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P R O B L E M S

1.What is the difference between a natural aggregate and

manufactured aggregate ?

Answer :

Natural aggregate are taken from natural deposits without

change in their nature during production, with the exception of

crushing, sizing, grading, or washing. In this group, crushed

stone, gravel, and sand at the most common, although pumice,

shells, iron ore, and limerock may also be included.

Manufacture aggregate are man-made, manufactured with

change from nature shape and size. Manufactured aggregates

include blast furnace slag, clay, shale, and lightweight

aggregates.

2.Aggregate may be classified as fine aggregate or coarse

aggregate, explain the difference !

Answer :

According to ASTM C125 (Concrete and Concrete Aggregate) :

Fine aggregate is defined as aggregate passing a 3/8-in. (9.5

mm) sieve and almost entirely passing a No.4 (4,75 mm) sieve

and predominantly retained on the No.200 (75-µm) sieve or that

portion of an aggregate passing the No.4 (4.75 mm) sieve and

retained on the No.200 (75-µm) sieve.

Coarse aggregate is defined as aggregate predominantly

retained on the No.4 (4.75-mm) sieve or that portion of an

aggregate retained on the No.4 ( 4.75-mm) sieve

These definitions are for concrete aggregates. For bituminous concrete

mixturs dividing line between fine and coarse aggregate is the No.8 (9.5-

mm) or the No.10 (11.8-mm).

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3.How aggregate are processed for use a portland cement

concrete ingredients or as a bituminous concrete ingredients.

Answer:

The main fundamental rule of good aggregate procssing is to obtain

aggregates of the highest quality at the least cost. Each process is

completed with these objectives in mind, but are not limited to,

excavation, transportation, washing, crushing and sizing. Processing

begins with excavation and quarrying of the material and ends upon being

stockpiled or delivered to the site.

In the excavation process the overburden is removed (if applicable), as its

presence in aggregate in the form of silt or clay cannot be tolerated. The

removal of the overburden is carried out thrugh the use of power shovels,

draglines, or scrapers. Overburden removal is ussualy considered only if

therre is a depth of 50 ft (15.24 m) or more. If the overburden is light, it

will wash out in the processing of the aggregate.

After the aggregate is excavated, it is transported by rail, truck, or

conveyor belt to the processing of the aggregate. At the processing plant,

unacceptable (deleterious) materials are removed. A deleterious material

is a material that may prove harmful to the final product for which the

aggregate is to be used. One method of removing deleterious materials

(clay, mud, leaves, etc) is to wash the raw material. Sometimes conveyor

belts are used to haul the aggregate through flumes that are flushed with

water.

The next process is to reduce the size of the stone or gravel. In this

process many types of crushers are used. The oldest is the jaw crushers,

which consists of a crushers have a higher capacity than the jaw crusher,

but this is the only disadvantage of the jaw crusher. The usual practice is

to reduce the size of the rock at a ratio of 1:6 or less.

For sizing, vibratory sieves are used for coarse material and

hydraulic classification devices for fine material. The screens vary in

design, capacity, and effeciency. In the screeing procces about 70 percent

of the material will pass through the screen so that the goals of high

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efficiecy and capacity are met. In most cases some removal of oversize

particles, called scrapping, will take.

4.How does particle shape affect the use of aggregate in base-

course materials? In portland cement concrete? In bituminous

concrete?

Answer:

In Base-Course Materials

Particle shape and surface texture influence the properties of freshly

mixed concrete more than the properties ofhardened concrete. Rough-

textured, angular, and elongated particles require more water to produce

workable concrete than smooth, rounded compact aggregate.

Consequently, the cement content must also be increased to maintain the

water-cement ratio. Generally, flat and elongated particles are avoided or

are limited to about 15 percent by weight of the total aggregate. Unit-

weight measures the volume that graded aggregate and the voids

between them will occupy in concrete.

The void content between particles affects the amount of cement paste

required for the mix. Angular aggregates increase the void content. Larger

sizes of well-graded aggregate and improved grading decrease the void

content. Absorption and surface moisture of aggregate are measured

when selecting aggregate because the internal structure of aggregate is

made up of solid material and voids that may or may not contain water.

The amount of water in the concrete mixture must be adjusted to include

the moisture conditions of the aggregate.

Abrasion and skid resistance of an aggregate are essential when the

aggregate is to be used in concrete constantly subject to abrasion as in

heavy-duty floors or pavements. Different minerals in the aggregate wear

and polish at different rates.Harder aggregate can be selected in highly

abrasive conditions to minimize wear.

In Portland Cement Concrete

The shape and texture of aggregate affects the properties of fresh

concrete more than hardened concrete. Concrete is more workable when

smooth and rounded aggregate is used instead of rough angular or

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elongated aggregate. Most natural sands and gravel from riverbeds or

seashores are smooth and rounded and are excellent aggregates. Crushed

stone produces much more angular and elongated aggregates, which

have a higher surface-to-volume ratio, better bond characteristics but

require more cement paste to produce a workable mixture.

The surface texture of aggregate can be either smooth or rough. A

smooth surface can improve workability, yet a rougher surface generates

a stronger bond between the paste and the aggregate creating a higher

strength.

The grading or size distribution of aggregate is an important

characteristic because it determines the paste requirement for workable

concrete. This paste requirement is the factor controlling the cost, since

cement is the most expensive component. It is therefore desirable to

minimize the amount of paste consistent with the production of concrete

that can be handled, compacted, and finished while providing the

necessary strength and durability. The required amount of cement paste

is dependent upon the amount of void space that must be filled and the

total surface area that must be covered. When the particles are of uniform

size the spacing is the greatest, but when a range of sizes is used the void

spaces are filled and the paste requirement is lowered. The more these

voids are filled, the less workable the concrete becomes, therefore, a

compromise between workability and economy is necessary.

