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Nghiên cứu độ bền thấm nước và thấm ion clo clorua của bê tông cốt liệu nhẹ ứng dụng trong dự đoán tuổi thọ kết cấu cầu. Nghiên cứu độ bền thấm nước và thấm ion clo clorua của bê tông cốt liệu nhẹ ứng dụng trong dự đoán tuổi thọ kết cấu cầu. Nghiên cứu độ bền thấm nước và thấm ion clo clorua của bê tông cốt liệu nhẹ ứng dụng trong dự đoán tuổi thọ kết cấu cầu. Nghiên cứu độ bền thấm nước và thấm ion clo clorua của bê tông cốt liệu nhẹ ứng dụng trong dự đoán tuổi thọ kết cấu cầu. Nghiên cứu độ bền thấm nước và thấm ion clo clorua của bê tông cốt liệu nhẹ ứng dụng trong dự đoán tuổi thọ kết cấu cầu. Nghiên cứu độ bền thấm nước và thấm ion clo clorua của bê tông cốt liệu nhẹ ứng dụng trong dự đoán tuổi thọ kết cấu cầu. Nghiên cứu độ bền thấm nước và thấm ion clo clorua của bê tông cốt liệu nhẹ ứng dụng trong dự đoán tuổi thọ kết cấu cầu. Nghiên cứu độ bền thấm nước và thấm ion clo clorua của bê tông cốt liệu nhẹ ứng dụng trong dự đoán tuổi thọ kết cấu cầu. Nghiên cứu độ bền thấm nước và thấm ion clo clorua của bê tông cốt liệu nhẹ ứng dụng trong dự đoán tuổi thọ kết cấu cầu. Nghiên cứu độ bền thấm nước và thấm ion clo clorua của bê tông cốt liệu nhẹ ứng dụng trong dự đoán tuổi thọ kết cấu cầu.
Ministry of Education and Training University of Transport and Communications LE QUANG VU DURABILITY OF LIGHTWEIGHT CONCRETE DUE TO WATER AND ION ABSORPTION AND ITS APPLICATION IN FORECASTING THE LIFESPAN OF BRIDGE STRUCTURE Discipline: Transport Construction Engineering Code: 9580205 Major: Bridge and Underground Infrastructure Engineering TECHNICAL DOCTORAL THESIS SUMMARY Hanoi - 2022 Work Completion Location: University of Transport and Communications Supervisor: Assoc Prof Dr Tran The Truyen University of Transport and Communications Assoc Prof Dr Do Anh Tu University of Transport and Communications Critical lecturer 1: Critical lecturer 2: Critical lecturer 3: The thesis will be defended in front of the members of the thesis committeee at the University of Transport and Communications Date: …/…/2022 Thesis can be found in: - National Library of Vietnam - Library of University of Transport and Communications Introduction The urgency of the Topic The application of lightweight concrete (Lightweight Concrete – LWC) in the construction in countries around the world shows prominent advantages such as: Reducing the self-weight of the bridge structure, thereby improving the exploitation capacity of the live load; Reduced costs of hoisting, mounting, and transporting prefabricated components due to reduced structural weight This is convenient for span by span erection method and reduces construction costs; Increases structural durability due to good adhesion between aggregate and cement; Reduces the effect of stress concentration normally created around the aggregate particles for ordinary concrete; Reduces micro-cracks caused by shrinkage and creep; Increased durability of concrete by reducing microcracks; Improved resistance to penetration of chlorine ions Evidence of Cl- ion content after 23 years of exploitation by US researchers shows that: As the thickness of the concrete layer increases, the Cl- ion content decreases compared to normal concrete Currently in Vietnam, the application of LWC in the construction of buildings has been relatively much done; Initially, there were applied studies in transport construction, especially the construction of bridge structural components Some typical projects such as Fortuna Hanoi Hotel, Long Bien Sports Center or Hanoi Club are implemented by Thien Giang Lightweight Concrete Production Joint Stock Company; Building with floors at No 132 Khuat Duy Tien; 6-storey house at 130 Giang Vo street; 11-storey hotel on Hang Thung street; 200 m2 floor of Xanh Plat restaurant at No 10 Pham Ngoc Thach… by CICO Investment Constructıon Consultancy Joınt Stock Company (CiCo)) The results obtained are very positive and highly appreciated by the Ministry of Construction However, in the traffic construction industry in general, and in the construction of bridge structures in particular, this is still an issue that needs to be studied and applied The mix composition of LWC and the experiment to determine the mechanical and physical characteristics of this concrete have been mentioned by many researchs The results have shown the similarities and differences of LWC compared to normal concrete (NC) at the same compressive strength grade However, the long-term durability of lightweight and reinforced concrete structures using LWC is still a question that needs to be answered, especially with LWC, and structures using this concrete type exploited in climatic conditions in Vietnam Evaluation of the durability of LWC and structures using it has been conducted by several studies around the world In principle, the measurement methods for assessing the water permeability, and chlorination of LWC as well as predicting the lifespan of reinforced concrete structures using LWC are carried out in the same way as for normal concrete However, the results obtained show large dispersion The main reason is due to different aggregate compositions, different concrete ages, different sample forms, and test methods Evaluation of water permeability and chloride ion permeability of LWC and structures using LWC is a very new issue in Vietnam; especially considering the influence of the load factor Thus for, no research has been conducted on this issue It is necessary to have studies evaluating the long-term durability of LWC structures to supplement the database for the design of LWC structures used in civil and traffic construction From the experimental results to evaluate the water permeability and chloride ion permeability of lightweight concrete, it is possible to build models to predict the lifespan of reinforced concrete structures using lightweight concrete according to the reinforcement corrosion criteria From the urgent requirements and important implications in proposing a model to evaluate the influence of loads on the permeability of lightweight aggregate concrete and its application in predicting the lifespan of reinforced concrete buildings in general and bridge works in particular, especially in line with the probabilistic bridge design philosophy of Vietnam bridge design standards, the research topic "Evaluation of water and chloride ion permeability of lightweight concrete and application in predicting the lifespan of bridge structure using probability theory" was selected as the thesis topic The thesis content consists of chapters: Introduction Chapter 1: Overview of Lightweight Concrete, Researchs relate to the durability of LWC and structures using this concrete type Chapter 2: Analyses of water and chloride ion permeability of Lightweight Concrete Chapter 3: Building model to predict the lifespan of Lightweight Concrete Structures Chapter 4: Calculation and prediction of lifespan of lightweight reinforced concrete structures considering the simultaneous influence of load effects and environmental impacts Conclusions Recommendations Target of the Thesis The targets of the thesis are: Determining the water and chloride ion permeability features of lightweight concrete; Building calculating model to forecast the lifespan of structures using lightweight concrete; Evaluating the mining lifetime of structures using lightweight concrete Research Object and Scope 3.1 Research Object The research object is concrete using lightweight aggregate keramzit and structures using this concrete The durability of lightweight concrete due to water and ion absorption and the lifespan of LWC structure 3.2 Scope of Research The thesis only focuses on the effect of chloride ions on steel corrosion, not on concrete corrosion of sulphate Research on the durability properties of lightweight concrete produced in Vietnam conditions: water repellency, chlorine ion permeability under the conditions of temperature, humidity and time as specified by the test standards Predicting the lifespan of reinforced concrete structures using LWC Research method Analysis, Synthesis, and Comparison The main research method is a combination of theoretical and experimental research methods Using advanced theories of concrete durability to determine empirical correlations and conduct experimental research with lightweight concrete materials and structures to verify Modeling to predict the lifespan of concrete bridge using lightweight concrete