Lect 7 pavement materials

Road Building Materials: Materials, Testings, Properties AnalysisMANAGEMENT OF INFRASTRUCTURE AND COMMUNITY DEVELOPMENT

What will you learn?  Basically you will learn about types and characteristics of road building materials, its testings, mix design method of asphalt for asphalt pavement, and green road materialsMANAGEMENT OF INFRASTRUCTURE AND COMMUNITY DEVELOPMENT

What competency do you want to expect?  Knowledge competency: You will recognize types and characteristics of road building materials, its testings, and mix design method of asphalt for asphalt pavement.  Skill competency: you are able to bridge communication between community and engineering service provider (road planner/designer/contractor) in regards with selecting appropriate materials for building roadMANAGEMENT OF INFRASTRUCTURE AND COMMUNITY DEVELOPMENT

Contents  Subgrade/soil  Aggregates  Asphalt and asphalt mixture  Portland cement concreteMANAGEMENT OF INFRASTRUCTURE AND COMMUNITY DEVELOPMENT

Soil/subgrade The soil investigation provides pertinent information about soil and rock for decisions related to the following:  selection of road alignment;  the need for subgrade or embankment foundation treatment;  investigation of slope stability in cuts and embankments;  location and design of ditches and culverts;  selection and design of road pavement;  location and evaluation of suitable borrow and construction materials;  design of foundations for bridges and other structures.MANAGEMENT OF INFRASTRUCTURE AND COMMUNITY DEVELOPMENT

Effect of poor design subgradeMANAGEMENT OF INFRASTRUCTURE AND COMMUNITY DEVELOPMENT

Preliminary soil investigation  An early phase of the soil investigation encompasses collection and examination of all existing information. This may include the identification of soil types from topographic maps, geological maps, soil maps, aerial photos, and satellite images, registration of groundwater conditions, and examination of existing road cuttings.  The visual examination may be coupled with a small amount of sampling and testing.  The preliminary soil investigation will help to secure a broad understanding of soil conditions and associated engineering problems that may be encountered.MANAGEMENT OF INFRASTRUCTURE AND COMMUNITY DEVELOPMENT

Topographic map  Most countries in the world are covered by topographic maps on the scale of 1: 50,000 to 1: 250,000.  These maps may be used as an aid to geological interpretation, to identify drainage networks, and to estimate gradients and earthworks volume.  However, topographic maps may be inaccurate, and they are often out of date.MANAGEMENT OF INFRASTRUCTURE AND COMMUNITY DEVELOPMENT

Geological map  Most countries are covered by national geological maps of scale 1: 100,000 or smaller. More detailed mapping may exist, but few developing or emerging countries have large-scale maps.  Geological maps normally depict the bedrock up to the level beneath the soil. In some cases, rock types can be correlated with particular soil types but, for the road engineer, the main use of geological maps is for planning and for providing background information for the interpretation of aerial photos.MANAGEMENT OF INFRASTRUCTURE AND COMMUNITY DEVELOPMENT

Soil maps  Soil maps are mainly produced for agricultural purposes, but only limited areas in developing and emerging countries are covered. Engineering particulars cannot be read from agricultural soil maps, but they are useful for planning purposes, because they indicate where variations in the soil types can be expected.MANAGEMENT OF INFRASTRUCTURE AND COMMUNITY DEVELOPMENT

Detailed soil investigation  The detailed soil investigations may be divided into field investigations and laboratory testing. The field investigations include geophysical explorations, test pits and borings, sampling of soils and rocks, registration of soil profiles, and measurements of groundwater levels. Laboratory testing includes testing of representative samplesMANAGEMENT OF INFRASTRUCTURE AND COMMUNITY DEVELOPMENT

Geophysical methods as field soil investigation for road  Two geophysical methods of soil exploration are used for road purposes. These are the electrical resistivity and the seismic refraction methods  The electrical resistivity method makes use of the varying electrical resistivity of different soils. The resistivity depends mainly on the content of clay minerals, moisture content, and the type and concentration of electrolyte in the soil–water. An increasing content of clay, water, or electrolyte causes decreasing resistivity. In performing the test, four electrodes are inserted in the surface of the soil and arranged on line symmetrical about a pointMANAGEMENT OF INFRASTRUCTURE AND COMMUNITY DEVELOPMENT

