Study On The Interaction Effect Of Defects And Humidity On The Mechanical Properties Of Concrete

In order to study the interaction effect of defects and humidity on the mechanical properties of concrete,it is necessary to obtain dry and saturated specimens,but different drying temperatures cause different damage to concrete.The change of the macroscopic properties of concrete in the drying process is the result of the accumulation and development of defects in the microscale.Therefore,this paper systematically carried out isothermal drying experiments of cement paste and mortar at different drying temperatures to provide a basis for reasonably determining the drying mechanism of concrete.Based on this,the influence of humidity on the mechanical properties of cement-based materials is systematically studied,and the prefabrication methods for different initial defects are discussed.Then,the interaction effects of defects and humidity on the mechanical properties of concrete are analyzed.Main work and conclusions are as follows:?1?Isothermal drying tests were carried out for cement paste and mortar with different water-cement ratios at 60?,75?,90?,105?and 120?.The influences of water-cement ratio and drying temperature on physical properties,mechanical properties and thermodynamic properties of the material were studied from cement paste and mortar,which provided the basis for determining the mechanism of concrete desiccants.The results showed the effective diffusion coefficient of water is between 0.41-3.30×10^-9 m²/s when the temperature is between 60?and 120?.?2?Based on the research of drying characteristics,the influence of humidity on the mechanical properties of cement-based materials treated at different drying temperatures was studied,and the compressive strength under dry and saturated conditions was measured,and found that humidity on mechanical properties of cement paste and mortar after 120?isothermal drying have stronger sensitivity.At the same time,compared the two kinds saturated specimen compressive strength.The results showed the compressive strength of re-saturated cement-based materials after drying treatment was all less than the compressive strength of the standard curing to saturation state of 28d,and the damage of the cement paste after drying treatment was greater than the mortar with the same water-cement ratio.?3?Carried out experimental research on precast defects by two ways,namely,different load preloading and different content of air entrainment agent,and analyzed the influence of different degree of damage on the mechanical properties of concrete.First,when the stress level is less than 30%,the compressive strength of concrete changes little.The critical stress may be between 30%and 60%.Secondly,when the gas content is less than 5.3%,the porosity caused by air entraining agent has a good negative linear relationship with the concrete strength and wave velocity.?4?Based on the previous research,the compressive strength of concrete with 4 kinds of defects under 4 kinds of humidity was measured and found whether or not the interaction effect is considered,both humidity and defects have the influence on the mechanical properties of concrete?P<0.01?.When the saturation is greater than 30%,the sensitivity of water to the compressive strength of concrete is decreasing,but as the porosity increases,its sensitivity increases.