*2.2. Methods*

#### 2.2.1. Vegetal Ash Preparation

Sunflower stalks (SS) were broken manually into pieces of around 0.5 m in length, and corn cobs (CC) were mechanically shredded with a mill for grinding animal feed in granules smaller than 6 mm in diameter. SS and CC were free burned in a brick kiln, after they were left to dry in outside natural conditions of the environment. The burning temperature was not controlled; it was measured, and it achieved around 700 ◦C in the case of SS case and 570 ◦C in the case of CC.

The raw ash obtained after free burning was sifted for 5 min through sieves of 20 mm, 10 mm, 2 mm, and 300 μm, using an automatic sieving equipment (Endocotts Powermatic Test Sieve Shaker). The 300 μm sieve was chosen as Bahuradeen et al., 2015 [10], stated that the pozzolanic properties of ash can be improved if the particles are smaller than this dimension.

The sieved ash was then ground for 120 min in a ball dust crusher to obtain even smaller dimensions of the ash particles. The ground ash (Figure 1) was noted as A quality ash and it was used as cement partial replacement in CCA1A, CCA2A, SSA1A, and SSA2A concrete mixes.

**Figure 1.** The SSA of A and B quality and CCA of A and B quality, compared with the cement aspect.

The vegetal material that did not passed through the 300 μm sieve was subjected to supplementary thermal treatment at around 550 ◦C for 120 min. After this treatment, the vegetal material was sieved again through 20 mm, 10 mm, 2 mm, and 300 μm sieves for 5 min, with the same sieving equipment, and then ground for 120 min in the ball dust crusher. This ground ash (Figure 1) was noted as B quality ash and it was used as cement partial replacement in CCA1B, CCA2B, SSA1B, and SSA2B concrete mixes.

The ashes' bulk density and specific gravity are presented in Table 1.


**Table 1.** The bulk density and specific gravity of CCA and SSA.

#### 2.2.2. Sunflower Stalk Ash Analysis

CCA and SSA were analyzed using Scanning Electron Microscopy (SEM, Vega Tescan LMH II, SE detector, 30 kV, Tescan Orsay Holding, Brno—Kohoutovice, Czech Republic) coupled with Energy Dispersive X-Ray Spectrometer detector (EDS, Bruker XFlash 6I30, Automatic mode, Bruker, Billerica, MA, USA) from composition and aspect point of view.2.

#### 2.2.3. Composite Mixes Preparation

In this study, concrete with 2.5 vol.% and 5.0 vol.% corn cob ash and sunflower stalk ash, of two qualities each, as a cement substitute were developed. The 9 mixes were prepared according to NE 012/1-2007 [31]. A portable electric concrete mixer was used for fresh mixes preparation. The concrete specimens were unmolded after 24 h from pouring in molds, and cured in ambient conditions for 28 days. The ambient conditions were: temperature of 20 ± 3 ◦C, and relative humidity of 55 ± 10%.

2.2.4. Concrete Specimens Properties
