## 3 Results and Discussion
### Compressive Strength  
The compressive strength of LWCM is recorded in Figure 6 for each mix, and the percentage changes in strength are exhibited in Figure 7. The original data from the compressive strength test are presented in Table 11, along with the values of standard deviation and weighting factors of each data group. T-test values were calculated in Table 12. Figure 8 displays the crack patterns of specimens RS, C5S0, C15S2, and C45S10 after compressive strength tests. It can be seen that compared to the other three specimens, sample C45S10 showed the greatest degradation after loading, corresponding to its lowest strength value. As can be seen in Figures 6 and 7, the hybrid use of nano additives cannot guarantee the improvement of compressive strength, and certain dosages of CNTs and NS can be associated with negative influence on strength gain. Five mixes (C5S0, C15S0, C5S2, C15S2, C15S6) demonstrated enhancement in compressive strength while the other seven (C45S0, C5S6, C5S10, C15S10, C45S2, C45S6, C45S10) indicated reduction. It is worth noticing that all specimens containing 0.45% of CNTs presented a decline in strength, which can be ascribed to the fact that an exceedingly high amount of CNTs leads to the agglomeration and increasing difficulty of dispersion, which causes agglomeration in the composites [59; 61]. Further, the incorporation of 1.0% NS resulted in different extents of strength loss regardless of the dosage of CNTs. Similarly, this can be attributed to the high amount of NS that adds up to the difficulty of dispersion due to agglomeration, and accounts for a weak zone, leading to the initiation of microcracks and the decline of strength [50]. The most considerable enhancement in compressive strength was measured for the specimen containing only 0.05% of CNTs and no NS, with a strength increase of 17.35% to 21.09 MPa compared to that of the reference sample (17.97 MPa); while by adding  
Figure 6: Compressive strength of LWCM. 0.45% CNTs and 1.0% NS, the greatest decrease in strength was observed, with the value declining by 61.36% to 6.94 MPa. Other dosages of nano additives were in correspondence with the growth of compressive strength in a range of 1% to 10% as well as a strength reduction by 10% to 20%. At the constant amounts of NS of 0.2% and 1.0%, the growth of CNT content from 0.05% to 0.45% contributed to the decrease of compressive strength by 20.60% and 58.67%, respectively. For specimens containing a constant content of 0.6% NS, nevertheless, the compressive strength of LWCM showed an increase to 19.48 MPa when the dosage of CNTs  
Figure 8: Degradation of representative specimens after compressive test: (a) RS; (b) C580; (c) C15S2; (d) C45S10. Figure 7: Changes in compressive strength of LWCM. grew from 0.05% to 0.15%. Afterwards, a 20.17% reduction in strength was observed as the content of CNTs increased to 0.45%. These findings indicate that despite the increasing amount, in the presence of NS, the synergic use of CNTs can partially account for the decline of compressive strength. [PERSON] et al. [37] ascribed this to the existing Van der Waals force that hinders the homogeneous dispersion of CNTs, negatively affecting the development of the strength. Compared to the samples with only CNTs, the addition of NS at all contents in the presence of CNTs led to the loss of compressive strength. This states that the hybrid incorporation of both CNTs and NS has inferior effects on the improvement of compressive behaviors compared to the single utilization of CNTs. According to [PERSON] et al. [37], the high demand for water by NS in cement composites can lead to an adverse influence on mechanical properties, and such a negative impact can also affect the extent of enhancement due to binary addition of CNTs and NS.