# The Size Effect on Flexural Fracture of Polyolefin Fibre-Reinforced Concrete
## 2 Experimental Programme
### Materials and Specim Fabrication  
Portland cement type EN 197-1 CEM I 52.5 R-SR5 (ManuCEMEX, Castillejo, Madrid, Spain) was used in the concrete mix called SCC10. The cement was mixed with limestone filler with a calcium carbonate content higher than 98%, a 45 um sieve retention of less than 0.05%, a density of 2700 kg/m\({}^{3}\) and a Blaine surface of 400-450 m\({}^{2}\)/kg. The silica aggregate contained two coarse size ranges: 4-8 mm grit and 8-12 mm gravel with a maximum size of 12.7 mm. The sand size range was 0-2 mm. Polycarboxiate-based superplasticizer, named Sika-Viscocrete 5720 (ManuSIKA, Madrid, Spain), with a density of 1090 kg/m\({}^{3}\) and a solid content of 36% was also included in the mix. The mix formulation is shown in Table 1 and was that used in previous experimental campaigns [25]. The 48 mm long macro fibres type SikaFiber, with an embossed surface, were added to the mix in a volume fraction of 1.1%, equivalent to 10 kg/m\({}^{3}\). Table 1 also shows the main fibre properties. The visual aspect of the fibres can be seen in Figure 2. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Material** & **SCC10** & **PF48 Fibre Properties** & \\ \hline Cement (kg/m\({}^{3}\)) & 375 & Length (mm) & 48 \\ Limestone (kg/m\({}^{3}\)) & 200 & Equivalent diameter (mm) & 0.903 \\ Water (kg/m\({}^{3}\)) & 188 & Aspect ratio & 53 \\ Water/cement & 0.5 & Tensile strength (MPa) & \textgreater{}400 \\ Gravel (kg/m\({}^{3}\)) & 245 & Density (g/cm\({}^{3}\)) & 0.91 \\ Grit (kg/m\({}^{3}\)) & 367 & Modulus of elasticity (GPa) & \textgreater{}6 \\ Sand (kg/m\({}^{3}\)) & 918 & Fibre shape & Straight \\ Superplasticizer (\% cement) & 1.25 & Surface structure & Rough \\ PF48 (kg/m\({}^{3}\)) & 10 & Fibres per kg & 32,895 \\ Fibre volume fraction (\%) & 1.10 & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Concrete composition and fibre properties. A 100-litre capacity vertical axis mixer was used in the concrete fabrication. The mixing sequence was as follows. First, the three types of aggregate were mixed for one minute, followed by the addition of 1/3 of the fibre content which was mixed for 30 more seconds. Then, cement and filler were added and mixed for another 30 s. After that, 30 more mixing seconds were needed before the incorporation of the other 1/3 of fibre content. Next, after 75% of water had been poured and mixed for another minute the rest of the water, the fibres and the superplasticizer were added, continuing the mixing action for 150 s. Then the mixer was stopped for 150 s. The mixing was then resumed for two minutes. Fresh concrete was tested in a slump-flow test according to the standard procedures [26]. The double-test average results were \(t_{500}\) = 6 s and the diameter of the patty \(d_{m}\) = 570 mm. Concrete was poured into the moulds from one end, leaving the concrete flows towards the opposite end with the only compaction action being its own weight as it is recommended by the standards and bibliography [24; 27]. The fresh specimens were covered with plastic film to keep the upper surface from drying. The beams were unmoulded 24 h later and placed in a humid chamber at 20 \({}^{\circ}\)C and 90% of relative humidity for a minimum of 28 days (the point when they were ready for testing). Before the bending tests, a half-depth cut was machined in the lower part of the beam central sections with a low-speed diamond disc, carefully maintaining the integrity and dimension of the upper half section of the specimen. The proportional dimensions based on the specimen depth \(D\) are shown in Figure 3. Under this procedure, three specimen size categories were obtained: large, medium and small, as defined in Table 2. Figure 4 shows a photo with the three sizes of the tested specimens. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Specimen** & **Units** & **Length (mm)** & **Width (mm)** & **High (mm)** \\ \hline Large & 3 & 1350 & 50 & 300 \\ Medium & 2 & 675 & 50 & 150 \\ Small & 3 & 340 & 50 & 75 \\ \hline \hline \end{tabular}
\end{table}