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Nghiên cứu chế tạo bê tông cốt sợi chất lượng siêu cao hàm lượng tro bay lớn sử dụng cho kết cấu công trình ở Việt Nam.Nghiên cứu chế tạo bê tông cốt sợi chất lượng siêu cao hàm lượng tro bay lớn sử dụng cho kết cấu công trình ở Việt Nam.Nghiên cứu chế tạo bê tông cốt sợi chất lượng siêu cao hàm lượng tro bay lớn sử dụng cho kết cấu công trình ở Việt Nam.Nghiên cứu chế tạo bê tông cốt sợi chất lượng siêu cao hàm lượng tro bay lớn sử dụng cho kết cấu công trình ở Việt Nam.Nghiên cứu chế tạo bê tông cốt sợi chất lượng siêu cao hàm lượng tro bay lớn sử dụng cho kết cấu công trình ở Việt Nam.Nghiên cứu chế tạo bê tông cốt sợi chất lượng siêu cao hàm lượng tro bay lớn sử dụng cho kết cấu công trình ở Việt Nam.Nghiên cứu chế tạo bê tông cốt sợi chất lượng siêu cao hàm lượng tro bay lớn sử dụng cho kết cấu công trình ở Việt Nam.Nghiên cứu chế tạo bê tông cốt sợi chất lượng siêu cao hàm lượng tro bay lớn sử dụng cho kết cấu công trình ở Việt Nam.Nghiên cứu chế tạo bê tông cốt sợi chất lượng siêu cao hàm lượng tro bay lớn sử dụng cho kết cấu công trình ở Việt Nam.Nghiên cứu chế tạo bê tông cốt sợi chất lượng siêu cao hàm lượng tro bay lớn sử dụng cho kết cấu công trình ở Việt Nam.Nghiên cứu chế tạo bê tông cốt sợi chất lượng siêu cao hàm lượng tro bay lớn sử dụng cho kết cấu công trình ở Việt Nam.Nghiên cứu chế tạo bê tông cốt sợi chất lượng siêu cao hàm lượng tro bay lớn sử dụng cho kết cấu công trình ở Việt Nam.Nghiên cứu chế tạo bê tông cốt sợi chất lượng siêu cao hàm lượng tro bay lớn sử dụng cho kết cấu công trình ở Việt Nam.Nghiên cứu chế tạo bê tông cốt sợi chất lượng siêu cao hàm lượng tro bay lớn sử dụng cho kết cấu công trình ở Việt Nam.
MINISTRY OF EDUCATION AND TRAINING HANOI UNIVERSITY OF CIVIL ENGINEERING Pham Sy Dong RESEARCH AND PRODUCTION OF ULTRA-HIGH PERFORMANCE FIBER CONCRETE WITH A HIGH VOLUME FA CONTENT TOWARD APPLYING IN BUILDING STRUCTURES IN VIETNAM Major: Material engineering Code: 9520309 SUMMARY OF DOCTORAL DISSERTATION Ha Noi - 2022 The work was completed at: HANOI UNIVERSITY OF CIVIL ENGINEERING (HUCE) Academic supervisor: Prof Dr Nguyen Van Tuan – HUCE Prof Dr Le Trung Thanh – VIBM Peer reviewer 1: Prof Dr Luong Duc Long - VIBM Peer reviewer 2: Prof Dr Nguyen Duy Hieu - HAU Peer reviewer 3: Prof Dr Le Thanh Ha - UTC The doctoral dissertation will be defended at the level of the University Council of Dissertation Assessment's meeting at the Hanoi University of Civil Engineering at hour .', day month year 2022 The dissertation is available for reference at the libraries as follows: - National Library of Vietnam; - Library of Hanoi University of Civil Engineering; INTRODUCTION Need for the research Ultra-high performance concrete (UHPC) is a new generation of concrete that has been developed since the 1990s The UHPC is well-known for its outstanding properties, such as workability, mechanical properties, and long-term durability, compared to normal concrete and high-strength concrete In addition, because of the dispersed steel fiber, this type of concrete has excellent bending and tensile responses similar to elasto-plastic materials or reinforced concrete (RC) Practical applications of UHPC have also been made to bridge structures, thin shell structures, large span structures, etc Nowadays, many studies on UHPC concrete have been carried out in many countries around the world However, research and applications in Vietnam are still underway, and the research and production of UHPC used for building structures in Vietnam is an advanced and very necessary scientific issue UHPC typically consists of a large amount of binder (about 800-1000 kg/m 3) Therefore, the study of using industrial and agricultural by-products as mineral admixtures to replace cement to produce UHPC has great significance for the environment and sustainable development of this concrete Fly ash (FA) is considered one of the most potential mineral admixtures among these by-products In particular, using FA with high content in the production of UHPC will bring economic, technical, and environmental benefits In fact, the study of using FA to make UHPC has also been carried out, but so far, only very few studies have been published on the possibility of using high-volume FA (high-volume fly ash-HVFA) with FA content over 50% by the amount of binder) because the replacement of cement with FA often causes a significant disadvantage in reducing the strength of concrete at an early age Based on the research situation of UHPC and current conditions in Vietnam in the context of the large amount of waste generated by thermal power plants in our country, a doctoral research topic was proposed "Research and production of ultra-high performance fiber concrete with a high volume FA content toward applying in building structures in Vietnam" The target of the research The research objective of the thesis is to successfully fabricate UHPC using high FA content (HVFA UHPC) with high workability, compressive