# Experimental Evaluation of Thermal Performance and Durability of Thermally-Enhanced Concretes
## 3 Results and Discussion  
### Physical Properties  
The air content of fresh concrete, the air-dry density at 28 days, and the compressive strength measured at 3, 7, and 28 days of hardened concrete are reported in Table 6. The measured air content ranges from 4.3 to 10.0%. NM and LM specimens with micro-form agent showed the highest air content of 10% for both normalweight aggregate (NWA) and lightweight aggregate (LWA). In the case of the air-dry density, NH and LH specimens showed the lowest value of 1843 and 1599 kg/m\({}^{3}\), respectively, due to the large volume replacement with hollow-micro spheres (see Figure 3). Thus, by using hollow-micro spheres, air-dry densities were reduced up to 19% and 11% for NH and LH compared to NM and LM, respectively. In addition, ND and NM specimens reduced by 13% and 8%, respectively, compared to the NN specimen. The air-dry density of all LWAC specimens was decreased by an average of 15% compared to NWAC specimens.  
The compressive strengths measured at the curing age of 28 days are compared in Figure 4. A decrease in strength by adding the insulating materials was clearly demonstrated regardless of the coarse aggregate types. However, the strength difference between NWAC and LWAC was very slight since the crushed strength of LWA itself was relatively higher [37]. Conversely, the strength of specimens NH and LH (with hollow micro-spheres) failed to reach the designed compressive strength of 24 MPa and recorded the lowest compressive strength, as expected from the density results. One of the interesting points is the low strength of ND and LD specimens, where diatomic powder is used as a replacement of the aggregates. Even if diatomic powder is a natural pozzolan, the compressive strength of ND and LD reached lower strength comparing to reference specimens of NN and LN by more than 31%. This means that there is a negligible pozzolanic reaction of diatomic powder and the influence on the strength is small when diatomic powder is used as a replacement of the aggregate. In the case of specimens NM and LM (with the micro-foam agent), it was expected to have a large strength reduction due to their foams within the concrete if the same water-to-cement ratio (W/C) of 0.55 with other specimens is applied. Thus, to achieve the design strength, W/C of NM and LM were set as 0.3 and the target compressive strength can be obtained. Thus, if W/C is reduced for NH and LH, the designed compressive strength may be achieved. Finally, it is known that the trend of the air-dry density and compressive strength is quite similar each other.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Coarse** **Aggregate Type**} & \multirow{2}{*}{**Labels**} & \multirow{2}{*}{**Insulation Materials**} & \multirow{2}{*}{**Air Content (\%)**} & \multirow{2}{*}{**Air-Dry Density (kg/m3)**} & \multirow{2}{*}{**Compressive Strength (MPa)**} \\ \cline{5-8}  & & & & & & **3 Days** & **7 Days** & **28 Days** \\ \hline \multirow{4}{*}{Normal (N)} & NN & None & 4.3 & 2267 & 24.9 & 32.0 & 37.3 \\  & ND & Diatomic & 7.6 & 1971 & 12.4 & 16.9 & 25.4 \\  & NH & Hollow micro-sphere & 6.2 & 1843 & 13.5 & 16.1 & 23.2 \\  & NM & Micro-form agent & 10.0 & 2080 & 20.5 & 29.0 & 33.2 \\ \hline \multirow{4}{*}{Light (L)} & LN & None & 5.2 & 1806 & 23.7 & 29.1 & 36.2 \\  & LD & Diatomic & 7.4 & 1691 & 13.6 & 18.0 & 26.3 \\  & LH & Hollow micro-sphere & 4.9 & 1599 & 10.1 & 13.4 & 20.2 \\  & LM & Micro-form agent & 10.0 & 1769 & 21.1 & 27.9 & 32.8 \\ \hline \hline \end{tabular}
\end{table}
Table 6: Test results of the physical properties.  
Figure 3: Experimental observations of concrete air-dry density measured at 28 days.