Nghiên cứu đánh giá một số yếu tố ảnh hưởng đến chất lượng khai thác của mặt đường BTXM đường ô tô và sân bay trong điều kiện việt nam TT TIENG ANH

MINISTRY OF TRANSPORT UNIVERSITY OF TRANSPORT AND COMMUNICATIONS PHAM DUY LINH INVESTIGATION AND EVALUATION OF SOME FACTORS AFFECTING OPERATION QUALITY OF OF HIGHWAYS AND AIPORTS IN VIETNAM’S CONDITIONS Department: Transport Engineering Code: 9580205 Major: Highway and Urban Road Construction SUMMARY OF TECHNICAL DOCTORAL DISSERTATION HANOI – 2021 The Study completed in: University of Transport and Communications Science Instructor: PhD Vu Duc Sy University of Transport and Communications Prof PhD Pham Cao Thang Military Technical Academy Reviewer 1: …………………………………… Reviewer 2: …………………………………… Reviewer 3: …………………………………… The dissertation is defended before University-Level Dissertation Committee held in University of Transport and Communications at … : … day… month … year … The dissertation can be looked up at: - Vietnam National Library - Library of University of Communications Transport and THE AUTHOR’S PUBLICATIONS Pham Duy Linh; Prof.PhD Pham Cao Thang; PhD Vu Duc Sy: “Research on calculation method to convert operating vehicle axle flow in designing highway rigid pavement structure” Bridge & Highway Magazine no 9/2017; Pham Duy Linh; Prof.PhD Pham Cao Thang; PhD Vu Duc Sy: Bridge & Highway Magazine no 10, 2017; Hoang Long Nguyen, Cao Thang Pham, Duy Linh Pham, Tuan Anh Pham, Duc Phong Pham, and Binh Thai Pham: Designing of concrete pavement expansion joints based on climate conditions of Vietnam: De Gruyter-Journal of the Mechanical Behavior of Materials, 28th issue dated 1/10/2019, (Scopus magazine); Pham Duy Linh; Prof PhD Pham Cao Thang; PhD Vu Duc Sy; PhD Luong Xuan Chieu; PhD Tran Nam Hung (2020): “Research on Field Experiments to determine temperature distribution in slab in Hanoi” Bridge & Highway Magaze June 2020; Pham Duy Linh; Prof PhD Pham Cao Thang; PhD Vu Duc Sy: “Calculation Method of multi-layer concrete pavement, considering the effect by thickness of the insulating layer between the courses” Transport Magazine June 2020; Pham Duy Linh; Prof PhD Pham Cao Thang; PhD Vu Duc Sy: ”Research on temperature Gradient and average temperature in , in Vietnamese climatic conditions” Tranport Magazine August 2020 PREFACE I NECESSITY OF THE STUDIED ISSUE With significant advantages, concrete pavement can be applied broadly as pavement structure for high-class roads, for roads in airports, and highways with high axle volume and heavy load lorries travelling on However, current procedures being applied in Vietnam are not quite compiled by Vietnamese authors, but based on reference to foreign standards which are suitable to foreign countries’ conditions To make the technical regulations in those procedures fit to specific conditions of Vietnam, it is necessary to carry out researches for adjustment, supplementation of some technical requirements to make them more adaptable to Vietnam’s conditions Therefore, the topic “Investigation and Evaluation of some Factors Affecting Operation Quality of Concrete Pavement of Highways and Airport in Vietnam’s Conditions” is a necessary research which is meaningful both scientifically and practically II RESEARCH OBJECTIVES The dissertation focuses on clarification of the effects of the insulating layer in multi-layer concrete pavement and the effects of ambient temperature conditions on working of the concrete pavement of highways and airports in Vietnam’s conditions III RESEARCH CONTENT The dissertation concentrates on following issues: Overview; Calculation to evaluate effects of the insulating layer to distribution of internal forces in concrete pavement courses; Theoretical investigation combined with field experiment, determining temperature profile distributed by depth in concrete pavement; Studying and calculation to determine temperature gradient and average temperature in concrete pavement by thickness and calculation of the necessity of expansion joint of concrete pavement slab row on highways, and airports; Study and calculation of digitalized experiment, quantifying effects of the insulating layer and ambient temperature on working of concrete pavement of highways and airports in climatic conditions of North Vietnam IV SCIENTIFIC AND PRACTICAL SIGNIFICANCES OF THE DISSERTATION TOPIC Scientific Significance: Setting calculation approach to evaluate effects of thickness and strength of the insulating layer on the performance of multi-layer concrete pavement Based on theoretical study and field survey, experiments, the temperature profile distribution is determined by depth of the concrete pavement and temperature gradient in the slab by each different pavement thickness The study determines the necessity of expansion joints for concrete pavement rows in Vietnam’s climatic conditions − Practical Significance: Calculation to recommend material types and insulating layer thickness suitable to Vietnam’s conditions; Building and suggesting calculation formulae of temperature gradient and average temperature by depth in the concrete slab depending on thickness, serving calculation