strength over 120MPa, flexural strength higher than 15MPa, elastic modulus over 40 GPa aims to apply to building structures in Vietnamese conditions Research objects and scope + Objectives: Ultra high-performance concrete using high FA content (HVFA UHPC) and evaluating the properties of HVFA UHPC Based on these attained properties, the HVFA UHPC beam was designed and fabricated to study the mechanical behavior in order to evaluate the applicability of this type of concrete + Scopes Based on the materials used to make HVFA UHPC concrete with the desired properties, the research scopes of this thesis include as follows: - Using a combination of available SF and FA in Vietnam in which FA was used with high content, i.e., over 50% by volume of the binder - Using dispersed steel fiber, including studying the influence of steel fiber content (0-4% by vol of concrete) on the properties of UHPC - Applying two curing conditions of UHPC, i.e., standard curing (27±2oC, RH≥95%) and heat curing (90±5oC, RH≥ 95%) - The concrete mixture has a mini-cone flow of 200-250 mm Compressive strength of concrete ≥ 120 MPa, flexural strength ≥ 15 MPa, elastic modulus E ≥ 40 GPa - Fabrication and evaluation of mechanical behavior of HVFA UHPC beams Scientific basic Based on the analysis of UHPC and the feasibility of developing materials using a high volume of FA (HVFA) to meet the current construction needs in Vietnam, the thesis sets out the scientific basis to achieve the research objectives as follows: - Research on improving the quality of HVFA UHPC - Studying a model to predict the strength of HVFA UHPC over time - Studying the mechanical behavior of the HVFA UHPC beam Research methods The thesis uses research methods, including theoretical methods combined with experiments; calculation methods combined with numerical simulation; statistical analysis and synthesis methods Scientific significance + Theoretical significance: - The scientific basis of using a high concentration of FA to make UHPC with a very low W/B ratio was analyzed and demonstrated Using mineral admixtures of FA and SF combined with superplasticizer reduces the W/B ratio This is an important factor in improving the workability of concrete mixes with a very low W/B ratio, increasing the homogeneity of the concrete mix, increasing the mechanical strength, and improving the durability of HVFA UHPC On that basis, the thesis evaluated the role of mineral admixtures in the UHPC - The scientific basis for the role of dispersed steel fibers in enhancing the flexural and tensile strength of UHPC was studied and demonstrated - A theoretical model was proposed to predict the strength of HVFA UHPC over time with different curing conditions Simultaneously study the calculation theory, numerical simulation, and experimental verification to determine the value of the destructive load of beam members subjected to flat horizontal bending - The mechanical behavior of the HVFA UHPC concrete element was studied and evaluated, which has great significance in theory and practical application, especially for concrete systems with very low W/B ratios and a high volume of FA + Practical significance: - Using available materials (sand, FA, SF, superplasticizer, steel fiber reinforcement) in manufacturing conditions in Vietnam to produce HVFA UHPC meeting desired technical properties will contribute to promoting sustainable construction and improving the quality of environmental protection in Vietnam - A theoretical model that predicts the compressive strength of HVFA UHPC over time with different curing conditions contributing to minimizing experiments, saving costs and research time have high practical significance in the application of HVFA UHPC in Vietnam New scientific contributions (1) Produced HVFA UHPC with a high volume (>50%) of fly ash in Vietnam (2) Optimized the HVFA UHPC mix proportions by designing the optimal granular composition based on De Larrard model and the experiments (3) Proposed a model to predict the compressive strength of HVFA UHPC over time with different curing regimes and FA contents (4) Studied the mechanical behavior of beam members using HVFA UHPC and evaluated the feasibility by numerical simulation and experimental verification Structure of the thesis The thesis includes five main chapters, i.e., (1) a literature review on HVFA UHPC, (2) a scientific basis for producing HVFA UHPC, (3) materials and research methods, (4) an experimental study on the properties of HVFA UHPC, (5) mechanical behavior of the HVFA UHPC beam CHAPTER : LITERATURE REVIEW ON HVFA UHPC 1.1 GENERAL CONCEPTS Ultra-High Performance Concrete (UHPC) is a new generation of concrete with outstanding properties in terms of workability, strength, and durability It can be seen that UHPC properties combine the features of some other particular types of concrete, such as self-compacting concrete (SCC), fiber- reinforced concrete (FRC), and high-performance concrete (HPC) Typically, the term UHPC concrete