Sand morphology and size effects on fracture and tensile behaviors of engineered cementitious composites with a roughness-based size effect model

Engineered cementitious composites (ECC) rely on fine aggregates to control matrix properties, yet the quantitative link between sand characteristics and the mechanical response of ECC has remained largely unexplored, which limits rational sand selection in material design. This paper examines how sand type and particle size influence the tensile and flexural behaviors of ECC, and seven sand types, namely dune sand, normal sand, sea sand, wind sand, glass sand, standard sand, and acrylic sand, were tested in three experimental series covering unsieved sands, sieved size ranges, and a fixed 100–120 mesh gradation, with uniaxial tensile, three-point bending, matrix fracture toughness, and surface roughness measurements. The results show that the sand type and particle size jointly determine matrix roughness ( S a = 28.23–180.04 μm) and matrix fracture toughness ( K m = 0.354–0.856 MPa·m 1/2 ); at 100–120 mesh in Series 3, spherical glass sand gave the lowest tensile strength (6.29 MPa) and the highest crack number (85), while its flexural strength (28.50 MPa) ranked second only to normal sand (29.56 MPa); this behavior is attributed to a weak interfacial transition zone, and a modified Griffith model links matrix roughness to fracture toughness ( n = 14.5, R 2 = 0.953) with the data suggestive of, but insufficient to firmly establish, superlinear defect growth, while tensile strength showed only a weak negative correlation with roughness ( R 2 = 0.469). These findings provide quantitative criteria for sand selection in ECC design, although the limited number of sand types, the mass-based dosing that makes the volumetric sand fraction differ among mixtures, and the lack of quantitative shape descriptors all call for a more systematic investigation.

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