Thermal Conductivity of Pyroclastic Soil (Pozzolana) from the Environs of Rome

Abstract

The paper reveals the experimental procedure and thermo-physical characteristics of a coarse pyroclastic soil (Pozzolana), from the neighborhoods of Rome, Italy. The tested samples are comprised of 70.7 % sand, 25.9 % silt, and 3.4 % clay. Their mineral composition contained 38 % pyroxene, 33 % analcime, 20 % leucite, 6 % illite/muscovite, 3 % magnetite, and no quartz content was noted. The effective thermal conductivity of minerals was assessed to be about $2.14\,\hbox {W}{\cdot } \hbox {m}^{-1}{\cdot } \hbox {K}^{-1}$. A transient thermal probe method was applied to measure the thermal conductivity ($\lambda$) over a full range of the degree of saturation $(S_{\mathrm{r}})$, at two porosities (n) of 0.44 and 0.50, and at room temperature of about $25\,^{\circ }\hbox {C}$. The $\lambda$ data obtained were consistent between tests and showed an increasing trend with increasing $S_{\mathrm{r}}$ and decreasing n. At full saturation ($S_{\mathrm{r}}=1$), a nearly quintuple $\lambda$ increase was observed with respect to full dryness ($S_{\mathrm{r}}=0$). In general, the measured data closely followed the natural trend of $\lambda$ versus $S_{\mathrm{r}}$ exhibited by published data at room temperature for other unsaturated soils and sands. The measured $\lambda$ data had an average root-mean-squared error (RMSE) of $0.007\,\hbox {W}{\cdot } \hbox {m}^{-1}{\cdot } \hbox {K}^{-1}$ and $0.008\,\hbox {W}{\cdot } \hbox {m}^{-1}{\cdot } \hbox {K}^{-1}$ for n of 0.50 and 0.44, respectively, as well as an average relative standard deviation of the mean at the 95 % confidence level $(\hbox {RSDM}_{0.95})$ of 2.21 % and 2.72  % for n of 0.50 and 0.44, respectively.

Appendix: \({\varDelta } T\) Versus ln(t) Trend for Tested Pozzolana Samples

See Fig. 6.

Fig. 6

${\varDelta } T$ versus ln(t) for Pozzolana at $S_{\mathrm{r}}=0.5$ and $n=0.44$