is used to describe a mixture consisting of fine quartz sand with a particle size less than 0.6mm, cement, SF, steel fiber, and superplasticizers with a very low W/B ratio The definition of UHPC is different in some countries with different compressive strengths, for example, over 150 MPa (the French standard), over 120 MPa (American and Asian standards), and according to ASTM standards of American C1856, UHPC is defined to have a compressive strength of 120 Mpa [10] Based on the recommendations and standards that many countries have not agreed on yet, the term UHPC that was suggested o be used in this thesis has a compressive strength of ≥ 120 MPa, which is suitable for local raw material sources and production capabilities in Vietnam today 1.2 MATERIALS Materials used in this study include aggregates (quartz sand), cement, mineral admixtures, superplasticizers, and steel fiber 1.3 RESEARCH AND APPLICATION OF UHPC IN THE WORLD AND VIETNAM 1.3.1 Research and application of UHPC in the world 1.3.2 Research and application of UHPC in Vietnam 1.4 PROPERTIES OF CONCRETE MIXTURE AND UHPC 1.4.1 Workability 1.4.2 Mechanical properties: compressive strength and elastic modulus, direct tensile strength, flexural tensile strength, toughness strength, impact strength and crack resistance 1.4.3 Shrinkage 1.4.4 Durability 1.5 RESEARCH AND PRODUCTION OF UHPC USING HIGH-VOLUME FLY ASH 1.5.1 Sustainable development of concrete 1.5.2 Potential of using high-volume fly ash to produce UHPFRC 1.6 RESEARCH ORIENTATION OF THE THESIS Based on the above analysis of UHPC and the possibility of developing this material to satisfy current construction needs in Vietnam, the thesis will present scientific problems that need to be solved: (1) Research and manufacture UHPC using high FA content: through research on the selection of available materials, while also proposing a method for designing a mix HVFA UHPC (2) Research optimizing the UHPC mix using the maximum FA content based on studying the properties of concrete and concrete mixes (3) Study of HVFA UHPC strength prediction model over time with different curing conditions (4) Experimental study and evaluation of mechanical behavior of HVFA UHPC beam members CHAPTER : SCIENTIFIC BASIS FOR PRODUCING HVFA UHPC Based on the analysis of UHPC and the feasibility of developing materials using a high volume of FA (HVFA) to meet the current construction needs in Vietnam, the thesis sets out the scientific basis to achieve the research objectives as follows: 2.1 RESEARCH FOR IMPROVING HVFA UHPC QUALITY For UHPC in general and HVFA UHPC in particular, the research to improve the quality of concrete is based on a number of main scientific bases as follows [128, 133]: - Reduce the maximum size of aggregate - Optimizing particle composition - Increase the consistency by using superfine particles - Improvement of microstructure by heat curing - Improve the durability of concrete - The scientific basis for using HVFA in concrete 2.2 RESEARCH OF HVFA UHPC STRENGTH FORECAST MODEL OVER TIME In order to establish simple empirical equations for the development of compressive strength of UHPC, the World Federation of Concrete Structures (fib) 2010 provides an exponential model of this development 2.3 RESEARCH OF MECHANICAL BEHAVIOR OF HVFA UHPC BEAM STRUCTURAL Based on the attained mechanical properties, the mechanical behavior of UHPC beam elements was studied to serve as a basis for practical applications for building structures This scientific thesis is based on studying the theory of structural calculations and proposing experimental models for basic beam elements From there, evaluate and propose a proper structural calculation theory and relevant coefficients, such as including the influence of fiber reinforcement content on UHPC tensile area calculation Based on experimental results, adjust the coefficient of concrete Rk in the theoretical calculation 2.3.1 Some theories of calculating UHPC beams The study of mechanical behavior of UHPC members has also been studied by many institutions around the world, and some calculation theories can be mentioned as follows: - According to AASHTO LFRD, concrete has a compressive strength between 16 MPa and 70 MPa - According to the Federal Highway Administration (FHWA) - According to Canadian bridge design standards - According to the French Association of Civil Engineers (AFGC\SETRA) - According to the Japan Society of Civil Engineers (JSCE) 2.3.2 Establishing the theoretical formula to calculate the beam breaking load HVFA UHPC From the research results of the countries mentioned above, the PhD student decided to calculate the theory according to the stress and strain relationships model in the tensile and compressive areas according to the Federal Highway Administration (FHWA) to find the factor Rk for UHPC beams 2.3.3 Using ABAQUS finite element analysis software for calibrating experiments to calculate the destructive load of the beam HVFA UHPC Research and simulate beam