Roads Department - Government of Botswana

Roads Department
TABLE OF CONTENTS
1. INTRODUCTION ...............................................................................................................................................9
1.1 Background .................................................................................................................................................9
1.2 Purpose and Scope of Guideline .................................................................................................................9
1.3 Structure of the Guideline ...........................................................................................................................9
2. OCCURRENCE AND CHARACTERISTICS................................................................................................11
2.1 General ......................................................................................................................................................11
2.2 Salt Damage Occurrence in Botswana .....................................................................................................12
2.3 Salt Damage World-wide ..........................................................................................................................14
2.3.1 India ................................................................................................................................................14
2.3.2 Australia..........................................................................................................................................14
2.3.3 Southern Africa ...............................................................................................................................15
2.3.4 Middle East .....................................................................................................................................16
2.3.5 North Africa ....................................................................................................................................16
2.3.6 North America.................................................................................................................................16
2.4 International Experience on Salt Damage, Limits and Preventative Measures.........................................16
2.4.1 Thickness of Surfacing/Permeability Ratio ....................................................................................17
2.4.2 Bituminous Surfacing Layers..........................................................................................................17
2.4.3 Brooming ........................................................................................................................................17
2.4.4 Immediate cover..............................................................................................................................17
2.4.5 Prevention of Moisture Rise - Cut Off............................................................................................18
2.4.6 Relevance of Published Literature to Botswana .............................................................................18
2.5 Factors Influencing Salt Damage................................................................................................................18
2.5.1 Climate............................................................................................................................................18
2.5.2 Geology and Hydrogeology............................................................................................................18
2.5.3 Materials Characteristics.................................................................................................................18
2.5.4 Pavement Surfacing Design ............................................................................................................21
2.5.5 Construction Practice ......................................................................................................................21
2.6 Appearance and Identification...................................................................................................................22
2.6.1 Damage to Primes ...........................................................................................................................22
2.6.2 Damage to Permanent Surfacings...................................................................................................22
2.7 Summary of Physico-chemical Influences on Salt Damage ........................................................................22
3. LABORATORY AND FIELD TESTING FOR SALT ...................................................................................25
3.1 General ......................................................................................................................................................25
3.2 Soil and Water Sampling...........................................................................................................................25
3.2.1 Water Samples.................................................................................................................................26
3.2.2 Soil Samples....................................................................................................................................26
3.3 Field Salt Content Tests.............................................................................................................................26
3.3.1 Field Electrical Conductivity test....................................................................................................26
3.3.2 Oral Testing (Taste).........................................................................................................................27
4 Guide to the Prevention and Repair of Salt Damage to Roads and Runways