The High Density Concrete Biology Essay

High denseness concrete can merely be manufactured by utilizing assorted high denseness natural or semisynthetic sums. High denseness concrete can be used for structural and/or specialised building intents. The chief usage of HDC is in the atomic industry as radiation shielding. Particular attention should be taken to the specific type of sums used and type of cements combined in the concrete mix.

High denseness concrete ( HDC ) consists of concrete with a denseness higher than normal 2300 to 2550 kg/mA? and is used for particular intents such as radiation shielding, counter weights, ballasts, safe walls and safe roofs.

The purpose and aim of this assignment is to:

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Outline the constitutional stuffs required for high denseness concrete.

Sketch the production, puting and compression processs for high denseness concrete.

Outline the quality control processs required for high denseness concrete.

Discuss an application for high denseness concrete and foregrounding any jobs encountered.

3. Constituent stuffs for high denseness concrete.

All constitute stuffs, cement, alloies, and H2O used in high denseness concrete should conform to the criterions as for normal denseness concrete, but the sums is different and may necessitate particular consideration during handling, batching, commixture, transporting and puting. ( ACI 304R-00, 2000 )

3.1 Sums.

High denseness concrete ( HDC ) , densenesss is achieved by utilizing high-density sums normally iron oxides and depends on its intended usage, physical and chemical belongingss, handiness and cost. Concrete densenesss of 3700 to 3800 kg/mA? , is gettable using sums with atom comparative densenesss of at least 4500 kg/mA? and for concrete densenesss of 4800 kg/mA? sums should hold a atom comparative denseness of at least 6000 kg/mA? . ( J. Goodman, 2009 )

Aggregate rating for HDC seldom conform to normal aggregative criterions as the sum are seldom made for concrete production, this should be accepted by possible users as it is non damaging to the production of HDC. The most of import portion of HDC sums is that the scaling should be changeless and that a feasible scaling bound be agreed on with the provider, to establish the mix design on.

The chemical belongingss of all high-density sums should be evaluated before usage, chemical responsiveness and peculiarly in high alkaline environments as found in cement pastes, long term lastingness such as alkali-aggregate responsiveness, sulfate and chloride onslaught and other drosss. The provider should be able to supply a full chemical analysis of all possible stuffs and alternate stuffs to be used. With proper proficient rating and planning, different types of sums can be combined at the provider pace to bring forth a concrete with predicted, specified denseness. Cost factor are really of import as these sums are normally more expensive than normal sums, it can besides be that the stuff may merely be available in comparative short supply. The cost of HDC additions with denseness but non necessary in direct proportion. ( E. Miller, 2003 )

Sums should be selected for their form ( cubelike or rounded and free of level or elongated, maximal denseness, workability, and cost. Particle comparative denseness of the all right sum should be similar to that of the harsh sum as lower denseness all right sum can take to segregation of the harsh sum through the howitzer. ( J. Goodman, 2009 )

The scaling of the harsh sum should be uniformly graded between 10 and 40mm, as per bounds in Table 1. The scaling of the all right sum should be within the bound as shown in Table 1 as this would assist to forestall segregation. ( ACI 304R-00, 2000 )

Table 1: Scaling demands for coarse and all right sums. ( ASTM C 637 )

Sieve sizes millimeter

Rating 1 for 37.5 millimeters maximal size sums % passing

Rating 2 for 19.0 millimeters maximal size sums % passing

Coarse sums

50.0

100

A

37.5

95 to 100

100

25.0

40 to 80

95 to 100

19.0

20 to 45

40 to 80

12.5

0 to 10

0 to 15

9.5

0 to 2

0 to 2

Fine sums

2.36

100

A

1.18

95 to 100

100

0.600

55 to 80

75 to 95

0.300

30 to 55

45 to 65

0.150

10 to 30

20 to 40

0.075

0 to 10

0 to 10

Fineness faculties

1.30 to 2.10

1.00 to 1.60

Two types of sums can be used for high denseness concrete viz. :

Natural happening sums.

Iron ores of assorted types have been used all around the Earth for many old ages ( outside the U.K ) , in the UK imported Fe ore is used. ( E. Miller, 2003 ) Using some natural happening sums concrete densenesss of about 4000 kg/mA? can be obtained. ( J. Goodman, 2009 )

Different types of natural high-density sums which can be used for high denseness concrete ( HDC ) available in South Africa and the UK refer to Postpone 2.

Man-made sums.

To accomplish concrete densenesss above 4000 kg/mA? man-made or man-made stuff such as ferrosilicon scoria, steel or lead shooting can be used. ( J. Goodman, 2009 )

For types of man-made sums which can be used for high denseness concrete ( HDC ) available in South Africa and the UK refer to Postpone 2.

