Evaluation of the Performance of Hollow Concrete Blocks in Residential Construction in Imo State

Hollow concrete blocks are the predominant walling unit in residential construction in Imo State, South East Nigeria, and the quality of locally produced blocks directly affects the structural safety and durability of residential buildings across the state. This study evaluated the compressive strength, water absorption, and dimensional accuracy of hollow concrete blocks produced by artisan block makers in Owerri, Orlu, and Okigwe Local Government Areas of Imo State. A total of 180 block samples (6-inch hollow blocks) were collected from 30 production sites, three per site, and tested in accordance with NIS 87:2004 requirements. Site surveys assessed production practices, curing methods, and mix proportions used. Results showed that only 37% of sampled blocks achieved the minimum compressive strength of 3.45 N/mm2, and 27% met the 1:6 mix ratio consistent with the standard. Water absorption exceeded the maximum standard of 12% in 54% of blocks. Mean block length and width dimensions were within NIS tolerances, but height varied significantly (coefficient of variation: 8.3%), indicating poor dimensional control. Inadequate curing (below 7 days) was observed at 70% of production sites. The most commonly reported mix ratio was 1:8 to 1:10 (cement:sand), well below the standard requirement. The study concludes that hollow concrete block quality in Imo State is broadly inadequate, and recommends certification of block production sites by the Imo State Ministry of Housing and state enforcement of NIS 87:2004.

Keywords: hollow concrete blocks, compressive strength, block production, Imo State, NIS 87:2004