The thesis's new contributions The thesis has conducted experimental studies, analysis of water permeability and chloride ion penetration through C30 lightweight concrete under the impact of loads Research results show that when increasing the compressive load, the water permeability of concrete increases significantly; especially after inside concete initiate changing the void structure due to the impact of pre-compressive load or direct compression A water penetration test model that considers direct compressive loads has been designed, manufactured and tested based on recent world research results; This experimental equipment has been improved to make the measurement process more convenient, especially the process of controlling the load and recording data completely automatically Research results show a significant effect of compressive load on chloride ion permeability of lightweight concrete A chlorine ion permeation test model that considers direct compressive loads has been designed, manufactured and tested based on recent world research results; This test equipment has been improved to make the measurement process more convenient, especially the process of controlling the compressive load in lightweight concrete The thesis has proposed the relationship between the chloride ion diffusion and the water permeability factor of lightweight concrete Determine the Ck coefficient to calculate the chloride ion diffusion coefficient from the water permeability coefficient of the same lightweight concrete Therefrom, a formula for calculating the relationship between water permeability and chloride ion diffusion coefficient of lightweight concrete is proposed, taking into account the effect of stress in concrete for the type of lightweight concrete under consideration The thesis builds a calculating model to predict the service life of lightweight concrete structures in Vietnam conditions, taking into account the influence of permanent loads and operational loads CHAPTER 1: OVERVIEW OF LIGHTWEIGHT CONCRETE, RESEARCHS RELATE TO THE DURABILITY OF LWC AND STRUCTURES USING THIS CONCRETE TYPE Lightweight Concrete and its applications According to European standard EN 206-1:2000 [43], lightweight concrete has a density less than 2,000kg/m3 and compressive strength ranges from - 80MPa (pier sample) Light-weight concrete according to ACI 213R-03 [25] is concrete with a density of 1,120 - 1,920 kg/m3 and a minimum compressive strength at 28-day of 17 MPa Consequently, when the density of normal concrete is reduced from 2,400kg/m3 to 1,900kg/m3 for lightweight concrete, it is possible to reduce the self-weight of the structure significantly, helping to reduce the weight of the structure saving rebar and prestressed reinforcement, reducing construction costs The use of light aggregates is a fundamental factor in achieving a small density In addition to the density of aggregates, the concrete density also depends on the aggregate grade, aggregate moisture content, gas content, cement content, water/binder ratio (w/b), chemical and mineral admixtures, etc Beside the materials, the concrete's density also depends on the compaction method, the curing conditions, etc The density of LWC withstood a variable load of 1200 - 2000 kg/m3 compared to 2300 - 2400 kg/m3 of heavy concrete Most of the properties of LWC are related to the density, especially the compressive strength Research of water permeability of lightweight concrete Water permeability is defined as the ability that allows fluids to pass through a porous medium due to a difference in potential energy The permeability of lightweight concrete or a hollow material is highly dependent on the parameters of the concrete environment such as porosity, and pore structure According to Scrivener (2001), when the porosity and inter-pore communication in concrete increase, the waterproofing durability of concrete is reduced; and the straighter the pores, the faster the seepage flow rate Under the mechanical impact or high enough amount of temperature, the destruction in concrete accompanied by cracks increases the preceding parameters, therefore, the permeability of concrete will also increase rapidly [61] Figure 1.1 - Impact of porosity, shape - size of voids and the connectivity of pores on the permeability of concrete (Scrivener (2001)) The studies of Abbas (2000) on the influence of void gap on the strength and permeability of LWC showed that the concrete strength depends on the void ratio of the material; however, the permeability depends mainly on the connectivity between the pores Once the concrete has a high hollow connection due to cracks appearing for many reasons (shrinkage, creep, mechanical impact, high temperature, corrosion ) during the exploitation process, the permeability of concrete increases rapidly The differences in humidity, hydrostatic pressure, stress, temperature, and chemical concentrations disturb the equilibrium of fluids in the porous material; Therefore, the movement of the fluid occurs to reestablish a new balance The migration process of this fluid is usually described in terms of adsorption, diffusion, absorption, and permeation In concrete, both the physical structure of the concrete and the state of the water in the pores affect these processes Dang Thuy Chi (2018) [3] studied determining the waterproofness of lightweight concrete Each concrete grade was tested on a sample set of cylinders with a diameter of 150 mm and height of 150 mm The results show that the LWC LC40 type is penetrated by water when the water pressure reaches 12 atm, achieving waterproofing grade B10 While the two types of LWC LC50 and LC60 have a water pressure of more than 12 atm, the sample has not been penetrated by water, achieving the maximum waterproof grade B12 This result is similar to that of normal heavy concrete Research of chlorine ion permeability of lightweight concrete According to the research results of Youm et al [70] on LWC using silica fume, silica fume improves the microstructure of cement mortar, thereby improving the chloride ion permeability of LWC Futhermore, LWC using silica fume has chlorine ion permeability test results less affected by the type of aggregate On the other hand, Liu et al [51] commented that the chloride ion permeability of LWC increased with increasing lighweight material content in concrete In addition, Liu et al also concluded that concrete using lightweight material and sand usually has the same permeability, chloride ion permeability compared to normal concrete with the same w/b ratio Basheer, & Long, 2005, Lo et al., 2008 [52] showed that as the percentage of lightweight aggregate increases, the strength of LWC decreases The reason is explained by the increased area of cement paste and aggregate, which increases the penetration ability of water and chlorine ions, although most chlorine ions not penetrate through lightweight aggregates (Chia & Zhang, 2002 [36]) Dang Thuy Chi (2018) conducted tests to measure the permeability of lightweight concrete with target strength grades of 30, 50, and 60 MPa The results of the chloride ion permeability test showed that the permeability gradually increased from 166 Columb to 193 Columb when the average compressive strength decreased from 69 to 50 MPa The permeability is very low, equivalent to the average value measured on heavy concrete with compressive strength of 80 MPa [33] Consequently, the experimental results seem to be suitable with Liu's comments [51] that LWC has a higher chloride ion permeability than heavy concrete with the same compressive strength at 28-day (but with a higher w/b ratio) Researchs on corrosion initiation time and corrosion propagation time, service lifespan In 1980, at the international conference on concrete in the marine environment organized by the American Concrete Institute (ACI), Tuuti [16] suggested that reinforced concrete structures working in the marine environment would be diffused into the concrete by chloride ion and accumulates on the surface of the reinforcement When the chloride ion concentration at the reinforcement surface reaches the critical concentration threshold, it will begin to corrode the reinforcement Corrosion of reinforcement will lead to two consequences The first is that it reduces the cross-sectional area of the reinforcement leading to a decrease the resistance Second, corroded reinforcement will produce corrosion products, volume expansion corrosion products cause tensile