The spreadsheet (.xlsx) contains research data supporting the paper "Interface bond strength of lightweight low-cement functionally layered concrete elements" by Giacomo Torelli and Janet M. Lees (2020) in Construction and Building Materials, v. 249, 20 July 2020, 118614. This includes the data associated with: • Table 1 - Mix compositions, design density and strength of the virtual materials A, B1 and B2. • Table 2 - Delay between the castings of the external layer and the core section, and treatment of the interface for each specimen. • Table 3 - Mix compositions for the external and internal layers. Superplasticizer content expressed in terms of % of cement mass. • Table 4 - Densities of the mix constituents. • Table 5 - Batches used for six layered-elements. • Table 6 - Fresh and hardened state properties of the different batches. • Figure 2 -Potential cement and weight savings for a beam with height h for various values of thickness t of the external layer, assuming h/b=2. • Figure 15 - Relationship between tensile strength and pour delay for layered specimens cut from top horizontal cores (HT1 and HT2), bottom horizontal cores (HB1 and HB2) and vertical cores (V1 and V2), (b) Relationship between tensile strength, pour delay and failure mode for layered cylinders cut from horizontal cores. • Figure 16 - Average tensile strength and (b) average tensile strength normalised with respect to the tensile strength of the weaker of the two materials versus pour delay. • Figure 18 - Maximum thickness of the external layer at the bottom of the element as a function of the pour delay. • Figure 19 - Composite graph: i) average tensile strength of the layered elements normalised with respect to the tensile strength of the weaker of the two materials versus pour delay, and ii) Rate of evolution of heat of Portland cement with a water/cement ratio of 0.4 [46]. *The first peak of 3200 J/s kg is off the diagram