PSI - Issue 42

Sabrina Vantadori et al. / Procedia Structural Integrity 42 (2022) 133–138 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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3. Experimental campaign The material examined in the present paper is a specific mixture of the shot-earth, named shot-earth 772 and consisting of 7 parts of excavated soil, 7 parts of aggregates, 2 parts of cement for stabilization of soil (by volume) , and about 3% of water (by volume). In particular, the soil is an excavated soil, extracted after removal of a layer from 25 to 50 cm of the top-soil, which is characterised by a large content of organic matter. After excavation, the soil is stockpiled and allowed to dry out, then sieved in order to remove the stones, and finally milled. Moreover, the aggregate is a commercial mixed aggregate 0 – 8 mm for concrete, made of carbonate sedimentary rocks (mainly limestone), and the cement is the Portland cement CEM I 42.5 N. The shot-earth mixture stream is projected at high velocity onto a surface, being such an impact able to compact the material. The receiving surface is the formwork panel, with sizes of 800mmx800mmx100mm, which is left to cure at a temperature of about 23° C and a relative humidity of about 50% for about two months. Then, six specimens employed for fracture tests are extracted from such a panel so that the direction of the applied load coincides with the spraying direction. The nominal sizes of the specimens are: width ( B )  depth ( W )  length ( L ) = 40 mm  80 mm  375 mm. Further: support span ( S ) = 320 mm and notch length ( 0 a ) = 27 mm. Three – point bending tests are performed by means of the universal testing machine Instron 8862 (available at the “Testing Laboratory of Materials and Structures” - University of Parma) under CMOD control, with an average rate of the clip gauge equal to 0.2 mm h -1 . 4. Results and discussion The fracture characterisation of the present shot-earth 772 is performed by means of the MTPM, outlined in Section 2. The experimental load-CMOD curves, used to compute the initial compliance, the unloading compliance and the peak load, are plotted in Fig. 2. Note that only five experimental curves are reported in the above Figure since one specimen is not characterised by an ‘acceptable’ failure (that is , crack does not start from the notch tip). It can be pointed out that the maximum value of max P is achieved for specimen T2, whereas the best performance in terms of load bearing capacity in the post-peak stage is observed for specimen T3.

T1 T2 T3 T4 T5

0.45

0.30

Load, P [kN]

0.15

0.00

0.00

0.20

0.40

0.60

CMOD [mm]

Fig. 2. Experimental load – CMOD curves for shot-earth 772 specimens.