stress in the protective concrete layer and cause cracking, splitting, and breaking of concrete Modeling predicting service lifespan of reinforced concrete structures due to chloride ion diffusion should show the processes leading to corrosion of steel in concrete caused by chloride ions These processes are basically described as follows: - Chloride ions in the environment accumulate on the concrete surface - Chloride ions are diffused into the concrete through a number of mechanisms, mainly diffusion - Chloride ion concentration is accumulated over time at the surface of the reinforcement - When the chloride ion concentration at the reinforcement surface reaches the critical threshold level, the passive film on the reinforcement surface is broken and the corrosion process begins - Products of corrosion have a larger volume than the corroded reinforcement, causing tensile stress in the protective concrete layer - Concrete has poor tensile strength, so cracks will appear either perpendicular or horizontally that forming layer separation between the reinforcements - Cracks forming cracks or breaking cause the structure to deteriorate such as function is no longer guaranteed or unsafe This can be seen as a time when a repair is required - Corrosion causes loss of steel cross-sectional area, leading to an unsatisfied bearing limit state Tuutti, K gave a two-stage model of the service life of reinforced concrete structures as shown in Figure 1.2 Accordingly, the service life consists of two successive stages: the corrosion initiation stage and the corrosion propagation stage according to Equation 1.1 (1.1) t = t1 + t ; Where: - t: The lifespan has already been used; - t1: The corrosion initiation stage; - t2: The corrosion propagation stage Figure 1.2 - Service lifespan of reinforced concrete structures: Tuuti's two-stage model (1980) Conclusion of Chapter Through many studies on the water permeability of LWC, it has been shown that the permeability of concrete is influenced by two main factors: One is the porosity characteristics such as size, structure, and the connection between the pores; The second is the micro-cracks in the concrete, especially at the interface between the aggregate and the binder In which, the effect of stress due to external influences on concrete permeability is still not clear Meanwhile, for construction works in the marine environment, an important damage phenomenon that needs to be taken into account is the process of corrosion of reinforcement in concrete due to chloride ions There have been many researchs that have proposed, the relationship between chloride ion diffusion coefficient of concrete, water/cement ratio, time, Coulombs quantity In addition, studies evaluating the effect of pre-stress state in concrete have also been carried out The ion diffusion experiments through concrete include steady state diffusion experiment, unstable state diffusion experiment, electric field migration experiment In general, performing chloride ion penetration tests is complicated (especially when considering stress states in concrete) Therefore, the indirect determination of chloride ion diffusion coefficient through simpler tests such as water penetration test is of great significance in assessing the durability and predicting the service lifespan of LWC structures CHAPTER 2: ANALYSES OF WATER AND CHLORIDE ION PERMEABILITY OF LIGHTWEIGHT CONCRETE 2.1 Problem The experiments in this chapter evaluate the water permeability of some typical lightweight concrete commonly used in bridge constructions in Vietnam LWC with a strength of 30 MPa (mark C30) was used in these tests The experimental process includes the following experiments: - Testing to determine the compressive strength of concrete - Testing to determine the water permeability and chlorination of pre-stressed concrete - Testing to determine the water permeability and chlorination of post-tensioned concrete To design the grade for concrete with compressive strength fc' = 30 MPa (C30), the PhD student used Bim Son cement - PC 40 (meeting the requirements of TCVN 2682:2009) Small Grain - Size (Sand - S) Sand used for concrete is natural sand with grain size from 0.14 to 5mm - according to TCVN 7570-2008; from 0.075 to 4.75 mm - according to the Unified Soil Classification System (USCS) and from 0.08 to 5mm according to French standards Sand used in this study is from Da River Large Grain - Size (Crushed stone) Using Crushed stone from Hoa Binh Stone materials for making concrete must have suitable strength and loss Crushed stone has good roughness, closely bonded with cement mortar, so the flexural strength of concrete made from it is higher than that of concrete made from gravel Water (W) Using domestic water for concrete production and curing Water used must be clean water according to TCVN 4056: 2012: Water for concrete and mortar - Technical requirements 2.2 Results of water permeability test with pre-stressed concrete samples Based on the results of the experiments, we build a diagram of the waterproofness of C30 concrete when considering the pre-compressive stress as follows (Figure 2.1): Figure 2.1 - Increase of water permeability (k) according to relatively stress max When max > 0.5 and the water pressure is larger than 10 atm, the water permeability increase rapidly This shows that the effect of pre-compressive stress is large enough to increase the water permeability of LWC, it is these residual mechanical effects that facilitate water penetration easier through the concrete specimen, especially when max > 0.5, the occurrence of concrete damage caused the water permeability to increase faster Especially in the experiment, we found that max equal to 0.8 showed a huge difference in water permeability in LWC Figure 2.2 - Plot of permeability coefficient (K) changing over time with stress class max = 0.6 Figure 2.3 - Plot of permeability coefficient (K) changing over time with stress class max = 0.7 The water permeability of concrete is almost unchanged or changes slowly when the relative stress value max < 0.5; After this threshold, the permeability coefficient starts to increase rapidly When the relative stress max ≥ 0.6, the water permeability increases very quickly; This can be explained by the fact that the microstructure of concrete is destroyed after this stress threshold - which is the threshold for the appearance of dispersed failure zones (according to the approach of concrete failure mechanics) - causing increase the water permeability of concrete The law of increasing the water permeability of concrete after 28 days in this experiment is similar to the law of increasing the water permeability of early-age concrete published by Banthia & al (2005) when mechanical failure has not yet appeared in concrete Charge (Coulombs) 1500 MẪU MẪU MẪU MẪU MẪU MẪU 1000 500 0 (max) 0.2 0.4 0.6 0.8 Figure 2.4 - Chloride ion permeability of LWC with strength of 30 Mpa according to compressive prestressed in concrete When the pre-compressive stress in concrete: max ≤ 0.5, the chloride ion permeability increases linearly and fairly evenly; After this threshold, the chlorine permeability increases sharply Chlorine ion permeability value of concrete grade 30Mpa at loads of 30% and 50% of f'c is from 200 300(C) - at medium grade, when load is 80% of f'c, the charge through the sample increases rapidly to 1300(C) - high Figure 2.5 - The increase law of chloride ion diffusion coefficient according to precompression stress of lightweight concrete C30 sample According to the chart in Figure 2.5, when the compressive stress is lower than 50% of max, the permeability change is not significant, but when the pre-compressive stress reaches 70% of max, the permeability coefficient increases about 2.7 times compared to the permeability of unloaded concrete The law of increasing the chloride ion permeability coefficient according to the precompression stress of C30 LWC is expressed by the following formula: Exponential Regression: D/Do = 9.1226(max)2 – 3.4256(max) + 1.0816 (2.12) Figure 2.6 - Experiment for determining the chloride ion permeability of lightweight concrete under direct compression The relationship of the chloride ion permeability (C) of concrete C30 according to the rapid permeability test corresponding to the stress values when compressing the concrete specimen at the same time is shown in Figure 2.7 The experimental results show that the chloride ion permeability changes much when