Terminologies Related to Pavement Materials
The abrasion test measures the abrasion or wear and tear resistance of the aggregate. The test is performed in the Los Angeles drum which is charged with a given weight of aggregate meeting one of the sieve grading. The drum containing the charge and the abrasion steel balls is rotated for 500 revolutions after which the material is screened through a No.12 sieve. The percentage passing is the wear percentage.
About 40 to 65 % of bitumen weight is due to aromatics. This is a dark brown viscous liquid consisting of non polar carbon chains. They have high dissolving ability and act as dispersion medium for asphaltenes. Increase in aromatic content results in reduced shear strength.
Asphaltenes are highly polar and complex aromatic hydrocarbons of high molecular weight. Asphaltene content largely affects the rheological (flow
The exudation of bituminous material on a roadway surface after construction.
A covering of stone chips, sand or other suitable material applied to a road surface after an application of asphalt.
All material used in making embankments which does not come from necessary excavation.
Braccia is a deposit containing a large proportion of coarse angular rock fragments.
A building and paving material made from moist fire clay, semi-fire clay, or shale or clayey-silt-sand, or combinations thereof, cut or moulded into blocks and hardened by burning.
Gypsum partially dehydrated by means of heat.
CALIFORNIA BEARING RATIO
The strength of the sub grade and unbound granular material is measured in the California Bearing Ratio test. In this test a circular piston 1932 mm2 in area is driven into the material at a specific rate. The load acting on the piston is recorded and that corresponding to a penetration of 2.5mm is determined. The ratio of that load to 1360 kg (The value obtained from a standard crushed stone sample) expressed as percentage is the CBR value of this material.
The term is applied to the wearing surface topping or top course of a bituminous surface laid in two or more coats.
Small angular fragments of stone containing no dust.
To fill up the voids.
Slag particularly from iron blast furnaces or the accumulation of clinkers, ashes and cinders resulting from burning coal.
A type of soil which contain colloidal scale-like particles which are the cause of plasticity. Plasticity and dry strength are affected by shape and mineral composition of the particles.
The force that binds the particles of any material together.
Ripples, waves or uniform undulations which are liable to appear in all types of road surfaces.
One or more layers of road metal spread and compacted separately for the formation of the road or pavement. Courses are often referred to in the order of their laying, as first course, second course, third course, etc.
The higher part of the curved surface of the road. Often used to designate the difference in elevation of the highest point of a roadway and the edge of the traveled way. Also the highest point on a cross-section, within the traveled way, usually at the centre.
Crushed gravel is considered suitable for use in bituminous mixtures if at least 95% of the particles have one fractured face due to crushing.
Crushed rock is obtained by mechanically crushing quarry stone, gravel or talus.
Stones obtained directly from crushers containing all fractures of the stone from maximum size to crusher dust.
Density is the unit weight of a given bituminous mix. This gives an indication of the bitumen content in designed mix and helps to establish the basis for controlling/ determination of compaction during construction. Density of specimens obtained from pavements determines the effectiveness of rolling.
A route the traffic follows in going around a closed portion of road, a temporary diversion or route.
Diatomaceous earth is composed essentially of siliceous skeletons of diatoms (extremely minute unicelled organisms). It is composed mainly of silica, white or light gray in colour and is extremely porous.
It is granite which has been subjected to natural weathering conditions to the extent that some of the minerals have been altered; e.g., feldspar to kaolin, mica to chlorite, which alterations are accompanied by considerable loss of mechanical strength in the rock structure.
DRY SIEVE ANALYSIS
This test determines the material retained on each sieve size as the material, thoroughly dried, is passed over a set of sieves of standard selected sizes of square openings. The sieves are held together in a frame so that the sieve with the largest opening is on top and those of smaller openings successfully follow one below other.
Ductility is an indication of the extension or stetchability of bitumen under standard conditions. A small briquette of bitumen of a given dimension at a standard test condition is pulled in an apparatus at a standard rate of speed until the thread of bitumen breaks. The length of the pull measured in cm is designated as ductility of the bitumen sample under test.
EFFECTIVE SPECIFIC GRAVITY
This determined the degree to which the water permeable voids in an aggregate are permeable to asphalt binder. As bitumen is more viscous than water it will coat these voids to a lesser extent.
Containing an excess of bituminous material. A fat asphalt mixture is one in which the asphalt cement is in excess and the excess is clearly apparent.
Flash point is the minimum temperature at which bitumen gives an instantaneous flash in the presence of an external open flame.
The condition of hot asphalt cement caused by rain or water getting into the hot bitumen and causing excessive building up of small steam bubbles.
The surface of the excavated or made up ground on which a road is constructed.