of thermal stress and determination of distance between expansion joints of concrete pavement slab row, in Hanoi city’s climatic conditions and and similar areas’ in North Vietnam CHAPTER OVERVIEW OF CALCULATION OF MULTI-LAYER CONCRETE PAVEMENT UNDER IMPACT OF WHEEL LOAD AND AMBIENT TEMPERATURE Chapter introduces and analyses the work of multi-layer concrete pavement under the impact of wheel load and the ambient temperature as the basis for continuing the study in subsequent chapters 1.1 General Construction of Concrete Pavement 1.1.1 Typical Construction of Concrete Pavement Concrete pavement has general construction comprised of the following: Upper course concrete pavement ; insulating layer; base; Sub-base; soil embankment; joints 1.1.2 Reason of Damages Reducing Operation Quality of Concrete Pavement Main reasons causing damage and deterioration of the concrete pavement include the following: Due to truck load: Due to climatic conditions: Operation, and construction conditions One thing worth notice is that the designing, especially designing of constructions are not quite suitable to operation conditions In the dissertation, it focuses on studying some issues relating to the insulating layer and effects of the ambient temperature in the designing calculation, which may affect operation quality of concrete pavement of highways and the airport in Vietnam’s climatic conditions 1.2 Calculation of Multi-Layer Concrete Pavement 1.2.1 Calculation Methods According to Designing Procedures of Vietnam 1.2.1.1 Vietnam’s design calculation method according to 22 TCN 22395 [2]: Design calculation method according to temporary regulation on ordinary concrete pavement with connection joint in transport works construction QD 3230/2012 [1] : In calculation, it is required that between the layers, insulating layer must be bituminous macadam or compacted asphalt concrete, but the insulating layer is only considered in structural role 1.2.1.2 Design calculation method of multi-layer concrete pavement in airport roads according to TCVN 10907-2015 [3]: The insulating layer is specified to be 1-2 layers of oil canvas, or bituminous sand with thickness not over 5mm In calculation the assumption that the upper course’s deflection is equal to that of the below course is acceptable 1.2.1.3 Some Researches Calculating Multi-Layer Concrete Payment in Vietnam [10, 11, 15] In [11], Prof.PhD Nguyen Van Lien has introduced calculation method for girder and one-layer, and multi-layer concrete slab under flexural stress on elastic ground by finite difference method (FDM) In calculation for multi-layer concrete pavement structure, only the assumption that there is no friction between the layers is acceptable, if there is really no friction between layers, the insulating layer is not arranged for surveying the effect of the insulating layer In 1995, Prof PhD Pham Huy Khang in his Technical Doctoral Dissertation[15], has suggested calculation method for multi-layer concrete pavement with different modulus (strongly bonded), had calculate conversion from multi-layer to one-layer course, featured by the conversion of multi-layer to one-layer with converted elastic modulus The dissertation of M.Sc Nguyen Hong Minh (2007) [10]: In calculation, the assumption that the insulating layer is small in thickness, thus effects of the insulating layer on redistribution of internal forces in layers 1.2.2 Design Calculation Methods for Two-Layer Concrete Pavement, with expansion joints in the world: 1.2.2.1 Calculation of concrete pavement by Westergaard semiexperimental method [16, 39]: In calculation, the rigid base does not participate in flexural strength 1.2.2.2 Design calculation method according to AASHTO [17, 18, 19, 20, 21, 22, 23, 24, 36, 37]: Bending and tensile stress calculation programme of multi-layer concrete with assumed thickness of the insulating layer is insignificant, not affecting distribution of internal forces among layers Then the bending and tensile stresses in layers is proportionate to stiffness of the layers 1.2.2.3 Mechanical Experimental of the US [33, 42, 45] In designing the additional strengthening concrete pavement on the existing concrete pavement, it states that the insulating layer is from hot asphalt concrete with allowable thickness of not over inch (~ 5cm) In calculation, it only plays the role of insulating layer, 1.2.2.4 According to US Federal Aviation Administration (FAA) [41, 43] In the design, it is specified that the insulating layer by construction structure, in case it is asphalt concrete, the thickness is not over inches (5cm) 1.2.2.5 According to calculation method in India’s Designing Procedure: Similar to Westergaard method 1.2.2.6 According to rigid pavement designing procedure of China JTG D40-2011 [78] In calculation of additional strengthening concrete pavement on the existing concrete pavement, it is compulsory to use leveling layer combined with insulating layer from hot asphalt concrete, thickness is equal 4cm But it is only considered structural layer, in consideration, the effects of insulating layer is not taken into account 1.2.3 Some Software Packages