Cast compressive strength tests performed on Portland cement concrete varies from one standard to another and from one country to another. In many situations, it may be necessary to compare compressive strength values tested using different specimen sizes specially in areas were no specific specimen size requirement is adapted. It is considered that the restraining effect of the platens of the testing machines extends over the entire height of the cube but leaves a part of a test cylinder unaffected. For that reason, many codes prefer to use cylinder of 300 ×150 mm rather than cubes, but this leaves the problem of preparation and handling of relatively large sample (300×150 mm), which creates a difficulty during construction. The proposed cylindrical specimen of 150x75 mm considered in this research will enable a practical and easy handling, at the same time it keeps the effect of machine plates at minimum. For the purpose of this research, specimens were prepared and tested having 100 mm and 150 mm for cubes, and 150x75 mm and 300x150 mm for cylinders. Ten mixes were used in preparation of specimen above having variable water-Cement ratio varying from 0.30 to 0.83. A compressive strength results shows that a relationship exists between the different specimens sizes especially the proposed 150x75 mm cylinder and the standard 300x150 mm cylinder. Based on the outcome of this research it is recommended to use the proposed 150x75 mm cylinder specimen and the correlation developed between the proposed specimen size and the standard cylindrical specimen.

Cast compressive strength tests performed on Portland cement concrete varies from one standard to another and from one country to another. In many situations, it may be necessary to compare compressive strength values tested using different specimen sizes specially in areas were no specific specimen size requirement is adapted. It is considered that the restraining effect of the platens of the testing machines extends over the entire height of the cube but leaves a part of a test cylinder unaffected. For that reason, many codes prefer to use cylinder of 300 ×150 mm rather than cubes, but this leaves the problem of preparation and handling of relatively large sample (300×150 mm), which creates a difficulty during construction. The proposed cylindrical specimen of 150x75 mm considered in this research will enable a practical and easy handling, at the same time it keeps the effect of machine plates at minimum. For the purpose of this research, specimens were prepared and tested having 100 mm and 150 mm for cubes, and 150x75 mm and 300x150 mm for cylinders. Ten mixes were used in preparation of specimen above having variable water-Cement ratio varying from 0.30 to 0.83. A compressive strength results shows that a relationship exists between the different specimens sizes especially the proposed 150x75 mm cylinder and the standard 300x150 mm cylinder. Based on the outcome of this research it is recommended to use the proposed 150x75 mm cylinder specimen and the correlation developed between the proposed specimen size and the standard cylindrical specimen.