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Field compaction methods
Field compaction methods
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  1. 1. Subgrade Soil
  2. 2. Desirable properties • Stability • Incompressibility • Permanency of strength • Minimum changes in volume and stability under adverse conditions of weather and ground water • Good drainage, and • Ease of compaction
  3. 3. • Soil should possess adequate stability or resistance to permanent deformation under loads and should possess resistance to weathering, thus retaining the desired sub grade support. • Minimum variation in volume will ensure minimum variation in differential expansion and differential strength values. • Good drainage is essential to avoid excessive moisture retention and to reduce the potential frost action. • Ease of compaction ensures highway dry density and strength under particular type and amount of compaction.
  4. 4. Soil Types • The wide range of soil types available as highway construction materials have made it obligatory on the part of the highway engineer to identify and classify different soils. • A survey of locally available materials and soil types conducted in India revealed wide variety of soil types, gravel, moorum and naturally occurring soft aggregates, which can be used in road construction. • Broadly, the soil types can be categorized as Laterite soil, Moorum / red soil, Desert sands, Alluvial soil, Clay including Black cotton soil.
  5. 5. Indian standard grain size soil classi cation system
  6. 6. • Gravel: These are coarse materials with particle size under 2.36 mm with little or no fines contributing to cohesion of materials. • Moorum: These are products of decomposition and weathering of the pavement rock. Visually these are similar to gravel except presence of higher content of fines.
  7. 7. • Silts: These are finer than sand, brighter in color as compared to clay, and exhibit little cohesion. When a lump of silty soil mixed with water, alternately squeezed and tapped a shiny surface makes its appearance, thus dilatancy is a specific property of such soil. • Clays: These are finer than silts. Clayey soils exhibit stickiness, high strength when dry, and show no dilatancy. Black cotton soil and other expansive clays exhibit swelling and shrinkage properties. Paste of clay with water when rubbed in between fingers leaves stain, which is not observed for silts. *Dilatancy- is the volume change observed in granular materials when they are subjected to shear deformations.
  8. 8. Tests on Soil • Sub grade soil is an integral part of the road pavement structure as it provides the support to the pavement from beneath. • The sub grade soil and its properties are important in the design of pavement structure. • The main function of the sub grade is to give adequate support to the pavement and for this the sub grade should possess sufficient stability under adverse climatic and loading conditions. Therefore, it is very essential to evaluate the sub grade by conducting tests.
  9. 9. Soil Compaction • Objects – Compaction of soil is a mechanical process by which the soil particles are constrained to be packed more closely together by reducing the air voids. – Soil compaction causes decrease in air voids and consequent increase in dry density resulting in increase in shearing strength. – Possibility of future settlement or compressibility decreases and also tendency for subsequent changes in moisture content decreases – Degree of compaction is measured by dry density
  10. 10. Subgrade soil Strength • Factors on which the strength characteristics of soil depend are – Soil type – Moisture content – Dry density – Internal structure of the soil – Type and mode of stress application
  11. 11. Evaluation of Soil strength • Shear tests – Direct Shear – Triaxial compression test – Unconfined compression test • Bearing tests – Plate bearing test • Penetration Tests – California Bearing Ratio
  12. 12. Shear Test • Shear tests are usually carried out on relatively small soil samples in the laboratory. In order to find out the strength properties of soil, a number of representative samples from different locations are tested. Some of the commonly known shear tests are direct shear test, triaxial compression test, and unconfined compression test.
  13. 13. Bearing tests • Bearing tests are loading tests carried out on sub grade soils in- situ with a load bearing area. The results of the bearing tests are influenced by variations in the soil properties within the stressed soil mass underneath and hence the overall stability of the part of the soil mass stressed could be studied.
  14. 14. Penetration tests • Penetration tests may be considered as small scale bearing tests in which the size of the loaded area is relatively much smaller and ratio of the penetration to the size of the loaded area is much greater than the ratios in bearing tests. The penetration tests are carried out in the field or in the laboratory.
