## 5 Conclusions  
* The field experiment was carried out to investigate the in-service pavement stiffness and roughness of lightweight cellular concrete subbase pavements and compare them with traditional unbound materials subbase pavements. This was done by examining the deflections induced by a lightweight deflectometer to measure the pavement stiffness and a Surpro walking profiler to measure the pavement roughness over varying seasons. Based on these evaluations, the following conclusions have been made.
* The findings show that flexible pavements with LCC subbase thicknesses \(\geq\) 250 mm could produce a 21% stiffer pavement structure compared with twice as thick unbound granular B subbase pavements. An increase of 36% in stiffness can occur when LCC thickness increases by 100 mm. Pavement stiffness was also noted to increase with LCC layer density and over time. LCC subbase thickness \(\geq\) 250 mm can produce over 22% smoother riding surfaces than unbound granular pavements. Time of testing, pavement temperature during testing, construction method, insufficient compaction, excessive truck traffic on LCC pavements before AC placement, and road gradient could influence LCC pavement stiffness.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Section**} & \multicolumn{4}{c}{**Southbound Section Mean IRI (m/km)**} \\ \cline{2-5}  & **Sept 21** & **Feb 22** & **April 22** & **June 22 (Baseline IRI)** \\ \hline LCC600 & 1.17 & 1.34 & 1.46 & 1.36 \\ LCC475 & 1.13 & 1.43 & 1.62 & 1.60 \\ LCC400 & 1.71 & 2.37 & 2.34 & 1.33 \\ Control & 1.13 & 1.29 & 1.28 & 1.50 \\ \hline \hline \multicolumn{5}{c}{**Northbound Section Mean IRI (m/km)**} \\ \hline LCC600 & 1.23 & 2.00 & 1.28 \\ LCC475 & 1.26 & 1.78 & 1.23 \\ LCC400 & 1.50 & 1.50 & 1.82 \\ Control & 1.33 & 1.18 & 1.68 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Notre Dame Drive mean IRI.  
* LCC thickness equal to 200 mm could yield over 20% smoother pavements for a 600 kg/m\({}^{3}\) LCC subbase. While varying results were seen for 400 kg/m\({}^{3}\) and 475 kg/m\({}^{3}\) LCC subbase pavements compared to unbound subbase materials due to varying reasons discussed, it was evident that they may function comparably or better than conventional pavements. Factors influencing roughness progression in LCC pavements include environmental conditions, seasonal variations, road class, road function, road gradient, subgrade conditions, initial construction process, and practices (compaction, early vehicular traffic).
* It is recommended that pavement sections be monitored over a longer period and that a correlation between LWD and FWD testing be performed to further assess the pavement sections' performance.  
Conceptualization, A.G.O., F.M.-W.N. and S.T.; methodology, A.G.O. and F.M.-W.N.; software, A.G.O.; formal analysis, A.G.O.; data collection, A.G.O. and F.M.-W.N.; data curation, A.G.O.; writing--original draft preparation, A.G.O.; writing--review and editing, A.G.O., F.M.-W.N. and S.T.; supervision, S.T.; funding acquisition, S.T. All authors have read and agreed to the published version of the manuscript.  
This research was funded by Natural Sciences and Engineering Research Council of Canada (NSERC) and CEMATRIX, grant number funding reference CRDPJ 514908-2017.  
Not applicable.  
The authors of this research gratefully acknowledge CEMATRIX (CANADA) Inc., the Region of Waterloo, Ontario, Canada, Natural Sciences and Engineering Research Council of Canada (NSERC), and Centre for Pavement and Transportation Technology (CPATT), University of Waterloo for supporting this research.  
The authors declare no conflict of interest.