Types of Bituminous Road And Construction Overview Overview Bituminous materials or asphalts are extensively used for roadway construction, primarily because of their excellent binding characteristics and water proofing 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. Bituminous Road Bitumenous road is a road construct by using bitumenous. It also called flexible pavment because it change its shape according to nature of load and sub base. This type of pavment has four layer namey, sub grade (bottom most), sub base, base and wearing surface (top most). Thickness of layer decrease normely from bottom to top. It is cheaper than concrete pavment. Concrete pavement is anather type, that also called rigid pavement. It has only two layer. Presently concrete pavments are more popular in city areas while bitumenous pavment still constructed in highways. What is bituminous road? A bituminous road is a road that has been covered with bitumen. If this is wrong, could I please have the correct Dept Of Civil Engg.. Page 1
Transcript
Types of Bituminous Road And Construction Overview
Overview
Bituminous materials or asphalts are extensively used for roadway construction, primarily because of their excellent binding characteristics and water proofing 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.
Bituminous RoadBitumenous road is a road construct by using bitumenous. It also called flexible
pavment because it change its shape according to nature of load and sub base. This type of pavment has four layer namey, sub grade (bottom most), sub base, base and wearing surface (top most). Thickness of layer decrease normely from bottom to top. It is cheaper than concrete pavment.
Concrete pavement is anather type, that also called rigid pavement. It has only two layer. Presently concrete pavments are more popular in city areas while bitumenous pavment still constructed in highways.
What is bituminous road? A bituminous road is a road that has been covered with bitumen. If this is wrong,
could I please have the correct answer. A bitumen road is different from tar road. bitumen is extracted from crude... What do road runners eat?
Roadrunners are omnivores, but mostly eat meat. They eat lizards, mice, snakes, other birds, bugs, millipedes and even RATTLESNAKES!!!!!!!!!I thought this question was about road road runners, not...
Bituminous Surface Types
Dept Of Civil Engg.. Page 1
Types of Bituminous Road And Construction Overview
The asphalt surface of the roadway consists of the wearing course placed over the sub-grade or on a prepared base. The basic asphalt surface type classifications are bituminous surfaces including surface treatments, bituminous mats, and asphaltic concrete decks or pavements.
Bituminous surfaces are classified according to the type and makeup of the wearing surface. All wearing surfaces are placed on some type of prepared base, and the thickness and stability of this base usually has a direct influence on the life of the surface. There are three main types of surfaces.
LOW-TYPE BITUMINOUS SURFACES
Low-type bituminous surfaces are those produced by surface treatment with light road oils or liquid bituminous materials such as oil earth, oil aggregate, seal coats, and leveling courses. Each surface treatment being less than 1 in. in thickness.
INTERMEDIATE-TYPE BITUMINOUS SURFACES Intermediate-type bituminous surfaces consists of a plant-mixed machine laid surface. The thickness of the surface course is usually greater than in the low-type classes, and may consist of one or more bituminous courses. The base course may be of the same material as described for the low-type bituminous surface.
HIGH-TYPE BITUMINOUS SURFACES
High-type bituminous surfaces consist of asphaltic concrete (dense and open graded) mixes, machine laid. This type of surface, because of traffic loads, usually require a more substantial base than low and intermediate types. The base may be of either rigid or non-rigid design. The surface wearing course is usually 1 1/4 in. or more in thickness.
Asphalt Surface and Roadbed Widths
Asphalt surface and roadbed widths shall be maintained according to their constructed widths. Uniformity in width is especially important at district and maintenance area boundaries. Efforts must be made to prevent abrupt changes in widths at these and other locations.
Low type bituminous surfaces are normally built and resurfaced by maintenance forces, and it is important that uniform surface width be established.
Surface width of high type bituminous surfaces is fairly well established when constructed. At some locations spot widening may be desirable to improve safety.
Dept Of Civil Engg.. Page 2
Types of Bituminous Road And Construction Overview
Roadbed width, which includes the width of the roadbed and shoulders, should not exceed current design standards without approval from the District Engineer. In some cases, it may be desirable and economical to widen roadbed widths during heavy ditching operations, and the widening of roadbeds less than 24 ft. in width is encouraged. Spot construction of bridges and culverts to new design standards may also make widening of the remaining portion of the roadbed desirable. The possible effect on traffic safety must be taken into consideration prior to widening any surface or roadbeds that have numerous bridges or culverts that limit the overall width. In no case shall surface or roadbed widths be decreased from the widths constructed or reconstructed. For more information regarding lane and shoulder widths, see Typical Section Elements for Roadways.
Types of Bituminous Materials
A working knowledge of the characteristics of all bituminous products employed in maintenance operations should be understood for satisfactory and efficient maintenance of bituminous surfaces. Quite as important as the type of bitumen to be used in surface maintenance is the selection of an aggregate having desirable qualities such as proper size and gradation, wearing qualities, adhesive quality, cleanliness, etc.
All bituminous surfaces should be repaired with materials best suited for the job. All materials used shall meet standard specifications unless otherwise approved by the State Maintenance Engineer.
AGGREGATE
Aggregate for bituminous surfaces shall meet standard specifications unless otherwise approved. Modification should be held to a minimum, but may be approved if justified and necessary. For specific jobs, a specific aggregate, limestone or gravel, may be approved, otherwise consideration must be given to both limestone or gravel as available. In addition, slag, trap rock and lightweight aggregates (haydite) may be used in special applications.
ASPHALT
Asphalt is a natural constituent of most petroleums in which it exists in solution. The crude petroleum is refined to separate the various fractions and recover the asphalt. Natural deposits of asphalts are also found in various parts of the world, some practically free from extraneous matter. Natural deposits in which asphalt occurs within a porous rock structure are known as rock asphalts.
All asphalt used for maintenance operations is refined from petroleum and must meet standard specifications. It is produced in a variety of types and grades with the three major types being asphalt cements or penetration asphalts, liquid asphalt, and asphalt
Dept Of Civil Engg.. Page 3
Types of Bituminous Road And Construction Overview
emulsions. Liquid asphaltic products are prepared by cutting back or blending asphalt cements with petroleum distillates, and asphalt emulsions are prepared by blending (homogenizing) asphalt cement with water.
1. PENETRATION ASPHALTS
These are asphalt cements with varying degrees of hardness or consistency. Penetration is determined by a penetration test which measures the distance a standard needle will penetrate vertically into a sample of asphalt under known conditions of temperature, loading, and time. It is evident that the softer the asphalt cement, the higher the penetration will be. Penetration asphalts are listed in Standard Specifications as 40-50, 60-70, 85-100, 120-150 and 200-300 penetration.
