# Waste Silt as Filler in Hot Mix Asphalt: A Laboratory Characterization
## 6 Conclusions  
Untreated and thermally treated waste silts from a local aggregate production plant were used as a replacement for convenient limestone filler to produce HMAs. The evaluation of the effects given by the adoption of the waste fillers was studied in a two-stage laboratory analysis, which involved studying the binder-filler interaction and the HMA's physical and mechanical properties.  
The following conclusions were drawn:  
* The addition of thermally treated silt did not have a significant impact on the rheological properties of the resulting mastic, as measured using the complex shear modulus and phase angle. However, untreated silt slightly reduced the stiffness of the mastic, as evidenced by a decrease in the complex shear modulus. No significant changes were observed in the phase angle master curves.
* In terms of rutting performance, thermally treated silt had the highest resistance against permanent deformation. This was observable via lower accumulated strain and lower non-recoverable compliance values. Untreated silt showed the lowest resistance against rutting. However, the substitution of control limestone filler with waste silts influenced the elastic response of the final bituminous mastics, reducing the percent recovery parameters.
* The replacement of limestone filler with waste silt did not alter the optimal binder content of the mixture or the porosity of the produced samples. Thus, the presence of waste silt did not negatively affect the workability or compactibility of the bituminous mixture.
* The inclusion of untreated silt as filler resulted in a reduction in the ITS values. In contrast, thermally treated silt demonstrated a similar performance to the control sample. The same trend was recorded for the water susceptibility of the mixtures.
* The ITSM results were in line with the static mechanical characterization A slight reduction in stiffness was recorded for the HMA-SC mixture, while a clear drop in ITSM values occurred when untreated silt was adopted. However, the thermal sensitivity of the mixture was not influenced by the substitution of limestone filler with waste powders.  
It can be stated that calcined silt exhibited comparable performance to the control samples, which can be attributed to its CaO content.  
Based on the presented preliminary results, the use of waste silt as a filler could be a potential solution for sustainable and eco-friendly HMAs. Silt calcination was found to be beneficial since it reduced the influence of the waste material on the rheological and mechanical properties of the bituminous mixture. Partial substitution of limestone filler instead of the current total replacement could provide better mechanical performance. Further studies are needed to back up this assumption.  
Conceptualization, A.S., P.T. and C.S.; data curation, A.S. and G.T.; formal analysis, A.S. and G.T.; funding acquisition, C.S.; investigation, A.S.; methodology, A.S. and G.T.; project administration, P.T. and C.S.; resources, P.T.; supervision, P.T. and C.S.; validation, A.S. and P.T.; writing--original draft, A.S. and G.T.; writing--review and editing, P.T. All authors have read and agreed to the published version of the manuscript.  
This paper was written for the SAFERUPI Project, which received funding from the European Union's Horizon 2020 research and innovation program under [PERSON] grant agreement no. 765057.  
Not applicable.  
The authors declare no conflict of interest.