效减水剂的使用量,这有助于降低UHPC整体的生产成本和CO2排放量,有利于UHPC的大规模普及利用和可持续发展。
[Abstract]:Ultra-High Performance Concrete (UHPC) is a new kind of civil engineering material. Compared with ordinary concrete, it has excellent mechanical properties and durability. It can be used not only as a new special component, but also in the maintenance and reinforcement engineering of infrastructure. However, the traditional UHPC is in practical engineering. One of the main reasons is that one of the main reasons is that the mixture contains only a large amount of cement (1100-1300 kg/m3) and silica fume (200-350 kg/m3), which makes the production cost extremely expensive; and the effective utilization of cement and silica fume is only 30-40%, which is a great wave of resources and energy. Therefore, the mineral admixture is used instead of the mineral admixture. The traditional UHPC mix proportion cement or silica fume is one of the effective methods to solve the high cost and high energy consumption of UHPC. However, there is a lack of systematic research on the macro and micro mechanism of UHPC with different mineral admixtures, which seriously restricts the progress of the research and application of ecotype UHPC. Test techniques systematically studied the effect of limestone powder, F grade and C grade fly ash, granulated blast furnace slag, high ridge soil and calcined clay on the macro properties of UHPC, cement hydration and microstructure evolution. (1) lime stone powder and C grade fly ash can improve the working property of UHPC matrix, reduce the viscosity of concrete, and F grade pulverized coal. The application of granulated blast furnace slag and calcined clay increases the consistency of concrete and reduces the workability of concrete. (2) the application of mineral admixtures will reduce the content of cement in the unit volume and change the w/c value of the effective water cement ratio in the UHPC system. The admixture will significantly increase the w/c, which makes the system lack enough cement to take part in the hydration reaction, and the concrete lacks sufficient C-S-H gel in the later hydration. When the mineral admixture is too low, a large number of cement still has not been used effectively in the.UHPC system to maintain a proper balance between the cement content and the total water content. The effective w/c value of complete hydration theory, that is about 0.4, is about 0.4. The UHPC matrix that meets the balance and the working property of the mixture can reach about 150 MPa at 56 days under the condition of normal temperature sealing. For example, the UHPC compressive strength of F grade fly ash and C grade fly ash is 169.6 MPa, 167.4 MPa and 142, respectively. The volcanic ash reaction of.9 MPa. (3) F grade fly ash and the hydration of granulated blast furnace slag have little effect on the hydration of cement. However, a large amount of aluminum ions can be dissolved in C grade fly ash and calcined clay (especially in metakaolin), and a large number of alunite AFt and single carbon aluminate AFm-Mc can be formed in the pore solution, which consumes the system. The chemical reaction and hydration of cement produce a competitive relationship with free water, and the hydration of cement is severely restrained, which also affects the formation and consumption of Ca (OH) 2 in the system. The chemical activity of limestone powder depends on the content of soluble aluminum ions in the UHPC system and the reaction of CaC03 with aluminum ions to produce AFm-Mc. calcium Ettringite The formation of a large number of single carbon aluminate phases can significantly reduce the porosity of UHPC. However, for the UHPC doped with C grade fly ash, due to the larger size of the ettringite, the refinement of the pore structure is not obvious with the mixture of silica fume and cement hydration products. But for the UHPC of the calcined clay, the particle accumulation system is due to the addition of the calcined altrite. The pore structure is refined to a certain extent. (4) choosing suitable mineral admixtures to replace cement or silica fume can not only maintain excellent mechanical properties of UHPC, improve the use efficiency of materials, but also improve the rheological properties of concrete and reduce the amount of high efficiency water reducing agent, which helps to reduce the overall production cost and CO2 of the UHPC. Emissions are conducive to large-scale popularization and utilization of UHPC and sustainable development.

【学位授予单位】：东南大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TU528

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