Denotes that portion of a road structure lying on the formation level.
Easily broken up.
GRADED STONE OR METAL
It is a stone metal that has been segregated into sizes suitable for use under various construction specifications. The maximum size rock in any one gradation is usually 6 to 8 cm max. & 2 to 4 cm min.
Granites are crystalline even graded rocks consisting essentially of feldspar and quartz with smaller amounts of mica and other ferro- magnesian minerals.
Gravel consists of bulky mineral grains larger than about 5 mm diameter. Pieces larger than 5mm are called stones and pieces larger than 25 cms are called boulders.
Applied to an aggregate or surface which will absorb a large quantity of bituminous binding material.
Applied to small sized stone used for binding road surfaces which have received a bituminous dressing.
To fill the joints and voids in smaller masonry or in courses of road metal with grout, such as asphalt.
Hydrous calcium sulphate, contains 32.5 % lime, 46.6 % sulphur trioxide and 20.9% water. Some varieties are alabaster, gypsite, satin spar & selenite.
Applied to large stones, boulders or bricks placed by hand or a road to form a foundation or bottom course.
HARD CORE CLINKER
Broken brick, rubble, etc., placed in a road structure to form a foundation or bottom course.
Fine sand, earthy gravel, moorum, laterite, limestone dust, crusher dust and other suitable fine material that forms the slurry grout in water bound macadem surfaces.
HOT LAID MIXTURES OR HOT MIX ASPHALT
Plant mixes of bitumen and aggregates which must be spread and compacted while in a heated condition. They are prepared directly with bituminous cements and lose their workability when cooled to atmospheric temperatures.
A dry powder obtained by treating quicklime with enough water to satisfy its chemical affinity under the condition of its hydration. It consists essentially of calcium hydroxide or a mixture of calcium hydroxide and magnesium oxide and magnesium hydroxide.
Kankar is much the same as moorum but with much higher degree of calcification. “Lime Kankar” is usually found in beds upto a depth of three metres, which when removed breaks up into high percentage of very hard nodules of limestone like pieces containing a matrix of sand & silt.
Asphalt deposits are found in the form of surface of deposits at a few places in the world. However there is the single lake of approximately 100 acres which is the single largest deposit of asphalt in the world. The lake is about 90m deep and is estimated to contain from 10 to 15 million tonnes of asphalt. This material cannot be used directly on the road as it is very hard and therefore it is blended with softer grades of bitumen to get the right results.
A name derived from the Latin word for brick earth and applied to the red residual soils or surface products that have originated in site from the atmospheric weathering of rocks. Especially found in the tropics. In many cases laterite is disintegrated granite which has become restablised by oxidation of contained minerals within the original stone such as iron, aluminum, etc. Laterite is quite often red in colour and extensively used in road construction in India.
Containing a deficiency of bituminous material or conversely containing excess of aggregate.
A course placed for the purpose of shaping old surfaces to proper cross section to receive a subsequent surface course.
Any natural rock of sedimentary origin composed principally of calcium carbonate or of calcium and magnesium carbonates in either its original chemical of fragmental or crystallised form.
The Marshall test consists of the manufacture of cylindrical specimens 102 mm in diametre & 64 mm high by using a standard compaction hammer and a cylindrical mould. The specimens are tested for their resistance to deformation at 600C at a constant rate of 50mm/min.in a testing rig. The top and bottom of the specimen remain unconfined. The maximum load before failure is called Marshall Stability and the amount of deformation of the specimen before failure is known as Marshall Flow. The ratio of stability to flow is called Marshall Quotient and is an indicator of the materials resistance to permanent deformation.
Masonry in its widest sense, includes all construction of stone or similar material, in which the separate pieces are either placed together with or without cementing material to join them; or encased in a matrix of firmly cementing material. In usual practice, the word “Masonry” is qualified by some proper term to more particularly describe the masonry under consideration, such as, stone, concrete, brick, wet, dry, coarsed, uncoarsed, ashler etc.
Moorum though often used in road construction is quite soft (softer than brick) and breaks down quite easily. It consists of silt and sand which have become partially stablised by calcification and other means due to filtering action of the original deposit on ground water. Moorum is also formed from disintegrated rocks and the two most common varieties are the yellow and the red moorum; it is reddish if the base is laterite and yellowish if the base is trap. Moorum is found in most parts of India and is especially prevalent in the Deccan.
Organic matter consists either of partly decomposed vegetation as in peats or of finely divided vegetable matter as in organic silts and organic clays.
A short lived dust layer. Applied to water, oils and other preparations with which roads are treated to temporarily lay dust.
Clean gravel, the particles of which equal the size of peas.
