Project application of the high-performance concrete of fly ash 原文 要PDF格式的要找的是PDF格式可以下载的原文

Project application of the high-performance concrete of fly ash 原文 要PDF格式的要找的是PDF格式可以下载的原文
Project application of the high-performance concrete of fly ash 原文 要PDF格式的
要找的是PDF格式可以下载的原文

Project application of the high-performance concrete of fly ash 原文 要PDF格式的要找的是PDF格式可以下载的原文
[The summary ]
Every performance of this text to high-performance concrete of fly ash has done detailed research, and to the concrete respectively to person who mix of fly ash Kinds of influence of performance and fly ash concrete some questions that should notice carry on analysis and discussion in not constructing.
1. Summary
Fly ash, as a kind of industrial waste material, resources are abundant , cheap, and contain a large amount of active composition , it is modern concrete Central Africa A often important component part . The high-quality fly ash is applied to the concrete rationally , not only can replace the cement partly , save the fabrication cost of the project, And, its peculiar performance can be used in the concrete of various kinds of instructions for use very effectively, improve the performance of the concrete, It is the ideal in the high-performance concrete that admixes the material . Among it is at concrete not modern, whose name is already with cement in fly ash, collect material , water , admixture and Kind is important, become a component part in concrete. Fly ash high-performance concrete regard durability as main goal go on design mix Congeal the soil . It regards excellent durability (instead of the high strength) as the main characteristic , that is to say, concrete capital of any grade of intensity Can make into the high durability concrete . In order to reach high durability, the performance that the fly ash concrete should possess is: Mixing the state newly well Work,namely, without emanating, secreting by water, so that shaping the even , closely knit by mobility, harden not shrinking subsiding early water and Water shrink light, warm to rise low, harden course is it dwindle to do, in order to reach having the initial crack, the permeability after hardenning is low.
2． " function " and " effect " of the fly ash are fly ash material technology and application foundation of the project.
Mix and add the powder of the concrete Coal ash, in conformity with understanding that the function of the fly ash is made overallly, by " volcanic ash react " and " economic component part" general to fly ash originally Read , expand technological consciousness of " fly ash effect " to , make fly ash function can serve performance of concrete improve with quality raising better. The role in concrete of fly ash has the following several points:
(1) . Shape effect: It is spongy vitreous body , little pearl of silicate glass of aluminium that the main mineral of the fly ash makes up , smooth the body surface of these spherical glass, the grain size is thin, the quality is pre-pressing, inside smaller than the surface area, the strength of absorbing to water is small, this line of physical characteristics, reduce concrete rub obstruction inside , favorable to improvement , concrete of mobility not merely; And, have " reducing water " function in various degree on the concrete;
(2) . Active effect: The active composition SiO2 of the fly ash and water result of AI2O3 and cement react in a situation that there is water, producing water silicic acid calcium (C-S-H ) and water sour calcium (C-A-S-H ) of sulphur aluminium, these responses nearly all go on in the grout hole, water that produce result pack , cut apart the heavy original hole , make the hole thinning, can reduce the hole rate within the concrete , change the hole structure , improve glueing the function of forming of concrete every component part ;
3) . Collect the material effect a little: Very small particle of fly ash even to is it among cement particle , pack the hole to distribute, play a role in getting to " thinning hole " , meanwhile , prevent glueing gathering each other of the cement particle, and make it in state of dispersing , help water of the mixture to react, the fly ash will not be totally with reacting with water result of the cement, can keep its " collecting the material effect a little " for a long time ;
(4) . Effect of the interface: It is the weak link in the concrete structure to collect the interface between the material and cement stone, width of transition area as water for dust than, collect there aren’t material , transition area have than grout body more, heavy hole. Mixing can reduce the regional width of the transition to add the fly ash , interfere Ca (OH ) orientation of 2 crystal in the transition area, improve the intensity of interface and density in the concrete.
(5) Performance of the fly ash concrete The change of the fly ash to concrete performance can be divided into three stages: 1 . Mix concrete stage newly: Influence the coagulation time of the concrete , is improving and easy , change rheology nature , can improve pump ,etc.;
(6) . The concrete stage while hardenning: Regulate the course of hardenning, reduce the heat of hydration; 3 . The concrete stage after hardenning: Raise the intensity on later stage , raise every durability, such as anti-permeability, resist the sulphate corroding, suppress the alkali - Collect the material and react etc..