there is the presence of simultaneously acting loads However, before and after loading, the chloride ion permeability is within the "average" grade according to TCVN 9337-2012 standard When increasing the load corresponding to the stress to 30% and 50% compared to the stress max, the permeability of concrete increases by 24.50% and 39.48%, respectively When increasing the stress to 80% of max, the permeability of concrete has a large increase In the case of reduced chloride ion permeability, it will lead to arisen, but on the contrary, the density increases and the voids of the concrete decreses thus reduce the permeability The rate of chloride ion penetration through concrete decreased when the stress was at 30% of max and increased at 50% of max and 70% of max Finally, the author proposes the relationship between water permeability coefficient and chloride ion diffusion coefficient of concrete For concrete C30: Kw = 29.05 S0.5 D CHAPTER 3: BUILDING A STRUCTURAL LIFESPAN PREDICTION MODEL USING LIGHTWEIGHT CONCRETE 3.1 Introduction The purpose of this chapter is to build a model to predict the influence of loads and environment on the service life of bridge structures using lightweight reinforced concrete according to the criteria of initiation of reinforcement corrosion in concrete The experimental results in Chapter will be used as the basis for establishing models to predict the lifespan of the building These models will be applied in forecasting the life of a specific bridge This chapter is structured into two main parts The first part of the chapter is the part to build a predictive model that considers the effects of loads and environmental conditions simultaneously The second part is the lifespan prediction calculations for a specific bridge structure taking into account the change of protective concrete layer thickness, surface chlorine ion concentration, pre-stress and direct compression in concrete 3.2 Scope of Research In the scope of research of this thesis, only referring to the service life according to the penetration of chlorine ions into the concrete bridge structure causing corrosion of reinforcement The service life of reinforced concrete bridges due to chloride ion intrusion is the time from the beginning of exposure to the environment with chlorine ions to the time when chlorine ions cause corrosion of reinforcement leading to cracking of protective concrete or until corrosion causes a loss of reinforcement cross-sectional area, reducing the resistance to a level that endangers the bearing limit state The service life of reinforced concrete bridges calculated according to chloride ion penetration will be calculated in years and is the sum of two successive stages: the corrosion initiation stage and the corrosion propagation stage Within the scope of this thesis, regarding the long-term damage of the structure due to corrosion, it only considers the evaluation of the service life of a reinforced concrete transport structure as the time when the corrosion begins in reinforcement due to the diffusion of chloride ions into the concrete or more precisely the time that the concentration of chlorine ions (C) at the surface of the reinforcement reaches the critical value (Ccr) The change in the lifespan of the building according to this corrosion criterion is expressed according to the changes in the thickness of the protective concrete layer and the permeability of the concrete related to the diffusion coefficient of chloride ions into the concrete with consideration to the stress factor 3.3 Building a model to predict the service life of lightweight reinforced concrete structures according to the criteria of reinforcement corrosion taking into account the stress state of the concrete The input parameters in the problem are important This thesis will be based on the input parameters from the experiments in chapter along with the results of domestic and foreign authors Those parameters will be recommended to be used for the model to be built 3.3.1 Building a model to predict the service life of reinforced concrete bridges according to the criteria of reinforcement corrosion initiation In 1975, Crank proposed a mathematical model for the diffusion process based on Fick II's law In case the diffusion coefficient is constant, the chloride ion concentration on the reinforcement surface in formula 3.1 with the boundary condition C0 = C (0, t) (the surface chloride ion content is constant) and the initial conditions C = 0, x > and t = 0, are determined by: x (3.1) )) ; Cx = Cs (1 − erf ( 2√Dt 11 Where: - Cx is chloride ion concentration at depth x ; - erf is the error function ; - Cs is the chloride ion concentration at the concrete surface of the structure ; - t is the corresponding time ; - x is the depth from the concrete surface of the structure to the determining point ; - D is the chloride ion diffusion coefficient The process of corrosion of reinforcement begins when Cx = Ccr; then x = h (thickness of the protective concrete layer) we have: h (3.2) )) Ccr = Cs (1 − erf ( 2√Dt In fact, the service life of buildings in general and traffic constructions in particular according to corrosion criteria is significantly higher than the results calculated by the above formula because of chloride diffusion and surface chloride concentration are time dependent factors To consider the time factor in the expression of chloride diffusivity values of normally intact concrete, Mangat & Molloy (1994) proposed the law of change of Kc with time of the following form: t0 m (3.3) D = D28 ( ) ; t Where: - D28: is the chloride ion diffusion coefficient at the age of 28 days; - t0 : concrete age (t0 = 28 days); - m: is the empirical coefficient taken as follows: (according to A.Costa and J.Appleton (1998)) Area affected by sea waves: m = 0.245 ; The tidal range: m = 0.2 ; Coastal climate zone: m = 0.29 To consider the time factor in representing the surface chloride concentration value of Cs in this thesis, the author took or changed the suggestion of A Costa & J Appeleton (1998) as follows: (3.4) Cs = Cso t n ; where: Cso is the concentration of surface chloride after year; n is the experimental coefficient According to different environmental conditions the values of Cso (as % by mass of concrete) and n for typical ordinary concrete are taken as follows (A Costa & J Appeleton (1999)): - Area affected by sea waves: Cso = 0.24; n = 0.47; - Tidal area range: Cso = 0.38; n = 0.37; - Coastal climate zone: Cso = 0.12; n = 0.54 Thus, considering the time change of chloride diffusion coefficient and surface chloride concentration, (3.2) is rewritten as follows: x ) Cx = Cso t n (1 − erf ( (3.5) 2√D28 𝑡0𝑚 t1−m The minimum thickness of the protective concrete layer h needed to prevent corrosion of reinforcement in concrete is calculated as follows: Ccr (3.6) ) h = 2√3D28 𝑡0𝑚 t1−m × erf −1 ( Cso t n 3.3.2 Building a model to predict the service life of reinforced concrete bridges according to the criteria of reinforcement corrosion taking into account the stress state of concrete Different from the state when not bearing the load, the concrete structure is intact, when subjected to a large enough load, the concrete structure is destroyed leading to a very rapid increase in the permeability of the concrete, which will 12 create favorable conditions for the faster the chloride diffusion into the concrete increases, the higher the concentration of chloride ions at the surface of the reinforcement and consequently the earlier corrosion of the reinforcement To explain this, when the stress in the concrete exceeds the crack limit, it will cause the concrete to crack and facilitate the rapid increase in water permeability and chloride ion diffusion To consider the effect of the stress state on the diffusion of chloride ions into the concrete, the formula determines the relationship between the increase in chloride ion diffusion coefficient with time and the preor direct compression state The next chapter will be used in the calculations Therefore, from formulas 3.5 and 3.6, we can establish a formula to determine the life of reinforced concrete constructions according to the criteria of starting corrosion of reinforcement in concrete a) The case of the pre-compressive stress state b) The case of direct compressive stress states 3.4 Model to predict lifespan of lightweight reinforced concrete structures with consideration of probability theory 3.4.1 Probability theory of