Table 2: Summary of typical belongingss of high-density sums

( J. Goodman, 2009, E. Miller, 2003 and ACI 304.3R-96 )

A

Type

Aggregate atom sizes

Relative denseness ( kg/mA? )

Approximated Concrete denseness ( kg/mA? )

Notes

Natural happening ores

Heavy spars

plus 9.5 millimeters minus 26.5 millimeter and minus 4.75 millimeter

4.2 to 4.45

3500

Used in big measures, contains lead and zinc may do deceleration, avoid extra handling may interrupt down.

Magnetite

plus 9.5 millimeters minus 26.5 millimeter and minus 1.18 millimeter

4.78 to 4.9

4000

Good atom form, high-density mulcts and clean.

Haematite

minus 9.5 millimeter to minus 37.5 millimeter

4.89 to 5.02

4130

Effluent job due to intense ruddy colour.

Limenite

minus 0.6 millimeter

3.7 to 4.4

4210

Available in measure in SA, inconsistent scaling, variable comparative denseness, high silt content, H2O soaking up possible.

Geothite

Beginning dependent

3.5

sodiums

A

Iliminte

Beginning dependent

4.6

sodiums

A

Serpitine

Beginning dependent

2.5

3920

Retains H2O at high-density temperatures, good neutron attenuator.

Zircon

minus 0.3 millimeter

4.79

sodiums

A

Galena

minus 19.0 millimeter

4.0

3220

Lead ore, lead soluble in base and can organize a gel.

Chromite

minus 26.5 millimeter and minus 1.18 millimeter

4.08 to 4.68

3530

Available as difficult lumpy ore and can be crushed to coarse and ticket sum.

Manufactured sums

Iron shooting

8 millimeter to 0.1 millimeters

7.6

& gt ; 4500

Grit usually added to increase cohesiveness mix.

Lead shooting

4 millimeter to 0.1 millimeters

11.3

A± 7000

Careful mix design and cement choice, soluble in base and can organize a gel, used with high aluminum oxide cement.

Fergran

20 millimeter to 5 millimeters

6.9

& gt ; 4000

Poor atom form, some oxide bed.

Feriron

& lt ; 2 millimeter

7.1

& gt ; 4000

Good form be givening to spherical.

Chilcon

20 millimeter to 5 millimeters

6.3

& gt ; 4000

Good atom form, highly high-density, good ocular impact for open applications.

3.2 Cements.

All cements conforming to SANS 50197 as for conventional concrete can be used for HDC if it produces the needed physical belongingss. If alkali-reactive components are present in the sums cements with low base contents or a suited blend of cements and cement extenders should be used. ( J. Goodman, 2009 ) Low-alkali cement non holding more that 0.6 % Na2O-eq may be used with a potentially alkali-reactive sum such as lead shooting. ( B. Oberholster, 2009 )

The undermentioned extenders: Land granulated blast furnace scoria ( GGBS ) , fly ash ( FA ) and Condensed silicon oxide smoke ( CFS ) have lower densenesss than Ordinary Portland Cement ( OPC ) and can be used if they do non cut down the denseness of the concrete below specified bounds, ( J. Goodman, 2009 ) Eric Miller ( 2003 ) nevertheless states “ The cement can be OPC or a blend of this with either Ground granulated blast furnace scoria, Pozzolanic fly ash ; the latter which will non cut down the denseness of the concrete but may heighten the otherwise hapless workability ” . Fly ash blends and lower H2O contents can successfully be used to increase the denseness of concretes. When lad shooting is used High alumina cement ( HAC ) must be used, ( J. Goodman, 2009 ) as it reduces the chemical responsiveness of lead in high alkaline conditions. ( E. Miller, 2003 )

When utilizing alkali-reactive sum ( lead shooting ) hurtful enlargement can be prevented when utilizing high-alkali cements by adding extenders following with SANS 1491 by utilizing a minimal per centum of the following extenders by entire mass of cement:

At least 40 % Slag ( S ) by mass

At least 15 % CSF by mass

At least 20 % FA by mass ( B. Oberholster, 2009 )

Heavy spars for illustration tend to hold a really harsh scaling, the coherence of the mix can be imoproved by adding extra cementitious stuff such as PFGA/GGBS. The cementitious content can be higher than required for normal strength or w/c design standards. Adding extra cementitious stuff to modify the mulcts content of the mix may, look expensive but in HDC it is the cheapest ingredient used and comparative easy to include. ( E. Miller, 2003 )

3.3 Admixtures.

Adding alloies can understate segregation, hemorrhage, both of which can be debatable with HDC. The lastingness can be improved with a low free water/cement ratio ( w/c ) particularly so in structural class HDC. Using ace plasticizers is recommended which in concurrence the cement type may marginally increase concrete denseness. Super plasticizers are good in cut downing H2O to understate hemorrhage and keep a cohesive mix that has minimum segregation. ( E. Miller, 2003 )