Geophysical methods as field soil investigation for road (continued)  The seismic refraction method relies on the principle that the velocity of sound in soils and rocks is different for different materials. A shock wave is created by detonation of a small explosive charge on the surface of the terrain. The time taken for the shock wave to reach detectors placed on a line at different distances from the source are recorded. Providing the soil is uniform to some depth, these time intervals are directly proportional to the distance from the point of detonation. If the sound velocity in a substratum is higher than in the overburden, then the time interval to more distant points is shortened because the shock wave travels through the substratum for some of the distance. By plotting travel time against distance from the point of detonation, the depth to the substratum can be calculated. The seismic refraction method is particularly useful in predicting the depth to bedrock.MANAGEMENT OF INFRASTRUCTURE AND COMMUNITY DEVELOPMENT

Laboratory soil testing  Particle-size distribution  Moisture content  Specific gravity  Atteberg limits  Plasticity  Free swell  Density  Compaction  California bearing ratio  Dynamic cone penetrometer  Soil classificationMANAGEMENT OF INFRASTRUCTURE AND COMMUNITY DEVELOPMENT

Particle-size distribution  The distribution of particle sizes in soils is important in road engineering since the value of many properties, such as internal friction, voids content, wear resistance, and permeability, depend on the gradation. The distribution of particle sizes larger than 75m is determined by sieving a sample through a number of standard sievesMANAGEMENT OF INFRASTRUCTURE AND COMMUNITY DEVELOPMENT

Test devicesMANAGEMENT OF INFRASTRUCTURE AND COMMUNITY DEVELOPMENT

Analysis  The results of a sieve analysis are normally displayed in a graph. The sieve seizes are plotted on a logarithmic scale as the abscissa. The proportions, by mass, of the soil sample passing the corresponding sieves are plotted on an arithmetic scale as the ordinate.  A well-graded soil is one with a gently sloping sieve curve, indicating that the soil contains a wide range of particle sizes.  A uniformly graded soil is one with predominance of single sized particles.  A gap-graded soil has one size range of particles missing.MANAGEMENT OF INFRASTRUCTURE AND COMMUNITY DEVELOPMENT

Soil gradation curveMANAGEMENT OF INFRASTRUCTURE AND COMMUNITY DEVELOPMENT

Coefficient of uniformity and Coeff. Of Curvature  The coefficient of uniformity is sometimes used as a single numerical expression of particle-size distribution for purposes of succinct communication. The coefficient is defined as the ratio of the sieve size through which 60 per cent of the material passes to that of the sieve size through which 10 per cent passes.   The coefficient of curvature is factor describing shape of gradationMANAGEMENT OF INFRASTRUCTURE AND COMMUNITY DEVELOPMENT

D10 Effective Size = D10 10 percent of the sample is finer than this sizeMANAGEMENT OF INFRASTRUCTURE AND COMMUNITY DEVELOPMENT

D30 and D60MANAGEMENT OF INFRASTRUCTURE AND COMMUNITY DEVELOPMENT

Well graded requirementsMANAGEMENT OF INFRASTRUCTURE AND COMMUNITY DEVELOPMENT

Well graded sand?MANAGEMENT OF INFRASTRUCTURE AND COMMUNITY DEVELOPMENT

Atteberg limitsMANAGEMENT OF INFRASTRUCTURE AND COMMUNITY DEVELOPMENT

Water content and specific gravity  The engineering properties of a soil, such as the strength and deformation characteristics, depend to a very large degree on the amount of voids and water in the soil. The moisture content is defined as the mass of water contained in a soil sample compared with the oven-dry mass of the sample. It is customarily expressed as a percentage, although the decimal fraction is used in most computations.  The specific gravity of a soil is used in the equations expressing the phase relation of air, water, and solids in a given volume of material. The specific gravity of a soil is calculated as the ratio between mass and volume of the solid particles of a sample. The volume of the particles is determined by placing the sample in a volumetric bottle (pycnometer) filled with water and measuring the volume of displaced water.MANAGEMENT OF INFRASTRUCTURE AND COMMUNITY DEVELOPMENT