  15. 15. California Bearing Ratio Test • California Bearing Ratio (CBR) test was developed by the California Division of Highway as a method of classifying and evaluating soil-sub grade and base course materials for flexible pavements. • CBR test, an empirical test, has been used to determine the material properties for pavement design. • Empirical tests measure the strength of the material and are not a true representation of the resilient modulus. • It is a penetration test wherein a standard piston, having an area of 3 in2 (or 50 mm diameter), is used to penetrate the soil at a standard rate of 1.25 mm/minute. • The pressure up to a penetration of 12.5 mm and it's ratio to the bearing value of a standard crushed rock is termed as the CBR.
  16. 16. California Bearing Ratio Test continued….. • In most cases, CBR decreases as the penetration increases. The ratio at 2.5 mm penetration is used as the CBR. • In some case, the ratio at 5 mm may be greater than that at 2.5 mm. If this occurs, the ratio at 5 mm should be used. • The CBR is a measure of resistance of a material to penetration of standard plunger under controlled density and moisture conditions. • The test procedure should be strictly adhered if high degree of reproducibility is desired. • The CBR test may be conducted in re-moulded or undisturbed specimen in the laboratory. The test is simple and has been extensively investigated for field correlations of flexible pavement thickness requirement.
  17. 17. Test Procedure • The laboratory CBR apparatus consists of a mould 150 mm diameter with a base plate and a collar, a loading frame and dial gauges for measuring the penetration values and the expansion on soaking. • The specimen in the mould is soaked in water for four days and the swelling and water absorption values are noted. The surcharge weight is placed on the top of the specimen in the mould and the assembly is placed under the plunger of the loading frame. • Load is applied on the sample by a standard plunger with dia of 50 mm at the rate of 1.25 mm/min. A load penetration curve is drawn. The load values on standard crushed stones are 1370 kg and 2055 kg at 2.5 mm and 5.0 mm penetrations respectively. • CBR value is expressed as a percentage of the actual load causing the penetrations of 2.5 mm or 5.0 mm to the standard loads mentioned above. Therefore,
  18. 18. • Two values of CBR will be obtained. If the value of 2.5 mm is greater than that of 5.0 mm penetration, the former is adopted. If the CBR value obtained from test at 5.0 mm penetration is higher than that at 2.5 mm, then the test is to be repeated for checking. • If the check test again gives similar results, then higher value obtained at 5.0 mm penetration is reported as the CBR value. The average CBR value of three test specimens is reported as the CBR value of the sample.
  19. 19. CBR Test Set up
  20. 20. Plate bearing test • Plate bearing test is used to evaluate the support capability of sub-grades, bases and in some cases, complete pavement. • Data from the tests are applicable for the design of both flexible and rigid pavements. • In plate bearing test, a compressive stress is applied to the soil or pavement layer through rigid plates relatively large size and the deflections are measured for various stress values. • The deflection level is generally limited to a low value, in the order of 1.25 to 5 mm and so the deformation caused may be partly elastic and partly plastic due to compaction of the stressed mass with negligible plastic deformation.
  21. 21. Plate bearing test continued…. • The plate-bearing test has been devised to evaluate the supporting power of sub grades or any other pavement layer by using plates of larger diameter. The plate-bearing test was originally meant to find the modulus of sub grade reaction in the Westergaard's analysis for wheel load stresses in cement concrete pavements.
  22. 22. Test Procedure of plate bearing test • The test site is prepared and loose material is removed so that the 75 cm diameter plate rests horizontally in full contact with the soil sub-grade. • The plate is seated accurately and then a seating load equivalent to a pressure of 0.07 kg/cm2 (320 kg for 75 cm diameter plate) is applied and released after a few seconds. The settlement dial gauge is now set corresponding to zero load. • A load is applied by means of jack, sufficient to cause an average settlement of about 0.25 cm. • When there is no perceptible increase in settlement or when the rate of settlement is less than 0.025 mm per minute (in the case of soils with high moisture content or in clayey soils) the load dial reading and the settlement dial readings are noted. • Deflection of the plate is measured by means of deflection dials; placed usually at one-third points of the plate near it's outer edge.
