2.5. Mechanical Properties

The compressive strengths (σ_c) of five cement samples of each formulation were evaluated in ambient air (23 ± 1 °C) according to ISO9917 [36]. Samples were tested after 1, 7 and 30 days using an Instron Universal Testing Systems (Instron Corp, Norwood, MA, USA) fitted with a ±2 kN load cell at a crosshead speed of 1 mm·min⁻¹. The moulds, 4 mm Ø, by 6 mm height in line with ISO9917 [36], were filled to excess with freshly mixed cement then covered with acetate sheet. The mould/cement/acetate constructs were then sandwiched between two stainless steel plates, clamped and incubated (37 °C, 1 h). The constructs were subsequently unclamped and excess flash around the moulds was removed using 1200 grit silicon carbide paper. Once ground the samples were de-moulded, placed in distilled water and incubated in water (37 °C) for 1, 7 and 30 days. Compressive strength, σ_c, was calculated according to Equation (2) [36]:

where ρ = maximum applied load (N), d = diameter of sample (mm).

Sixty seconds after mixing commenced for each cement, rubber moulds (8 mm Ø, 2 mm thick) were filled to excess with cement and placed between 2 stainless steel plates, clamped, and incubated (37 °C, 1 h). The samples were subsequently de-moulded and incubated in distilled water for 1, 7 and 30 days. The biaxial flexural strength (σ_f) of the cements was determined in a similar fashion to that of Williams et al. [37] which uses three support bearings on the test jig fixed to an Instron Universal Testing Systems (Instron Corp, Norwood, MA, USA) apparatus using a load cell of 1 kN. Testing was performed at a crosshead speed of 1 mm·min⁻¹. Five samples for each cement formulation and incubation time were tested. σ_f was calculated according to Equation (3) [37].

where ρ = fracture load (N), t = sample thickness (mm), r = radius of the support diameter (mm).