Abstract: Series of unconfined compression and indirect tensile tests were performed to study the effects of curing age and delayed compaction on strength and stiffness of magnesium oxychloride cement (MOC) solidified sludge, analyzing the strain rate effect of solidified sludge under constant multi-strain rate loading and alternative strain rate loading. The obtained results indicate that the tensile strength, compressive strength, elastic modulus, failure strain, and total strain energy of sludge increase with an increased strain rate. The compressive strength, tensile strength, and total strain energy of MOC solidified sludge has an upward trend with strain rate, while the elastic modulus and failure strain have no apparent change. The faster the strain rate is, the more distorted and rugged the fracture surface is. With the prolongation of curing age, the compressive strength and total compressive strain energy are significantly increased, while the tensile strength and total tensile strain energy are reduced slightly. Significantly, different calculation methods adopted would result in different strain rate sensitivity coefficients for curing age. The delayed compaction would reduce the tensile strength, compressive strength, elastic modulus, total strain energy, and strain rate sensitivity coefficient of solidified sludge. The stress jump induced by a sudden change of strain rate is enlarged owing to the increase of applied stress, and it first increases and then levels off as the strain is extended. The strain rate sensitivity coefficient shows that solidified sludge is less sensitive than pure sludge, and the tensile strength is more sensitive than the compressive strength. The obtained results can provide an essential theoretical reference for the strain rate effect analysis of solidified sludge.

Key words: sludge, magnesium oxychloride cement (MOC), solidification, strain rate