混凝土工艺中英文对照外文翻译文献

混凝土工艺中英文对照外文翻译文献

混凝土工艺中英文对照外文翻译文献

混凝土工艺中英文对照外文翻译文献(文档含英文原文和中文翻译)

Concrete technology and development

Portland cement concrete has clearly emerged as the

material of choice for the construction of a large number and

variety of structures in the world today. This is attributed mainly

to low cost of materials and construction for concrete structures

as well as low cost of ore, it is not surprising

that many advancements in concrete technology have occurred

as a result of two driving forces, namely the speed of construction

and the durability of concrete.

During the period 1940-1970, the availability of high early

strength portland cements enabled the u of high water content

in concrete mixtures that were easy to handle. This approach,

however, led to rious problems with durability of structures,

especially tho subjected to vere environmental exposures.

With us lightweight concrete is a development mainly of the

last twenty years.

Concrete technology is the making of plentiful good

concrete cheaply. It includes the correct choice of the cement and

the water, and the right treatment of the aggregates. Tho which

are dug near by and therefore cheap, must be sized, washed free

of clay or silt, and recombined in the correct proportions so as to

make a cheap concrete which is workable at a low water/cement

ratio, thus easily comoacted to a high density and therefore

hardens with age and the process of hardening

continues for a long time after the concrete has attained

sufficient strength.

Abrams’law, perhaps the oldest law of concrete technology,

states that the strength of a concrete varies inverly with its

water cement ratio. This means that the sand content

(particularly the fine sand which needs much water) must be

reduced so far as possible. The fact that the sand “drinks” large

quantities of water can easily be established by mixing veral

batches of x kg of cement with y kg of stone and the same

amount of water but increasing amounts of sand. However if

there is no sand the concrete will be so stiff that it will be

unworkable thereforw porous and weak. The same will be true if

the sand is too coar. Therefore for each t of aggregates, the

correct mix must not be changed without good reason. This

applied particularly to the water content.

Any drinkable and many undrinkable waters can be ud for

making concrete, including most clear waters from the a or

rivers. It is important that clay should be kept out of the concrete.

The cement if fresh can usually be chon on the basis of the

maker’s certificates of tensile or crushing tests, but the are

always made with fresh cement. Where strength is important ,

and the cement at the site is old, it should be tested.

This stress , causing breakage,will be a tension since

concretes are from 9 to 11times as strong in compression as in

tension, This stress, the modulus of rupture, will be roughly

double the direct tensile breaking stress obtained in a tensile

testing machine,

so a very rough guess at the conpressive strength can be

made by multiplying the modulus of rupture by 4.5. The method

can be ud in combination with the strength results of machine-

crushed cubes or cylinders or tensile test pieces but cannot

otherwi be regarded as reliable. With the comparisons,

however, it is suitable for comparing concretes on the same site

made from the same aggregates and cement, with beams cast

and tested in the same way.

Extreme care is necessary for preparation,transport,plating

and finish of concrete in construction is important to

note that only a bit of care and supervision make a great

difference between good and bad following factors

may be kept in mind in concreting works.

Mixing

The mixing of ingredients shall be done in a mixer as

specified in the contract.

Handling and Conveying

The handling&conveying of concrete from the mixer to the

place of final deposit shall be done as rapidly as practicable and

without any objectionable paration or loss of

er the length of haul from the mixing plant

to the place of deposit is such that the concrete unduly compacts

or gregates,suitable agitators shall be installed in the

conveying concrete is being conveyed on chutes

or on belts,the free fall or drop shall be limited to 5ft.(or 150cm.)

unless otherwi concrete shall be placed in

position within 30 minutes of its removal from the mixer.

Placing Concrete

No concrete shall be placed until the place of deposit has

been thoroughly inspected and approved,all

reinforcement,inrts and embedded metal properly curity in

position and checked,and forms thoroughly wetted(expect in

freezing weather)or g shall be continued without

avoidable interruption while the ction is completed or

satisfactory construction joint made.

Within Forms

Concrete shall be systematically deposited in shallow layers

and at such rate as to maintain,until the completion of the unit,a

plastic surface approximately horizontal layer

shall be thoroughly compacted before placing the succeeding

layer.