2. LIQUID ASPHALT MATERIALS
Liquid asphaltic materials are produced by cutting back or blending asphalt cement with petroleum distallates or by emulsifying with water. The liquid asphalt materials used are
a. RC Cut-Back Asphalts, Rapid Curing Type This material is produced by cutting back asphalt cement with naptha or gasoline-type distillate. This distillate evaporates more rapidly than kerosene, and this type of cut-back is known as rapid curing. RC cut-backs are often used for seal coat work. Lighter grades are also used for tack, fly, and prime coats. AASHTO designations are RC 70, 250, 800 and 3,000.
b. MC Cut-Back Asphalts Medium Curing Type
This material is produced by cutting back asphalt cement with kerosene type material. The presence of kerosene makes the asphalt workable in a relatively low temperature. The kerosene evaporates slowly when exposed to air and to heat leaving the asphalt cement intact. Medium curing cut-backs are commonly used for maintenance repair work, maintenance leveling course (road mix or pre-mix) and cold patch mix. AASHTO designations are MC 30, 70, 250, 800 and 3,000.
c. SC Cut-Back Asphalt Slow Curing Type or Road Oils
This material may be asphaltic residual oil which contains little or no volatile portions, or it may be a blend of asphalt cement and residual oil. The slow curing liquid asphalts are used mostly for dust alleviation work. The lighter grades have relatively poor binding
Dept Of Civil Engg.. Page 4
Types of Bituminous Road And Construction Overview
characteristics and do not form a hard mat when used for dust alleviation work. AASHTO designations are SC-70, 250, 800 and 3,000. The rapid curing and slow curing asphalts all come in four grades while the medium asphalts come in five grades. The higher the indicating number, the greater the percent of asphaltic cement and more viscous the material.
3. ASPHALTIC EMULSIONS Emulsified asphalt may be either anionic (negative) charged asphalt globules or cationic (positive) charged clobules, types depending on emulsified agents. The major types are RS, MS, and SS indicating rapid, medium, or slow setting.
COMMERCIAL PLANT MIX BLADE MIX - Blade mix material is normally used for all patching on low-type bituminous surface due to the economy. It shall be mixed on "mixing boards" off the roadway surface if large quantities are desired for future use as patch material. Blade mix materials for blade seals, leveling courses, or spot decks are normally mixed on the roadway at the time needed.
PRE-COATED AGGREGATE Pre-coated aggregate or "half-mix" for use during adverse weather or ground conditions has proved successful. It is produced by blade mixing the aggregate with just a sufficient quantity of asphalt to precoat the aggregate and exclude moisture until such time as it is needed for sealing or patching. It is used as is for sealing or with additional asphalt added, just prior to use, for patch material.
SAND-ASPHALT MIX A sand-asphalt mix called "Black Annie" or "Hannibal Rock Asphalt" has proved very useful for certain types of patching on asphaltic concrete and concrete surfaces. It can also be used for filling spalled or open joints and cracks but not for expansion joints. It is not recommended for deep patches, unless larger aggregate is substituted for a portion of the sand, or for use on low type surfaces due to the cost. This mix is prepared as follows: Materials: 1000 lbs. - Sand 250 lbs. - Agricultural lime 1/2 sack - Portland cement 10-12 gallons - MC-250 asphalt
The sand, lime, and cement must be dry and mixed thoroughly in a pugmill or by hand. MC-250 is added at pouring temperature and the exact quantity will depend on working temperature. Mixing is continued until complete. The material may be used immediately or place in a stockpile for future use. Stockpiling for future use will require reheating. 470.4 Changing Grades of Asphalt
It is necessary at times to change the grade of asphalt in the field for emergency use. While this practice is not recommended for extensive use, the percentage or quantities of
Dept Of Civil Engg.. Page 5
Types of Bituminous Road And Construction Overview
kerosene to add to the available grade may be determined from the following formula or table. Where: X = Percent of kerosene to be added 100 - X = Percent of available grade to be added a = Percent kerosene in desired grade b = Percent kerosene in available grade. Note: a and b are determined from residue percentages given in Standard Specifications.
The quantities to mix as obtained by use of this formula for reducing MC-3000, MC-800 and MC-250 to lower grades are as follows: MC-3000 gal. Kerosene gal. Result 94 6 100 gal. MC-800 84 16 100 gal. MC-250 69 31 100 gal. MC-70 62 38 100 gal. MC-30 a MC-800 gal. Kerosene gal. Result 89 11 100 gal. MC-250 73 27 100 gal. MC-70 67 33 100 gal. MC-30 a MC-250 gal. Kerosene gal. Result 82 18 100 gal. MC-70 75 25 100 gal. MC-30
Types of Bituminous Failures
All bituminous surface failures with the exception of raveling and oxidation can be attributed to a base or subgrade failure, either because of improper materials, poor construction, under-design, or the influence of moisture.
Breaks, potholes, and settlements in the surface may be due to inadequate base or to continued lack of support due to moisture in the base and subgrade. Edge failures often result from a reduced thickness of the base and deterioration of the base along the shoulder due to porous shoulders, inadequate drainage, and lack of lateral support. High shoulders or the presence of a traffic rut at the edge of the surface may be contributing causes.
Slippery, bleeding and fat surfaces are caused by an excess of bituminous material and a dense surface texture. The excess may result from excessive bituminous material applied during construction, the loss of aggregate due to dampness and cold temperatures during application, the bleeding of fat patches, or stripping of aggregate material.
Ruts, corrugations, and other distortions of the surface may be due to an unstable or fat surface, inadequate base, or a base permeated by moisture.
Dept Of Civil Engg.. Page 6
Types of Bituminous Road And Construction Overview
Cracking may be due to brittleness of the surface, expansion and contraction as temperatures change or the presence of moisture in a base or subgrade that destroys stability.
Raveling usually results from poor aggregate which degrades badly, from lack of sufficient asphalt binder, wrong class of bituminous material, or from a dry oxidated surface.
Oxidized surfaces usually result from years of use and exposure to the elements.
Bituminous Surface MaintenanceBituminous surfaces require continuous inspection so that preventive or corrective
maintenance may be initiated without delay. This is of primary importance during the winter and early spring when low type bituminous surfaces with negligible bases are subjected to freeze-thaw cycles and after periods of wet weather. Every advantage should be taken of favorable weather during such periods to carry out repairs or preventive maintenance. Methods of maintenance will vary with the type of surface and base and type of failure but in all cases the quality and timing of maintenance will have a direct bearing on the life of the surface. Priorities for maintenance should be based on traffic volumes and degree of failure.
Traffic Controls for Bituminous RepairsTraffic controls for bituminous repairs shall be according to EPG 616.23 Traffic
Control for Field Operations. All standard signing shall be in place before operations start and shall remain in place as long as any hazards or inconvenience for traffic exists.
All windrows of premix left on the roadway edge or adjacent to the roadway shall be marked at intervals with required signing if left overnight. The windrows should be vented to avoid ponding of water on the roadway surface.
Extreme care must be exercised by all crew members, particularly by equipment operators, while working near at-grade railroad crossings. Working near at-grade railroad crossings shall be in accordance with department requirements. Coordination with the specific railroad company responsible for track maintenance is required to ensure that the tracks are checked for damage and the flange ways cleaned of debris if necessary.
