Summary of doctoral dissertation Effect of initial physical properties of roller compacted concrete to construction schedule of concrete gravity dam in Vietnam

MINISTRY OF EDUCATION MINISTRY OF AGRICULTURE AND TRAINING AND RURAL DEVELOPMENT THUY LOI UNIVERISITY LE QUOC TOAN EFFECT OF INITIAL PHYSICAL PROPERTIES OF ROLLER COMPACTED CONCRETE TO CONSTRUCTION SCHEDULE OF CONCRETE GRAVITY DAM IN VIETNAM Major: Hydraulic engineering Code No: 62.58.40.01 SUMMARY OF DOCTORAL DISSERTATION HANOI, 2016 This scientific work has been accomplished at: Water Resources University Supervisor 1: Prof.Dr Vu Thanh Te Supervisor 2: Assoc.Prof.Dr Do Van Luong Reviewer 1: Assoc.Prof.Dr Nguyen Thanh Sang Reviewer 2: Assoc.Prof.Dr Vu Huu Hai Reviewer 3: Assoc.Prof.Dr Hoang Pho Uyen This doctor dissertation will be defended at university graduate council of Thuy Loi Univeristy At h00, date month year 2016 It is possible to find out information about this document at: - National Library of Vietnam - Library of Thuy Loi University, Hanoi INTRODUCTION Reasons for choosing the research The outstandingly advantages of Roller Compacted Concrete (RCC) are faster speed of construction, lower price At present, its applications have been quite common in Vietnam Almost the principal calculations in design and construction of RCC Dam inherited from basic concepts of normal concrete or taking from foreign documents Recently, there have been some incidents happened at main dam of RCC dams, but no evaluations or deeply summaries addressed Even though the scientific evident and theoretical calculations in applications of RCC technology used in Vietnam, but there is lack of in-depth research The studies about construction schedule of RCC dams are vital in order to make projects become more reasonable and effective The Purpose of Research This study focus on the behaviour and quantify initial physical properties of RCC, from the beginning of hydration to designated characteristic of RCC, in order to define the thermal evolution, thermal stresses By doing this, the appropriate speed of construction can be established when building RCC dam project Research Objectives RCC dams are constructed and under construction in Vietnam Research scope This research aims at the effect of initial physical propertieson construction schedule of RCC dams, from the beginning of hydration to designated characteristic of RCC Methodology of Research This study uses the research methods according to present design codes Significance of Research - Clarify behavior, quantify and determine the impact of initial physical properties of RCC on the thermal evolution, thermal stress and construction schedule Propose methods for determining reasonable construction schedule in the conditions of Vietnam - RCC technology has been applied on more than 20 concrete gravity dam in Vietnam However, the quality of these buildings have not considered properly and researched in systematical way Therefore, results of this study aim to determine the method, providing reliable calculation tools for the design and construction of RCC It is also suggested solutions to monitor, repair and ensure the safety for constructed buildings and under construction projects New aspects of Research This study has gained new points as follow: Find out information about relationships of two RCC aggregate gradation such as compressive strength development over time, tensile strength development over time, shrinkage strain over time, Elastic Modulus of Concrete over time Completing and supplementing thermal evolution calculation and thermal stresses in ANSYS software in order to using as a tool for inspecting the construction speed of Dong Nai dam Structure of Dissertation This dissertation includes introduction, four chapters, conclusion and discussions 49 references, 04 authority publications The main content of the document presented in 144 pages, with 69 tables, 116 figures and 06 appendices CHAPTER 1: OVERVIEW OF ROLLER-COMPACTED CONCRETE AND RESEARCH QUESTIONS AND OBJECTIVES 1.1 History and development of roller compacted concrete in the world 1961, it was first used at Alpe Gera dam - Italia, Manicongan dam – Canada and Thach Mon - Taiwan; 1970 there is research about RCC in America; 1980 Willow Creek dam was built at Oregon state with a height of 52 m, and a length of 