The moisture content of an aggregate is an important factor when

developing the proper water/cementitious material ratio. All aggregates

contain some moisture based on the porosity of the particles and the

moisture condition of the storage area. The moisture content can range

from less than one percent in gravel to up to 40 percent in very porous

sandstone and expanded shale. Aggregate can be found in four different

moisture states that include oven-dry (OD), air-dry (AD), saturated-surface

dry (SSD) and wet. Of these four states, only OD and SSD correspond to a

specific moisture state and can be used as reference states for calculating

moisture content. In order to calculate the quantity of water that

aggregate will either add or subtract to the paste, the following three

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quantities must be calculated: absorption capacity, effective absorption,

and surface moisture.

Most stockpiled coarse aggregate is in the AD state with an absorption

of less than one percent, but most fine aggregate is often in the wet state

with surface moisture up to five percent. This surface moisture on the fine

aggregate creates a thick film over the surface of the particles pushing

them apart and increasing the apparent volume. This is commonly known

as bulking and can cause significant errors in proportioning volume.

The density of the aggregates is required in mixture proportioning to

establish weight-volume relationships. Specific gravity is easily calculated

by determining the densities by the displacement of water. All aggregates

contain some porosity, and the specific gravity value depends on whether

these pores are included in the measurement. There are two terms that

are used to distinguish this measurement; absolute specific gravity and

bulk specific gravity. Absolute specific gravity (ASG) refers to the solid

material excluding the pores, and bulk specific gravity (BSG), sometimes

called apparent specific gravity, includes the volume of the pores. For the

purpose of mixture proportioning, it is important to know the space

occupied by the aggregate particles, including the pores within the

particles. The BSG of an aggregate is not directly related to its

performance in concrete, although, the specification of BSG is often done

to meet minimum density requirements.

For mixture proportioning, the bulk unit weight (a.k.a. bulk density) is

required. The bulk density measures the volume that the graded

aggregate will occupy in concrete, including the solid aggregate particles

and the voids between them. Since the weight of the aggregate is

dependent on the moisture content of the aggregate, a constant moisture

content is required. This is achieved by using OD aggregate. Additionally,

the bulk density is required for the volume method of mixture

proportioning.

The most common classification of aggregates on the basis of bulk

specific gravity is lightweight, normal-weight, and heavyweight

aggregates. In normal concrete the aggregate weighs 1,520 – 1,680

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kg/m3, but occasionally designs require either lightweight or heavyweight

concrete. Lightweight concrete contains aggregate that is natural or

synthetic which weighs less than 1,100 kg/m3and heavyweight concrete

contains aggregates that are natural or synthetic which weigh more than

2080 kg/m3.

Although aggregates are most commonly known to be inert filler in

concrete, the different properties of aggregate have a large impact on the

strength, durability, workability, and economy of concrete. These different

properties of aggregate allow designers and contractors the most

flexibility to meet their design and construction requirements.

Bituminous Concrete

Aggregate particle shape and surface texture are important for

proper compaction, deformation resistance, and workability. However, the

ideal shape for HMA and PCC is different because aggregates serve

different purposes in each material. In HMA, since aggregates are relied

upon to provide stiffness and strength by interlocking with one another,

cubic angular-shaped particles with a rough surface texture are best.

However, in PCC, where aggregates are used as an inexpensive high-

strength material to occupy volume, workability is the major issue

regarding particle shape. Therefore, in PCC rounded particles are better.

Rounded particles create less particle-to-particle interlock than angular

particles and thus provide better workability and easier compaction.

However, in HMA less interlock is generally a disadvantage as rounded

aggregate will continue to compact, shove and rut after construction. Thus

angular particles are desirable for HMA (despite their poorer workability),

while rounded particles are desirable for PCC because of their better

workability (although particle smoothness will not appreciably affect

strength) (PCA, 1988).

5.Explain the use of Fuller’s masimum density curve!

Answer :

Mathematically, Fuller Grading Curves offer the maximum density and

minimum voids:

6 pi=√ d iD×100%

[ ]

where pi = total % passing sieve size i

di = width of opening of sieve size i

D = largest size (sieve opening) in gradation

Fuller Grading Curves

#200

0.149 0.297 0.59 1.19 2.38 4.76 9.52 12.7 19.1 25 37.5 50 630%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0.01 0.1 1 10 100

Sieve Opening (mm)

% P

assi

ng

0.074

#100 #50 #30 #16 #8 #4 ⅜" ½ ¾" 1" 1½" 2" 2½"

The maximum density curve give approximation of gradation. If employed

properly, it can be a valuable tool as a point of beginning in designing

aggregate blends for maximum density.

6.Why is gradation important in portland cement concrete?

Answer :

Aggregates properties for portland cement concrete are in many

cases different from aggregates used for base courses or for use in

bituminous concrete. Aggregate gradation becomes a key factor as it

control the workability of the plastic concrete.

Grading limits and maximum aggregate size are specified because

these properties affect the amount of aggregate used as well as cement

and water requirements, workability, pumpability, and durability of

concrete. In general, if the water-cement ratio is chosen correctly, a wide

range in grading can be used without a major effect on strength. When

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gap-graded aggregate are specified, certain particle sizes of aggregate

are omitted from the size continuum. Gap-graded aggregate are used to

obtain uniform textures in exposed aggregate concrete. Close control of

mix proportions is necessary to avoid segregation.

The specific impact of a failed aggregate gradation not only

depends on whether the aggregates fail on the coarser or the finer side of

the gradation but also on the extent of the failure away from the

acceptable gradation limits. Surface texture affect the water cement ratio

so the strength of concrete will be affected.

7.Which type of aggregates (igneous, sedimentary, or

metamorphic) would you expect to be most suitable as a base –

course material ? Why ?