bending experiments using ABAQUS finite element analysis software This simulation method, at the same time, will help reduce the cost of sample testing and determine the sample failure load quickly when surveying the change of input parameters when manufacturing UHPC beams CONCLUSION The research topic of the thesis was proposed based on an overview analysis of the need for UHPC development in the world in general and Vietnam in particular, and at the same time, considering the specific aspects of available materials and suitable in Vietnamese conditions, the research and development of HVFA UHPC is necessary, towards sustainable development and costeffectiveness and environment To implement this idea, the topic sets out scientific arguments to be solved, including: - Researching and manufacturing UHPC using a large amount of FA is reasonable and feasible, and the study of properties of HVFA UHPC is based on the research and proposed method of HVFA UHPC mix design, while at the same time, this study optimizes concrete mix on the experimental results to evaluate the influencing factors Besides, studying the influence of high FA content on cement hydration in UHPC through the change of CH content over time is also analyzed and evaluated - Research and propose a model to predict HVFA UHPC compressive strength over time - Study the mechanical behavior of HVFA UHPC beam members, then propose an appropriate structural calculation method Based on analyzing the disadvantages of this type of concrete using HVFA content, the first target of the thesis is to produce HVFA UHPC using available materials in Vietnam, and then concrete mix design was proposed CHAPTER : MATERIALS AND RESEARCH METHODS 3.1 MATERIALS USED IN THE STUDY 3.1.1 Aggregate (quartz sand): The fine aggregate used in the project is quartz sand with a particle size of 100-600 µm 3.1.2 Cement: The cement used in the study is Nghi Son PC50 cement 3.1.3 Mineral admixture a Silica fume: the undensified SF type (Elkem) b Fly Ash: the F-type and fine FA collected from Pha Lai thermal power plant 3.1.4 Superplasticizer: a liquid polycarboxylate-based superplasticizer with a solid content of 30% 3.1.5 Steel fiber: Dramix OL13/0.20 type 3.1.6 Water: tap water 3.2 METHODS 3.2.1 Standard research methods 3.2.2 Non-standard research methods 3.3 RESEARCH AND PROPOSED MIX DESIGN METHOD OF HVFA UHPC 3.3.1 Optimal design method of granular composition HVFA UHPC The compaction model [14, 15] includes the compaction process to achieve theoretical compaction γi, defined as the maximum compacted volumetric mass of the particles, when the particles are partially replaced The calculation formula for optimal compaction with n grain grades and i components according to formula (3-2) is as follows: �� γi = 1−∑𝑖−1 [1−�+� (1− � =1 � )� −∑� � − −� � ]� [1 �� �� = + (3-2) � 𝑖 � 𝑖 𝑖 𝑖 Loose effect (aij): occurs when small particles fill in, and the size exceeds the gap between larger groups of particles when naturally arranged, then larger particles will be pushed apart (loose), and the effect of this effect is included in the calculation in formula (3-3) as follows: aij = √1 − (1 − dj 1,0 2) di (3-3) The wall effect (bịj): occurs when larger particles will form surfaces (retaining wall form), and some space near this surface does not allow small particles to arrange and fill naturally into these voids, creating a pore system surrounding larger particles, the effect of this effect is included in the calculation according to formula (3-4) as follows: bij = – (1-di/dj)1,50 (3-4) For a particle class βj can be determined by the following formula: (3-5) 𝑖𝑖 αj =1+ � The compaction coefficient is determined as follows: yi n n K = ∑ K i = ∑ βi i=1 i=1 1 − Φ γi (3-6) 3.3.2 Proposed HVFA UHPC mix design method Increase W/B ratio (YES) (NO) Select raw materials (Sand, cement, SF, FA) and input expected performance for UHPC Mini-slump flow = 200 - 250 mm (YES) Optimize granular composition (F.de Larrard & T Sedran) Reasonable setting Maximum SP dosage (NO) Increase SP dosage (NO) (YES) Standard curing, heat treatment Select S/B, FA/B ratios Select W/B ratio and/or SP dosage and evaluate Compressive strength 120 MPa (standard curing) or 150 MPa (heat(NO) treatment) UHPC performance (YES) Increase FA/B ratio (NO) Maximum FA/B ratio (YES) Heat curing duration (1-2-3-4-5-6-7 days) Final HVFA UHPC mixture Figure 3.9 Proposed concrete mix design method of HVFA UHPC 3.3.3 Calculation of the HVFA UHPC component 3.3.4 HVFA UHPC mixing process and curing conditions 3.3.5 HVFA UHPC mix proportions CONCLUSION This chapter presents the selection of materials and research methods that were used in the thesis, including: - Standard research methods: applied to evaluate raw materials and properties of concrete and concrete mixtures - Non-standard research methods: applied to the proposed study of the concrete mix design method of HVFA UHPC, the hydration process, the compressive strength prediction model over time, and the