自密实混凝土细观结构的优化及其对渗透性的影响
发布时间：2018-09-10 17:02
【摘要】：混凝土细观结构包括骨料、水泥砂浆及二者之间的过渡区。与普通混凝土相比，自密实混凝土具有胶凝材料用量大、砂率大、骨料粒径小等特点，这导致硬化混凝土中界面区（石和砂表面）的数量增多，但大的界面区减少，以及浆体的硬化细观结构等都发生了较大变化，从而直接影响到混凝土抵抗外界介质渗透的能力。 本文以氯离子扩散系数来表征混凝土的渗透性能，利用了压汞测孔技术（MIP）、毛细孔吸水速率试验、背散射电子成像图像处理技术和光学显微镜测孔技术等试验方法，分别研究了自密实混凝土浆体孔隙结构和界面过渡区的影响因素及其与渗透性能的关系，提出了基于优化混凝土细观结构的配合比设计方法，为自密实混凝土的广泛应用提供参考。 研究了水灰比和矿物掺合料对自密实混凝土浆体孔隙结构及渗透性的影响。研究结果表明：水灰比为0.34时，水泥等颗粒的水膜厚度适中，毛细孔相互连通程度较低，最可几孔径与临界孔径均较小，分别为5.178nm、40.283nm。合适掺量（小于30%）的矿渣能显著减少SCC毛细孔隙，降低Cl-扩散系数，但对粗大孔隙的改善作用不大。粉煤灰能提高混凝土密实度，减少粗大孔隙，但对微小的毛细孔隙改善作用不大，最佳掺量在40%以内。硅灰能降低骨料界面处的孔隙，且能有效切断毛细孔的连通，同时其水化产物形成更细小的凝胶孔隙，硅灰的掺量不宜超过7%。双掺矿渣粉煤灰能利用各自的优势；矿渣对改善较细毛细孔作用明显，粉煤灰对改善较大孔隙作用明显，粉煤灰能改善新拌混凝土的流动性，弥补了矿渣使混凝土变稠的缺点，双掺矿渣粉煤灰充分发挥了各自的优势更好改善SCC孔隙结构。 研究了粗细骨料和粗骨料数量、级配和骨料粒径对自密实混凝土细观结构及其渗透性的影响。结果表明：细骨料表面积为3480m2/m3（砂率为51%）时，新拌混凝土流动性较好，密实度较高，细骨料界面较少，混凝土内毛细孔相互连通程度较低。骨料总表面积为3716m2/m3时，最可几孔径和临界孔径较小，分别为9.064nm、40.284nm，大孔含量较少而毛细孔相对较多，孔隙率较低，孔径也较小。Cl-扩散系数与骨料的总表面积呈线性相关，相关系数高达0.974。适中的骨料总表面积（216m2/m3左右）可以降低Cl-扩散系数，有助于提高SCC渗透性。细粒径骨料（5~10mm）含量在30%~40%时，骨料堆积密度较高，骨料界面孔隙率均较低，形成的空隙率较小，界面结合较好。随着骨料粒径的增大，骨料表面的孔隙增多，界面也越明显，界面结合变差。在细粒径骨料与粗粒径骨料表面Ca、O、Al元素富集，有较大结晶的CH和硫铝酸盐水化产物。在SCC配合比设计中，应该选用合适的中间粒径骨料（10~16mm）含量。 随后引入灰色关联分析，研究各影响因素对自密实混凝土的渗透性的贡献程度。研究结果表明，各影响因素对自密实混凝土氯离子扩散系数的贡献程度顺序是：10~16mm骨料表面积大于1000μm孔隙20~50nm孔隙粗骨料表面积总表面积100~400μm孔隙50~200nm孔隙。 最后，本文对配合比进行了优化设计，胶凝材料用量下降至448~430kg/m3，使用较大含量的中细粒径骨料、掺入20%的矿渣和30%粉煤灰时，制备出的SCC的工作性能、力学性能符合要求和氯离子扩散系数较低。此时的最可几孔径和临界孔径分别是6.032nm和40.258nm，大孔数量与孔径并无大幅增加，孔隙结构并没有劣化；在骨料表面处的孔隙减少，裂缝宽度减少；而在近表面，，均匀分布着CH、C-S-H等水化产物，粉煤灰等颗粒能分布在骨料表面，填充孔隙；具有更有利的界面过渡区。
[Abstract]:The meso-structure of concrete includes aggregate, cement mortar and the transition zone between them. Compared with ordinary concrete, self-compacting concrete has the characteristics of large amount of cementitious materials, large sand ratio and small aggregate size, which leads to the increase of the number of interface areas (stone and sand surface) in hardened concrete, but the decrease of large interface areas and the fine hardening of mortar. Great changes have taken place in the apparent structure, which directly affects the ability of concrete to resist the permeability of external media.