Answer :

Materials and Sources Natural aggregate materials include a variety of

rocks and minerals that can be excavated from quarries or mines.

Geologically, these materials can be categorized as one of three types:

Sedimentary rocks – limestone and other rocks created by

sedimentary deposits.

Igneous rocks – granite and other rocks created by cooling volcanic

or molten rock material.

And the last is Metamorphic rocks, this type expect to be

most suitable as a base – course material because sedimentary

or igneous rocks that have been subjected to enough heat or

pressure to change their mineral structure.One type is necessarily

superior to the others, as the quality of aggregate depends on the

physical and chemical properties of the specific material. This types

are commonly available will depend on the geologic history of a

region., especially in Indonesia

Some regions in Indonesia have sources of aggregate, as local quarry

resources may be too scarce or of insufficient quality for pavement

construction. If the cost of obtaining natural aggregate is prohibitive, it

may be possible to substitute suitable manufactured materials or

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byproducts. Both reclaimed asphalt pavement (RAP) and recycled

concrete can be used to make high-quality base layers. Other industrial

byproducts including furnace slag and waste glass are also feasible

alternatives.

A number of material properties and characteristics affect the

performance of an aggregate base layer. One of the most important is

the gradation, or the size distribution of aggregate particles in the

material. Others include the ability of the aggregate to resist damage and

its particle shape, texture, and angularity.Bases may consist of uncrushed

virgin aggregate or material that has been crushed in order to create

more rough surfaces and angles

In considering the base as a layer within the pavement structure, its

density along with its moisture content and drainage characteristics are

also important. Achieving the desired density typically requires using

compaction equipment before the pavement surface layers are placed. A

base layer of dense-graded aggregate, with a mix of particles sizes tightly

packed together, will generally provide the most structural support for the

pavement surface. An aggregate base may be hidden from sight after the

pavement is completed, but it remains a critical part of the pavement

structure.

8.Review various refrence on the subject of freezingand thawing

and write short report on how they eventually lead to concrete

failure.

Answer :

Freeze – Thaw Resistance When water freezes, it expands about 9

percent. As the water in moist concrete

freezes it produces pressure in the pores of

the concrete. If the pressure developed

exceeds the tensile strength of the concrete,

the cavity will dilate and rupture. The

accumulative effect of successive freeze-thaw

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cycles and disruption of paste and aggregate can eventually cause

expansion and cracking, scaling, and crumbling of the concrete.

Deicing chemicals for pavements include sodium chloride, calcium

chloride, magnesium chloride, and potassium chloride. These chemicals

reduce the freezing point of the precipitation as it falls on pavements. A

recent trend has seen a wide variety of blends of these materials to

improve performance while reducing costs, and best practice indicates

that a liberal dosage greater than four percent in solution tends to

decrease the potential for scaling of pavement surfaces. The high

concentration of deicers reduces the number of freezing and thawing

cycle exposures to the pavement by significantly lowering the freezing

point.

Deicers for special applications such as airport pavements require non-

chloride materials to prevent damage to aircraft. The list of deicers used

for these applications includes urea, potassium acetate, propylene glycol,

and ethylene glycols.

Since scaling damage to pavements of all types is caused by physical salt

attack, the use of high strength (4,000 psi or more), low permeability, air

entrained concrete is crucial to good durability in these applications.

D-Cracking - Cracking of concrete pavements caused by the

freeze-thaw deterioration of the aggregate within concrete is called D-

cracking. D-cracks are closely spaced crack formations parallel to

transverse and longitudinal joints that later multiple outward from the

joints toward the center of the pavement panel. D-cracking is a function of

the core properties of certain types of aggregate particles and the

environment in which the pavement is placed.

Due to the natural accumulation of water

under pavements in the base and subbase

layers, the aggregate may eventually become

saturated. Then with freezing and thawing

cycles, cracking of the concrete starts in the

saturated aggregate at the bottom of the slab

and progresses upward until it reaches the

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wearing surface. This problem can be reduced either by selecting

aggregates that perform better in freeze-thaw cycles or, where marginal

aggregates must be used, by  reducing the maximum particle size. Also,

installation of effective drainage systems for carrying free water out from

under the pavement may be helpful.

Cross section of air-entrained (right)

and non-air-entrained concrete. Large

size air voids are entrapped air. Small

pinpoint size bubbles (entrained air)

uniformly distributed through the

paste are beneficial air voids. Note

comparison with common pin.

Air entrainment - The severity of freeze-thaw exposure varies with

different areas of the United States. Local weather records can help

determine the severity of exposure. The resistance of concrete to freezing

and thawing in a moist condition is significantly improved by the use of

intentionally entrained air. The tiny entrained air voids act as empty

chambers in the paste for the freezing and migrating water to enter, thus

relieving the pressure in the pores and preventing damage to the

concrete. Concrete with a low permeability (that is, a low water-cement

ratio and adequate curing) is better able to resist freeze-thaw cycles. In

rare cases, air-void clustering can occur, leading to a loss of compressive

strength. 

Typical example of scaled concrete

surface

Prevention of Concrete Scaling. Scaling is defined as a general

loss of surface mortar or mortar surrounding the coarse aggregate

particles on a concrete surface. This problem is typically caused by the

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expansion of water due to freezing and thawing cycles and the use of

deicing chemicals; however properly specified, produced, finished, and

cured quality concrete need not suffer this type of deterioration. There is a

distinct chain of responsibility for the production of scale resistant

concrete.

Closeup view of ice impressions in

paste of frozen fresh concrete. The ice

crystal formations occur as unhardened

concrete freezes.

Freezing temperatures. Concrete gains very little strength at low

temperatures. Accordingly, freshly placed concrete must be protected

against freezing until the degree of saturation of the concrete has been

sufficiently reduced by cement hydration. The time at which this reduction

is accomplished corresponds roughly to the time required for the concrete

to attain a compressive strength of 500 psi. Concrete to be exposed to

deicers should attain a strength of 4,000 psi prior to repeated cycles of

freezing and thawing.

