Hysical Properties of Soil

8/3/2019 Hysical Properties of Soil

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hysical Properties of Soil

Permeability (the rate at which water moves through the soil) and Water-Holding

Capacity (WHC; the ability of a soils micropores to hold water for plant use) are affected by

The amount, size and arrangement of pores

Macropores control a soils permeability and aeration.

Micropores are responsible for a soils WHC

Porosity is in turn affected by

Soil texture

Soil structure

Compaction

Organic matter

Soil texture (the relative proportions of sand,

silt, and clay) is important in determining the

water-holding capacity of soil:

1. Fine-textured soils hold more water

than coarse-textured soils but may not

be ideal

2. Medium-textured soils (loam family) are

most suitable for plant growth

- Sands are the largest particles and feel gritty

- Silts are medium-sized and feel soft, silky, or

floury

- Clays are the smallest sized particles and feel

sticky and are hard to squeeze.

- Relative size perspective: Sand (house) > Silt >

Clay (penny)

Four main types of soil structure (the arrangement of aggregates in a soil):

Platy - common with puddling or ponding of soils

Prismatic (columnar) common in subsoils in arid and semi-arid regions

Blocky common in subsoils especially in humid regions

Granular (crumb) common in surface soils with high organic matter content

Properties of soil particle size

Sand Silt Clay

Porositymostly

large pores

small pores

predominate

small pores

predominate


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Permeability rapid low to moderate slow

Water holding

capacitylimited medium very large

Soil particle

surface small medium very large

Soil Compaction destoys the quality of the soil because it restricts rooting depth and decreases

pore size. The effects are more water-filled pores less able to absorb water, increasing runoff

and erosion, and lower soil temperatures. To reduce compaction:

Add organic matter

Make fewer trips across area

Practice reduced-till or no-till systems

Harvest when soils are not wet

Next page: Soils, water, and plant growth

Updated July 15, 2004

Contact us:[email protected]|Accessibility|Copyright |Policies

Tree Fruit Research & Extension Center,Washington State University,1100 NWestern Ave., Wenatchee, WA, 98801 USA

Properties of concrete

From Wikipedia, the free encyclopedia

Concrete has relatively high compressive strength, but significantly lowertensile strength, and as such is

usually reinforced with materials that are strong in tension (often steel). The elasticity of concrete is relatively

constant at low stress levels but starts decreasing at higher stress levels as matrix cracking develops. Concrete

has a very lowcoefficient of thermal expansion, and as it matures concrete shrinks. All concrete structures will

crack to some extent, due to shrinkage and tension. Concrete which is subjected to long-duration forces is

prone tocreep.

Tests can be made to ensure the properties of concrete correspond to specifications for the application.

The density of concrete varies, but is around 2,400 kg/m (150 pounds per cubic foot or 4,050 lb/yd). [1]
http://soils.tfrec.wsu.edu/mg/water.htmmailto:[email protected]:[email protected]:[email protected]://www.scs.wsu.edu/atc/http://www.scs.wsu.edu/atc/http://www.scs.wsu.edu/atc/http://www.wsu.edu/copyright.htmlhttp://www.wsu.edu/copyright.htmlhttp://www.wsu.edu/policies.htmlhttp://www.wsu.edu/policies.htmlhttp://www.tfrec.wsu.edu/http://www.tfrec.wsu.edu/http://www.wsu.edu/http://www.wsu.edu/http://www.wsu.edu/http://en.wikipedia.org/wiki/Concretehttp://en.wikipedia.org/wiki/Compressive_strengthhttp://en.wikipedia.org/wiki/Compressive_strengthhttp://en.wikipedia.org/wiki/Tensile_strengthhttp://en.wikipedia.org/wiki/Tensile_strengthhttp://en.wikipedia.org/wiki/Coefficient_of_thermal_expansionhttp://en.wikipedia.org/wiki/Coefficient_of_thermal_expansionhttp://en.wikipedia.org/wiki/Creep_(deformation)http://en.wikipedia.org/wiki/Creep_(deformation)http://en.wikipedia.org/wiki/Creep_(deformation)mailto:[email protected]://www.scs.wsu.edu/atc/http://www.wsu.edu/copyright.htmlhttp://www.wsu.edu/policies.htmlhttp://www.tfrec.wsu.edu/http://www.wsu.edu/http://en.wikipedia.org/wiki/Concretehttp://en.wikipedia.org/wiki/Compressive_strengthhttp://en.wikipedia.org/wiki/Tensile_strengthhttp://en.wikipedia.org/wiki/Coefficient_of_thermal_expansionhttp://en.wikipedia.org/wiki/Creep_(deformation)http://soils.tfrec.wsu.edu/mg/water.htm


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As a result, without compensating, concrete would almost always fail from tensile stresses even when loaded

in compression. The practical implication of this is that concrete elements subjected to tensile stresses must be

reinforced with materials that are strong in tension.