Operations shall be coordinated between areas and districts in order to complete blade seal and leveling course operations on specific routes to minimize the disruption to the traveling public. Every effort shall be made to complete work on major through routes or on heavy traffic sections as soon as possible. Consideration should be given to local activities such as fairs and carnivals and seasonal tourist attractions when scheduling major bituminous repair work.
Dept Of Civil Engg.. Page 7
Types of Bituminous Road And Construction Overview
Maintenance LimitationsThe definitions and limitations for various types of bituminous surface repairs
have been established.
Spot sealing and spot patching consists of spot sealing or patching small areas, and is to be done by Maintenance Forces.
Maintenance leveling course consists of mixing and laying from 3.0 cubic yards and not to exceed 5.0 cubic yards of aggregate per station. Work is to be done by maintenance forces.
Seal coats consist of applying asphalt to the roadway surface at a specified rate and covering the asphalt with aggregate. All continuous seal coats will be contracted and financed from the District Maintenance Budget.
Contract leveling course is based on 650 tons per mile, regardless of the width. For a route to qualify, it must meet the following: 1. A bituminous surface route without a constructed base. 2. Have a minimum of 225 AADT. 3. Have sufficient thickness to support this type surface and be relatively free of base failures. 4. Bituminous decks generally financed from Construction funds should be considered for improvement of bituminous surfaced routes on a constructed base.
The maintenance of bituminous surfaces includes maintenance of distorted surface and fat or slippery areas, sealing or pouring of cracks, priming and tacking to provide a bond for added surfacing, spot seal coating to correct dry oxidized gravel, cracked, or slick surfaces, and fly or fog coating.
Production of Bitumen
Bitumen is the residue or by-product when the crude petrolium is refined. A wide variety of refinery processes, such as the straight distillation process, solvent extraction process etc. may be used to produce bitumen of different consistency and other desirable properties. Depending on the sources and characteristics of the crude oils and on the properties of bitumen required, more than one processing method may be employed.
Vacuum steam distillation of petroleum oils
In the vacuum-steam distillation process the crude oil is heated and is introduced into a large cylindrical still. Steam is introduced into the still to aid in the vaporization of the more volatile constituents of the petroleum and to minimise decomposition of the distillates and residues. The volatile constituents are collected, condensed, and the
Dept Of Civil Engg.. Page 8
Types of Bituminous Road And Construction Overview
various fractions stored for further refining, if needed. The residues from this distillation are then fed into a vacuum distillation unit, where residue pressure and steam will further separate out heavier gas oils. The bottom fraction from this unit is the vacuum-steam-refined asphalt cement. The consistency of asphalt cement from this process can be controlled by the amount of heavy gas oil removed. Normally, asphalt produced by this process is softer. As the asphalt cools down to room temperature, it becomes a semi solid viscous material.
Different forms of bitumen
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. There are different types of cutback bitumen like rapid curing (RC), medium curing (MC), and 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.
Bitumen Emulsion
Bitumen emulsion is a liquid product in which bitumen is suspended in a finely divided condition in an aqueous medium and stabilised 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. Three types of bituminous emulsions are available, which are Rapid setting (RS), Medium setting (MS), and Slow setting (SC). 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.
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 stabilised surfaces and water bound macadam base courses. Bituminous primers are generally prepared on road sites by mixing penetration bitumen with petroleum distillate.
Dept Of Civil Engg.. Page 9
Types of Bituminous Road And Construction Overview
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.
The advantages of using modified bitumen are as follows
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 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.
Tests on Bitumen
There are a number of tests to assess the properties of bituminous materials. The following tests are usually conducted to evaluate different properties of bituminous materials. Penetration test. Ductility test. Softening point test. Specific gravity test. Viscosity test. Flash and Fire point test.Float test. Water content test. Loss on heating test.
Penetration test
Dept Of Civil Engg.. Page 10
Types of Bituminous Road And Construction Overview
It measures the hardness or softness of bitumen by measuring the depth in tenths of a millimeter to which a standard loaded needle will penetrate vertically in 5 seconds. BIS had standardised the equipment and test procedure. The penetrometer consists of a needle assembly with a total weight of 100g and a device for releasing and locking in any position. The bitumen is softened to a pouring consistency, stirred thoroughly and poured into containers at a depth at least 15 mm in excess of the expected penetration. The test should be conducted at a specified temperature of 25 C. It may be noted that penetration value is largely influenced by any inaccuracy with regards to pouring temperature, size of the needle, weight placed on the needle and the test temperature. A grade of 40/50 bitumen means the penetration value is in the range 40 to 50 at standard test conditions. In hot climates, a lower penetration grade is preferred. The Figure 4.1 shows a schematic Penetration Test setup.
Figure 1: Penetration Test SetupDuctility test Ductility is the property of bitumen that permits it to undergo great deformation or elongation. Ductility is defined as the distance in cm, to which a standard sample or briquette of the material will be elongated without breaking. Dimension of the briquette thus formed is exactly 1 cm square. The bitumen sample is heated and poured in the mould assembly placed on a plate. These samples with moulds are cooled in the air and then in water bath at 27 C temperature. The excess bitumen is cut and the surface is leveled using a hot knife. Then the mould with assembly containing sample is kept in water bath of the ductility machine for about 90 minutes. The sides of the moulds are removed, the clips are hooked on the machine and the machine is operated. The distance up to the point of breaking of thread is the ductility value which is reported in cm. The ductility value gets affected by factors such as pouring temperature, test temperature, rate of pulling etc. A minimum ductility value of 75 cm has been specified by the BIS. Figure 4.2 shows ductility moulds to be filled with bitumen.
Types of Bituminous Road And Construction Overview
Figure 2: Ductility Test
Softening point test
Softening point denotes the temperature at which the bitumen attains a particular degree of softening under the specifications of test. The test is conducted by using Ring and Ball apparatus. A brass ring containing test sample of bitumen is suspended in liquid like water or glycerin at a given temperature. A steel ball is placed upon the bitumen sample and the liquid medium is heated at a rate of 5 C per minute. Temperature is noted when the softened bitumen touches the metal plate which is at a specified distance below. Generally, higher softening point indicates lower temperature susceptibility and is preferred in hot climates. Figure 4.3 shows Softening Point test setup.
Figure 3: Softening Point Test Setup
Specific gravity test
In paving jobs, to classify a binder, density property is of great use. In most cases bitumen is weighed, but when used with aggregates, the bitumen is converted to volume using density values. The density of bitumen is greatly influenced by its chemical composition. Increase in aromatic type mineral impurities cause an increase in specific gravity.
Types of Bituminous Road And Construction Overview
The specific gravity of bitumen is defined as the ratio of mass of given volume of bitumen of known content to the mass of equal volume of water at 27 C. The specific gravity can be measured using either pycnometer or preparing a cube specimen of bitumen in semi solid or solid state. The specific gravity of bitumen varies from 0.97 to 1.02.