calculating pavement structure on deformed base Currently in the world there are several commercial applications that are able to solve the question of multi-layer construction structure on deformed base Each software package is built with its own strength in solving interaction questions In calculation, only the insulating layer is required according to construction structure, provided that the concrete layers are bonded, half-bonded or freely slippery , without taking into account the effects of the insulating layer on performance of the structure 1.2.4 General Comments: In design calculation, designing procedures all use thin-sheet principle In case calculation of 2-layer concrete pavement with insulating layer, but in the calculation diagram, the insulating layer is only considered as a constructional layer However, in some procedures, the specified thickness of the insulating layer is relatively high In hot sunny temperature in Vietnam, some materials will have their strength decreased (elastic modulus) will cause large deformation, increasing surface deflection, causing redistribution of internal forces in layers of multilayer concrete pavement This issue needs to be considered and clarified 1.3 Calculation of Concrete Pavement Under Effects of Ambient Temperature 1.3.1 Effects of Temperature on Concrete Pavement 1.3.1.1 Temperature Gradient and concrete pavement cambering due to temperature gradient : Due to temperature difference between concrete sub-layer by depth, layering can have different expansion When the surface temperature is higher than that in bottom of the pavement in hot summer days, the slab can be cambered , causing flexural stress at bottom of the pavement Meanwhile, it is on contrary in case of deflection, the wheel load also cause bending and tensile stresses in the bottom of the pavement So the most disadvantage of the concrete pavement is that in hot summer days, the thermal stress magnitude depends on difference between the surface temperature and that of the bottom (temperature gradient ): ∆t=T bm-T đ (1.14) 1.3.1.2 Concrete Slab Shrinking/Expanding under changing temperature by season When the ambient temperature changes between seasons, the average temperature (T tb ) by depth in the pavement is also changing, resulting in shrinking and expanding concrete slabs 1.3.2 Temperature Gradient calculation method 1.3.2.1 Temperature Ambient calculation method according to Standard No 22TCN 223-95 [2]: In the process, the nearly true approx assumption acceptable is that the heat conduction line by pavement depth is linear to the unchanged rate of 0.84 1.3.2.2 Calculation Method of Gradient Temperature of the Concrete Pavement according to Decision no 3230/QD-BGTVT [1] It is specified in the procedure that the internal process by depth is linear with unit gradient (T g , C/cm) in a concrete layer as constant in cement concrete for each Area; 1.3.2.3 Calculation Method of thermal stress, Cement Concrete Pavement for airport roads according to TCVN 10907-2015 [3] In the process, the flexural strength for the load is 70% of that of the Concrete, the remaining 30% is for thermal stress The distance of expansion joints is specified according to constructional structure s 1.3.2.4 The method of calculation of thermal stress of concrete pavement taking into account American temperature’s effect (According to AASHTO-1998 [21, 22]) In calculation, it is taken into account the effects of temperature on dimensions and work force of cement concrete applies some of experimental factors 1.3.2.5 Calculation of the Thermal Effects in the surface cement concrete pavement slab according to Russian concrete pavement designing [52, 58, 65] In calculation of temperature gradients between the surface and bottom of the slab It is accepted that the surface temperature fluctuates in finite space by Fourie law according to explanation 1.3.3 Regulation on Arrangement of Expansion Joint on Concrete Pavement 1.3.3.1 According to Regulation of Concrete Pavement Association US [22, 25, 26, 27, 30, 31, 32, 34, 38, 40, 45] The expansion joints are arranged according to constructional structure On the main axis, in case of really crucial, it is possible to arrange expansion joints with distance of up to 500fit( ~ 150m) The American Concrete Institute also specifies that expansion joints are only arranged in either of the below conditions 1.3.3.2 According to US Federal Aviation Administration [16, 18, 20] The expansion joints are only arranged at intersections with neighbouring projects (runway with taxiways, taxiways with apron) 1.3.3.3 According to pavement designing procedure of India [28, 35] It also states that expansion joints should be arranged the same as the US 1.3.3.4 According to pavement designing process of some other countries [17, 34, 45] [34] has stated practical experiments of Western World Countries (Belgium, Denmark, Dutch, Deutscheland), the expansion joint is only arranged at the approaches of the bridge, on curves, while on straight roads, if necessary, they are arranged at 30-60m interval (98-196ft) Fwa has suggested that with concrete pavement’s thickness