Atteberg test deviceMANAGEMENT OF INFRASTRUCTURE AND COMMUNITY DEVELOPMENT

Plasticity  The plasticity limits are used to estimate the engineering behaviour of clayey soils and form an integral part of several engineering classification systems.  The plasticity limits include the liquid limit (LL) and the plastic limit (PL), and they are determined by arbitrary tests on the fine soil fraction passing the 42m sieve.  The LL is determined by performing trials in which a sample is spread in a metal cup and divided in two by a grooving tool. The LL is defined as the moisture content of the soil that allows the divided sample to flow together, when the cup is dropped 25 times on to a hard rubber base.  The PL is determined by alternately pressing together and rolling a small portion of soil into a thin thread causing reduction of the moisture content. The PL is defined as the moisture content of the soil when the thread crumbles.  The difference between the LL and the PL is called the plasticity index (PI).MANAGEMENT OF INFRASTRUCTURE AND COMMUNITY DEVELOPMENT

Free swell  Expansive clays are a problem in many regions in the tropics.  A simple test can be used to verify swelling tendencies. A measured volume of dry, pulverized soil is poured into a graduated glass containing water. After the soil comes to rest at the bottom of the cylinder, the expanded volume is measured. The free swell is calculated as the increase of volume as a percentage of the initial volume.MANAGEMENT OF INFRASTRUCTURE AND COMMUNITY DEVELOPMENT

Density  The field density (in-place density) has a great influence on the bearing capacity and the potential for settlement. Soil compaction is therefore an important component of road construction because it increases the density. Measurements of field density are made during soil investigation, but most measurements are taken to assist with compaction control during construction.MANAGEMENT OF INFRASTRUCTURE AND COMMUNITY DEVELOPMENT

Sand cone  The sand cone or sand replacement method is widely used to determine the density of compacted soils.  A sample is removed by hand excavation of a hole in the soil. The in situ volume of the sample is then determined by measuring the volume of dry, free- flowing sand necessary to fill the hole. A special cone is used to pour the sand into the hole. The dry mass of the sample is determined in the laboratory. The method is not recommended for soils that are soft, friable or in a saturated condition. The method is rather time-consumingMANAGEMENT OF INFRASTRUCTURE AND COMMUNITY DEVELOPMENT

Sand coneMANAGEMENT OF INFRASTRUCTURE AND COMMUNITY DEVELOPMENT

Compaction  The level of compaction to be achieved in the field during construction is normally specified as a percentage of the maximum dry density obtained in a compaction test in the laboratory. The traditional laboratory tests are the „standard‟ and the „modified‟ AASHTO compaction or the „light‟ and „heavy‟ British Standard (BS) compaction. They are also known as standard and modified „proctor tests‟ after the person who invented the laboratory compaction tests.MANAGEMENT OF INFRASTRUCTURE AND COMMUNITY DEVELOPMENT

CompactionMANAGEMENT OF INFRASTRUCTURE AND COMMUNITY DEVELOPMENT

MANAGEMENT OF INFRASTRUCTURE AND COMMUNITY DEVELOPMENT

ExampleMANAGEMENT OF INFRASTRUCTURE AND COMMUNITY DEVELOPMENT

California bearing ratio  The California bearing ratio (CBR) test is the most common test for evaluating the bearing capacity of subgrade soils.  It measures the force needed to cause a plunger to penetrate 2.5 or 5mm into a soil sample compacted into a 2-litre cylindrical mould with a diameter of 150 mm.  The measured force is taken as a percentage of a standard force.MANAGEMENT OF INFRASTRUCTURE AND COMMUNITY DEVELOPMENT

Laboratory CBR equipmentMANAGEMENT OF INFRASTRUCTURE AND COMMUNITY DEVELOPMENT

CBR value  It is the ratio of force per unit area required to penetrate a soil mass with standard circular piston at the rate of 1.25 mm/min. to that required for the corresponding penetration of a standard material.  The C.B.R. values are usually calculated for penetration of 2.5 mm and 5 mm. Generally the C.B.R. value at 2.5 mm will be greater that at 5 mm and in such a case/the former shall be taken as C.B.R. for design purpose. If C.B.R. for 5 mm exceeds that for 2.5 mm, the test should be repeated. If identical results follow, the C.B.R. corresponding to 5 mm penetration should be taken for design.MANAGEMENT OF INFRASTRUCTURE AND COMMUNITY DEVELOPMENT

