Nghiên cứu bê tông có độ bền ăn mòn cao sử dụng muội silic cho kết cấu công trình ở môi trường biển Việt Nam. Nghiên cứu bê tông có độ bền ăn mòn cao sử dụng muội silic cho kết cấu công trình ở môi trường biển Việt Nam. Nghiên cứu bê tông có độ bền ăn mòn cao sử dụng muội silic cho kết cấu công trình ở môi trường biển Việt Nam. Nghiên cứu bê tông có độ bền ăn mòn cao sử dụng muội silic cho kết cấu công trình ở môi trường biển Việt Nam. Nghiên cứu bê tông có độ bền ăn mòn cao sử dụng muội silic cho kết cấu công trình ở môi trường biển Việt Nam. Nghiên cứu bê tông có độ bền ăn mòn cao sử dụng muội silic cho kết cấu công trình ở môi trường biển Việt Nam. Nghiên cứu bê tông có độ bền ăn mòn cao sử dụng muội silic cho kết cấu công trình ở môi trường biển Việt Nam. Nghiên cứu bê tông có độ bền ăn mòn cao sử dụng muội silic cho kết cấu công trình ở môi trường biển Việt Nam. Nghiên cứu bê tông có độ bền ăn mòn cao sử dụng muội silic cho kết cấu công trình ở môi trường biển Việt Nam. Nghiên cứu bê tông có độ bền ăn mòn cao sử dụng muội silic cho kết cấu công trình ở môi trường biển Việt Nam. Nghiên cứu bê tông có độ bền ăn mòn cao sử dụng muội silic cho kết cấu công trình ở môi trường biển Việt Nam. Nghiên cứu bê tông có độ bền ăn mòn cao sử dụng muội silic cho kết cấu công trình ở môi trường biển Việt Nam. Nghiên cứu bê tông có độ bền ăn mòn cao sử dụng muội silic cho kết cấu công trình ở môi trường biển Việt Nam. Nghiên cứu bê tông có độ bền ăn mòn cao sử dụng muội silic cho kết cấu công trình ở môi trường biển Việt Nam. Nghiên cứu bê tông có độ bền ăn mòn cao sử dụng muội silic cho kết cấu công trình ở môi trường biển Việt Nam.NhËn xÐt 3 §å thÞ h×nh 4 MINISTRY OF EDUCATION AND TRAINING UNIVERSITY OF TRANSPORT AND COMMUNICATIONS NGUYEN LONG KHANH RESEARCH ON HIGH CORROSION RESISTANCE CONCRETE USING SILICA FUME FOR BUILDING S.
MINISTRY OF EDUCATION AND TRAINING UNIVERSITY OF TRANSPORT AND COMMUNICATIONS NGUYEN LONG KHANH RESEARCH ON HIGH CORROSION RESISTANCE CONCRETE USING SILICA-FUME FOR BUILDING STRUCTURES EXPOSED TO MARINE ENVIRONMENT OF VIETNAM Major: Special works engineering Code: 958.02.06 SUMMARY OF THE THESIS Hanoi – 2023 The thesis was completed at: UNIVERSITY OF TRANSPORT AND COMMUNICATIONS Instructors: Assoc Prof Dr Nguyen Thi Tuyet Trinh Prof Dr Pham Duy Huu Reviewer No.1: Prof Dr Nguyen Dong Anh Reviewer No.2: Assoc Prof Dr Khuc Dang Tung Reviewer No.3: Dr Do Huu Thang The thesis is defended in front of the Doctoral Dissertation Judging Committee meeting at the University of Transport and Communications at … of …/…/ 2023 The thesis can be found at: - National Library of Vietnam - Information and Library Communications Center, University of Transport and INTRODUCTION Context The durability of concrete structures in the marine environment has been a matter of concern for decades, because seawater is corrosive not only to reinforcement but also to concrete In the world in the 1970s, the problem of the corrosion resistance of concrete structures began to be researched However, it was not until 2005 that the Netherlands began a formal research program, conducted under the supervision of Committee B23 of the CUR (Global Council for Postgraduate Research), which surveyed sixty results structure at different ages Research shows that the biggest cause affecting the durability of concrete structures is the corrosion of reinforcement due to Cl - ion penetration, mainly in old structures with relatively low protective concrete layer [Wiebenga 1980] Vietnam is a country with more than 3,200 km of coastline Faced with the urgent requirements of the construction and protection of seas and islands, the Party and State pay special attention to the socio-economic development of coastal and island regions with many priority policies for development That includes infrastructure development In fact, the problem of improving the quality and longevity of concrete constructions in the sea or coastal areas is mainly solving the problem of improving the corrosion resistance of concrete in the structure From the above analysis, the thesis selected the topic "Research on high corrosion resistance concrete using silica-fume for building structures exposed to marine environment of Vietnam" to research, analyze and test concrete types Concrete uses silica-fume admixture to enhance the durability of Cl- ion waterproofing for concrete structures in the marine environment Objectives of the research The research objective of the thesis is to study the use of silica-fume concrete with high corrosion