Physical Science Applications in Agriculture

1. Physical Science Applications in Agriculture Unit Physical Science Systems

2. Problem Area Agricultural Structural Systems

3. Construction Materials: Bulking of Sand Lesson

4. 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.

5. Learning Objectives • Describe how sand and water are related, in terms of weight and volume. • Define bulking of sand. • Explain cause and effect of bulking of sand and its relationships to texture, surface tension, and capillarity. • Apply the knowledge of bulking to volume measurements of sand and water when batch mixing quality concrete.

6. Terms • Bulking • Capillarity • Friction • Surface tension castle.is.gatech.edu/sand_castle

7. 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.

8. Interaction of sand and water primarily affects volume. • 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 pore spaces filled with water.

9. 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.

10. 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”.

11. 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

12. What is the bulking of sand? • 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.

13. What is the bulking of sand? • 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.

14. What is the bulking of sand? • 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.

15. 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.

16. Bulking of Sand

17. 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.

18. 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.

19. 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.

20. 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.

21. 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.

22. SPACES BETWEEN THE AGGREGATE PARTICLES ARE THE VOID SPACES

23. How would the knowledge of bulking affect batch mixing quality ofconcrete by volume of ingredients (sand and water)? kneipencity.de/Haupt/.../White%20Sand.htm

24. 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

25. 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.

26. 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

27. 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.

28. 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.

29. 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.

30. 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)?