Viscosity test
Viscosity denotes the fluid property of bituminous material and it is a measure of resistance to flow. At the application temperature, this characteristic greatly influences the strength of resulting paving mixes. Low or high viscosity during compaction or mixing has been observed to result in lower stability values. At high viscosity, it resist the compactive effort and thereby resulting mix is heterogeneous, hence low stability values. And at low viscosity instead of providing a uniform film over aggregates, it will lubricate the aggregate particles. Orifice type viscometers are used to indirectly find the viscosity of liquid binders like cutbacks and emulsions. The viscosity expressed in seconds is the time taken by the 50 ml bitumen material to pass through the orifice of a cup, under standard test conditions and specified temperature. Viscosity of a cutback can be measured with either 4.0 mm orifice at 25 C or 10 mm orifice at 25 or 40 C.
Figure 4: Viscosity Test
Flash and fire point test
At high temperatures depending upon the grades of bitumen materials leave out volatiles. And these volatiles catches fire which is very hazardous and therefore it is essential to qualify this temperature for each bitumen grade. BIS defined the flash point as the temperature at which the vapour of bitumen momentarily catches fire in the form of flash under specified test conditions. The fire point is defined as the lowest temperature under specified test conditions at which the bituminous material gets ignited and burns.
Dept Of Civil Engg.. Page 13
Types of Bituminous Road And Construction Overview
Float test
Normally the consistency of bituminous material can be measured either by penetration test or viscosity test. But for certain range of consistencies, these tests are not applicable and Float test is used. The apparatus consists of an aluminum float and a brass collar filled with bitumen to be tested. The specimen in the mould is cooled to a temperature of 5 C and screwed in to float. The total test assembly is floated in the water bath at 50 C and the time required for water to pass its way through the specimen plug is noted in seconds and is expressed as the float value.
Water content test
It is desirable that the bitumen contains minimum water content to prevent foaming of the bitumen when it is heated above the boiling point of water. The water in a bitumen is determined by mixing known weight of specimen in a pure petroleum distillate free from water, heating and distilling of the water. The weight of the water condensed and collected is expressed as percentage by weight of the original sample. The allowable maximum water content should not be more than 0.2% by weight.
Loss on heating test
When the bitumen is heated it loses the volatility and gets hardened. About 50gm of the
sample is weighed and heated to a temperature of 163 C for 5hours in a specified oven designed for this test. The sample specimen is weighed again after the heating period and loss in weight is expressed as percentage by weight of the original sample. Bitumen used in pavement mixes should not indicate more than 1% loss in weight, but for bitumen having penetration values 150-200 up to 2% loss in weight is allowed.
Table 1: Tests for Bitumen with IS codes
Type of test Test Method
Penetration Test IS: 1203-1978
Ductility test IS: 1208-1978
Softening Point test IS: 1205-1978
Specific gravity test IS: 1202-1978
Viscosity test IS: 1206-1978
Flash and Fire Point test IS: 1209-1978
Float Test IS: 1210-1978
Determination of water content IS: 1211-1978
Determination of Loss on heating IS:1212-1978
Dept Of Civil Engg.. Page 14
Types of Bituminous Road And Construction Overview
Summary Requirements of bitumen as a binding material and its different forms were discussed. Various tests conducted on bitumen to assess its consistency, gradation, viscosity, temperature susceptibility, and safety. Standard test procedures on bitumen were also covered in this chapter.
A road in the process of being resurfacedRoad surface (British English) or pavement (American English) is the durable surface material laid down on an area intended to sustain vehicular or foot traffic, such as a road or walkway. In the past cobblestones and granite setts were extensively used, but these surfaces have mostly been replaced by asphalt or concrete. Such surfaces are frequently marked to guide traffic. Today, permeable paving methods are beginning to be used for low-impact roadways and walkways.Contents[hide]1 Metalling 2 Asphalt 3 Concrete 4 Composite surfaces 5 In-place recycling 6 Bituminous Surface Treatment (BST) 6.1 Thin membrane surface 6.2 Granular 6.3 Otta seal 7 Other surfaces 8 Acoustical implications 9 Surface deterioration 10 See also 11 References 12 External links
Types of Bituminous Road And Construction Overview
The term road metal refers to the broken stone or cinders used in the construction or repair of roads or railways,[1] and is derived from the Latin metallum, which means both "mine" and "quarry".[2] Metalling is known to have been used extensively in the construction of roads by soldiers of the Roman Empire (see Roman road) but a limestone-surfaced road, thought to date back to the Bronze Age, has been found in Britain.[3]
Metalling has had two distinct usages in road surfacing. The term originally referred to the process of creating a gravel roadway. The route of the roadway would first be dug down several feet and, depending on local conditions; French drains may or may not have been added. Next, large stones were placed and compacted, followed by successive layers of smaller stones, until the road surface was composed of small stones compacted into a hard, durable surface. "Road metal" later became the name of stone chippings mixed with tar to form the road surfacing material tarmac. A road of such material is called a "metalled road" in Britain, a "paved road" in the USA, or a "sealed road" in Australia.[4]
Asphalt
Close up of asphalt on a drivewayAsphalt (specifically, asphalt concrete) has been widely used since 1920–1930. The viscous nature of the bitumen binder allows asphalt concrete to sustain significant plastic deformation, although fatigue from repeated loading over time is the most common failure mechanism. Most asphalt surfaces are built on a gravel base, which is generally at least as thick as the asphalt layer, although some 'full depth' asphalt surfaces are built directly on the native subgrade. In areas with very soft or expansive subgrades such as clay or peat, thick gravel bases or stabilization of the subgrade with Portland cement or lime may be required. Polypropylene and polyester materials have also been used for this purpose [5] and in some northern countries, a layer of polystyrene boards have been used to delay and minimize frost penetration into the subgrade.[6]
Depending on the temperature at which it is applied, asphalt is categorized as hot mix asphalt (HMA), warm mix asphalt, or cold mix asphalt. Hot mix asphalt is applied at temperatures over 300 F with a free floating screed. Warm mix asphalt is applied at temperatures of 200 to 250 degrees F, resulting in reduced energy usage and emissions of volatile organic compounds.[7] Cold mix asphalt is often used on lower volume rural roads, where hot mix asphalt would cool too much on the long trip from the asphalt plant to the construction site.[8]
Types of Bituminous Road And Construction Overview
An asphalt concrete surface will generally be constructed for high volume primary highways having an Average Annual Daily Traffic load higher than 1200 vehicles per day.[9] Advantages of asphalt roadways include relatively low noise, relatively low cost compared with other paving methods, and perceived ease of repair. Disadvantages include less durability than other paving methods, less tensile strength than concrete, the tendency to become slick and soft in hot weather and a certain amount of hydrocarbon pollution to soil and groundwater or waterways.In the 1960s, rubberized asphalt was used for the first time, mixing crumb rubber from used tires with asphalt. In addition to using tires that would otherwise fill landfills and present a fire hazard, rubberized asphalt is more durable and provides a 7–12 decibel noise reduction over conventional asphalt. However, application of rubberized asphalt is more temperature-sensitive, and in many locations can only be applied at certain times of the year.