543 m, constructed of roller-compacted concrete; 1970 England, Dunstan, the Construction Industry Research and Information Association (CIRIA) carried out studies for high fly ash content RCC, testing at Water Treatment Plant Tamara – Coruwall (1976) & Wimbledall (1979); 1974, Japan began research about RCC and Shimajigawa dam, 89 m high and 240m length, was the first Japanese RCC dam with 165,000m3 placed RCC in total of 317,000m3 concrete for this dam 1980, China researched and applied RCC technology; so far China is now the leading country of the world in the construction RCC dams; 1.2 Construction of RCC dam in Vietnam From 1996 to 2006, the number of RCC dams with higher cemetious content increased from 43.3% in 1996 to 47.4% in 2002 and 53.4% in 2006 Since December 2005, total 285 RCC dams have been constructed 1.3 Researches of Roller-Compacted Concrete in Vietnam Vietnam has been researched about RCC dams since 1990 In 2003, Pleikrong hydraulic dams is the first RCC buildings in Vietnam Until now, there were more than 20 gravity concrete dams completed or being under construction by using RCC technology 1.4 Literature review of RCC research in Vietnam and the world 1.4.1 Literature review of RCC research in the world 1.4.1.1 Findings of roller compacted concrete in France From 1988 to 1996, France has implemented research projects nationally Bacara of RCC dam [4] 1.4.1.2 Findings of roller compacted concrete in US The American Concrete Institute: provide high speed of construction and cost savings, but seepage and cracks easier occur easily 1.4.1.3 Findings of roller compacted concrete in Japan RCC has quality of waterproofing and strength as CVC 1.4.1.4 Findings of roller compacted concrete in China The method of RCCD in China based on the experience and lessons of two approaches RCD and RCC combined with fly ash additives available in domestic market 1.4.2 Research on RCC in Vietnam Research about using domestic material to design aggregate gradation: documents [9]; [10]; [11] Research about using mineral admixture: documents [12], [13], [14], [15], [16], [17], [18], [19] Research about applying waterproofing material for RCC: documents [20], [21]; Research about thermal in RCC: documents [22], [23], [24], [25]; Research about construction technologies for RCC: documents [26], [27], [28], [29] 1.5 The remaining issues of RCC research, objective of dissertation 1.5.1 The remaining issues of RCC research - Improving the quality combined with surface layer to satisfy dam height - The quality of combined surface layer is a cause of seepage - The RCC construction schedule: it depends on thermal evolution, thermal stress, which ensure anti cracking ability of dam These factors directly influenced by the initial physical parameters of RCC Therefore, research is necessary to determine a reasonable construction schedule while building RCC dams 1.5.2 Research orientation content of this research To select materials for RCC aggregate gradation, provide experimental method to figure out physical properties of RCC by current codes To carry out experiments to manufacture 02 RCC aggregate gradation, which commonly use in Middle and South of Tay Nguyen, namely pozzolanic active mineral RCC and fly ash active mineral RCC Design of experiments to figure out the development of RCC initial physical properties of optimum aggregate RCC over designated time by using nonlinear functions Integrate ANSYS to calculate the heat & thermal stress in RCC dams Using integrated ANSYS to find out the appropriate construction speed based on temperature control and thermal stresses in RCC dam Research Process Flowchart shown in Figure 1.1 Figure 1 Research process of Construction Schedule of RCC CHAPTER SCIENTIFIC BASIS AND EXPERIMENTAL METHODS TO DETERMINE AGGREATE GRADATION & PHYSICAL PARAMETORS RCC 2.1 Factors affecting the physical parameter of RCC The characteristic of materials manufactured RCC Ingredients of aggregate gradation RCC Construction Environment of RCC Construction process of RCC 2.2 Choice materials used in the research and manufacture of aggregate gradation RCC Testing materials are ensured about the number and the stability quality It is also has been used in RCC building, near the construction site, the quality of materials to satisfy technical requirements for RCC 2.2.1 