failure and long-term age The simplest computational model to describe the failure case of one load variable S and one resistance variable R In principle, the variables R and S can be multiple loads and be represented in multiple units The only requirement is that they have proportions If R and S are independent of time, the failure case can be understood as follows (Kraker, de Tichler and Vrouwenvelder, 1982): {Failure} = {R < S} (3.7) In other words, failure occurs when the resistance is less than the load acting on the structure The failure probability Pf is now defined as the failure probability Pf = P (R < S) (3.8) Resistance R or load S or both can be time dependent loads Therefore, the failure probability can also be a time-dependent load Considering that R(г) and S(г) are instantaneous natural-law values of resistance and load at time the probability of failure in a lifetime г can be defined by: Pf(г) = P{R(г)< S(г)} with every г < t (3.9) Determining the function Pf(г) according to the above equation is very difficult mathematically Normally, resistance and load cannot be treated as instantaneous natural values That is why R and S are considered as random loads with time dependent distributions or constant density distributions Consquently, the failure probability usually defines: Pf(t) = P {R(t)< S(t)} (3.10) According to the above definition, the probability of failure increases continuously over time as shown in the chart below Figure 3.1 - The probability of failure increases continuously over time At time t = 0, the density distributions of the loads are very far apart and the probability of initial failure is small With the moment the distributions approach each other, the resulting 13 overlapping area increases The overlap area illustrates the failure probability area The function Pf(t) is characterized as a distribution function If the long-term life is so defined, then the case tL < t is the same as the failure case with the long-term life t, the long-term life distribution function is defined as: FL = P (tL < t) = Pf(t) (3.11) Where FL is the cumulative distribution of the long-term lifetime The probability density function is defined as the origin of the distribution function: f L (t ) d FL (t ) dt (3.12) At random point, the probability of failure can be determined by the sum of the products of two probabilities: (1) the probability that R < S at S = s and (2) the probability that S = s, open wide for all sequences of S: Pf P{R S / S s}.P{S s} (3.13) s To consider continuous distributions, the failure probability Pf at random point in time can be determined using convolutional integration: Pf F (s) f (s)ds R (3.14) s Where: FR(s) is the distribution function of R fs(s) is the probability density function of S s is the common load or deviation of R and S The general method for solving this integration problem with the time-dependent distributions of R and S can be very complex Direct resolution of these integrals is only available in some cases, for example the distribution of R and S is normal However, integrals can be solved by approximation The distribution of the long-term life can be found by calculating the failure probability values at different times such as t = 10, 20, 30 3.4.2 Probabilistic design method With the probabilistic durable design method, the distributions of the load, the characteristic curve and the longterm life are also taken into account The condition is understood as the probability that the design formula is incorrect The design formulation can be established according to the working principle or the long-term life principle being essentially the same as in the defined design According to the working principle, the following requirement must be satisfied: The probability of the structural resistance that is less than the load during service time must be less than a certain allowable failure probability: Mathematically the request is understood as: P{Failure}tg = P{R – S < 0}tg < Pfmax (3.15) Where P{failure}tg is the probability of failure of the structure in the desired long-term life tg Pfmax is the maximum allowable failure probability The problem can be solved if the distributions of load and resistance are found When the long-term life rule is used, the requirement is established as follows: The probability that the long-term life of the structure is shorter than the desired life is less than some allowable failure probability P{Failure}tg = P{tL < tg} < Pfmax (3.16) The problem can be solved if the distribution of the long-term life is determined If the pattern of the distribution is not known, it must be inferred against some known distribution One solution to the distributions of the long-run lifetimes is assumed to be lognormal 3.4.3 Design according to the working principle in the case where R and S have a normal distribution The case that the working principle is used in the durable design, and the loads and resistances are normally distributed loads, the probability of failure is determined using the test index β: 14 ( R, t ) ( S , t ) (3.17) ( [R, t ] [S , t ])1/2 μ is the mean, σ is the standard deviation The test index β is normally distributed (0, 1) The failure probability corresponding to β is available in tables or in updated functions in spreadsheet applications In structural design, the test index β is considered as the factor of safety or the reliability index Usually, R or S is constant The above relationship is shortened as follows: r [S , t ] (t ) (3.18) [S , t ] [R, t ] s (t ) (3.19) [R, t ] Where r and s are constants In the case where r is a constant and s is a function of time and is approximated by an attenuation model, the problem is called a performance problem Since the mean and standard deviations are time dependent, the β index is also time dependent To find the distribution of long-term life, the failure probabilities must be solved with some value of t (t = 0, 10, 20, etc annually) 3.4.4 Building a model to predict the service life of reinforced concrete structures using lightweight concrete taking into account the uncertainty of the input parameters The service life of reinforced concrete structures using lightweight aggregate concrete is calculated as the time from the time the construction is put into operation to the time when the reinforcement in the concrete begins to corrode The service life depends on factors: chloride diffusion coefficient D, equilibrium chloride concentration at the concrete surface Cs, limit chloride concentration and concrete coating Ccr, and protective concrete layer thickness h In recent studies, the limiting chloride concentration Ccr was considered to be normally distributed with mean and coefficient of variation (COV) of 0.027 - 0.045% and 0.05 - 0.296 (Enright and Frangopol 1998a; Stewart 2009); Stewart and Rosowsky 1998; Yanaka 2004 The surface chloride concentrations (CS) were modeled using a logarithmic normal distribution with mean and COV ranges of 0.10 - 0.40% and 0.05 - 0.50, respectively (Vu and Stewart 2000) The thickness of the protective concrete layer is influenced by the quality of construction, which is modeled according to a normal distribution or a normal logarithmic probability distribution (Enright and Frangopol 1999a) The chloride diffusion coefficient in this study is described according to the normal distribution law with the mean value and the COV range of 0.32-2.58 cm2/year and 0.05-1.6 respectively (the normal distribution model proposed by many authors as Yanaka (2004)) Conditions for the reinforcement in lightweight concrete structures to corrode are: C (x, t) ≥ Ccr or f = C(x, t) – Ccr ≥ The probability that a corrosion event will occur is shown as follows: Pf = P[C(x, t) – CCr ≥ 0] Using the Monte-Carlo simulation it is possible to easily calculate the probability of a corrosion failure occurring The probability of corrosion occurring is calculated by the formula: Pf = ∑𝑁 𝐼(𝑓(𝑥, 𝑡)) 𝑁 Where I is the instruction function: I = if f (x, t) < I = if f (x, t) ≥ Applying the above formulas with the parameters from research and experimental experiments, it is possible to calculate the probability of the occurrence of reinforcement corrosion incidents The expected design lifespan of the building is 100 years (t ) 15 3.5 Conclusions of Chapter In order to propose a model to predict the service life according to chloride ion permeability, at the beginning of chapter III, the author presented the basic concepts, characteristics