Soil composed predominantly of organic material, considerably decomposed but slightly fibrous with easily recognizable plant remains.
Penetration determines the relative hardness or consistency of bitumen by measuring the distance that a standard needle will penetrate vertically into a sample of bitumen at 25OC under a load of 100 grams applied for 5 seconds.
The degree to which any material permits the injection of water.
Pit stone is usually gravel dug from pits or conglomerate quarry faces. Most pit stones vary from rounded to subrounded.
Portland cement is a product obtained by finely pulverizing clinker produced by calcining incipient fusion an intimate and properly proportioned mixture of agrillaceous and calcareous materials with no additions subsequent to calcination excepting water and calcined or uncalcined gypsum.
Quarry stone is stone that has been mined by blasting or otherwise from solid rock at quarry site. Usually all faces of such stones are fractured.
A metamorphosed quartz sandstone, formed by deposition of secondary silica between the original grains, so that the rock is more firmly cemented and less porous than before and tends to break across the grains.
A calcined material, the major part of which is calcium oxide or calcium oxide in natural association with lesser amount of magnesium oxide, capable of slaking with water.
Resins are dark brown in colour, are solid or semi-solid and are highly polar in nature. The polar nature of resins imparts strong adhesive properties to bitumen. Normally, resin accounts for 10 to 20 % of bitumen by weight. Increase in Resin content hardens the bitumen, reduces penetration index and increases shear strength & viscosity.
ROAD METAL OR AGGREGATES
Hard granular materials of many types and sizes used in road construction, i.e., sand, gravel, crushed gravel, crushed rock, slag, cinder, moorum, kankar, laterite, portland cement clay, limestone dust, diatomaceous earth, mineral fillers, etc.
In France, Switzerland & Italy naturally coated bituminous aggregate is found at a few places. The natural asphalt in these regions is found in rocky terrain consisting mainly of calcerous porous rocks like limestone and sandstone. Over the period of time the asphalt has seeped into the stones and hence naturally occurring stones coated & impregnated with asphalt are found in these areas.
Sand consists of mineral grains varying from about 5 mm to 0.05 mm in diameter.
Saturates are aliphatic hydrocarbons and are non polar in nature. They are white or straw in colour. Saturates account for 5 to 20% of the weight of bitumen. Increasing Saturates can make the bitumen softer.
In highway use, that portion of the roadbed between the traveled way or pavement and the top of the ditch slope in cuts or top of embankment in fills.
Silt consists of natural mineral grains smaller than 0.05 mm which lack plasticity and have little or no dry strength.
Fused or partially fused composed of silica in combination with lime or other bases, resulting in secondary products from the reduction of metallic ores.
Slaked lime is calcium hydroxide, a compound formed by hydration of free lime.
Softening point is the temperature at which a standard quantity of bitumen will become fluid. It is usually tested by a ball/ring test method.
The portion of bitumen which fully dissolves in carbon tetrachloride represents the actual binder material in the bitumen sample.
Talus is naturally broken stone as is often found in slides and at the base of rocky heights. Talus rock, with some exceptions, has all faces fractured and is usually classified angular to subangular.
Tar is obtained during the process of destructive distillation of wood or coal. Tar was used in road construction in India till 1950s. Today due to better quality and availability Bitumen has completely replaced tar in the road construction industry.
THEORETICALLY GRADED STONE
Theoretically graded stone is obtained by uniformly mixing calculated percentages of known graded sizes to yield a combined gradation suited to the work proposed. Gradation limits are ordinarily specified in writing or are shown on a gradation chart, in either case the allowable minimum and maximum amounts passing or retained on the various screens and sieves used are indicated.
THIN FILM OVEN TEST
This test indicates the amount of hardness that may be expected to occur in bitumen during plant mixing. The tendency to harden is measured as a percentage of penetration after and before the thin film oven test. 50grams of the sample is held in a standard size cup, rotated on a shelf inside a well ventilated oven maintained at 1650C for 5 hours. Penetration is taken before and after the test.
Trap rock includes the dark – coloured fine grained and dense igneous rocks composed essentially of the ferro magnesian minerals, basic feldspars, and little or no quartz. The ordinary commercial variety of trap is basalt, diabase or grabo. “Black Trap” refers mainly to the basalt rocks.
Viscosity of bitumen determines the flow characteristics of bitumen at a given temperature. It is taken in the Saybolt Furol seconds.
Determination of voids in a compact specimen of paving mixture is done by checking the specific gravity of aggregate and the specific gravity of bitumen used.
WASH SIEVE ANALYSIS
Where the aggregate contains extremely fine dust which may stick to the coarse aggregate particles, the particle size distribution is made by washing procedure.