Investigation on the compression behavior of ancient brick masonry strengthened by modified horizontal mortar joints with composite grouting and natural hemp fiber rope reinforcement

This study fabricated ancient brick column specimens with two different mortar joint spalling depths based on the common material deterioration mode of ancient masonry. Specifically, modified composite sticky rice-lime mortar and natural hemp fiber rope were used as the raw materials, and horizontal mortar joint grouting and fiber rope reinforcement methods were adopted to prepare performance-enhanced ancient brick column specimens with six different strengthening conditions. Through uniaxial compression tests, the compression failure morphology and mechanical properties of the specimens under different strengthening conditions were studied, and the variation patterns of mechanical performance indicators with the strengthening conditions were analyzed. The calculation formula for the compressive strength of performance-enhanced ancient masonry was proposed, and the full stress-strain relationship model under compression and the crack length development model were established. The results show that the non-strengthened brick columns exhibit brittle failure morphology under compression, and the compressive strength and deformation modulus decrease with the increasing mortar joint spalling depth. The crack development process of reinforced brick columns under compression presents ductile characteristics. The compressive strength and crack density increase with an increasing grouting depth and mortar joint grouting-fiber rope reinforcement significantly enhances the elastoplastic deformation capacity of brick columns under compression. Under the 25% grouting depth ratio, the characteristic stress and corresponding deformation modulus of the stress-strain curve increase first and then decrease with the increasing fiber rope reinforcement ratio. The compressive strength and crack density of ancient brick column with the 12.5% grouting depth ratio and 0.25% reinforcement ratio increase by 57.1%, 24.7%, respectively. The established formula and models can clearly describe the evolution of mechanical properties of ancient masonry, offering good engineering applicability.