Reinforced concrete is the most common form of concrete. The reinforcement is often steel, rebar(mesh,

spiral, bars and other forms). Structural fibers of various materials are available.

Concrete can also beprestressed (reducing tensile stress) using internal steel cables (tendons), allowing

forbeamsor slabs with a longerspan than is practical with reinforced concrete alone. Inspection of concrete

structures can be non-destructive if carried out with equipment such as a Schmidt hammer, which is used to

estimate concrete strength.

The ultimate strength of concrete is influenced by the water-cementitious ratio (w/cm), the design constituents,

and the mixing, placement and curing methods employed. All things being equal, concrete with a lower water-

cement (cementitious) ratio makes a stronger concrete than that with a higher ratio. The total quantity ofcementitious materials (portland cement,slag cement,pozzolans) can affect strength, water demand,

shrinkage, abrasion resistance and density. All concrete will crack independent of whether or not it has

sufficient compressive strength. In fact, high Portland cement content mixtures can actually crack more readily

due to increased hydration rate. As concrete transforms from its plastic state, hydrating to a solid, the material

undergoes shrinkage. Plastic shrinkage cracks can occur soon after placement but if the evaporation rate is

high they often can actually occur during finishing operations, for example in hot weather or a breezy day. In

very high-strength concrete mixtures (greater than 70 MPa) the crushing strength of the aggregate can be

a limiting factorto the ultimate compressive strength. In lean concretes (with a high water-cement ratio) the

crushing strength of the aggregates is not so significant.

The internal forces in common shapes of structure, such as arches,vaults, columns and walls are

predominantly compressive forces, with floors and pavements subjected to tensile forces. Compressive

strength is widely used for specification requirement and quality control of concrete. The engineer knows his

target tensile (flexural) requirements and will express these in terms of compressive strength.

Wired.com reported on April 13, 2007 that a team from theUniversity of Tehran, competing in a contest

sponsored by theAmerican Concrete Institute, demonstrated several blocks of concretes with abnormally high

compressive strengths between 340 and 410 MPa (49,000 and 59,000 psi) at 28 days.[2]The blocks appeared

to use an aggregate ofsteel fibres and quartz a mineral with a compressive strength of 1100 MPa, much

higher than typical high-strength aggregates such asgranite(100140 MPa or 15,00020,000 psi).

Reactive Powder Concrete, also known as Ultra-High Performance Concrete, can be even stronger, with

strengths of up to 800 MPa (116,000 PSI).[3] These are made by eliminating large aggregate completely,

carefully controlling the size of the fine aggregates to ensure the best possible packing, and incorporating steel

fibers (sometimes produced by grinding steel wool) into the matrix. Reactive Powder Concretes may also make
http://en.wikipedia.org/wiki/Reinforced_concretehttp://en.wikipedia.org/wiki/Rebarhttp://en.wikipedia.org/wiki/Fiber_reinforced_concretehttp://en.wikipedia.org/wiki/Prestressed_concretehttp://en.wikipedia.org/wiki/Prestressed_concretehttp://en.wikipedia.org/wiki/Tensile_stresshttp://en.wikipedia.org/wiki/Beam_(structure)http://en.wikipedia.org/wiki/Beam_(structure)http://en.wikipedia.org/wiki/Span_(architecture)http://en.wikipedia.org/wiki/Span_(architecture)http://en.wikipedia.org/wiki/Schmidt_hammerhttp://en.wikipedia.org/wiki/Portland_cementhttp://en.wikipedia.org/wiki/Portland_cementhttp://en.wikipedia.org/wiki/Slag_cementhttp://en.wikipedia.org/wiki/Pozzolanhttp://en.wikipedia.org/wiki/Pozzolanhttp://en.wikipedia.org/wiki/Pozzolanhttp://en.wikipedia.org/wiki/Limiting_factorhttp://en.wikipedia.org/wiki/Archhttp://en.wikipedia.org/wiki/Archhttp://en.wikipedia.org/wiki/Vault_(architecture)http://en.wikipedia.org/wiki/Vault_(architecture)http://en.wikipedia.org/wiki/University_of_Tehranhttp://en.wikipedia.org/wiki/University_of_Tehranhttp://en.wikipedia.org/wiki/University_of_Tehranhttp://en.wikipedia.org/wiki/American_Concrete_Institutehttp://en.wikipedia.org/wiki/American_Concrete_Institutehttp://en.wikipedia.org/wiki/Steelhttp://en.wikipedia.org/wiki/Quartzhttp://en.wikipedia.org/wiki/Quartzhttp://en.wikipedia.org/wiki/Granitehttp://en.wikipedia.org/wiki/Granitehttp://en.wikipedia.org/wiki/Granitehttp://en.wikipedia.org/wiki/Reinforced_concretehttp://en.wikipedia.org/wiki/Rebarhttp://en.wikipedia.org/wiki/Fiber_reinforced_concretehttp://en.wikipedia.org/wiki/Prestressed_concretehttp://en.wikipedia.org/wiki/Tensile_stresshttp://en.wikipedia.org/wiki/Beam_(structure)http://en.wikipedia.org/wiki/Span_(architecture)http://en.wikipedia.org/wiki/Schmidt_hammerhttp://en.wikipedia.org/wiki/Portland_cementhttp://en.wikipedia.org/wiki/Slag_cementhttp://en.wikipedia.org/wiki/Pozzolanhttp://en.wikipedia.org/wiki/Limiting_factorhttp://en.wikipedia.org/wiki/Archhttp://en.wikipedia.org/wiki/Vault_(architecture)http://en.wikipedia.org/wiki/University_of_Tehranhttp://en.wikipedia.org/wiki/American_Concrete_Institutehttp://en.wikipedia.org/wiki/Steelhttp://en.wikipedia.org/wiki/Quartzhttp://en.wikipedia.org/wiki/Granite


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use of silica fume as a fine aggregate. Commercial Reactive Powder Concretes are available in the 170210

MPa (25,00030,000 psi) strength range.

Contents

[hide]

1 Elasticity

2 Expansion and

shrinkage

3 Cracking

3.1 Shr

inkage

crackin

g

3.2 Te

nsion

crackin

g

4 Creep

5 Concrete

testing

6 References

[edit]Elasticity

The modulus of elasticity of concrete is a function of the modulus of elasticity of the aggregates and the cement

matrix and their relative proportions. The modulus of elasticity of concrete is relatively constant at low stress

levels but starts decreasing at higher stress levels as matrix cracking develops. The elastic modulus of the

hardened paste may be in the order of 10-30 GPa and aggregates about 45 to 85 GPa. The concrete

composite is then in the range of 30 to 50 GPa.

The American Concrete Instituteallows the modulus of elasticity to be calculated using the following equation:[4]

(psi)

where
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wc = weight of concrete (pounds per cubic foot) and where

f'c = compressive strength of concrete at 28 days (psi)

This equation is completely empirical and is not based on theory. Note that the value ofEc found

is in units of psi. For normalweight concrete (defined as concrete with a wc of 150 lb/ft3 and

subtracting 5 lb/ft3 for steel) Ec is permitted to be taken as .

[edit]Expansion and shrinkage

Concrete has a very low coefficient of thermal expansion. However, if no provision is made for

expansion, very large forces can be created, causing cracks in parts of the structure not capable

of withstanding the force or the repeated cycles ofexpansion and contraction. The coefficient of

thermal expansion of Portland cement concrete is 0.000008 to 0.000012 (per degree Celsius) (8

to 12 microstrains/C)(8-12 1/MK).[5]

As concrete matures it continues to shrink, due to the ongoing reaction taking place in the

material, although the rate of shrinkage falls relatively quickly and keeps reducing over time (for

all practical purposes concrete is usually considered to not shrink due to hydration any further

after 30 years). The relative shrinkage and expansion of concrete and brickwork require careful

accommodation when the two forms of construction interface.

