Which one of the following is utilized to determine the long-term deformation of concrete under sustained loading?

The correct option is Creep.

To understand why this option is correct, let us break down the concepts associated with concrete deformation and strength:

1. Creep: Creep is defined as the time-dependent, progressive deformation of a material (such as concrete) under a constant, sustained load. When concrete is subjected to long-term compressive stress, it continues to deform over time even if the load remains unchanged. This long-term deformation is critical in structural design to estimate long-term deflections and prestress losses.

2. Shrinkage: Shrinkage is the reduction in volume of concrete, primarily due to the loss of moisture during drying or hydration. Unlike creep, shrinkage occurs independently of any external load or sustained stress.

3. Modulus of Rupture: This is a measure of the tensile strength of concrete in bending (flexural strength). It represents the maximum bending stress concrete can sustain before cracking, rather than a deformation under sustained loading.

4. Split Tensile Strength: This is an indirect method of determining the tensile strength of concrete by applying a compressive line load along the length of a concrete cylinder until it splits. It is a strength property, not a long-term deformation property.

Therefore, Creep is the specific phenomenon utilized to determine the long-term deformation of concrete under sustained loading.