  23. 23. Test Procedure of plate bearing test • To minimize bending, a series of stacked plates should be used. • Average of three or four settlement dial readings is taken as the settlement of the plate corresponding to the applied load. Load is then increased till the average settlement increase to a further amount of about 0.25 mm, and the load and average settlement readings are noted as before. The procedure is repeated till the settlement is about 1.75 mm or more. • Allowance for worst subgrade moisture and correction for small plate size should be dealt properly. Calculation A graph is plotted with the mean settlement versus bearing pressure (load per unit area) as shown in Figure. • The pressure corresponding to a settlement is obtained from this graph. The modulus of subgrade reaction is calculated from the relation
  24. 24. Stone Aggregates • Functions o Bear different magnitudes of stresses due to the wheel loads stresses. o They should resist wear due to abrasive action of traffic o They should resist deterioration due to weathering
  25. 25. Desirable properties of Aggregates • Resistance to impact or toughness • Resistance to abrasion or hardness • Resistance to crushing or crushing strength • Resistance to weathering or durability • Resistance from getting polished or smooth/ slippery • Good shape factors to avoid too flaky and elongated particles of coarse aggregates • Good adhesion or affinity with bituminous materials in presence of water or less stripping of bitumen coating from the aggregates
  26. 26. Tests on Road aggregates • Aggregate impact test • Los Angeles Abrasion Test • Polished stone value test • Aggregate crushing Test • Shape test (Flakiness index, Elongation Index and Angularity number) • Soundness test or durability test or accelerated weathering test • Specific gravity test and water absorption test • Bitumen adhesion Test or Stripping Value test of aggregates
  27. 27. Bitumen adhesion test • Bitumen adheres well to all normal types of road aggregates provided they are dry and free from dust. In the absence of water there is practically no adhesion problem of bituminous construction. • Adhesion problem occurs when the aggregate is wet and cold. This problem can be dealt with by removing moisture from the aggregate by drying and increasing the mixing temperature. • Further, the presence of water causes stripping of binder from the coated aggregates. This problems occur when bitumen mixture is permeable to water. Several laboratory tests are conducted to arbitrarily determine the adhesion of bitumen binder to an aggregate in the presence of water. Static immersion test is one specified by IRC and is quite simple. • The principle of the test is by immersing aggregate fully coated with binder in water maintained at 400°C temperature for 24 hours. IRC has specified maximum stripping value of aggregates should not exceed 5%.
  28. 28. Tests on Aggregates and IS codes
  29. 29. Overview on Bitumen • Bituminous materials or asphalts are extensively used for roadway construction, primarily because of their excellent binding characteristics and water proof ng properties and relatively low cost. • Bituminous materials consists of bitumen which is a black or dark coloured solid or viscous cementitious substances consists chiefly high molecular weight hydrocarbons derived from distillation of petroleum or natural asphalt, has adhesive properties, and is soluble in carbon disulphide. • Tars are residues from the destructive distillation of organic substances such as coal, wood, or petroleum and are temperature sensitive than bitumen. • Bitumen will be dissolved in petroleum oils where unlike tar.
  30. 30. Requirements of Bitumen • The desirable properties of bitumen depend on the mix type and construction. In general, Bitumen should posses following desirable properties. – The bitumen should not be highly temperature susceptible: during the hottest weather the mix should not become too soft or unstable, and during cold weather the mix should not become too brittle causing cracks. – The viscosity of the bitumen at the time of mixing and compaction should be adequate. This can be achieved by use of cutbacks or emulsions of suitable grades or by heating the bitumen and aggregates prior to mixing. – There should be adequate affinity and adhesion between the bitumen and aggregates used in the mix.