CBR value  C.B.R. = (Test load/Standard load) * 100 Penetration of Standard load plunger (mm) (kg) 2.5 1370 5 2055 7.5 2630 10.0 3180 12.5 3600MANAGEMENT OF INFRASTRUCTURE AND COMMUNITY DEVELOPMENT

CBR CurveMANAGEMENT OF INFRASTRUCTURE AND COMMUNITY DEVELOPMENT

Quick estimation of CBRMANAGEMENT OF INFRASTRUCTURE AND COMMUNITY DEVELOPMENT

Dynamic cone penetrometer  The dynamic cone penetrometer (DCP) is a quick and cheap alternative to in situ CBR tests. A 30o steel cone is forced into the soil by use of a drop hammer, and the penetration is measured in millimetres per blow. Empirical relations between penetration and CBR may be derivedMANAGEMENT OF INFRASTRUCTURE AND COMMUNITY DEVELOPMENT

Exercise: what the unified soil classification system?MANAGEMENT OF INFRASTRUCTURE AND COMMUNITY DEVELOPMENT

Range of CBR values by soil typesMANAGEMENT OF INFRASTRUCTURE AND COMMUNITY DEVELOPMENT

Exercise: what is AASHTO classification?MANAGEMENT OF INFRASTRUCTURE AND COMMUNITY DEVELOPMENT

Aggregates  Mineral aggregates make up 90 to 95% of a HMA mix by weight or approximately 75 to 85% by volume. Their physical characteristics are responsible for providing a strong aggregate structure to resist deformation due to repeated load applications.  Aggregate is defined as “a granular material of mineral composition such as sand, gravel, shell, slag, or crushed stone, used with cementing medium to form mortars or concrete or alone as in base courses, railroad ballasts, etc.”  These aggregates can be divided into three main categories natural, processed, and synthetic (artificial) aggregates.MANAGEMENT OF INFRASTRUCTURE AND COMMUNITY DEVELOPMENT

Natural aggregates  Natural aggregates are mined from river or glacial deposits. They are frequently referred to as pit- or bank-run materials. Gravel and sand are examples of natural aggregates. Gravel is normally defined as aggregates passing the 3 in. (75 mm) sieve and retained on the No. 4 (4.75 mm) sieve. Sand is usually defined as aggregate passing the No. 4 sieve with the silt and clay fraction passing the No. 200 (0.075 mm) sieve. These aggregates in their natural form tend to be smooth and round.MANAGEMENT OF INFRASTRUCTURE AND COMMUNITY DEVELOPMENT

Processed aggregates  Processed materials include gravel or stones that have been crushed, washed, screened, or otherwise treated to enhance the performance of HMAC. Processed materials tend to be more angular and better graded.MANAGEMENT OF INFRASTRUCTURE AND COMMUNITY DEVELOPMENT

Synthetic aggregates  Synthetic aggregates are not mined or quarried. Rather, they are manufactured through the application of physical and/or chemical processes as either a principal product or a by-product. They are often used to improve the skid resistance of HMAC. Blast furnace slag, lightweight expanded clay, shale or slate are examples of synthetic aggregatesMANAGEMENT OF INFRASTRUCTURE AND COMMUNITY DEVELOPMENT

Testing of aggregates: Particle size analysis  Particle size analysis on aggregates is carried out using the same procedure as described for soils. Circular sieves with a frame diameter of 200mm are normally used for analysis of soils and fine aggregate. However, for analysis of coarse aggregate it is useful to employ sieves with a frame diameter of 300 mm or more, because bigger samples are needed to obtain representative results. An important use of the sieve curve is for estimating the volume occupied by different fractions of the soil.  In some types of natural gravel, particularly laterite, there may be a significant difference between the specific gravity of the coarse and the fine particles. For these types of soils, it may be useful to convert mass proportions to volume proportions when plotting the sieve curveMANAGEMENT OF INFRASTRUCTURE AND COMMUNITY DEVELOPMENT

