Effect Of Ultraviolet Radiation On The Surface Structure And Properties Of Cement-based Material

UV is an important cause of aging of materials,but for cement-based materials,the effect of UV on its structure and properties has not been systematically studied.Ultraviolet radiation can cause the fracture of typical chemical bonds of the material,or the molecule can become an electronic excited state after absorbing ultraviolet rays,and a photochemical reaction or photophysical reaction takes place.Deterioration of common cement pastes is mostly attributed to climatic conditions such as temperature and humidity.Hydrogen bonds and C-S-H chain structures also exist in cement pastes.Ultraviolet light may also damage these structures.Since the solid particles in the hardened cement slurry coexist in one form with various forms of water and have the same microstructure units as organic molecular groups,ultraviolet light may affect the structure and properties of the hardened cement paste.In order to verify this idea,an ultra-violet weather resistant test chamber was used to irradiate the hardened cement slurry,and the surface topography,type of hydration products,and major physical properties of the hardened cement paste irradiated for a certain period of time were tested and analyzed.Get the following conclusions:(1)Irradiation of ultraviolet rays accelerates the carbonization of cement-based materials,and the effect of accelerating the carbonization of cement-based materials with different ages and different admixtures is not same.The UV content of cement paste for ultraviolet radiation,curing for 1 day,curing for 7 days,and curing for 28 days after UV irradiation was 0.58 times,1.12 times,and 1.43 times the surface area of the corresponding backlight.The longer the curing period,the faster the carbonization of the ultraviolet rays.The effect is more obvious;for cement-based materials containing volcanic ash active mineral admixtures,ultraviolet irradiation can also have the effect of accelerating the carbonization;for cement-based materials containing non-volcanic ash active mineral admixtures,ultraviolet irradiation also accelerates carbonization,but The content of calcite in the phase composition has declined.For cement-based materials designed with ultra-high performance mix ratios,the effect of accelerated carbonization is more pronounced.(2)Ultraviolet irradiation reduces the surface roughness of the cement-based material.When the friction pair moves,the actual effective contact area between the cement stone and the relative moving surface increases,and the friction coefficient increases.Ultraviolet ray prime cement slurry increases the friction coefficient of primed cement slurry at different ages,and the increase range decreases with the increase of curing time.Ultraviolet irradiation irradiates cement-based materials containing different mineral admixtures,so that the friction coefficient is approximately On the ascension,some groups have decreased(for example,fly ash samples with a curing age of 28 days),and the friction coefficient of mineral admixtures at different ages has not undergone too much fluctuation due to different curing ages under ultraviolet irradiation.For the ultra-high performance mix designed cement paste maintenance 28 days sample after UV irradiation significantly higher than the maintenance of 1 day and 7 days sample.(3)The microhardness test results of cement-based materials meet the 3-parameter lognormal distribution.UV-irradiated cement slurry can increase its micro-hardness value.Ultraviolet irradiation makes the microhardness of the irradiated surface for 1 day,7 days and 28 days correspond to 3.17 times,2.4 times and 1.7 times of the corresponding backlight surface,respectively,with the curing age.The increase of the microhardness of the phase decreases;the microhardness of the cement-based material containing ultraviolet-active mineral admixture is increased by ultraviolet irradiation;and the cement-based material containing non-pozzolanic active mineral admixture is irradiated by ultraviolet rays(such as the reef-containing powder Cement slurry),the micro-hardness of the irradiated surface is higher than that of the backlight surface,but compared with the plain cement paste without added admixture,the ultraviolet irradiation surface,the backlight surface and the standard curing group all show a decline;for ultra high performance mix ratio The micro-hardness of the cement paste is generally higher than that of the plain cement paste and the cement paste containing other admixtures.After irradiation with ultraviolet rays,the micro-hardness of the irradiated surface increases more significantly,which is approximately 1.94 times that of the backlight surface.