# Effect of Fibre Reinforcement on Creep in Early Age Concrete
## 2 Materials and Methods
### Methods
#### 2.2.2 Creep Test  
The specimens manufactured for this test were cylinders with a diameter of 15 cm and a height of 30 cm. Until the time of the test, the specimens were cured in a humidity chamber under controlled conditions (20 \(\pm\) 2 \({}^{\circ}\)C and 95 \(\pm\) 5% humidity). To determine the creep deformation of the concrete, three strain gauges were installed on each specimen to measure the deformation due to applied load.  
For the loading of the specimens, the authors designed a loading gantry that enabled the analysis of the evolution of creep deformation of several specimens simultaneously. In this investigation, four concrete specimens with fibres were loaded in each load frame. These frames were composed of two reaction beams, four Dywidag bars that perform the  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline  & **Fe\({}_{2}\)O\({}_{3}\)** & **CaO** & **SiO\({}_{2}\)** & **Al\({}_{2}\)O\({}_{3}\)** & **MgO** & **TiO\({}_{2}\)** & **SO\({}_{3}\)** & **K\({}_{2}\)O** & **Others** \\ \hline Compound [wt.\%] & 3.38 & 66.60 & 17.81 & 4.79 & 1.30 & 0.20 & 4.49 & 0.78 & \textless{}0.5 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Chemical composition of the cement used.  
Figure 2: Hooked-end fibres used. (**a**) photograph; (**b**) schematic diagram.  
loading of the specimens, and a spherical hinge that enabled the specimen to be axially loaded, avoiding the introduction of bending stresses (as shown in Figure 3).  
The Dywidag bars load the specimens, which are tensed using a 60-ton hollow jack in four load steps, corresponding to 25%, 50%, 75%, and 100% of the stressing strength. To control the stress in the Dywidag bars, it was decided to fit these structural elements by installing two bidirectional extensometers per bar, connected to each other by means of an electronic assembly in a complete Wheatstone bridge [27]. The deformation experienced by the fibre-reinforced concrete specimens is experimentally measured by installing three unidirectional strain gauges in three generatrices at 120\({}^{\circ}\) in each specimen. These bands are individually connected with control strain gauges that enable compensation for thermal effects during the test. The connection of the bands is made by means of an electronic mounting in a half Wheatstone bridge [27] (Figure 4).  
In order to analyse the creep evolution of the concrete specimens with fibres and obtain the creep curves associated with this type of concrete at different loading ages, the specimens were divided into four groups and each group was tested at four different loading ages. The loading configuration for each specimen is shown in Table 4. The need to submit specimens of different ages, 24 h and 3 d, and 7 d and 28 d, to the same load, arises from the availability of only two loading frames. In one of the loading frames, the analysis of the creep undergone by the specimens loaded at 24 h and 3 d is carried out, and in the other the specimens loaded at 3 d and 28 d. Young specimens (loaded at 1 and 3 days) were loaded at 265 kN (around 80% of the compressive strength at 24 h and 40% at 3 d), while the others (loaded at 7 and 28 days) were loaded at 353 kN (around 50% of the compressive strength at these ages). In the case of 24 h and 3 d age specimens, the load was chosen to be sufficiently representative at 3 d, but to be able to be supported by 24 h age specimens. In the case of 7 and 28 d age specimens, a load of 50% of its compressive strength was considered adequate to see a significant evolution in the concrete.  
Figure 3: Test gantry configuration. (**a**) Schematic drawing; (**b**) photograph.