Optimizing the Use of Fly Ash in

Concrete  Cold weather and winter

conditions can be challenging when

concrete contains fly ash. Especially when

used at higher levels, fly ash concrete

typically has extended setting times and slow strength gain, leading to

low early-age strengths and delays in rate of construction. In addition,

concretes containing fly ash are often reported to be more susceptible to

surface scaling when exposed to deicing chemicals than portland cement

concrete. It is therefore important to know how to adjust the amount of fly

ash to minimize the drawbacks, while maximizing the benefits. Optimized

the amount of fly ash on the basis of the requirements of the concrete

specification, the construction schedule and the temperatur, then limited

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the amount of fly ash in slabs on grade placed during winter months to 20

percent. If adequate curing cannot be provided or if the concrete is

exposed to freezing and thawing in the presence of deicer salts, the

amount of fly ash should always be less than 25 percent. 

Effect of Fast Freeze-Thaw Cycles on Mechanical Properties

of Ordinary-Air-Entrained Concrete : Freezing-thawing resistance is a

very significant characteristic for concrete in severe environment (such as

cold region with the lowest temperature below 0°C). Durability of concrete

is the ability to retain its original form and quality without significant

deterioration for a long time. Factors causing the damage of concrete

material in structure can be divided into two categories: physical effects

(such as freeze-thaw damage and abrasion) and chemical effects (such as

sulfate attack and corrosion of reinforcing steel), in the whole design life.

As a widely used construction material, the durability characteristics of

concrete are all significant to its sustained use. Due to the need of

practical application, many reinforced concrete structure were (will be)

built in cold regions that inevitably subjected to freezing and thawing

action. One main reason of durability problem in reinforced concrete

structures in cold environment is the damage caused by action of freezing

and thawing.

The effects of action of freeze/thaw cycles on air-entrained concrete

and plain concrete are well documented and many researchers have

documented the improvement on the freeze/thaw resistance of air-

entrained concrete over plain concrete. Reference introduced the

experiment study about freezing and thawing resistance of air-entrained

concrete in which the coarse aggregate was produced from air-entrained

concrete and non-air-entrained concrete, respectively. Reference

investigated behavior (strength and durability) of air-entrained CSF

(condensed silica fume) concrete after the action of freezing and thawing

cycles. As one of the main measures to improve the frost resistance of

concrete, ordinary-air-entrained concrete has been applied to many kinds

in civil engineering in cold regions and has got very obvious economic

benefits and social effects.

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The main reason that induced cracks in concrete is the volume

expansion caused by water frozen into ice. The second reason that

induced cracks is the thermal stress developed under the action of

repeated freeze-thaw. The third reason the durability of concrete can be

improved greatly by adding air-entraining agent into concrete, and the

last is the freeze-thaw durability of concrete should be taken into

consideration in structure design and maintenance.

9.Review several references and explain why aggregate

beneficiation is necessary. Include in your report the methods

used for aggregate beneficiating.

Answer :

First References Jackson F H.“The Durability of Concrete in

Service”. Prociding American Concrete Institute. 43 (1942). page

165

This journal discusses the problemofconcretedurability withreference

primarily to highway bridgestructures located in regionssubjecttosevere

frost action. Four major types of deteriorationare definedand illustrated

and several specific mattersthat have bearing on the problem, including

the effect of construction variables, modern versus old fashioned

cements, air entrainment, and the so-called cementalkali aggregate

reaction, arediscussed. The reportconcludes with a series of

recommendations indicating correctivemeasuresthat shouldbe taken.

Second References Abdun Nur E A. “Concrete and Concrete

Making Materials”. ASTM Spech. Tech. Pblication 169-A. 1966. PP 7-

17.

Size Gradation

Grading or aggregate size distribution is a major characteristic in

concrete mix design. Cement is the most expensive material in concrete.

Therefore, by minimizing the amount of cement, the cost of concrete can

be reduced.

Sieve Analysis -- determines the grading of an aggregate. Coarse

aggregate is that retained on the #4 sieve and fine aggregate is

that passing a #4 sieve. In a sieve analysis a series of sieve are

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used with smaller and smaller openings. Coarse aggregates are

analyzed with standard sieves and fine aggregates with half-sized

sieves. 

Maximum Aggregate Size -- Smallest sieve in which the entire

sample will pass through. The maximum nominal size is the smallest

sieve in which at least 95%, by weight, of the sample will pass.

Maximum size should not be larger than 1/5 the minimum

dimension of a structural member, 1/3 the thickness of a slab, or 3/4

the clearance between reinforcing rods and forms. These

restrictions limit maximum aggregate size to 1 1/2 inches, except in

mass applications. Higher maximum aggregate size lowers paste

requirements, increases strength and reduces w/c ratios. However,

excessively large aggregate tends to lower strength by reducing

available bonding area. ASTM has limits for grading of concrete

aggregates.

Fineness Modulus -- a parameter for checking the uniformity of

grading. Generally calculated for fine aggregates but also for coarse

aggregates assuming 100% is retained on #8 - #100 sieves.

Therefore, for fine and coarse aggregates respectively, the fineness

modulus is:

F.M. = (Cumulative percent retained on half-sized sieves)/100

F.M. = (Cumulative percent retained on standard sieves including

#4 + 500 )/ 100

A fineness modulus for fine aggregates should be 2.3 - 3.1. Two

aggregates with the same fineness modulus can have different grading

curves. A low fineness modulus requires more cement paste to maintain

workability. Variations from mix design requirements for fineness modulus

should not exceed 0.2 (ASTM standards). ASTM allows for an increase in

fine aggregates (% passing #50 and #100) if smoother surface finishing is

required. However, there are solid restrictions on very fine particles to

prevent increased water demand and volume instability.

