Seawater sea sand concrete (SSC) has a wide range of applications in the construction of islands and coastal projects. In marine environments

concrete is prone to cracking

which can significantly affect the durability of structures. In order to ensure the safe service of this new type of concrete in the marine environment

it is crucial to study the fracture mechanical properties of SSC and to determine the fracture parameters reasonably. However

the size effect is inevitably present due to the neglect of material inhomogeneity when using the determined fracture parameters based on traditional linear elastic fracture model. To address this issue

this article aims to determine the size-independent fracture parameters of SSC

utilizing a non-linear fracture theory based on boundary effect model

taking into account the material discontinuity and heterogeneity. In this paper

SSC with the maximum aggregate sizes of 10 and 20 mm were prepared. Three-point bending tests of with heights of 100 and 200 mm were carried out respectively

and the initial crack length-to-beam depth ratios were set from 0.1 to 0.7 in each group. Additionally

fresh water and river sand were used to replace seawater and sea sand in order to prepare ordinary Portland concrete (OPC) as the control group for the experiments. Based on the boundary effect model and by incorporating the average aggregate size of concrete

the size-dependent tensile strength ft

fracture toughness KIC of SSC can be obtained analytically from small and medium-sized specimens. Furthermore

the means

upper and lower limits of two fracture parameters with 95% reliability were determined based on the normal distribution analysis. The ultimate load of SSC specimens under any size condition was successfully predicted by using obtained tensile strength. Moreover

the results show that under the same aggregate gradation

compared with ordinary Portland concrete

SSC exhibits a higher proportion of aggregate fracture on the fracture surface and demonstrates higher tensile strength and fracture toughness. With the increase in the maximum aggregate size

the proportion of aggregate fracture in both SSC and OPC decreased. However

the fracture toughness KIC increased

while ft decreased. The above model and related results can provide references for the practical engineering design of seawater sea sand sea sand concrete.