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 maintenance.Therefore, 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 su
bjected 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 strong.It 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 wate
r 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 resu
lts 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 works.It is important to note that only a bit of care and supervision make a great difference between good and bad concrete.The 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 ingredi
ents.Whenever 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 system.Where concrete is being conveyed on chutes or on belts,the free fall or drop shall be limited to 5ft.(or 150cm.) unless otherwi permitted.The 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 oiled.Placing 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 maint
ain,until the completion of the unit,a plastic surface approximately horizontal throughout.Each 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 depositing.The concrete shall be worked around all reinforcement,embedded fixtures,and into the comers of the forms.Every precaution shall be taken to keep the reinforcement and embedded metal in proper position and to prevent distortion.