resistance for building structures exposed to marine environment of Vietnam, specifically as follows: Determining the effect of the ratio of Water/Binder (W/B), silica-fume content on compressive strength, Cl- ion permeability, Cl- ion diffusion coefficient to evaluate compressive strength, Cl- ion impermeability of silica fume concrete in marine environment Determine the relationship between the W/B ratio, the silica-fume content, the compressive strength, and the Cl- ion permeability to serve as a basis for building a method for designing silica-fume concrete components taking into account the durability of ionic waterproofing Cl- Determine the change of pore volume over time to analyze the influence of pore volume on the durability of silica-fume concrete Evaluation of the time of onset of corrosion for silica-fume concrete and Portland cement concrete structures in the marine environment of Vietnam Application of silica fume concrete mix design for building structures in the marine environment of Vietnam through assessment of corrosion initiation time Object and scope of research The research object of the thesis is concrete using silica fume with specific strength > 60 MPa and Cl- ion permeability < 1000 Coulomb The scope of the thesis is to study the influence of the W/B ratio and the silica-fume content in order to evaluate the durability of Cl- ion waterproofing of concrete in the marine environment, at the high and low tide in the environment sea school Research Methods The method of combining theory and experiment in the laboratory, namely: Theoretical methods are based on the results and contents of studies in the world and in the country, from which appropriate methods and data are selected to be included in the research Experimental research method, Taguchi method for planning, processing experimental data, combined with the use of Life-365 software to evaluate the time of onset of corrosion of structures in the marine environment Room The test method is a laboratory test method based on Vietnamese and foreign standards to determine the strength and pore volume characteristics of concrete Scientific and practical significance Scientific significance: (1) Give more clear evidences on the influence of W/B ratio, silica fume content on the durability of concrete (compressive strength, Cl- ion permeability, Cl- ion diffusion coefficient) ; (2) Establishing the relationship between the ratio of W/B, the silica fume content, the compressive strength, and the Cl- ion permeability of the silica fume concrete Thereby proposing a method to design silica fume concrete considering the durability of Cl- ions; (3) Evaluation of the influence of pore volume on the durability of silica fume concrete over time; (4) Proposing the grade of silica-fume concrete for structures in the marine environment of Vietnam to meet the requirements of durability Practical significance: (1) Contributing to perfecting the method of designing silica-fume concrete components in the marine environment to improve the durability of Cl- ion waterproofing; (2) Promote the utilization of silica-fume materials from industrial products for the construction of transport infrastructure works in the marine area, contributing to reducing environmental pollution, increasing economic and technical efficiency Thesis layout The thesis consists of an introduction, 04 main chapters, conclusions, recommendations and directions for further research, references and appendices CHAPTER OVERVIEW OF CONSTRUCTION WITH HIGH CORROSION RESISTANCE IN THE MARINE ENVIRONMENT 1.1 Overview of marine environment effect on durability of concrete 1.1.1 Conception of the marine environment According to the research of K Mehta (France), corrosion in the marine environment is divided into three main areas [94] : The area is constantly flooded; The tidal zone (including the breaking wave); Atmospheric regions of the sea and the coast The marine environment contains many factors that adversely affect the quality and durability of concrete, reducing the life of the structures In fact, more than 50% of concrete and reinforced concrete structural parts are corroded, severely damaged or destroyed after only 10-30 years of use The aggressive impact of the marine environment on the durability of concrete and reinforced concrete works is mainly as follows: + Carbonation process + The process of permeation of SO42- ions into concrete + The process of diffusion of oxygen, Cl- ions and moisture into concrete + Corrosion process caused by