Materials used for grading RCC-P (pozzolanic additives) - Concrete: concrete PCB40 Fico, TCVN 6260: 2009 [30] - Pozzolan: mine number 4A Dak Nong, TCVN 8825: 2011 “Mineral admixtures for RCC” [31] - Water: TCVN 4506: 2012 "Water for mixing concrete and mortar - Technical specification” [32] - Small aggregate: in Dak Nong, TCVN 7570: 2006 and ASTM C29: 2003 - Crushed stone: in Dak Nong, TCVN7570:2006“Aggregates for concrete and mortar - Specifications” - Plasticizers and set-controlling admixtures: Plastiment 96, ASTM C494 type D 2.2.2 Materials used for grading RCC-T (RCC using fly ash additives) - Concrete: concrete PC40 Ha Tien 1, TCVN 2682: 2009 [34] - Fly ash: Formosa, TCVN 8825: 2011 “Mineral admixtures for RCC” - Water: TCVN 4506: 2012 "Water for mixing concrete and mortar - Technical specification” - Sand: in Ninh Thuan, TCVN7570:2006“Aggregates for concrete and mortar Specifications” - Crushed stone: in Ninh Thuan, TCVN7570:2006“Aggregates for concrete and mortar - Specifications” - Fine admixtures: Non-active fillers, about 15% of the volume of sand - Plasticizers and set-controlling admixtures: Plastiment 96, ASTM C494 type D 2.3 Determine the optimum gradation RCC 2.3.1 Method to determine the optimum gradation RCC This study use the method to design gradation ACI 211.3R-2002 [5], using experiments and theory "Experimental planning" to figure out the optimum gradation RCC, especially in strength and using materials 2.3.2 Experimental planning theory in determine gradation RCC [35] 2.4 Methods to determine physical properties of RCC The experimental procedure show in Figure below: Material of RCC Aggregate gradation Mixing, , making Test Test Specimens Curing Test Specimen Experim ental apparatus Experim ental Results Formula Summary Define Propert ies Figure 2.3 Experimental procedure determine the physical properties RCC (There are physical factors found in this procedures through headings 2.4.1 to 2.4.6, namely standard, sample and experimental apparatus; formula to determine these properties) 2.5 Determine optimum aggregate gradation RCC 2.5.1 Planning manipulate experimentally determined gradation 2.5.2 Determine optimal aggregate gradation RCC-P Ratio: mineral admixture/ adhesives = 0.63, 0.65 and 0.67; water/ adhesives = 0.56; 0.58 and 0.60; adhesives = 190 kg/m3; Sucking sand level Sand/(sand+ crushed stone) = 0.37; mineral admixtures = 1.8 liter/100kg adhesives Table Table encryption empirical coefficient Real variable PGK/CKD N/CKD Variable code X1 X2 -1 0,55 0,56 0,6 0,58 Δ 0,05 0,02 0,65 0,6 Table 2 The composition of aggregate RCC - P empirical C1 C2 Real variable MA/A G1 -1 -1 0,55 0,56 85 106 1414 830 106 15 G2 -1 0,65 0,56 66 125 1417 832 106 13 G3 -1 0,55 0,60 85 106 1401 823 114 G4 1 0,65 0,60 66 125 1404 825 114 G5 -1,412 0,529 0,58 88 102 1407 826 110 16 G6 1,412 0,671 0,58 62 128 1411 829 110 G7 -1,412 0,60 0,552 75 115 1418 833 105 17 G8 1,412 0,60 0,608 75 115 1400 822 116 G9 0 0,60 0,58 75 115 1409 828 110 G10 0 0,60 0,58 75 115 1409 828 110 11 G11 0 0,60 0,58 75 115 1409 828 110 10 G12 0 0,60 0,58 75 115 1409 828 110 G13 0 0,60 0,58 75 115 1409 828 110 10 Case Variable code Consumption materials for m3 (Kg) W/A C MA S S W Vc (s) The samples according to the gradation on the result compressive strength Rn (MPa) at the age of 90 days and 365 days of age as follows: Table Results compressive strength RCC - P G G1 G2 G3 G4 G5 G6 G7 G8 G9 G10 G11 G12 G13 Rn90 Rn365 14,8 15,4 13,8 15,11 14,2 15,1 14 15,0 14,5 15,4 13,5 15,0 15,2 15,5 14,6 15,2 14 15,2 14,3 15,1 14,5 15,3 14,3 15,4 14,8 15,3 The regression equation for compressive strength of 365 days (2.1): Rn365 =+15,26 - 0,12X1 – 0,10X2 + 0,047X1X2 – 0,061X12 + 0,014X22 The rate of mineral admixture/adhesives and rate of water/adhesives saw influences to strength of RCC, by following results: Figure 2.12 The correlation of MA/adhesion and ratio Water/adhesion of Rn365 RCC-P Figure 2.13 The correlation contour plots of MA/adhesion and ratio Water/adhesion of Rn365 RCC-P The optimum aggregate gradation RCC-P: Cement: 75kg, mineral admixtures: 115Kg, sand 804kg, crushed stone 4, 75÷19 (mm): 722kg crushed stone 20÷50 (mm): 670kg, water 110 liter, chemical admixture 3.4 liter 2.5.3 Determine optimal aggregate gradation RCC-T Ratio of admixture/ adhesives: 0.58; 0.6 and 0.62; water/ adhesives:0.56,0.58 