Compacting

Method. Concrete shall be thoroughly compacted by means

of suitable tools during and immediately after

concrete shall be worked around all reinforcement,embedded

fixtures,and into the comers of the precaution shall

be taken to keep the reinforcement and embedded metal in

proper position and to prevent distortion.

Vibrating. Wherever practicable,concrete shall be internally

vibrated within the forms,or in the mass,in order to increa the

plasticity as to compact effectively to improve the surface texture

and appearance,and to facilitate placing of the concrete.

Vibration shall be continued the entire batch melts to a

uniform appearance and the surface just starts to glisten.A

minute film of cement paste shall be discernible between the

concrete and the form and around the

vibration causing gregation,unnecessary bleeding or

formation of laitance shall be avoided.

The effect spent on careful grading, mixing and compaction

of concrete will be largely wasted if the concrete is badly cured.

Curing means keeping the concretethoroughly damp for some

time, usually a week, until it has reached the desired strength. So

long as concrete is kept wet it will continue to gain strength,

though more slowly as it grows older.

Admixtures or additives to concrete are materials are

materials which are added to it or to the cement so as to improve

one or more of the properties of the concrete. The main types

are:

1. Accelerators of t or hardening,

2. Retarders of t or hardening,

3. Air-entraining agents, including frothing or foaming

agents,

4. Gassing agents,

5. Pozzolanas, blast-furnace slag cement, pulverized coal ash,

6. Inhibitors of the chemical reaction between cement and

aggregate, which might cau the aggregate to expand

7. Agents for damp-proofing a concrete or reducing its

permeability to water,

8. Workability agents, often called plasticizers,

9. Grouting agents and expanding cements.

Wherever possible, admixtures should be avouded,

particularly tho that are added on site. Small variations in the

quantity added may greatly affect the concrete properties in an

undesiraale way. An accelerator can often be avoided by using a

rapid-hardening cement or a richer mix with ordinary cement, or

for very rapid gain of strength, high-alumina cement, though this

is very much more expensive, in Britain about three times as

costly as ordinary Portland cement. But in twenty-four hours its

strength is equal to that reached with ordinary Portland cement

in thirty days.

A retarder may have to be ud in warm weather when a

large quantity of concrete has to be cast in one piece of formwork,

and it is important that the concrete cast early in the day does

not t before the last concrete. This occurs with bridges when

they are cast in place, and the formwork necessarily bends under

the heavy load of the wet concrete. Some retarders permanently

weaken the concrete and should not be ud without good

technical advice.

A somewhat similar effect,milder than that of retarders, is

obtained with low-heat cement. The may be sold by the

cement maker or mixed by the civil engineering contractor. They

give out less heat on tting and hardening, partly becau they

harden more slowly, and they are ud in large casts such as

gravity dams, where the concrete may take years to cool down to

the temperature of the surrounding air. In countries like Britain or

France, where pulverized coal is burnt in the power stations, the

ash, which is very fine, has been mixed with cement to reduce its

production of heat and its cost without reducing its long-term

strength. Up to about 20 per cent ash by weight of the cement

has been successfully ud, with considerable savings in cement

costs.

In countries where air-entraining cement cement can be

bought from the cement maker, no air-entraining agent needs to

be mixed in .When air-entraining agents draw into the wet

cement and concrete some 3-8 percent of air in the form of very

small bubbles, they plasticize the concrete, making it more easily

workable and therefore enable the water |cement ratio to be

reduced. They reduce the strength of the concrete slightly but so

little that in the United States their u is now standard practice

in road-building where heavy frost occur. They greatly improve

the frost resistance of the concrete.

Pozzolane is a volcanic ash found near the Italian town of

Puzzuoli, which is a natural cement. The name has been given to

all natural mineral cements, as well as to the ash from coal or the

slag from blast furnaces, both of which may become cements

when ground and mixed with water. Pozzolanas of either the

industrial or the mineral type are important to civil engineers

becau they have been added to oridinary Portland cement in

proportions up to about 20 percent without loss of strength in

the cement and with great savings in cement cost. Their main

interest is in large dams, where they may reduce the heat given

out by the cement during hardening. Some pozzolanas have

been known to prevent the action between cement and certain

aggregates which caus the aggregate to expand, and weaken

or burst the concrete.

