## 3 Results and Discussion
### Flexural Strength  
The flexural strength of each mix is presented in Figure 3 and the changes in flexural performance due to the addition of nanomaterials are recorded in percentages as is shown in Figure 4. Figure 5 exhibits four representative samples after the flexural test. After failure, the surfaces of specimens C5S0 and C15S2 displayed comparatively less roughness than C45S10 and RS which were also of high spalling. This addressed the lower strength values obtained in the experiment for samples C45S10 and RS. The original data of the flexural strength test are recorded in Table A1, together with the standard deviation and weighting factors. T-test values are presented in Table A2. It can be clearly seen from Figures 3 and 4 that positive results were obtained in the experiments for the modified specimens, proving that the presence of nanomaterials effectively ameliorated the flexural capacity of LWCM with FAC. This is attributed to the outstanding characteristics of CNTs and NS which can greatly improve the hydration reaction and microstructure of LWCM. For sample C15S2, the maximal flexural strength of 2.13 MPa was measured, with an 89.02% increase compared to the control mix (1.13 MPa), while specimen C45S10 showed the lowest enhancement of flexural strength, with only 7.53% of growth to 1.21 MPa. Other dosages of nano additives contributed to the strength development of LWCM within the range of 10% to 50%.  
On average, based on the acquired outcomes, specimens with the addition of 0.15% CNTs outperformed those with 0.05% or 0.45% CNTs, which suggests that 0.15% CNTs in this experiment is the optimal dosage in the hybrid use for improving flexural strength. Samples with constant 0.0%, 0.2%, and 1.0% of all NS exhibited an uptrend on flexural strength by 8.85%, 35.37%, and 21.87%, respectively, followed by a decline by 0.12, 0.52, and 0.45 MPa,  
Figure 3: Flexural strength of LWCM.  
accordingly, when the dosage of CNTs grew from 0.05% to 0.15% to 0.45%. Specimens with 0.6% of NS presented an increasing tendency initially and then maintained the same level. The initial improvement in strength can be ascribed to the positive effect of CNTs to bridge the microcracks in cement materials and introduce additional closing against crack propagation [55,56]. Further, the inferior flexural behaviors of samples with 0.45% CNTs are associated with exceeding the amount of CNTs which can agglomerate and flocculate, negatively affecting the hydration process and further hindering the strength gain [57]. Furthermore, the sliding of CNTs in the cement matrix under growing loads results in a weak bond between CNTs and the matrix, negatively influencing the strength of NS-modified cement materials [58].  
Figure 4: Change in flexural strength of LWCM.  
Figure 5: Degradation of representative specimens after the flexural test: (**a**) RS; (**b**) C5S0; (**c**) C15S2; (**d**) C45S10.  
The dosage of 0.2% NS bcw shows a moderately better modifying impact than other dosages, which highlights that 0.2% content of NS in the hybrid additives is optimal for the enhancement of flexural strength. For samples containing constant 0.15% CNTS, the incorporation of NS in three dosages all accounted for the further enhancement of flexural strength, with the most impressive increase, 49.95%, measured for the sample C15S2. Reductions of strength were only observed for samples C5S6 and C45S10, in contrast with the specimens without NS. This shows that the use of NS cannot always lead to further improvement of flexural performance in binary usage together with CNTs. The initial strength improvement of adding 0.2% NS is related to the ameliorated adhesion between cement matrix and CNTs, but with the growing amount of NS added to LWCM, the tendency of NS to absorb water leads to an incomplete hydration reaction, negatively affecting strength [24; 59; 60].