The undermentioned alloy can be used in HDC:

Air-entraining alloies as it controls shed blooding and colony improve workability and aid in obtaining more homogeneous concrete but will cut down the denseness of the concrete. Water-reducing alloies as it will increase concrete denseness by cut downing the sum of H2O in the mix, H2O is the stuff used in HDC with the lowest denseness. Shrinkage-reducing alloies as it guarantee dense, crack-free concrete used for radiation-shielding concrete. ( J. Goodman, 2009 )

When lead shooting or lead containing sums are to be used, the followers should be considered when choosing a chemical alloy. The alkali content of chemical alloies for concrete used in South Africa is between about 0.2 and 7 % . In many cases the part to the alkali content of the pore solution is important and can non be ignored. One of the widely used super plasticizers has a Na2O-eq of approximately 5 % and if added at 1 % of cement to concrete with a cement content of 350 kg/mA? it will ad 0.17 kg/mA? Na2O-eq to the concrete. Lithium based compounds can be used with lead shooting to command the alkali responsiveness. ( B. Oberholster, 2009 )

The consequence of alloies should be established under field conditions, sooner by proving, to find if the alloies achieve the needed consequences or wholly unsuitability. ( J. Goodman, 2009 )

Admixtures may merely be used in liquid signifier and batched in solution in the commixture H2O. Admixtures shall follow with the demands of ASTM C 94 or AASHTO M I94 ; air entraining agents shall follow with the demands of ASTM C 260 or AASHTO M 154. Admixtures shall non incorporate any chlorides.

( COLTO, 1998 )

3.4 Water.

Water shall be clean and free from damaging concentrations of acids, bases, salts, sugar and other organic or chemical substances that could impair the lastingness and strength of concrete or imbedded steel. ( COLTO, 1998 )

4. Production, puting, compression and quality control of high denseness concrete.

4.1. Production.

Standard batching processs can be used for of course happening sums such as Heavy spars and Magnetite with volume alterations to let for the addition in aggregative comparative denseness. These, and on occasion other types, are sometimes required in important volumes to warrant large-scale batching through conventional works. It is sometimes necessary to utilize smaller membranophone sociables about 0.5mA? and even smaller for lead shooting. ( E. Miller, 2003 )

Normal batching ( if sufficiently accurate ) and managing equipment can be used but great attention should be taken non to overload the equipment as HDC is much denser. It is imported to clean all equipment used to minimise cross taint. ( J. Goodman, 2009 )

To help production sums can be purchased from some providers pre-weighted in ‘dump pokes ‘ or other containers to accommodate the size of the batching works, the extra cost being more than the offset by an about nil wastage, and supplying extra protection from external taint. Iron or lead shooting can besides be purchased in 25 and 12.5 kilogram bags severally but this tends to do batching really boring. The usage of shit pokes for providing comparatively little sums of sums has obvious advantages as providers have the flexibleness to intermix precise measures of all right and harsh sums of different types to offer bespoke premixed all-in blends every bit good as bespoke densenesss.

Batching times will take longer per cubic meter, due to smaller unit batch volumes, but single batch blending times should be similar to those for standard sums concretes. Care must be taken with Barytes to measure possible atom interrupt down, since this stuff can be weak and delicate. Conversely blending times may necessitate to be extended for stuffs such as Fergran, which has a really unsmooth and irregular form. It is advisable to pre-grout sociables when little measures are produced. ( E. Miller, 2003 )

Particular attention should be taken to forestall loss of mulcts, taint, segregation, aggregative breakage when shipped, handled and stored. The sum should be kept every bit dry as possible. Aggregate container should be marked decently incorporating the mass and type of the sum. ( J. Goodman, 2009 )

4.2 Placing.

Conventional arrangement methods may be used for HDC, provided that the mixture is feasible and the signifiers are comparatively free of embedded points. Such concrete, nevertheless, nowadayss particular jobs due to the inclination of the high-density aggregates atoms to segregate. Segregation is greatest where the sums are non unvarying in rating or denseness, the mixture contains inordinate H2O, or the slack is inordinate. The slack for high-density sums mixtures should usually be between 40 and 75 millimeter.

Placement of conventionally assorted HDC is subjected to the same consideration of quality control as normal concrete, except that it is far more susceptible to fluctuations in quality due to improper handling. HDC is peculiarly capable to segregation which consequences in fluctuations of strength and denseness.

HDC will non flux in a signifier and must be placed in each distinct country and compacted in topographic point with minimal quiver. Under no fortunes should an effort be made to travel HDC with quiver equipment. Concrete should be placed in beds non more that 300 millimeters thick. If an inordinate sum of grout builds up on the surface, it should be removed while the concrete is still in plastic. When segregation can non be avoided or when embedded points or limitations prohibit conventional arrangement, the pre-place sum method may be used.