of over 20cm, the distance between the expansion joints is 60m And thickness of the smaller concrete pavement for thickness of the concrete slab is equal or minus 20cm, taking the distances between the expansion joint of 40m 1.3.3.5 According to Concrete Pavement Designing Procedure by Russia [52, 53, 55, 56, 62, 63, 65] The distance between expansion joints, is specified based on construction structure included in specific table which is suitable to Russian’s climatic condition 1.3.3.6 According to Rigid Pavement Designing Process by China JTG D40/2011 [78] Only arrange expansion joint at intersection with other works, bridges on the road While in the general route, expansion joints are only arranged when it is really necessary according to calculations As such, arrangement of expansion joints on a highway is only according to constructional structure 1.3.3.7 Vietnam’s TCVN 10907/2015 specifies: [3] The expansion joints, the expansion joints are classified by structure, at fixed distance for each region, with expansion joint structure being the typical design 1.3.3.8 Decision no 3230/2012 specifies arrangement of contraction joints, expansion joints for concrete pavement slab rows[1] The expansion joints are arranged depending on the constructional structure, depending on temperature at working hours, the Consultant may arrange some additional expansion joints, but the interval between the joints should not be over 12-15 times of the concrete pavement slab’s length 1.3.3.9 In TCVN 9345/2012 [4], The regulation on arrangement of expansion joint in concrete pavement Also arranging expansion joint provided that thermal expansion of the concrete pavement slab is ensured 1.3.3.10 Actual arrangement of expansion joints of concrete pavement slab row in Vietnam On concrete pavement of Vietnam, there are always expansion joints by structure However, actual condition of concrete pavement shows that the phenomena of heart shake rarely appear beside contraction joint but beside expansion joints in all North, South, Central Regions 1.3.4 In some other Works, Researches on temperature gradient and distance of contraction, expansion joints of cement concrete in Vietnam and the world In the world there are some studies on temperature profile in concrete pavement and regulations on arrangement of concrete pavement’s expansion joint, it is remarkable that determination of average temperature in concrete pavement is by the formula: h (1.30) T = T ( z ).dz , tb h ∫0 z ,t In Vietnam, there are some research results on effect of temperature on performance of the concrete pavement slab In the state-level project accepted in 1996 [6], the conclusion is made that up to 80% slab had cracks due to too large slab size and the expansion joints’ interval is too high And in some doctoral dissertations of Candidate Ngo Ha Son (1996) [7]; Doctoral Dissertation of Candidate Nguyen Duy Dong (2007) [8]; Doctoral Dissertation of Candidate Pham Dang Nguyen (2016) [12]; Doctoral Dissertation of Candidate Nguyen Hoang Long [9] However, in these researches, only temperature profile and temperature gradient are surveyed for specific cases of concrete pavement of specific thicknesses, they have not demonstrate calculations to determine general temperature profile for concrete pavement slabs of different thickness 1.3.5 General Comments Based on overview of regulations of countries on calculation to determine the distance of expansion joints on concrete pavement, there are many differences, depending on conditions and regulations of each country In hot weather of Vietnam, it is required to study to apply experiences of nations in calculation of distance of expansion joints on concrete pavement to fit Vietnam’s conditions 1.4 Issues to be Studied and Clarified in Concrete Pavement Designing Calculation in Vietnam’s Condition 1.4.1 Effect of the insulating layer in multi-layer pavement In case the insulating layer is asphalt concrete with high thickness, in hot weather of Vietnam, large deformation may happen, affecting performance and redistribution among concrete layers in multi-layer system This issue is to be studied to clarified 1.4.2 Calculation of temperature profile by depth of the slab with different thicknesses So far, in the designing process according to QD 3230/2012 accepts the assumption that heat conduction line in the concrete slab is linear to 10 conforming to the cement concrete pavement calculation theory 2.2.3 Survey of Influence of the Insulating Layer of High thickness 2.2.3.1 Using insulating layer from bitumen - sand and SAMI a Using insulating layer of Bitumen – sand In calculation, only influence of Table 2.10: Survey result of the insulating layer on internal influences of the thickness of the force of the layers: select the insulating on deflection and flexural insulating of bitumen, sand, the stress inside the Concrete pavement insulating layer’s thickness varies Insulating Flexural from 0,5 to cm, showing the layer’s Concrete stress of thickness pavement ‘s cement result as in table 2.10: Bitumensand,cm deflection ,mm concrete layer (Mpa) 0.5 1.5 0.133 0.137 0.140 0.143 15.172 16.230 