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 the purpose of adding gravel to make concrete?
Gravel is added to make concrete to increase the compressional strength of the concrete. The larger the size of the gravel, the stronger the concrete. However, gravel of too large a size increases the friction within the concrete and increases the difficulty of mixing the concrete. The ideal amount of gravel to add to make the strongest, workable concrete is about 40% of the total ingredients.
What is the purpose of adding sand to make concrete?
Sand is used to bind the gravel and other materials together to make an artificial “solid” rock. The sand increases the concrete’s ability to expand and contract with changing temperatures, increases the compression strength of the concrete, and improves the concrete’s tensile strength to a lesser degree. The ideal amount of sand to add to make the strongest, workable concrete is about 25% of the total ingredients.
What is the purpose of adding water to make concrete?
When mixed with cement, water forms a paste that binds together the sand and gravel used to make concrete. However, the more water added, the weaker the mixture becomes. The ideal amount of water to add to make the strongest, workable concrete is about 15% of the total ingredients. The water hardens the ingredients used to make concrete in a hydration chemical reaction.
What is the purpose of adding cement to make concrete?
Cement reacts with water through the hydration reaction and serves as an agent to bind all the ingredients of concrete together. The cement adds to the compression strength of the concrete, reduces the shrinkage of the concrete, and improves the overall durability of the concrete. The ideal amount of cement to add to make the strongest, workable concrete is about 20% of the total ingredients.
What is the purpose of adding air to make concrete?
The addition of air to concrete improves the concrete’s resistance to temperature changes that would normally cause the concrete to expand and contract, producing cracks in the concrete. Air also improves the workability of the concrete; however, any air voids reduce the overall strength of the concrete. The ideal amount of air to add to make the strongest, workable concrete is about 5% of the total ingredients. Air is added to the concrete by mixing the ingredients and exposing more surface area of the ingredients to air.
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.
Here are some definitions to help you in your Grade 3-5 Lesson 1 investigation.
Substance - a kind of matter that has the same properties all through the matter
Property - a way used to describe matter
Chemical Reaction - when two or more substances combine to make a new substance with different properties
Hydration Reaction - when two or more substances combine with water to make a new substance with different properties
Chemical Bond - a force that connects two or more atoms together
Proportion - a way to state how two or more values are related to each other or to a whole
Percentage - a relative value that states what part of a hundred a certain value is
Here are some definitions to help you in your Grade 3-5 Lesson 2 investigation.
Substance - a kind of matter that has the same properties all through the matter
Property - a way used to describe matter
Chemical Reaction - when two or more substances combine to make a new substance with different properties
Curing Time - the length of time for a chemical reaction to happen in concrete
Atoms - the basic unit that makes up all matter
Molecules - two or more atoms chemically bonded together
Chemical Bond - a force that connects two or more atoms together
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.
