| Along with the economic development in our country,the continuous improvement of infrastructure and the implementation of the strategy of "developing the western region" and the "Belt and Road" concept,large concrete structures such as highways and bridges and culverts continue to extend to the northwest.Because of the harsh climatic conditions in Northwest China,the distribution of saline soil with large amount of dry and cold evaporation is very wide,and the durability of roads and bridges and culverts built in saline soil areas is taken seriously,especially the sulfate resistance of concrete materials in saline soil areas.To solve the problem of anti-sulphate erosion of concrete in saline soil,the durability of concrete structures in northwest saline soil will be greatly improved.Baiming Expressway is located in saline soil areas where the climate is dry and cold with large evaporation.There are salt lakes distributed along the route,and there is a serious phenomenon of soil caustic alkalis.This poses more stringent requirements for the concrete materials used by Baiming Expressway.In this paper,Baiming high-speed site and laboratory conditions,from the following several aspects to study the sulfate resistance of cement mortar erosion:(1)Based on the actual ambient temperature in the field,a reasonable indoor dry-wet cycle cycle accelerated test was developed to simulate the dry and wet evaporating environment of the Bai-Ming high-speed on-site,and the corrosion resistance of cement mortar test blocks was determined by indoor test to determine their respective anti-sulfate Erosion ability.(2)Comparing the sulfate resistance of cement mortar with different water cement ratios and mineral admixtures at different temperature and humidity under cyclic wet-dry conditions.(3)The changes of the appearance of the test piece and the change rules of the indexes such as the flexural strength,the compressive strength,the relative dynamic elastic modulus and the mass loss rate under different erosion ages were analyzed.(4)The corrosion resistance of cement mortar was analyzed based on four indexes of flexural strength,anticorrosion coefficient,compressive strength and corrosion resistance,relative dynamic elastic modulus and mass loss rate respectively.(5)The samples after the wet-dry cycle test were sampled and analyzed by SEM,EDS and XRD.The microscopic products after the sulfate attack were analyzed and the sulfate attack mechanism under the condition of low temperature and humidity was analyzed.Through testing the macroscopic indexes and microscopic products of cement mortar under different erosion ages,the changing rules of each index were compared and analyzed.The results showed that: Under the conditions of low temperature drying and wetting,the sulfate resistance of cement mortar increased obviously with the decrease of water cement ratio;0.5 water-cement ratio case,complex mineral admixture to reduce the corrosion resistance of cement mortar,0.36 water-cement ratio case,complex mineral admixture significantly improved the corrosion resistance of cement mortar.And the corrosion resistance of mortar with 3% silica fume + 15% slag is better than that with 1% silica fume + 15% slag at 5?.The corrosion resistance of the mortar mixed with 1% silica fume + 15% slag is better than that of 3% silica fume + 15% slag at 10?;Compared with ordinary Portland cement,sulfur resistant cement shows better corrosion resistance;In the condition of low temperature drying and wetting,the cement mortar damaged by sulfate attack not only has the physical crystal destruction,but also has the chemical corrosion.The corrosion products include ettringite,glauberite and gypsum.In this paper,through the experimental study of sulfate resistance of cement mortar under low temperature and wet-dry conditions,some preliminary results were obtained.On the one hand,these achievements are rich in the scientific research contents of sulfate attack concrete and on the other hand,they have certain guiding significance for practical projects: It provides some theoretical basis for the design,construction and maintenance of mixture ratio of sulphateeroded concrete in construction of cold and salty saline soil area.It can also provide certain technical guarantee for ensuring the concrete construction in cold and salty soil area to avoid or reduce the erosion of sulfate.It also has important scientific significance for the safe operation of highways,bridges and culverts and other structures.It is also an important means of protecting people's lives and property and their assets from being affected. |
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