The best way of waterproof a concrete is to reduce its

permeability by careful mix design and manufacture of the

concrete, with correct placing and tighr compaction in strong

formwork ar a low water|cement ratio. Even an air-entraining

agent can be ud becau the minute pores are discontinuous.

Slow, careful curing of the concrete improves the hydration of the

cement, which helps to block the capillary passages through the

concrete mass. An asphalt or other waterproofing means the

waterproofing of concrete by any method concerned with the

quality of the concrete but not by a waterproof skin.

Workability agents, water-reducing agents and plasticizers

are three names for the same thing, mentioned under air-

entraining agents. Their u can sometimes be avoided by

adding more cement or fine sand, or even water, but of cour

only with great care.

The rapid growth from 1945 onwards in the prestressing of

concrete shows that there was a real need for this high-quality

structural material. The quality must be high becau the worst

conditions of loading normally occur at the beginning of the life

of the member, at the transfer of stress from the steel to the

concrete. Failure is therefore more likely then than later, when the

concrete has become stronger and the stress in the steel has

decread becau of creep in the steel and concrete, and

shrinkage of the concrete. Faulty members are therefore

obrved and thrown out early, before they enter the structure,

or at least before it The main advantages of prestresd concrete

in comparison with reinforced concrete are :

①The whole concrete cross-ction resists load. In reinforced

concrete about half the ction, the cracked area below the

neutral axis, does no uful work. Working deflections are smaller.

②High working stress are possible. In reinforced concrete

they are not usually possible becau they result in vere

cracking which is always ugly and may be dangerous if it caus

rusting of the steel.

③Cracking is almost completely avoided in prestresd

concrete.

The main disadvantage of prestresd concrete is that much

more care is needed to make it than reinforced concrete and it is

therefore more expensive, but becau it is of higher quality less

of it needs to be needs to be ud. It can therefore happen that

a solution of a structural problem may be cheaper in prestresd

concrete than in reinforced concrete, and it does often happen

that a solution is possible with prestressing but impossible

without it.

Prestressing of the concrete means that it is placed under

compression before it carries any working load. This means that

the ction can be designed so that it takes no tension or very

little under the full design load. It therefore has theoretically no

cracks and in practice very few. The prestress is usually applied

by tensioning the steel before the concrete in which it is

embedded has hardened. After the concrete has hardened

enough to take the stress from the steel to the concrete. In a

bridge with abutments able to resist thrust, the prestress can be

applied without steel in the concrete. It is applied by jacks forcing

the bridge inwards from the abutments. This methods has the

advantage that the jacking force, or prestress, can be varied

during the life of the structure as required.

In the ten years from 1950 to 1960 prestresd concrete

cead to be an experinmental material and engineers won

confidence in its u. With this confidence came an increa in

the u of precast prestresd concrete particularly for long-span

floors or the decks of motorways. Whereever the quantity to be

made was large enough, for example in a motorway bridge 500

m kong , provided that most of the spans could be made the

same and not much longer than 18m, it became economical to

u

factory-precast prestresd beams, at least in industrial areas

near a precasting factory prestresd beams, at least in industrial

areas near a precasting factory. Most of the beams are heat-

cured so as to free the forms quickly for re-u.

In this period also, in the United States, precast prestresd

roof beams and floor beams were ud in many school buildings,

occasionally 32 m long or more. Such long beams over a single

span could not possibly be successful in reinforced concrete

unless they were cast on site becau they would have to be

much deeper and much heavier than prestresd concrete beams.

They would certainlly be less pleasing to the eye and often more

expensive than the prestresd concrete beams. The school

buildings have a strong, simple architectural appeal and will be a

pleasure to look at for many years.

The most important parts of a precast prestresd concrete

beam are the tendons and the concrete. The tendons, as the

name implies, are the cables, rods or wires of steel which are

under tension in the concrete.

Before the concrete has hardened (before transfer of stress),

the tendons are either unstresd (post-tensioned prestressing)

or are stresd and held by abutments outside the concrete ( pre-

tensioned prestressing). While the concrete is hardening it grips

each tendon more and more tightly by bond along its full length.

End anchorages consisting of plates or blocks are placed on the

ends of the tendons of post-tensioned prestresd units, and

such tendons are stresd up at the time of transfer, when the

concrete has hardened sufficiently. In the other type of

pretressing, with pre-tensioned tendons, the tendons are

relead from external abutments at the moment of transfer, and

act on the concrete through bond or archorage or both,

shortening it by compression, and themlves also shortening

and losing some tension.

