Sự lan truyền vết nứt được thí nghiệm bằng cách sử dụng dầm vật liệu với vết nứt bắt đầu ở mặt dưới. Nghiên cứu cho thấy tốc độ lan truyền vết nứt có thể được mô tả bằng mối quan hệ quyền lực giữa độ cứng của hỗn hợp và số chu kỳ đến sự thất bại, đó là hỗn hợp và phụ gia kết dính. Một phương trình chung được phát triển cho phép tính toán tuổi thọ của các vỉa bitum và được so sánh với hai phương pháp thiết kế vỉa hè truyền thống, cho kết quả tương đương đối với các hỗn hợp chưa biến đổi nhưng mang lại kết quả thực tế hơn cho hỗn hợp polyme biến đổi. Hình ảnh phân tích các vết nứt cho thấy rằng chúng lan truyền xung quanh cốt liệu thô cố gắng tách nó ra khỏi ma trận và chúng di chuyển theo đường thẳng nhất có thể giữa điểm khởi đầu bẻ gãy và điểm tải áp dụng.Có hai phương thức của sự thất bại kết cấu mà nhà thiết kế tìm cách tránh trong suốt thời gian thiết kế của vỉa hè; Nứt và rãnh. Khái niệm cuộc sống thiết kế đặc biệt quan trọng đối với vỉa hè vì chúng không bị vỡ đột ngột (trừ những trường hợp hiếm hoi của các chuyển động nhiệt hoặc mặt đất rất lớn, điều này không khả thi về mặt kinh tế ở giai đoạn thiết kế) nhưng dần dần xấu đi Thời kỳ dài. Đây thực sự là một hiện tượng mỏi, theo nghĩa là sự xuống cấp, gây ra bởi các căng thẳng và căng thẳng trong cấu trúc, kết quả từ cả cường độ và số lượng các ứng dụng tải mà trải nghiệm vỉa hè.Tất cả các phân tích của ITFT báo cáo cho đến nay đã được hướng tới việc tính toán căng thẳng kéo dài nhất ở trung tâm của mẫu giả định rằng đây là chế độ duy nhất thất bại. Tuy nhiên, có thể chỉ ra rằng trong một số điều kiện kiểm tra (áp suất nén cao và hoặc nhiệt độ cao) có thể xảy ra sự cố nén hoặc cắt. Các công thức 3 .10 và .11 mô tả các áp lực cơ bản dọc theo đường kính dọcCủa ITFT, sau Timoshenko (4).áp lực ITSM được sử dụng khi có thể, do đó, cho phép nhà khai thác thực hiện một kiểm tra như được mô tả trong Tiêu chuẩn Anh Quốc về Phát triển 213 để có được mô đun độ cứng của mẫu ở mức căng thẳng ITFT
Read, John (1996) Fatigue cracking of bituminous paving mixtures PhD thesis, University of Nottingham Access from the University of Nottingham repository: http://eprints.nottingham.ac.uk/12605/1/318631.pdf Copyright and reuse: The Nottingham ePrints service makes this work by researchers of the University of Nottingham available open access under the following conditions This article is made available under the University of Nottingham End User licence and may be reused according to the conditions of the licence For more details see: http://eprints.nottingham.ac.uk/end_user_agreement.pdf For more information, please contact eprints@nottingham.ac.uk FATIGUE CRACKING OF BITUMINOUS PAVING MIXTURES JOHN MADDISON READ A dissertation submitted to the University of Nottingham for the Degree of Doctor of Philosophy University of Nottingham, Department of Civil Engineering May, 1996 To Jane CKNOWLEDGEMENTS AND DECLARATION I would like to thank all those people who helped, encouraged and generally cajoled me into writing this thesis, without their efforts it would certainly never have been completed I am forever in the debt of Professor S.F.Brown and Professor P.S.Pell, my supervisors, who's enthusiasm and energy meant they were always there with encouragement, and constructive criticism, whenever required I would also like to thank Todd and Mike who worked with me for nearly years without losing their minds, a feat which nobody else has ever achieved, and Dr N.H.Thom with whom I had many fruitful discussions and from whom I learnt much Over the latter stages of this project I had many interesting and stimulating talks with Dr A.C.Collop, and for this I thank him I would also like to mention all the researchers of the Pavement and Geotechnics Research Group with whom, over numerous cups (or buckets) of tea, I had lots of discussions (or sometimes arguments) from which I feel I learnt a great deal The experimental work would have been impossible without the tremendous amount of hard work by Ehsan and Shane and the mechanical wizardry of Denis and to them I would like to say the biggest thankYou of all Keith Cooper, the Chief Experimental Officer, who guided me at the beginning and taught me much before he retired was an inspiration to me and for that I am extremely grateful I would also like to thank all the other technical staff who have helped me along the way, especially Barry Broderick This work was funded by the Environmental and Physical Sciences Research Council (EPSRC), the Department of Transport, Cooper Research Technology Limited, Esso Petroleum Company Limited, Foster Yeoman Limited, Mobil Oil Company Limited, Nynas Bitumen, Shell Bitumen, SWK Pavement Engineering Limited, Tarmac Roadstone Limited Wimpey Environmental Limited, the Worshipful Company of 111 Paviors, the County Surveyor's Society and the Rees Jeffreys Road fund, and I am grateful for their generous support I would also like to mention all the people at the various County Council Laboratories who managed to help me immensely even though they had no financial means to so Finally, let me thank all those who have assisted me in some way but have not been specifically mentioned above The work described in this dissertation was carried out at the University of Nottingham, Department of Civil Engineering between June 1992 and September 1995 This dissertation is the result of my own work, except where specific reference has been made to the work of others No part of the work has been, or is currently being, submitted for any degree, diploma or other qualification IV BSTRACT This dissertation is concerned with the fatigue cracking of bituminous paving mixtures It considers both the life to crack initiation and the life for crack propagation, including the development of a method for calculating the number of wheel load applications to either critical or failure condition The development and subsequent validation of the Indirect Tensile Fatigue Test (ITFT) are described Both the repeatability and reproducibility of the method are examined as well as its correlation with two other fatigue test methods The test is shown to be a suitable method for measuring the life to crack initiation of bituminous paving mixtures as well as being an economically viable test Poisson's ratio for bituminous paving mixtures is examined showing that, provided at least 500 conditioning pulses are used in order to achieve steady state conditions, 0.35 is an appropriate value Prior to these early load applications Poisson's ratio is shown to be variable and often in excess of 0.50, an explanation of which is given in detail Crack propagation was experimentally simulated using beams of material with a crack initiated on the underside The work shows that the rate of crack propagation can be described by a power relationship between the stiffness of the mixture and the number of cycles to failure, which is mixture and binder dependent A general equation is developed which allows the critical and failure lives of bituminous pavements to be calculated and these are compared to two traditional pavement design methods, giving equivalent results for unmodified mixtures but, giving more realistic results for polymer modified mixtures Image analysis of the cracks demonstrates that they propagate around coarse aggregate trying to separate it from the matrix and that they travel in the straightest line possible between the point of crack initiation and the point of applied load v ONTENTS ACKNOWLEDGEMENTS AND DECLARATION 111 ABSTRACT v CONTENTS LIST OF FIGURES " VI x LIST OF PLATES xvii LIST OF TABLES xviii Chapter Introduction 1.1 A Brief History of UK