and differences in the service life and durability of a structure Direct deterioration and indirect deterioration are considered to be the two main mechanisms leading to the deterioration of reinforced concrete bridge structures, in which, within the scope of this research, the author only mentions to the service life according to the penetration of chloride ions into the concrete bridge structure causing corrosion of reinforcement The model to predict the life of reinforced concrete structures is built based on Tuutti.K's model and consists of two stages according to the penetration of chlorine ions into the concrete bridge structure causing corrosion of reinforcement And in this study, regarding the longterm damage of the structure due to corrosion, the author only considers the assessment of the service life of a reinforced concrete traffic structure as the time when the corrosion begins Corrosion of reinforcements in concrete due to diffusion of chloride ions into concrete or more precisely time that concentration of chlorine ions (C) at the surface of reinforcement reaches the critical value (Ccr) The equation for calculating the concentration of chlorine ions at the reinforcement surface is taken according to Fick's 2nd law (RILEM 14 (2005) - A Sara & E Vesikari) At the end of the chapter, the author provides a model for predicting life according to probability theory when considering the process of chloride penetration causing corrosion of reinforcement And the design according to the working principle in the case of R and S with normal distribution is selected in this study CHAPTER 4: CALCULATION OF FORECASTING THE LIFESPAN OF LIGHTWEIGHT REFORCED CONCRETE STRUCTURES CONCERNING EFFECTS OF LOAD EFFECTS AND IMPACTS OF ENVIRONMENT 4.1 Calculation and prediction of service life of lightweight concrete used in slab structure of railway bridge deck with defined model The proposed model and experimental values presented in chapter are applied in this calculation Figure 4.1 - Relationship between the thickness of the protective concrete layer and the life of the building according to the pre-compressive stress In Figure 4.1, with the case of pre-compressive load, the rule of changing the life of the building according to the thickness of the protective concrete layer is quite similar; an increase in pre-compressive stress will require a thicker protective concrete layer thickness In Figure 4.2 we see, with the case of direct compressive load; the rule of changing the life of the structure according to the thickness of the protective concrete layer depends on the state of pre-compressive stress in different stages When max = 0.3, the thickness of the concrete layer decreases, but when max = 0.5, the thickness of the concrete layer increases and increases significantly when max = 0.7 16 Figure 4.2 - Relationship between the thickness of the protective concrete layer and the lifespan of the building under direct compressive stress 4.2 Calculation and prediction of service life of lightweight concrete used in slab structure of railway bridge deck with probability model Table 4.1 - Input parameter Standard Coefficient of deviation variation 𝝈 (%) 38,00 5,70 15 0,06 0,009 15 0,24 0,03 15 Factor, n 0,47 0,0705 15 Thickness of protective concrete layer, h 60 15 Experimental coefficient, m 0,245 3,675 15 Input Parameter Initial chloride ion diffusion coefficient (mm2/năm) Threshold corrosive concentration Surface chlorine ion concentration after year: The average value 𝝁 Cv In this study, the parameters D, m, C s , Ccr , and m are considered as random variables of the normal distribution form N (µ, σ) where µ is the mean and σ is the standard deviation Others are treated as constants The reference coefficient of variation C v is 15% and don’t change (with a standard deviation of 15% of the mean) for all parameters in Table 4.1 D = 38.00 (mm2/year) (D = 1.205x10-12 (m2/s)) with lightweight concrete according to the corrosion initiation criteria; with water/cement ratio (w/c) = 0.27; hmin = 60mm for coastal concrete structure Choosing herein h = 60mm; Δh = (mm) with marine atmosphere; the design service life is 100 years; m = 0.245 for lightweight concrete, CCr = 0.06% (by weight of concrete), kcu = 1.0 with 7-day concretre structure curing and ken = 0.68 for marine atmospheres 4.2.2.1 Effect of chloride ion diffusion coefficient D The effect of the diffusion coefficient D on the probability of corrosion incident Pf is shown in Figure 4.10 We see that over a certain period of time, keeping other parameters constant, an increase in D leads to an increase in Pf, this is because the higher the diffusivity represents the higher transport of chloride ions into the concrete The D0 factor depends on the quality of the concrete mainly the w/c ratio and the type of binder Assuming Pmt = 0.1 (β = 1.3), Figure 4.3 shows that the time to start corrosion of concrete structure is about 28, 20 and 19 years respectively with diffusion coefficient D = 47.50 ; 38.00 and 57.01 (mm2/year) 17 The probability of corrosion Pf D=57,01 0.8 D=38,00 0.6 0.4 =1,3 D=47,50 0.2 0 10 20 30 40 50 60 70 80 90 100 Time(year) Figure 4.3 - Effect of diffusion coefficient D on the probability of corrosion failure 4.2.2.2 Effect of the thickness of the protective concrete layer, h The effect of h on Pf is shown in Figure 4.4 When h increases, Pf decreases, or in other words, if Pf is the same, the time to start corrosion of reinforcement increases In order to initiate corrosion, the external chloride ions must be transported from the concrete surface through the protective layer and to the reinforcement, so the greater the thickness of the protective concrete layer, the longer the chloride concentration will reach the reinforcement at the critical level and the longer the service life of the reinforced concrete Thus, the thickness of the protective concrete layer is one of the most important parameters affecting the service life of the reinforced concrete If we take Pmt = 0.1 (β = 1.3), the corrosion start time of the reinforced concrete is about 29, 41 and 57 years, respectively, with the thickness of the protective concrete layer h = 60, 75 and 90mm, respectively The probability of corrosion Pf 0.8 h=75mm 0.6 h=60mm 0.4 h=90mm =1,3 0.2 0 10 20 30 40 50 60 70 80 90 100 Time (year) Figure 4.4 - Effect of protective concrete layer thickness h on the probability of corrosion incident 4.2.2.3 Effect of critical chloride concentration Ccr Figure 4.5 shows that the effect of C Cr on Pf is similar to the thickness of the protective concrete layer, which means if CCr increases, Pf will decrease It is clear that as the C Cr increases, the time it takes for chloride ions from outside to penetrate the concrete to reach the level of CCr increases and thus Pf decreases The concentration of C Cr depends on the quality of the concrete (w/c ratio, binder grade) and the type of steel used If we take P mt = 10-1 (β = 1.3), the corrosion time of concrete structure is about 29, 38 and 46 years, respectively, with CCr = 0.06, 0.075 and 0.09%, respectively 18 The probability of corrosion Pf 0.8 CCr = 0,075% 0.6 CCr = 0,06% 0.4 CCr = 0,09% 0.2 =1,3 0 10 20 30 40 50 60 70 80 90 100 Time (year) Figure 4.5 - The effect of the critical chloride concentration Ccr on the probability of corrosion incident 4.2.2.4 Effect of chloride concentration on concrete surface CS The effect of CS on Pf is shown in Figure 4.6, increasing CS causes Pf to increase Since the higher the CS, the greater the difference in chloride concentration between the surface and the interior of the concrete that led to the chloride transport faster into the concrete, resulting in the faster the chloride reaching the CCr concentration CS concentration depends on time, quality of concrete (w/c ratio, binder type) and type of contact environment Corrosion start time of concrete is about 25, 39 and 42 years, respectively, with CS = 0.36; 0.3 and 0.24% The probability of corrosion Pf 0.8 CS = 0,36% CS = 0,3% 0.6 0.4 CS = 0,24% 0.2 =1,3 0 10 20 30 40 50 60 70 80 90 100 Time (year) Figure 4.6 - Effect of concrete surface chloride concentration CS on the probability of corrosion incident 4.2.2.5 Effect of age factor, n The effect of n on P f is shown in Figure 4.7 The larger n represents, the greater resistance of concrete to chloride penetration from the environment over time (the lower the chloride ion diffusion coefficient of concrete over time) They