Figure 1:

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Figure 6:
![Flowchart indicating the execution process of the GEP model [69].](https://sciendo-parsed.s3.eu-central-1.amazonaws.com/69388d63a2cfbc128b1cffde/j_rams-2025-0183_fig_006.jpg?X-Amz-Algorithm=AWS4-HMAC-SHA256&X-Amz-Content-Sha256=UNSIGNED-PAYLOAD&X-Amz-Credential=ASIA6AP2G7AKBBM74A4T%2F20251212%2Feu-central-1%2Fs3%2Faws4_request&X-Amz-Date=20251212T231138Z&X-Amz-Expires=3600&X-Amz-Security-Token=IQoJb3JpZ2luX2VjEEcaDGV1LWNlbnRyYWwtMSJHMEUCIQCSDFPXoBx8KZl1JnEbdah40IdHkMYigz%2Fuc%2FSTS1xdfwIgKyEwuYwFB4fC1i%2FlmTTEeV11fS3x%2B3syRomnHgSkJ%2F8qvQUIEBACGgw5NjMxMzQyODk5NDAiDNmcanWJdL7QX77z4yqaBSVVZ4aykYGiy0gH2aOP3Vvu6kOj%2FY9imVDLOK8ljiYEmNB6169t3NT6AmkKHLmzu95NZzeI58EuHBHBEAEMNOXtHwS128qFT0ElRsj39%2Flbu013o0xhAgHztYBlfBCcb2Y%2BrwLuSIIjdKPtoFq%2B0UX5F%2BT4tqXjeASF7qIDNs7WcUVCZ7owirnrNIjh1aNIfUDdQtDyYkJQlHtPLB4rQzDvWOzhqhiygdo8s3o0jvTQSFjob3PtidqI6ackbtGUXjIhXWvEnc8kcGN8vLlNVJccx%2FgOr0jIRUnLvuIxFVTJ7vCopRxpGGpBOV%2Bpx3B7vWF8h%2F7tv1k%2B8QDKOhxS3gKHiXzlVCeiOueMuT1wBoAyvjilmaIN1PBsaqE1Ukyt8TfyloJgKrhI%2BXDARz%2ByoGnuT59w%2B5cUqv4WQejYkz%2FGUcU1yD%2BVnCe13sXk5dVnxGAP3GcasUkwZsikRFFM%2FZN1VT7boO2nuftzTD3ImVWqEZWDQk6huPs0PJYb6LqVxYdQ%2B3uYUyyjfGWOu4Epb%2B6Rz59U57yGThYWQYq8mY0dYsOeVxa0UWQhfJRvBbmfkzVJRpC175ICQtac4q%2FjCbLe4UaheFseaDorrweOMyqzaXpkp3Jk5CV0BpwIonj84rnSm7QgXbmZIYyeSTGRU2rHLxpzHKRX%2F387PDEhFcYqGTM%2Blvv6U3Y7WDDTBCViADcZFPX6Fdj7cX4lOIOa4n64lz6DtBl%2BlORVDIFPy%2Br4HHJfvASeEX19GMNHBDk6MwNK8s8vX52VSyIfJYZaYdveCaT0GgP2MY4cqqTEzNmesazW0iE9SwWmdx%2Fs24wC5Dj%2Bq1HDAM%2BRQ8HhxV9iMIy4MU55JtB%2FaonrCcTWlLCPNGIMXP9TV%2BYSmDCGsvLJBjqxAcUMnNCUuGRg7%2Bbmf9HGOeVkesZWhTtnsGfFwGd0F%2FPCb%2Bajq6RvD2FM1fM95bITTq6hCyIeU9Q1KmvP1bsZHeUQ5UozZABX%2FBEQxpUD0SLMwtY3RHpnF2xUNxDcfAHNnKC5CaENpOT83ddozoTkNR5gJab5RnzbpL4I5GRopi504YJ%2BwoXE8wBySmT%2BW8GO8A93Vny0JEe8IV6igkgdyjQVBDFUTKoK41%2F6iF0P51S00Q%3D%3D&X-Amz-Signature=f5026e7d2c75c618be931c03e5e2cb00aea49173ec2cd9e9059db13f97a77f74&X-Amz-SignedHeaders=host&x-amz-checksum-mode=ENABLED&x-id=GetObject)
Figure 7:
![Steps involved for the final prediction by AdaBoost model [70].](https://sciendo-parsed.s3.eu-central-1.amazonaws.com/69388d63a2cfbc128b1cffde/j_rams-2025-0183_fig_007.jpg?X-Amz-Algorithm=AWS4-HMAC-SHA256&X-Amz-Content-Sha256=UNSIGNED-PAYLOAD&X-Amz-Credential=ASIA6AP2G7AKBBM74A4T%2F20251212%2Feu-central-1%2Fs3%2Faws4_request&X-Amz-Date=20251212T231138Z&X-Amz-Expires=3600&X-Amz-Security-Token=IQoJb3JpZ2luX2VjEEcaDGV1LWNlbnRyYWwtMSJHMEUCIQCSDFPXoBx8KZl1JnEbdah40IdHkMYigz%2Fuc%2FSTS1xdfwIgKyEwuYwFB4fC1i%2FlmTTEeV11fS3x%2B3syRomnHgSkJ%2F8qvQUIEBACGgw5NjMxMzQyODk5NDAiDNmcanWJdL7QX77z4yqaBSVVZ4aykYGiy0gH2aOP3Vvu6kOj%2FY9imVDLOK8ljiYEmNB6169t3NT6AmkKHLmzu95NZzeI58EuHBHBEAEMNOXtHwS128qFT0ElRsj39%2Flbu013o0xhAgHztYBlfBCcb2Y%2BrwLuSIIjdKPtoFq%2B0UX5F%2BT4tqXjeASF7qIDNs7WcUVCZ7owirnrNIjh1aNIfUDdQtDyYkJQlHtPLB4rQzDvWOzhqhiygdo8s3o0jvTQSFjob3PtidqI6ackbtGUXjIhXWvEnc8kcGN8vLlNVJccx%2FgOr0jIRUnLvuIxFVTJ7vCopRxpGGpBOV%2Bpx3B7vWF8h%2F7tv1k%2B8QDKOhxS3gKHiXzlVCeiOueMuT1wBoAyvjilmaIN1PBsaqE1Ukyt8TfyloJgKrhI%2BXDARz%2ByoGnuT59w%2B5cUqv4WQejYkz%2FGUcU1yD%2BVnCe13sXk5dVnxGAP3GcasUkwZsikRFFM%2FZN1VT7boO2nuftzTD3ImVWqEZWDQk6huPs0PJYb6LqVxYdQ%2B3uYUyyjfGWOu4Epb%2B6Rz59U57yGThYWQYq8mY0dYsOeVxa0UWQhfJRvBbmfkzVJRpC175ICQtac4q%2FjCbLe4UaheFseaDorrweOMyqzaXpkp3Jk5CV0BpwIonj84rnSm7QgXbmZIYyeSTGRU2rHLxpzHKRX%2F387PDEhFcYqGTM%2Blvv6U3Y7WDDTBCViADcZFPX6Fdj7cX4lOIOa4n64lz6DtBl%2BlORVDIFPy%2Br4HHJfvASeEX19GMNHBDk6MwNK8s8vX52VSyIfJYZaYdveCaT0GgP2MY4cqqTEzNmesazW0iE9SwWmdx%2Fs24wC5Dj%2Bq1HDAM%2BRQ8HhxV9iMIy4MU55JtB%2FaonrCcTWlLCPNGIMXP9TV%2BYSmDCGsvLJBjqxAcUMnNCUuGRg7%2Bbmf9HGOeVkesZWhTtnsGfFwGd0F%2FPCb%2Bajq6RvD2FM1fM95bITTq6hCyIeU9Q1KmvP1bsZHeUQ5UozZABX%2FBEQxpUD0SLMwtY3RHpnF2xUNxDcfAHNnKC5CaENpOT83ddozoTkNR5gJab5RnzbpL4I5GRopi504YJ%2BwoXE8wBySmT%2BW8GO8A93Vny0JEe8IV6igkgdyjQVBDFUTKoK41%2F6iF0P51S00Q%3D%3D&X-Amz-Signature=255dd4de5649a7c9f67b7b36d1836c2b988ae0d7b5a73cd11f1ea1fae10d787e&X-Amz-SignedHeaders=host&x-amz-checksum-mode=ENABLED&x-id=GetObject)
Figure 8:
