This paper investigates the effectiveness of applying continuous high-compression pressure on the initial setting of fresh concrete to produce hardened concrete materials with excellent mechanical properties. A novel experimental apparatus was self-designed and used for the pre-setting pressure application. The utilization of the completely decomposed granite (CDG) soil as an alternative aggregate in concrete production was also explored. A total of twenty-eight specimens were fabricated using two types of fine aggregates, six mix ratios, two initial pressure values, and two distinct durations of the initial pressure application. The density and uniaxial compressive strength (UCS) of the specimens were examined to evaluate their mechanical qualities, while micro-CT tests with image analysis were used to quantify their porosity. The results indicated that the 10 MPa initial pre-setting pressurization can effectively eliminate the excess air and voids within the fresh concrete, therefore enhancing the mechanical properties of the hardened concrete specimens of various types. Compared with non-pressurized specimens, the porosity values of pressurized specimens were reduced by 73.11% to 86.53%, the density values were increased by 1.43% to 8.31%, and the UCS values were increased by 8.42% to 187.43%. These findings provide a reference for using a continuous high pre-setting compression pressure and using CDG soil as an aggregate in the fabrication of concrete materials with improved mechanical performance.

In this study, the undrained mechanical behavior of saturated completely decomposed granite (CDG) with different weathering degrees is investigated. To this end, a series of consolidation undrained (CU) triaxial compression tests are conducted on saturated CDG, and the effects of weathering degree on the main undrained mechanical properties are analyzed. Based on the experimental results, a poromechanical model is then established with the concept of effective plastic stress in a poroplasticity framework. Plastic distortion is described using a particular yield surface and a nonassociated plastic potential, which are both functions of the effective plastic stress and a subtly unified smooth hardening/softening variable. As an original contribution, an enhanced semi-implicit return mapping (ESRM) algorithm is developed to integrate the proposed model. This algorithm is based on a semi-implicit return mapping procedure and is combined with a new adaptive substepping technique. The model is subsequently implemented and validated by comparing the numerical simulation results with the experimental data. The main undrained mechanical characteristics of saturated CDG with different weathering degrees are well reproduced. A discussion follows regarding the parameter sensitivity analysis and robustness of the ESRM algorithm. Interestingly, the high accuracy of the ESRM algorithm is almost step-size independent, and the computational efficiency is also greatly improved.