microorganisms, by waves In the world The earth's surface area is covered 71% by water bodies and of which nearly 96,5% is covered by sea water In Vietnam Vietnam has a coastline of more than 3200 km from o37' to 21o32' North with hot and humid conditions typical of Vietnam's climate [40] 1.1.2 Influence of the marine environment on the durability of concrete The marine environment has many harmful effects on the durability of concrete, but the main effects can be summarized as follows: Corrosion of steel reinforcement caused by Cl- ions The actual survey shows that the reinforced concrete works after a period of use all show signs of rust in the reinforcement at different levels, leading to no guarantee on the life of the works Effects of hydration The main products of Portland cement hydration are easily decomposed by components of seawater such as CO2, MgCl2 and MgSO4 Effect of carbonation Carbonization reactions with all hydrated cement products can lead to concrete deterioration Effects of magnesium salts The typical MgCl2 content of seawater is 3200 ppm, which is enough to cause the deterioration of Portland cement's workability due to the invasion of Mg 2+ ions Effects of sulfate invasion Sulfate ions from seawater react with the hydrate products of Portland cement and cause deterioration of concrete structures 1.1.3 Requirements for strengthening concrete in marine environment Requirements on input material selection Requirements on design, concrete composition Requirements on manufacturing and construction technology [40] 1.2 Overview of durability of concrete 1.2.1 Concrete durability According to ASTM E 632, "durability" is the ability to maintain the usability of a product, structure, or structure for a specified time Service life usability is considered the ability of components to perform the function for which they were designed, built The durability of concrete is divided into two main groups: mechanical strength (erosion, washout, freezing/thawing ) and chemical resistance (corrosion of reinforcement due to Cl- ions, corrosion of concrete, etc.) tones due to the phenomenon of carbonation, sulphate invasion, etc.) 1.2.2 Research on corrosion of steel reinforcement caused by Cl- ions The characteristic of corrosion of reinforcement due to Cl- ions is to create "holes" on the metal surface (micropilc), making the ratio of cathode/anodic area large, so the local corrosion current density is very high Only Cl- ions in free form cause corrosion of reinforcement and their diffusion in the porous structure of concrete This process is illustrated in Figure 1.7 From that, Fe2O3 and Fe(OH)3.3H2O are formed, which are products of the electrochemical process Figure 1.7: Mechanism of electrochemical corrosion of steel in concrete exposed to Cl- ions [21] According to Nielsen A (1985), Fe2O3 has twice the volume of the steel it replaces But when converted to Fe(OH)3.3H2O, it expands to 6.5 times, causing cracking and breakage of the protective concrete 1.2.3 Research on the mechanism of influence voids effect on durability of concrete Cl- ions penetrate into concrete through pores and micro-cracks Furthermore, as concrete is a heterogeneous material, the porous properties are directly related to the permeability of concrete [127], including pore structure, strength, curing conditions and environmental factors [77] Therefore, the voids of concrete is also an important criterion to evaluate the durability of the structure 1.3 Overview of silica fume concrete with high corrosion resistance in marine environment 1.3.1 Conception of concrete with high corrosion resistance in marine environment Concrete with high corrosion resistance is essentially high quality concrete Compared with ordinary concrete, in the composition of high-quality concrete, there is an indispensable ingredient, which is mineral admixture There are many types of mineral additives of natural and artificial origin (silica-fume, fly ash, blast furnace slag ) However, silica-fume is one of the most common pozzolans, adding them to the concrete mix results in lower porosity, permeability and water separation because their oxides (SiO2) react with Ca(OH)2, is created from the normal hydration of Portland cement to produce the product C-S-H which is the main component of the strength of concrete 1.3.2 Effect of silica fume on concrete Silica-fume is a kind of pozzolanic mineral additive, which has some characteristic properties such as very small particle size (about 0.1 µm), spherical shape, amorphous