Concrete surfaces (specifically, Portland cement concrete) are created using a concrete mix of Portland cement, gravel, sand and water. The material is applied in a freshly-mixed slurry, and worked mechanically to compact the interior and force some of the thinner cement slurry to the surface to produce a smoother, denser surface free from honeycombing. The water allows the mix to combine molecularly in a chemical action called hydration.Concrete surfaces have been refined into three common types: jointed plain (JPCP), jointed reinforced (JRCP) and continuously reinforced (CRCP). The one item that distinguishes each type is the jointing system used to control crack development.Jointed Plain Concrete Pavements (JPCP) contains enough joints to control the location of all the expected natural cracks. The concrete cracks at the joints and not elsewhere in the slabs. Jointed plain pavements do not contain any steel reinforcement. However, there may be smooth steel bars at transverse joints and deformed steel bars at longitudinal joints. The spacing between transverse joints is typically about 15 feet for slabs 7–12 inches thick. Today, a majority of the U.S. state agencies build jointed plain pavements.Jointed Reinforced Concrete Pavements (JRCP) contains steel mesh reinforcement (sometimes called distributed steel). In jointed reinforced concrete pavements, designers increase the joint spacing purposely, and include reinforcing steel to hold together intermediate cracks in each slab. The spacing between transverse joints is typically 30 feet or more. In the past, some agencies used spacing as great as 100 feet. During construction of the interstate system, most agencies in the Eastern and Midwestern U.S. built jointed-reinforced pavement. Today only a handful of agencies employ this design, and its use is generally not recommended as JPCP and CRCP offer better performance and are easier to repair.Continuously Reinforced Concrete Pavements (CRCP) does not require any transverse contraction joints. Transverse cracks are expected in the slab, usually at intervals of 3–5 ft. CRCP pavements are designed with enough steel, 0.6–0.7% by cross-sectional area, so that cracks are held together tightly. Determining an appropriate spacing between the cracks is part of the design process for this type of pavement.Continuously reinforced designs generally cost more than jointed reinforced or jointed plain designs initially due to increased quantities of steel. However, they can demonstrate
Types of Bituminous Road And Construction Overview
superior long-term performance and cost-effectiveness. A number of agencies choose to use CRCP designs in their heavy urban traffic corridors.One advantage of cement concrete roadways is that they are typically stronger and more durable than asphalt roadways. They also can easily be grooved to provide a durable skid-resistant surface. Disadvantages are that they typically have a higher initial cost and are perceived to be more difficult to repair.The first street in the United States to be paved with concrete was Court Avenue in Bellefontaine, Ohio, but the record for first mile of concrete pavement to be laid in the United States is claimed by Michigan.
Composite surfacesComposite surfaces combine Portland cement concrete and asphalt. They are usually used to rehabilitate existing roadways rather than in new construction.Asphalt overlays are sometimes laid over distressed concrete to restore a smooth wearing surface. A disadvantage of this method is that the joints between the underlying concrete slabs usually cause cracks, called reflective cracks in the asphalt.White topping uses Portland cement concrete to resurface a distressed asphalt road.
In-place recyclingDistressed road materials can be reused when rehabilitating a roadway. The existing pavement is ground or broken up into small pieces, then compacted to form the base or subbase for new pavement. Some methods used include:Rubbishing of concrete pavement. Existing concrete pavement is broken into gravel-sized particles, compacted, and then overlaid with asphalt pavement.[10]
Cold in-place recycling. Bituminous pavement is ground or milled into small particles, compacted, and overlaid with asphalt pavement. The asphalt millings are blended with a small amount of asphalt emulsion, paved and compacted, allowed to cure for seven to ten days, then overlaid with asphalt.[11]
Hot in-place recycling. Bituminous pavement is heated to 250 to 300°F (120 to 150°C), milled, combined with a rejuvenating agent or virgin asphalt binder, and compacted. It may then be overlaid with a new asphalt overlay. This process only recycles the top two inches (50 mm) or less, so it can be used to correct rutting, polishing or other surface defects. It is not a good procedure for roads with structural failures. It also generates high heat and vapor emissions, and may not be a good candidate for built-up areas.[11] Full depth reclamation is a process which pulverizes the full thickness of the asphalt pavement and some of the underlying material to provide a uniform blend of material. A binding agent may be mixed in to form a base course for the new pavement, or it may be left unbound to form a subbase course. Common binding agents include asphalt emulsion, fly ash, Portland cement or calcium chloride. It can also be mixed with aggregate, recycled asphalt millings, or crushed Portland cement to improve the gradation of the material.[11] Bituminous Surface Treatment (BST)
Types of Bituminous Road And Construction Overview
Concrete paversBituminous Surface Treatment (BST) is used mainly on low-traffic roads, but also as a sealing coat to rejuvenate an asphalt concrete pavement. It generally consists of aggregate spread over a sprayed-on asphalt emulsion or cut-back asphalt cement. The aggregate is then embedded into the asphalt by rolling it, typically with a rubber-tired roller. BSTs of this type are described by a wide variety of regional terms including "chip seal", "tar and chip", "oil and stone", "seal coat", "sprayed seal"[12] or "surface dressing".[13]
BST is used on hundreds of miles of the Alaska Highway and other similar roadways in Alaska, the Yukon Territory, and northern British Columbia. The ease of application of BST is one reason for its popularity, but another is its flexibility, which is important when roadways are laid down over unstable terrain that thaws and softens in the spring.Other types of BSTs include micropaving, slurry seals and Novachip. These are laid down using specialized and proprietary equipment. They are most often used in urban areas where the roughness and loose stone associated with chip seals is considered undesirable.
Thin membrane surfaceA thin membrane surface (TMS) is an oil treated aggregate which is laid down upon a gravel road bed producing a dust free road.[14] A TMS road reduces mud problems and provides stone free roads for local residents where loaded truck traffic is negligible. The TMS layer adds no significant structural strength, and so is used on secondary highways with low traffic volume and minimal weight loading. Construction involves minimal subgrade preparation, following by covering with a 50 to 100 millimetres (2.0–3.9 in) cold mix asphalt aggregate.[9] The Operation Division of the Ministry of Highways and Infrastructure in Saskatchewan has the responsibility of maintaining 6,102 kilometers (3,792 mi) of thin membrane surface (TMS) highways.[15]
GranularA granular surface can be used with a traffic volume where the average annual daily traffic is 1,200 vehicles per day or less.[citation needed] There is some structural strength as the road surface combines a sub base, base and is topped with a double graded seal aggregate with emulsion.[9][16] Besides the 4,929 kilometers (3,063 mi) of granular pavements maintained in Saskatchewan, over 90% of New Zealand roads are unbound granular pavement structures.[15][17]
Otta sealOtta seal is a low-cost road surface using a 16–30-millimetre (0.63–1.2 in) thick mixture of bitumen and crushed rock.[18]
This article needs attention from an expert on the subject. See the talk page for details. WikiProject Civil engineering may be able to help recruit an expert. (May 2010)
As pavement systems primarily fail due to fatigue (in a manner similar to metals), the damage done to pavement increases with the fourth power of the axle load of the vehicles traveling on it. Civil Engineers consider truck axle load, current and projected truck traffic volume, supporting soil properties (can be measured using the CBR) and sub-grade drainage in design. Passenger cars are considered to have no practical effect on a pavement's service life, from a fatigue perspective.