  31. 31. Bitumen • It is obtained by fractional distillation of Crude Petroleum (in the presence of air) and it is the last stage end product (which is having maximum waste characteristic in this processing) as LPG-Gasoline- Petrol-Kerosene-Diesel-Lubricant Oil-Wax-Bitumen. • It is widely used in Road construction and also used for Priming • It have less affinity to water. • Also it is have less temperature susceptibility. • It have less free carbon content and it have more workability. Susceptibility: the state or fact of being likely or liable to be influenced or harmed by a particular thing. • Ex: "lack of exercise increases susceptibility to disease"
  32. 32. TAR • Coal Tar: It is obtained by destructive distillation of Coal and Wood (in the absence of air). • Earlier is was used as a Seal-Cot over pavements i.e. in Road Construction but because of several Research Papers it is found that it is harmful for using as a Road Construction material (it has Human Carcinogenic PAH’s) but however it is used in few States of Central and Southern America, in spite of being banned in other states. • So it is widely used in medicinal applications and Steel Manufacturing, which shows it’s great importance. • It have more affinity to water. • It has more temperature susceptibility. • It have more free carbon content and less workability due to high viscosity.
  33. 33. Different forms of Bitumen • Cutback Bitumen • Bitumen Emulsion • Bituminous Primers • Modified Bitumen
  34. 34. Cutback Bitumen • Normal practice is to heat bitumen to reduce its viscosity. In some situations preference is given to use liquid binders such as cutback bitumen. • In cutback bitumen suitable solvent is used to lower the viscosity of the bitumen. • From the environmental point of view also cutback bitumen is preferred. • The solvent from the bituminous material will evaporate and the bitumen will bind the aggregate. • Cutback bitumen is used for cold weather bituminous road construction and maintenance. • The distillates used for preparation of cutback bitumen are naphtha, kerosene, diesel oil, and furnace oil.
  35. 35. Different types of cutback bitumen • There are different types of cutback bitumen like – Rapid Curing (RC) – Medium Curing (MC) – Slow Curing (SC) • RC is recommended for surface dressing and patchwork. MC is recommended for premix with less quantity of fine aggregates. SC is used for premix with appreciable quantity of fine aggregates.
  36. 36. Rapid Curing • Rapid Curing Cutbacks (RC) These are bitumen, fluxed or cutbacks with a petroleum distillate such as naphtha or gasoline, which will rapidly evaporate after using in construction, leaving the bitumen binder. The grade of the RC cutback is governed by the proportion of the solvent used. The penetration value of residue from distillation upto 360°C of RC cutback bitumen 80 to 120.
  37. 37. Medium Curing • Medium Curing Cutbacks (MC) This bitumen fluxed to greater fluidity by blending with a intermediate boiling-point solvent like kerosene or light diesel oil. MC cutbacks evaporate relatively at slow rate because the kerosene-range solvents will not evaporate rapidly as the gasoline-range solvents used in the manufacture of RC cutbacks. MC products have good wetting properties and so satisfactory coating of fine grain aggregate and sandy soils is possible.
  38. 38. Slow Curing • Slow Curing Cutbacks (SC) These are obtained either by blending bitumen with high-boiling-point gas, oil or by controlling the rate of flow and temperature of the crude during the first cycle of refining. SC cutbacks or wood soils hardens or set way slowly as it is a semi volatile material.
  39. 39. Important Points • RC-2 means it is the rapid curing cutback of grade 2 • RC-0, MC-0, SC-0 are the lowest viscosity cutback bitumen
  40. 40. Bitumen Emulsion • Bitumen emulsion is a liquid product in which bitumen is suspended in a finely divided condition in an aqueous medium and stabilized by suitable material. • Normally cationic type emulsions are used in India. The bitumen content in the emulsion is around 60% and the remaining is water. • When the emulsion is applied on the road it breaks down resulting in release of water and the mix starts to set. • The time of setting depends upon the grade of bitumen. The viscosity of bituminous emulsions can be measured as per IS: 8887- 1995.
