PSI - Issue 44

Andrea Meoni et al. / Procedia Structural Integrity 44 (2023) 1632–1639 Andrea Meoni et al. / Structural Integrity Procedia 00 (2022) 000–000

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2.1. Components

The base material was constituted of cement, earth, and sand mixed in dry conditions in the proportions of 2, 7, and 7, respectively. The cement was Portland type 42.5R, the earth was raw clay taken from a quarry close to a furnace, located in the central regions of Italy, while the sand was composed of quarry aggregates with a maximum dimension of 6 mm. For smart composites, carbon microfibers, with a diameter of 5 µ m and length of 6 mm, were dispersed in the dry components. The water was added to the dry mixture until a dough with suitable workability was obtained. 2.2. Preparation of samples After the proper mixing of dry components and water, the composite was poured and compressed in plastic molds, previously oiled. The samples had dimensions of 40 x 40 x160 mm 3 . Five specimens were produced for each type of mix design. After the compression and leveling procedure, eight copper wires, with a diameter of 0.8 mm, were embedded and aligned in the central part of the longer dimension of each sample, at a mutual distance of 20 mm. The samples were kept in plastic bags until they were unmolded after five days; then, they finished their curing time of 30 days in laboratory conditions. 3. Tests and setups This Section collects the methodologies adopted in the performed experimental laboratory campaigns. 3.1. Mechanical tests on beam and cube samples Smart-earth samples were subjected to three-point bending tests, after which, the two portions of each fractured sample were tested under compression, as shown in Fig. 1. The bending tests were performed at displacement control with a rate of 0.5 mm/min using the Instron machine 5567, equipped with a 30 kN load cell. Each test was acquired with electrical and DIC monitoring, deeply described in Sections 3.2 and 3.3, respectively. Tests were performed up to the failure of the specimen. Such a test provides the flexural strength of the material as follows: = 1 .5 + , being F the maximum monitored force, l the distance between the supports of the specimen ( l =100 mm), while b and d are the geometries of the transversal cross-section of the specimen. At the end of each bending test, two portions of each specimen tested were obtained due to the failure of the specimen. Each of these portions was used to perform compressive test. The compressive tests were performed using steel load plates of 40 × 40 × 10 mm 3 , by which the load is applied with a displacement rate of 2 mm/min. Such tests provided the maximum compressive strength of the material. Results of mechanical tests are reported in Section 4.1 in terms of average values and standard deviation of the flexural and compressive strength.

Fig. 1. Setup adopted to test beam samples under bending and compression.

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