Experimental study on improving the performance of historical grey bricks by amide polymer

The in-situ enhancement of grey brick walls' resistance to weathering and mechanical performance remains a critical and challenging aspect of historic building conservation. Based on the requirement for historical building restoration to maintain the original appearance, the water-soluble amide polymer (AP) solution was prepared by cross-linking copolymerization, and AP was infiltrated into the grey brick by negative pressure infiltration technology to achieve the purpose of filling the pores and improving the strength and durability. The appearance color difference, physical properties, mechanical properties, dry-wet cycle test and scanning electron microscope (SEM) analysis of different groups of modified grey bricks were carried out by orthogonal test. The results show that the most important factor affecting its physical and mechanical properties is acrylamide (AM). When the concentration of AM is 25 % and the mass of crosslinking agent is 2–3 % of the monomer mass, the mechanical properties of the modified grey bricks increase significantly. The modified grey brick No.7 (AB7) show optimal performance enhancement, exhibiting 14.51 % and 31.56 % increases in dry density and wave velocity respectively, along with a 37.54 % porosity reduction, while achieving compressive strength of 11.73 MPa and peak load strain of 8.59 % compared to the original grey bricks. After 30 wet-dry cycles, both mass and compressive strength of the modified grey bricks decreased, with AB7 exhibiting the least reduction at 1.56 % mass loss and 24.22 % strength loss. SEM observations of modified grey bricks revealed that AP effectively filled the pore structures and formed continuous polymeric surface layers, enhancing the performance of grey bricks. The research results provide a new approach for the conservation of weathered grey brick in historic buildings.