Testing of aggregates: Specific gravity  The specific gravity of aggregates is used for converting mass to volume. Volume calculations of aggregates are primarily used in connection with mix design for cement and asphaltic concrete. The test procedure is similar to that described for soils, except that bigger samples and bigger pycnometers are needed for coarse aggregate. Instead of using a volumetric bottle, the volume of the sample may be determined by placing the sample in a wire basket and weighing it before and after immersing in water.MANAGEMENT OF INFRASTRUCTURE AND COMMUNITY DEVELOPMENT

Specific aggregates equipment kitsMANAGEMENT OF INFRASTRUCTURE AND COMMUNITY DEVELOPMENT

Water absorption  High porosity of aggregates may be a sign of low mechanical strength. Furthermore, aggregates with high porosity may be difficult and costly to dry during processing of asphalt hot mix. The porosity is estimated by measuring the water absorption. This is determined by immersing a dry sample in water for 24h. The surfaces of the particles are then dried by rolling the sample gently in a dry cloth. The water absorption is calculated as the difference in mass between the saturated, surface-dry sample and the dry sample as a percentage of the mass of the dry sampleMANAGEMENT OF INFRASTRUCTURE AND COMMUNITY DEVELOPMENT

Sand equivalent test  The sand equivalent test is useful for evaluating the plastic properties of the sand fraction of aggregates. A volume of damp aggregate passing the 4.75mm sieve is measured. The material should not be dried before testing as this may change its properties. The sample and a quantity of flocculating (calcium chloride) solution are poured into a graduated glass and agitated. After a prescribed sedimentation period, the height of sand and the height of flocculated clay are determined.  The sand equivalent (SE) is the height of sand as a percentage of the total height of sand and flocculated clay in the glass.MANAGEMENT OF INFRASTRUCTURE AND COMMUNITY DEVELOPMENT

CBR test  The CBR test is unsuitable for testing of crushed stone and coarse gravel, because of the need for removing particles bigger than 20mm. For design purposes, the CBR is sometimes estimated based, not on testing, but on previous experience combined with evaluation of the shape of the particle-size distribution curveMANAGEMENT OF INFRASTRUCTURE AND COMMUNITY DEVELOPMENT

Particle shape  The particle shape influences the compaction and strength characteristics of aggregate mixtures. Cubic particles are less workable but more stable than flaky and elongated particles. The particle shape test is performed on coarse particles, for example, particles retained on the 6mm sieve. Each particle is measured using a length gauge. Particles with a smallest dimension less than 0.6 of their mean size are classified as „flaky‟. Particles with a largest dimension more than 1.8 times their mean size are classified as „elongated‟. The mean size is defined as the mean of the two sieve sizes between which the particle is retained in a sieve analysis. The percentage by mass of flaky particles in a sample is called the „flakiness index‟.MANAGEMENT OF INFRASTRUCTURE AND COMMUNITY DEVELOPMENT

Soundness  The soundness test is used as part of the materials survey and design process to estimate the soundness of aggregate when subjected to weathering. The test subjects samples to repeated immersion in saturated solutions of sodium or magnesium sulphate, followed by drying. The internal expansive force, derived from the rehydration of the salt upon re-immersion, simulates the weathering action. The sample is sieved before and after the test, and the percentage of loss for each fraction is calculated.  The precision of the test is poor, and it is not usually considered for outright rejection of aggregates without confirmation by other testsMANAGEMENT OF INFRASTRUCTURE AND COMMUNITY DEVELOPMENT

Field density  Field density tests are used in construction to evaluate the compaction achieved in aggregate base and sub-base. Common methods are sand cone and nuclear density gauge, as described earlier. However, measurements of field density are not very precise when dealing with coarse material. In some countries, this has led to the use of method-specifications for compaction instead of end-product specificationsMANAGEMENT OF INFRASTRUCTURE AND COMMUNITY DEVELOPMENT

Los Angeles abrasion test  The los angeles abrasion test gives an indication of the resistance to abrasion in combination with the impact strength of coarse aggregates. The test is used for selecting the most suitable aggregate sources for quarrying. A sample is loaded together with a number of steel balls into a steel drum, which revolves on a horizontal axis. The los angeles abrasion value is the percentages of fines passing the 1.7 mm sieve after a specified number of revolutions of the drum.MANAGEMENT OF INFRASTRUCTURE AND COMMUNITY DEVELOPMENT

