# Experimental Evaluation of Thermal Performance and Durability of Thermally-Enhanced Concretes
## 3 Results and Discussion
### Thermal Conductivity  
The thermal conductivity measured by a quick thermal conductivity meter (QTM), depicted in Figure 5 and Table 7, tended to be proportional to the corresponding air-dry density in Figure 3. Specimen NN, having a normalweight aggregate concrete without the insulating materials, showed the thermal conductivity of 1.94 W/m\(\cdot\)K, while the LN specimen, having lightweight aggregate concrete without the insulating materials, showed a thermal conductivity of 1.22 W/m\(\cdot\)K. The thermal conductivity values of all specimens decreased by adding the insulating materials, as shown in Figure 5. Specimens ND, NH, and NM had thermal conductivities of 1.25 W/m\(\cdot\)K, 1.15 W/m\(\cdot\)K, and 1.37 W/m\(\cdot\)K, respectively. Compared with the thermal conductivity value for NN (1.94 W/m\(\cdot\)K), the insulation materials contributed to reducing the thermal conductivity by an average of 34%. For LWAC, LD, LH, and LM specimens had thermal conductivities of 0.87 W/m\(\cdot\)K, 0.81 W/m\(\cdot\)K, and 1.0 W/m\(\cdot\)K, respectively. For both NWAC and LWAC, it can be seen that the effect of hollow micro-spheres (H) on the reduction of the thermal conductivity is better than others, such as diatomic (D) and micro-foam agent (M). Hollow micro-spheres lowered the thermal conductivity by 18% with lightweight aggregates and 29% with normalweight aggregates compared to the reference results. The average thermal conductivity decrease in specimens with NWA and LWA were 34% and 27%, respectively. Test results by using the guarded hot wire method (GHW), shown in Figure 6 and Table 7, dropped by 9-36% compared with those by QTM. This might be attributed to the evaporation of pore water in the concrete, which increases the vacant pores and reduces the thermal conductivity, since specimens were thoroughly oven-dried to eliminate the moisture content and residual water in concrete. This showed that the accuracy of QTM depended on the water contents and residual water in the pores of concrete as QTM was generally used at ambient conditions without drying the specimens [24]. The differences between QTM and GHW of NN and LN (specimens without insulation materials) was approximately 18% for both. However, the differences for ND and LD (specimens with diatomic powder) were 9% and 6%, respectively, which did not vary significantly since they had insufficient water-filled pores in the concrete. Conversely, specimens with micro-foam agent (M) and hollow micro-spheres (H) experienced considerable reductions by 13-36% due to the higher water-filled pores in the concrete. Figure 5: Experimental observations of concrete thermal conductivity measured by quick thermal conductivity meter (QTM). Figure 6: Experimental observations of concrete thermal conductivity measured by guarded hot wire method (GHW). NH and LH (specimens with hollow micro-spheres) had the lowest thermal conductivities of 0.97 and 0.70 W/m\(\cdot\)K, respectively. This showed the same trends as QTM since they had the lowest density values. The testing results by GHW varied by 0.85 W/m\(\cdot\)K-1.59 W/m\(\cdot\)K in NWAC, and by 0.70 W/m\(\cdot\)K-0.99 W/m\(\cdot\)K in LWAC. The average thermal conductivity reduction ratios from QTM were 35% and 27% for NWAC and LWAC, respectively, by adding insulation materials. These values are similar with those from GHW. From GHW, the thermal conductivity reduction ratios were 31% and 23% for NWAC and LWAC, respectively. This result indicates that the insulation materials have the same reduction effects on thermal conductivity reduction regardless of the aggregate types, and the insulation materials used in this study can be applicable to enhance thermal performance for both NWAC and LWAC. Taken as a whole, it can be found that the trend of the air-dry density is similar with that of the thermal conductivity. Additionally, thermal conductivities measured by QTM and GHW had similar trends. However, the thermal conductivities measured by GHW showed somewhat lower values than QTM.