自密實混凝土細觀結構的優(yōu)化及其對滲透性的影響
發(fā)布時間：2018-09-10 17:02
【摘要】：混凝土細觀結構包括骨料、水泥砂漿及二者之間的過渡區(qū)。與普通混凝土相比，自密實混凝土具有膠凝材料用量大、砂率大、骨料粒徑小等特點，這導致硬化混凝土中界面區(qū)（石和砂表面）的數量增多，但大的界面區(qū)減少，以及漿體的硬化細觀結構等都發(fā)生了較大變化，從而直接影響到混凝土抵抗外界介質滲透的能力。 本文以氯離子擴散系數來表征混凝土的滲透性能，利用了壓汞測孔技術（MIP）、毛細孔吸水速率試驗、背散射電子成像圖像處理技術和光學顯微鏡測孔技術等試驗方法，分別研究了自密實混凝土漿體孔隙結構和界面過渡區(qū)的影響因素及其與滲透性能的關系，提出了基于優(yōu)化混凝土細觀結構的配合比設計方法，為自密實混凝土的廣泛應用提供參考。 研究了水灰比和礦物摻合料對自密實混凝土漿體孔隙結構及滲透性的影響。研究結果表明：水灰比為0.34時，水泥等顆粒的水膜厚度適中，毛細孔相互連通程度較低，最可幾孔徑與臨界孔徑均較小，分別為5.178nm、40.283nm。合適摻量（小于30%）的礦渣能顯著減少SCC毛細孔隙，降低Cl-擴散系數，但對粗大孔隙的改善作用不大。粉煤灰能提高混凝土密實度，減少粗大孔隙，但對微小的毛細孔隙改善作用不大，最佳摻量在40%以內。硅灰能降低骨料界面處的孔隙，且能有效切斷毛細孔的連通，同時其水化產物形成更細小的凝膠孔隙，硅灰的摻量不宜超過7%。雙摻礦渣粉煤灰能利用各自的優(yōu)勢；礦渣對改善較細毛細孔作用明顯，粉煤灰對改善較大孔隙作用明顯，粉煤灰能改善新拌混凝土的流動性，彌補了礦渣使混凝土變稠的缺點，雙摻礦渣粉煤灰充分發(fā)揮了各自的優(yōu)勢更好改善SCC孔隙結構。 研究了粗細骨料和粗骨料數量、級配和骨料粒徑對自密實混凝土細觀結構及其滲透性的影響。結果表明：細骨料表面積為3480m2/m3（砂率為51%）時，新拌混凝土流動性較好，密實度較高，細骨料界面較少，混凝土內毛細孔相互連通程度較低。骨料總表面積為3716m2/m3時，最可幾孔徑和臨界孔徑較小，分別為9.064nm、40.284nm，大孔含量較少而毛細孔相對較多，孔隙率較低，孔徑也較小。Cl-擴散系數與骨料的總表面積呈線性相關，相關系數高達0.974。適中的骨料總表面積（216m2/m3左右）可以降低Cl-擴散系數，有助于提高SCC滲透性。細粒徑骨料（5~10mm）含量在30%~40%時，骨料堆積密度較高，骨料界面孔隙率均較低，形成的空隙率較小，界面結合較好。隨著骨料粒徑的增大，骨料表面的孔隙增多，界面也越明顯，界面結合變差。在細粒徑骨料與粗粒徑骨料表面Ca、O、Al元素富集，有較大結晶的CH和硫鋁酸鹽水化產物。在SCC配合比設計中，應該選用合適的中間粒徑骨料（10~16mm）含量。 隨后引入灰色關聯(lián)分析，研究各影響因素對自密實混凝土的滲透性的貢獻程度。研究結果表明，各影響因素對自密實混凝土氯離子擴散系數的貢獻程度順序是：10~16mm骨料表面積大于1000μm孔隙20~50nm孔隙粗骨料表面積總表面積100~400μm孔隙50~200nm孔隙。 最后，本文對配合比進行了優(yōu)化設計，膠凝材料用量下降至448~430kg/m3，使用較大含量的中細粒徑骨料、摻入20%的礦渣和30%粉煤灰時，制備出的SCC的工作性能、力學性能符合要求和氯離子擴散系數較低。此時的最可幾孔徑和臨界孔徑分別是6.032nm和40.258nm，大孔數量與孔徑并無大幅增加，孔隙結構并沒有劣化；在骨料表面處的孔隙減少，裂縫寬度減少；而在近表面，，均勻分布著CH、C-S-H等水化產物，粉煤灰等顆粒能分布在骨料表面，填充孔隙；具有更有利的界面過渡區(qū)。
[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.
【學位授予單位】：華南理工大學
【學位級別】：碩士
【學位授予年份】：2014
【分類號】：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.
【學位授予單位】：華南理工大學
【學位級別】：碩士
【學位授予年份】：2014
【分類號】：TU528
【參考文獻】
相關期刊論文 前10條
1 楊錢榮,朱蓓蓉;混凝土滲透性的測試方法及影響因素[J];低溫建筑技術;2003年05期
2 駱冰冰;畢巧巍;;混雜纖維自密實混凝土孔結構對抗壓強度影響的試驗研究[J];硅酸鹽通報;2012年03期
3 盧木,王嫻明;結構耐久性多層次綜合評定[J];工業(yè)建筑;1998年01期
4 王碩太,馬國靖,劉曉曦,吳永根,蔡良才;機場自密實道面混凝土微觀分析[J];混凝土;2004年06期
5 宗蘭;曾麗娟;王元綱;張高勤;;干拌自密實混凝土孔結構的試驗研究[J];混凝土;2009年10期
6 韋江雄;余其俊;曾小星;白瑞英;;混凝土中孔結構的分形維數研究[J];華南理工大學學報(自然科學版);2007年02期
7 昊中偉;;混凝土科學技術的反思——吳中偉教授在祝賀其七十壽辰時的學術報告[J];混凝土與水泥制品;1988年06期
8 楊玉紅;李悅;杜修力;;自密實混凝土早期自收縮及微觀孔結構研究[J];建筑材料學報;2010年05期
9 吳中偉;綠色高性能混凝土與科技創(chuàng)新[J];建筑材料學報;1998年01期
10 張長清;吳海兵;杜明月;劉齊霞;鄭力
本文編號：2235067
本文鏈接：http://sikaile.net/guanlilunwen/chengjian/2235067.html
