# Long-Term Deformations and Mechanical Properties of Fine Recycled Aggregate Earth Concrete
## 3 Results
### Acoustic Emission (AE) Analysis  
Figure 9 shows the correlation between the stress and distribution of AE hits as functions of strain for NS and RS specimens subjected to different curing and loading conditions. The AE activity in RS specimens is lower than that of NS ones. This can be attributed to the lower strength of the former in addition to the porous state, possible defects and pre-saturation of RS that may have lowered its ITZ properties [2]. Note here that [PERSON] et al. [13; 14; 15] have showed a good correlation between creep displacement and the variation of the AE parameters with an important coupling between creep and damage during desiccation. In addition, the AE activity presented three regimes as that of the creep displacement, and three different mechanisms have been identified based on the quantitative analysis of the AE data [13; 14; 15]. [PERSON] et al. [17] showed that the AE technique can detect low energy processes during shrinkage of earth concrete as well as damage evolution. Different phases have been identified during drying indicating different mechanisms such as moisture/shrinkage gradients that develop at different depths in the specimens and by the presence of aggregates. The AE activity at the beginning of all mixtures can be attributed to the compaction taking place due to initial loadings. This phase demonstrates evidence for the closure of cracks and pores without the formation of new cracks. It can be seen that BC specimens exhibited lower AE activity in the pre-peak phase than the AS specimens. This can be attributed to several different aspects:  
* The low Young's modulus in AS specimens will accommodate more stress buildup before cracking occurs [46]. This stress buildup will be accompanied by more AE signals.  
* [PERSON] et al. [2] monitored earth concrete specimens with AE under compressive tests at different curing ages and observed a reduction in AE activity with curing age and, thus with strength development. Therefore, the strength increase in the BC specimens will be reflected by lower pre-peak AE activity in addition to the [PERSON] effect [13; 14; 15]
* The compaction phase exhibited lower AE in the specimen that was previously loaded during the durability tests (BC specimen); thus, such pre-loading acted as pre-compaction process [25].  
Figure 9: The correlation between the stress-strain curves and distribution of AE hits.  
These four factors are valid between NS-DS and NS-DC from one side and between RS-DS and RS-DC specimens from the other side. Nevertheless, it was to a lower extent in RS specimens, which can be attributed to the less significant variations in strength and Young's modulus. DS and DC specimens reported the highest AE activity. This can indicate that AE reflected successfully:  
* the suction effect where the particles got closer to each other, and thus higher friction takes place upon loading.
* the shrinkage induced cracking where friction along already existing drying cracks can take place upon loading.  
This resulted friction based on the two processes will be accompanied by AE activity during the application of external stress. An increase in AE activity rate can be noticed for DS and DC specimens before the peak (as shown in sky blue arrows). This points out that these specimens exhibited a higher rate of damage directly before the peak than the sealed specimens (AS and BC). Thus, the dried specimens are more vulnerable to crack formation and propagation. It is worthwhile to state that DC specimens reported lower pre-peak AE activity than DS specimens due to the four aforementioned aspects (higher strength, higher Young's modulus, lower peak strain, and Kaiser effect).  
Regarding the post peak phase, a more gradual increase of the AE activity can be noticed in the sealed specimens, in contrast with the ones that were subjected to drying and, thus, the former experienced less brittle behavior.