STUDIES OF FLEXIBLE ROAD AND AIRPORT PAVEMENTS IN KENYA Sixtus Kinyua Mwea (B.Sc. Eng. Civil, (VOS), At.Sc. Found.man Eng. (B'hani). MIEK, Rcng.) A thesis submitted in fulfillment for the degree of DOCTOR OF PHILOSOPHY in the University of Nairobi UWIVER8ITY OF NAIROBI eastafricana collection 2001 Declaration This thesis is my original work and has not been presented for a degree in any other University This thesis has been submitted for examination with our JfoiL.4^ Dr. 0.0. Mbeche - 1 - Abstract This thesis presents results of a long-term study initiated in the late 1960s on flexible pavements in Kenya. The study was conducted through field and laboratory studies. It was prompted by the need for continuing research and development of rational design, construction and maintenance of a large network of paved roads in Kenya and increasing runway and taxiway pavements for rising air traffic. The geotechnical properties of some subgrade soils in Kenya have been presented. In addition a method for determining the optimum moisture content and maximum dry density from bulk density and percentage of water added to specimens during experimentation has been developed. The use of locally available construction materials has been found to be acceptable with good compaction and selection of suitable materials. Timely maintenance of flexible pavements and in particular protecting the pavement structures from ingress of water has been found to enhance their supporting capacity. The properties of the entire pavement structure have been shown to change with age and environment. The bituminous surfacing hardens with age while the base and subbase materials strength characteristics change upon loading. The net effect of all this is a continuously changing structural capacity of flexible pavements. The study of bituminous materials has shown that the voids content of the bituminous structure is a critical consideration. A minimum voids content is required to give the mixture the necessary elasticity while at the same time the voids contents should be minimised for the reduction of hardening of the binder. The hardening of the bituminous materials has been shown to be associated with increasing asphaltene content in the binder. The penetration of bitumen recovered from thin asphalt - ii - • iii - surfacings has been found to follow a hyperbolic function with age. For the thick bituminous concrete surfacing, as the air voids content increase the bitumen penetration and ductility reduce with a power relationship. Evaluation of the pavement structures can be done by quantification of surface condition distress indicators. These include cracking, rutting, roughness and present serviceability index (PSI). A multiple regression equation has been developed showing that PSI is a function of rutting, roughness and cracking. A new maintenance criterion has been developed using a new total rut concept. The current roughness at which maintenance for road pavements was required was found to be high. In effect even when other surface conditions namely cracking, rutting and the present serviceability index indicated the pavement required maintenance, the roughness would pass the road as well performing. A new roughness criterion has therefore been proposed. The structural capacity can be established using deflection measurements and the dynamic cone penetrometer. Deflection data together with finite element analysis has been shown to be a method of determining pavement deflection and pavement stresses. When finite element is carried out with varying pavement moduli the modulus, which gives the same deflection as the field deflection is regarded as the pavement resilient modulus. A more relaxed specification for construction of pavements carrying light traffic has been proposed. For the more heavily loaded pavements including runways and taxiways, maintenance is a key element, which seems to have escaped the attention of those responsible for maintaining them. This is because timely maintenance and especially clearing of water under the sealed pavement layers is crucial in maintaining the structural capacity of the entire pavement structure. Acknowledgements I would like to acknowledge the guidance and encouragement of my University supervisors. First Professor Francis J. Gichaga who despite his busy office of the vice chancellor found time to discuss the progress of this work from inception to its completion. Secondly, Dr. O. O. Mbeche who made invaluable comments. I would also like to thank Dr. B. N. K. Njoroge the chairman of Department of Civil Engineering for his encouragement at the time of completion of this study. I would further like to extend my thanks to Germany academic exchange service (DAAD) who provided financial support for the research. These acknowledgements would be incomplete without recognising the many colleagues who have assisted me during the study. There are those who assisted wittingly in the collection of data and test results and those who unwittingly made