Study On Mechanical Properties Of Composite Limestone Powder Concrete And Flexural Properties Of Composite Slabs

As a big country in the construction industry,China has a huge demand for concrete,cement as an important part of it,in the production process produces a large number of greenhouse gases,natural sand resources are gradually depleted.With the proposal of the national "carbon peak" strategy,the concrete industry also attaches great importance to the environmental problems caused by production.In order to achieve sustainable development,the use of admixtures can be rationally used to reduce the amount of cement used,and industrial waste can be used to replace natural sand.In this thesis,limestone powder,slag and other admixtures are used to replace cement,and the mixed sand of machine sand and tailings sand is used as fine aggregate to explore the mechanical properties of composite limestone powder concrete and the stress performance of composite limestone powder concrete laminate plate,and the main research contents are as follows:(1)The compressive resistance,splitting tensile resistance and flexural resistance tests were carried out on the test blocks of different ages of concrete of each formula,and the failure form and mechanical properties of composite limestone powder concrete test blocks made of different admixtures,different water-to-adhesive ratios and different fine aggregates were obtained.According to the experimental data,the relationship model between splitting tensile strength and compressive strength of composite limestone powder concrete was obtained,and the time-varying models of compressive strength,splitting tensile strength and flexural strength of composite limestone powder concrete were fitted.(2)Through the two-point symmetrical static loading test,the crack development status and failure form of the composite limestone powder concrete laminate plate with different formulas after bending were obtained,and the load-rebar strain curve,crossconcrete strain curve and load-cross-medium deflection curve of each test piece plate were drawn.The test data of composite concrete laminates with different formulations were co MPared,and it was found that the change of admixture had a significant effect on the cracking load of the slab,and had little effect on the ultimate bearing capacity of the slab.The cracking and ultimate loads of cast-in-place plates using mechanismtailings mixed sand as fine aggregates are similar to those of cast-in-place plates using natural sand.Comparing the bearing capacity values of the laminated plate and the castin-place plate,it is found that the laminated plate can effectively improve the ultimate bearing capacity of the plate.(3)The finite element software was used to numerically simulate the bending performance of the composite limestone powder concrete laminate,and the results of the simulated load-deflection curve,the longitudinal stress steel bar strain and the ultimate bearing capacity at the bottom of the plate were compared with the test results.After analysis,the simulation results are close to the test results,which shows that the constitutive model,boundary conditions and parameters used in the simulation have good applicability to the finite element calculation of composite limestone powder concrete laminates,and on this basis,the finite element software is used to further analyze the effects of truss steel height,truss steel bar length and plate thickness on the bending properties of composite limestone powder concrete laminates.(4)Using the formulas in the current specification,the cracking load,ultimate bearing capacity,and stiffness of the test plates are calculated,and the theoretical values are compared with the obtained test values.The measured cracking load is slightly lower than the theoretical calculation value,and a reduction factor of 0.88 is proposed on the basis of the current specification.The ultimate bearing capacity test value is higher than the theoretical value,and there is a certain safety reserve,the ultimate bearing capacity of composite limestone powder concrete laminate and cast-in-place plate can be calculated by the formula in the "Code for the Design of Concrete Structures".For laminates,considering the contribution of truss reinforcement rebar to stiffness,the stiffness is corrected on the basis of the formula used in the current specification,and the calculated result of the revised formula is close to the test value.