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Carbon dioxide (CO 2 ) pretreatment to concrete at the early curing ages is a feasible technique towards achieving a greener and more sustainable concrete industry. However, the carbonation efficiency of ordinary concrete blocks is greatly limited due to their dense compactness. Here we proposed that the aeration of concrete blended with high-volume industry wastes may bring about improved sustainability of the precast concrete industry by enhancing the carbonation efficiency. We designed two different CO 2 pretreatment courses: that is, the gas pressure of CO 2 = 0.1 atm (0.01 MPa) for 8 h and 1 atm (0.1 MPa) for 4 h. The strength and microstructure of the aerated concrete with and without the CO 2 pretreatments were investigated by macro-and microscopic tests. Results showed that the CO 2 pretreatments greatly altered the minerals and pore structure of the aerated concrete blocks. The higher CO 2 pressure with less curing time raised the carbonation extent, crystal size, and compressive strength at 3 days. Compared with ordinary solid concrete, the aerated concrete showed a higher CO 2 sinking efficiency by more than one order of magnitude. This technique would potentially sink millions of tons of CO 2 from the precast aerated concrete industry.

Structural members carry spatial loads owing to, for example, gravity, winds, and earthquakes. Loads along multiple degrees of freedoms (DOF) should be synchronously imposed on the loading point for accurately reproducing structural responses under spatial loading. Strong coupling may exist among the multiple DOFs owing to specimen rigidity, posing significant challenges for actuator control. Two major problems should be solved to address this challenge. The first is the nonlinear coordinate transformation from the local actuator space (LAS) to the global Cartesian coordinate (GCC) system, depending on the current GCC position of the loading point. The second is the mixed control scheme for engineering specimens, that is, force control in rigid directions and simultaneous displacement control in soft directions, which depends greatly on the nonlinearities developed in specimens. To overcome these difficulties, a modified Newton-Raphson (NR) iteration integrated with a PI control (MNR-PI) is developed to handle material nonlinearity, and the incremental kinematic transformation method integrated with PI control (IKT-PI) is proposed to solve the nonlinear coordinate transformation problem. The theoretical background of the MNR-PI, which can be synchronously incorporated with the control process of the loading system to solve nonlinear problems, is first provided. The control gains are then designed by discrete control theory, and a new MDOF force-displacement mixed control method is accordingly formulated and numerically simulated. Finally, three-DOF cyclic tests on a steel column are conducted to demonstrate the feasibility and accuracy of the proposed method.

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