invaluable contributions in general discussions. To all of you thank you. S. K. Mwea Nairobi August 2001 - iv- Dedication This work is dedicated To my wife Eleanor And To my children Lemmy and Winnie Their special place in me made it happen. Table of Contents Declaration i Abstract ii Acknowledgements iv Dedication v Notation index xi 1. Introduction 1 1.1 General 1 1.1.1 Road pavements 1 1.1.2 Runway and taxiway pavements 3 1.2 Statement of the problem 7 1.3 Specific objectives of the study 8 1.4 Scope of the study 9 1.4.1 Pavement materials 11 1.4.2 The performance of pavements 12 1.4.3 The finite element analysis 12 1.5 Justification of the study 12 2 Literature review 14 2.1 General 14 2.2 Environmental conditions in Kenya 15 2.3 Common embankment materials 16 2.4 Pavement materials 20 2.4.1 Introduction 20 2.4.2 The subgrade soils 21 2.4.3 Non bituminous subbase and base materials 25 2.4.4 Bituminous bound materials 34 2.4.5 Effects of changes in chemical composition of bitumen 44 2.4.6 Changes in physical properties of bitumen on ageing 46 2.4.7 Ageing of bitumen under Kenyan environments 48 - vi - 2.5 Pavement performance 50 2.5.1 General 50 2.5.2 Pavement characteristics 51 2.5.3 Functional assessment 52 2.5.4 Objective pavement distress parameters 56 2.5.5 Deflection 59 2.5.6 Dynamic cone penetrometer measurements 62 2.6 Airport pavements 63 2.6.1 Airport pavement design 63 2.6.2 Airport pavement evaluation 66 2.6.3 Observed airport pavement behaviour 67 2.7 Pavement management systems and geographical information systems 69 2.7.1 Pavement management systems 69 2.7.2 Geographical information systems 72 2.8 Finite element method of evaluating pavements 73 2.9 Literature review conclusion 75 2.9.1 Overall conclusions 75 2.9.2 Areas that this research thesis aims to address 76 3 Methodology and data collection I: Flexible road pavements 78 3.1 Introduction 78 3.1.1 General 78 3.1.2 Analyses of data 79 3.2 Laboratory testing of pavement materials 80 3.2.1 Sampling and laboratory tests on subgrade soils 80 3.2.2 Bituminous materials 82 3.3 Effect of environmental and traffic factors on pavement materials 90 3.3.1 Introduction 90 3.3.2 Low volume bitumen roads 91 3.3.3 High volume asphalt concrete pavements 95 3.3.4 Laboratory work 95 3.4 Non destructive pavement evaluation of high and low volume roads 99 3.4.1 General 99 3.4.2 Surface condition survey 101 - viii - 3.4.3 Deflection measurements 104 4 Methodology and data collection-ll: Case study: Airport flexible pavements 107 4.1 Introduction 107 4.2 Design, construction and pavement capacity 107 4.2.1 Design and construction 107 4.2.2 Pavement capacity 110 4.3 Visual inspection 111 4.3.1 Cracking and surface disintegration 111 4.3.2 Pavement distortion and ponding 112 4.3.3 Drainage system 112 4.3.4 General condition of the pavement 113 4.4 Preliminary investigations 113 4.4.1 Introduction 113 4.4.2 Runway 114 4.4.3 Taxiway 115 4.4.4 Overall assessment 115 4.5 Field and laboratory investigations 115 4.5.1 Introduction 115 4.5.2 Field sampling and testing for non-bituminous materials 115 4.5.3 Field sampling and testing for bituminous materials 119 4.6 Roughness and deflection measurements 121 4.6.1 Introduction 121 4.6.2 Roughness 121 4.6.3 Deflection measurements 122 5. Analyses and discussion of test results. 125 5.1 Introduction 125 5.1.1 General 125 5.1.2 Analyses of data 125 5.2 Subgrade, and non bituminous subbase and base materials 126 5.2.1 Geotechnical properties of Kenyan subgrade materials 126 5.2.2 Properties of the fine-grained soils with respect to pavement performance 132 - ix - 5.2.3 Properties of lateritic gravels with respect to base and subbase construction 133 5.3 Bituminous mixtures 135 5.3.1 Effect of binder content 135 5.3.2 Re-healing behaviour 138 5.3.3 Effect of temperature 140 5.3.4 Elastic modulus determination 142 5.4 Effect of the environmental factors on flexible pavements 143 5.4.1 Ageing of bituminous surfacings 144 5.4.2 Ageing of asphalt concrete pavements 146 5.4.3 Chemical composition and penetration 147 5.4.4 Effect of geographical location 148 5.4.5 Behaviour of non bituminous subbase and base materials 149 5.5 Pavement condition surveys 151 5.5.1 Rutting 151 5.5.2 Relationship of total rutting to cracking and roughness 152 5.5.3 Present serviceability index 154 5.6 The performance and remedial measures of the test roads 156 5.6.1 Performance 156 5.6.2 Proposed remedial measures 157 5.6.3 Proposed lower roughness criteria 160 5.7 Deflection data analysis 162 5.7.1 Determination of radius of curvature 162 5.7.2 Rutting at the experimental sites 164 5.7.3 Deflection variation with time 165 5.7.4 Deflection bowls 169 5.7.5 General observations 172 5.7.6 Structural performance of the test sections 173 5.8 Case airport flexible pavements investigations 178 5.8.1 Introduction 178 5.8.2 Materials below the bituminous layers and drainage considerations 179 5.8.3 Bituminous materials 182 5.8.4 Roughness test results 184 5.8.5 Runway deflection test results 185