Gap Grading -- An aggregate where one or more of the intermediate-sized

fractions is omitted. Advantages of gap grading are more economical

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concrete, use of less cement, and lower w/c ratios. The resulting concrete

is very stiff and has low workability. An extreme case is no-fines concrete.

This concrete is difficult to handle and compact; developing low strength

and high permeability.

Durability of Aggregates

Aggregates makeup the largest part of concrete mixes and are

responsible for the durability of the mix. Durability is a measure of how

well concrete will handle freezing and thawing, wetting and drying, and

physical wear. Chemical reactions also can contribute to problems with

durability.

Soundness -- rocks that undergo volume changes due to wetting

and drying are rare. However, aggregate is susceptible to volume

change during freezing and thawing cycles. Freezing can cause

internal stresses to build up as water inside the aggregate freezes

and expands. A critical size can be calculated below which freeze-

thaw stress is not a problem; however, for most rock it is greater

than normal sizes. 

Wear Resistance -- a good aggregate will be hard, dense, strong,

and free of porous material. The abrasion resistance of aggregate

can be tested by the Los Angeles abrasion test; however, this test

does not match well with concrete wear in the field. 

Alkali-Aggregate Reaction -- An expansive reaction between

some reactive forms of silica with the aggregate and alkalis in the

cement paste. The result is overall cracking in the structure,

manifesting itself in map or pattern cracking at the surface. This

reaction can be controlled most easily by using low-alkali cements.

However, due to changes in manufacturing, low-alkali cements may

not be feasible. A better approach is to avoid aggregate with the

potential or proven record of reactivity. A low w/c ratio is very

impermeable and will slow down the reaction but not stop it. No

adverse reactions will occur without external water. 

Other Alkali-Silica Reactions -- sand-gravels found in river

systems of Kansas and Nebraska are highly reactive and cause map

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cracking. Replacement of 30% of the aggregate with crushed

limestone is effective in reducing the damage. Basically, it results in

the separation of flat clay minerals causing very slow expansion. 

Alkali-Carbonate Reactions -- an expansive reaction involving

clayey carbonate rock. Reaction can be controlled by using low-

alkali cements or blending aggregate with other less reactive

material. ASTM has set standards for deleterious substances in

aggregates, which depend on application. This can be divided into

two categories: 

o Impurities

Solid materials - particles passing a 200-mesh sieve.

These fine particles may increase water requirements

and interfere with surface bonding between cement and

coarse aggregates.

Soluble substances - organic matter may interfere

chemically with alkaline cement pastes affecting setting

time. Aggregates obtained from the sea should be

thoroughly cleaned to avoid problems from salt

contamination.

o Unsound particles -- Soft particles such as clay lumps,

wood, and coal will cause pitting and scaling at the surface.

Organic compounds can be released which interfere with

setting and hardening. Weak material of low density which

have low wear resistance should also be avoided.

Why aggregate beneficiation is necessary?

Aggregate Beneficiation -- If an aggregate does not pass the ASTM

tests, an engineer may choose to try to upgrade the material.

Beneficiation as applied to aggregate production has a precise meaning: it

refers to the selective removal of undesirable constituents in an

aggregate. It is therefore the additional processing to upgrade or improve

the quality of the raw material by a variety of means, most of which rely

on gravity separation, or occasionally on centrifugal separation.

Beneficiation is usually used to remove unsound, lightweight, or

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deleterious materials from aggregates, as well as removal of mica flakes

by modified washing procedures. Beneficiation must be distinguished from

the normal production processes of crushing, screening, and washing

which are intended to provide proper gradation and cleanliness. In effect,

the removal of unwanted clay and silt fractions can be regarded as

‘beneficiation’, althouggh this is normally accomplished in conventional

washing or scrubbing operations. Of necessity, beneficiation is expensive

not least because some acceptable material is always lost, and producers

would rather avoid this is possible. Beneficiation may be useful in areas

where aggregate is scarce. There are several possible ways of treatment: 

Crushing -- Soft, porous rock may be removed by crushing.

Heavy-media separation -- Lightweight particles may be

separated by floating them to the top of a liquid.

Reverse water flow or air flow -- used to remove lightweight

particles like wood.

Hydraulic jigging -- Stratification of aggregate in a vertical

pulsation of water. Lightweight particles separate to the top.

Elastic fractionation -- Aggregate is dropped on an incline steel

plate. Hard particles bounce higher off the plate than do softer

particles. Appropriate placement of collection bins can provide good

separation.

Washing and scrubbing -- Removes fine surface particles.

10.Review the ASTM specifications for tests concerning the

general quality of aggregates, deletirious materials in

aggregates, and the specification used in the design of

portland cement and bituminuous concrete mixes, and write a

short report on the purposes, proceduresm and reasons for

the tests.

Answer :

In the following section we will look at various ASTM test specifications,

with special emphasis on the following categories:

1) Tests concerning thegeneral quality of aggregates.

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2) Tests concerning deleterious mterials in aggregates.

3) Tests used in the design of portland cement concrete and

bituminous mix design.

Tests Concerning The General Quality of Aggregates

ASTM C131 (resistance to degredation of small size coarse

aggregate by abrasion and impact in the Los Angeles machine)

Purpose:The purpose of this specification is to test coarse aggregate

smaller than 1.5 in. (3.81 cm) for resistance abration using the Los

Angeles testing machine and to evaluate base-course aggregates for

possible degradation.