and 0.6.Adhesives=200kg Admixtures:15% weight of sand; Sucking sand level Sand/(sand+crushed stone)=0.34; chemical admixture=1.0 liter/100kg/adhesive The regression equation for compressive strength of 365 days (2.2): Rn90 = - 785,34+1291,5X1+1471,34X2+ 231,25X1X2 - 1204,06X12 1391,56X22 Figure 16 The correlation of MA/adhesion ratio and Water/adhesion ratio of Rn90 RCC-T Figure 17 The correlation contour plots of MA/adhesion ratio and Water/adhesion ratio of Rn90 RCC-T Optimum gradation of RCC-T: Concrete: 80kg, Mineral Admixture: 120Kg, sand 687 kg; crushed stone: 5÷19 (mm): 479kg, 20÷39 (mm): 295kg, 40÷60 (mm): 628kg, water 115 liter, Chemical Admixture liters 3.1.3.2 Study of thermal coefficient of RCC Table 3.12 Some thermal coefficient of RCC Original of Aggregate River sand, gravel Artificial sand, Crushed stone, limestone Water/(Cement Mineral Additives) 0.44 Water (Kg/m3) 70 Coef BDN 10-6/0C 0.86 93 5.803 9.064 3.1.3.3 Research shrinkage due to dehydration (dry shrinkage) of RCC Table 3.13 Volumetric shrinkage of RCC Coefficient of Volumetric shrinkage Cn (%*10-2) Age RCCP RCCT 14 28 56 90 365 0.30 0.61 1.11 1.51 1.91 2.11 2.48 2.79 3.44 3.95 4.02 4.23 0.42 0.61 0.90 1.11 1.61 1.80 2.02 2.21 2.51 2.65 2.78 - Figure 3.10 The relationship of shrinkage~time for two gradation: RCCP&RCC-T Correlation and regression of shrinkage with time of gradation RCC-P: Ycn1 = 0.0075ln(x) + 0.0057 with R2= 0.9216 (3.3a); gradation BTĐL-T: Ycn2 = 0.0057ln(x) + 0.005 with R = 0.9116 (3.3b) 3.1.4 Heat transfer coefficient, Coefficient of thermal conductivity 3.1.4.1 Heat transfer coefficient Heat transfer coefficient (HSTN) shows the diffusion of heat from concrete (unit m2/h and was marked as a) The bigger value of HSTN, the less time require to 11 temperature at points of concrete sample reach same values HSTN of concrete depends on type of aggregate, the amount of aggregate, amount of water and weight of concrete Generally, HSTN has the reverser trend when temperature increase, but it has the same pattern with proportion of aggregate in concrete The reason for this is that RCC used less water and more aggregate than CVC so that HSTN of RCC larger than CVC, but the different are not so significant [41] 3.1.4.2 Coefficient of thermal conductivity  =  C γ; with  is Coefficient of thermal conductivity of concrete [KJ/(m.h 0C)]; : HSTN(m2/h); C: heat capacity of concrete [KJ/(Kg.0C)]; γ: Weight of concrete [Kg /(m3)] Table 3.14 Research results on the thermal characteristics of RCC Amount of 120 150 160 210 236 adhesive (kg/m ) t (0C) 40 60 40 60 40 60 40 60 40 60 ( m2/h) 0.0039 0.0038 0.0039 0.0038 0.0034 0.0033 0.0046 0.0049 0.0039 0.0038  8.25 8.46 8.25 8.46 7.2 7.91 7.0 8.21 8.46 [kJ/(m.h 0C)] C [kJ/(kg 0.87 0.91 0.84 0.9 0.84 0.9 0.96 0.87 0.91 0C)] -6 a (10 / C) 9.06 9.06 9.25 9.25 8.35 8.35 10.4 10.4 9.06 9.06 3.1.5 Research Elastic modulus of RCC 3.1.5.1 Static Elastic modulus (EM) in compression Figure 13 Evolutions of EM of RCC-P & RCC-T 12 The correlation functions saw EM of gradation RCC-P: Yđh1 = 0.4823ln(x) + 0.0946 with R2= 0.9758 (3.5a); gradation RCC-T: Yđh2 = 0.5031ln(x) + 0.0808 with R2 = 0.9831 (3.5b) EM of two gradation RCC-P & RCC-T shows no significant in the total amount of aggregate However, the EM of RCC-T is higher than RCC-P due to the higher amount of adhesion of RCC-T in comparison to RCC-P 3.1.5.2 Static Elastic modulus in tensile of RCC Static Elastic modulus in tensile of RCC influenced by many factors, which have similar rule By [38], Elastic modulus in tensile of RCC at the age of 90 days (with RCC of level gradation) = 1.3 ÷ 1.48 Elastic modulus in compression Particularly, CVC has similar of Elastic modulus in tensile and compression 3.1.5.3 Ultimate tensile strain of RCC It is the biggest value of Rk when the sample split of and using maximum value to present It influenced by the amount of adhesion, Rk, Elastic modulus in tensile, age of concrete etc (mainly on adhesion and Rk; when fixed Rk, then it depends on adhesion) Ultimate tensile strain of concrete conducted from laboratory experiment saw massive bigger value than Ultimate tensile strain This is due to using wet sieve to remove coal aggregate, which has diameter larger than 40 mm, then the rate of mortar in laboratory sample than in dam 3.1.6 Study of maximum increase of temperature