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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material provides several advantages: CO 2 reduction for long distance transport, conservation of mined natural resources, reduction of environmental and ecological impact, and economic benefits (Schroeder (2016)). In the context of civil constructions, different techniques to build with soil have been developed, such as: cut blocks, poured earth, superadobe, adobe, cob, rammed earth, compressed stabilised earth blocks, wattle and daub, shaped earth. These techniques are still being optimized, and alternative binders, additives, fibres and surface treatments are employed in order to enhance the mechanical properties and durability of soil constructions (Vyncke et al. (2018)). An innovative earth construction technique is the shot-earth technique, which employs a material (i.e. the shot earth) composed by a mixture of excavated soil, aggregates and water, where the soil may be either unstabilised or stabilised by a chemical binder (Curto et al. (2020), Vantadori et al. (2022)). In particular, the dry mixture is blown by a high velocity air stream into a spraying hose. Water under high pressure is added to the above mixture steam by a separate hose in correspondence of the spraying nozzle. The impact onto the surface compacts the material. The applications of shot-earth are those typical of dry shotcrete, and mainly consist in new structures, repairs and rehabilitations, and slope and surface protection. The goal of the present paper is the fracture characterisation of a specific mixture of shot-earth (named shot-earth 772), consisting of 7 parts of soil, 7 parts of aggregates, 2 parts of cement by volume, and about 3% of water by volume. The fracture characterization is performed by means of experimental tests according to the RILEM Recommendations (RILEM Technical Committee, 50-FMC (1985), RILEM Technical Committee, 89-FMT (1990)), where the shot-earth fracture toughness is analytically determined by employing the Modified Two-Parameter Model (MTPM), originally proposed by the present authors for concrete (Vantadori et al. (2018)).

Nomenclature a

effective crack length

0 a B i C u C

notch length specimen width

initial linear elastic compliance unloading linear elastic compliance

elastic modulus

E

S IC K

Mode I fracture toughness

( S I II C K + Mixed Mode fracture toughness L specimen length max P peak load S support span W specimen depth  kinking crack angle )

2. Fracture toughness computation: Modified Two-Parameter Model The method employed for fracture toughness computation is the Modified Two-Parameter Model (MTPM) (Vantadori et al. (2018)), which follows the same framework of the Two-Parameter Model (TPM), originally proposed by Jenq and Shah (1985) to determine the value of Mode I plane-strain fracture toughness of plain concrete. However, unlike the original model, the MTPM is able to take into account the possible crack deflection (or kinked crack), typically observed during the stable crack propagation in quasi-brittle materials. According to the MTPM, the prismatic specimens present a straight notch in the lower part of the middle cross section, and the geometrical properties (Fig. 1(a)) are functions of the specimen width, B : depth 2 W B = and notch length 0 2 3 a B = . The tests are performed under three-point bending loading and crack mouth opening displacement control (CMOD), with a support span, S , equal to 8 B . In particular, the specimen is monotonically