Procedure: In this procedure, the test sample is placed in the Los

Angeles testing machine after it has been prepared for testing in

accordance with this specification. The machine is rotated at a speed of

30 to 33 rpm for 500 revolutions. The material discharged from the

machine and a preliminary separation of the sample is made of a sieve

coarser than the No. 12. The finer portion is sieved using the No. 12 sieve

in a manner conforming to the specification. The material coarser than the

No. 12 sieve is washed and oven-dried at 221 to 230F (105 to 110C) to

constant weight and weighed to the nearest gram. The differnce between

the original weight and the final weight of the test sample is expressed as

a percent of the original weight. The value is reported as a precent of

wear.

ASTM C88 (soundness of aggregates by use of sodium sulfate or

magnesium sulfate)

Purpose: The purpose of this specification is to determine the potential

resistance of an aggregate to weathering.

Procedure: In this procedure a specific weight of an aggregate having a

known sieve analysis is immersed in a solution of sodium or magnesium

sulfate for 16 to 18 hours. Next, it is placed in an oven at 230 F (110C)

and dried constant weight. The procedure is repeated for the desired

period (usually 5 or 10 cycles); the sample is cooled, washed, and dried to

constan weight; then sieved, weighed, and recorded as the percent of

weight lost.

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ASTM C666 (resistance of concrete to rapid freezing and thawing)

Purpose: The purpose of this spesification is to determine how concrete

will react under continous cycles of freezing and thawing and to rank

aggregates.

Procedure: In this procedure two methods are used. Method A involves

rapid freezing and thawing in water, and method B involves rapid freezing

in air and thawing in water. Immediately after curring, the specimen is

brought to a temperature within -2F and +4F (-1.1C and 2.2C) of the

target thaw temperature that will be used in the freeze-thaw cycle and

tested for fundamental transverse frequency, weighed, and measured in

accordance with ASTM C215 (Fundamental Transverse, Longitudinal. And

Torsional Frequence of Concrete Specimens). The spesimen is protected

against loss of moisture between the time of removal from curing and the

start of the freeze-thaw test.

ASTM C215 (fundamental transvers, longitudinal, and torsional

frequencies of concrete specimens)

Purpose: The purpose of this test in to determine the relationship

between strength loss and cycles of freezing and thawing.

Procedure: The spesimen is forced to vibrate at various frequencies.

Record the frequency of the test spesimen that result in maximum

indication having a well-defined peak on the indicator and at which

observation of nodal ponts indicates fundamental transverse vibration as

the fundamental transverse frequency. Young’s modulus is then

calculated as follows :

durability factor=DF300=PNM

=(relative E )(N cycles)durationof test

In this test it is not necessary to perform the test for 300 cycles of

freezing and thawing. It is only necessary to perform the test for 150

cycles and then calculate the durability factor at 50 percent and the

DF300can becalculated.

ASTM C597 (pulse velocity through concrete)

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[ ]

Purpose: The major purpose of this specification is to check the

uniformity in mass concrete, to indicate characteristic changes in

concrete, and in the survey of fields stuctures estimate the severity of

deterioration, cracking, or both.

Procedure: In this procedure a sound wave is transmitted through the

concrete mass and the length of time it takes to travel from one end to

the other is recorded. Knowing the time and the path length, the velocity

can be computed.

ASTM C671 (critical dilation of concrete specimens subjected to

freezing)

Purpose: The purpose of thos specification is to determine the test period

of frost immunity of concrete specimens meansured by the water

immersion the time required to produce critical dilation when subjected to

a prescribed slow-freezing procedure.

Procedure: In this procedure, the test specimen is molded and cured as

prescribe by ASTM C192 (Making and Curing Concrete Test Specimens in

the Laboratory). Once the test spescimen is prepare and conditioned, the

test starts. The test cycle consist by cooling the specimen in water-

saturated kerosene from 35 to 15F (1.67 to -9.44C) at a rate of 5 1F (-

2.8 0.5C) per hour; followed immediately by returning the specimen to

the 35F (1.67C) water bath, where the specimen will remain until the

next cycle. Normally, one test cycle would be carried out every 2 weeks.

The length changes are measured during the cooling process. The test is

continued until critical dilation is exeeded or until the period of interest is

over.

ASTM C682 (evaluation of frost resistance of coarse aggregates in

air-entrained concrete by critical dilation procedure)

Purpose: The purpose of this procedure is to evaluate the frost resistance

of coarse aggregates in air-entrained concrete.

Procedure: The procedure is basically the same as that for the preceding

specification. The only difference is that the sample is prepared in

accordance with ASTM C295 (Petrographic Examination of Aggregates for

Concrete). The aggregate is grade in accordance with field use; otherwise,

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[ ]

equal portions of the No. 4, 38 -in.,

12 -in., and 1 –in. Sieved are used.

Further, the aggregate should be used in this test as it is used in the field.

Portland cement should meet the specifications of ASTM C33 (Concrete

Aggregates). The mix proportion should be in accordance with the ACI

method of mix design with an air content of 6 percent and a slump of 2.5

0.5 in.

ASTM C672 (scaling resistance of concrete surfaces exposed to

deicing chemicals)

Purpose: The purpose of this specification is to evaluated the effect of

mix design, surface treatment, curing, or other variables of concrete

subjected to scaling because of freezing and thawing, and to determine

the resistance to scaling of a horizontal concrete surface subjected to

freezing and thawing in the presence of deicing chemicals.

Procedure: In this specification the concrete at the age of 28 days, after

proper curing, is a covered with approximately 0,25 in. (0.64 cm) of

calcium chloride and water solution having a concentration such that each

100 ml of solution contains 4 g of anhydrous calcium chloride. The

specimen is than placed in a freezing chamber for 16 to 18 hours. The

specimen is the removed and place in air at 75 3F (23 1.7C) with a

relative humadity of 45 to 55 percent for 6 to 8 hours. Water is added to

the chamber between each cycle to maintain the depth of the solution.

The procedure is repeate daily, and at the end of five cycles the surface of

the concrete is flushed thoroughly. A visul inspection of the concrete is

mnade with the rating given in Table 2-3. These ratings are recorded and

the test continues.

