Research On Influence Mechanism Of Strength Development Of Fast-strength Concrete

Under the trend of building industrialization,the factory production of prefabricated components is the most important link in the development process.Steam curing is the most widely used method to promote the rapid development of concrete strength,which can improve the strength of concrete in a short time,and meet the requirements of concrete formwork removal and hoisting.In the prefabrication plant,the concrete is generally steam cured for 8 hours(two shifts a day),and then the formwork is removed and hoisted to the storage yard.However,the strength required for concrete formwork removal and lifting is far from the design strength,and the concrete is exposed to the natural environment after steam curing,the internal moisture is evaporated and the hydration process is terminated,which makes it difficult for the later strength to continue to develop.Therefore,it is difficult to achieve the design strength of concrete in a short time only by steam curing process,which restricts the application of prefabricated components in prefabricated buildings.In this paper,by adding active silicon material as fast strength agent,improve the preparation process and maintenance system,prepare fast strength and good workability of concrete.By means of theoretical research and microscopic analysis,the relationship between the type and content of reactive silicon,the composition of mineral admixtures,and the curing system and the development of concrete strength is studied.The dynamic characteristics of the effect of reactive silicon on the strength of concrete in advanced age are analyzed,and the influence mechanism of rapid water loss on the micro environment and microstructure of concrete in the process of steam curing is explored.We have done exploratory and innovative work in the following aspectsUnder the condition of steam curing,the compressive strength of 8h can be greatly improved by adding active silicon,and the effect is most obvious at 2h and 4h.In the case of low content of reactive silicon,silica sol has the best effect on improving the compressive strength of ordinary concrete.When the content of liquid sodium silicate is 2.5%,the improvement effect and economic benefit of concrete strength are the best.Silica fume has the most obvious effect on improving the compressive strength of quick strength concrete,and the dosage should not exceed 20%.Adding silica sol is the most disadvantageous to the performance of concrete,followed by liquid sodium silicate.The addition of solid sodium silicate has no effect on the workability of concrete.The order of adding solid sodium silicate has no effect on the workability of concrete,and the later adding liquid sodium silicate and silica sol has better workability.Adding liquid sodium silicate and silica sol first will make the steric hindrance effect of polycarboxylate superplasticizer invalid,which makes it difficult for polycarboxylate superplasticizer to play its role and the concrete performance is poor.Active silicon consumes Ca(OH)2 content and reacts to form continuous chain C-S-H gel.These chain structures interweave into mesh structure,fill the gap between cement,and form a C-S-H gel with cement particles to form a structural bond.(2)Mechanism of curing methods on the strength development of fast-strength concreteThe higher the steam curing temperature is,the greater the increase range of compressive strength is;the compressive strength of quick strength concrete still has a large growth space in 8h-48 h,and it slows down in 48h-72 h.The higher the temperature is,the steeper the curve is.The lower the temperature is,the slower the heat release curve is.Adding active silicon material can advance the time when the heat release reaches the maximum curvature of the curve,and the higher the temperature is,the more obvious the effect is.Adding active silicon can accelerate the hydration process of cement and increase the hydration heat release rate of cement.The most suitable curing method for quick strength concrete after steam curing is standard curing,and the least recommended curing method is natural curing.It is suitable for natural curing and soaking curing,The result of quadratic function fitting is better.(3)Influence mechanism of steam curing environment on water vapor balance and strength development of fast strength concreteThe water vapor transformation inside and outside the concrete depends on the AH value of the surrounding atmosphere,not the RH value.The RH recorded by the embedded probe is always kept at 100%,regardless of the RH and temperature changes of the external atmosphere.The RH in the cavity gradually decreases with time,and finally tends to a stable value.The higher the external RH,the higher the stable value.With the change of relative humidity,the pore water saturation presents a "S" shape.The larger the environmental RH is,the higher the pore water saturation is.For the same RH,the pore water saturation decreases with the increase of external temperature.Moreover,the response of pore water saturation to high temperature is more intense,and the decline range is larger.The rapid water loss during steam curing has a serious impact on the internal pores and microenvironment of fast strength concrete,resulting in the decrease of compressive strength.The rapid loss of water in the early stage of steam curing may lead to the shrinkage of concave liquid surface,which will connect with the air bubbles in concrete and develop into irreversible micro cracks.With the increase of time,the cracks extend and expand,resulting in the decrease of compressive strength.