Study On Interface Properties Of Highland Barley Straw Ash Modified Magnesium Oxychloride Cement Mortar And Ordinary Concrete

The"Belt and Road Initiative"has injected a strong impetus for trade cooperation between China and Eurasian countries along the route,and is of great importance to the social and economic development of the western region of China.In the process of advancing with the construction of railroads,bridges,highways and other infrastructure in the relevant areas also emerged some problems:salt lake areas,saline soil areas with a large number of chlorine salts,sulfates and other salts containing corrosive ions can cause serious erosion of local concrete buildings,resulting in ordinary silicate cement concrete in the region is difficult to meet the durability requirements and early damage,the western plateau zone high altitude,day and night temperature difference The natural climatic characteristics of the western plateau zone with high altitude and large temperature difference between day and night may also accelerate the erosion rate.Magnesium oxychloride cement is a magnesium based gas hardening cementing material composed of Mg O-Mg Cl₂-H₂O system,which has excellent resistance to salt brine,and has the advantages of high hardness,high wear resistance,and low consumption in the early stage,it has a good development prospect in the salt lake area,but at the same time,the magnesium oxychloride material has defects such as poor water resistance,which greatly affects its application prospect.Highland barley has a wide planting area in the plateau area of western China,and is an important crop for local farmers and herdsmen.Most of the harvested highland barley straw is used as fuel,and the content of Si O₂ in the straw ash powder obtained after incineration is high,which has the advantages of preparation potential to be a pozzolanic material.Due to the early erosion and water resistance issues of magnesium oxychloride cement in the salt lake region,as well as the characteristics of the western salt lake area,the abandoned crop highland barley straw was incorporated into the magnesium oxychloride cement mortar as a modified material after certain treatment.In order to improve the water resistance of magnesium oxychloride cement mortar,the modified magnesium oxychloride cement mortar is used as the outer protective layer of ordinary Portland concrete to jointly resist the erosion of brine.If the feasibility of this method is verified,it will not only provide a new idea for concrete to resist brine erosion in the salt lake area,but also alleviate the accumulation of old brine in the salt lake and the resource disposal of waste straw to a certain extent,which is conducive to ecological sustainable development.In order to study the application feasibility of magnesium oxychloride cement mortar（MOCM）modified by highland barley straw ash（HBSA）as the outer protective layer of ordinary concrete（OPCC）,it is necessary to carry out the preparation,optimization,trial mixing of HBSA and the MOCM-OPCC interface.The performance research,the experimental research conducted in this paper and the main conclusions are as follows:（1）Preparation and activity research of highland barley straw ashThe highland barley stalks were treated with calcination temperature,calcination time and grinding time as variables to obtain ash powder,and the preparation method of HBSA with the highest activity was studied by means of strength test after incorporation of MOCM,HBSA particle size parameter test and microscopic test.The results showed that the highland barley stalks were initially incinerated outdoors,followed by secondary calcination at a temperature of 600°C for 2 h,and the HBSA activity effect obtained by cooling the obtained ashes naturally and then grinding them for 2 hours reached the highest level.（2）Study on the influence of HBSA on the mechanical and durability properties of MOCMHBSA was mixed into MOCM according to different dosages and mixing methods,and the mechanical properties of each group of specimens were tested for short-term28 days under dry and saturated state of MOCM.Then,the MOCM was subjected to the durability test under freeze-thaw cycles,salt lake brine immersion,and salt-freeze coupling,and the change law of the influence of HBSA on the durability of MOCM was analyzed to determine the optimal dosage and mixing method of HBSA.The results show that when HBSA with a mass ratio of 10%Mg O is added,the water-saturated MOCM specimens have the least loss of flexural strength and compressive strength,and the best water resistance;The smallest,the best durability.（3）Research on interface properties of MOCM-OPCCThe comprehensive interface performance of MOCM-OPCC is studied,mainly the bonding performance and ion corrosion resistance.The control group was set with variables such as whether HBSA was mixed into MOCM,whether the bonding interface was coated with interface agent,and the thickness of MOCM,and the law of bond strength degradation of MOCM-OPCC under different erosion environments and the change law of ion concentration on the surface of OPCC under the one-way transport erosion of salt lake brine were studied.Combined with microscopic testing methods,further The influence of factors such as HBSA on the interface performance of MOCM was analyzed.The results show that:（1）When MOCM is mixed with HBSA,interface agent is applied to the bonding interface,and MOCM with a thickness of 18 mm is used as the outer protective layer of OPCC,the comprehensive interface performance of MOCM-OPCC is the best.（2）YJ-302 can optimize the interface structure when applied as an interface agent on the bonding interface,and play a role in strengthening the interface.（3）The content of active Si O₂ in HBSA is high,which can undergo secondary hydration reaction with MOCM to form M-S-H gel,which can evenly cover the surface of five-phase crystals,fill the gaps between crystals,and make the structure more compact,thereby Improve performance of MOCM-OPCC interface.