lead to a decrease in P f (increasing the life of the concrete structure) The dependent coefficient n depends mainly on the type of binder and the environmental exposure conditions Corrosion start time of concrete is about 32, 42 and 56 years, respectively, with the coefficient n = 0.47; 0.5875 and 0.705 19 The probability of corrosion Pf 0.8 n = 0,47 n = 0,5875 0.6 0.4 n = 0,705 0.2 =1,3 0 20 40 60 80 100 Time (year) Figure 4.7 - Effect of age factor n on the probability of corrosion failure 4.4 Conclusions of Chapter Applying the calculation to predict the lifespan of the railway bridge deck structure using lightweight reinforced concrete with parameters from the experiment and taken according to the recommendations of some typical standards in the world, the results show that the service life of the bridge deck structure using the lightweight reinforced concrete according to the corrosion initiation criterion is significantly reduced when the pre-compressive stress increases The change of protective concrete layer thickness has a great influence on the lifespan of reinforced concrete structures - In the case of pre-compressed load; the law of changing the lifespan of the construction according to the thickness of the protective concrete layer is quite similar; An increase in pre-compressive stress will require a thicker protective concrete layer thickness - In case of direct compressive load; the rule of changing the lifespan of the structure according to the thickness of the protective concrete layer depends on the state of pre-compressive stress in different stages When max = 0.3, the thickness of the protective concrete layer decreases, but when max = 0.5, the thickness of the protective concrete layer increases and increases significantly when max = 0.7 Through the application of probability theory when considering the process of chloride intrusion causing corrosion of reinforcement to predict the lifespan of reinforced concrete structures using lightweight materials The life prediction model is designed based on the working principle in case the normal distribution of resistance R and load S are selected in this study Combining Monte - Carlo simulation with input parameters: chloride diffusion coefficient (D), equilibrium chloride concentration at the concrete surface (Cs), limiting chloride concentration (Ccr) and protective concrete layer thickness (h) inferred the relationship between the probability of corrosion incidents and concrete-related factors From the research results, some conclusions are drawn as follows: - The thickness of the concrete protection layer (h) has the greatest influence on the probability of corrosion incident (Pf), followed by the parameters n, Ccr, Cs and D - Under the penetration of chloride ions, in order to increase the quality of the concrete structure or increase the life of the concrete structure, it is necessary to increase the values of the parameters n, Ccr and at the same time reduce the parameters D and Cs to reduce the probability of corrosion incident Pf - The thickness of the protective concrete layer has an extremely important role under the impact of the environment on reinforced concrete structures Therefore, the thickness of the protective concrete layer must be selected as reasonably as possible 20 CONCLUSION AND RECOMMENDATION Conclusion The thesis has carried out the research contents related to the analysis of water permeability and chloride ion permeability of some types of lightweight concrete used in construction with consideration of compressive stress effects in concrete The new contributions of the thesis are summarized as follows: 1/ Experimental studies, analysis of water permeability through lightweight concrete under the influence of loads for concrete C30 Research results show that when increasing the compressive load, the water permeability of concrete increases significantly; especially after in concrete there is a change in the void structure due to the action of pre-compression or direct compression A water penetration test model that considers direct compressive load has been designed, manufactured and tested based on recent world research results; This experimental equipment has been improved to make the measurement process more convenient, especially the process of controlling the load and recording data completely automatically The test results of water permeability measurement under the influence of pre-compression load show that, when max > 0.5, marking a rapid increase of water permeability when water pressure is greater than 10atm, this proves the influence of pre-compression stress is large enough to increase water permeability of lightweight concrete, it is these residual mechanical effects that facilitate water penetration thr ough the concrete specimen, especially when max > 0.5 , the occurrence of concrete destruction caused the increase in water permeability to increase more rapidly Especially in the experiment, we found that when max = 0.8 showed a huge difference in water permeability in lightweight concrete The test results of water permeability measurement under the influence of direct compressive load show that the water permeability of concrete is almost unchanged or changes slowly when the relative stress value max < 0.5; After this threshold, the permeability coefficient starts to increase rapidly When the relative stress max ≥ 0.6, the water permeability increases very quickly; This can be explained because the microstructure of concrete is destroyed after this stress threshold - which is the threshold for the appearance of dispersed failure zones (according to the approach of concrete failure mechanics) - causing increase the water permeability of concrete The law of increasing the water permeability of concrete after 28 days in this experiment is similar to the law of increasing the water permeability of young concrete published by Banthia & al (2005) when mechanical failure has not yet been appeared in concrete 2/ Experimental studies analyzing chloride ion permeability through lightweight concrete under the influence of load for concrete C30, the research results show a significant influence of compressive load on chloride ion permeability of lightweight concrete A chloride ion permeation test model considering direct compressive load has been designed, fabricated and tested based on recent world research results; This test equipment has been improved to make the measurement process more convenient, especially the process of controlling the compressive load in concrete The results of chloride ion penetration test with lightweight concrete samples subjected to pre-compression load show that, Chlorine ion permeability at load levels when /max = 0; 0.3; 0.5 of lightweight concrete C30 is low level and has a litter change than that of normal concrete C30 The large change at grade 0.8P marks a rapid increase in the chloride ion permeability of lightweight concrete C30 compared to normal concrete C30 This change has a big difference because the compressive stress approaches the destructive value, the 21 structures in the concrete are broken into, allowing chloride ions to penetrate This is in full agreement with the rating scale of coercivity according to ASTM C1202 [24] The reason for lightweight concrete has an aggregate shell that may contain water or chlorine ions When compressed with a load of 0.8P, the clay particles are broken, losing their ability to block chlorine ions, so that chlorine ions can quickly penetrate through the concrete The clay particles of lightweight concrete are filled with water to a state of water saturation in the concrete, when the sample is saturated with water, seepage begins to occur In contrast to normal concrete, seepage occurs earlier because the aggregate is gravel, so it is impervious to water In addition, when adding fine mineral admixtures to the composition for lightweight concrete, the effectiveness of chlorine ion waterproofing increases sharply The law of increasing the chloride ion permeability coefficient according to the precompression stress of lightweight concrete C30 is expressed by the following formula: Exponential Regression: D/Do = 9.1226(/max)2 – 3.4256(/max) + 1.0816 The results of chloride ion permeability test with lightweight concrete samples subjected to direct compressive loads show that the chloride ion permeability changes strongly when there is the presence of simultaneous acting loads