# Influence of Aggregate Gradation on the Engineering Properties of Lightweight Aggregate Concrete
## 3 Results and Discussion
### Influences of Aggregates' Gradation on the Durability of Concrete  
Test results for three-hour water permeation of LWAC and NWC are shown in Table 5 and Figure 8. Water permeation of LWAC with the standard grade (SSA = 573 m\({}^{2}\)/m\({}^{3}\)) is 16 cm\({}^{3}\) at 0.7 w/c, while the value of NWC is 31 cm\({}^{3}\). Water permeation of LWAC is obviously smaller than that of NWC. It can also be found that the influence of the variation in coarse aggregates' gradation on the permeability of NWC is comparatively apparent. When the SSA of NWC increases, water permeation increases as well. However, the effect of variation of coarse aggregates' gradation on the permeability of LWAC is not prominent.  
Water permeation inside the concrete predominantly occurs via the bonding interface of aggregates and mortar. For NWC, the smaller grain size aggregates have, the more SSA is. So that the path for water to pass through is increased, the permeant volume increases too. For example, the permeant volume for NWC with 7 mm grain size aggregates approaches 41 cm\({}^{3}\). A comparatively superior interface zone forms because the surface pores of lightweight aggregates could be provided for mortar to lock [23; 24]. Therefore, the permeant volume for LWAC is less regardless of variations in aggregate gradation. That is to say that LWAC possesses comparatively preferable anti-permeability.  
Nevertheless, the effect of variation of coarse aggregates gradation on the permeability of both LWAC and NWC is not obvious at 0.4 w/c (see Figure 8b). The main reason is that the mortar strength is considerably high. Whether using normal weight aggregates or lightweight aggregates, the interface zone between the aggregates and mortar was substantially strengthened. The influence of  
Figure 7: Strength efficiency of NWC and LWAC.  
the foregoing interface locking effect will be virtually eliminated. Hence, NWC and LWAC represent a similar permeation behavior regardless of various gradations.  
The electrical resistance test results for LWAC and NWC are shown in Table 5 and Figure 9. The results show that the electrical resistances of LWAC are all slightly higher than that of NWC. It is especially conspicuous at a low water-cement ratio (w/c = 0.4).  
The electrical resistance depends on the water path to conduct electricity inside the concrete. Due to the better bonding between the surface pores of lightweight aggregates and mortar, LWAC possesses a comparatively better interface zone. A part of the water path to conduct electricity between the interface of mortar and aggregates was obstructed so that the electrical resistance of LWAC is higher than that of NWC. When the uniform grain size was used, the electrical resistance of LWAC increased as the grain size decreased. On the contrary, the electrical resistance of NWC decreased as the grain size decreased. The primary reason is that the SSA of natural aggregates increased as the grain size decreased. It brings on the increment of the path to conduct electricity, following with the decrement of the electrical resistance of concrete. However, mortar of LWAC is comparatively dense [23; 24; 25; 26; 27]; as a result electrical resistance increased.  
Figure 8: Permeability of NWC and LWAC.  
Figure 9: Electrical resistance of NWC and LWAC.