structure and high SiO2 content Studies on silica-fume [54], [59] show that the influence of soot on concrete properties is caused by two chemical and physical effects The chemical effect is related to the ability to form calcium calcium silicate hydrogen product CSH, which is the binder that gives strength to concrete On the other hand, the physical effect of silica-fume is the microaggregation effect to fill the gaps between the aggregate particles and between the cement particles, making the concrete denser and stronger These are the main effects of silica-fume on the strength and durability properties of concrete Previous studies related to the use of silica fume in concrete have shown that the optimum silica-fume content used is from 5% to 15% by weight of cement to achieve the required strength [110] 1.3.3 Research situation on concrete with high corrosion resistance using silica fume In the world, research on corrosion, solutions to increase durability for concrete reinforced concrete works in general has been interested since the beginning of the 19th century In developed countries in Europe and America and Nordic countries Some famous scientists in the field related to corrosion of concrete - reinforced concrete structures in the marine environment can be named as P.K Mehta, V.M Malhotra, J P Olivier… [94], [89] with many scientific publications, many reference books, monographs on durability and corrosion resistance of concrete In Vietnam, the research problem of concrete with high corrosion resistance has also been studied before These include the studies of Dao Van Dinh [15], Ho Van Quan [33], Ho Xuan Ba [11], Ngo Van Thuc [33] However, the authors have only focused on researching and evaluating the Cl- ion waterproofing ability of concrete using silicabased mineral admixtures, there have been no in-depth studies on the Cl- ion diffusion coefficient and the effect of silica fume on voids and concrete strength over time Also, no method has been given to design concrete components with regard to durability 1.3 Conclusion of Chapter - In Vietnam, the hot and humid marine climate conditions contain a high concentration of Cl- ions, so reinforced concrete structures are often corroded and degraded at a relatively fast rate Therefore, for concrete used as structures in the marine environment in Vietnam, higher requirements are required in terms of strength and durability of Cl- ion waterproofing - Infiltration of Cl- and SO42- ions are thought to be the two main causes of the destruction of reinforced concrete structures However, the corrosion caused by SO42ions takes place after a long time, so the corrosion caused by Cl- ions is the biggest threat to reduce the service life of reinforced concrete structures in the marine environment - From the overview analysis, the thesis focuses on the research direction affecting the composition factors, pore volume on the resistance to Cl- ion penetration of silica fume concrete Proposing a method to design silica-fume concrete taking into account the resistance to Cl- ion penetration and assessing the corrosion initiation time of reinforced concrete structures in the marine environment.1.5 Thesis's research direction From the analysis in Chapter I, the thesis has identified specific research directions as follows: Study on the influence of composition factors such as W/B ratio, silica-fume content on compressive strength, Cl- ion permeability of silicon black concrete Developing a method to design silica-fume concrete components taking into account the durability of Cl- ion waterproofing Study on the influence of silica-fume on the pore volume of concrete Thereby analyzing the influence of pore volume on the durability of concrete over time Evaluation of the corrosion initiation time of structures when using silica-fume concrete and conventional concrete in the marine environment From there, it is proposed to match the requirements of the corrosion initiation time of 100 years for works in the marine environment CHAPTER THEORETICAL BASIS FOR ASSESSING THE DURABILITY OF SILICA FUME CONCRETE 2.1 Theoretical basis for assessing resistance to Cl- ion penetration of silica-fume concrete 2.1.1 Cl- ion penetration resistance of concrete Cl- ions can be present in concrete constituents, especially in sand and water According to European Standard EN 206-1 (2001) [141], the Cl- ion content per mass of cement should not exceed 0.4% for reinforced concrete or concrete with steel core Cl- ions can be present in concrete as ions in the