Because concrete is continuously shrinking for years after it is initially placed, it is generally

accepted that under thermal loading it will never expand to its originally placed volume.

Due to its lowthermal conductivity, a layer of concrete is frequently used for fireproofing of steel

structures.

[edit]Cracking
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Salginatobel Bridge,Switzerland.

All concrete structures will crack to some extent. One of the early designers of reinforced

concrete,Robert Maillart, employed reinforced concrete in a number of arched bridges. His first

bridge was simple, using a large volume of concrete. He then realized that much of the concrete

was very cracked, and could not be a part of the structure under compressive loads, yet the

structure clearly worked. His later designs simply removed the cracked areas, leaving slender,

beautiful concrete arches. The Salginatobel Bridgeis an example of this.

Concrete cracks due to tensile stress induced by shrinkage or stresses occurring during setting or

use. Various means are used to overcome this. Fiber reinforced concreteuses fine fibers

distributed throughout the mix or largermetal or other reinforcement elements to limit the size and

extent of cracks. In many large structures joints or concealed saw-cuts are placed in the concrete

as it sets to make the inevitable cracks occur where they can be managed and out of sight. Water

tanks and highways are examples of structures requiring crack control.

[edit]Shrinkage cracking

Shrinkage cracks occur when concrete members undergo restrained volumetric changes

(shrinkage) as a result of either drying, autogenous shrinkage or thermal effects. Restraint is

provided either externally (i.e. supports, walls, and other boundary conditions) or internally

(differential drying shrinkage, reinforcement). Once the tensile strength of the concrete is

exceeded, a crack will develop. The number and width of shrinkage cracks that develop are

influenced by the amount of shrinkage that occurs, the amount of restraint present and the

amount and spacing of reinforcement provided.These are minor indications and have no real

structural impact on the concrete member.

Plastic-shrinkage cracks are immediately apparent, visible within 0 to 2 days of placement, while

drying-shrinkage cracks develop over time. Autogenous shrinkage also occurs when the concrete

is quite young and results from the volume reduction resulting from the chemical reaction of the

Portland cement.

[edit]Tension cracking

Concrete members may be put into tension by applied loads. This is most common in

concrete beamswhere a transversely applied load will put one surface into compression and the

opposite surface into tension due to inducedbending. The portion of the beam that is in tension

may crack. The size and length of cracks is dependent on the magnitude of the bending moment

and the design of the reinforcing in the beam at the point under consideration. Reinforced

concrete beams are designed to crack in tension rather than in compression. This is achieved by
http://en.wikipedia.org/wiki/Salginatobel_Bridgehttp://en.wikipedia.org/wiki/Salginatobel_Bridgehttp://en.wikipedia.org/wiki/Switzerlandhttp://en.wikipedia.org/wiki/Switzerlandhttp://en.wikipedia.org/wiki/Switzerlandhttp://en.wikipedia.org/wiki/Robert_Maillarthttp://en.wikipedia.org/wiki/Robert_Maillarthttp://en.wikipedia.org/wiki/Robert_Maillarthttp://en.wikipedia.org/wiki/Salginatobel_Bridgehttp://en.wikipedia.org/wiki/Salginatobel_Bridgehttp://en.wikipedia.org/wiki/Fiber_reinforced_concretehttp://en.wikipedia.org/wiki/Fiber_reinforced_concretehttp://en.wikipedia.org/wiki/Rebarhttp://en.wikipedia.org/wiki/Rebarhttp://en.wikipedia.org/w/index.php?title=Properties_of_concrete&action=edit&section=4http://en.wikipedia.org/w/index.php?title=Properties_of_concrete&action=edit&section=4http://en.wikipedia.org/w/index.php?title=Properties_of_concrete&action=edit&section=5http://en.wikipedia.org/w/index.php?title=Properties_of_concrete&action=edit&section=5http://en.wikipedia.org/wiki/Beam_(structure)http://en.wikipedia.org/wiki/Beam_(structure)http://en.wikipedia.org/wiki/Bendinghttp://en.wikipedia.org/wiki/Bendinghttp://en.wikipedia.org/wiki/Salginatobel_Bridgehttp://en.wikipedia.org/wiki/Switzerlandhttp://en.wikipedia.org/wiki/Robert_Maillarthttp://en.wikipedia.org/wiki/Salginatobel_Bridgehttp://en.wikipedia.org/wiki/Fiber_reinforced_concretehttp://en.wikipedia.org/wiki/Rebarhttp://en.wikipedia.org/w/index.php?title=Properties_of_concrete&action=edit&section=4http://en.wikipedia.org/w/index.php?title=Properties_of_concrete&action=edit&section=5http://en.wikipedia.org/wiki/Beam_(structure)http://en.wikipedia.org/wiki/Bending