Higher water absorption, poorer abrasion resistanceMANAGEMENT OF INFRASTRUCTURE AND COMMUNITY DEVELOPMENT

Affinity for bitumen/asphalt  Different test methods exist for determining the resistance to stripping, that is, the separation of a bitumen film from the aggregate resulting from the action of water.  However, none of the methods are very reliable. In the simplest method, the resistance to stripping is determined by immersing an uncompacted sample of bitumencoated aggregate in water. At the end of a soaking period, the percentage of surfaceMANAGEMENT OF INFRASTRUCTURE AND COMMUNITY DEVELOPMENT

Asphalt  Asphalt pavements consist of selected mineral aggregates bound together by a bituminous binder.  Asphalt layer is used as different asphalt pavement types, ranging from thin surface dressings to thick layers of asphalt concrete.MANAGEMENT OF INFRASTRUCTURE AND COMMUNITY DEVELOPMENT

Bituminous binders  Bitumen or asphalt cement is a black to dark brown sticky material, composed principally of high molecular-weight hydrocarbons.  It can be found as a component of natural rock asphalt, but most bitumen is derived from the distillation of crude oil.MANAGEMENT OF INFRASTRUCTURE AND COMMUNITY DEVELOPMENT

Basic Characteristics of Bitumen  Bitumen is a thermoplastic material that gradually softens, and eventually liquefies when heated. Bitumen is characterized by its consistency at certain temperatures.  Traditionally, the consistency is measured by a penetration test, a softening point test and a viscosity test.MANAGEMENT OF INFRASTRUCTURE AND COMMUNITY DEVELOPMENT

Asphalt Cement Specifications and TestsMANAGEMENT OF INFRASTRUCTURE AND COMMUNITY DEVELOPMENT

Bitumen Tests  Penetration test. Penetration is the number of units of 0.1 mm penetration depth achieved during the penetration testMANAGEMENT OF INFRASTRUCTURE AND COMMUNITY DEVELOPMENT

 Softening points testMANAGEMENT OF INFRASTRUCTURE AND COMMUNITY DEVELOPMENT

Ductility test  Ductility is the number of centimeters a standard briquette of asphalt cement will stretch before breakingMANAGEMENT OF INFRASTRUCTURE AND COMMUNITY DEVELOPMENT

Flash point  Flash point is the temperature to which asphalt cement may be heated without the danger of causing an instantaneous flash in the presence of an open flameMANAGEMENT OF INFRASTRUCTURE AND COMMUNITY DEVELOPMENT

Solubility test  Solubility is the percentage of an asphalt cement sample that will dissolve in trichloroethylene. In this procedure, an asphalt cement sample is dissolved in trichloroethylene and then filtered through a glass-fiber pad where the weight of the insoluble material is measured. The solubility is calculated by dividing the weight of the dissolved portion by the total weight of the asphalt cement sample. This test is used to check for contamination in asphalt cement. Most specifications require a minimum of 99% solubility in trichloroethyleneMANAGEMENT OF INFRASTRUCTURE AND COMMUNITY DEVELOPMENT

Bitumen grade  Bitumen is available commercially in several standard grades. In many countries, the grades are based on the penetration value. The grade is usually expressed in a penetration value bracket, for example, 80–100. The British Standard (BS) specifies 10 different grades ranging from pen 15 to pen 450. Earlier standards in the United States specified five types, with pen 40–50 as the hardest and pen 200–300 as the softest. In Indonesia used bitumen has penetration grade 60-80.MANAGEMENT OF INFRASTRUCTURE AND COMMUNITY DEVELOPMENT

Volumetric Properties of Asphalt MixturesMANAGEMENT OF INFRASTRUCTURE AND COMMUNITY DEVELOPMENT

Mass – volume relationship diagramMANAGEMENT OF INFRASTRUCTURE AND COMMUNITY DEVELOPMENT