liquid phase 2.1.2 Test methods for Cl- ion penetration resistance of concrete Long-term experiment: Salt Ponding Test – AASHTO T259); Bulk Diffusion Test (ASTM C1556) Long-term experiment: Rapid Chloride Permeability Test – ASTM C1202); Electrophoresis engineering; The Rapid Chloride Migration Test - AASHTO TP64 2.2 Theoretical basis for evaluating the influence of pore volume on the durability of concrete 2.2.1 Effects of pore volume on the durability of concrete Many studies have shown that porosity is the space between C-S-H and small capillary pores that does not cause permeability for high-quality concrete In contrast, when the degree of hydration increases which leads to a significant increase in the void volume due to the increase of the space between the C-S-H layers and the capillary voids, the permeability decreased sharply Therefore, there is the existance of a direct relationship between permeability and pore volume greater than 100 nm This may be because in the pore system, which includes many small pores, there is a tendency to discontinuity (discontinuous) which affects the durability of concrete 2.2.2 Method to determine the pore volume of concrete The pore volume of concrete was determined by the N adsorption-desorption isotherm method (Brunauer - Emmett - Teller/BET method) This method is used to determine properties of capillary materials such as specific surface area, pore volume, pore size distribution as well as surface properties From the results of the BET method, the Barret - Joyner - Halenda (BJH) method is applied to determine the pore volume distribution and pore size, thereby determining the pore distribution in concrete 2.3 Introduction to the Taguchi method 2.3.1 Experimental design according to Taguchi's method The Taguchi method combines experimental planning and data processing to figure out the relationship between the input variable and the objective function In particular, the experimental matrix design applied in many technical fields for high efficiency is simple The experimental matrices are designed based on fixed orthogonal matrices The process is done as follows: Determine the parameters Determine the levels of each parameter Select a suitable OA orthogonal array Assign parameters to columns of orthogonal array Conduct experiments Analyze data 2.3.2 Building regression equation according to Taguchi method In the Taguchi method, to build the relationship between the objective functions and the input variables, the analysis of the model variance, the consideration of the model's correlation coefficient, and the determination of the terms in the model are supported by the Minitab software [23] The overall regression equation has the following form [23]: q y b0 b j x j j 1 j u q b ju x j xu b1,2,3 k x1 x2 xk (2.38 Where: y is the hypothetical function xj, xu are hypothetical variables bju: are the coefficients that estimate the change of the hypothetical function for each unit change of the hypothetical variables 2.4 Conclusion of Chapter - Studying the theoretical basis of Cl- ion penetration resistance and the influence of pore volume on the durability of concrete, studying methods to determine permeability, Cl- ion diffusion coefficient and pore volume voids of concrete - Selecting method to determine Cl- ion diffusion coefficient through rapid Clpermeation method and rapid electrophoresis method - Selecting the Taguchi method combined with Minitab software to analyze the data, building the correlation between the W/B ratio and the intensity of silica fume, Cl- ion permeability - Selecting the method of adsorption - desorption (BET/BJH) to determine the pore volume of concrete CHAPTER RESEARCH ON THE EFFECT OF COMPOSITION FACTORS ON THE DURABILITY OF SILICA-FUME CONCRETE 3.1 Design and manufacture of silica-fume concrete 3.1.1 Applied standards and scientific basis in selecting design components of silica-fume concrete Applied standards Applying TCVN 10306:2014 on High-strength concrete – Design of cylindrical sample components [9] and other national standards specifying specifications for concrete components Scientific basis for selecting components in the design of silica-fume concrete Design of silica-fume concrete composition with compressive strength at 28 days greater than 60 MPa (cylindrical sample) and Cl- ionic permeability < 1000 Coulomb 3.1.2 Materials for making silica-fume concrete Coarse aggregate (crushed stone) - Origin: Sunway quarry - Luong Son - Hoa Binh - The intensity was determined at the laboratory of the