However, before and after loading, the chloride ion permeability is within the "average" level according to TCVN 9337-2012 When the stress is increased to 30% and 50% of max, the permeability of concrete increases by 24.50% and 39.48%, respectively When increasing the stress to 80% of max, the permeability of concrete has a large increase In the case of reduced chloride ion permeability, it will lead to a longer time of chloride ion penetration through the protective concrete layer to cause corrosion of reinforcement in reinforced concrete constructions From this result, it is shown that in prestressed concrete structure, when compressive stress in concrete is within the appropriate limit, it can prolong the penetration time and increase the service life due to chloride ion penetration The law of increasing the chloride ion permeability coefficient according to the precompression stress of lightweight concrete C30 is expressed by the following formula: Exponential Regression: D/Do = 4.4975(max)2 – 1.9529(max) + 0.9543 3/ Determine the coefficient C to calculate the chloride ion diffusion coefficient from the water permeability coefficient of the same type of concrete From there, a formula for calculating the relationship between water permeability coefficient and chloride diffusion coefficient of concrete is proposed, taking into account the influence of stress in concrete C30 as follows: Kw = 29.05 S0.5 D 4/ The thesis has used the proposed model to calculate and predict the service life of reinforced concrete structures using lightweight concrete in Vietnam conditions, taking into account the influence of permanent load and operational load - The case of the pre-compressive stress state (operational load) h= 2√D0 t1−m t m σ σ Ccr (9.1226 ( ) − 3.4256 ( ) + 1.0816) × erf −1 ( ) σmax σmax Cso t n - The case of direct compressive stress states (permanent load) h= 2√D0 t1−m t m (4.4975 ( σ σ Ccr ) − 1.9529 ( ) + 0.9543) × erf −1 ( ) σmax σmax Cso t n In the case of pre-compressed load; the law of changing the lifespan of the construction according to the thickness of the protective concrete layer is quite similar; an increase in precompressive stress will require a thicker protective concrete layer thickness 22 In the case of direct compression loads; the rule of changing the life of the structure according to the thickness of the protective concrete layer depends on the state of pre compressive stress in different stages When /max = 0.3, the thickness of the protective concrete layer decreases, but when /max = 0.5, the thickness of the protective concrete layer increases and increases significantly when /max = 0.7 In the model of predicting the life of reinforced concrete structures using lightweight materials, the uncertainty of input parameters and Monter-Carlo simulation were taken into account to calculate the probability of a corrosion occurring 5/ Carrying out the calculation and prediction of the service life of the railway bridge deck structure using lightweight reinforced concrete with parameters from the experiment and taken according to the recommendations of some typical standards in the world, the results showed that the service life of the bridge deck structure using the lightweight reinforced concrete according to the corrosion initiation criterion was significantly reduced when the pre-compressive stress increased The change of protective concrete layer thickness has a great influence on the lifespan of reinforced concrete structures 6/ Applying the calculation to predict the service life of the lightweight aggregate concrete slab structure of the railway bridge deck with the probabilistic model gives some conclusions: - The thickness of the concrete protection layer (h) has the greatest influence on the probability of corrosion incident Pf, followed by the parameters n, Ccr, Cs and D - Under the penetration of chloride ions, in order to increase the quality of the concrete structure or increase the life of the concrete structure, it is necessary to increase the values of the parameters n, Ccr and at the same time reduce the parameters D and Cs to reduce the probability of corrosion incident Pf - The thickness of the protective concrete layer has an extremely important role under the impact of the environment on reinforced concrete structures Therefore, the thickness of the protective concrete layer must be selected as reasonably as possible Recommendations for future research Future research directions are expected as follows: - Studying the accumulation of chloride ions on the lightweight concrete surface of different types of concrete for different regions of Vietnam - Studied random characteristics of diffusion and corrosion processes - Studying the simultaneous effects of many factors such as: mechanical, physical, chemical, and thermal - Study of water permeability and chloride permeability for lightweight concrete structures subjected to flexion and tension simultaneously 23 REFERENCES Hồ Xuân Ba (2019), "Đánh giá độ thấm nước thấm ion clorua bê tơng có xét đến yếu tố ứng suất, ứng dụng kết cấu cầu", Luận án tiến sỹ kỹ thuật Đặng Thùy Chi (2017), “Nghiên cứu thành phần, tính chất bê tơng cốt liệu nhẹ dùng xây dựng cầu Việt Nam”, Luận án tiến sĩ kĩ thuật Đặng Thùy Chi, Ngô Thị Thanh Hương (2019), "Nghiên cứu thiết kế chế tạo bê tông cốt liệu nhẹ đề xuất sử dụng cho cơng trình giao thơng", Đề tài nghiên cứu khoa học cấp Bộ, DT184012 (2019) Nguyễn Duy Hiếu (2009), "Nghiên cứu chế tạo bê tông keramzit chịu 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Saito, Mitsuru and Ishimori, Hiroshi (1995), "Chloride permeability of concrete under static and repeated compressive loading", Cement and Concrete Research 25(4), pp 803-808 20 Truyen T Tran (2009), "Contribution to the study of mechanical and hydro mechanical behaviors of concrete", PhD Thesis (in French), University of Liege 21 Tegguer, A Djerbi, et al (2013), "Effect of uniaxial compressive loading on gas permeability and chloride diffusion coefficient of concrete and their relationship", Cement and concrete research 52, pp 131-139 22 Tuutti, K (1980) “Service life of structures with regard to corrosion of embedded steel”, Proceedings of the International Conference on Performance of Concrete in Marine Environment, ACI SP-65, pp 223-236 23 Zhang, Tiewei and Gjørv, Odd E (2005), "Effect of chloride source concentration on chloride diffusivity in concrete", ACI materials journal 102(5), p 295 24 LIST OF STUDENTS PUBLISHED PAPERS Tran The Truyen, Le Quang Vu, Ho Xuan Ba, Service life estimation of high performance reinforced concrete structures in considering the damage of concrete cover¸ Procedings of the International Conference EASEC-14, HCM City, 1/2016 Hồ Xuân Ba, Lê Quang Vũ, Ảnh hưởng trạng thái chịu tải đến khả chống thấm bê tơng, Tạp chí KHGTVT số 51, 4/2016 Trần Thế Truyền, Hồ Xuân Ba, Thái Khắc Chiến, Lê Quang Vũ” Ảnh hưởng trạng thái chịu tải nén trước đến độ thấm ion clo số loại bê tông, ứng dụng dự báo tuổi thọ kết cấu bê tông cốt thép” Tạp chí KHGTVT, số 57, 7/2017 Lê Quang Vũ, Hồ Xuân Ba, Đoàn Bảo Quốc Trần Thế Truyền, “Ảnh hưởng ứng suất nén trước bê tông đến độ thấm bê tông nhẹ, Tuyển tập hội nghị học toàn quốc lần thứ X, Hà nội, 12/2017 Lê Quang Vũ, Thái Khắc Chiến, Trần Thế Truyền: Thực nghiệm ảnh hưởng tải trọng nén trước đến độ thấm ion clo bê tông sử dụng cốt liệu nhẹ”, Tạp chí KHGTVT, số 61., 6/2018 Hồ Xuân Ba, Lê Quang Vũ, Thái Khắc Chiến, Trần Thế Truyền, Ảnh hưởng ứng suất nén đến độ khuếch tán ion clo bê tơng, Tạp chí Khoa học GTVT số 66, 10/2018 Lê Quang Vũ, Thái Khắc Chiến, Trần Thế Truyển, Ảnh hưởng ứng suất nén trực tiếp đến xâm nhập clorua qua bê tơng keramzit, Tạp chí GTVT số 7/2019 Trần Thu Minh, Lê Quang Vũ, Trần Đức Mạnh, Hồ Xuân Ba, Trần Thế Truyền, Dự báo tuổi thọ kết cấu bê tơng cốt thép cốt liệu nhẹ có xét đến lý thuyết xác suất, Tạp chí GTVT, số 5, 2022 ... trước đến độ thấm ion clo số loại bê tông, ứng dụng dự báo tuổi thọ kết cấu bê tông cốt thép” Tạp chí KHGTVT, số 57, 7/2017 Lê Quang Vũ, Hồ Xuân Ba, Đoàn Bảo Quốc Trần Thế Truyền, “Ảnh hưởng ứng suất... 308 Hồ Văn Quân, Phạm Duy Hữu Nguyễn Thanh Sang (2015), "Cải thiện độ chống thấm ion clo kéo dài tuổi thọ kết cấu bê tông môi trường biển cách sử dụng kết hợp muội silic tro bay", Tạp chí GTVT... độ thấm ion clo bê tông sử dụng cốt liệu nhẹ? ??, Tạp chí KHGTVT, số 61., 6/2018 Hồ Xuân Ba, Lê Quang Vũ, Thái Khắc Chiến, Trần Thế Truyền, Ảnh hưởng ứng suất nén đến độ khuếch tán ion clo bê tơng,