ASTM C295 (petrographic examintion of aggregates for concrete)

Purpose: The purpose of this speciication is to screen the good from the

bad aggregates. It has eight specific purpose :

1. Preliminary determination of quality

2. Establishing properties and probable performances

3. Correlating samples with aggregates previously tested and

used.

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[ ]

4. Selecting and interpreting other tests.

5. Detection contamination

6. Detremining effects of processing

7. Determining physical and chemical properties

8. Describing and classifying constituents.

Table 1.CONCRETE SCALING RATINGS

Rating

Condition of Surface

0 No scaling1 Very slight scaling

2Slight to moderate scaling

3 Moderate scaling

4Moderate to severe scaling

5 Severe scaling

Procedure: In this specification the procedure should be carried out by

geologist untilizing x-ray diffraction, differential thermal analysis, electron

microscopy, electron diffraction, electron probe, infrared spectroscopy

microscope, and the naked eye.

ASTM D1075 (effect of water on cohesion of compacted bituminous

mixtures)

Purpose: The purpose of this specification is to measure the loss of

cohesion resulting from the action of water on compacted bituminous

mixtures contraining penetration-grade asphalts. In other words, it

evaluates the stripping properties of aggregates.

Procedure: In this specification a 4-in. (10.16 cm) cylindrical specimen 4

in. (10.16 cm) high is tested in accrordance with ASTM D1074

(Comperessive Strength of Bituminous Mixtures). Then the bulk specific

gravity of each specimen is determined. Each set of six test spcimens is

sorted into two groups of three specimens each so that the average bulk

specific grafity is the same in each group. Group 1 is tested in accordance

with procedure A and group 2 in accordance with procedure B. In test

procedure A, the test specimens are brought to the test temperature of 77

1.8F (25 1C) by storing them in air bath maintained at the test

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[ ]

temperature for not less than 4 hours, their compressive strength

determined in accordance with ASTM D1074. In test procedure B, the test

specimen is immersed in water for 4 days at 120 1.8F (49 1C). The

specimen is transferred to a second water bath at 77 1.8F (25 1C)

and stored for 2 hours. At that time the compressive strength is

determined and the numercial index of resistance of bituminous mixtures

to the detrimental effect of water as the percentage of the original

strength that is retained after the immersion period is calculated as

follows :

index of retained strength () = S2S1

x 100

where S1 = compressive strength of dry specimens (group 1)

S2 = compressive strength of immersed specimens (group 2)

Tests Concerning Deleterious Materials in Aggregates

ASTM C33 (concrete aggregates)

Purpose: The purpose of this specifications is to ensure that satisfactory

materials are used in concrete.

Procedure: Thespecification cover both fine and coarse aggregates but

does not cover lightweight aggregates. Establishes definitions for fine and

coarse aggregate and place restrictions on grading, deleterious

substances, and soundness. The specification also establishes methods for

testing and sampling.

ASTM C142 (clay lumps and friable particles in aggregates)

Purpose:The purpose of this specification is to measure only particles

that might cause unsightly blemishes in concrete surfaces. It is an

approximate method for the determination of clay lumps and friable

particles in natural aggregates.

Procedure: Aggregates for this test consist of the material remaining

after the completion of ASTM C117 [Materials Finer Than No. 200 (75-m)

Sieve in Minerals Aggregates by Washing]. The aggregate is dried to a

onsistant weight at a temperature of 230F (105 5C). Weight the test

sample spead it into a thin layer on the bottom of the container , cover it

with water, and examine it for clay lumps or friable particles. Particles that

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[ ]

can be broken down with the fingers ito finely divided particles are

calssified as friable particles, prvided that they can be removed by wet

sieving. The residue is removed and weighed. The amount of clay lumps

and friable particles in fine aggregate or individual sizes of coarse

aggregate is computed as follows :

P=W−RW

x 100

Where P = percent of clay lumps or friable particles

W = weight of test sample passing the layer of sieves but coaser

than the No. 16 sieve

R = weight of particles retained in designated sieve

ASTM C117 (materials finer than no.200 (75-μm) sieve in mineral

aggregates by washing)

Purpose: The purpose of this test is to determine the amount of material

finer than a No. 200 (75-m) sieve in aggregate by washing. Clay particles

and other aggregate particles that are dispersed by the wash water as

well as water-soluble materials will also be removed from the aggregate

during the test.

Procedure: A sample of aggregate is washed in a prescribed manner and

the decantes wash water containing suspended and dissolved materials is

passed trough a No. 200 (75-μm) sieve. The loss in weight resulting from

the wash treatment is calculated as weight percent of the original sample

and is reported as the percentage of material finer than a No.200 (75-μm)

sieve, by washing.

A=B−CB

x 100

Where A = percentage of material finer than a No. 200 (75-μm) sieve, by

washing

B = original dry weight of sample, grams

C = dry weight of sample, after washing, grams.

ASTM C123 (light weight pieces in aggregates)

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[ ]

Purpose: The purpose of this specification is to determine the

approximate percetage of lightweight pieces in aggregates by means of

sink-float separation in aheavy liquid of suitable specific gravity.

Procedure: In this procedure the fine aggregate is allowed to dry and

cooled to room temperature after following the procedure prescric=bed in

ASTM D75. The material is sieved using a No. 50 sieve and then brought

to saturated-surface dry conditions. It is put into a heavy liquid such as

kerosene with 1,1,2,2,-tetrabromethane. The particles will be separated

by the float-sink method provided that the specific gravities are different

enough to permit separation. The liquid is poured off into a second

container and passed through a skimmer. Care is taken that only the

floating pieces are poured off with the liwuid and that none of the sand is

decanted into the decanting process is reparated until the liquid is free of

friable particles. The pieces are dry and thr weight determined. For a

coarse aggregate the particles are sieved using a No. 4 sieve and the

foregoing process is repeated.