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providing reinforcing steel which yields before failure of the concrete in compression occurs and

allowing remediation, repair, or if necessary, evacuation of an unsafe area.

[edit]Creep

Creep is the term used to describe the permanent movement or deformation of a material in order

to relieve stresses within the material. Concrete which is subjected to long-duration forces is

prone to creep. Short-duration forces (such as wind or earthquakes) do not cause creep. Creep

can sometimes reduce the amount of cracking that occurs in a concrete structure or element, but

it also must be controlled. The amount of primary and secondary reinforcing in concrete

structures contributes to a reduction in the amount of shrinkage, creep and cracking.

[edit]Concrete testing

Compression testing of a concrete cylinder

Same cylinder after failure
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Engineers usually specify the required compressive strength of concrete, which is normally given

as the 28 day compressive strength in megapascals (MPa) or pounds per square inch (psi).

Twenty eight days is a long wait to determine if desired strengths are going to be obtained, so

three-day and seven-day strengths can be useful to predict the ultimate 28-day compressive

strength of the concrete. A 25% strength gain between 7 and 28 days is often observed with

100% OPC (ordinary Portland cement) mixtures, and up to 40% strength gain can be realized

with the inclusion of pozzolans and supplementary cementitious materials (SCMs) such as fly ash

and/or slag cement. Strength gain depends on the type of mixture, its constituents, the use of

standard curing, proper testing and care of cylinders in transport, etc. It is imperative to accurately

test the fundamental properties of concrete in its fresh, plastic state.

Concrete is typically sampled while being placed, with testing protocols requiring that test

samples be cured under laboratory conditions (standard cured). Additional samples may be field

cured (non-standard) for the purpose of early 'stripping' strengths, that is, form removal,

evaluation of curing, etc. but the standard cured cylinders comprise acceptance criteria. Concrete

tests can measure the "plastic" (unhydrated) properties of concrete prior to, and during

placement. As these properties affect the hardened compressive strength and durability of

concrete (resistance to freeze-thaw), the properties of workability (slump/flow), temperature,

density and age are monitored to ensure the production and placement of 'quality' concrete. Tests

are performed perASTM International, European Committee for Standardization orCanadian

Standards Association. As measurement of quality must represent the potential of concrete

material delivered and placed, it is imperative that concrete technicians performing concrete tests

are certified to do so according to these standards. Structural design, material design and

properties are often specified in accordance with national/regional design codes such

asAmerican Concrete Institute.

Compressive strength tests are conducted using an instrumentedhydraulic ramto compress a

standard cylindrical or cubic sample to failure. Tensile strength tests are conducted either by

three-point bending of a prismatic beam specimen or by compression along the sides of a

standard cylindrical specimen. These are not to be equated with nondestructive testingusing

arebound hammeror probe systems which are hand-held indicators, for relative strength of the

top few millimeters, of comparative concretes in the field.