![Schematic workflow of the MLP model showing the flow of data from input parameters through hidden layers to the output node responsible for compressive strength prediction [71].](https://sciendo-parsed.s3.eu-central-1.amazonaws.com/69388d63a2cfbc128b1cffde/j_rams-2025-0183_fig_008.jpg?X-Amz-Algorithm=AWS4-HMAC-SHA256&X-Amz-Content-Sha256=UNSIGNED-PAYLOAD&X-Amz-Credential=ASIA6AP2G7AKBBM74A4T%2F20251212%2Feu-central-1%2Fs3%2Faws4_request&X-Amz-Date=20251212T231138Z&X-Amz-Expires=3600&X-Amz-Security-Token=IQoJb3JpZ2luX2VjEEcaDGV1LWNlbnRyYWwtMSJHMEUCIQCSDFPXoBx8KZl1JnEbdah40IdHkMYigz%2Fuc%2FSTS1xdfwIgKyEwuYwFB4fC1i%2FlmTTEeV11fS3x%2B3syRomnHgSkJ%2F8qvQUIEBACGgw5NjMxMzQyODk5NDAiDNmcanWJdL7QX77z4yqaBSVVZ4aykYGiy0gH2aOP3Vvu6kOj%2FY9imVDLOK8ljiYEmNB6169t3NT6AmkKHLmzu95NZzeI58EuHBHBEAEMNOXtHwS128qFT0ElRsj39%2Flbu013o0xhAgHztYBlfBCcb2Y%2BrwLuSIIjdKPtoFq%2B0UX5F%2BT4tqXjeASF7qIDNs7WcUVCZ7owirnrNIjh1aNIfUDdQtDyYkJQlHtPLB4rQzDvWOzhqhiygdo8s3o0jvTQSFjob3PtidqI6ackbtGUXjIhXWvEnc8kcGN8vLlNVJccx%2FgOr0jIRUnLvuIxFVTJ7vCopRxpGGpBOV%2Bpx3B7vWF8h%2F7tv1k%2B8QDKOhxS3gKHiXzlVCeiOueMuT1wBoAyvjilmaIN1PBsaqE1Ukyt8TfyloJgKrhI%2BXDARz%2ByoGnuT59w%2B5cUqv4WQejYkz%2FGUcU1yD%2BVnCe13sXk5dVnxGAP3GcasUkwZsikRFFM%2FZN1VT7boO2nuftzTD3ImVWqEZWDQk6huPs0PJYb6LqVxYdQ%2B3uYUyyjfGWOu4Epb%2B6Rz59U57yGThYWQYq8mY0dYsOeVxa0UWQhfJRvBbmfkzVJRpC175ICQtac4q%2FjCbLe4UaheFseaDorrweOMyqzaXpkp3Jk5CV0BpwIonj84rnSm7QgXbmZIYyeSTGRU2rHLxpzHKRX%2F387PDEhFcYqGTM%2Blvv6U3Y7WDDTBCViADcZFPX6Fdj7cX4lOIOa4n64lz6DtBl%2BlORVDIFPy%2Br4HHJfvASeEX19GMNHBDk6MwNK8s8vX52VSyIfJYZaYdveCaT0GgP2MY4cqqTEzNmesazW0iE9SwWmdx%2Fs24wC5Dj%2Bq1HDAM%2BRQ8HhxV9iMIy4MU55JtB%2FaonrCcTWlLCPNGIMXP9TV%2BYSmDCGsvLJBjqxAcUMnNCUuGRg7%2Bbmf9HGOeVkesZWhTtnsGfFwGd0F%2FPCb%2Bajq6RvD2FM1fM95bITTq6hCyIeU9Q1KmvP1bsZHeUQ5UozZABX%2FBEQxpUD0SLMwtY3RHpnF2xUNxDcfAHNnKC5CaENpOT83ddozoTkNR5gJab5RnzbpL4I5GRopi504YJ%2BwoXE8wBySmT%2BW8GO8A93Vny0JEe8IV6igkgdyjQVBDFUTKoK41%2F6iF0P51S00Q%3D%3D&X-Amz-Signature=9d95ef88396250c366ff2c5e3b38b6bf6b21b8a14dc092646c5d9ff3b4114e0c&X-Amz-SignedHeaders=host&x-amz-checksum-mode=ENABLED&x-id=GetObject)
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Predictive accuracy measure for the employed models_
| Metric | Formula | Description |
