*2.2. Preparation of Biochar-Concrete Specimens*

A total of 6 mix ratios were established to calculate the impact of biochar in standard strength concrete; 16 cylinders and two beams were cast for each mix. Five mixes contain various dosages of biochar, and one mix consists of ordinary Portland Cement (OPC) only. Biochar was added to the mix at a rate of 0.25%, 0.50%, 0.75%, 1.00%, and 1.50 wt% of the overall volume of concrete (Table 1), representing one mix with OPC only and five mixes with different percentages of biochar addition, as described by Akhtar et al. [2]. The water to cement ratio was kept constant at 0.45. MasterGlenium 110M was utilised as a superplasticiser. Initially, materials were dry mixed for about 2 min in a rotary mixer containing special blades. Then, water was added and mixed for another 3–4 min to achieve a homogenous mix. All specimens were cast as per ASTM C192 [24]. Beam specimens (100 mm × 100 mm × 500 mm) and cylindrical specimens (100 mm × 200 mm) were fabricated after putting the concrete mixture in the individual moulds in two consecutive layers and compacted each layer for 10 sec. Afterwards, it was levelled and covered the surface for 24 ± 2 h for setting and then submerged in a curing tank at room temperature 26 ± 2 ◦C for 28 days. Water curing helps to minimise the loss of mixing water from the concrete's surface, and the additional water accelerates the strength gain. After 28 days, the samples are taken out from the curing tank to determine the mechanical properties of the concrete (Figure 1).


**Table 1.** Mix design composition of Biochar-concrete specimen.

**Figure 1.** Concrete cylinder and beam specimens.