University of Transport Technology Small aggregate (yellow sand) - Origin: Red River (Viet Tri) - The physico-mechanical parameters of sand were determined at the laboratory of the University of Transport Technology Cement But Son Cement PC40 according to TCVN 2682 - 2009 Specifications are provided by the manufacturer Silica-fume mineral additive Sikacrete PP1 silica-fume product from Sika, conforms to ASTM C1240-03 Superplasticizers Sika Viscocrete 3000-20, grade G, meets ASTM C494 Water for pouring concrete The tap water of Hanoi's domestic water supply system meets the quality standard TCVN 4506: 2012 – Water for concrete and mortar 3.1.3 Calculation, design and fabrication of silica-fume concrete Input parameter selection Based on the analysis of previous research in Vietnam and in the world, the thesis selects input parameters for the research as follows: - Substitute silica-fume content: 8% – 10 % – 12% - W/B ratio: 0,25 – 0,30 – 0,35 Experimental design according to Taguchi's method - Objective function: Compressive strength and Cl- ion permeability - Input parameters: Substitute silica-fume content: 8% – 10 % – 12% W/B ratio: 0,25 – 0,30 – 0,35 Experimental arrangement according to Taguchi's method According to the Taguchi quality technical manual [117], the case of factors, levels each, the selection of L9 type planning with 09 experimental levels, the combination of experiments arranged orthogonally Design of the composition of silica-fume concrete Within the scope of the research, the thesis does not consider the influence of aggregates, only focuses on the composition of the binder in silica fume concrete including the composition of the binder and the amount of water used Applying TCVN 10306:2014 with silica fume content (8% - 10% - 12%) and W/B ratio (0.25 - 0.30 0.35), calculating the design of components concrete mix as follows: Table 3.13: Silica-fume concrete components used in the research X N MS C Đ PG Types of concrete W/B %MS (kg) (liter) (kg) (kg) (kg) (liter) 11 N N 2 R 135,19 738, 14,80.MS 906, 7.( ) 0, 7083.MS n CKD CKD (3.1) Evaluation of the fit of the regression equation by Minitab software Table 3.19: Results of analysis of variance of correlation model Source DF Adj SS Adj MS F-Value P-Value Regression 600,498 150,124 1777,79 0,00001 W/B 18,868 18,868 223,43 0,00012 MS 17,465 17,465 206,82 0,00014 (W/B)2 10,276 10,276 121,68 0,00038 MS 16,056 16,056 190,13 0,00016 Where: Adj SS is the adjusted sum of squares; Adj MS is the adjusted mean square; F- Value is the F-statistic value; P-Value is the statistic P P-Value of W/B factors; MS; (W/B)2; MS2 are all less than 0,05, showing that these factors have a significant influence in the regression model Table 3.20: Correlation coefficient of compressive strength regression equation S R-sq R-sq(adj) R-sq(pred) (Standard (Coefficient of (Adjusted correlation (Predicted correlation deviation) determination) coefficient) coefficient) 0,290593 99,94% 99,89% 99,72% The correlation coefficients of the regression equation, R-sq = 99,94%, R-sq(adj) = 99,89%, R-sq(pred) = 99,72% (Table 3.44) show that regression has a strong correlation with experimental data Therefore, this equation can be used to predict the compressive strength of silica fume concrete b Evaluating the fit of the regression equation through the experimental results Table 3.21: Comparison of experimental compressive strength and predicted compressive strength according to Taguchi Method Name of Rn28 Rn28 according to Difference MS No concrete W/B experiment Taguchi method between (%) mix (MPa) (1) (MPa) (2) (1) and (2) T01 80,2 80,43 + 0,29% 0,25 T02 10 84,5 84,53 + 0,04% T03 12 83,2 82,96 - 0,29% T04 68,5 68,46 - 0,06% T05 0,30 10 72,4 72,56 + 0,22% T06 12 71,1 71,00 - 0,14% T07 61,2 61,03 - 0,28% 0,35 T08 10 65,3 65,13 - 0,26% T09 12 63,2 63,57 + 0,58% The results calculated from the regression equation obtained are similar to the experimental results, the error ranges from -0,29% to +0,58% Evaluating the fit of the regression equation through other studies 12 Compared with previous studies, the regression equation drawn in the thesis is similar to the research results of Sanjay Kumar, Baboo Rai (2020) [81]; M Shafieyzadeh (2013) [112] 3.3 Study on the influence of the compositional factors on the Cl- ion permeability of silica-fume concrete 3.3.1 Test to determine Cl- ion permeability The test to determine the Cl- ion permeability was carried out according to TCVN 9337:2012 at the Laboratory of the University of Transport Technology