Types of Bituminous Road And Construction Overview
Other failure modes include aging and surface abrasion. As years go by, the binder in a bituminous wearing course gets stiffer and less flexible. When it gets "old" enough, the surface will start losing aggregates, and macrotexture depth increases dramatically. If no maintenance action is done quickly on the wearing course potholing will take place. If the road is still structurally sound, a bituminous surface treatment, such as a chipseal or surface dressing can prolong the life of the road at low cost. In areas with cold climate, studded tires may be allowed on passenger cars. In Sweden and Finland, studded passenger car tires account for a very large share of pavement rutting.Several design methods have been developed to determine the thickness and composition of road surfaces required to carry predicted traffic loads for a given period of time. Pavement design methods are continuously evolving. Among these are the Shell Pavement design method, and the American Association of State Highway and Transportation Officials (AASHTO) 1993 "Guide for Design of Pavement Structures". A new mechanistic-empirical design guide has been under development by NCHRP (Called Superpave Technology) since 1998. A new design guide called Mechanistic Empirical Pavement Design Guide (MEPDG) was developed and is about to be adopted by AASHTO.According to the AASHO Road Test, heavily loaded trucks can do more than 10,000 times the damage done by a normal passenger car. Tax rates for trucks are higher than those for cars in most countries for this reason, though they are not levied in proportion to the damage done.[20]
The physical properties of a stretch of pavement can be tested using a falling weight deflectometer.Further research by University College London into pavements has led to the development of an indoor, 80-sq-metre artificial pavement at a research centre called Pedestrian Accessibility and Movement Environment Laboratory (PAMELA). It is used to simulate everyday scenarios, from different pavement users to varying pavement conditions.[21] There also exists a research facility near Auburn University, the NCAT Pavement Test Track, that is used to test experimental
MISCELLANEOUS SURFACING MATERIALS
13.1 There are a wide variety of surfacing materials that are not covered in the other chapters of this Part. These are products that are either undergoing development or that are little used on trunk roads.
Dense bitumen macadam13.2 Dense bitumen macadam wearing course to BS 4987 is available with a 6 mm nominal aggregate size. It has a very low texture depth and therefore it is only suitable as a surfacing for roads with a low speed restriction. With good compaction it is reasonably durable, however its resistance to deformation does not make it suitable for very heavily trafficked roads carrying a large proportion of commercial vehicles.
Types of Bituminous Road And Construction Overview
13.3 Open graded bitumen macadam wearing course to BS 4987 is available with both 10 and 14 mm nominal aggregate sizes. They are not however, designated ‘preferred mixtures’ in BS 4987. These products have low strength and their durability is suspect. They are not suitable as surfacings for high speed or heavily trafficked roads.8/1
Dept Of Civil Engg.. Page 22
Types of Bituminous Road And Construction Overview
Figure 8.6 Flow Charts for Specification and Design of Surface Dressing
LAYING BITUMINOUS SURFACE COURSES
2.1 Advice on laying bituminous materials is given in Part 2 of both BS 594 and BS 4987. An additional advice nregarding particular material is given in the Chapters on specific materials in this Part.
Weather Conditions2.2 The weather conditions during the construction of bituminous surface courses affect both the laying operation and the subsequent performance. Although materials may appear satisfactory in the short term, even to the end of their maintenance period, the life expectancy of a surface course laid in inclement weather may be reduced. The requirements of the specificationshould be strictly adhered to. Available Research Reports and Weather Forecasting
2.3 TRL Research Reports RR 4 and RR 280 provide details of research into the effects of various factors that influence the rate of cooling of an asphalt layer. In order of priority, the principal factors are layer thickness, wind speed and ambient temperature.
2.4 The Meteorological Office can provide historicalinformation relating to weather conditions, such as month by month analysis of temperatures, to form a statistical forecast of conditions that affect aspects of road building and in particular, the weather sensitive operation of surfacing.
2.5 The Meteorological Office can also provide 24-hour local forecasts, including wind speeds, from regional weather centres. Information on these services can be obtained from the Meteorological Office, Climatological Services (Met 03), London Road, Bracknell, Berkshire RG12 2SZ (Tel: 01344 420242). Planning the laying of surface courses should always be done in conjunction with an up to date weather forecast.
Specification
2.6 The Specification (MCHW 1) Series 700 and 900, with the associated Notes for Guidance (MCHW 2) set out the requirements for acceptable weather conditions for laying bituminous surface courses. For performance specifications Series 700 does not apply but it provides a useful guide to good practice. (For some special materials the requirements are included inSeries 900). Where modified binders are used advice rom the binder supplier via the Contractor should be obtained.
2.7 Various assumptions have been made in draftingThe Specification (MCHW 1). These are:a) No allowance has been made for solar gain,b) The temperature of the substrate has been assumed to be at ambient temperature initially,c) The binder is an unmodified bitumen to BS 3690, andd) That for materials with 50 pen binder, the temperature of the asphalt immediately behind thePaving machine is at least 140°C and compaction is effectively completed when the laid asphaltTemperature has fallen to about 100°C. A similar temperature differential is applicable to otherGrades of binder.
2.8 Great care should always be taken when the
Dept Of Civil Engg.. Page 23
Types of Bituminous Road And Construction Overview
Temperature is, or has recently been below 0°C as ice may be present on the substrate. Under no circumstances should material be laid on a frozen substrate as inevitably the lower part of the layer will cool prematurely and may not be compacted properly. A zone of weak material may then be present which is likely to shorten the life of the surface course.
Measuring Wind Speed and Temperature2.9 Except where local conditions apply, such as shelter in a cutting or exposure on an embankment, or when conditions are transient with gusting or squalls, wind speed is fairly consistent over a sufficiently large area to enable a single wind speed to characterize aWhole site. To account for gusting it is necessary to define wind speed as the average over the preceding hour. It should be measured using a recording anemometer with an accumulative digital output. Hand-held devices averaging readings over a few seconds should only be used as approximate indicators. For general guidance the Beaufort scale is given in.2.10 The Specification (MCHW 1) allows for wind speed to be measured at heights of either 2 m or 10 m. Measurement at 2 m height, using a portable anemometer, is appropriate for monitoring on site. Measurement at 10 m height is more suited for use on a major contract where there is a site office compo
Surfacing and Mi Slurry cro-surfacing
2.21 These materials are made with bituminous emulsions and therefore should not be laid in icyConditions. It is necessary for a proportion of the initial water content to evaporate from the slurry before it can be trafficked. Laying in wet or humid conditions, particularly when combined with low temperatures, will significantly delay the setting process. It should be borne in mind that even in good conditions the material takes at least 30 minutes to become sufficiently stable to open to traffic. Adverse conditions can increase this period to several hours. Very high temperatures may cause problems such as pre-setting and efficient breaking of the emulsion may be inhibited, leading to failure. 2.22 With these constraints, slurry surfacing and micro-surfacing, like some of the hot paver-laid thin surfacings, have a closed season in winter. Their use is also restricted at maximum road temperatures, similar to surface dressing.