In this paper, chloride ion diffusion coefficient is used to characterize the permeability of concrete. The influence factors of pore structure and interfacial transition zone of self-compacting concrete paste are studied by means of mercury intrusion porosimetry (MIP), capillary water absorption rate test, backscattering electron imaging image processing technique and optical microscope porosimetry. The mix proportion design method based on optimizing concrete microstructure is proposed to provide reference for the wide application of self-compacting concrete.
The effects of water cement ratio and mineral admixture on pore structure and permeability of self-compacting concrete paste were studied.The results show that when the water cement ratio is 0.34,the water film thickness of cement and other particles is moderate,the degree of capillary interconnection is low,the most probable pore diameter and critical pore diameter are small,they are 5.178 nm and 40.283 nm respectively. Fly ash can improve the compactness of concrete and reduce the coarse pore, but it can not improve the tiny pore. The optimum content of silica fume is less than 40%. At the same time, the hydration products form finer gel pores, and the content of silica fume should not exceed 7%. The double-admixture slag fly ash can make use of their advantages; the slag can improve the finer pore obviously; the fly ash can improve the larger pore obviously; the fly ash can improve the fluidity of fresh concrete and make up the slag can change the concrete. The disadvantages of thickening slag and fly ash make full use of their respective advantages to better improve the pore structure of SCC.
The effects of the quantity, gradation and particle size of coarse and fine aggregates on the microstructure and permeability of self-compacting concrete were studied. When aggregate total surface area is 3716 m2/m3, the most probable pore size and critical pore size are smaller, which are 9.064 nm and 40.284 nm, respectively. The macropore content is less, the capillary pore is relatively large, the porosity is relatively low, and the pore size is also small. In order to reduce the Cl-diffusion coefficient, it is helpful to improve the permeability of SCC. When the content of fine aggregate (5-10mm) is between 30% and 40%, the aggregate packing density is higher, the porosity of aggregate interface is lower, the void ratio is smaller, and the interface bonding is better. With the increase of aggregate particle size, the porosity of aggregate surface increases, the interface is more obvious, and the interface bonding becomes worse. Ca, O, Al elements on the surface of diameter aggregate and coarse size aggregate are enriched, and CH and sulphoaluminate hydrate products with larger crystallization are obtained.
Then the grey relational analysis is introduced to study the contribution degree of each influencing factor to the permeability of self-compacting concrete. The results show that the order of contribution degree of each influencing factor to the chloride diffusion coefficient of self-compacting concrete is: the total surface area of coarse aggregate with 10-16 mm aggregate surface area greater than 1000 micron pore 20-50 nm pore is 100-400 micron. Pore 50~200nm pore.
Finally, the optimum design of the mix proportion is carried out. The dosage of cementitious material is reduced to 448-430 kg/m3, the working performance, mechanical properties and chloride diffusivity of SCC prepared by mixing 20% slag and 30% fly ash with medium and fine aggregate with large content are satisfied. The most probable pore size and critical pore size are 6. At 0.032 nm and 40.258 nm, the number and pore size of macropores did not increase significantly, and the pore structure did not deteriorate; the pores on the aggregate surface decreased, and the crack width decreased; while near the surface, the hydrated products such as CH, C-S-H were uniformly distributed; the particles such as fly ash could be distributed on the aggregate surface and filled the pores; and there was a more favorable interface transition zone.
【学位授予单位】：华南理工大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TU528
[Abstract]:The meso-structure of concrete includes aggregate, cement mortar and the transition zone between them. Compared with ordinary concrete, self-compacting concrete has the characteristics of large amount of cementitious materials, large sand ratio and small aggregate size, which leads to the increase of the number of interface areas (stone and sand surface) in hardened concrete, but the decrease of large interface areas and the fine hardening of mortar. Great changes have taken place in the apparent structure, which directly affects the ability of concrete to resist the permeability of external media.
In this paper, chloride ion diffusion coefficient is used to characterize the permeability of concrete. The influence factors of pore structure and interfacial transition zone of self-compacting concrete paste are studied by means of mercury intrusion porosimetry (MIP), capillary water absorption rate test, backscattering electron imaging image processing technique and optical microscope porosimetry. The mix proportion design method based on optimizing concrete microstructure is proposed to provide reference for the wide application of self-compacting concrete.
