American Institute Of Constructors (AIC) Level 1 Practice Test

Concrete resists compression much better than tension because its cement paste and aggregate mixture distributes and bears loads effectively when squeezed. Under compression, the particles press together and the internal microstructure can close cracks, so concrete can carry heavy loads smoothly. When pulled apart, cracks form quickly and propagate because there’s limited natural resistance to opening cracks in the cement paste and at the cement–aggregate interfaces, so tensile strength is much lower. In structural design, this is why reinforced concrete pairs concrete's high compressive capacity with steel reinforcement to handle tensile forces; the steel takes the tension while the concrete handles the compression. Shear strength is a factor in some scenarios, but it isn’t the primary property of concrete, and “fluid strength” isn’t a standard characteristic of concrete. So the primary strength of concrete is compressive strength.