behavior bending of the HVFA UHPC beam Figure 4.5 Effect of a combination of 10% SF and (30-70)% FA on the CH content of the hardened binder paste under standard curing conditions, the W/B ratio = 0.16 Figure 4.6 Effect of a combination of 10% SF and (30-70)% FA on CH content in hardened binder paste under heat treatment, the W/B ratio = 0.16 Figure 4.7 Effect of mineral admixtures on the CH content of the hardened binder paste under standard curing conditions and heat treatment at the age of 28 days 4.2 RESEARCH ON THE PROPERTIES OF HVFA UHPC AND CONCRETE MIXTURES 4.2.1 Workability of the UHPC mixtures The dosage of the superplasticizer was adjusted to the UHPC blend to obtain an average flow diameter value of 200-250 mm, as shown in Figure 4.8 Figure 4.8 Relationship between the superplasticizer dosage and amount of mineral admixtures, flow of concrete mix from 200-250 mm, the W/B ratio = 0.16 The workability of the mixture decreased linearly as the fiber content increased from to 4% to determine the workability of the concrete mix 300 250 230 200 205 Fl ow 150 , m 100 180 150 115 50 21 32 43 Fiber content, % Figure 4.9 Relationship between flowability and the steel fiber content 4.2.2 Effect of the SF content on compressive strength of UHPC Figure 4.10 Effect of the SF content on compressive strength of UHPC (a) 27±2oC, (b) 90±5oC 4.2.3 Effect of the FA content on compressive strength of UHPC Figure 4.11 Effect of the FA content on compressive strength of UHPC (a) 27±2oC, (b) 90±5oC 4.2.4 Effect of a combination of SF and FA on the compressive strength of UHPC Effect of a combination of SF and FA on the compressive strength of UHPC Figure 4.12 Effect of FA content on the development of compressive strength of UHPC with time, SF = 10%, (a) 27±2oC, (b) 90±5oC 4.2.5 Effect of heat curing duration from to days on the 28-day compressive strength Co m pr es siv e str en gt h, M Heat treatment duration, days (b) W/B = 0.16 Figure 4.17 Effect of different heat treatment duration from 1-7 days on the 28-day compressive strength of UHPC using different fly ash and W/B content Figure 4.19 Relationship between the highest 28-day compressive strength of UHPC and different FA contents 4.2.6 Effect of sample size on compressive strength of HVFA UHPC 4.2.7 Elastic modulus of HVFA UHPC Test the modulus of elasticity according to ASTM C469 for cylindrical specimens at 28 days E=σ/ɛ (4-1) 4.2.8 Split compressive strength of HVFA UHPC The split press test to determine the split compressive strength was tested according to the ASTM C496 standard for cylindrical specimens at 28 days Rk=2P/πdl (4-2) 4.2.9 Tensile strength in bending of HVFA UHPC The 4-point bending test to determine the tensile strength in bending was tested according to ASTM C1018 for beam samples at 28 days Rku=P.L/b.h2 (4-3) 4.3 PROPOSED HVFA UHPC COMPRESSIVE STRENGTH PREDICTION MODEL OVER TIME 4.3.1 General introduction To establish simple empirical equations for the development of compressive strength of UHPC, the World Federation of Concrete Structures (fib) has developed this exponential growth model (fib 2010) 4.3.2 Model to predict concrete compressive strength according to fib 2010 Figure 4.22 shows the typical compressive strength development (ƒc’(t)) normalized by the 28-day compressive strength for the UHPC with a W/B ratio of 0.16 1.4 1.2 1.0 fib 2010 Rf = 0% Rf = 20% Rf = 30% Rf = 50% Rf = 70% Series6 Series1 Series2 Series3 Series4 Series5 fc(t 0.8 )/f' 0.6 c 0.4 0.2 0.0 50 100 Time (days) 150 200 (b) W/B = 0,16 Figure 4.21 Predicted compressive strength development at standard curing conditions 1.4 1.2 1.0 fc(t 0.8 )/f' 0.6 Series6 fib 2010 Series1 Rf = 0% Series2 Rf = 20% Rf = 30% Series3 Rf = 50% Series4 Rf = 70% Series5 c 0.4 0.2 0.0 50 100 Time (days) 150 200 (b) W/B = 0,16 Figure 4.22 Predicted compressive strength development under heat treatment 4.3.3 Proposed empirical equation to predict compressive strength development of HVFA UHPC with time To build simple empirical equations to evaluate the compressive strength development of UHPC, the present study follows the exponential function established in the 2010 fib model [13]: 28 0.5 ' fc)(t)/fc = EXP [Sl (1- ( )] (4-4) t From the NLRA approach, ƒc’, for UHPC with FA can be estimated as follows: f ' = 6.4[ξ(M/M )1.3/ (W/B)]0.4f c c0 (4-5) In there ξ is the coefficient depending on the fly ash content Rƒ as follows: ξ = (1 + Rf)0.1 with Rf ≤ 0.3 (4-6a) ξ = (1-Rf) with Rf > 0.3 (4-6b) The coefficient ξ is to explain the effect of FA on ƒc’, indicating that ƒc’ increases with an increase of Rƒ up to 30%, in addition ƒc’ decreases, as shown in Fig 4.23 21 18 15 f'c / fco 12 Best fit curve y = 6.4x0.4 R² = 0.80 0 10 15 ξ(M/Mo)1.3/(W/B) Figure 4.23 Regression analysis for the 28-day compressive strength of HVFA UHPC From NLRA considering these influence parameters, the parameter S l in formula (4-4) is shown in Figure 4.24 Sl = 0.083[(1 + Rf)3/(W/B)0.3]0.65 for standard curing condition (4-7a) Sl = 0.02 for heat