Transport and Mechanical Properties of Hollow Concrete Blocks Produced Using Sharp Sand and Fine/soft Sand

The mechanical and durability characteristics of hollow concrete blocks are heavily dependent on the nature of mineral aggregate used. In North Western Nigeria, sharp sand (SS) is scarce and expensive; therefore, many block makers relied on locally available fine sand (FS), despite insufficient proof of its viability for structural purposes. This study evaluated the transport and mechanical performance of hollow concrete blocks produced with varying blends of SS and locally available FS. Five sand combinations—100SS:0FS, 75SS:25FS, 50SS:50FS, 25SS:75FS, and 0SS:100FS—were produced using a cement-to-sand mix ratio of 1:6 and a water–cement ratio of 0.55. Sieve analysis, fineness modulus, sedimentation, bulk density, and specific gravity tests of aggregates were conducted. Hardened blocks and cubes were then assessed for water absorption, capillary sorption, abrasion resistance, and compressive strength at 7, 14, 21, and 28 days. Results indicates that SS improved aggregate grading and mechanical behavior, due to its higher fineness modulus (3.38) and lower silt content (2.96%). Conversely, mixtures containing FS exhibited improved transport-related properties: the 25SS:75FS blend recorded the lowest water absorption and capillary sorption, attributed to improved particle packing and reduced pore connectivity. The control mix (100SS:0FS) achieved the highest 28-day compressive strength (4.64 N/mm²) and best abrasion resistance, while full FS (0SS:100FS) replacement reduced compressive strength to 3.65 N/mm² However, all mixes met the Nigerian Industrial Standard minimum requirement of 3.45 N/mm² for load-bearing hollow concrete blocks. The results show that partial or total substitution of SS with FS is a realistic, cost-effective, and long-lasting alternative for producing sustainable hollow concrete blocks without sacrificing structural adequacy.

Keywords: Sharp sand, fine sand, transport properties, mechanical properties, abrasion resistance.