Rheological, deformation behaviors and mechanical changes of MgO-containing concretes with different strength

MgO content is of importance to the compensation feasibility and soundness of concrete, especially for concrete with different strength grades. The rheological, deformation behavior, and mechanical changes of MgO expansive agent (MEA) (5–8 wt%) in different strength grades of concrete were revealed. Results show that MEA replacement of cement makes the yield stress and plastic viscosity increasing because of the high specific surface and agglomeration of MEA. Although same quantity of Mg(OH)2 is generated, concretes with different strength grades display different expansion behaviors because of their different pore structures and Mg(OH)2 morphology. Mg(OH)2 that growing around MgO particles presents a colloidal morphology, while Mg(OH)2 that growing in the surrounding pores presents a hexagonal flake-like morphology. The restrained deformation of Grade 40 concrete with 6 wt% MEA after curing in water for 14 d increases to the maximum expansion, reaching 237 × 10−6.6 wt% MEA replacement does not affect the compressive strength and splitting tensile strength of concrete with different strength grades. However, 7–8 wt% MEA replacement reduces the splitting tensile strength of Grade 40 concrete, and the negative impact is particularly pronounced after air curing.