treatment (at 90°C) (4-7b) 0.5 0.45 0.4 0.35 Slo pe 0.3 fac 0.25 tor 0.2 Best fit curve y = 0.083x0.65 Sl 0.15 R² = 0.88 0.1 0.05 0 (1+Rf) /(W/B)0.3 10 Figure 4.24 Modeling Sl in formula (4-4) to predict the development of compressive strength 4.3.4 Calibration of the proposed models Table 4.9 Summary of statistical values determined from comparing experiments and predictions The ratio of experimental and predicted compressive strength at different ages, days Standard curing condition Heat treatment 28 90 180 Tổng 28 90 180 Tổng 𝑖𝑖 0.95 0.93 0.99 0.99 0.97 0.97 1.08 1.09 1.09 1.06 1.01 1.07 𝑖𝑖 0.15 0.13 0.12 0.10 0.10 0.12 0.12 0.12 0.11 0.11 0.12 0.12 4.3.5 CO2 emission of HVFA UHPC 4.3.6 Conclusion Based on the experimental results, the following conclusions about the material properties and the methods used: (1) When the heat curing time is increased to days, the ratio of compressive strength of heat curing to standard curing (ƒc’)H/(ƒc’)S does not increase much, and it is not significantly affected by heat curing time, where (ƒc’)H is the 28-day compressive strength of UHPC concrete at different heat curing ages and (ƒc’)S is the UHPC sample for are maintained under standard conditions This confirms that days of heat curing is sufficient for UHPC to reach high strength (2) With the same heat curing time, a higher value of (ƒc’)H/(ƒc’)S was observed for UHPC blends with high FA content and lower W/B ratio In addition, with the condition of heat curing, the higher the FA content, the higher the values (ƒc’)H/(ƒc’)S, especially UHPC using FA with 70% content (3) Appropriate addition of FA to enhance the compressive strength of UHPC requires an early age heat curing process that can be recommended for at least days below 90°C in hot water The rate of strength increase of UHPC cured under heat curing conditions was not significantly affected by FA content, and the study showed that the rate at days ranged from 0.92 to 0.99 for all experimental samples In general, the compressive strength of UHPC with FA under heat treatment mainly reached the 28-day strength in only days The FA content can be increased up to 50% for heat-curing UHPC at an early age while considering the equivalent value of the compressive strength of UHPC without FA and curing under standard conditions (4) To predict compressive strength development of moisture-cured UHPC composites, the 2010 fib model underestimates early age and overestimates long-term age, regardless of FA content The predictions obtained from the proposed models are consistent with the experimental results at different ages Therefore, the proposed models have a high potential for accurately estimating the compressive strength development of UHPC (with different FA content (up to 70% FA content) and cured in different conditions (5) This model is applied to HVFA UHPC with time from to 180 days combining FA type F 0-70%, cement type I, W/B from 0.12 to 0.18 by weight, compressive strength from 80 to 165 MPa, curing under standard conditions and heat conditions However, the predictive model of compressive strength over time is only reliable within the scope of the study and has reference value with other studies CHAPTER : RESEARCH OF BEHAVIOR OF HVFA UHPC BEAM 5.1 GENERAL INTRODUCTION Concrete often has increased toughness behavior when compressive strength increases due to changes in internal microstructure and still maintains load capacity even when reaching ultimate strength but with UHPC, brittle material behavior relationship leading to the structure will be destroyed suddenly when the load increases The biggest drawback of UHPC concrete is its low tensile strength and toughness To increase the toughness for UHPC, it is necessary to use a certain fiber content The use of special steel fiber reinforcement makes the mixture dense and homogenous in the microstructure of the finegrained components The stresses concentrated in the material can be mutually transmitted through the steel fiber On the other hand, the effect of using fiber reinforcement is that randomly dispersed steel fiber can control crack propagation, prevent crack expansion, and increase toughness One of the most important functions of steel fiber reinforcement in concrete is to transmit tensile stress through cracked areas, maintaining tensile strength after cracking 5.2 RESEARCH AND PRODUCTION OF STRUCTURAL MODELS OF REINFORCED HVFA UHPC BEAMS a Test beam size: 150×200×2200 mm b Testing concrete mix 5.3 BEAM 4-POINT BENDING TEST TO ASSESS DEFORMATION The experimental diagram and arrangement of measuring points for UHPC beams are shown in Figure 5.2 Figure 5.2 Experimental diagram and arrangement of measuring points for concrete HVFA UHPC beams 5.4 LOADING BENEFITS OF REINFORCED UHPC BEAMS Predefined steps increase the payload The load test ended when the beam was observed to be soft Lo ad (k N) Deflection (mm) Figure 5.8 Load relationship and beam deflection of HVFA UHPC using 0-3% steel fiber The bending resistance and