Research On Basic Performance Of Medium And High Strength Composite Fly Ash-Slag-Tailing Mixed Sand Concrete

In recent years,mineral admixtures and new fine aggregate have gradually become important components of commercial concrete.Adding fly ash,slag,machine-made sand and tailings fine sand into concrete can not only improve the performance of concrete,but also conform to the concept of sustainable development.In this thesis,the influence of fly ash,slag and tailings mixed sand on the workability,mechanical properties and durability of medium and high strength concrete with water binder ratio of 0.33,0.28 and 0.25 is studied by physical test and theoretical analysis.The concrete samples of three strength grades are tested by rebound method,core drilling method,ultrasonic method and ultrasonic rebound comprehensive method The applicability of the four detection methods in the strength detection of medium and high strength concrete is verified by experiments.The main conclusions and innovative achievements are as follows:1.Reveal the factors affecting the workability of the medium and high strength composite fly ash-slag-tailing mixed sand concrete.The concrete mixture prepared according to the optimally designed formula has good workability and basically meets the requirements of pumping concrete;single-mixed fly ash concrete has better fluidity than single-mixed slag concrete,and its water retention and cohesion The performance is also better than that of single-mixed slag concrete;the early activity of slag is higher than that of fly ash,the hydration is faster,and the water retention of slag is poor,which makes the slump loss of slag concrete larger;the beads of fly ash and slag The combined effect of the morphological effect of grain-like particles and the filling effect of micro-aggregates can improve the workability of the concrete mixture.2.Reveal the evolution law of the compressive strength of the medium and high strength composite fly ash-slag-tailing mixed sand concrete,and establish a prediction model of the compressive strength of the standard cube over time.The compressive strength,core sample compressive strength,resilience value and sound velocity value of the concrete standard cube gradually increase with the development of age under natural curing.The increase is faster before the 28d age and slower after the 28d age;water The glue ratio is a decisive factor affecting the strength of concrete,and standard curing is obviously better than natural curing;the standard cubic compressive strength,core compressive strength and resilience value of double-mixed fly ash-slag concrete are greater than those of single-mixed fly ash For ash or slag concrete,in the later period of curing,the active effect of fly ash makes the increase of the strength of single-mixed fly ash concrete increase;the way of mixing mineral admixtures has no significant influence on the sound velocity value of concrete;the mathematical model f_cu^c=Aln d_t+B is used to establish the relationship between the standard cube compressive strength and curing age of medium high strength concrete under natural curing,and the fitting degree is high.3.Reveal the deterioration law of the durability of medium and high strength composite fly ash-slag-tailing mixed sand concrete.The continued progress of the test will aggravate the damage of concrete in various corrosive environments until the concrete completely loses its resistance;the durability of concrete is negatively related to the water-to-binder ratio,and reducing the water-to-binder ratio can effectively improve the anti-carbonization and resistance of concrete.Freeze-thaw performance and sulfate corrosion resistance;fly ash and slag mainly play the micro-aggregate filling effect and pozzolanic effect in hardened concrete.The slag maintains and improves the durability of concrete better than fly ash,fly ash and The micro-aggregate filling effect and"hydration superposition"effect brought by the double mixing of slag can greatly improve the durability of concrete;The mathematical model d_m^c=αt^λ is used to establish the prediction model of carbonation depth of medium and high strength concrete under accelerated carbonation and natural carbonation,and the fitting degree is high.4.Obtain the strength measurement model of the four detection methods of rebound method,core drilling method,ultrasonic method and ultrasonic rebound comprehensive method to detect the compressive strength of high-strength concrete.Statistical methods are used to analyze the degree of fit,hypothesis test and error accuracy analysis of the strength measurement model.The results show that the correlation and accuracy of the rebound method,core drilling method,and ultrasonic rebound comprehensive method are all ideal,which is suitable for medium and high strength.In the field strength test of concrete,the correlation coefficient of the high-strength concrete strength test model in the ultrasonic method is small,and the degree of fitting is low,indicating that it is not accurate to evaluate the strength of concrete based on the sound velocity value.5.Establish the relationship model between carbonation depth and mass loss rate,relative dynamic modulus of elasticity,corrosion resistance coefficient and chloride ion migration coefficient.Statistical method was used to analyze the fitting degree and error precision of the relationship model.The results show that the correlation coefficient of each relationship model is close to 1,the fitting degree is high,and the accuracy is ideal,which provides a certain reference for concrete life prediction based on carbonation depth.6.The optimal mixing ratio of machine-made sand and extra-fine tailings sand in this test is 7:3.The tailings mixed sand with good grading effect can be obtained by mixing the machine-made sand with the extra fine tailings sand according to this mixing ratio.The concrete prepared with the tailings mixed sand as fine aggregate has relatively close working performance,mechanical performance and durability to that of natural sand concrete.This thesis has 72 pictures,43 tables and 108 references.