Comparative Evaluation of the Compressive Strength of Concrete Cubes Cast Using 4 mm Thick Steel and Plastic Moulds

Abstract

The accuracy of compressive strength testing of concrete is highly dependent on the quality and dimensional stability of cube moulds used during specimen preparation. While steel moulds have traditionally been regarded as the standard because of their rigidity and durability, plastic moulds are increasingly being adopted due to their affordability, light weight, and ease of handling. However, questions remain regarding their influence on the measured compressive strength of concrete. This study comparatively evaluates the compressive strength of concrete cubes cast using 4 mm thick fabricated steel moulds and commercially available plastic moulds. A Grade 15 concrete mix with a nominal proportion of 1:2:4 and a water-cement ratio of 0.5 was prepared. Ninety six  (96) concrete cubes measuring 100 × 100 × 100 mm were cast equally between the two mould types and cured in water for 7, 14, 21, and 28 days. Compressive strength tests were conducted using a calibrated compression testing machine in accordance with BS EN 12390-3. The fabricated steel moulds demonstrated excellent dimensional stability and consistently produced higher compressive strength values than the plastic moulds. At 28 days, the average compressive strengths were 28.8 MPa and 27.2 MPa for steel and plastic moulds, respectively, representing approximately a 5.9% difference. Statistical analysis indicated that the difference was significant at the 95% confidence level. The study concludes that 4 mm thick fabricated steel moulds provide greater reliability and repeatability in compressive strength determination and are therefore recommended for research laboratories, quality control, and structural concrete testing. The findings support the use of fabricated steel moulds for laboratory and field quality control where high precision, durability, and repeatability of concrete strength testing are required. They also suggest that while plastic moulds remain suitable for routine or less demanding applications, steel moulds are preferable when accurate assessment of concrete strength is essential for structural design, research, and compliance with testing standards.