Concrete As A Structural Material

gif video from: Marta Ambrosetti, DensityDesign Research Lab

Concrete is a man-made material

Concrete is made from natural materials but concrete itself is a man-made material. It consists of cement, steel reinforcing, fine aggregate (sand) and gravel or rock (large aggregate).

Water is used in the mix but water is a catalyst. It is necessary for the cement to become hard, but it is not in the finished product.  

Concrete is neither homogeneous nor isotropic

A homogeneous material has the same physical and mechanical properties at any location in a specimen. Isotropic material has the same properties in any direction.

For design purposes, concrete is considered a homogeneous and isotropic material. It is important to understand that this is a simplification.  In materials science, a homogeneous material is a This is necessary to get a practical design, but it is unrealistic. What do structural engineers mean by a homogeneous material? A homogeneous material is a material that has the same characteristics throughout the material. An example of a true homogeneous material is steel. 

Concrete is made of cement, water, and aggregate. Cement is like a glue that holds everything together. Water is necessary to initiate a chemical reaction in the cement. Aggregate includes sand (fine aggregate) and a coarse aggregate of stone. 

How engineers mitigate the lack of homogeneity

Concrete is initially mixed at a concrete plant where all the components are placed into the barrel of a mixer truck. The mix consists of a precise amount of rock, sand, water, and cement. Inside the barrel, the concrete is continuously mixed.

Next, the concrete is placed into a Ready-Mix truck barrel or rotating drum. The rotating drum continuously keeps the concrete mixed. The more the concrete is mixed, the more it will resemble a homogeneous mass. 

Inside the rotating drum, a version of  Archimedes screw shown below) is used to pump the mixed concrete to a chute where it directed to where the concrete is needed. 

Marta Ambrosetti, DensityDesign Research Lab



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