The effects of water cement ratio and mineral admixture on pore structure and permeability of self-compacting concrete paste were studied.The results show that when the water cement ratio is 0.34,the water film thickness of cement and other particles is moderate,the degree of capillary interconnection is low,the most probable pore diameter and critical pore diameter are small,they are 5.178 nm and 40.283 nm respectively. Fly ash can improve the compactness of concrete and reduce the coarse pore, but it can not improve the tiny pore. The optimum content of silica fume is less than 40%. At the same time, the hydration products form finer gel pores, and the content of silica fume should not exceed 7%. The double-admixture slag fly ash can make use of their advantages; the slag can improve the finer pore obviously; the fly ash can improve the larger pore obviously; the fly ash can improve the fluidity of fresh concrete and make up the slag can change the concrete. The disadvantages of thickening slag and fly ash make full use of their respective advantages to better improve the pore structure of SCC.
The effects of the quantity, gradation and particle size of coarse and fine aggregates on the microstructure and permeability of self-compacting concrete were studied. When aggregate total surface area is 3716 m2/m3, the most probable pore size and critical pore size are smaller, which are 9.064 nm and 40.284 nm, respectively. The macropore content is less, the capillary pore is relatively large, the porosity is relatively low, and the pore size is also small. In order to reduce the Cl-diffusion coefficient, it is helpful to improve the permeability of SCC. When the content of fine aggregate (5-10mm) is between 30% and 40%, the aggregate packing density is higher, the porosity of aggregate interface is lower, the void ratio is smaller, and the interface bonding is better. With the increase of aggregate particle size, the porosity of aggregate surface increases, the interface is more obvious, and the interface bonding becomes worse. Ca, O, Al elements on the surface of diameter aggregate and coarse size aggregate are enriched, and CH and sulphoaluminate hydrate products with larger crystallization are obtained.
Then the grey relational analysis is introduced to study the contribution degree of each influencing factor to the permeability of self-compacting concrete. The results show that the order of contribution degree of each influencing factor to the chloride diffusion coefficient of self-compacting concrete is: the total surface area of coarse aggregate with 10-16 mm aggregate surface area greater than 1000 micron pore 20-50 nm pore is 100-400 micron. Pore 50~200nm pore.
Finally, the optimum design of the mix proportion is carried out. The dosage of cementitious material is reduced to 448-430 kg/m3, the working performance, mechanical properties and chloride diffusivity of SCC prepared by mixing 20% slag and 30% fly ash with medium and fine aggregate with large content are satisfied. The most probable pore size and critical pore size are 6. At 0.032 nm and 40.258 nm, the number and pore size of macropores did not increase significantly, and the pore structure did not deteriorate; the pores on the aggregate surface decreased, and the crack width decreased; while near the surface, the hydrated products such as CH, C-S-H were uniformly distributed; the particles such as fly ash could be distributed on the aggregate surface and filled the pores; and there was a more favorable interface transition zone.
【学位授予单位】：华南理工大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TU528
【参考文献】
相关期刊论文 前10条
1 杨钱荣,朱蓓蓉;混凝土渗透性的测试方法及影响因素[J];低温建筑技术;2003年05期
2 骆冰冰;毕巧巍;;混杂纤维自密实混凝土孔结构对抗压强度影响的试验研究[J];硅酸盐通报;2012年03期
3 卢木,王娴明;结构耐久性多层次综合评定[J];工业建筑;1998年01期
4 王硕太,马国靖,刘晓曦,吴永根,蔡良才;机场自密实道面混凝土微观分析[J];混凝土;2004年06期
5 宗兰;曾丽娟;王元纲;张高勤;;干拌自密实混凝土孔结构的试验研究[J];混凝土;2009年10期
6 韦江雄;余其俊;曾小星;白瑞英;;混凝土中孔结构的分形维数研究[J];华南理工大学学报(自然科学版);2007年02期
7 昊中伟;;混凝土科学技术的反思——吴中伟教授在祝贺其七十寿辰时的学术报告[J];混凝土与水泥制品;1988年06期
8 杨玉红;李悦;杜修力;;自密实混凝土早期自收缩及微观孔结构研究[J];建筑材料学报;2010年05期
9 吴中伟;绿色高性能混凝土与科技创新[J];建筑材料学报;1998年01期
10 张长清;吴海兵;杜明月;刘齐霞;郑力
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