[edit]References
http://en.wikipedia.org/wiki/ASTM_Internationalhttp://en.wikipedia.org/wiki/ASTM_Internationalhttp://en.wikipedia.org/wiki/European_Committee_for_Standardizationhttp://en.wikipedia.org/wiki/Canadian_Standards_Associationhttp://en.wikipedia.org/wiki/Canadian_Standards_Associationhttp://en.wikipedia.org/wiki/Structural_designhttp://en.wikipedia.org/wiki/American_Concrete_Institutehttp://en.wikipedia.org/wiki/American_Concrete_Institutehttp://en.wikipedia.org/wiki/Compressive_strengthhttp://en.wikipedia.org/wiki/Hydraulic_ramhttp://en.wikipedia.org/wiki/Hydraulic_ramhttp://en.wikipedia.org/wiki/Hydraulic_ramhttp://en.wikipedia.org/wiki/Nondestructive_testinghttp://en.wikipedia.org/wiki/Nondestructive_testinghttp://en.wikipedia.org/wiki/Schmidt_hammerhttp://en.wikipedia.org/wiki/Schmidt_hammerhttp://en.wikipedia.org/w/index.php?title=Properties_of_concrete&action=edit&section=8http://en.wikipedia.org/w/index.php?title=Properties_of_concrete&action=edit&section=8http://en.wikipedia.org/wiki/ASTM_Internationalhttp://en.wikipedia.org/wiki/European_Committee_for_Standardizationhttp://en.wikipedia.org/wiki/Canadian_Standards_Associationhttp://en.wikipedia.org/wiki/Canadian_Standards_Associationhttp://en.wikipedia.org/wiki/Structural_designhttp://en.wikipedia.org/wiki/American_Concrete_Institutehttp://en.wikipedia.org/wiki/Compressive_strengthhttp://en.wikipedia.org/wiki/Hydraulic_ramhttp://en.wikipedia.org/wiki/Nondestructive_testinghttp://en.wikipedia.org/wiki/Schmidt_hammerhttp://en.wikipedia.org/w/index.php?title=Properties_of_concrete&action=edit&section=8


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Properties of asphalt. Hot asphalt, asphalt in cold, asphalt prefabricated. Acrylic Base water, bases reliable. Al-Koat introduces the latest in technology for waterproofing: TPO. It surpasses in everything to any other waterproofone, because it reunites in only a product, the best attributes of the APP and the SBS. Al-Koat is in the market a newtechnology that exceeds the physical properties waterproof asphalts modified used in the conventional ones oftoday. TPO represents a technological revolution, innovating the chemical composition of the used materials,marking the beginning of a new era of waterproof products of high performance. The compound TPO is the result ofan extensive investigation and development. The product has distilled asphalt base selected, modified withcomplex mixtures of thermoplastic poliolefinas and specific elastomers, forming these the "skeleton" or structure of

the compound, that is a cohesive with excellent impermeable properties and releases durability. PROPERTIES. Highcompatibility between the polymeric asphalts and components. Flexibility to low temperatures exceeding the one acompound SBS of high quality. Superior resistance to the intemperismo that the one of a compound APP of highquality. Durability that exceeds any previous modified asphalt formulation. ADVANTAGES. The waterproof TPOexceptionally work in an ample rank of temperatures, doing advantageous their use in all the variety of climaticregions, increasing the productivity of the contractor. The compound TPO dramatically increases the durability ofthe impermeable system. Products TPO such offer prefabricated waterproof attributes of the conventional ones fortheir application. Superior mechanical resistance (tension, punching and sharp effort), conferred by the highgramaje (250 grs./m2) of the polyester reinforcement no woven.

Characteristics of the mixtures of asphalts. Asphalts are miscible among them in all the proportions. Thepenetration and the point of softening of a mixture of two asphalts can soon be considered using the attachedtables uniting with an air line the points of the vertical scales offering to the penetration or point of softening of thedegrees to be mixed and using the horizontal scale to read the proportions of the mixture or the requiredproportions. These graphs are extremely safe when asphalts that have the same conditions, like for example thesame index of penetration are used or that are oxidized asphalts or asphalts of direct obtaining.

Diluted asphalts.Asphalt can be mixed with an ample variety of fractions of distillation of petroleum for different applications. Lightvolatile fractions are used for diluted asphalts where a fast drying is required. Fractions as kerosene or oil gas isused where allow a prolonged masking time but. Heavy fractions are used where a permanent softening is required(these mixtures are virtually equal to very soft asphalts). Two general rules are applied for reliable with asphalts:When but "heavy" it is the fraction of reliable, better it will be the dissolution. When but "aromatic" it is the fractionof reliable, better it will be the dissolution. For oxidized degrees, reliable aromatic they must be used inexorably, inorder to avoid some separation of phases.

Asphalt mixtures and paraffin. The paraffin can be added to asphalt by two intentions: In order to reduceviscosity when this it warms up. In order to reduce the " stickseed" when this one cools off. Paraffin with a point offusion of around 50-60 c is usually used, to concentrations of between 5-10c. The paraffin concentration does nothave to exceed 20% to avoid the precipitation of asfaltenos. Other average ones to reduce the "superficial adhesionof asphalt are: To cover the surface with talc or others fine fillers to use hard asphalts but to incorporate a metallicsalt organ like for example: 5% of resinato of manganese.

