Issue 41

S. Zhao et alii, Frattura ed Integrità Strutturale, 41 (2017) 412-423; DOI: 10.3221/IGF-ESIS.41.52 420 many. Moreover, no obvious cracks can be found in the vicinity of the heat transfer tubes. After the application of the vertical load, the pile also cracks, but the concrete on it does not break off as what occurs in opposed to what occurred in Diagram b. Fig. 15 shows the comparison between the test strength of the pile with buried pipes and the its theoretical strength. It can be seen from the figure that the theoretical strength of the second and third groups of test piles is supposed to be 97.5% of the theoretical strength of the first group. However, the test results show that the experimental strength of the second group of test piles with heat transfer tubes embedded in the concrete piles is only 47.8% of the theoretical strength. This result is far less than the result that the test strength is 58.8% of the theoretical strength in the first group of piles. The test group has a strength of 61.7% of the theoretical strength in the third group of teats piles with embedded heat transfer tubes with steel fiber. It can be verified by the experiment that the heat transfer tubes in the pile foundation can greatly reduce the compressive strength of the pile foundation, but the energy piles with the mixing ratio of A 2 B 2 C 3 D 1 can improve the compressive strength of the pile foundation. The strength of the piles with the mixing ratio of A 2 B 2 C 3 D 1 of the steel fiber, the heat storage material, and the thermal conductivity material will not be reduced, but improved to some extent. Figure 15: Comparison between the test of the pile with buried pipes and the its theoretical strength The measurement of the thermal conductivity The fourth group and the fifth group of the materials with the best compressive strength and the first group of the ordinary concrete materials are made as the test blocks to measure the thermal conductivity. The test blocks are made to be cuboid, the size of which is 0.03m × 0.1m × 0.1m. Three blocks are included in each test block, with a total of nine in this test. The evaporation of water of the test block is processed in the drying oven after its steel mold is taken out. The test block is taken out of the drying oven and the thermal conductivity is measured when the quality is kept constant. The main instruments for measuring the thermal conductivity are shown in Fig. 16, and the test results of the thermal conductivity are shown in Tab. 8. As can be seen from Tab. 8, the thermal conductivity of the test blocks in the fourth and fifth group is improved greatly. The thermal conductivity of the block in Group 5 is over twice than that in Group 1, and the thermal conductivity of the block in Group 4 improves 1.5 times than that in Group 1. The comparison of the heat storage capacity The degree of the capacity of heat storage of the material is represented as the heat storage coefficient: T c s πλρ 2 = (1) In the equation, λ — the thermal conductivity of the material (W/m∙• K); ρ — density of the dry matter of the material (kg/m 3 );