Experimental Study And Reliability Analysis Of Recycled Aggregate Concrete

With the continuous aging of reinforced concrete buildings and demolition and renovation of urban construction,more and more construction waste is generated.Recycled aggregate concrete not only can save total resources,also reduces environmental pollution caused by abandoned concrete.It is a kind of sustainable development of green concrete and is in line with the scientific concept of development proposed by our country.It is one of the basic theoretical research topics that are urgently needed to be solved in the current implementation of the“One Belt and One Road”strategy and has very important practical significance.The development of recycled aggregate concrete technology is the key to realizing large-scale industrial applications.However,the research on recycled aggregate concrete at home and abroad is mostly in the laboratory research stage,and the real practical application is very few.In this paper,16 kinds of recycled aggregate concrete blocks with different mix ratios were designed,and the regeneration was studied through tests including gas content,bleeding rate,slump,tensile strength,compression resistance,non-destructive testing,rapid freezing and thawing,and sulfate wet-dry cycle.The physical and mechanical properties and durability of aggregate concrete are analyzed and preliminary reliability analysis is performed.The main conclusions are as follows:?1?The incorporation of recycled coarse aggregate and fine aggregate has reduced the construction performance of recycled aggregate concrete.When the amount of recycled crude and fine aggregate is 15%and 10%,the compressive strength of the concrete is higher,and the tensile strength of the crack is relatively high at 30%and10%.?2?Through single-parameter and two-parameter regression fitting analysis of the compressive strength,rebound strength,and ultrasonic speed of sound of recycled aggregate concrete,it was found that the correlation coefficient of ultrasonic-rebound dual parameter fitting was 0.9,that is,the non-destructive testing technology of compression of recycled aggregate concrete should be focused on the ultrasonic-rebound synthetic method,and it is more suitable for the preference in engineering practice.The split tensile strength increases with the increase of compressive strength,and the correlation coefficient of the power function model reaches 0.68,which is consistent with the models given at home and abroad.The correlation between splitting tensile strength and ultrasonic sound velocity and rebound strength is not enough to be applied in practice.?3?The increase of the content of regenerated coarse and fine aggregates results in the decrease of the dynamic elastic modulus and the increase of the mass los s of the specimens,that is,the degree of loss of the specimens under the freeze-thaw cycles is gradually becoming severe.The Weibull distribution was used to model the degradation process of the specimen.It was found that the Weibull distribution can effectively describe the degradation process of the frost resistance of the recycled concrete specimen,and the index mass loss dynamic elastic modulus is more sensitive.The reliability function established by this method can intuitively reflect the relationship between the reliability of the test piece and the number of freeze-thaw cycles and indirectly reflect the remaining life of the test piece.?4?Analysis of experimental data shows that the dynamic elastic modulus and mass appear to increase first and then decrease with the increase in the number of wet and dry cycles of the sulphate,and the change trend is similar to that of ordinary concrete;the recycled coarse aggregate is more accurate than the recycled fine aggregate on concrete specimens.The effect of resistance to sulfate erosion is more pronounced,and its performance is greatly reduced.Using the Wiener distribution can effectively describe the degradation process of sulfate resistance of recycled concrete specimens for reliability evaluation.This method can be used to evaluate the sulphate erosion damage and quantify it,making the analysis of sulfate resistance of recycled concrete more digital and predictable.?5?Through ESM,EDS and XRD analysis,the corrosion products of calcium alum and gypsum were produced by the sulfite and wet cycling test.Concrete is subjected to the double destruction of the crystallization expansion of Na ₂SO₄·10H₂O in the process of swelling and damage of calcium alum and gypsum.