2.1.2. Concrete Mixture Proportions

In addition to CC, three binary and three ternary concrete mixture proportions were designed. The CC having 100% cement, whereas the binary concrete mixtures were designed by partial substitution of cement with 10%, 20%, and 30% WSA, and are respectively identified as WSA10, WSA20, and WSA30. The ternary mixtures incorporating blends of WSA and SF were designed by substituting high amounts of cement ranging from 30% to 50% as 25% WSA + 5% SF (WSA25SF5), 33% WSA + 7% SF (WSA33SF7), and 40% WSA + 10% SF (WSA40SF10). Table 3 shows the corresponding ingredients of each concrete mixture and the related details of test specimens.

Adding SF to ternary concrete mixtures was primarily to increase the percent of cement replaced by WSA without compromising the mechanical or durability characteristics. Thus, to improve the mechanical strength of binary concrete as compared to those of CC, SF is added at a rate of 5%, 7%, and 10% to concrete mixtures containing a high percentage of WSA as 25%, 33%, and 40%, respectively. The water-to-binder ratio was maintained at 0.35 for all the concrete mixtures. In accordance with the constant water-to-binder ratio and binder content (457 kg/m3), the water content for the concrete mixtures was maintained at 160 kg/m3. Consequently, to achieve the target workability corresponding to slump

values of 120 ± 30 mm, additional dosages (wt.%) of the naphthalene-based water-reducing admixture were employed for each concrete mixture, as listed in Table 3.

**Figure 1.** (**a**) XRD pattern and (**b**) FTIR of WSA after heat treatment at 550 ◦C for 4 and 8 h, and at 800 ◦C for 30 min.


**Table 3.** Mixture proportions for control, binary, and ternary concretes (w/b = 0.35; a/b = 3.37; s/a = 0.40).

#### *2.2. Methods*

### 2.2.1. Concrete Mixing and Preparation of Concrete Specimens

Concrete ingredients were mixed using a rotating pan mixer driven by power, following ASTM C192 guidelines. As soon as the required slump was achieved, cylindrical specimens measuring 100 mm in diameter and 200 mm in height were poured with fresh concrete according to ASTM C39. A total of 18 specimens were cast for each concrete mixture to determine the evolution of compressive and splitting tensile strengths after 7, 28, and 91 days of aging (3 identical specimens at each age). The cylindrical molds were covered with plastic sheets after fabrication and kept under standard laboratory temperature of 20 ± 1 ◦C and relative humidity of 60 ± 5% for 24 h. Concrete specimens were demolded 24 h after casting and moist cured in a curing tub until being tested at 7, 28, and 91 days. The upper and lower surfaces of concrete specimens were leveled by an end-surface grinder after reaching the desired curing period.
