Comparing Strength and Modulus of Elasticity Values for Prisms Constructed with Lightweight and Normal Weight Grout

Current masonry design standards allow for the use of lightweight concrete masonry unit (CMUs), but lightweight grout is not an approved building material. An experimental test program was conducted to compare the compressive strength and modulus of elasticity of masonry prisms constructed with lightweight and normal weight grout. Three strength categories were considered: 13,780, 20,670, and 27,560 kPa (2,000, 3,000, and 4,000 psi). The experimental results indicated that at prism compressive strengths near 13,780 kPa (2,000 psi), there was no statistical strength difference between prisms made with lightweight and normal weight grout. As a result, the authors suggest that for compressive strengths near 13,780 kPa (2,000 psi), lightweight grout should be a code-acceptable alternative to normal weight grout. At higher prism compressive strengths, the values obtained for lightweight and normal weight materials diverged, and the lightweight prisms could not sustain the same loads and stresses as those made with normal weight grout. The results suggest that the difference in strength between lightweight and normal weight prisms can be accounted for by applying a lightweight reduction factor to the data set.