in RCC Maximum temperature T of RCC can be measured by the increase of T0 in state of RCC, in which it did not dissipate heat and did not absorb external energy In 0 construction, T of dam < the maximum T This is due to the absorption or release energy into environment Regarding the released heat by hydration process in RCC, if the absorbs heat lower the built up heat, T will increase over time, until the speed radiating heat transmission rate, then T start decreasing to stability of T Table 3.16 Hydration heat of RCC used mineral additives (MA) Type of cement MA Pozzolan Ba Ria PC40 Ha Tien Fly-ash Fomosa Proportion of mineral admixture (%) 40 60 40 60 13 Heat of Hydration by age (J/g) day day day 230.1 138.4 100.5 234.5 140.6 101.5 263.7 175.6 137.2 269.3 180.2 142.3 321.2 214.6 161.3 342.4 219.6 166.2 Table 3.17 Time to reach maximum temperature according to the amount of mineral additives Type of cement PC40 Ha Tien Proportion of mineral additives (%) 40 60 Record time when appear rising temperature (hours) 18 38 72 3.2 Construction technology and changes in temperature, crack due to heat in RCC dam 3.2.1 Construction technology of RCC dam [5] Diagram of RCC’s technical construction shown in Figure 3.1 Mixing Compact rolling Transportation Curing dam’s surface Leveling Compacting Make rough Cast Sand mortar Cut horizontal slots Setup horizontal slots Figure Construction phrases of RCC 3.2.2 Thermal evolution, crack due to heat in RCC dam [45], [44] [41] [38] The process of temperature changes of RCC saw in Figure 3.2 Figure The process of temperature changes in concrete block 3.3 Factors affecting construction schedule of RCC dam Construction schedule of RCC, called as the dam’s construction speed, is an important factor to determine plans for the building Construction speed is detailed by some parameter such as the number of layer in one casting phrases, layer thickness, the resting time between each phrases Furthermore, there are other factors related to construction like transportation, determine the casting 14 areas, making construction slots etc., and intensity of construction, construction speed of the dam related to loading problems, as well as heat accumulation in the RCC dam’s body The speed of RCC based on principal of temperature control, thermal stress It depends mainly on RCC’s gradation, initial temperature of RCC mixture and environmental temperature at the constructing time of RCC dam The findings of study about the initial physical parameter of RCC conducted that: - Rn of RCC at the age < 28 day achieved low values, especially at 10-day age This affected to the construction process if the building require fast execution For example, the machine loadings can make lower development of RCC graded - The development speed of Rk is initially slow and the rate of increase is lower than Rn Rk is a substantial parameter of construction This due to the fact that if Rk of RCC reach low value, the tensile stress get higher value, caused by loads in construction process, temperature etc., leading to cracks of concrete - Young Modulus of RCC goes in line with normal concrete, and it focus on the first days after mixing and concreting - Young Modulus of RCC is higher than of CVC It mainly depends on the ingredients and aggregate gradation This parameter increase crack resistance of RCC - Based on the correlation function of physical properties, which conducted by experiments of two gradation RCC, the relationships of Rn over time (Rn~ t); Rk over time (Rk~ t); Coefficient of shrinkage over time (ε ~ t) and Young Modulus (E ~ t) etc These results can be used to controlled thermal evolution and calculated thermal stresses CHAPTER USING ANSYS SOFTWARE AND THE RESULT OF INITIAL PHYSICAL PROPERTIES OF RCC RESEARCH INSPECT THE CONSTRUCTION SCHEDULE OF DONG NAI DAM 4.1 ANSYS software and ability to compute heat and thermal stress 4.1.1 Ability to compute heat, thermal stress of ANSYS [46] ANSYS is a simulation analysis software based on finite element method to carry research of structural, thermal, fluid, electromagnetic, sound etc The 15 current version is ANSYS 16 ANSYS has many modulus with specific figures are ANSYS/Multiphysics, ANSYS/Mechanical, ANSYS/Thermal, ANSYS/FLOTRAN, ANSYS/ED, which are contains thermal analysis capabilities The process of thermal analysis