stiffness of the HVFA UHPC beam with different fiber content are illustrated in the diagram showing the relationship between the weight and the deflection in the middle of the beams, t From the relationship chart and the experimental monitoring process, it is possible to determine the load when the beam appears at the first crack, the load when the tensile steel is ductile, and the critical load of the test sample 5.5 LOAD PREDICT OF UHPC BEAMS FOR THE PROPOSED THEORETICAL MODEL The method of predicting flexural resistance based on the stress-strain relationship diagram proposed by FHWA has taken into account the tensile performance of concrete This stress-strain relationship is simple and convenient to calculate However, it is relatively simple to derive a stress-strain relationship and only take the tensile strength to be 0.5 times the pre-cracking tensile strength Figure 5.9 Computational cross-section of the UHPC beam From the equation of axial force balance on the cross-sectional cross-section of the beam is zero, the position of the neutral line can be determined Nz = 1/2×b×x×(0,007×x/(h-x))×Eb + 0,007×(x-a’)/(h-x)×Et×As’ - As×Fy - Fct×(h-x)×b=0 From the position of the neutral line, the flexural resistance of the beam Mx and the concentrated load P can be calculated Mx = b×(h-x)×Fct×((h-x)/2+x-a’) + As×Fy×(h-a-a’) + 1/2×b×x×(0,007×x/(h-x))×Eb×(-1/3×x+a’) P = 2×Mx/0,75 Table 5.4 Calculation of bending resistance of UHPC beams with 0-3% fiber content Grade CP2 Beam dimensions Fiber Elasticity content Modulus E 1% 44.9 150×200×2200mm Rk Concrete Mu Load P 0.9×9.2 37.12KNm 98.98KN With a fiber content of 1%, the Rk coefficient of concrete was chosen as 0.9 which is consistent with experimental results CP3 2% 45.5 0.8×11.8 39.83KNm 106.22KN 150×200×2200mm With a fiber content of 2%, the Rk coefficient of concrete was chosen as 0.9, which is consistent with experimental results CP4 150×200×2200mm 3% 46.1 0.8×13.8 43.53KNm 116.08KN With a fiber content of 3%, the Rk coefficient of concrete was chosen as 0.8, which is consistent with experimental results The results of theoretical and experimental research show that completely ignoring the R k in the calculation of UHPC will favor safety and is not fit the experimental results The study proposed to choose a factor Rk of 0.8 for UHPC to determine the load 5.6 DEFINITION OF THE DESTRUCTIVE LOAD OF HVFA UHPC BEAMS USING ABAQUS 5.6.1 Finite element method FEM Currently, the finite element method is used more and more widely to simulate the work and evaluate the load capacity of reinforced concrete structures One of the commercial FEM software used a lot to simulate structural works is ABAQUS of the US The study of the destructive load prediction model of HVFA UHPC concrete beam members made by ABAQUS is very important in practice Figure 5.10 Model of ABAQUS beam HVFA UHPC 5.6.2 Material model To build this model, the stress-strain relationship curves were taken from the experimental results 5.6.3 Element type, model meshing, bonding between concrete and reinforcement The linear 8-node 3-dimensional block element is assigned to the concrete elements and the rebar Elements are automatically divided into partitions about 20 mm in size for concrete and reinforcement materials The longitudinal reinforcement elements and the concrete were considered to have absolute bonding 5.6.4 Numerical simulation results Lo ad (k N) Deflection (mm) Figure 5.13 Relationship of load and strain of the HVFA UHPC beam (2% steel fiber) With a fiber content of 2%, the breaking load determined according to ABAQUS is 111.48 kN Compared with the experimental results, Pph is 105 kN, and the prediction by simulation gives the results with accuracy up to 94.19% From the results of studying the behavior of HVFA UHPC beams, it can be seen that it is possible to use the HVFA UHPC concrete mix to fabricate load-bearing structural details for the work Theoretical and experimental results found that the coefficient R k = 0.8 for HVFA UHPC beams It is possible to use simulation theory to predict the destructive load of HVFA UHPC beams Using simulation reduces the cost of experiments while still providing highly accurate results CONCLUSIONS AND RECOMMENDATIONS CONCLUSIONS Based on the obtained research results, the thesis makes some conclusions as follows: (1) Based on scientific principles about UHPC and available materials (including cement PC50, FA, SF, SP, and dispersed steel fiber) and the conditions of machinery and equipment in the laboratory in Vietnam, HVFA UHPC with FA content used higher than 50% was completely produced to achieve compressive strength over 120 MPa, flexural strength over 15 MPa (when using dispersed steel fiber), and elastic modulus greater than 40 GPa (2) Only UHPC with a compressive strength greater than 120 MPa and a maximum FA content of 30% can be made using only FA However, when combined with 10%SF, the compressive strength of UHPC has reached 120 MPa under standard curing conditions, and