UHPC Compressive Strength Conversion Factors: Cubes versus Cylinders

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High demand for high early strength materials such as UHPC has risen lately due to its rapid strength gain of more than 25 MPa after 12 hours. Such attribute can help reduce construction time significantly in precast or ABC field applications. However, it is usually challenging, especially in remote sites, to test UHPC cylinders at early age such as 12 or14 hours due to the required cylinders preparation and end grinding. At early ages or relatively low strength levels, compression test results are very sensitive to cylinders preparation and grinding, and there might be even discrepancies in the results due to the quality of the surface cutting and grinding procedure. The operations performed on cylinders at an early age affect the results and weaken the specimens. Thus, cubes could be used as an alternative to cylinders at least for on-site and early age quality control purposes. Cubes do not require operations before testing, hence leading to consistent results. This paper presents a comprehensive study that uses results from about 900 cubes and cylinders of five different UHPC mixtures with varying steel fiber content and curing regimes. Cubes and cylinders from same batches were tested and compared to deduce robust conversion factors between different cube sizes (2-inch and 4-inch cubes) and the standard 3×6 inch cylinder. The proposed conversion factors accounts for different ages and strength range, and as such, can be used for the 1 to 20 ksi (7 to 140 MPa) range.

Keywords: compressive strength, cubes testing, shape conversion factor

How to Cite: Ibrahim, M. S. & Moustafa, M. A. (2023) “UHPC Compressive Strength Conversion Factors: Cubes versus Cylinders”, International Interactive Symposium on Ultra-High Performance Concrete. 3(1). doi: