07.Structural Characteristics -2011

8/10/2019 07.Structural Characteristics -2011

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Sem 1. Laboratory Notebook phd.eng.Dan Babor

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Laboratory work No.07

STRUCTURAL CHARACTERISTICS

The structural characteristic refers to the repartition mode of the matter and of the

pores in the material apparent volume (in the structures of a material).

Because, we cant determinate all of them making measurements in the material

structure, one of them are calculated using the ascertain technical characteristics.

1. Compactness

Compactness (C) represents the degree of a solid matter volume (Vr),

filing of the samples apparent volume (Va).

C=a

r

V

Vx 100 [%]

Because the real volume (Vr) can be calculated only by destroying the materials

structure, we can calculate the compactness using the following formula:

C=

a

a

a

r

m

m

V

V== (x100) [%]

a= the material apparent density, determinates in accordance with Laboratory

work No.7;

= the material density, determinates in accordance with Laboratory work No.6.

2. Humidity

Humidity (W) represents a relative quantity of water (A) which is in the material

content at a given moment.

W=m

mm

m

A w = (x100) in which

Com actness; humidit ; water absor tion; orosit ; bulkin of sand


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will start after 30 minutes and will last 3 hours. After the boiling the samples are left into

the water to cool up.

Tab.1. Conditions of saturation

For the conditions from I =3 to saturate the samples we introduce them in a

water bath, which is into a vacuum exicator, from which we extract air until we get a

pressure of 20mmHg. When the liberation of air bubbles is stopped, we shut off the

vacuum pump and open up the exicator to get again the normal pressure.

For the conditions from I =4 to saturate the samples we introduce them in a

water bath, which is in a steel recipient in which we pomp air to obtain a pressure of 15

N/mm2.

To determinate the water absorption we must follow the next operations:

1. the sample is dried at constant mass and we weigh (m)

2.

than is saturated in the conditions from I = 1 and we weigh (msa1); ifthe condition s are other (I =24) the sample is saturated after the

index in ascending order, we make the weigh for every state of

saturation (msal).

3. we calculate the water absorption using the relation [8.4.]

The water absorption represents the highest value of humidity which the

material can have.

4. Porosity

4.1. Total porosity

The total porosity (Pt) represents the proportion in which the volume of pores (Vp)

forms the apparent volume (Va) of the material.

Pt=a

p

V

V(x100) [%]

Characteristic

factor l

Conditions for saturation

pressure temperature

1 Atmospheric 20C

2 Atmospheric Boiling

3 20mmHg 20C

4 15N/mm 20C


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Because the pores volume (Vp) can not be measured, the total porosity (Pt) is

calculated with the following relation:

Pt=

a

a

r

a

ra

a

p

m

m

V

V

V

VV

V

V

==

= 11 = 1-C (x100) [%]

We must observe that total porosity (Pt), calculated like a complementary amount

of the compactness, express the volume of pores (Vp) unconcerned of their type (closed

or opened).

4.2. Apparent porosity (open)

The character of the pores has a big influence over the material properties,

especially in the case of durability; through the open pore (which communicates with theexterior) can get in the material structure, gasses, liquids, or liquid solutions which can

produce phenomenons of expansion corrosion at freezing. Thats why is necessary to

determinate the porosity which is formed from the open pores, called open porosity or

apparent porosity (Pa).

The apparent porosity (Pa) represents the proportion in which the volume of the

open pores (Vpo) forms the apparent volume (Va) of the material:

Pa=La

sa

a

L

sa

a

pd

V

mm

V

mm

V

V

=

= (x100) in which

Vpo=the volume of the open pores;

Va = the sample apparent volume;

m = the sample mass at constant mass and dry state;

ma = the mass of the saturated sample with condition I -1;

L =the density of the reference liquid;

for determination, we apply the phenomenon which the phenomenon of porosityprovokes: the absorption of reference liquid in the open pores.

The determination resides in the following succession of operations:

the material sample is died at constant mass and we weigh (m);

the sample is saturated in the conditions from I =1and we weigh (msa);


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we determinate the apparent volume (Va) using the method of hydrostatic

balance;

we calculate the apparent porosity with the relation [8.7.].

The apparent porosity can be calculated using the water absorption (a1) and the

apparent density (a) of the material, because:

Pa= aa

sa

A

sa

a

saa

V

m

m

mm

Vm

mmm

V

mm=

==

1

1)( [%]

4.3. Closed porosity

Closed porosity represents (Pt) represents the proportion in which the volume of

closed pores (Vpc) forms the apparent volume (Va) of the material.

Closed porosity is calculated doing the difference between the total porosity (P t) and the

apparent porosity (Pa), because:

Pc=a

pd

a

p

a

pop

a

pc

V

V

V

V

V

VV

V

V=

= = Pt- Pa [%] [

5. Bulking of sand

The hydrophile materials can bind (through absorption) a layer of water which

will act like a solid and will push on the grains between them, when are in bulk state. The

phenomenon is more intense if the material is smaller and its specific surface is bigger.

The thickness of waters layer grows together with the material humidity until

the thickness becomes approximately of 15m, which corresponds for a humidity of

(58) %. At a bigger humidity the water in excess stays free, as liquid.

The effect of this phenomenon can be measured after the variation of the unit

mass of bulk volume, in refine state, at the humidity variation.

The process resides in the following succession of operations: we form sample with a mass m = 2000g, from the granular material (sand),

dried at constant mass and we introduce it into a bowl.

we determinate the bulk density, in refine state (b), as in laboratory work No.

8;


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in a bowl we introduce the material, and over it we cast 40cm3of water and

then well immix until the content gets a homogenous humidity; knowing that

the water (1g/cm3), the humidity that we obtain becomes:

W= %21002000

40=

xg

g

we determinate the unit of volume mass of the granular material (gW) for this

humidity;

we repeat the operations, of introducing the water in stages of 40cm3, of

mixing to homogenize the sample and of determination of the unit of volume

mass until we flood the sample.

During this operations we must take care of the sample because if we lose from

material, the mass of the corning material will be modified and the calculated humidity

wrong.

For every humidity that we obtain we make three parallel determinations of the unit

of volume mass (Table 2.), and the medium values will be marked in a diagram fig. 8.1.

Well follow the graphic to see if it indicates an uniform variation; if not we must

repeat the last determination of gW.


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Table 2. Bulking of sand

W%

No.oftest

Mbowl

(kg)

gW

(Kg/m3)

gW

med

(Kg/m3)

Ii

%

0

1

2

3

2

1

2

3

4

1

2

3

6

1

2

3

8

1

2

3

10

1

2

3

12

1

2

3

For every humidity we calculate the bulking index with the relation:

Ii= 100%)100(

+

gw

ga W

[%]

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07.Structural Characteristics -2011