Study On The Preparation And Properties Of The Non-autoclaved Ultra-high-strength Concrete

Ultra-high-strength concrete is important material for engineering structures,with the advancement of construction industrialization its demand is increasing.The production of ultra-high-strength concrete is dominated by autoclaved curing,but the production process has some disadvantages such as serious pollution and high energy consumption.At present,it is difficult to optimize the mix design and curing system of ultra-high strength concrete in its production and application.This article aims to prepare ultra-high-strength concrete with stable performance development and environmental and efficient production system,and the effect of concrete mix design and curing system on concrete performance are studied.In this paper,525 cement mixed with silica fume,fly ash and mineral powder are used as cementing materials,and pebble and machine-made sand are used as aggregates.The Fuller curve and Dinger-Funk tight packing theory are used to design the mix ratio of ultra-high-strength concrete to study different combinations Compare the workability and mechanical properties of concrete to determine the optimal mix ratio;on this basis,the influence of different curing systems on the strength and durability of ultra-high-strength concrete is discussed,combined with tests such as heat of hydration,XRD,SEM,MIP,etc.The research method is to study the hydration process and micro-morphology of concrete,and conduct a preliminary analysis of the micro-mechanism of the strength development law under different curing systems;after designing the preparation process of autoclaved ultra-high-strength concrete,the equivalent age method is used to analyze the early concrete Compressive strength is predicted.The main results obtained are as follows:(1)Using Fuller curve and Dinger-Funk formula to optimize the mix ratio of ultra-high-strength concrete,it can significantly improve the working performance,compactness and mechanical properties of the concrete.When optimized design mixes,the highest compressive strength of 28 d increased by 21.2%compared to the unscreened aggregate concrete.The optimal mix ratio of the designed concrete is:cement dosage 360kg/m~3,mineral admixture dosage 240 kg/m~3,water-binder ratio 0.22,sand ratio 40.2%.(2)The compressive strength of concrete after natural curing in summer and steam curing at 35℃ for 3 days are relatively high and develop steadily,reaching 105.8 MPa and 107.9 MPa respectively in 28 days.60℃ steam curing can greatly increase the early strength of concrete,but the hydration process of concrete slows down after the curing,and the strength shrinks easily.After 7 days of autoclaved curing,the compressive strength of concrete hardly develops.(3)Through the analysis of hydration products,pore structure and micro-morphology,it is concluded that the early hydration of concrete under high temperature curing causes uneven distribution of hydration products in the slurry,deterioration of the pore structure,and insufficient hydration in the later stage,which leads to the development of concrete strength slowly.When the concrete is cured at 60℃ for 3 days,a large amount of delayed ettringite will be produced internally,which will destroy the later concrete structure and cause the concrete strength to shrink.(4)The equivalent age formula after the correction coefficient can accurately predict the early compressive strength of ultra-high-strength concrete cured by 35℃ steam,and can predict its early strength based on the concrete compressive strength curve at the reference temperature.Excessive silica fume content,60℃ steam curing and other factors will change the hydration and hydration process of the cementitious material,which will affect the accuracy of the equivalent age method to predict the early strength of concrete.In the preparation process of ultra-high strength concrete,the use of ultra-early strength agent and the use of natural laminating curing in summer or the use of 35℃ wet and hot curing in winter can meet the demolding requirements of pipe pile concrete products,which provides theoretical reference for the energy saving production of ultra-high strength concrete.