*2.1. Materials*

The main binders used in this study were conventional OPC, consistent with ASTM C150, and commercially available SF and WSA (processed in the laboratory). The specified physical and chemical properties of these materials are listed in Table 1.


**Table 1.** Physical and chemical properties of cement, WSA, and SF.

\* ASTM C618-15; \*\* LOI = loss on ignition; \*\*\* data from local cement manufacturer.

Besides binder materials, aggregates from local sources were obtained for using as fillers in concrete. Table 2 shows the sieve analysis results for fine and coarse aggregates. Blending percentages for coarse aggregates are 50% (20 mm down) and 50% (10 mm down). In accordance with ASTM C33, fine aggregate possessed specific gravity of 2.60 and water absorption of 1.03%, while its fineness modulus was 2.54 (Table 2). Specifically, the coarse aggregates had a specific gravity of 2.65 and water absorption of 0.82%, respectively.


**Table 2.** Sieve analysis of aggregates (ASTM C136).

#### 2.1.1. Burning and Grinding of Wheat Straw Ash

The chemical properties of WSA are largely dependent on the source (wheat straw), the organic composition, and the sintering temperature [20]. Further, climatic conditions the chemical composition of WSA is influenced by both climatic conditions and geographical location [48]. The WSA obtained was burned at control temperature at 550 for 4 and 8 h and finally at 800 ◦C for 30 min in a kiln. Each of these samples exposed to different elevated temperatures were subjected to analysis using XRF, XRD, and FTIR to determine their chemical and mineralogical properties. Accordingly, XRD and FTIR results revealed that the maximum amount of amorphous silica was achieved for the sample when burned at 550 ◦C for 4 h (Figure 1). Based on chemical composition, FTIR, and XRD analyses, the WSA obtained after burning at 550 ◦C for 4 h was ground to obtain a fine powder. After cooling under normal air, the WSA was ground in a rotary mill for 12 h at 15 rpm. Using this ground WSA, binary concrete specimens containing only WSA and ternary concrete specimens having blends of WSA with SF were prepared in order to evaluate its effectiveness as a partial substitute of cement. The physical and chemical properties of WSA are listed in Table 1.