in ANSYS includes steps: modeling, load assignment, validation step load, analyze and view the results Thermal analysis in the RCC dam follows these basic steps 4.1.2 The limitations when calculating heat & thermal stress of RCC dam using ANSYS It is difficult or impossible to calculate unstable form of heat transfer In common practice, many factors consider at the same time such as the environmental temperature, the heat generated during the hydration of cement, mechanical indicator of concrete changes over time, boundary conditions also change over time in the calculation of thermal evolution and thermal stresses in RCC dam 4.1.3 Implement, complete using ANSYS to calculate the thermal evolution & thermal stress of RCC dam There is outstanding points of ANSYS is can use the designated parameter APDL (using in programing language of FORTRAN) to build the simulation of construction process based on some predetermined variables and study of initial physical properties of RCC According the construction process in Vietnam, the main contents of study is present below: Using the results of research on behavior and quantify the initial physical parameter of RCC such as compressive strength - time, tensile strength - time, Elastic modulus - time, Shrinkage – time, providing into the software Using mathematical models show temperatures hydration of cement of roller compacted concrete with consideration to the influence of active mineral additives (fly ash, pozzolanic) for hydration heat of cement The process temperature changes in the concrete construction process considering the concreting time and finishing time, time bet Establish criteria of destructive roller compacted concrete When thermal stress in a certain position exceeds the capacity of the concrete tensile, then concrete block will automatically form and develop cracks under the change of temperature ( appendixes 02, 03, 04 & 05) 16 4.2 Analyze thermal in RCC dam using ANSYS 4.2.1 Building the Model Thermal analysis obeys the law of conservation of energy law The concepts of heat conduction, convection, radiation, steady conduction heat transfer, unsteady state heat transfer, linear and non-linear, which are shown in Appendix 01 Based on the temperature balance equation of conservation of energy, finite element method obtained to calculate the temperature at the nodes In addition, other thermal physical parameters such as heat conduction, convection and radiation Elements used in thermal analysis: There are about 40 types, included purely thermal analysis are 14 kinds For example, two-dimensional entities use PLANE55 elements, and 3-D entity used ANSYS’s element SOLID70 (element hexahedron eight nodes) The basic process of thermal stability analysis in ANSYS: including steps (4.1.1) Define step load: For each type of thermal analysis can define basic options, choose non-linear categories and select the output categories Start analysis process: Main menu > Solution > Analysis Options Newton – Raphson Display result: file *.rth 4.2.2 Input parameters of the model Input parameters of the model: used 68 parameter (Appendix 02) 4.3 Criteria for Design of RCC at Hydropower Dong Nai 4.3.1 Introduction of building 4.3.2 Thermal Characteristics of RCC and stone 4.3.3 The initial physical properties of RCC-P The nonlinear function represents the initial physical properties of RCC-T over time identified in Chapter as follows: Compressive strength Yn1=2.64ln(x) + 2.24; Rk: Yk1=0.258ln(x) + 0.029; Shrinkage strain Ycn1=0.0075ln(x) + 0.0057; Elastic Modulus Yđh1=0.4823ln(x)+0.0946 17 4.4 Obtain ANSYS as a calculation tool for thermal evolution, thermal stress & define the construction speed, and inspect Dong Nai with gradation RCC-P 4.4.1 The RCC construction cases for inspecting Dong Nai Table 4.7 The script execution RCC inspection Dong Nai Nhiệt độ hỗn hợp BTĐL đổ (0C) 21 Chiều dày lớp đổ sau đầm lèn 30 23 Số lớp đổ liên tục/ngày Thời gian nghỉ giãn cách mùa khô (ngày) Thời gian nghỉ giãn cách mùa mưa (ngày) 30 25 30 4 23 30 5 23 30 5 21 30 4 KB 4.4.2 Thermal evolution, thermal stresses for each construction case of RCC Table 14 Comparison of heat calculated for each case (0C) Time 120 days 200 days 375 days 504 days 625 days Case TH1 TH2 TH1 TH2 TH1 TH2 TH1 TH2 TH1 TH2 Case 30.114 29.558 33.960 33.378 38.208 37.839 39.621 39.302 