especially in heat curing conditions, it is completely possible to use 50%FA to make UHPC with compressive strength reach 127-135 MPa at an early age of days to 28 days This is one of the scientific relationships demonstrated in this thesis, which claims that combining FA with highly active mineral admixture SF and heat treatment has improved the properties of HVFA UHPC (3) The relationship between the highest compressive strength and the corresponding FA content of HVFA UHPC has been established The maximum FA content to make HVFA UHPC to achieve a compressive strength of 120 MPa under standard curing conditions and 150 MPa under heat treatment was 52.5% Of which concrete already contains 10%SF, thus, the total content of mineral admixtures was 62.5%, and cement content is only 37.5% (equivalent to 450 kg) to make UHPC When reaching the compressive strength of 120 MPa under heat treatment, it is possible to use up to 80% of mineral admixtures, using less than 220 kg of cement needed to make UHPC (4) HVFA UHPC mix design method was proposed ịn five steps based on (1) research on selection of input materials, (2) optimization of grain composition of materials according to compaction model De Larrard compression form, while accounting for (3) the selection and adjustment of the W/B ratio and (4) the curing conditions, including (5) the optimal heat curing time for the HVFA UHPC (5) The prediction model of UHPC HVFA strength over time with different maintenance regimes was established based on the 2010 fib model, which includes the amount of FA used f ' = 6.4[ξ(M/M )1.3/(W/B)]0.4f c c0 Where ξ is the coefficient based on the fly ash content R ƒ, M is the maturity function which depends on curing temperature and time, and the W/B ratio (6) The mechanical behavior of the HVFA UHPC beam element has proven the feasibility of the application of HVFA UHPC, with the adjustment coefficient R k in the calculation proposed to be 0.8 to be suitable for the reinforced HVFA UHPC beam The appropriate fiber content to ensure all three conditions of strength, stiffness, and crack opening is 2% within the scope of the thesis Besides, using the theoretical model and simulated finite element analysis both give similar research results on predicting destructive load of HVFA UHPC beam, which helps to reduce experimental cost while still for high accuracy RECOMMENDATIONS Based on the obtained results, some specific recommendations on development directions for the next HVFA UHPC are as follows: (1) Studying the process of guiding mixing, casting and curing HVFA UHPC to ensure the homogeneity of the mixture and improve the stability of the quality of HVFA UHPC concrete (2) Research using common natural sand to replace quartz sand finely while ensuring the mechanical and physical properties of HVFA UHPC (3) Research and produce HVFA UHPC using different fibers and hybrid fibers (4) Research the long-term durability of HVFA UHPC research (5) Apply HVFA UHPC in specific structures LIST OF PUBLICATIONS Pham Sy Dong, Le Trung Thanh, Nguyen Van Tuan, and Nguyen Cong Thang (2018), Sustainable development of ultra high performance concrete mixture using high volume of fly ash in Vietnam, Proceedings of the 2nd International Conference on UHPC Materials and Structures UHPC – China (PRO-129), RILEM, pp 161-170 (ISBN:978-2-35158-219-0) Sy Dong Pham, Van Tuan Nguyen, Trung Thanh Le, Cong Thang Nguyen (2019), possibility of using high volume fly ash to produce low cement Ultra High Performance Concrete, Proceedings of the International Conference on Sustainable Civil Engineering and Architecture (ICSCEA), Ho Chi Minh city, Vietnam, pp 589-597, ISBN 978-981-15-5144-4, DOI https://doi.org/10.1007/978-981-15-5144-4_56 (Indexed by SCOPUS) Pham Sy Dong, Nguyen Van Tuan, Le Trung Thanh, Nguyen Cong Thang, Viet Hung Cu and Ju-Hyun Mun (2020), Compressive Strength Development of High-Volume Fly Ash Ultra-High-Performance Concrete under Heat Curing Condition with Time, Applied Sciences, 10, 7107, ISSN 2076-3417, IF=2.474, DOI: https://doi.org/10.3390/app10207107 (SCIE, Q2) Pham Sy Dong, Le Trung Thanh, Nguyen Van Tuan, Nguyen Cong Thang, Yang Keun-Hyeok (2021), Mix design of High Volume Fly Ash Ultra High Performance Concrete, Journal of Building Science and Technology, Vietnam, 15(4) (10-2021): 197-208, ISSN 1859-2996, DOI: https://doi.org/10.31814/stce.huce(nuce)2021-15(4)-17 (ACI) ... for reference at the libraries as follows: - National Library of Vietnam; - Library of Hanoi University of Civil Engineering; INTRODUCTION Need for the research Ultra-high performance concrete (UHPC)... world However, research and applications in Vietnam are still underway, and the research and production of UHPC used for building structures in Vietnam is an advanced and very necessary scientific... in Vietnam to produce HVFA UHPC meeting desired technical properties will contribute to promoting sustainable construction and improving the quality of environmental protection in Vietnam - A