Surface Dressing2.23 Surface dressing has a very short laying season, particularly for heavily trafficked roads, although the advents of superior binder grades and improved processes have lengthened the season. Full guidance is given in Road Note 39. The main reason for the short season is that the chippings have to adhere to the binder at temperatures close to ambient, while the binder mustMaintain sufficient cohesive strength to resist traffic forces when the road is opened.
2.24 For successful surface dressing, it must not be raining and the road surface should be dry. In wet conditions the binder will not adhere to the surface and rapid failure may occur. The sprayed binder film will not adequately adhere to wet or cold chippings and the time taken for the surface dressing to gain adequate stability to resist the traffic forces can significantly increase.Obtaining accurate weather forecasts and making good use of them is more important for the successful outcome of surface dressing than for most other surface treatments.
2.25 When emulsion binders are being used the work should stop if the relative humidity exceeds 80%, as the binder will not break properly and will lack adequate cohesion for the safe opening of
Dept Of Civil Engg.. Page 24
Types of Bituminous Road And Construction Overview
the road to traffic. Relative humidities between 60% and 80% can lengthen the breaking time and care should be exercised when making the decision to open to traffic. The use ofBreaking agents and multiple-layer dressings may alleviate this problem.
Site Preparation2.26 For all surface course materials it is essential that an adequate bond is achieved and maintained between the surface course and the underlying pavement nstructure. The thinner the surface course, the greater the traffic generated stresses at the interface. To achieve anadequate bond the substrate must be clean and free of all loose material.
2.27 Where the substrate is new or nearly new, with the binder film still intact, and no contamination, further treatment should not be necessary. Where it has been contaminated by site traffic for example, it is essential to remove the contamination by sweeping, and if necessary by the use of water jetting or other methods. Where an existing road is being resurfaced, all packed mud, excess oil droppings, any other accretions or organic growth must be removed.
2.28 Treatment with a suitable weedkiller may be necessary some days or weeks prior to the work beingCarried out. The advice of the weedkiller manufacturer should be followed with regard to timing. There are areas where the use of some weedkillers is constrained and the Overseeing Organisation should be consulted to check on any limitations that are in place.
2.29 Existing roads may need some pre-treatment or shaping before the proposed surface course can be used. This should be carried out using an appropriate basecourse material with the necessary properties, strength and resistance to rutting, for the expected traffic levels. Another way of regulating is to plane off any high areas. The most suitable method will depend on theAmount of regulation necessary, threshold levels and the level of street furniture.2.30 In order to obtain best value for money from the resurfacing, any local weaknesses in the underlying pavement should be repaired and cracks sealed using an appropriate treatment, see HD 31 (DMRB 7.4.1). In general the thinner the surfacing, the lower its ability to regulate the existing surface. Surface dressing follows the existing profile and will not smooth out irregularities. Similarly slurry surfacings, which are laid with a spreader box following the existing profile, are too thin to regulate the surface, although the thicker micro-surfacings can improve the transverse profile. Hot paver-laid thin surfacings can regulate the existing surface to a significant degree and guidance is given in the Notes for Guidance (MCHW 2). The limits on the regulating ability of proprietary thin surfacings may be given in the BBA HAPAS Certificates – see Chapter 6of this Part. Porous asphalt must not be laid on a surface that will prevent the free drainage of water (ie the existing surface must be free of depressions).
2/4 Thor packs a mighty punchSeven Atlas Copco CDS 8-inch hammers equipped with 10-inch bits and mounted
in one assembly drill, made a formidable tool for foundation specialist Anderson Drilling of California. They called it Thor, after the Nordic god, and put it to work on a complex bridge building project near San Diego. The challenge was to install 37 piles ranging from 60 - 108 inches in diameter and 55 - 80 feet deep. The solution was cluster drilling.
Dept Of Civil Engg.. Page 25
Types of Bituminous Road And Construction Overview
Anderson Drilling is a respected and experienced foundation contractor known for tackling big foundation jobs in California. Anderson operates a high quality and well maintained fleet of foundation drills, cranes and the traditional tooling capable of completing these often monumental projects. In order to be more efficient in the recent downturn in the construction economy, Anderson looked at newer technology, specifically Atlas Copco’s 48-inch cluster drill, as a way to speed up the foundation drilling process.Anderson Drilling’s management, including Sr. Project Manager Mike Kennedy, Director of Business Development Dennis Poland, San Diego area General Superintendent Charlee Bixby and Vice President of Operations Kelly Hawes, got together with Atlas Copco Vista Store personnel Tom Liebl, Area Sales Representative, Service Manager Chris Woods, Ken McClanahan, geotechnical Sales Specialist, and DTH Center Business Development Manager Al Waltry. From the point of discovery through the bid process, the team looked at the project knowing if the job was successful both would benefit.Anderson Drilling’s scope of work included the installation of 37 foundation piles to support two new bridge structures over the San Luis Rey River and Ostrich Creek near San Diego, California. The drilled piles varied in size from 60-inch to 108-inch in diameter and ranged from 55 – 80 feet in depth. Each pile was designed with rock sockets that ranged from 48-inch to 96-inch in
Dept Of Civil Engg.. Page 26
Types of Bituminous Road And Construction Overview
diameter up to 20 feet in length. The granitic rock of southern California is known for high strength and with compressive strengths nearing 25,000 psi the rock on this project was no exception. The critical issue facing Anderson Drilling was reducing the drill time within the rock socket zones. The construction process was complicated by loose overburden materials and high groundwater conditions above the hard rock that required the installation of permanent steel casing and use of “wet-hole” construction methods (blind drilling with polymer drill fluids) for pile installation.Atlas Copco and Anderson Drilling worked together to obtain a scalable solution that included multiple cluster drills to chew through the hard rock found in the rock socket zones. As the team contemplated the optimal size for the cluster hammer we considered several things like, the frequency of a particular rock socket diameter, tool weight, tool support equipment requirements, and especially consideration of our existing rock tool capabilities that included a wide range of double wall air or water calculating coring tools and other specialized tooling like mini carbide roller cutters and disc type cutters. Ultimately, we determined that a 48-inch tool was the optimal size allowing us to excavate all of the abutment shaft (21 total) rock sockets to their final design diameter, as well as, provide a sizable ‘pilot hole’ at each of the larger 72-inch to 96-inch rock sockets required at the bent pile locations. The pilot holes would be reamed out (enlarged) to the ultimate design diameter utilizing our repertoire of in-house rock tools. Dating back to the original founders of Anderson Drilling nearly everything in Anderson’s fleet is christened with a name. Through the set up process in our MFG plant, plant manager, Rick Watson and his team of dedicated employees came up with a name for the 48-inch cluster drill…. It was affectionately called ‘Thor’ after the Norse hammer-wielding god of thunder.