The results of Cl- ion penetration are averaged from the measurement results of test samples/mixture at 28 days of age Table 3.23: Experimental results to determine the Cl- ion permeability of silicafume concrete Average Types of cement No W/B MS (%) Electricity concrete (Coulomb) 8MS 0,25W/B 107,11 10MS 0,25W/B 10 90,00 0,25 12MS 0,25W/B 12 82,22 8MS 0,30W/B 211,44 10MS 0,30W/B 10 151,11 0,30 12MS 0,30W/B 12 110,22 8MS 0,35W/B 250,00 10MS 0,35W/B 10 196,67 0,35 12MS 0,35W/B 12 140,00 0,30 10 0MS 0,30W/B 1070,00 3.3.2 Analysis of the influence of compositional factors on Cl - ion permeability of silica-fume concrete The experimental results in Table 3.23 are depicted in the following Figure 3.9: Figure 3.9: Relationship of W/B ratio, silica-fume content and Cl- ion permeability - The Cl- ion permeability of silica fume concrete is significantly improved compared to conventional concrete The degrees of Cl- ion permeability are all classified as very low permeability, even with the ratio W/B = 0,25 the charge through the sample is less than 100 Coulomb - From Figure 3.9, it can be seen that the permeability of Cl - ions is inversely proportional to the silica-fume content - When using the ratio W/B = 0,25, the Cl- ion permeability reached the lowest value, the difference in the value of electric charge through concrete when changing the silicafume content ratio was not significant This shows that when using the ratio W/B = 13 0.25, silica-fume concrete achieves the best quality, leading to negligible Cl- ion permeability 3.3.3 Building a regression equation describing the relationship between the W/B ratio, the silica fume content and the Cl- ionic permeability of the silica-fume concrete by the Taguchi method Building a regression equation describing the relationship between the W/B ratio, the silica-fume content and the Cl- ion permeability of the silica fume concrete using Minitab software The equation is as follows: Q 600 3152 N CKD 44, 2.MS 212, 8.( N CKD ).MS (3.2) Evaluate the fit of the regression equation through Minitab software The results of analysis of correlation coefficients and variance of regression equations by Minitab software are summarized in tables 3.26 and 3.27 as follows: Table 3.26: Correlation coefficient of Cl- ion permeability regression equation S R-sq R-sq(adj) R-sq(pred) (standard (Coefficient of (Adjusted correlation (Predicted correlation deviation) determination) coefficient) coefficient) 97,07% 95,31% 88,26% 12,7364 Table 3.27: Correlation model analysis results Source DF Adj SS Adj MS F-Value P-Value Regression 26845,2 8948,4 55,16 0,00030 W/B 3871,4 3871,4 23,87 0,00453 MShq 850,8 850,8 5,25 0,05063 (W/B).MS 1810,9 1810,9 11,16 0,02053 The correlation coefficients of the regression equation, R-sq = 97,07%; R-sq(adj)= 95,31%; R-sq(pred) = 88,26% (Table 3.26) shows that the relationship between the regression equation has a strong correlation with experimental data Therefore, this equation can be used to predict the Cl- ion permeability of silica-fume concrete Evaluating the fit of the regression equation through the experimental results Table 3.28: Comparison of experimental Cl- ion permeability and predicted Clion permeability according to Taguchi method The Q28 According to MS Q28 experiment difference STT W/B Taguchi's Method (%) (Cu lông) (1) between (Coulomb) (2) (1) and (2) 107,11 116,00 +7,66% 0,25 10 90,00 98,00 +8,16% 12 82,22 80,00 -2,78% 211,44 198,48 -6,52% 0,30 10 151,11 149,20 -1,28% 12 110,22 109,82 -0,27% 0,35 250,00 260,96 +4,20% 14 10 196,67 200,40 +1,86% 12 140,00 139,84 -0,84% The experimental results of measuring electric charge through concrete and the formula derived from Taguchi method are similar (deviation from -6,52% to +8,16%) 3.3.4 Study on the influence of the compositional factors on the Cl - ion diffusion coefficient of the silica fume concrete The value of Cl- ion diffusion coefficient of silica-fume concrete (D28) is calculated according to the formula of Berke and Hicks [56] from the experimental results to determine the Cl- ion permeability by the cosmological method (Q28) D28 = 1,03 x 10-14(Q28)0,84 (m2/s) (3.3) Apply the formula (3.3) to determine the Cl- ion diffusion coefficient of the silica fume concrete The results are summarized in Table 3.29 below Table 3.29: Results of determination of Cl- ion diffusion coefficient of silica fume concrete Symbol of cement MS Q28 TT W/B D28 (m2/s) concrete (%) (Coulomb) 8MS 0,25W/B 107,11 5,22E-13 10MS 0,25W/B 10 90,00 4,51E-13 0,25 12MS 0,25W/B 12 82,22 