3.1 Intensity
The fly ash has three kinds of influence on the intensity of concrete: Reduce water consumption , increase glued material content and reflect through the long-term volcanic ash that raises his intensity. The particle in the fly ash of low calcium is the silicon oxygen tetrahedron structure, one’s own activation is very low. In the final result of the cement, high alkaline water silicic acid calcium and crystallization of 2 colloid of Ca (OH ) are very low in intensity, especially Ca (OH) 2 ask vigorous to come 1-2% , stone of intensity only, but Ca (OH) 2 volume account for whole cement 25% , stone of volume. A large number of silicon , aluminium oxide that contain in the fly ash, can and high alkaline water silicic acid calcium 2 responses take place with Ca (OH ) 2 progressively, produce intensity than high low alkaline water silicic acid calcium , so , make cement stone water glue congeal quantity of material increase, and make its quality improved by a large margin , is favorable to the improvement of the intensity of concrete. Meanwhile, to is it can disperse cement particle to mix fly ash, make cement to be ink sufficient, improve closely knit degree of the grout , make the intensity of the interfaces of the aggregate and grout in the concrete improve. Fly ash is it draw intensity compare with contribution of the bending strength compression strength to be heavy to confront with each other, this is useful to resisting the performance of splitting of concrete. The elastic mould amount of the fly ash concrete is similar to compression strength, it is early and on the low side, improve progressively later stage , get 28d the constant basic concrete is raised by 5-10%. With to hold strength of wrapping up in reinforcing bar, 28d , fly ash of concrete is it form intensity the same with ,etc. basic concrete of grade basically to glue, but homogeneity, fly ash of concrete fine, is it form intensity person who test getting dispersed and kind than basic concrete to glue.
Water two times of the fly ash reacts and generally starts after the concrete builds 14d, when temperature is low , will reflect necessary time is longer. If strict with early intensity of the concrete, the mixing amount of the fly ash is unsuitable to exceed 30%, winter construction large volume at the concrete, the mixing amount of the fly ash is unsuitable to exceed 20% non-. Because modern concrete China and foreign countries add use of pharmaceutical, on one hand, reducible concrete mix and stir water consumption, it reduce by dust water than,of not lasting concrete density of cement; On the other hand, water-reducing agent can make cement silicic acid calcium ink Ca (OH ) produced 2 increase, help fly ash and water two times of 2 of Ca (OH ) to reflect , excites the activation of the fly ash, this effectual for early intensity to improve fly ash, in addition use fly ash activation excite pharmaceutical or in large volume use strong cement early among the concrete non-, can compensate mixing the impact on early intensity of concrete of fly ash too.
3.2 and easy
Whether fly ash there are the following several points to concrete and getting easy improvement function. ⑴.The high-quality fly ash contains more than 70% of the spherical vitreous bodies, too smooth to have raised angle the body surface of these spherical glass, performance is steady, play a kind of lubricated function which is similar to the bearing in the pump sending , shaking the course of smashing of the concrete; ⑵.Mix particle apt to gather group cement in the concrete newly, to is it can disperse cement particle effectively to mix fly ash, release more thick liquid body is it lubricate aggregate to come , help concrete work the improvement of performance ; ⑶.Mix fly ash can compensate detailed deficiency of bits in the detailed aggregate , cut off mortar base body secrete continuity , water of channel, the fly ash that at the same time quality is good can reduce the mixing water consumption of the concrete under the same consistency, make water dust of concrete than reduce light level to , is it secrete ink and emanate the phenomenon to reduce.
