The SFs were added to the trans-mixer truck at a rate of 20 kg/min, and the drum was rotated at high speed for 5 min afterwards [11]. All the cylindrical samples were kept at room temperature in the materials aboratory, while being covered by burlap, and water was splashed over them regularly every day. When the samples were 28 days old, each of them was subjected to compression test in a universal compression machine with a standard compresso-meter mounted on it at a load rate of about 0.25 N/mm2 per second, and the loads (in kN) and deformations (in 10–2 mm) were accurately recorded at 20 kN load increments up to the final crushing. The toughness of each concrete type was computed as the total area under the curve averaging the experimentally obtained plots of load versus compressive shrinkage, which could be interpreted as ability of plain concrete to absorb energy under direct compression. The results of these tests are summarized in both Table 1 and Fig. 1.
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