Study On Application Of Large Dosage Of Compound Mineral Admixtures In High Strength Concrete

The preparation of high-strength concrete usually takes low water-binder ratio and increasing cement dosage as the main technical route.Problems such as large viscosity of concrete mix,long inverted emptying time and slow strength growth in the later stage often occur in the production process.In addition,with the implementation of the “emission peak”and “carbon neutrality” policy,the work of energy conservation and emission reduction will be promoted accordingly.It is necessary to study low carbon with high quality performance.In order to high strength concrete achieve the requirement of “emission peak” and “carbon neutrality ” policy,effective control of cement dosage is the main path.Therefore,the development of high quality concrete with composite admixture to replace cement is particularly important.This is not only expected to solve various problems in the production of high strength concrete,but also to promote the low carbon development of high strength concrete.In this context,the research and development of high strength concrete compound mineral admixtures(without silica fume,contain silica fume),and different dosages(30%,40%,50%,60%)in C60,C70 and C80,C90 high strength concrete application as the main research content,to explore the large amount of compound mineral admixtures on the performance of high strength concrete.In the compound mineral admixtures(without silica fume,contain silica fume)system,the mixture ratio of ground slag powder,grade I fly ash,ground limestone powder and silica fume was first determined.Secondly,with the compound mineral admixtures content(30%,40%,50%,60%),different admixtures of desulfurized gypsum and different kinds of alkali activators as variables,the influence of different compound mineral admixtures on the performance of cement mortar was investigated through single factor test,and the best excitation method was determined.Finally,the influence of polycarboxylic acid water reducer on the compatibility of compound mineral admixtures and the properties of cement sand was investigated.In the compound mineral admixtures(without silica fume,contain silica fume),the type of without silica fume composite ratio is 70% ground slag powder,15%grade Ⅰ fly ash and 13% ground limestone powder.The type of contain silica fume compound ratio is 65% pulverized slag powder,15% grade Ⅰ fly ash,8% pulverized limestone powder,10% silica fume,and 2% desulfurized gypsum mix in compound mineral admixtures(without silica fume,contain silica fume).The performance test of the paste and mortar showed that polycarboxylic acid water reducer had good compatibility with the compound mineral admixtures,which greatly improved the fluidity of mortar and had almost no effect on the mechanical properties.With the increase of compound mineral admixtures(without silica fume,contain silica fume),the dosage of polycarboxylic acid water reducer gradually decreases,slump and expansion of high strength concrete gradually increase,the emptying time of inverted slump cylinder is obviously reduced,and the workability is significantly improved.For the high strength concrete of each strength grade,the hydration degree of cement in the early and middle stages is low under the dosage of 50% and 60% compound mineral admixtures,and the secondary hydration process is slow.Therefore,it shows that the strength of high strength concrete in the early and middle stages is lower than that of 30% and 40% compound mineral admixtures,but 60 d and 90 d can still meet the strength requirements of preparation.According to XRD of paste and SEM of high strength concrete at each age,the 60 d and 90 d secondary hydration of high strength concrete with 50% and 60% compound mineral admixtures is still in progress,which improves the compactness of concrete structure and greatly increases the strength.Therefore,the compressive strength increased greatly in the later period.Compared with the high-strength concrete containing 30% and 40% compound mineral admixtures(without silica fume,contain silica fume),the brittleness coefficient and shrinkage value of the concrete with 50% and 60% compound mineral admixtures are significantly reduced,and good durability can be maintained.Compared with the compound mineral admixtures currently being sold on the market,the compound mineral admixtures developed in this subject have more excellent performance in all aspects of high strength concrete.The compound mineral admixtures developed in this topic was put into production,and was used in practical engineering instead of 50% cement dosage in cementing materials.The results show that the compound mineral admixtures developed in this project can meet the engineering needs and bring benefits to enterprises and society.