# Susceptibility to Expansive Reactions of a _Greener_ Uhpc: Micro to Macro-Scale Study
## 3 Results and Discussion
### Asr  
Figure 6a presents ASR expansion evolution up to 14 days (the standard test time). This indicates that the average expansion of three UHPC bar specimens was far above 0.10% after 14 days of testing (0.0180 \(\pm\) 0.002%). In the present study, the test was performed up to specimens achieve 0.1% expansion, which took about half a year, as depicted in Figure 6b. It was also noticed from Figure 6b that after a certain period of exposure, the ASR-induced expansion started to increase more significantly (84 days). This phenomenon was also observed by [PERSON] et al. [65]. Photos of the bar specimens after the ASR test, i.e., after the long period of immersion in alkaline solution, are shown in Figure 7, and no damage was observed.  
Figure 5: SEM images and XRD diffraction analysis: (**a**) site of calcium hydroxide and location of zones Z2 and Z3; (**b**) XRD diffraction analysis of material in zone Z2; and (**c**) XRD diffraction analysis of material in zone Z3.  
Figure 6: Linear length change due to ASR up to (**a**) 14 days (standard test days) and (**b**) half a year (extended test in the current study).  
[PERSON] and [PERSON] [31] argue that even in UHPC, ASR may occur but not causing damage. Moreover, the authors denoted that besides no damages due to ASR occurred, they found locally concentrated ASR gel by SEM observations. [PERSON] and [PERSON] [32] stated that accelerated curing provoked by the ASTM C 1260 procedure, i.e., 24 h in hot water, may veil ASR occurrence in UHPC. It is recognised that ASR phenomena take place when a combination of conditions are verified, namely, (i) aggregates with a certain amount of reactive siliceous minerals, (ii) rich concrete pore solution, (iii) high moisture, and iv) calcium ions available [45]. Considering the very low permeability of UHPC, as discussed in Section 3.1, ASR may not manifest even considering long-term UHPC durability.  
On the other hand, it is of utmost importance to use pozzolanic SCM as a mitigation/prevention measure against ASR. Pozzolanic SCM reacts with Ca(OH)\({}_{2}\), ensuring no more calcium ions are available for ASR. Silica time is particularly effective against ASR since it preferentially reacts with the alkalis. Moreover, the inclusion of ECat was already found to mitigate the ASR when used as partial replacement of cement [66] or fine aggregate [67].  
After half a year in NaOH immersion, samples from UHPC bars were examined using SEM. Since the specimens have no visual damage (see Figure 7), the author's analysed samples are taken from the specimen's surface and the inside. It must be noted that no signals of ASR products were found in samples taken from the interior of the UHPC specimens after half a year in the aggressive alkali environment. The typical gel formed in ASR was found in a few pores on surface samples, as shown in Figure 8. Moreover, traces of silico-alkali gel were found on the surface of the aggregate, as dipicted in Figure 9.  
Figure 8: _Cont._  
Figure 7: UHPC specimens after ASR test (extended up to 180 days).  
Figure 8: SEM images and XRD diffraction analysis: (**a**) site of ASR gel formation over a pore; (**b**) location of zones Z1 (gel); and (**c**) XRD diffraction analysis of material in zone Z1.  
Figure 9: SEM images and XRD diffraction analysis: (**a**) site of ASR gel formation on aggregate surface and location of zones Z4 (aggregate) and Z5 (gel); (**b**) XRD diffraction analysis of material in zone Z4; and (**c**) XRD diffraction analysis of material in zone Z5.