2.3.2. Setting Times Test

The setting times (initial and final) of the HPC mixtures were determined using a penetration resistance method under ASTM C403 [33]. A standard 4.75 mm sieve was used

to obtain mortar samples from the fresh HPC mixtures which were cast in two layers into 150 mm cube moulds to about 10 mm below the height edge. The specimens were then kept in a climate control room set at 24 ± 2 ◦C temperature and 70 ± 5% humidity. The pocket type H-4134 concrete mortar penetrometer was then used to measure the concrete's resistance by forcing the penetrometer's shaft into the mortar to a depth of 25 mm at a constant rate and time intervals. The resistance in MPa is shown on the penetrometer's direct-reading scale. The initial set of concrete is reached when the penetration resistance is 3.50 MPa. The initial set is the semi-hardened, partially hydrated condition of the concrete beyond which it can no longer be worked or consolidated by vibration. The plot of penetration resistance on (*Y*-axis) against time in minutes (*X*-axis) gives the initial (3.5 MPa resistance) and final setting (27.6 MPa resistance) times, respectively.

#### 2.3.3. Mechanical Properties

Compressive and splitting tensile strengths were determined in line with BS EN 12390-3 and 6 [34] and RILEM Technical Recommendation TC14-CPC 4 [35], respectively. 210 triplicates of 100 mm cubes and 126 Ø100 × 200 mm cylinders were used to investigate the compressive and splitting tensile strengths using the digitised materials testing machine (Model YES-2000, Eccles Technical Engineering Ltd., Eccles, England) with 2000 kN maximum loading capacity. In addition, 126 prismatic beams of 100 × 100 × 500 mm were tested for flexural strength test using a manually operated three-points contact 50 kN Impact AO 320 flexural machine following BS EN 12390-5 [36].

#### 2.3.4. Non-Destructive Tests on HPC Mixtures

Selected HPC cube specimens of the respective MCC contents (control, 10% and 20%), at constant SAP cured for 90 days, were subjected to SEM-EDX and XRD examinations. Thus, this procedure enables the understanding of the effect of MCC contents on the mechanical behaviours of the HPC. SEM data was collected on thin sections of about 3 mm thickness samples after hydration stoppage. The hydration of the specimen was truncated by soaking the crushed HPC samples in acetone. XRD analysis of HPCs samples was carried out on remains of crushed hardened specimen passing through 75 μm standard sieve.

#### **3. Results and Discussions**
