What are the major ingredients in concrete? Does the amount of time you let concrete cure affect the strength of the concrete? How does rebar impact the strength of concrete? You'll investigate all of these factors in this module during your challenge to make the strongest concrete beam possible. Are you ready to begin? Well let's get cracking.
What is concrete?Many different types of concrete exist; however, most are mixtures of Portland cement, sand, gravel, water, and air. Varying the amounts of these components affects the strength and durability of the concrete. Concrete is a durable building material that has been used for centuries. The ability to be formed into various shapes is one of the most useful characteristics of concrete. The downside of using concrete as a building material is that it is very heavy and is prone to cracking.
What is reinforced concrete?While concrete is a relatively strong material in terms of its compressive strength, it is weak in tensile strength. Imagine a concrete beam resting on two columns at either end of the beam. When a load is placed in the middle of a long concrete beam, the middle of the beam is likely to crack and possibly fail due to the increased tension at the load point. Reinforced concrete has steel reinforcing rods, called rebar, placed inside to help carry the tensile forces. This reinforcement also improves the shear strength of the concrete. Rebar comes in different diameters, all related to x/8". For instance, #3 rebar has a diameter of 3/8" and #5 rebar has a diameter of 5/8".
What is curing time?Curing is the process in which concrete gains its maximum strength and durability. Curing depends on the correct moisture and temperature conditions; however, the main factor that impacts concrete curing is time. Typical concrete reaches about 90% of its optimal strength after about 3 weeks. The complete curing of concrete can take decades.
What forces act on a concrete beam?A concrete beam supported on both ends has a number of different forces acting on the beam. First, gravity pulls the entire beam downward, applying compression forces to where the beam rests on the end supporting structures. The weight of the beam itself creates a tension force on the bottom side of the middle of the beam. Any load placed on the middle of the beam will increase the magnitude of the tensile force.
Tier 2 Lessons: Grades 7 - 12+
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