4,18E-13 8MS 0,30W/B 211,44 9,25E-13 10MS 0,30W/B 10 151,11 6,97E-13 0,30 12MS 0,30W/B 12 110,22 5,35E-13 8MS 0,35W/B 250,00 1,06E-12 10MS 0,35W/B 10 196,67 8,70E-13 0,35 12MS 0,35W/B 12 140,00 6,54E-13 10 0MS 0,30W/B 0,30 1070,00 3,61E-12 From the experimental results, build a relationship chart according to Figure 3.11: Figure 3.11: Relationship of W/B ratio, silicon-fume content and Cl- ion diffusion coefficient - Figure 3.11 shows that the Cl- ion diffusion coefficient increases as the W/B content increases When using the ratio of W/B = 0,25, silica-fume concrete has the lowest value of Cl- ion diffusion coefficient - With the same W/B ratio, the Cl- ion diffusion coefficient decreases with increasing silica-fume content in the concrete The Cl- ion diffusion coefficient reached the lowest value when the silica-fume content used was 12% 3.4 Study on the effect of pore volume on the durability of silica-fume concrete 3.4.1 Determination of pore volume of silica-fume concrete 15 The thesis uses the adsorption-desorption isotherm method (BET/BJH) by nitrogen gas at the temperature of 77K to determine the pore volume (surface area, size and pore distribution) The experiment was conducted at the Department of Chemistry, Hanoi National University of Education The results of the BET/BJH test to determine the pore volume in silica-fume concrete are presented in Table 3.30 Table 3.30: Experimental results to measure the pore volume of concrete Pore volume BET/BJH (cm3/g) Total pore Age of volume Concrete type 10 – 50 50 – 200 concrete 46 MPa • Corresponding to the 90% confidence level, when using 10% silica-fume, the Clion permeability is < 330 Coulomb and the compressive strength is > 50 MPa • Corresponding to the 90% confidence level, when using 8% silica-fume, the Cl- ion permeability is < 220 Coulomb and the compressive strength is > 48,5 MPa 3.5.3 Design of silica fume concrete according to specific compressive strength requirements Objective: To design silica-fume concrete with characteristic compressive strength (f'c > 60 MPa) and Cl- < 1000 Coulomb ionic permeability Figure 3.20: Relationship between W/B ratio and characteristic compressive strength, electric charge through concrete with 10% silica fume Figure 3.19: Relationship between W/B ratio and specific compressive strength, electric charge through concrete with 8% silica fume Figure 3.21: The relationship between the W/B ratio and the characteristic compressive strength, electric quantity transmitted through concrete with 12% silica fume Calculation results show that, in order to design the silica-fume concrete composition to reach f'c > 60 MPa and Q28 < 1000 Coulomb), it is necessary to choose the W/B ratio from 0,25 to 0,26 and the content Silica-fume from 8% - 12% 3.6 Conclusion of Chapter Based on the experimental results, the following conclusions can be drawn: - The compressive strength increases from 8% - 10%, but will decrease when the silica-fume content increases from 10% - 12% The maximum value is 84,5 MPa when the silica-fume content is 10% and the W/B ratio is 0,25 - The Cl- ion permeability and Cl- ion diffusion coefficient decreased with increasing silica-fume content and increasing W/B ratio The smallest Cl- ion diffusion coefficient of concrete when using the silica fume content is 12% and W/B = 0,25 Equation of relationship between W/B ratio, silica fume content and compressive strength: N N 2 R 135,19 738, 14,80.MS 906, 7.( ) 0, 7083.MS n CKD CKD ( The relationship equation between W/B ratio, silica-fume content and Cl- ion permeability: Q 600 3152 N CKD 44, 2.MS 212, 8.( N CKD ).MS (3.2) From 02 regression equations, developing a method to design silica-fume concrete components with consideration of durability (11 steps) - The Cl- ion diffusion coefficient decreases with time The rapid electrophoresis method can be used to directly measure the Cl- ion diffusion coefficient of concrete ... durability of silica-fume concrete Evaluation of the time of onset of corrosion for silica-fume concrete and Portland cement concrete structures in the marine environment of Vietnam Application of silica... between the ratio of W/B, the silica fume content, the compressive strength, and the Cl- ion permeability of the silica fume concrete Thereby proposing a method to design silica fume concrete considering... the main effects of silica-fume on the strength and durability properties of concrete Previous studies related to the use of silica fume in concrete have shown that the optimum silica-fume content