Physical Science Applications

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29 Νοε 2013 (πριν από 3 χρόνια και 7 μήνες)

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Physical Science Applications
in Agriculture

Unit

Physical Science Systems

Problem Area

Agricultural Structural
Systems

Construction Materials:
Bulking of Sand

Lesson

What is used to bake a cake?


Discuss what might happen if incorrect
amounts of ingredients were used in
making a cake.


Relate student responses to the critical
need for control when designing a batch
mix of concrete.


Learning Objectives

1.
Describe how sand and water are related, in
terms of weight and volume.

2.
Define bulking of sand.

3.
Explain cause and effect of bulking of sand
and its relationships to texture, surface
tension, and capillarity.

4.
Apply the knowledge of bulking to volume
measurements of sand and water when batch
mixing quality concrete.

Terms


Bulking



Capillarity



Friction



Surface tension


castle.is.gatech.edu/
sand
_castle

How are sand and water related,
in terms of weight and volume
?


Sand is composed mainly of weathered
grains of quartz stone.


Grains of sand do not stick to each other, so
the individual grains contain a greater amount
of surface area around each particle to
interact with water molecules.


Therefore, the finer the sand, the greater
surface area.


Interaction of sand and water primarily
affects volume.

1.
The relationship between sand and water
volume forms a plateau curve.

2.
Dry sand (<6% moisture) has a minimum
volume, then increases as moisture is added
(6

12% moisture) and reaches a maximum
volume when fully wet (>12% moisture).

3.
The maximum volume is reached when all
sand particles have their surface completely
covered and pore spaces filled with water.


How are sand and water related,
in terms of weight
?


The addition of water to sand will increase the
weight of the sample.


This is because lighter air spaces between
each sand grain particle are filled with water.


Weight can determine the percent of moisture
in the sample.


Weight is not as important as the volume
change in construction.


What is the bulking of sand?


Bulking
occurs when there is a change in
volume due to the addition of water to the
sand particles.


When dry sand comes in contact with moisture,
thin film is formed around the particles, which
causes them to get apart from each other.


This results in increasing the volume of sand.


This phenomenon is known as “bulking of sand”.

What is the bulking of sand?


When mixes are specified by volume,
the sand is assumed to be dry.


The volume of a given weight of sand,
however, varies according to its
moisture content.


growabrain.typepad.com/.../

wow_
sand
_sculpt.html

What is the bulking of sand?

1.
It may be demonstrated by filling a
beaker with dry sand.


If the sand is flooded with water the level
will sink a little, but not to any great extent.


When the beaker is similarly filled with
damp sand and the surface is flooded the
drop in level will be very much greater.

What is the bulking of sand?

2.
There are several things going on with the
sand and the water.


As the sand particles become fully
saturated, the air spaces are lost as the
air is forced out.


Also, the sand particles become
lubricated by the water and will move or
“settle” in the container as they move to
points of least resistance.


Therefore, saturated sand will take less
space
.

What is the bulking of sand?

3.
In construction scenarios, allowance
can be made for bulking by volume.


The mortar may contain too little sand.


This is one of the reasons why
measurement by weight is desired.



Bulking occurs far more with fine sand.

What is the bulking of sand?


The water molecules grab onto the sand
particle surface and also fill the air
spaces to create a bulking effect.


Finer sands tend to bulk more than
coarse sands due to the increased ratio
of surface area to volume available for
water molecules to interact with the
sand particles.

Bulking of Sand

How does texture, surface tension,
and capillarity effect bulking?


The composition of concrete is a mixture of
cement, sand, gravel or broken stone, and
water.


“Bulking of Sand” is an extremely important
event that must take place for the proper
make
-
up of concrete.


The texture, surface tension and capillarity
will affect the bulking factor of sand.

How does texture effect bulking?


Texture is the relative proportions of soil
separates (sand, silt, and clay).



Bulking tends to occur more readily in smaller
particles (fine vs. coarse sand).


This is because the smaller particles tend to hold
more water in, to increase the total volume of the
sample.


Therefore water tends to move toward the
micropores found in sand and allows for other
substances to fill the macropores found in other
separates.

How does surface tension effect
bulking?


Surface tension
is defined as the force
exerted by the sand particle to pull in the
water molecules.


Tension has an effect on bulking due to the
force pulling in the water making sand
particles pull farther apart from each other
and increasing the volume.


Volume increase creates more bulk.


Finer sand has a greater surface area to
create a larger force, thus increasing the
bulking potential.

How does capillarity effect
bulking?


Capillarity
is the force of the molecules of
water.


This force also increases the total volume by
filling in the air spaces with water.


The volume of water around each sand
particle increases as the percentage of water
added increases to 12% (maximum water
holding capacity).


As soon as the mixture reaches this 12%
level, all the capillary spaces are filled.

How does capillarity effect
bulking?


The force remains for a short time (until
hydration of water in the cement occurs) and
prevents the sand particles from settling back
down to its dry volume.


The amount of bulking increases as the force
increases.


There are more air spaces available in finer
sands to increase the bulking potential.

SPACES BETWEEN THE
AGGREGATE PARTICLES ARE THE
VOID SPACES

How would the knowledge of bulking
affect batch mixing quality of

concrete by volume of ingredients
(sand and water)?

kneipencity.de/Haupt/.../

White%20
Sand
.htm

Quality of Concrete


The knowledge of bulking can help in
developing the high quality of concrete
desired for its purpose.


Mixture is too moist


Decreased yield


Reduced strength


Difficulty in placing the mixture in molds

www.ibtstw.org/occupations/hotjobs.html

Quality of Concrete


One must not only consider the amount
of water but the amount of moisture
present in the sand for a successful
placement.


Sand is usually delivered in a moist
condition to decrease the chance of
varying results.


Quality of Sand


Dry or fully wet sand occupies a
minimum volume;


damp sand (6%

12% moisture by weight)


may increase in volume causing
measurement errors when proportioning
concrete batch mixes.


mikedgreen.com/house/PorchPour/porchpour.html

Quality of Sand


The increase in volume is due to
capillary water surrounding each sand
particle.


Surface tension holds the particles
apart, thus increasing the volume.


The coefficient of friction also increases,
preventing the particles from settling
freely as dry sand particles.

Quality of Sand


Friction
is defined as the resistive forces
opposing the motion of bodies in contact with
each other.


As water content increases beyond
approximately 12%, the coefficient of friction
decreases and gravitational forces cause the
sand particles to collapse, returning the
volume to that similar to dry sand.

Quality of Concrete


Failure to adjust for bulking when
proportioning ingredients for mixing concrete
may cause decreased yields, under
-
sanded
mixes that are difficult to place, and reduced
strength.


Most sands are delivered in a moist condition,
thus adjusting for variations in volume are
critical to mixing quality concrete.

Review/Summary


How are sand and water related, in terms of
weight and volume?


What is the bulking of sand?


How do texture, surface tension, and
capillarity effect bulking?


How would the knowledge of bulking affect
batch mixing quality of concrete by volume of
ingredients (sand and water)?