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Bricks and Superbricks You will need: Modeling clay Fine straw Sand Nylon thread A 9-ounce plastic cup A plastic cup Kitchen scales Scissors A sharp knife A ruler What to do: Break off three lumps of clay. Using the ruler and knife, mold and trim the first into a brick 4" long, ¾" wide, and ¼ high. Cut off about 20 pieces of straw, each roughly ½" long. Combine these pieces thoroughly with the second lump of clay and make a brick the same size as the first. Finally, mix about three pinches of sand with the remaining lump of clay before molding it into a third brick. Allow all three bricks to harden overnight. Poke two small holes in the top of the cup and pass the nylon thread through. Tie the thread in a loop about 2 feet long. Pass the thread over the middle of the plain clay brick and rest the ends of the bricks on two supports, such as two piles of books, as shown. Place the bowl under the cup. Begin to slowly pour sand into the cup. Do this until the brick snaps under the load. Pour all the sand back into the cup and weigh it. Make a note of your measurements. Repeat the experiments with the straw-and-clay brick and with the sand-and-clay brick. What do you notice? Can you explain your results? Taking it further: Try using other mixtures of straw and sand. What amounts of each produces the strongest brick? What happens if you mix bath straw and sand in with the clay? Experiment with other materials in the clay, such as strands of human hair. You might also try to obtain different types of clay – from river banks or the ground (if there is clay soil in your area) or from craft stores. Which type of clay makes the best bricks?

Trials of Strength

Bricks in a decorative pattern in a wall

In days gone by, the way to see if a new substance or design worked was to build an actual structure, such as a bridge, and hope that it stayed up! Today, however, new building materials are checked thoroughly in laboratories before being used in practice. Equipment is used to measure accurately the strength of a substance under different kinds of stretching, pressing, and twisting forces. Scientists do experiments on the material to find out how it is affected by high and low temperatures, water, and fire.

Often, a pure substance can be made stronger by adding other substances to it. For example, iron becomes tougher and more flexible when turned to steel by mixing it with a small amount of carbon. In a similar way, mud and clay can be made stronger by reinforcing them with sand, straw, animal hair, cow dung, or even blood. The particles of the added substance provide something for the clay particles to bind to and help to stiffen the finished brick.

The Rock That Pours

Pouring concrete to make a foundation

Cement is the great, all-purpose building material of today. It consists of a very fine powdered mixture of substances such as calcium silicates and calcium aluminates that are obtained from naturally occurring rocks. When sand and water are added to it, complex chemical reactions take place and the cement sets into a hard, solid mass called concrete.

Aside from being strong, concrete has the big advantage that it can be poured while in the form of wet cement. This makes it ideal for filling in the foundation holes at a building site or for being precast at a factory into any desired shape. The precast sections are then delivered to the building site for assembly.

Like clay, cement can be mixed with various amounts of sand, water, gravel, and other additives to give different types of concrete suitable for different jobs. For large structures, the concrete is given extra strength by molding it around steel bars up to two inches thick. The result is called reinforced concrete.

The steel bars are kept tightly stretched while the concrete sets, then upon being released they squeeze of "prestress" the concrete, giving it even more strength. Prestressed concrete will not crack even under exceptionally heavy loads.