Study On The Effect Of Pore Structure On Concrete Performance In Deicing Salt Environment

In addition to the conventional deterioration problems such as carbonation and reinforcement corrosion,concrete in cold icing areas in winter is more significantly affected by freeze-thaw cycles.Under the action of this environment,to ensure the traffic safety of pedestrians and vehicles,the pavement is usually reduced by spreading de-icing salt or fine sand to reduce icing or increase friction,while the concrete pavement is highly susceptible to surface scaling and spalling of cement concrete structures in the urban road range under the coupling effect of de-icing salt and freezethaw cycles.The phenomenon will gradually develop into aggregate loss,reinforcement exposure,and accelerated rusting,the section under loss,and other results after further development,which seriously affects the aesthetics and safety,and reliability of the structure.To address the above phenomenon,based on the existing mechanism of salt freezing damage,this paper adopts the oscillation method to test the bubble-forming ability and bubble-stabilizing ability of air-entraining agent species,and analyzes the bubble structure formed and the pore structure before and after salt freezing by the linear conductivity method and low-frequency nuclear magnetic resonance technology to reveal the influence of construction methods on the bubble structure.To explore the resistance of cementitious materials to salt freeze exfoliation under different pore structures and to analyze their destructive effects in combination with microscopic characteristics before and after the salt freeze,the main conclusions are as follows:(1)The bubble parameters and mechanical properties of cement mortar under different air-entraining agents are different.The flexural strength,compressive strength,and splitting tensile strength of cement mortar decreased with the increase of airentraining agent;when the air content was the same,the compressive strength and splitting tensile strength of cement mortar specimens with triterpene saponin airentraining agent were higher than other groups as a whole.(2)Under the same conditions,triterpene saponin air-entraining agent solution foaming volume and defoaming speed is better;combined with the linear conduction method to test its internal bubble structure,with the increase in air content,the mortar internal bubble structure gradually more dense distribution of small-sized bubbles,the introduction of triterpene saponin air-entraining agent,cement mortar bubble parameters better,and the loss of air content after hardening is smaller.(3)When the air content is 8%,the appearance morphology after the introduction of triterpene saponin and sodium dodecyl sulfate K12 air-entraining agent is mainly based on the increase of surface pore size,the mass loss is 4.2% and 2.3%,respectively,and the appearance flaking is more after the introduction of sodium α-alkenyl sulfonate and AE bamboo this grease air-entraining agent,the mass loss is 11.2% and 9.5%,respectively;when the air content is 10%,the triterpene saponin group When the gas content was 10%,the appearance of triterpene saponin group changed less,and the mass loss was 4.2%,the surface of sodium α-alkenyl sulfate group showed partial flaking,and the mass loss was 6.3%,the surface of sodium dodecyl sulfate K12 group flaked more,and the mass loss was 10.9%,and the mass loss of AE bamboo oil group was6.1%.(4)When the gas content was 8%,after 60 cycles of salt freezing,the compressive strength of the triterpene saponin group decreased by 7.8%,the smallest decrease;when the gas content was 10%,the compressive strength decreased by 5.1%;when the gas content was 12%,the compressive strength decreased by 9.2%,after mixing with triterpene saponin air-entraining agent,its compressive strength loss was the smallest in the same group.After mixing with sodium dodecyl sulfate K12 air-entraining agent,the strength loss was smaller when the air content was lower or higher;after mixing with sodium α-alkenyl sulfonate and AE bamboo benzene grease,the strength loss was relatively small when the air content was 12%.(5)Different parts of the same mortar specimen differed in their salt freezing resistance due to their different bubble structures.The overall performance ofφ100×200mm cylindrical mortar specimen from the forming surface to the bottom of the average bubble diameter and bubble spacing coefficient is decreasing trend,and the specific surface area of bubbles gradually increases,and the appearance of its morphological peeling degree after the salt freezing cycle is influenced by the bubble parameters,the surface bubbles are mainly loose distribution of large size bubbles,and the bottom bubbles are mainly closely arranged small size bubbles,so the surface damage The surface layer damage is significantly higher than the bottom damage.(6)After the salt freezing cycle,the pore structure evolution law inside the airbearing mortar increases the number of large-size pores.When the gas content is 8%,the percentage of pores of 0.1～1μm increases by 0.1%,4%,2.3% and 0.2% respectively after mixing with triterpene saponin,sodium α-alkenyl sulfonate,sodium dodecyl sulfate K12 and AE Takemoto grease air-entraining agent,and the percentage of pores >10μm increases when the gas content is higher;it can be obviously seen by scanning electron microscopy that the cracks inside the mortar increase after the saltfreezing cycle,the hydration It is obvious from SEM that the internal cracks of mortar increase,the hydration products are loosely arranged,and both C-S-H gel and calcium alumina structure are partially fractured.