16.880 17.347 Survey Result Remarks: When increasing thickness of the isolating layer made of bitumen sand, from 0.5cm to 2cm , insulating settlement also increases consequently It causes changes of redistribution of flexural stress in the layers, increasing significantly flexural stress of the upper layer(14.35%) and decrease flexural stress of the lower layer (26.54%), then most effect of the load will be born by the concrete pavement above b Using SAMI insulating layer In calculation, use SAMI insulating layer , Table 2.11: Calculation result replace the thickness of the insulating layer to of surveying influence of 1.5 - 3cm, the results are as in table 2.16: SAMI insulating layer’s Survey Result Remark: thickness on deflection and When increasing thickness of the isolating layer flexural stress made of SAMI, 1.5cm – 3cm insulating Insulating Concrete Flexural settlement also increases consequently, It causes layer’s pavement stress of thickness ‘s cement changes of redistribution of flexural stress in the Bitumendeflection concrete layers, increasing significantly flexural stress of sand,cm ,mm layer, Mpa the upper layer (6.97%), higher deflection 1.5 0.133 1.517 (2.89% ) Because SAMI material has higher 0.135 1.560 elastic modulus than that of sand bitumen, thus 2.5 0.136 1.594 when increasing the insulating layer’s thickness, 0.137 1.623 the influence degree of the insulating degree of SAMI is smaller, compared to influence of bitumen - sand material 11 2.2.3.2 Survey of influence of deformation of the insulating layer from compacted asphalt concrete to deformation stress in the cement concrete layer when changing the insulating layer thickness: In the dissertation, the author calculates to survey and evaluate influence of the insulating layer with high thickness (minimum 3cm as stated in Regulation QD 3230), inside the multi-layer surface course, in hot sunny weather of Vietnam Elastic modulus value of the Table 2.22: Calculation result of compacted AC layer with group A surveying influence of compacted aggregate, depending on AC insulating layer’s thickness on temperature, within 10 to 65 C deflection and flexural stress in the range, determinable by formula cement concrete pavement Compacted (2.18) [69] :E BTN =-6T+600, Concrete Flexural AC In Vietnam conditions: Elastic pavement stress of Insulating ‘s cement modulus of AC at 47 C following layer’s concrete deflection thickness formula (2.18) we get 310-315Mpa ,mm layer, Mpa ,cm (calculate with EBTN = 312 Mpa) 0.133 1.512 Calculate the compacted AC 0.134 1.554 insulating layer with thickness 0.136 1.588 varying from to cm produce the results as in Table 2.22: Survey Result Remark: With rigid pavement structure having average concrete slab’s thickness of 20-25cm, if the insulating layer is made of compacted AC of 4cm thickness up, it will cause redistribution of stresses inside the layers, increasing significantly flexural stress in the concrete layer, resulting in decreased operation quality of the pavement 2.2.3.3 Survey of influence of the Compacted AC Insulating Layer’s deformation on deformation stress in the cement concrete layer when changing temperature in the insulating layer To calculate the temperature at the bottom of the cement concrete payment as the basis to calculate the elastic modulus of AC insulating layer , in the survey example, T h is determined by formula (1.20) of Russia The elastic modulus of AC insulating layer is calculated by (2.18)when it is known that AC layer’s temperature gives the same result as in Table 2.23 Table 2.23 : Calculation of elastic modulus of depending asphalt with surface temperature Max Surface temp., 0C Ave Surface temp., 0C 65 60 50 46.5 42 33.5 Surface temperature fluctuation margin , 0C Concrete slab bottom temperature , 0C 18.5 18 16.5 48.0 43.6 34.9 Elastic modulus of insulating layer of AC, MPa 312 338 390 12 When knowing the value of elastic modulus of the AC insulating layer at different temperatures according to Table 2.23, declaring input data as thickness and elastic modulus of the AC corresponding to temperature level on the surface of the slab, according to calculation of the software Multi-Layer Concrete Pavement -MLCP, it would calculate the stress and displacement of of surface courses For result see tables 2.24 and chart 2.35: Table 2.24: Flexural stress in the cement concrete course (corresponding to surface temperature) by thickness of Compacted AC Insulating Layer Surface temperature , 0C Flexural stress of cement concrete , Mpa Hcl= 3,0cm Hcl= 3,5cm Hcl= 4,0cm Hcl= 4,5cm Hcl= 5,0cm Hcl= 5,5cm Hcl= 6,0cm 65 1.512 1.534 1.554 1.569 1.588 1.599 1.617 60 1.499 1.52 1.539 1.556 1.571 1.585 1.597 50 1.482 1.502 1.52 1.537 1.551 1.565 1.578 40 1.467 1.487 1.504 1.52 1.535 1.548 1.56 Survey Result Remark: When the concrete slab’s surface temperature decreases, it will also allow increase of thickness of the AC insulating layer without increasing flexural stress of the concrete This is also the reason why, for the countries with more moderate weather, it is allowed to use AC insulating layer with to 5cm thickness (such as the US [19, 50] allowing