ASTM C40 (organic impurities in sands for concrete)

Purpose: This specification covers an approximate determination of the

presence of injurious organic compounds in natural sands that are to be

used in cement mortar or concrete. The principal value of the test is to

furnish warning that further tests of the sands are necessary before they

are approved for use.

Procedure: The procedure for this specification involves the color test.

The sand and a 3 % solution of sodium hydroxide are mixed vigorously in

a graduate and allowed to stand for 24 hours. The color of the liquid is

then compared to the color of a solution of potassium dichromate in

sulfuric acid. If the solution of the sand and sodium hydroxide is darker

than the potassium, organic impurities are present in the sand.

ASTM C227 (potensial alkali reactivity of cement-aggregate

combinations (mortar-bar method))

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[ ]

Purpose: The purpose of this specification is to determine if an aggregate

will react with the alkalies in cement. This test is basically to predict the

alkali-silica reaction.

Procedure:The test method consists of molding bars of mortar 1 in. X 1

in. X 12 in. (2.54 cm x 2.54 cm x 30.5 cm) in which the aggregate in

question is combined with cement that is to be used in the field. The

proportion should be 1 part cement to 225 parts of graded aggregate by

weight. Use enough water to develop a flow of 105 to 120. After 24 hours

in the molds, the length of the bars are measured, and they are stored at

a constant temperature of 100ᴼF (37.8ᴼC) in sealedcontainers that

containing a small amount of water in the bottom but not in contact with

the speciment.

ASTM C289 (potential reactivity of aggregates (chemical method))

Purpose : The purpose of this test procedure is to determine the potential

reactivity of an aggregate with alkalies in portland cement concrete in a

very short time. This is a test for the alkali-silica reaction and is not

intended for the alkali-carbonate reaction.

Procedure: In this procedure the material is ground to the point when it

is finer than the No.50 sieve but coarser than the No.100 sieve. Twenty

five grams of the materuia are mixed with 25ml of a 1 N solution of NaOH

in a steel vessel about 2 in. (5.08 cm) in diameter and 2-1/2 in. (6.35 cm)

high. The vessel is sealed at a temperature 176ᴼF (80ᴼC) 24 hours and

then the liquid is filtered and tested for alkalinity and dissolved silica.

Tests Used in The Design of Portland Cement Concrete and

Bituminous Mix Design

ASTM D75 (sampling aggregates)

Purpose: The purpose of this test is to sample fine and coarse aggregate

for the following purposes:

Preliminary investigation of the potential source of

supply;

Control of the product at the source of supply;

Control of the operations at the site of use;

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[ ]

Acceptance or rejection of the material.

Procedure:In this procedure, sampling plans and acceptance and control

tests vary with the type of construction in which the material is used.

Samples for preliminary investigation tests are obtained by the party

responsible for developmen of the potential source. Samples must be

inspected and sampling taken from conveyor belts, flowing aggregate

stream, or stockpile.

ASTM C136 (sieve or screen analysis of fine and coarse aggregates)

Purpose:The purpose of this specification is to determine the particle size

of fine and coarse aggregates to be used in various tests.

Procedure: In this procedure, a weighed sample of dry aggregate is

separated through a series of sieves or screens of progressively smaller

openings for determination of particle-sixe distribution.

ASTM C127 (specific gravity and absorption of coarse aggregates)

and ASTM C128 (specific gravity and absorption of fine aggregates)

Purpose:The purpose of this specification is to ultimately determined the

solid volume of coarse aggregate / fine aggregate and the unit volume of

the dry rodded aggregate such that a weight volume characteristic can be

determined so that a concrete design mix can be determined. The bulk

specific gravity is used to determine the volume occupied by the

aggregate.

Procedure: Test methods for determining relative densities forcoarse and

fine aggregates are described in ASTM C 127 (AASHTO T 85) and ASTM C

128 (AASHTO T 84), respectively.

The relative density of an aggregate may be determinedon an ovendry

basis or a saturated surface-dry (SSD) basis. Both the ovendry and

saturated surface-dry relative densities may be used in concrete mixture

proportioning calculations. Ovendry aggregates do not contain any

absorbed or free water. They are dried in an oven to constant weight.

Saturated surface-dry aggregates are those in which the pores in each

aggregate particle are filled withwater but there is no excess water on the

particle surface. The density of aggregate particles used in mixture

proportioning computations (not including voids between particles) is

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[ ]

determined by multiplying the relative density (specific gravity) of the

aggregate times the density of water. An approximate value of 1000

kg/m3 (62.4 lb/ft3) is often used for the density of water. The density of

aggregate, along with more accurate values for water density, are

provided in ASTM C 127 (AASHTO T 85) and ASTM C 128 (AASHTO T 84).

Most natural aggregates have particle densities of between 2400 and

2900 kg/m3 (150 and 181 lb/ft3).

ASTM C29 (unit weight of aggregate)

Purpose:This method covers the determination of the unit weight of fine,

coarse, or mixed aggregate.

Procedure: In this procedure, the sample is dried to constant weight in

an oven at 220 to 230ᴼF (105 TO 110ᴼC) And thoroughly mixed. a

cylindrical metal bucket is calibrated using water (knowing that water

weighs 62.4 lb/ft3). The mrasure is filled one-third full and the surface is

leveled wth the fingers. The layer of aggregate is rodded 25 times with a

tamping rod. The strokes are apllied evenly over the sample. This

procedure is repeated at two-thirds full and at full. The measure is leveled,

weighed, and multiplied by the volume of the bucket. This method applies

to aggregates of 1.5 in. (3.81 cm) or less. For aggregate over 1.5 in. (3.81

cm), use the jigging method.

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