ExampleMANAGEMENT OF INFRASTRUCTURE AND COMMUNITY DEVELOPMENT

SolutionMANAGEMENT OF INFRASTRUCTURE AND COMMUNITY DEVELOPMENT

Portland cemen concretet (PCC)  PCC is composed of cement paste and aggregates. The cement paste consists of Portland cement mixed with water while the aggregates are composed of fine and coarse fractions.MANAGEMENT OF INFRASTRUCTURE AND COMMUNITY DEVELOPMENT

Portland cementMANAGEMENT OF INFRASTRUCTURE AND COMMUNITY DEVELOPMENT

Portland cement  Portland cement is composed of approximately 60 to 65% lime (CaO), 20 to 25% silica (SiO2), and 7 to 12% iron oxide (Fe2O3) and alumina (Al2O3). The percentages of the different components may be varied to meet different physical and chemical requirements based on its intended useMANAGEMENT OF INFRASTRUCTURE AND COMMUNITY DEVELOPMENT

Aggregate  Particle size distribution can be further divided into coarse- aggregate and fine aggregate grading. The particle size and distribution has an impact on the workability of the mix. In general, the larger the maximum particle size, the less Portland cement is necessary. Particle shape and surface texture have a greater impact on the properties of fresh concrete than they do on the properties of hardened concrete. The rougher and more angular the particles are, the more water is required to produce workable concrete. However, rougher and more angular particles tend to have a stronger bond with the cement and water mixture. Voids between aggregates also increase with increased aggregate angularity. Specific gravity is not generally considered a measure of aggregate quality, but is required in the mix design process. Absorption and surface moisture are used to determine the aggregate’s appetite for moisture and its current moisture condition. The results of these tests are used to control concrete batch weightsMANAGEMENT OF INFRASTRUCTURE AND COMMUNITY DEVELOPMENT

Water, chemical admixtures  Almost all naturally occurring water that is safe for drinking should be suitable for making PCC.  Chemical admixtures may be used to enhance Portland cement properties based on the requirements for a specific application. The primary reasons for using admixtures are to reduce the cost of concrete construction, to enhance certain concrete properties, and to ensure the quality of concrete during the different stages of construction.MANAGEMENT OF INFRASTRUCTURE AND COMMUNITY DEVELOPMENT

 Water-reducing admixtures are used to reduce the quantity of mixing water required to produce concrete of a specific slump, reduce the water– cement ratio, or increase slump. Regular water reducers may decrease the water content by 5 to 10%. High-range water reducers (also called Superplasticizers) may decrease the water content by 12 to 30%. While high-range water reducers are typically more effective than regular water reducers, they are more expensive. Water reducers typically produce an increase in strength because of the reduction in the water– cement ratio. The effectiveness of water reducers is dependent on its chemical composition, concrete temperature, cement composition, cement fineness, cement content, and the presence of other admixtures. The effectiveness of water reducersdiminishes with time after it is introduced into the batch.MANAGEMENT OF INFRASTRUCTURE AND COMMUNITY DEVELOPMENT

 Retarding admixtures are used to slow down the rate at which concrete sets. Retarders may be used tocomp ensate for accelerated setting due to hot weather or delay initial set for prolonged concrete placements. The presence of retarders may reduce early (first few days) strength gain. Accelerating admixtures have the opposite effect from retarding admixtures in that they increase early strength gain.  However, the use of accelerating admixtures may lead to increase in drying shrinkage, potential reinforcement corrosion, discoloration, and scaling.MANAGEMENT OF INFRASTRUCTURE AND COMMUNITY DEVELOPMENT

 Fly ash, ground granulated blast-furnace slag, and condensed silica fume are commonly used mineral admixtures.MANAGEMENT OF INFRASTRUCTURE AND COMMUNITY DEVELOPMENT

Finely divided mineral admixtures Finely divided mineral admixtures are powdered or pulverized materials added to PCC to enhance the properties of fresh and/or hardened concrete. They may be broadly put into four categories:  Cementitious materials,  Pozzolanic materials,  Pozzolanic and cementitious materials,  Inert materials.MANAGEMENT OF INFRASTRUCTURE AND COMMUNITY DEVELOPMENT

Lect 7 pavement materials

by M Firdaus on Nov 26, 2011

Accessibility

Categories

Upload Details

Usage Rights

Statistics

Lect 7 pavement materials Presentation Transcript