Chemical Properties


10/13

Asphalt binders can be characterized by their chemical composition although they rarely are

for HMA pavements. However, it is an asphalt binders chemical properties that determine

its physical properties. Therefore, a basic understanding of asphalt chemistry can help one

understand how and why asphalt behaves the way it does. This subsection briefly describes

the basic chemical composition of asphalts and why they behave as they do.

3.3.1 Basic Composition

Asphalt chemistry can be described on the molecular level as well as on the intermolecular

(microstructure) level. On the molecular level, asphalt is a mixture of complex organic

molecules that range in molecular weight from several hundred to several thousand.

Although these molecules exhibit certain behavioral characteristics, the behavior of asphalt

is generally ruled by behavioral characteristics at the intermolecular level the asphalts

microstructure (Robertson et al., 1991).

The asphalt chemical microstructure model described here is based on SHRP findings on the

microstructure of asphalt using nuclear magnetic resonance (NMR) and chromatography

techniques. The SHRP findings describe asphalt microstructure as a dispersed polar fluid

(DPF). The DPF model explains asphalt microstructure as a continuous three-dimensional

association of polar molecules (generally referred to as "asphaltenes") dispersed in a fluid of

non-polar or relatively low-polarity molecules (generally referred to as "maltenes") (Little et

al., 1994). All these molecules are capable of forming dipolar intermolecular bonds of

varying strength. Since these intermolecular bonds are weaker than the bonds that hold

the basic organic hydrocarbon constituents of asphalt together, they will break first and

control the behavioral characteristics of asphalt. Therefore, asphalts physical

characteristics are a direct result of the forming, breaking and reforming of these

intermolecular bonds or other properties associated with molecular superstructures (Little et

al., 1994).

The result of the above chemistry is a material that behaves (1) elastically through the

effects of the polar molecule networks, and (2) viscously because the various parts of the

polar molecule network can move relative to one another due to their dispersion in the fluid

non-polar molecules.

3.3.2 Asphalt Behavior as a Function of its Chemical

Constituents

Robertson et al. (1991) describe asphalt behavior in terms of its failure mechanisms. They

describe each particular failure mechanism as a function of an asphalts basic molecular or

intermolecular chemistry. This section is a summary of Robertson et al. (1991).

Aging. Some aging is reversible, some is not. Irreversible aging is generally

associated with oxidation at the molecular level. This oxidation increases an asphalts

viscosity with age up until a point when the asphalt is able to quench (or halt)

oxidation through immobilization of the most chemically reactive elements.

Reversible aging is generally associated with the effects of molecular organization.

Over time, the molecules within asphalt will slowly reorient themselves into a better
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packed, more bound system. This results in a stiffer, more rigid material. This

thixotropic aging can be reversed by heating and agitation.

Rutting and permanent deformation. If the molecular network is relatively simple

and not interconnected, asphalt will tend to deform inelastically under load (e.g., not

all the deformation is recoverable). Additionally, asphalts with higher percentages of

non-polar dispersing molecules are better able to flow and plastically deform because

the various polar molecule network pieces can more easily move relative to one

another due to the greater percentage of fluid non-polar molecules.

Fatigue cracking. If the molecular network becomes too organized and rigid,

asphalt will fracture rather than deform elastically under stress. Therefore, asphalts

with higher percentages of polar, network-forming molecules may be more

susceptible to fatigue cracking.

Thermal cracking. At lower temperatures even the normally fluid non-polar

molecules begin to organize into a structured form. Combined with the already-

structured polar molecules, this makes asphalt more rigid and likely to fracture

rather than deform elastically under stress.

Stripping. Asphalt adheres to aggregate because the polar molecules within the

asphalt are attracted to the polar molecules on the aggregate surface. Certain polar

attractions are known to be disrupted by water (itself a polar molecule).

Additionally, the polar molecules within asphalt will vary in their ability to adhere to

any one particular type of aggregate.

