## 2 Experimental Program
### Properties of Constituent Materials and Reinforcing Systems  
#### 2.4.1 Fibre-Reinforced Cemertitious Materials  
Two types of FRC were used in the production of the manholes: cement-based mortar reinforced with PAN fibres (PFRM) and hybrid fibre-reinforced concrete (HFRC). To produce the PFRM, PAN fibres of 6 and 12 mm length, PAN6 and PAN12, respectively, were used with the properties indicated in Table 3.  
The HFRC was reinforced with 90 kg/m\({}^{3}\) hooked end steel fibres and 3 kg/m\({}^{3}\) of polymer macro fibres, whose relevant properties are indicated in Table 3.  
The production technology of the PFRM is described elsewhere [8]. The mix composition of PFRM is indicated in Table 4, where it is visible that the aggregates are limited to fine river sand, and a content of fly ash equal to the cement content was adopted. As a result of an optimization process for the PAN-type fibres to be adopted in the PFRM, a fibre volume of 4% was obtained, composed of 3% of PAN12 and 1% of PAN6. This material was selected for producing a group of manholes (PFRM80_c15_g35 and PFRM100_c15_g35) due to its self-compacting nature, fibres and aggregates were much smaller than the centreline open grid of the G-Type1, therefore the probability of segregation of these material constituents occurring when flowing through this GFRP grating was very small. This PFRM presented a deflection hardening behaviour in tests with un-notched specimens under bending [6], which was assumed to be very convenient for the stiffness of the manholes \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Type of Concrete** & **PFRM** & \multicolumn{2}{c}{**HFRC**} \\ \hline Fibre type & \multicolumn{2}{c}{Polyacrylonitrile fibres} & \multicolumn{2}{c}{Hooked end steel fibres} & Polymer macro fibres \\ Length (mm) & 6 & 12 & 33 & 54 \\ Diameter (mm) & 0.058 & 0.026 & 0.50 & Not available \\ Elasticity modulus (MPa) & 9910 & 6856 & 210,000 & 7000 \\ Tensile strength (MPa) & 564 & 264.4 & 1100 & 450 \\ Density (g/cm\({}^{3}\)) & 1.17 & 1.17 & 7.9 & 0.91 \\ Elongation & 13–17 & 14–18 & - & - \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Properties of the fibres used in the production of the PFRM and HFRC. Figure 6: Setup adopted for testing the manhole cover specimens including (**a**) G_Type1 and (**b**) G_Type2; (**c**) view of the LVDTs recording the specimen’s central deflection (dimensions in mm). in their post-cracking phase due to the favourable tension-stiffening effect provided by PFRM [51]. In fact, the flexural strength was much higher than the flexural stress at crack initiation, as a consequence of the fibre-resisting mechanisms that promoted the formation of a diffuse crack pattern [8]. This behaviour has the potential to better distribute the tensile forces along the elements of the GFRP grating, postponing rupture localization for higher load levels on the manhole. The production technology of the HFRC is described elsewhere [52], and its mix composition is included in Table 4. This HFRC presented self-compacting nature, with a spread diameter of 500 mm within 3.5 s, and a total spread diameter of 660 mm [53]. No visual sign of segregation was detected in the developed HFRC, and the mixture presented good homogeneity and cohesion while flowing through the Abrams cone. By executing compressive tests according to the ASTM C 109/C109M-11b [54] recommendations with four cubic PFRM specimens of 50 mm edge of 28 days of age, an average compressive strength of 24 MPa was obtained. An average Young's modulus of 10 Gpa was registered by performing tests according to the ASTM C469 [55] recommendations with four cylindrical specimens of 50 mm diameter and 100 mm height at 28 days of age. To characterize the flexural behaviour of the developed PFRM, four-point bending tests were executed with specimens of 250 \(\times\) 80 \(\times\) 18 mm\({}^{3}\) (length \(\times\) width \(\times\) thickness). The span length of these specimens was 230 mm, with 80 mm between the reaction support and its closest applied load.