Illinois Physical Science Applications in Agriculture Lesson B3 2 Page 1
CONSTRUCTION MATERIALS:
BULKING OF SAND
Illinois Physical Science Applications in Agriculture Lesson B3–2 • Page 1
Student Learning Objectives. Instruction in this lesson should result in students achieving the following 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.
Anticipated Problem: How are sand and water related, in terms of weight and volume?
I. 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.
A. The interaction of sand and water primarily affects volume and is important to consider when dealing in construction settings.
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.
B. 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.
Anticipated Problem: What is the bulking of sand?
II. Bulking occurs when there is a change in volume due to the addition of water to the sand particles.
A. 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”.
Illinois Physical Science Applications in Agriculture Lesson B3–2 • Page 3
B. 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.
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.
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.
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.
C. 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.
Anticipated Problem: How do texture, surface tension, and capillarity effect bulking?
III. 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.
A. 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.
B. 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.
C. 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. 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.
Anticipated Problem: How would the knowledge of bulking affect batch mixing quality of concrete by volume of ingredients (sand and water)?
IV. The knowledge of bulking can help in developing the high quality of concrete desired for its purpose. If the mixture is too moist, there could be decreased yield, reduced strength, and difficulty in placing the mixture in molds. One must not only consider the amount of water added to the mixture but also the amount of moisture present in the sand particles for a successful placement. Sand is usually delivered in a moist condition to decrease the chance of varying results.
A. 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.
B. 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. 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.
C. 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.
Illinois Physical Science Applications in Agriculture Lesson B3–2 • Page 7
CONSTRUCTION MATERIALS:
BULKING OF SAND
Part One: Matching
Instructions: Match the word with the correct definition.
a. Bulking c. Friction
b. Surface tension d. Capillarity
______1. A force exerted by the surface of a liquid.
______2. Molecular forces on some liquids causing them to rise in tubes or channels.
______3. Occurs when there is a change in volume due to the addition of small amounts of moisture.
______4. Resistive forces opposing the motion of bodies in contact with each other.
Part Two: Fill-in-the-Blank
Instructions: Complete the following statements.
1. The finer the sand, the ______surface area.
2. The addition of water to sand will ______the weight of the sample.
3. ______sands tend to bulk more than ______sands.
4. ______is the force of the molecules of water.
Illinois Physical Science Applications in Agriculture Lesson B3–2 • Page 8
Part Three: Multiple Choice
Instructions: Write the letter of the correct answer.
______1. Sand is composed mainly of
a. gravel
b. weathered grains of quartz stone
c. grains of limestone
d. grains of silt and clay
______2. When dry sand comes in contact with moisture
a. increase in volume
b. decrease in volume
c. no change in weight
d. no change in volume
______3. What are the three main factors that can affect bulking?
a. texture, moisture, light
b. texture, surface tension, temperature
c. texture, surface tension, capillarity
d. moisture, capillarity, light
Part Four: Short Answer
Instructions: Answer the following questions.
1. How can “bulking” occur more readily in smaller particles?
2. Explain how tension has an effect on “bulking”.
3. How would an increase of knowledge of “bulking” affect mixing quality concrete?
Illinois Physical Science Applications in Agriculture Lesson B3–2 • Page 9
Assessment
Illinois Physical Science Applications in Agriculture Lesson B3–2 • Page 20
TS–A
Technical Supplement
CONSTRUCTION MATERIALS:
BULKING OF SAND
1. 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. The finer the sand is, the
greater available surface area.
The interaction of sand and water primarily affects volume and is important to consider
when dealing in construction settings. The relationship between sand and
water volume forms a plateau curve. 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). The maximum volume is reached when
all sand particles have their surface completely covered and pose spaces filled with
water.
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 percentage moisture in the sample. Weight is not as important as the
volume change in construction.
2. What is the bulking of sand?
Bulking occurs when there is a change in the volume due to the addition of water to
the sand particles. 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.
Illinois Physical Science Applications in Agriculture Lesson B3–2 • Page 21
3. How do surface tension, capillarity and texture affect bulking?
Surface tension is defined as the force exerted by the sand particle surface 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.
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% (max. water
holding capacity). As soon as the mixture reaches this 12% level, all the capillary
spaces are filled. 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.
Texture is the relative proportions of soil separates (sand, silt, and clay). Bulking
tends to occur more readily in smaller particle states (fine vs. coarse sand) because
the smaller particles tend to hold more water in to increase the total volume of the
sample. This is because water tends to move toward the micropores found in sand
and allows other substances to fill the macropores found in other separates.
4. How would the knowledge of bulking affect batch mixing quality of concrete
by volume of ingredients (sand and water)?
The knowledge of bulking can help in developing the high quality of concrete
desired for its purpose. If the mixture is too moist, there could be decreased yield,
reduced strength, and difficulty in placing the mixture in molds. One must not only
consider the amount of water added to the moisture but also the amount of moisture
present in the sand particles for a successful placement. Sand is usually delivered
in a moist condition to decrease the chance of varying results.
Illinois Physical Science Applications in Agriculture Lesson B3–2 • Page 22