Strength and durability of mortar containing spent coffee grounds as a part of fine aggregate

Abstract

Vietnam is a major coffee-consuming country, generating a significant amount of spent coffee grounds. Meanwhile, natural sand is increasingly depleted, making it necessary to seek alternative materials. This study investigates the potential of using spent coffee grounds as a partial replacement for sand in mortar production, with replacement levels of 0, 2.5, 5, 7.5, and 10% by weight. The evaluated properties include compressive strength after immersion in water and 5% Na₂SO₄ solution, water absorption, drying shrinkage, and sulfate expansion. The results show that replacing sand with spent coffee grounds reduces the compressive strength of mortar, while increasing water absorption, drying shrinkage, and sulfate expansion. Mortar samples containing 7.5% or more spent coffee grounds exhibited slower strength development at early ages and demonstrated equal or even higher strength when immersed in a Na₂SO₄ solution compared to those cured in water. On the other hand, all mortar samples containing spent coffee grounds achieved compressive strengths ranging from 17 to 44 MPa at 28 days, which is comparable to conventional mortars commonly used in practice.