Strength and deformation properties of structural lightweight concrete under true tri-axial compression

In this paper, the strength and deformation of structural all lightweight concrete (ALWC), structural semi-lightweight concrete (SLWC) and normal weight concrete (NWC) subjected to uniaxial, equibiaxial and truly tri-axial compression was experimentally studied and compared. The stress-strain curves in three principal directions were recorded, and the failure modes of different specimens under various stress states were observed. Test results showed that the failure modes were mainly dependent on the stress ratio, but independent of concrete types. For all types of concrete, the peak strength under biaxial and triaxial compression is substantially higher than uniaxial compressive strength. At the lower compression stress ratio, i.e. σ1/σ3 = 0.1, all the concrete exhibited relatively brittle behavior, the relative tri-axial compressive strength of ALWC and SLWC was in a range of 1.61–2.05 and 1.93–2.63 respectively, compared to 2.25–3.21 for NWC. The peak deformation in three principal directions for ALWC and SLWC was far greater than that of NWC. At the higher compression stress ratio, i.e. σ1/σ3 = 0.25, all concretes showed pseudo-ductile behavior, the relative tri-axial compressive strength and peak deformation in three principal directions of ALWC and SLWC became close to those of NWC. Considering the role of the intermediate principal stress for concrete under true triaxial compression, a 4-parameter failure criterion model with different material constants was developed. The proposed failure surface was verified against experimental data of NWC, ALWC, and SLWC under multiaxial loads in this paper, as well as low strength LWC under truly tri-axial compression in the literature. It provided the experimental and theoretical foundations for strength analysis of LWC structures subject to complex loads.