Experimental Study On Sea Sand And Basalt Fiber Ultra High Stength Concrete

Ultra-high-strength concrete has the characteristics of high strength,good durability and more economic efficiency,and gradually meets the requirements of the new era for mid-to-high-rise,large-span,and light weight.Therefore,research on ultra-high-strength concrete is of great significance.However,the use of untreated sea sand to prepare ultra-high-strength concrete contains impurities such as shells,which will affect the ultra-high strength of mechanical properties and later durability.Due to the high cost of desalinated sea sand,it is necessary to consider how to reasonably use undisturbed sea sand to prepare sea sand ultra-high-strength concrete with excellent durability.Based on the excellent mechanical and durability characteristics of Ultra-High Performance Concrete（UHPC）,this paper researches the 100MPa-level sea sand ultra-high strength concrete mix ratio and guarantees excellent durability to realize the safe use of undisturbed sea sand.On the basis of the optimal mix ratio,through micro-experiment XRD and SEM,research the hydration process of different highly active mineral admixtures,qualitatively analyze the curing of free chloride ion and the transition zone of ultra-high strength concrete interface,so as to improve the strength development mechanism of ultra-high-strength concrete at the micro level,the main conclusions are as follows:（1）Using the method of"ordinary Portland Cement+highly active mineral admixture+polycarboxylate high-performance water-reducing agent"and remove coarse aggregate,it is possible to prepare ultra-high-strength concrete with 28d compressive strength,flexural strength of 115MPa、15.8MPa,and fluidity of 220mm.（2）Based on the orthogonal test research,the optimal mix ratio of sea sand basalt fiber ultra-high strength concrete is Cement:Water Slag powder:Micro silica fume:Sea sand:Water:Water reducing agent=0.7:0.2:0.1:1.0:0.16:0.03,basalt fiber is 0.15%by volume.（3）The compressive strength and flexural strength of the sea sand ultra-high-strength concrete cured by hot water at 70℃are 48.8%and 17%higher than that of the standard 7-day curing.However,the compressive and flexural strengths of 28 days after thermo-cultivation were reduced by 5.7%and 8.1%,compared with those of 7-day thermo-cultivation.The phenomenon of mechanical strength"reversed"appeared.（4）The sea sand ultra-high-strength concrete has excellent durability,the a nti-chloride ion penetration grade is the highest Q-V level and the frost resista nce>F500,and the test results meet the《reactive powder concrete》（GB/T31387-2015）anti-chloride ion penetration and frost resistance Performance requirem ents.（5）The XRD and SEM results show that after hot water curing,the mineral powder can consume a large amount of Ca（OH）₂produced by cement hydration to undergo a secondary reaction（pozzolanic reaction）to generate a large amount of C-S-H gel,making the structure more compact,There is no obvious transition interface zone,so that the early strength of concrete is increased sharply.A large amount of C-S-H gel and part of Friedel’Salt are generated inside the concrete.The physical adsorption and chemical combination of the C-S-H gel are used to effectively solidify free chloride ions in the concrete.