the insulating layer having thickness not over inch (5cm) 2.3 Conclusion of Chapter II The Dissertation has built a calculation software package of multi-layer concrete pavement by FDM method using Visual Basic 6.0 language (Multi-Layer Concrete Pavement – MLCP) The Calculating result is reliable, usable in calculation of 2-layer rigid pavement structure when using different insulating layer Structure of the insulating layer with the role of levelling and limiting friction between the cement concrete pavement and the base course Through calculation and survey, it is shown that with with insulating layer of high thickness, in sunny weather condition of Vietnam, the settlement will be high , which would result in redistribution of internal force in the layers, increasing significantly flexural stress of the cement concrete slab, resulting in decreased quality of the pavement In case of improvement of the existing cement concrete pavement with new cement concrete pavement, to level the defects, pot holes, settled places of the existing pavement, according to [5], it is regulated to use cement concrete or cement mortar to fill up, cover the defect, avoiding to use asphalt concrete both as insulating layer and filling material for the pot holes, defects, which increase the thickness of the insulating layer 13 CHAPTER CALCULATION OF TEMPERATURE GRADIENT IN CEMENT CONCRATE PAVEMENT WITH DIFFERENT THICKNESSES IN VIETNAM’S CONDITIONS Chapter III continues experimental research combined with theoretical study on temperature profile in cement concrete pavement to build retrospective formulae to calculate parameters to use for calculating influence of temperature on performance and operation quality of concrete pavement in Vietnam’s climatic conditions 3.1 Calculating temperature distribution in concrete pavement in Vietnam’s conditions 3.1.1 Ambient temperature’s effect on concrete pavement’s surface The temperature in the concrete pavement, provided by two heat source including the atmosphere and solar radiation, in windless condition To determine the slab surface’s temperature, it is necessary to carry out field survey or use below formula: T = Tkk + Tbx , (3.1) For example, to calculate surface temperature of cement concrete pavement in Hanoi city, the result is : T bm=39.0+26.0 = 65.2 C 3.1.2 Temperature distribution by depth of the of the concrete pavement slab To determine the temperature profile by depth of the concrete pavement slab at any time in a day, one can survey on field or use correct answer of the question of one-way heat conduction in halfinfinite-space according to Fourie law, to calculate the temperature profile in the concrete pavement [14, 67, 68, 74] following the equation: ∂T ∂ 2T = α , (3.3) ∂t ∂z To answer equation (3.3) to calculate temperature at any depth in the concrete pavement, and at any time in a day, the dissertation suggests to use finite difference method (FDM) 3.2 Field Survey to Determine Temperature Distribution by depth of the concrete pavement in Hanoi city In the dissertation, the Candidate carried out on testing field, nd entity of Military Technical Academy, Xuan Phuong commune, Nam Tu Liem district - Hanoi city on June 2018 and June 2019 Applied temperature survey in cement concrete pavement at different depth with the model as in table 3.2 beside: 14 Depth of measuring tip cm Meas uring hour 0.02 -10 -20 -30 10 11 12 29.5 29 29 29 29.3 30 32 36 41 47.5 53.5 58.5 34.86 33.9 33.34 32.79 32.6 32.52 33.19 34.69 36.99 40.22 43.68 47.12 38.25 37.2 36.51 35.74 35.33 34.87 34.94 35.26 36.2 37.59 39.41 41.36 39.75 38.86 38.31 37.55 37.15 36.55 36.41 36.2 36.53 36.93 37.82 38.73 39.98 38.98 38.33 38.15 37.52 37.21 36.55 36.32 35.92 35.99 35.85 35.94 36.49 Depth of measuring tip cm Meas uring hour 0.02 -10 -20 -30 13 14 15 16 17 18 19 20 21 22 23 24 62.5 65 63.5 60 55.5 50 45 40 36 32.5 30.5 30 50.32 52.89 53.81 53.61 52.33 50.12 47.66 44.73 42.1 39.39 37.43 35.97 43.5 45.39 46.76 47.54 47.72 47.2 46.38 45.01 43.67 41.97 40.64 39.27 40.01 41.14 42.31 43.09 43.75 43.88 43.92 43.43 42.97 42.07 41.39 40.42 39.98 37.09 37.62 38.22 38.95 39.74 40.15 40.5 40.43 40.47 40.08 40.05 39.31 3.3 Calculation of temperature profile distribution in cement concrete pavement in Vietnam’s conditions Temperature surveyed data on the surface of the concrete is used to calculate temperature by depth of the concrete slab for the cases where the slab thickness are different, using finite difference method (FDM) to answer the equation (3.3) as mentioned above An equation is set up to calculate Temperature Profile (TPCP) in Concrete Pavement Results of a cement concrete slab of 40cm thickness are shown in figures 3.7 and 3.8: Figure 3.7: Temperature profile in Figure 3.8: Temperature 40cm-thick concrete slab varies distribution by concrete slab’s hourly in a day at different depths depth at 40 cm Comparing the calculation result from the equations, and field survey data, it is shown that : the difference is not over 0.3 C -0.5 C (not more than 2.34%), which is not too high, thus it is reliable Similar calculations are done for cement concrete pavement slabs of 22cm; 