“A number of things came together to make this the perfect situation for us to utilize this cluster drill,” Sr. Project Manager Mike Kennedy points out some of the key detail that were taken into consideration for the project. “The project is located just 10 minutes away from Atlas Copco’s Vista store. This would mean nearly immediate support in the event it was needed. To try something new requires purchasing equipment, which is hard to justify in a tough economic environment. But most importantly a new process would require a steep learning curve until the crew was efficient at the new drilling method,” explained Kennedy.Speaking for the Anderson team, Kennedy said, “After five years of on and off renting of this type of tooling we started talking about purchasing a cluster drill. It was the working relationship we had developed over the years along with communication and trust that gave us the confidence to go with Atlas Copco. We have watched others try this with [competitive] drills, but we wanted to go with someone we could trust,” said Kennedy.Hard foundationsThe project can be described in two parts. The first includes 20 bore holes for the 1,000 foot bridge over the San Luis Rey River requiring four bridge abutment holes and 16 bent holes that run parallel, supporting the length of the bridge. The second part includes a total of 17 abutments shafts that support the bridge spanning over the 50-foot wide Ostrich Creek. The subsurface is comprised of sand and unconsolidated rock overburden in the river beds to approximately 60 feet in depth, with a weathered rock transition into solid granite rock. To meet the earthquake regulations for the state of California the piles have been engineered to provide bridge foundation support capable of withstanding an 8.0 magnitude earthquake event. “Really it’s not the depth of the hole that engineers are looking for; the driving factor is the skin friction of the caisson in competent ground. The support value and shear strength comes from the rock socket at the bottom of the caisson,” said Kennedy.To reach the desired depth and diameter the hole needs to be completed in a series of steps. The cluster drill isn’t utilized until solid granite bedrock is reached. Bedrock contact is achieved by installing a series of casings through the overburden soils each new casing installed is slightly smaller in diameter and longer than the previous casing providing a “telescoping” effect. The
Dept Of Civil Engg.. Page 27
Types of Bituminous Road And Construction Overview
overburden material within the each casing is drilled out using an auger tool under a polymer fluid head used to control bottom heave. (See illustration).The final piece of casing installed was a 51-inch (ID) segmental pipe. This pipe is “seated” into the bedrock and provides an airtight annulus for the cluster drill. The segmental pipe also assisted in maintaining the drilled shaft alignment.In the hole photographed, the segmental pipe is 63 feet long extending nearly 60 feet below ground surface. The rock socket will be nearly 20 feet deeper into the bedrock. The cluster drill is being used to drill a pilot hole for our core barrel tool that will follow resulting in a final rock socket diameter of 96-inch.The balance of time Anderson Drilling has been drilling foundations for years with large diameter core barrels and other rock tools. The process is slow and laborious, but effective. As the large core barrel with cutter teeth rotates, it forms a “curf” or groove leaving a rock core in the center. To cut this core could take days depending on the depth, quality and hardness of the rock. After the initial coring effort, the process of removing and disposing of the core is another major task that requires time, special resources and skills. Fractured or broken rock cores may be augered out however, large solid cores may require heavy crane lifting capabilities.The cluster drill approaches the rock in a different way, essentially pulverizing the rock mass into sand and gravel sized pieces making cutting removals relatively easy and efficient. During drilling the cuttings rise above the drill tool and settle in what is called a Calyx basket. The driller monitors the tool advancement by markings on the drill string. In this case, when the tool advanced approximately 4 feet it was time to retrieve the tool to dump the cuttings. A forklift at ground surface assisted raising the basket allowing the cuttings to fall away from the tool.There is something to be said about the right combination of “parts” to make for an efficient operation. Anderson Drilling paired the cluster drill with one of their newest heavy drill units, a SoilMec SR 100 (a 100 Ton Class machine) and an experienced operator in Ronnie Nourse. Ronnie has been drilling for Anderson for 15 years and is a top operator of the SR 100. “This is Anderson’s baby,” he said, referring to the drill rig with pride. He says its standard depth capacity is 134 feet, with the ability to drill to 205 with an optional feed system. As for drilling with Atlas Copco’s cluster drill Nourse said, “This is one bad-ass 4x4!”He likes the fact it drills fast, and when he’s finished with the 4-foot lift, the rock goes with it. It takes 45 to 50 minutes to drill the 4-foot depth and another 20 minutes to remove the cuttings and get back in the hole. Using a core barrel, Nourse said, “It would take much longer and, then the core has to be removed and hopefully it breaks off clean, not always so easy when you’re underwater.”Cluster drill processOnce the outer casings and segmental guide casing is in place, Nourse has a special cutter that gives the bottom of the hole a flat surface. Then once the hole is drilled with the cluster drill, the segmental guide casing is removed and the ream process begins to the desired 72-inch or 96-inch diameter. To complete a hole will take approximately a week and a half.Drilling with the cluster drill makes the job work very smooth. When the cluster drill was brought on site Atlas Copco’s Chris Woods stayed with the project for the first few days. Nourse said, “Chris assisted us on site to make sure we had it right correct down pressure rotation speed etc. Once we got the sweet spot for rotation, it has gone great.” As an example, when they had it set at 2 RPM the hammers were regrinding the rock. Nourse found that 4 RPM with the 150 psi air worked well. The 50,000 pound weight of the drill stem and Kelly bar is all the pressure needed on the bit.Anderson is using three Atlas Copco XAS 1600 CD6 compressors on the job. Each of the seven Atlas Copco Secoroc CDS 8-inch hammers, with the 10-inch bit, requires 527 cfm. Together the units put out the required 4800 cfm for the job.
Dept Of Civil Engg.. Page 28
Types of Bituminous Road And Construction Overview
References
1. Francisco J. Sanchez-Sesma et.al.(2002),-“Estimation of local site effects during earthquakes:An overview”,ISET Jou. Of Earthquake Technology, Vol.39,No.3.Sep.2002,pp.167-193.
2. Baidya,D.K. and Krishna,G.M.(2001)-“Investigation of Resonant frequency and amplitude of vibrating footing resting on a layered soil system”,Geotechnical Testing Journal,GTJODJ,Vol.24,No.4,December 2001,pp 409-417.
3. Francisco J. Sanchez-Sesma et.al.(2002),-“Estimation of local site effects during earthquakes:An overview”,ISET Jou. Of Earthquake Technology, Vol.39,No.3.Sep.2002,pp.167-193.
4. Finn W.D.L.(2000),-“Earthquake Engineering”, in Geotechnical and Geoenvironmental Engineering Handbook, edited by Rowe,R.K.,Kluwer Academic Publishers
5. Idriss.I.M.(1978)-“Characteristics of Earthquake ground motions”,Extract from Earthquake engineering and soil dynamics,Volume III,Proc. Of ASCE Geotechnical Engineering Division Speciality conference,June 19-21,1978,Pasadena,CA.
6. Kramer,S.L.(1996)-“Geotechnical Earthquake Engineering”, Prentice Hall Publishers, New Jersey.
