Vol. 16 No. 01 (2026): Journal of Materials & Construction
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JOURNAL OF MATERIALS & CONSTRUCTION

ISSN: 2734-9438

Website: www.jomc.vn

Evaluation of the strength, dimensional stability, and microstructure of lightweight alkali-activated mortar incorporating used coffee grounds

Nguyen Van Dung , Ngo Si Huy , Huynh Trong Phuoc

Keywords:

Compressive strength
Drying shrinkage
Lightweight composite
Microstructure
Segregation

Abstract

Due to the shortage of natural river sand and the uncontrolled disposal of coffee waste, this study investigates the use of used coffee grounds (UCG) as a partial replacement for fine aggregate in producing lightweight alkali-activated mortar (LAAM). Coal bottom ash (BA) was replaced with UCG at 0%, 5%, 10%, and 15% by volume. Experimental evaluations included segregation resistance, compressive strength, ultrasonic pulse velocity (UPV), drying shrinkage, and microstructural analysis. The results showed that all mixtures exhibited acceptable homogeneity without significant segregation. A 5% UCG replacement increased compressive strength and UPV compared with the control mixture, owing to improved matrix compactness and internal curing. However, higher UCG contents led to reduced compressive strength and UPV values. Drying shrinkage decreased in UCG-modified mixtures, with LC-15 exhibiting the lowest shrinkage (best dimensional stability). SEM observations confirmed denser gel formation and better particle matrix bonding in LC-05, whereas LC-10 and LC-15 showed weaker interfaces and more voids. A 5% UCG content is recommended for practical application. These findings highlight the potential of UCG as an environmentally friendly alternative to fine aggregate for lightweight composites, supporting waste valorization and reducing the consumption of natural sand.

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How to Cite

Nguyen Van Dung, Ngo Si Huy, & Huynh Trong Phuoc. (2026). Evaluation of the strength, dimensional stability, and microstructure of lightweight alkali-activated mortar incorporating used coffee grounds. JOURNAL OF MATERIALS & CONSTRUCTION, 16(01). https://doi.org/10.54772/jomc.v16i01.1219

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