26cm; 30cm; 36cm thicknesses Remarks: The heat conduction line along the depth of the concrete pavement is not a linear route but a non-linear curve; The highest temperature at different depths is not at the same time The highest temperature gradient is at 2:00pm for concrete slabs of different thickness 15 3.4 Building formulae to calculate temperature gradient and average temperature in the concrete pavement 3.4.1 Introduction to Mınitab software and Retrospective Analysis: Minitab is the mini-version of OMNITAB software, the analysis and statistic software by NIST 3.4.2 Calculation to determine temperature gradient in the concrete pavement of different thicknesses Target: To calculate Table 3.9: Statistics of temperature camber flexural stress in difference between surface and bottom of the concrete slab cement concrete pavement slabs of Field testing and different thickness in Hanoi city software run show the Concrete Slab surface Slab bottom Temperature slab temperature, temperature,0C Gradient , results of temperature depth,cm C (Th) ∆T,0C difference between the 22 65 44.4 20.6 surface and bottom for 26 65 42.5 22.5 slabs of different 30 65 41.0 24.0 36 65 39.3 25.7 thicknesses, see table 40 65 37.6 27.4 3.9 In the analysis, we have retrospective function to determine the temperature gradient in the cement concrete pavement slab in following format: ∆ T = 12 3226 ln( * h + 1) (3.5) , we have the function to determine temperature at the bottom of a concrete slab with thickness h: Th = −12.3226* ln(0.2 * h + 1) + Tbm , (3.6) in form of relation function, with slab thickness in form of logarithmic function, similar to formula (1.24) of Russia 3.4.3 Calculate of Average Temperature by Depth of The Concrete Pavement Slab Purpose: To calculate the Table:3.11 Average temperature necessity for arrangement and inside cement concrete pavement in calculate the distance between Hanoi expansion joints of the concrete Temperatur e Gradient slab row Temperature difference Concr Average in cement is for calculating the most adverse ete Slab temperature concrete surface inside the slab expansion joint, especially pavement thickn temperatur slab,0C (Th) slab , average temperature difference of ess e, 0C by formula ∆Ttb,0C ,cm (3.11) the slab in hot season and Following construction temperature for the (3.12) slab in cold season Thereby, one 22 65 53.87 11.13 can calculate to determine the 26 65 52.29 12.71 30 65 50.87 14.13 necessity of the expansion joints 36 65 49.05 15.95 and calculate the distance 40 65 47.95 17.05 between the expansion joints Average temperature inside the 16 concrete slab in the hottest day by its depth for Hanoi city area The analysis induces in retrospective formula to calculate average temperature function by depth of the cement concrete slab: T tb =-17.8388*ln(0.04.h+1)+ T bm, (3.14) 3.4.4 Remarks The heat conduction line along the depth of the concrete pavement is not a linear route but non-linear curves The above calculation results show that the unit temperature gradient ( C/cm) is not a consent for each climatic region, but depends on thickness of the pavement One can apply formulae (3.5), (3.6) and (3.14) to determine temperature gradient in the middle of the surface and bottom of the concrete slab, and average temperature by depth of the concrete slab The above formulae applies to Hanoi’s and similar locations’ climatic conditions 3.5 Calculation of Expansion Joint for Concrete Pavement Currently in the world, Figure 3.21 Structure of an expansion based on specific joint following [75] temperature conditions of each location to review the necessity of the expansion joints with appropriate interval In Vietnam, an expansion joint has typical structure as in Figure 3.21: 3.5.1 The Basis To Calculate The Necessity Of Expansion Joints On Cement Concrete Pavement For a concrete pavement not requiring expansion joint, it should meet below two conditions: The First case (Condition 1): not to let fracture, breaking happened at side of the concrete slab (as on figures 1.5 -1.7), the condition of below formula must be met: τ max k = σ T ≤ 0,26.[Rn ] (3.22) The second case (Condition 2): Longitudinal stability condition of the slab row in case of heat expansion, not to let the slab split or come up from the base course, causing longitudinal instability of the slab row, so condition of the following formula should be met: σ T ≤ σ Tcp , ( σ Tcp = 031 E bt ρ h; ) (3.23) 3.5.2 Bases for Calculation of Distance of Expansion Joints for Concrete Pavement If the two condition (3.22) and (3.23) are not met, the concrete pavement needs expansion joints The interval between the expansion joints is determined based on the following grounds: Omitting friction at the bottom of the cement concrete slab; Part of thermal stress caused by 17 expanding cement concrete is absorbed by compression strength of the joint-filling board; Thermal expansion of the cement concrete slab row is equal compression of the joint-filling board (taking into account the effect of the joint-filling board’s height versus thickness of cement concrete pavement slab), which is determined by below formula: E BT ∆ v L= , (3.30) σT −σV hv h 3.6 Conclusion of Chapter III Survey has been made for temperature on concrete pavement surface and by depth of the cement concrete pavement of 40cm thickness in Hanoi city as the data grounds for calculating the temperature profile in the cement concrete slab of different thickness; The dissertation has set up software calculating distribution of temperature profile by depth of concrete pavement slab by FMD method, it can be applied to calculate the temperature profile in the concrete slabs in different climatic regions The study gives initial remarks on non-linearity of the heat conduction line the centre of the cement concrete pavement, and the quantity of unit temperature gradient (T g , C/cm) is not a constant but it varies depending on the slab thickness The author has suggested retrospective function to determine the temperature Gradient inside the cement concrete in Hanoi city, following (3.5), (3.6) and the function to determine average calculating temperature inside the concrete pavement following (3.14).Meanwhile, formulae (3.22), (3.23), and (3.30) are presented to serve calculation of the necessity of expansion joints and interval of the expansion joints of the concrete pavement slab row in Vietnam’s climatic conditions, for highways and airports CHAPTER APPLICATION IN CALCULATION OF CEMENT CONCRETE PAVEMENT IN VIETNAM’S CONDITIONS In thí Chapter IV, the author carries digital investigation and survey to evaluate the influence of the insulating layer and the ambient temperature when calculating to design cement concrete pavement, thereby making recommendations suitable to Vietnam’s conditions , helping to complete regulations on cement concrete pavement structure for highways and airports in Vietnam 18 4.1 Calculation to determine appropriate thickness of the insulating layer in Vietnam’s conditions Table 4.1 The result of comparison of maximum flexural stress at bottom of cement concrete pavement by different calculation methods Insulating layer 2-layer oil canvas: E=30MPa h=0.3cm Bitumen - sand layer: E=50MPa h=0.5cm SAMI layer: E=150MPa.h=1.5cm Compacted AC 12.5: E=313MPa.h=3cm Compacted AC12.5: E=313MPa.h=4cm Compacted AC12.5: E=313MPa.h=5cm Compacted AC12.5: E=313MPa.h=6cm Flexural stress of the Cement Concrete Pavement Calculated by different methods, MPa TCV Recome BCH 197N ded 91 method 10907 1.517 1.485 1.519 1.517 1.485 1.519 1.517 1.485 1.519 1.512 1.485 1.519 1.554 1.485 1.519 1.588 1.485 1.519 1.617 1.485 1.519 Table 4.2 Calculation Result of Axle volume allowable on Cement Concrete Pavement Rku=4Mpa Insulating layer Compacted AC course 12.5: E=312MPa,h =4cm Compacted AC course 12.5: : E=312MPa,h =5cm Compacted AC course 12.5: : E=312MPa,h =6cm σ0 (Μπα) Fatique factor, km Total allowable axle volume in operation, N 1.554 0.38 11 402 927 1.588 0.39 585 320 1.617 0.40 004 138 In the hot weather condition of Vietnam, it is recommended that the insulating layer can be used from different materials with corresponding thickness : oil canvas (1-2 layers), bitumen - sand (0.30.5cm thickness), SAMI which is max 1.5cm thick From the compacted asphalt concrete of not over 3.5cm thickness, in special case, when it is necessary to combine to level up the base course surface (the existing cement concrete pavement) the maximum thickness should be 4cm only 4.2 Survey to calculate thermal stress in the cement concrete pavement by the suggested temperature gradient determination approach The dissertation has calculated thermal stress for the cement concrete pavement according to QD 3230, then re-calculate the thermal stress, thereby comparing the result with calculation method by formula (3.5) with cement concrete pavement‘s thicknesses Hbt = 22cm; 26 cm; 30 cm, respectively 19 4.2.1 Calculation of flexural stress accordingly (QD 3230/2012) Table 4.5 Comparison of camber flexural thermal stress calculation result σ t,max (Mpa) by two methods Calculation method According to QD 3230 As proposed Deviation, % caused by temperature difference Table 4.1 Chart on comparison of temperature-induced flexural stress Concrete slab’s thickness, cm 22 26 30 1.699 1.496 1.266 1.833 1.504 1.176 7.89% 0.53% -7.11% The calculation results shown in table 4.4 and figure 4.1 demonstrate that concrete slab have small thickness, thus the camber flexural stress calculating temperature gradient following the suggested formula will be higher that that from temperature gradient calculation method according to QD 3230 (up to 7.89%) For slabs with high thickness, it is the contrary In deed, concrete pavement in Vietnam currently often has 23-25cm thickness, if applying camber flexural stress according to QD 3230, resulting in the fact that the concrete pavement has smaller thickness than required, which affects operation quality 4.2.2 Calculation of Thermal Stress in Concrete Pavement of Airport Roads Table 4.6 Calculation of camber Table 4.7 Appropriate slab size flexural stress according to calculation Ứng suất nhiệt , MPa TCVN10907 Calculation method Strength following TCVN10907 Stress following (4.1) Deviation, % Thermal stress, MPa 25 to 35 to > 40 cm