  41. 41. Types of Emulsion • Rapid setting: If the bitumen emulsion is intended to break rapidly, the emulsion is said to possess rapid-set quality and this type is used in surface dressing & penetration macadam. • Medium setting: Emulsion which does not break spontaneously on contact with stone but break during mixing or by fine mineral dust are MC. Used in premixing with coarse aggregate. • Slow setting: When specified type of emulsifying agent is used to make the emulsion relatively stable, they are called slow setting grade. Used in surface course along with the coarse aggregate. • Emulsifiers for road emulsions may be divided into four main groups: a) Anionic emulsifiers b) Cationic emulsifiers
  42. 42. Important Points • Bitumen emulsions are ideal binders for hill road construction. Where heating of bitumen or aggregates are difficult. • Rapid setting emulsions are used for surface dressing work. • Medium setting emulsions are preferred for premix jobs and patch repairs work. • Slow setting emulsions are preferred in rainy season.
  43. 43. Bituminous primers • In bituminous primer the distillate is absorbed by the road surface on which it is spread. The absorption therefore depends on the porosity of the surface. Bitumen primers are useful on the stabilized surfaces and water bound macadam base courses. Bituminous primers are generally prepared on road sites by mixing penetration bitumen with petroleum distillate.
  44. 44. • Modified Bitumen Certain additives or blend of additives called as bitumen modifiers can improve properties of Bitumen and bituminous mixes. • Bitumen treated with these modifiers is known as modified bitumen. • Polymer modified bitumen (PMB)/ crumb rubber modified bitumen (CRMB) should be used only in wearing course depending upon the requirements of extreme climatic variations. • The detailed specifications for modified bitumen have been issued by IRC: SP: 53-1999. • It must be noted that the performance of PMB and CRMB is dependent on strict control on temperature during construction.
  45. 45. Advantages of using modified bitumen • Lower susceptibility to daily and seasonal temperature variations • Higher resistance to deformation at high pavement temperature • Better age resistance properties • Higher fatigue life for mixes • Better adhesion between aggregates and binder • Prevention of cracking and reflective cracking
  46. 46. Tests on bitumen 1. Penetration test 2. Ductility test 3. Softening point test 4. Specific gravity test 5. Viscosity test 6. Flash and Fire point test 7. Float test 8. Water content test 9. Loss on heating test
  47. 47. Bitumen tests Sl. No. Tests Test Method Limits Requirements 1 Penetration Test IS: 1203 - 80-100 2 Ductility Test IS: 1208 Min 75 3 Softening Point Test IS: 1205 Min 40 4 Specific Gravity IS: 73-1961 Min 0.97-1.02 5 Flash Point IS: 1209 Min 220
  48. 48. Crushing test
  49. 49. Impact test
  50. 50. Abrasion test
  51. 51. Flakiness and elongation Index
  52. 52. Specific Gravity of Aggregates
  53. 53. Requirements of Bitumen • The bitumen should not be highly temperature susceptible: during the hottest weather the mix should not become too soft or unstable, and during cold weather the mix should not become too brittle causing cracks. v • The viscosity of the bitumen at the time of mixing and compaction should be adequate. This can be achieved by use of cutbacks or emulsions of suitable grades or by heating the bitumen and aggregates prior to mixing. • There should be adequate affinity and adhesion between the bitumen and aggregates used in the mix.
  54. 54. Tests conducted on bitumen • Penetration test • Ductility test • Viscosity test • Float test • Specific gravity test • Softening point test • Flash and fire point test • Solubility test • Spot test • Loss on heating test • Water content test
  55. 55. Viscosity of bitumen
  56. 56. Softening Point test
  57. 57. Specific gravity test
  58. 58. Penetration test
  59. 59. Thin Film oven test
  60. 60. Ductility test
  61. 61. Flash and fire point test • The flash point of a material is the lowest temp at which the vapour of a substance momentarily takes fire in the form of a flash under specified condition of test. • Fire point is the lowest temp at which the material gets ignited and burns under specified condition of test.
