2.1.3. Mix Proportions

In order to investigate the combined effect of the SAP and steel fibers, eight concrete mixtures were prepared according to Table 2. These included three reference compositions, two without SAP or fibers (REF-035 and REF-040), and another with fibers and without SAP (REF-035F). The remaining five mixtures included SAP or SAP and fibers.



<sup>1</sup> Including water absorbed by SAP.

All mixtures presented low w/c ratio and high strength. The total water–cement (w/c) ratio was set at 0.35 or water–binder of 0.32. A reference mixture with w/c of 0.4 was also prepared for comparison with the mixture where additional water was placed due to SAP. In the mixtures without fibers, the content of the superplasticizer was adjusted in order to reach the required workability.

The mortar compositions all had the same proportions of binder and aggregate and the content of SAP varied from 0 to 0.6%. In the mixtures with fibers, the amount of superplasticizer was fixed at 2% and the fibers content was set constant at 1.28% in volume.

The mortars were prepared in a mechanical mixer (Solotest São Paulo, Brazil) under the following steps. The first step was dry mixing the cement, the SAP, and the sand for 5 min at a slow speed. The second step was the water and superplasticizer addition for 2 min, and then mixing at a high speed for 5 min. Then, the mixer was stopped, the edges of the bowl were scraped, and followed by mixing for another 3 min at high speed. In the correspondent mixtures, the fibers were then added constantly in motion for 5 min at slow speed, preventing the ball bearing effect, then the edges were scraped again for 3 min. Finally, the mortar was mixed for 5 min at high speed to ensure a uniform consistency. For proper compaction, the mixes were cast into molds placed on a vibrating table. The specimens were moved to a room with 100% relative humidity and 22 ± 1 ◦C. They were demolded after 24 h and continued in this room until the testing date.
