## 2 Research Program  
### Materials, Mix Compositions and Specimens' Production  
The experimental program was planned and performed analogously to the description presented in the previous conference publication [39]. The ingredients used to make SCCs incorporated cement (C), sand (S), gravel (G), ground granulated blast furnace slag (GGBS), water (W), as well as a mix of three kinds of high range water-reducing admixtures (HRWA). To study the influence of polypropylene fibre on the fresh properties and strength development of ecological SCCs, a control mix without fibre was developed in which ordinary Portland cement CEM 142.5R, complying with PN-EN 197-1:2012 standard [40], and GGBS were used as binder components. Fibre-reinforced concrete mixtures were made with the addition of PP fibres to the reference mix in 0.025, 0.05, 0.075, 0.125, and 0.25% fractions. The specific chemical compositions of the cement and GGBS are given in Table 1.  
The high content of SiO\({}_{2}\) in GGBS was advantageous in terms of material strength.  
In all compositions, three types of HRWAs based on lignosulfonates and polyacrylamide ethers were applied. Their total amount was kept at 3% of the weight of binders in all mixes. The HRWA dose was selected to obtain the slump flow of 720 \(\pm\) 10 mm for the reference blend, meeting the requirements for the SF2 flow class in accordance with the European guidelines [41]. The total amount of cementitious materials was 650 kg/m\({}^{3}\) and the W/B ratio was maintained at 0.32. As a coarse aggregate, gravel with a maximum diameter of 8 mm was used in the amount of 400 kg/m\({}^{3}\). Quartz sand with a fineness modulus of 1.84 and a grain size of 0.5/2 mm was used in the amount of 980 kg/m\({}^{3}\). The particle sizes of gravel and quartz sand were determined in accordance with a known standard. The polypropylene fibre was provided by BAUCON(r) Co. (BAUTECH(r), Piaseczno, Poland). It was crimped with 12 mm length and 25 \(\upmu\)m diameter filaments. Other PP fibre properties, based on the manufacturer's technical data, were as follows: density 910 kg/m\({}^{3}\), modulus of elasticity 35,000 N/mm\({}^{2}\) and tensile strength = 350 N/mm\({}^{2}\). Polypropylene fibres used in this study are shown in Figure 1.  
\begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline
**Compound** & **SiO\({}_{2}\)** & **Al\({}_{2}\)O\({}_{3}\)** & **Fe\({}_{2}\)O\({}_{3}\)** & **CaO** & **MgO** & **SO\({}_{3}\)** & **K\({}_{2}\)O** & **Na\({}_{2}\)O** & **Cl** & **LOI** & **Insoluble Matter** \\ \hline Cement & 20.19 & 4.30 & 3.25 & 64.61 & 1.41 & 2.96 & 2.59 & 0.26 & 0.111 & 3.41 & 0.48 \\ GGBS & 33.14 & 13.55 & 1.30 & 43.36 & 6.48 & 0.29 & 0.31 & 0.29 & 0.006 & 0.76 & 0.31 \\ \hline \end{tabular}
\end{table}
Table 1: Chemical constituents of cement and GGBS (in %).  
The mixed compositions of polypropylene-fibre-reinforced HPSCs are displayed in Table 2. HPSCC denotes the plain concrete and PPHPSCC indicates the PP-fibre-reinforced concrete. The number directly following the abbreviation represents the percentage of PP fibres. The amount of the other ingredients was identical in order to determine the impact of the PP fibre on the self-compacting concrete properties.  
The mixing procedure for PPHPSCC is presented in Figure 2. The order of adding the mix components was as follows: gravel and quartz sand (G+S), cementitious materials (C+GGBS), uniformly mixed water (W) with three types of HRWAs, as well as polypropylene fibres (PP). The times of mixing for above components were 2, 2, 4, and 4 min, respectively. Then, the L-box and slump flow tests were performed. After the tests of rheological properties, the moulds were filled with concrete and left covered with foil for 24 h in the laboratory. The specimens were then demoulded and placed in a tank with water at 20 \(\pm\) 2 \({}^{\circ}\)C to mature for testing.