Moisture damage. Since it is a polar molecule, water is readily accepted by the

polar asphalt molecules. Water can cause stripping and/or can decrease asphalt

viscosity. It typically acts like a solvent in asphalt and results in reduced strength

and increased rutting. When taken to the extreme, this same property can be usedto produce asphalt emulsions. Interestingly, from a chemical point-of-view water

should have a greater effect on older asphalt. Oxidation causes aged (or older)

asphalts to contain more polar molecules. The more polar molecules an asphalt

contains, the more readily it will accept water. However, the oxidation aging effects

probably counteract any moisture-related aging effects.

In summary, asphalt is a complex chemical substance. Although basic chemical

composition is important, it is an asphalts chemical microstructure that is most influential in

its physical behavior. Although most basic asphalt binder failure mechanisms can be

described chemically, currently there is not enough asphalt chemical knowledge to

adequately predict performance. Therefore, physical properties and tests are used.

3.4 Physical PropertiesAsphalt binders are most commonly characterized by their physical properties. An asphalt

binders physical properties directly describe how it will perform as a constituent in HMA

pavement. The challenge in physical property characterization is to develop physical tests
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that can satisfactorily characterize key asphalt binder parameters and how these

parameters change throughout the life of an HMA pavement.

The earliest physical tests were empirically derived tests. Some of these tests (such as

the penetration test) have been used for the better part of the 20th century with good

results. Later tests (such as the viscosity tests) were first attempts at using fundamental

engineering parameters to describe asphalt binder physical properties. Ties between testedparameters and field performance were still quite tenuous. Superpave binder tests,

developed in the 1980s and 1990s, were developed with the goal of measuring specific

asphalt binder physical properties that are directly related to field performance by

engineering principles. These tests are generally a bit more complex but seem to

accomplish a more thorough characterization of the tested asphalt binder.

This subsection, taken largely from Roberts et al. (1996), describes the more common U.S.

asphalt binder physical tests. Asphalt binder tests specifically developed or adopted by

theSuperpave research effort are noted by a " Superpave" in their title. Sections that

discuss Superpave tests also discuss relevant field performance information as well as the

engineering principles used to develop the relationship between test and field performance.

3.4.1 Durability

Durability is a measure of how asphalt binder physical properties change with age

(sometimes called age hardening). In general, as an asphalt binder ages, its viscosity

increases and it becomes more stiff and brittle. Age hardening is a result of a number of

factors, the principal ones being (Vallerga, Monismith and Grahthem, 1957 and Finn, 1967

as referenced by Roberts et al., 1996):

Oxidation. The reaction of oxygen with the asphalt binder.

Volatilization. The evaporation of the lighter constituents of asphalt binder. It is

primarily a function of temperature and occurs principally during HMA production.

Polymerization. The combining of like molecules to form larger molecules. These

larger molecules are thought to cause a progressive hardening.

Thixotropy. The property of asphalt binder whereby it "sets" when unagitated.

Thixotropy is thought to result from hydrophilic suspended particles that form a

lattice structure throughout the asphalt binder. This causes an increase in viscosity

and thus, hardening (Exxon, 1997). Thixotropic effects can be somewhat reversed

by heat and agitation. HMA pavements with little or no traffic are generally

associated with thixotropic hardening.

Syneresis. The separation of less viscous liquids from the more viscous asphalt

binder molecular network. The liquid loss hardens the asphalt and is caused by

shrinkage or rearrangement of the asphalt binder structure due to either physical or

chemical changes. Syneresis is a form ofbleeding (Exxon, 1997).

Separation. The removal of the oily constituents, resins or asphaltenes from the

asphalt binder by selective absorption of some porous aggregates.
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There is no direct measure for asphalt binder aging. Rather, aging effects are accounted for

by subjecting asphalt binder samples to simulated aging then conducting other standard

physical tests (such as viscosity, dynamic shear rheometer (DSR), bending beam rheometer

(BBR) and the direct tension test (DTT)). Simulating the effects of aging is important

because an asphalt binder that possesses a certain set of properties in its as-supplied state,

may possess a different set of properties after aging. Asphalt binder aging is usually splitup into two categories:

Short-term aging. This occurs when asphalt binder is mixed with hot aggregates

in an HMA mixing facility.

Long-term aging. This occurs after HMA pavement construction and is generally

due to environmental exposure and loading.

Typical aging simulation tests are:

Thin-film oven (TFO) test

Rolling thin-film oven (RTFO) test

Pressure aging vessel (PAV)
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