Study On The Basic Performance Of Composite Fly Ash-Slag-Mixed Sand Commercial Concrete

While the concrete industry is developing towards commercial concrete,industrial by-products such as fly ash and slag are widely used as auxiliary cementing materials to improve the performance of concrete,new fine aggregates such as machine-made sand and extra-fine sand came into being under the condition of shortage of natural sand resources.In this paper,through the combination of physical test research,numerical calculation and theoretical analysis,the working life,mechanical properties and durability of commercial concrete poured from the common proportions and raw materials of Xuzhou area are analyzed for full life reliability.In response to the requirements of the sustainable development of the concrete industry,study the application of commonly used non-destructive testing technology on concrete specimens,and indirectly provide references for practical projects.The main conclusions and innovations are as follows:1.Working performance of composite fly ash-slag—mixed sand commercial concrete.In terms of the slump loss rate of concrete,the smaller the water-binder ratio,the greater the slump loss rate.The different mineral composition of cement,the hydration performance of cement is different,and the content of C₃A and C₄AF in minerals in cement is the main factor affecting the slump loss of concrete.Fly ash and slag mainly play the morphological effect and micro-aggregate filling effect in the initial stage of concrete mixture formation.Machine sand and extra fine sand mixed in appropriate ratio can play a good gradation effect similar to natural sand.2.Compressive strength of composite fly ash-slag—mixed sand commercial concrete.The compressive strength of concrete cubes gradually increases with age in natural curing,and the strength increases fastest during 7day to 14day,and the concrete strength growth rate gradually decreases after 60day;the smaller the water-binder ratio,the stronger the concrete,the higher the development level.The strength increase of concrete under standard curing is obviously better than that of natural curing.The volcanic ash effect and micro-aggregate interface effect exerted by fly ash and slag are worthy of recognition for the feasibility of later strength development of concrete.Machine-made sand and extra fine Mixing sand in appropriate proportions can play the same physical role as natural sand The mathematical model is used to establish the relationship among concrete compressive strength,temperature and age under natural curing,with a high degree of fitting.Under the model,the measured compressive strength of each strength grade concrete increases with age,and the compressive strength of high-strength grade concrete responds more significantly to temperature changes.3.Durability of composite fly ash-slag—mixed sand commercial concrete.Under the condition that the total material is fixed,reducing the water-binder ratio can slow down the progress of the carbonization process.Under the condition that the cement type is determined,the greater the volume of cement per unit volume,the smaller the concrete carbonization rate;reducing the water-binder ratio can improve the freezing resistance of commercial concrete;reducing the water-binder ratio and optimizing the mineral composition of cement clinker can effectively improve the sulfate resistance of concrete.The effects of fly ash and slag on the durability of concrete are mainly divided into micro-aggregate filling effect and active effect.As an auxiliary cementing material,it reduces the carbonation resistance of concrete,improves the freeze-thaw resistance of concrete,and enhances the performance of concrete against sulfate erosion.The development of the test cycle will aggravate the destruction of concrete in various erosive environments until it completely loses its resistance.4.Nondestructive testing of the compressive strength of composite fly ash-slag—mixed sand commercial concrete.The smaller the water-binder ratio of concrete,the higher the corresponding rebound value and the greater the sound velocity value;the rebound value and sound velocity value of concrete under standard curing are significantly higher than the corresponding value of concrete under natural curing;The influence mechanism of fly ash and slag on the change of rebound value and sound velocity value is similar to that of strength development.There is a positive correlation between the strength of concrete and the rebound value,but the rebound value does not fully represent and evaluate the actual strength of concrete;The sound velocity value is not sensitive enough to the response of the strength change.It is not true to use the sound velocity value to reflect and evaluate the concrete strength;The national unified strength curve does not apply to the rebound method and the ultrasonic rebound method in Xuzhou area to detect the compressive strength of concrete.The strength curve in line with local conditions should be supplemented and improved.5.Economic benefit analysis of composite fly ash-slag—mixed sand commercial concrete.Through market research and evaluation of the economic benefits of commercial concrete in the common proportions in Xuzhou,explore the feasible measures for maximizing the benefits of commercial concrete production and application.Adjusting the strength level of cement,promoting and applying fly ash and slag,machine-made sand and extra-fine sand can all drive the development of economic benefits of commercial concrete.There are 49 figures,42 tables and 118 references in this paper.