3.3 shrinking
The shrink of the concrete relates to the fact that the mixing water consumption and thick liquid body body of the concrete are accumulated, the less water consumption is, shrink the smaller. High-quality fly ash water requirement than smaller than 100% , mix and stir reduction , water of quantity make mix fly ash concrete after the 28d since dry to shrink and not dry to shrink little. Fly ash concrete is it is it mix with fly ash improvement of quantity reduce too to contract to do. But because water , fly ash of concrete reponse slowly, moisture evaporate fast, so between fly ash and to do epitome to be loud and very much heavy in early days concrete. For prevent early shrink , fly ash of concrete from fracture , should strengthen in early days raising to it
3.4 creeps
Issue in the past will it be age one day, intensity of concrete relatively low, issue is it it meets an emergency to be heavy than ordinary concrete too to creep corresponding age, but with ordinary concrete fly ash in one age one creep and was smaller than the ordinary concrete after this concrete of intensity.
3.5 carbonization performance
Fly ash concrete resist carbonization to be performance relatively poor. Cement consumption , fly ash of concrete reduce, cement water Ca (OH ) 2 too corresponding to reduce quantity that appear, and volcanic ash is it consume Ca (OH ) 2 of a certain amount too to react, make hydrogen ion index of the concrete reduce, will increase the speed of carbonization of the concrete. Unless especially at water in early days, fly ash the low in degree in response in volcanic ash,fly ash- there is the loose in structure in hole in system cement, CO2 , O2 , moisture ,etc. invade obstruction small, so carbonization is relatively large in depth. With the growth of one and gradual full play of the fly ash volcanic ash effect of age, the speed of carbonization will be reduced gradually. Carbonization , fly ash of concrete as water for dust in depth than and fly ash last increase of quantity and not increased to some extent. Than 0.5-0.55 in water dust, fly ash person who mix greater than 30% and under the general construction situation of competence, the depth of carbonization of the concrete can reach about 20mm in 15-17. Carbonization reacts and goes on within the range of certain relative humidity fastest, otherwise, the response is relatively slow. Under or is close to 100% 25% in the relative humidity, namely the occasion in the abundant dryness or water saturation of concrete, have more difficult to produce carbonization shrink concretes. In such concrete projects not contacted with the atmosphere as the foundation works ,etc., because of isolating with CO2, can take place carbonization react , so can mix and add the fly ash more , in order to fully reduce the heat of hydration of the concrete, improve the durability of the concrete. It is ultra to be adopt law quantity replace,water glue not lower than,mix carry on match ratio design water-reducing agent for admixture of main fact at the same time, can make fly ash concrete resist carbonization performance improve to some extent.
3.6 reinforcing bar corrosion
Reinforcing bar of concrete can it antirusts to be because concrete getting alkaline to form one pre-pressing passivation membrane in metal surface. Is it add fly ash to mix among concrete, on one hand it consume Ca (OH ) 2, reduce the alkali environment of the concrete; On the other hand, fly ash 2 responses turn into the hyrate with Ca (OH), raise closely knit degree of the concrete, increase the impermeability of the concrete and obstruction spread to the chlorine ion, hinder and prevent the invasion of CO2, can shield the reinforcing bar , so fly ash is mixed, in preventing the reinforcing bar corrosion, can offset because alkali degree reduce adverse effect that bring. The fly ash is on certain range (FA≤ 24% ) of mixing amount, have not influenced the reinforcing bar corrosion basically, even superior to the blank concrete. But if the mixing amount of the fly ash is greater than 30%, the carbonization of the concrete can make hydrogen ion index of the concrete dropped to about 8.5 from 12.5 , under so low a hydrogen ion index condition, the reinforcing bar is no longer passivated. Reach reinforcing bar position by depth as carbonization, complete carbonization , on terms that water and oxygen are permeated antiabrasion layer, reinforcing bar can take place but corrosion lead to the fact fracture of the concrete even destroy.
3.7 heat of hydration
The fly ash is very obvious to reducing the function of the concrete heat of hydration. Low calcium fly ash water in the first several days obvious degree have, heat of hydration produced only and half of cement. Replace 20% of the cement with fly ash in the concrete , can make the heat of hydration of concrete 7d drop by 11% . 1-28d in the issue, roughly for mix percentage of fly ash, Sheng Wen and percentage that heat of hydration reduce age. Fly ash is it can make heat of hydration time that peak appear is it appear to 3d to delay generally to mix among large volume concrete, can prevent the concrete from producing the temperature crack effectively .
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