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.