Mechanical properties and size effects in lightweight mortars containing expanded perlite aggregate

The study presented here investigates the effect of density in cementitious mortar on its mechanical properties under quasi-static loading. The reduction in density was achieved through the addition of expanded perlite as a lightweight aggregate into cement paste by volume replacement of cement in the ratio from 0 to 8. This yielded a range of densities between 1000 and 2000 kg/m3. The compressive and flexural response of these mixes were determined for geometrically scaled specimens to study the size effect. Some mixes were reinforced with polymer microfibres and the Mode I fracture toughness parameters were evaluated through flexural testing of notched beams. When compared with a reference Portland cement paste, the compressive strength and elastic modulus scaled as the cube of the density, while the fracture toughness varied linearly with it. The study shows that the specimen size effect on compressive and flexural strength decreases with a drop in the density of the mix and also with fibre reinforcement. On the other hand, the specimen size effect on the critical crack mouth opening displacement was more pronounced at lower densities.