Roads 1.1 1.2 Analytical Pavement Design 1.5 1.3 Bituminous Materials 1.7 1.4 1.3.1 Asphalt Mixture Types 1.10 1.3.2 Macadam Mixture Types 1.12 Material Properties 1.15 1.4.1 - Stiffness 1.16 1.4.2 Permanent Deformation 1.16 1.4.3 1.5 Chapter Fatigue Cracking 1.18 References 1.19 Background 2.1 Introduction 2.1 2.2 Test Methods for Fatigue 2.2 2.3 Factors Affecting Fatigue 2.12 2.3.1 Stresses Induced in a Pavement 2.12 2.3.2 Mode of Loading 2.13 2.3.3 Loading Waveform 2.15 2.3.4 RestPeriods 2.17 VI 2.3.5 Mixture Variables 2.18 2.4 Fatigue Relationships 2.21 2.5 Use of Fatigue Relationships 2.24 2.6 Summary 2.25 2.7 References 2.26 Chapter Indirect Tensile Fatigue 3.1 Introduction 3.1 3.2 Analysis of the ITFT 3.3 3.3 Equipment Development 3.10 3.3.1 Hardware Development 3.10 3.3.2 Software Development 3.12 3.4 Stiffness Modulus _ •~ 3.15 3.5 Fatigue Test Methods 3.24 3.5.1 Trapezoidal Cantilever 3.24 3.5.2 Uniaxial Tension Compression 3.25 3.5.3 Indirect Tensile Fatigue Testing 3.26 3.6 ITFT Protocols 3.27 3.7 Main Test Programme 3.29 3.8 Additional Test Programme 3.33 3.9 Chapter 3.8.1 Repeatability of the ITFT 3.33 3.8.2 Reproducibility of the ITFT 3.33 3.8.3 Practical Use of the ITFT 3.34 3.8.4 Contractual Use of the ITFT 3.34 3.8.5 Further Validation of the ITFT 3.39 References 3.39 Results of the Indirect Tensile Fatigue Testing 4.1 Introduction 4.1 4.2 IF·Ind·Ings Initia 4.3 Results of the Main Test Programme 4.3 va 4.4 Repeatability of the ITFT 4.11 4.5 Reproducibility of the ITFT 4.16 4.6 Practical Use of the ITFT 4.24 4.7 Further Validation of the ITFT 4.29 4.8 Additional Results 4.35 4.9 Summary of Results 4.39 4.10 References 4.42 Chapter Poisson's Ratio 5.1 Introduction " 5.1 5.2 Test Programme " 5.8 5.3 Results 5.9 5.3.1 Aluminium Cube 5.12 5.3.2 Aluminium Core 5.14 5.4 Summary 5.16 5.5 References 5.16 Chapter Crack Propagation 6.1 Introduction 6.1 6.2 Fracture Mechanics 6.3 6.3 Image Analysis 6.10 6.4 Pilot Test Programme 6.11 6.4.1 Results 6.12 6.5 Main Test Programme 6.17 6.6 References 6.22 Chapter Results of the Crack Propagation Test Programme 7.1 Introduction 7.1 7.2 Image Analysis 7.1 7.3 Analysis of Crack Propagation Data 7.5 7.4 Summary , 7.9 Vlll 7.5 Chapter References 7.11 Practical Application of Research Results 8.1 Introduction 8.1 8.2 Mixture Design 8.1 8.3 Pavement Evaluation 8.2 8.4 Pavement Design 8.4 8.5 References 8.11 Chapter Discussion and Conclusions 9.1 Introduction 9.1 9.2 Indirect Tensile Fatigue 9.1 9.3 Poisson's Ratio 9.5 9.4 Crack Propagation 9.7 Chapter 10 Recommendations for Future Research 10.1 Indirect Tensile Fatigue 10.1 10.2 Poisson's Ratio 10.1 10.3 Crack Propagation 10.2 Appendix A Protocols Appendix B Data for ITFT Work Appendix C Data for the Poisson's Ratio Work Appendix D Data for Crack Propagation Test Programme Appendix E Crack Propagation Photographs IX APPENDIX E RACK PROPAGATION PHOTOGRAPHS This appendix contains the 47 images which were obtained during the crack propagation test programme The caption below each image is the specimen identification and is made up as follows: fIRJ\ L L The first letters refer to the mixture type: HRA Hot Rolled Asphalt DBM Dense Bitumen Macadam The next character refers to the type of bitumen: 50 pen 100 pen E EVA modified S SBS modified The next letter refers to the void content: H High void content L Low void content The next letter refers to the binder content: H Optimum plus 10/0 o Optimum L Optimum minus 1% The last number refers to the replicate number: 1st Replicate 2nd Replicate 3rd Replicate E.2 HRA5LLl HRA5LO HRA5L03 HRA5L02 EJ HRA5LH2 HRA5LHl HRA5HOI HRA5HL3 E.4 HRA 5H03 HRA 5HO HRA5HH2 HRA 5HH E.5 HRA5HH3 E.6 E.7 BRA lL03 BRA lLH BRA lLB2 E.8 E.9 HRAIRRI E.I0 DBM5L02 DBM5LH3 DBM5H03 DBM5HO2 DBM5HH3 E.II E.12 E.13 DBM IH02 DBM IHH DBMIH03 E.14 DBMIHH3 E.IS