Issue 41

Y. Yang et alii, Frattura ed Integrità Strutturale, 41 (2017) 339-349; DOI: 10.3221/IGF-ESIS.41.45 342 In order to eliminate the friction between the load head, the support and the specimen, we use a cylindrical load head and a cylindrical support and apply butter to the load head and the support before the test. The loading rate includes 0.1mm/min, 0.4mm/min, 0.7mm/min, 1mm/min four grades. Figure 1: Testing Principle for Tensile, Compression and Flexural moduli (1-beam specimen; 2-cylindrical support; 3-micrometer; 4- strain gage). The strain gages are foil resistance strain gages, with a grid length of 80mm and a resistance of 120Ω. Due to the rough beam surface of the cement stabilized macadam specimen, it is necessary to put cement paste on the upper and lower surfaces to fill the gaps in areas where strain gages will be put on one week before the test. While attaching 4 strain gages on the upper and lower surfaces respectively, i.e. 8 strain gages in total, we measure the compressive and tensile strains of the test beam (as shown in Fig. 1 and Fig. 2). At the same time, considering the edge effect of strain, the center of the most marginal strain gage should be 20mm away from the edge of the beam. The strain gage pasting method and test device are shown in Fig. 2 and Fig. 3. The center of the most marginal strain gage is 20mm away from the edge of the beam. The way the strain gage is pasted and the test device are shown in Fig. 2 and Fig. 3. Figure 2: Schematic of Strain Gauges Pasted Figure 3: Installation Drawing of Modulus Test D ERIVATION OF THE T ENSILE , C OMPRESSION AND F LEXURAL M ODULI C ALCULATION F ORMULAS Traditional flexural modulus calculation formula hen the length of the bar l is much greater than the cross-sectional height h, i.e. l>5h , the analytical formula for pure bending can be used. The current test procedure calculates the flexural modulus without considering the shear effect [14]. The calculation and derivation process is as follows: P/2 P/2 P/2 P/2 P (a) P/2 (b) P/2 L/2-x L/2 x L/6 L/3 L/3 L/3 Figure 4: Force Analysis Diagram of Specimen W