40.391 40.142 Case 30.691 30.073 34.318 33.628 38.272 37.895 39.642 39.322 40.399 40.149 Case 31.269 30.589 34.529 33.879 38.336 37.951 39.663 39.342 40.407 40.157 Case Case 30.491 31.232 34.565 35.957 39.843 42.672 41.892 45.512 43.031 47.230 Case 30.673 30.125 35.050 34.528 40.425 39.992 42.333 42.003 43.419 43.133 Results are shown in the Table 4.16 The result of this study conducted that: - Case had the safety factor of tensile strength, K= 1.63 > [K] = 1.26 Thus it seems achieve cracking safe more than enough; - Case attained the safety factor of tensile strength, K= 1.33 > [K] = 1.26 Thus, it ensures reasonable safety; - Case 3, case 4, case & case reached the safety factor of tensile strength, Ktemperature with RCC-P, regarding less significantly different in aggregates Regarding thermal stress: the molecular structure of pozzolan is rod-shaped, while fly ash have spherical structures This different make hydration process of RCC-P consume more water than RCC-T, leading to shrinkage strain larger, even though RCC-T contain more adhesion ratio higher than in RCC-P about 10kg/m3 According to the research results in Chapter 3, the development speed of tensile strength, compression strength and elasticity modulus of RCC-T are higher than in BTĐL-P This is the main reason of the different in stress of Dam, which using these type of material On the other hand, the strength of RCC-T develop faster than RCC-P Therefore, safety factors of RCC-T are higher than RCC-P, despite using the same age of concrete and construction time The differences of heat and thermal stress in RCC dam using gradation RCC-P and RCC-T did not show significantly This due to the fact that the calculation 21 conditions are almost similar, except slightly changes of physical parameter in two gradation It is noted worthy that the fluctuation of temperature impact directly to thermal stress, causing the change in safety factor of each case CONCLUSION AND SUGGESTIONS Conclusion Construction technologies concrete gravity dam with roller compacted method is a significant advantage of 20th-century concrete Such technology are applying in Vietnam and other countries in irrigation dams, hydropower with faster construction time and reduced cost However, studies of RCC are not so in depth, there were incidents appeared during the construction, affect to lifespan of building, and then determine the advantage of this technology Therefore, study about RCC is vital The study has conducted experiments using experimental planning method to determine the optimum gradation used two common types of admixture: gradation RCC-T (RCC used fly ash active mineral additives with designed age of 90 days) and RCC-P (RCC used pozzolanic active mineral additives, designed age of 365 days) with domestic materials This study clarify and quantify changes in physical properties of RCC such as compressive strength, tensile strength; shrinkage strain, elasticity modulus; thermal parameters etc These factors make a great contribution to improve the speed of RCC construction Determine the development of heat and thermal stresses in RCC dam over time as the basis to select logically construction speed Firstly, ANSYS software rent to analyze thermal properties, with additions and updates are: + Using Parametric Design Language (APDL) (as a kind of programming language like FORTRAN run on open-source ANSYS software) to program RCC dam construction problem based on predetermined parameters + Simulate cross section of RCC gravity dam (partition materials, drainage corridors, multi-layer ground); + Study thermal evolution and thermal stress regarding the development of physical parameters of RCC by using nonlinear functions These factors are 22 compressive strength- time, tensile strength - time, shrinkage - time, elastic modulus – time + Obtained Thermal evolution of hydration models for cementitious materials of RCC in ANSYS, considering the influence of additives such as fly ash and pozzolan, to study the heat of hydration in RCC + Consider the time for concrete casting and resting time between phrases + Able to draw the development of cracks when tensile stress > tensile strength of concrete It is easy to calculate dams with similar sections Based on the initial physical properties of RCC this study helps to define reasonable construction