  62. 62. Questions • The minimum ductility value specified by BIS for bitumen is 1. 50 cm 2. 25 cm 3. 75 cm 4. 100 cm • The allowable maximum water content in bitumen should not be more than 1. 2%by weight 2. 0:2% by weight 3. 2:5% by weight 4. 5% by weight
  63. 63. 1. IRC has specified the maximum value of stripping value of bitumen not to exceed (a) 2% (b) 3% (c) 4% (d) 5% 2. Which property of aggregate is tested by conducting aggregate impact test? (a) Durability (b) Hardness (c) Toughness (d) Porosity
  64. 64. • The load value on standard crushed stone for 2.5mm penetration in CBR test is • (a) 1370kgp • (b) 1730 kg • (c) 2055kg • (d) 1500kg • 2. Modulus of subgrade reaction is • (a) K = P/2.15 kg/cm2 /cm • (b) K = P/0.125 kg/cm2 /cm • (c) K = P2 /2.15 kg/cm2 /cm • (d) K = P/2.5 kg/cm2 /cm
  65. 65. Evolution of road surface • Unsurfaced earthen roads, or cart-track • Unsurfaced earthen roads upgrades with natural soil from borrow pits and attention to drainage, and compaction is by traffic • Dry aggregate and sand-clays mix, in which the former act as wear resistant and the latter as natural binder • Water-bound macadam, the above constituents, mixed together (pre-mix or in-situ) with water and compacted to improve the strength • Oiled roads, introduced to reduce dust by bitumen stabilized soils • Seal coat: the base course is protected from traffic and moisture by sealing the surface with a thin lm of bitumen aggregate mix, which is structurally strong surface for pneumatic-tyred traffic. This is provided on firm and smooth base course after a tack coat using cutback bitumen or bitumen emulsions with a penetration of 5 mm.
  66. 66. • Asphaltic concrete: Traffic and the axle configuration are increasing very much which raises demand for the new type of pavement which can meet the above requirements. The asphaltic concrete is one which is the high dense graded premix and it is termed as the highest quality pavement surface course. • Bitumen mix or asphalt mix overlays of minimum 20 - 40 mm to as high as 300 - 500 mm or even more.
  67. 67. Objectives of mix design • The objective of the mix design is to produce a bituminous mix by proportionating various components so as to have – sufficient bitumen to ensure a durable pavement, – sufficient strength to resist shear deformation under traffic at higher temperature, – sufficient air voids in the compacted bitumen to allow for additional compaction by traffic, – sufficient workability to permit easy placement without segregation, – sufficient flexibility to avoid premature cracking due to repeated bending by traffic, and – sufficient flexibility at low temperature to prevent shrinkage cracks.
  68. 68. Constituents of a mix • Coarse aggregates: Offer compressive and shear strength and shows good interlocking properties. E.g. Granite • Fine aggregates: Fills the voids in the coarse aggregate and stiffens the binder. E.g. Sand, Rock dust • Filler: Fills the voids, stiffens the binder and offers permeability. E.g. Rock dust, cement, lime • Binder: Fills the voids, cause particle adhesion and gluing and offers impermeability. E.g. Bitumen, Asphalt, Tar
  69. 69. Pavements
  70. 70. Flexible Pavement • Flexible pavements are so named because the total pavement structure defects, or exes, under loading. • A flexible pavement structure is typically composed of several layers of materials. • Each layer receives loads from the above layer, spreads them out, and passes on these loads to the next layer below. Thus the stresses will be reduced, which are maximum at the top layer and minimum on the top of subgrade. • In order to take maximum advantage of this property, layers are usually arranged in the order of descending load bearing capacity with the highest load bearing capacity material (and most expensive) on the top and the lowest load bearing capacity material (and least expensive) on the bottom.
  71. 71. Flexible and Rigid Pavement
  72. 72. Rigid Pavement • As the name implies, rigid pavements are rigid i.e, they do not ex much under loading like flexible pavements. • They are constructed using cement concrete. • In this case, the load carrying capacity is mainly due to the rigidity ad high modulus of elasticity of the slab (slab action). • H. M. Westergaard is considered the pioneer in providing the rational treatment of the rigid pavement analysis
  73. 73. Difference between Flexible and Rigid Pavement
  74. 74. Difference between Flexible and Rigid Pavement
  75. 75. Difference between Flexible and Rigid Pavement