| Ancient buildings are important historical and cultural heritage in China,and their main forms of existence are brick and stone structures,and there are a large number of existing buildings.However,due to long-term environmental erosion and loading,the gray joints between the masonry are seriously damaged,and repair and repair are urgently needed.In the restoration of ancient buildings,the performance of mortar bonding materials is an important factor affecting the quality of restoration.In order to meet the bearing capacity requirements,durability requirements and cultural relics protection requirements such as "repairing the old as the old" after structural restoration,it is necessary to analyze the performance of traditional mortar and improve it.In this paper,referring to the ratio of masonry mortar of ancient buildings,glutinous rice pure ash mortar and glutinous rice ash mortar were prepared as the control group,and the performance of basic glutinous rice mortar was improved by using hemp knife fiber,nano silica and other materials.A total of 15 groups of mortar test blocks were produced,including glutinous rice pure ash mortar,glutinous rice ash mortar,hemp knife fiber modified mortar,hemp knife fiber modified mortar,hemp knife fiber plus nano silica mixed modified mortar and hemp knife fiber modified ash mortar.Through the comparative analysis of the test test,the parameters such as consistency,shrinkage and surface hardness during the preparation and curing of the mortar test block were obtained,and the mechanical property test,durability performance test and combined with the microstructure and composition were combined to analyze the performance improvement effect of mortar after adding modified materials.The main work and conclusions are as follows:(1)Study on physical properties during mortar preparation and curingThe consistency test is carried out in the preparation of mortar,the shrinkage test and surface hardness test are carried out in the curing period,and the physical properties of sticky rice mortar in the preparation and curing process are obtained by combining the quality change,and the improvement effect of additive addition on the physical properties of sticky rice mortar is analyzed.The results showed that the commonly used water-cement ratio of 0.8 was the suitable consistency of sticky rice mortar water-cement ratio,the suitable consistency water-cement ratio of sticky rice mortar was 1.0,and the water-cement ratio was increased by adding hemp knife fiber or nano silica for modification;the shrinkage rate of sticky rice mortar was relatively stable at 7 days,while the waxy rice mortar slurry continued to shrink within 90 days,and the shrinkage rate of sticky rice mortar was greater than that of sticky rice mortar.The single doping of nano-silica was not conducive to mortar shrinkage,and the shrinkage rate of single hemp knife fiber was improved.Compared with the mixed addition of the two,the shrinkage rate of nano-silica was significantly reduced.The hardness value of each group of mortar was close after 90d curing.The early surface hardness value of sticky rice ash slurry was low,and the addition of nano-silica and hemp knife fiber could increase the early surface hardness of mortar.(2)Analysis of mechanical properties and modification improvement of sticky rice mortarThe unconfined compression test was carried out on each group of mortar test blocks,the failure phenomenon of the test was observed,the stress-strain curve was drawn,the change law of compressive strength was analyzed,and the reasons for the performance change and strength improvement mechanism of the modified sticky rice mortar of each group of additives were compared and analyzed by combination with microscopic XRD and SEM.The results showed that the traditional sticky rice mortar and sticky rice mortar had lower strength and similar strength.The addition of nano silica can improve the compressive strength of mortar by improving the microstructure of mortar,and when its mass ratio does not exceed 4%,the compressive strength increases with the increase of its mass ratio;The hemp knife fiber has good compatibility with sticky rice mortar,and its addition can improve the mechanical properties of mortar under pressure,and within the additive mass ratio,with the increase of mass ratio,the strength increase amplitude decreases and the ductility increases;The addition of fiber and nano silica mixed modification,fiber can make up for the uneven distribution defect of nano silica and its products,significantly improve compressive strength and improve the brittleness of destruction,the strength of adding(0.1%)hemp knife fiber and nano silica(2%)is 87%stronger than that of nano silica(2%),and the strength of sticky rice mortar is increased by 143%.(3)Analysis of sticky rice mortar durability modification and improvementBy testing the water resistance of sticky rice mortar,combined with the test phenomenon and the compressive strength of the softening test block,the softening coefficient was calculated to analyze the water resistance of the mortar.The freeze-thaw test was carried out on the mortar,the strength loss after freeze-thaw was tested,and the durability of the mortar was summarized by combining the freeze-thaw to failure test phenomenon and the freeze-thaw surface microscopic observation.The results showed that sticky rice mortar and sticky rice mortar had poor durability.The addition of nano silica will cause unevenness inside the mortar,freeze heave or cracks in the process of freeze-thaw water resistance,and reduce the durability of the mortar.The connection effect and water retention of hemp knife fiber itself relieve hydrophilic ablation on the surface of mortar or ash slurry,reduce frost heave,and improve water resistance and strength after freeze-thaw.The addition of nano silica and hemp knife fiber can effectively improve the frost heave crack of single plus silica,while maintaining strength,and effectively improving the durability of mortar. |
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