case of dams had similar conditions Some of properties are the initial temperature condition of mortar RCC (210C, 230C & 250C), thickness of layer after compacting (0,30m), speed of construction (the number of layer in one stage are 3, 4&5 layers) and the resting time between phrases are 2, or days depends on seasons The results of this study are in good agreement with the site inspection New scientific contributions and practical application There are findings about the relationships of compressive strength over time, tensile strength over time, shrinkage strain over time and Elastic Modulus over time of 02 gradation RCC, details are following: Aggregate gradation RCC-P (RCC used concrete with pozzolanic active mineral admixture with 365 day-old designed age): compressive strength development over time: Rn~t by formula 3.1a: Yn1=2,64ln(x)+2,24 với R2=0,9 Tensile strength development over time: Rk ~ t by formular 3.2a: Yk1 = 0,258ln(x)+0,029 với R2=0,9764 The coefficient of shrinkage: ε~t by formula 3.3a: Ycn1=0,0075ln(x)+0,0057 với R2=0,9216 Elastic Modulus over time: E~t by formula 3.5a: Yđh1 = 0,4823ln(x) + 0,0946 với R2 = 0,9758 Aggregate gradation RCC-T (RCC used concrete with fly ash active mineral admixture with 90 day-old designed age) Compressive strength development over time: Rn~t by formula 3.1b: Yn2 = 4,54ln(x) + 2,52 với R2 = 0,93 Tensile strength development over time: Rk~t by formula 3.2b: Yk2=0,289ln(x)+0,051 với R2 = 0,971 Coefficient of shrinkage over time: ε ~ t by formula 3.3b: Ycn2 = 23 0,0057ln(x) + 0,005 với R2 = 0,9116 Elastic Modulus of over time: E~t by formular 3.5b: Yđh2 = 0,5031ln(x) + 0,0808 with R2 = 0,9831 Completing and supplementing thermal evolution calculation and thermal stresses in ANSYS software, using as a tool to analysis thermal evolution, thermal stress, inspecting construction speed of RCC dam Dong Nai Practical application: Results of the study can be applied to construction of new RCC dam The results of the study help examine and evaluate the quality and safety of constructed RCC dams, combined with actual monitoring data to develop plans for the dam safety inspection The results of the study help examine and evaluate the quality of aggregate gradation design and construction plans for RCC dams, which are in the design phases, preparation for implementation of investment projects Limitations and recommendations for future research 3.1 Limitations The research results of new topics at an early stage, should continue to study and apply the test and compare with the actual monitoring results to evaluate and verify the model of ANSYS software to complement and complete 3.2 Recommendations Take research results in the design and construction of RCC dam have similar conditions in Vietnam There is the need to continue research about the thermal evolution and thermal stress of RCC dam, applied in constructed and under constructing buildings by using ANSYS software It is important to make comparison with site inspection at design stages in order to make adjustments accordingly the safety of dams and the effectiveness of projects (3) Complete the new ANSYS to serve as a tool of research and study about temperature measurement, thermal stress in RCC dams / 24 LIST OF REFERENCES Le Quoc Toan, Vu Thanh Te, Vu Hoang Hung (2015) Additional properties to perfect temperature and software ANSYS thermal stresses of the RCC dam in Vietnam Journal of Science and Technology Hydraulic and Environment Engineering, Thuy Loi University, No 50, September/2015, page 9-15; Le Quoc Toan, Vu Thanh Te (2015) Research of Initial physical properties of Roller Compacted Concrete (RCC) Journal of Structural Engineering and Construction Technology, Vietnamese Association of Structural Engineering & Construction Technology, No 18/III-2015, pages 32-34; Le Quoc Toan, Do Van Luong, Dinh Xuan Anh (2013) Influence of several preliminary characteristics of Roller compacted Concrete (RCC) for Construction Progress of Concrete Gravity Dam in Vietnam Journal of Science and Technology Hydraulic and Environment Engineering, Thuy Loi University, No 41, June 2013, pages 54-62; Le Quoc Toan (2010) Some Results of studies on thermal evolution and thermal stress of RCC Journal of Science and Technology Hydraulic and Environment Engineering, No 30 September 2010, pages 53-58