Experimental Study On Repairing Materials For Cracks In Rammed Earth Wall And Their Bonding Performance

Rammed earth buildings are characterized by environmental protection,low cost and local materials.Apart from ancient buildings and earthen ruins,there are many rammed earth buildings widely distributed in rural areas of the central and western regions.Due to the poor mechanical properties and durability of traditional rammed earth walls and materials,rough construction technology,unreasonable house structure layout,unstable foundation and other reasons,the rammed earth building walls are prone to cracking.The cracks will damage the rammed earth wall to different extents,which seriously affects the normal use function,durability and appearance of rammed earth houses.If effective measures are not taken in time,cracks will further develop and cause greater hazards.The existing research on repairing technology of cracks on rammed earth walls is restricted.The first reason is that the crack repairing materials are mainly used for concrete,brick masonry and other structures,and their applicability in rammed earth walls is still not clear;secondly,there are relatively few researches on repairing materials and technologies applicable to rammed earth houses in rural areas.Based on the above,we selected various repairing materials and their mix ratios,and conducted mechanical property test.The specific contents and conclusions are as follows:(1)We carried out in-depth analysis on the cracking status and causes of cracks in rammed earth walls through extensive and in-depth investigation in various regions.Through the investigation,we found that the main forms of cracks in rammed earth walls are those caused by drying shrinkage and stress,and the main causes include dehydration shrinkage,stress cracking,uneven settlement of foundations,original defects of tamping technology,etc.(2)We selected seven repairing materials and their different mix ratios,and conducted experimental study on their solidification,flow and permeability,and found that some mix ratios of these seven materials can be used for repairing cracks in rammed earth walls,including epoxy resin,sodium silicate solution,epoxy mortar,cement-silicate slurry,soil slurry,cement mortar and gypsum.Among various materials,the grouting process of epoxy resin,epoxy mortar and cement mortar is more convenient in terms of curing time and fluidity.epoxy resin and sodium silicate solution have a better permeability to rammed earth in terms of permeability.Through the electron microscope scanning experiment on the bonding fracture surface between undisturbed soil and repairing materials,we mastered their microstructure,and summarized their reinforcement mechanism,thus providing the basis for subsequent research.(3)In order to study the bonding properties between repairing materials and rammed earth walls,we fabricated 14 groups of rammed earth specimens,and carried out shearing and bending test to examine the bonding force between different materials and earth body as well as the strength of bonding interface.The test results showed that epoxy resin,epoxy mortar,partially mixed cement-silicate slurry and sodium silicate solution have a good bonding performance with rammed earth,and are suitable for repairing stress cracks;The partially mixed sodium silicate solution and soil slurry containing sodium silicate solution have certain bonding force,and can be used for repairing cracks in parts with low requirements for cohesive force.Cement mortar,gypsum and soil slurry without adding other cohesive components have a poor bonding performance with rammed earth,but their partial mixture have a good filling effect and can be used for repairing shrinkage cracks.Sodium silicate has a reinforcing effect on soil.Compared with soil slurry,the soil slurry infiltrated with sodium silicate has a better bonding performance and does not change the appearance and color of soil,and can be used for repairing the surface layer of rammed earth walls.(4)Through the test and analysis of seven repairing materials,we obtained the performance parameters of these materials and their mix ratios,and evaluated their comprehensive performance.Combined with practical engineering applications,we presented the suggestions for material selection,cost analysis and process parameters of rammed earth walls under different crack conditions.Through a series of tests on rammed earth specimens and repairing materials,we verified the feasibility of applying partially mixed repairing materials to cracks in rammed earth walls,and optimized their mix ratio in combination with rammed earth materials,and obtained good test results.