Further shortening of the concrete (and therefore of the steel)

takes place with time. The concrete is said to creep. This means

that it shortens permanently under load and spreads the stress

more uniformly and thus more safely across its ction. Steel also

creeps, but rather less. The result of the two effects ( and of the

concrete shrinking when it dries ) is that prestresd concrete

beams are never more highly stresd than at the moment of

transfer.

The factory precasting of long prestresd concrete beams is

likely to become more and more popular in the future, but one

difficulty will be road transport. As the length of the beam

increas, the lorry becomes less and less manoeuvrable until

eventually the only suitable time for it to travel is in the middle

of the night when traffic in the district and the route, whether the

roads are straight or curved. Precasting at the site avoids the

difficulties; it may be expensive, but it has often been ud for

large bridge beams.

混凝土工艺及发展

波特兰水泥混凝土在当今世界已成为建造数量繁多、种类复杂结

构的首选材料。这主要归功于混凝土结构的材料和施工成本以及维修

费用低。因此,随着技

术的不断提高在施工速度和混凝土耐久性两个方面取得突破已不

足为奇。

1940至1970年期间,提高高强硅酸盐水泥混凝土混合物中的含水

量从而使混凝土易于搬运和处理的方法被广为使用。然而，这种做法

却对结构的耐久性产生很大的影响，特别是那些处于恶劣环境中的结

构。

对于我们来说，轻质混凝土主要是最近二十年来发展起来的。

混凝土工艺就是便宜地制备大量优质混凝土的过程，包括正确选

是针对于用水量。

任何可饮用水和一些非饮用水都可用以配制混凝土，包括大部分

取自海或河流的清洁水。在混凝土中清除粘土是很重要的。水泥如果

是新制成的，通常可根据制造厂的拉伸或压碎实验证明书来选用，但

是这种实验经常是用新制成的水泥来做的。在强度极为重要的情况下，

水泥在工地上存放过久时，水泥必须经过试验。

由于混凝土的抗压强度为其抗拉强度的9到11倍，引起断折的应

力是拉应力。此应力即断裂模量，大约为拉伸试验机所得直接拉伸断

裂应力值的两倍。因此将弯折强度乘以4.5，可粗略地估计出抗压强度。

此方法可同机械压碎立方体或圆柱体或拉伸试件等的强度试验结果配

合使用，否则，这种方法就适宜于用梁对各种混凝土进行比较，梁是

以同样同样方式浇制和试验的，而混凝土是在同一工地上由同样的骨

料和水泥配制的。

施工过程中必须要特别注意混凝土的准备、运输、浇筑及浇筑完

成等工作。稍许的留意和监督就会使混凝土质量的好坏产生很大的差

异，注意到这一点很重要。混凝土施工中，以下因素应当谨记。

搅拌

各组成材料应当按合同中的规定在搅拌机中搅拌。

装卸输送混凝土

混凝土从搅拌机到最终浇筑位置间的装卸运输应当既快又好的完

成，不发生离析或成分损失。无论什么时候，从搅拌设备到浇筑地点

之间的距离，不应使混凝土变稠或离析，运输系统中要安装合适的搅

入模

混凝土应当有条理地按薄层浇注，并保持这种的速度，直到浇筑

完整个单元，整个单元的塑形表面大致水平。每一层混凝土应当在后

一层浇筑前进行压实。

密实

方法: 混凝土在浇筑期间或浇筑后立即使用合适的工具进行密实。

混凝土应包裹钢筋及内置夹具，填满模板空间。要采取措施保证钢筋

和预埋金属的准确位置，防止变形。

振捣: 浇筑过程中，混凝土应当在模板内进行内部振捣，以此来增

加可塑性，使其充分密实从而改善表面组织及观感，还便于混凝土的

浇筑。

振捣应持续到整批混凝土完全混合，外观均匀且表面开始泛光。

在混凝土与模板间以及钢筋周围，可以看出一薄层水泥浆膜。过度的

振捣会引起离析、不必要的泌水，或生成浮浆，应当避免。

如果混凝土养护得很差，那么在精心选定的混凝土的级配、拌合

和密实成型上所耗费的精力将是徒劳无益的。养护是指在一定的时间