1. The World of Materials Linking Physics and Chemistry to Engineering
Prof. Subramaniam (“Subby”) D. Rajan, Prof. Narayanan Neithalath and Amie Baisley
Graduate Students: Kirk Vance, Matt Aguayo, Joseph Harrington and Canio Hoffarth

2. Structural Materials Concrete (Plain, Reinforced, Prestressed)
Metals (Steel, Aluminum)
Timber/Wood
Masonry
Reinforced concrete
Steel beams and columns
Wood beams and columns
Concrete masonry blocks

3. What are all Materials made of?
Fundamental chemistry – all materials are basically comprised of elements/molecules, which are comprised of atoms
Investigate the periodic table.

4. Focus of this activity
There are a number of building materials. However this activity will focus on CONCRETE.

5. What is CONCRETE? From the Latin word “Concretus”
Means : To hold together or grow together
It is a “Formable Rock”
A composite material – Binder(s) + Filler(s)

6. Where do you see Concrete?
EVERYWHERE – Most used material by humans after water

7. Scale of Concrete Use
Present consumption of concrete of the order of 12 billion tons every year
Humans consume no material except water in such tremendous quantities

8. Hoover Dam The dam overall weighs 6.6 million tons
Took 3.25 million cubic yards of concrete
Enough to lay a 4 foot wide sidewalk around the earth

9. Ingredients of Concrete
Cement
Water
Fine Aggregate
Coarse Aggregate
Many chemicals for specific functions

10. Proportions - Range

11. What is CEMENT?
A fine powder, when mixed with water, reacts with it, to form a glue that binds the aggregates together
The heart and soul of concrete
An old material, but “modern”
Cement is to concrete, what flour is to bread….

12. Basic Constituents of Cement
Calcium
Silica
Alumina
Iron
Their oxides are present – see the table

13. A Typical Cement Plant

14. Other Constituents Cement production is environmentally sensitive
Takes large amounts of energy
Releases a large amount of CO2 into the atmosphere
GLOBAL WARMING - ???
Several waste materials from other sources used in concrete
Fly ash, slag etc. (look at the table in Slide 11 for their composition too)
They serve several functions in concrete
Chemical ingredients are also used to enhance concrete properties

15. Tailoring the Material

16. Aggregate Production These are the rocks used to make concrete
In order to meet large volumes and ensure
better properties, we need aggregates

17. Grading of Aggregates
Carefully notice the different sizes that are used

18. Why should we worry about Grading ?
What happens when you add smaller and smaller balls into the given volume?
Can you see voids reducing?
Voids (or holes) are bad for concrete
When there are more voids, the strength is lower and the material is susceptible to more damage
Thus we need to “pack” the materials better in a volume

19. Mixing – Ready Mixed Concrete
Central mixed concrete – Stationary mixed
Mixed completely in a stationary mixer
Delivered in
A truck agitator
Non agitating truck
Truck mixer operating at agitating speed

20. Placing concrete in a bridge

21. What is important in placing concrete?
It should flow well
You should be able to spread it evenly and consolidate so that it provides a dense and strong material

22. Methods to enhance flow and control setting
Special chemicals to enhance flow, yet keep the cement paste and rocks together
Called Superplasticizers
Set controlling chemicals
How to speed up reactions in cold climate?
Use an Accelerator (Calcium chloride)
How to slow down reactions in hot weather?
Use a retarder (Sugar)

23. Then……Cement reacts with water
And keeps on reacting as it ages…
See how the black spaces (pores) are being filled in with yellow regions (reaction products) which are the result of the reaction of cement (red and blue particles)

24. Cement’s love for water
Reaction of cement with water is called Hydration
Reaction of cement with water produces heat
This is an exothermic reaction

25. And then?
14-28 days
Curing – providing water for
chemical reactions to proceed
Concrete is hard and strong to
carry load
After casting the concrete in the bridge, you need to take care of it by providing nourishment for it to strengthen
Water is its nutrient

26. How do you test concrete?
Concrete is strong in compression – it can take a large load when crushed.
Strength = Load taken to fail the material divided by the area of cross section.
You have a circular cross section for the cylinder shown.
Units of strength is pounds per square inch (pounds of load needed to break divided by the number of square inches of cross sectional area)

27. How do you test concrete?
For a bridge, concrete is under bending load
The response is different when the concrete is tested alone, or when it has steel “reinforcement” in it.
Concrete is a brittle material and steel makes it ductile
See next slide to know the difference

28. Brittle and Ductile Materials
Brittle and Ductile Property – Key to engineering / structural materials
Brittle materials do not deform (bend, as an example) much before it fails. Thus it is not desirable for structural applications such as in bridges. Examples of brittle materials include glass, cast iron etc.
Ductile materials deform significantly before failure. This is the most desirable set of materials for structural applications because they give you warning before failure in the form of deflections. Steel is a very good example
Since many common and cheaper materials are generally brittle, we can combine them with a ductile material (e.g.: steel + concrete) to make the “composite material” somewhat ductile.

29. Questions – Level 1 Q1: Materials in general applications
(a) What are all the elements in nature made of (fundamental building blocks)?
(b) What is the most abundant element in the earth’s crust?
(c) In the periodic table, you have metals and nonmetals. Enumerate the key structural and physical differences between them.
Q2: Cement and Concrete
(a) Distinguish between cement and concrete.
(b) What are the ingredients of concrete?
(c) Name three items you have encountered today which are concrete.
(d) How much concrete was used in Hoover Dam?
(e) What is an exothermic and an endothermic reaction? Give examples.

30. Questions – Level 1 Q3: Why is concrete important?
(a) Enumerate one very critical use of concrete that no other material can satisfy.
(b) Can you think of an application for concrete for the future (i.e., it is not used now, but can be used later)?

31. Questions – Level 2
Q4: Why is packing of different concrete ingredients important?
(a) The square boxes are 50 mm in size, the black circles are 10 mm in diameter, red circles are 5 mm in diameter and blue circles are 1 mm in diameter. What is the percentage increase in the filling efficiency of the second square when red and blue balls are used in addition to black balls?
(b) In concrete, what does black, red, and blue balls stand for?

32. Questions – Level 2
Q5: We will build on the concepts learned on Day 1 – Enumerate on why you chose the materials you chose to build the bridge. Think about both the concepts of ductility/brittleness and strength.
Cardboard as the bridge slab – what would have happened if you used a piece of glass?
Wooden columns – could you have used something else?
Suspension wires – would spaghetti work?

33. Research and Write on a Concrete Structure
Prepare a 2-page technical document on a well known concrete structure (use internet to choose the structure)
Introduction on what the structure is.
Location, application
What makes it unique/famous/innovative?
Who designed and built it?
What type of concrete and how much was used?
Estimated construction cost
Your assessment of what attracted you most to this structure.
Illustrate your report with photographs, drawings, tables etc.