|---|---|---|
| Mean Absolute Error (MAE) | MAE = | Average magnitude of prediction errors;measures absolute deviation between predicted and experimental values. |
| Mean Squared Error (MSE) | MSE = | Penalises larger deviations more strongly by squaring error terms. |
| Root Mean Squared Error (RMSE) | RMSE= | Square root of MSE;interpretable in the same units as the target variable. |
| Adjusted R2 | Adj.R2 = 1 | Adjust R2 for the number of predictors (ρ) to account for model complexity and avoid overfitting. |
Statistics obtained for the parameters used in forecasting the CS of concrete material_
| Parameters | Cement (Kg/m3) | Water/Binder | W/Cement | Aggregate (Kg/m3) | Sand (Kg/m3) | GGBS Kg/m3 | Admixture (kg/m3) | Age (days) |
|---|---|---|---|---|---|---|---|---|
| Mean | 253.36 | 0.44 | 0.88 | 912.78 | 818.47 | 177.47 | 5.1 | 64.07 |
| Standard error | 3.72 | 0 | 0.02 | 3.34 | 5.33 | 2.53 | 0.24 | 3.42 |
| Median | 240 | 0.41 | 0.75 | 932 | 800 | 173 | 1.75 | 28 |
| Mode | 425 | 0.3 | 0.67 | 932 | 594 | 189 | 0 | 28 |
| Standard deviation | 104.39 | 0.13 | 0.47 | 93.73 | 149.59 | 71.09 | 6.65 | 96.06 |
| Skewness | 0.19 | 0.43 | 1.24 | −0.26 | 0.5 | 0.47 | 1.5 | 2.27 |
| Range | 405 | 0.51 | 2.21 | 461.3 | 560.25 | 322 | 32.2 | 362 |
| Lower | 70 | 0.24 | 0.29 | 683.7 | 594 | 38 | 0 | 3 |
| Higher | 475 | 0.75 | 2.5 | 1,145 | 1,154.25 | 360 | 32.2 | 365 |
| Confidence level (95.0 %) | 7.3 | 0.01 | 0.03 | 6.56 | 10.47 | 4.97 | 0.47 | 6.72 |
Statistical results of the 5-fold cross-validation for all the employed models_
| K-fold | GEP | MLP | AdaBoost | ||||||
|---|---|---|---|---|---|---|---|---|---|
| MAE (MPa) | RMSE (MPa) | R2 | MAE (MPa) | RMSE (MPa) | R2 | MAE (MPa) | RMSE (MPa) | R2 | |
| 1 | 5.64 | 7.35 | 0.86 | 4.74 | 6.25 | 0.90 | 5.86 | 6.92 | 0.88 |
| 2 | 5.16 | 6.81 | 0.90 | 5.43 | 7.76 | 0.87 | 6.11 | 8.09 | 0.86 |
| 3 | 5.41 | 7.16 | 0.90 | 4.90 | 6.22 | 0.92 | 6.69 | 8.06 | 0.87 |
| 4 | 6.40 | 8.02 | 0.85 | 4.68 | 6.03 | 0.92 | 7.52 | 9.04 | 0.81 |
| 5 | 5.93 | 7.76 | 0.86 | 4.37 | 5.54 | 0.93 | 6.70 | 8.09 | 0.84 |