Pre-placed sum building consists of raising formwork, pre-placing coarse sum in the signifiers, and commixture and puting high-density grout utilizing the same process as those employed with normal grout.

Pressures exerted on formwork by HDC are greater than those exerted by normal concrete and formwork must be designed consequently. Pressure on perpendicular signifiers can be reduced by puting concrete in slow rise lifts. ( J. Goodman, 2009 )

If possible the usage of long, stiff chutes or bead pipes should be avoided. If HDC concrete is placed in narrow signifiers or through restricted countries, it is advisable to utilize short, flexible bead chutes that can fall in and curtail the autumn. ( ACI 304R-00, 2000 )

4.3 Compaction.

Compaction is of great importance when utilizing HDC due to the particular intents i.e. radiation screening it is used for which requires maximal denseness, and the concrete should be free of segregation and nothingnesss. Compacting HDC is more hard to pack than normal concrete and excess particular attention should be taken to guarantee proper compression. Both internal quiver and external quiver are used. However attention should be taken when utilizing high-density sums some are crumbly and can easy interrupt down. Poker vibrators insert points should be spaced closer to guarantee that HDC are compacted decently.

Normal frequences vibrators every bit good as high frequence ( 180 Hz ) can be used successfully satisfactory. Higher frequences vibrators must be used for shorter periods, to cut down the danger of segregation. Over-vibration causes segregation of the high-density sums by colony intending the big sum migrate to the underside of the component casted. ( J. Goodman, 2009 )

The country radius of action of vibrators used in HDC is less effectual. This consequence in HDC non being compacted decently and greater attention should be exercising to see proper compression of the concrete. Excessive grout can be lifted to the lift surface top due to quiver and re-vibration, as to take entrapped air and set up aggregate-to-aggregate contact. The lift surface grout should be removed while the concrete is still fresh. ( ACI 304R-00, 2000 )

4.4 Quality Control.

HDC requires careful be aftering at design phase, stamp appraisal and pre-production phases of a contract every bit good as during existent production on-site. Cost can be really high compared with standard concrete as volumes are frequently excessively little to be successfully produced in conventional ready-mixed or site-mixing concrete workss. Workability can be hard to measure, hence the demand for test mixes which should be attended by site forces including those really puting the stuff. A higher grade of quality control is needed, with fresh densenesss being often measured prior to blend being placed. This requires appropriate equipment that is non normally on site. Full method statements and quality programs for all phases, including stuffs procurance, planning, production, puting and proving, should be prepared and approved prior to get downing of work.

Because of the demand to fulfill particular demands, proving and quality control are highly of import. In many instances, proving of the construction, including the remotion of nucleuss is non allowable. Care must be taken to guarantee that good concreting techniques are used.

The denseness of HDC is of import, if non more so at times, than strength and a suited testing government should be adopted to continually supervise this belongings utilizing fresh denseness trials on site before concrete is placed. Cubes and cylinder trials are similar to normal concrete. By and large 100 millimeters and 150 millimeters regular hexahedrons can be really heavy and are of important cost. Hence extra proficient staff will be required to set about the increased degree of quality control necessary both at the commixture works and on-site. A fresh denseness trial can be evaluated utilizing a all right sum denseness pot. The normal 0.01 mA? pots will be really heavy – up to 90 kilograms for lead shooting concrete. Test methods are the same as for standard denseness merchandises though extra tamping may be required to to the full pack mixes incorporating ill shaped sums. ( E. Miller, 2003 )

The belongingss of newly assorted HDC needs to be tested and should include the undermentioned: denseness, temperature, slack and air content. Specification bound for should be specified for all the of import belongingss. ( J. Goodman, 2009 )

When HDC is required it is advisable that the design applied scientist issues an addendum specification to the standard concrete subdivision as some facets of its usage are basically different from standard concrete production.

Points for consideration:

Sums

Beginning restriction and bringing ;

Cost ;

Appropriate physical, chemical and petrological belongingss.

Concrete

Strength ;

Low free w/c ;

Compulsory usage of ace plasticizers ;

Full graduated table research lab test mixes to corroborate fresh and hard-boiled belongingss including fresh denseness.

Interior designers should see the deduction of non-compliant mixes, peculiarly with respect to fringy densenesss. This may be importuned and some statistical safety borders may necessitate to be included on a footing similar to those used for compaction strengths. A concluding point to see is the possible disbursal of remedial work as some classs of HDC, peculiarly those with Fe sum, will be highly hard to take. ( E. Miller, 2003 )

Table 3: Summary of typical belongingss of high-density concretes.

Concrete type/ Property

Unit of measurement

Heavy spars

Magnetite

Chilcon harsh natural sand

Chilcon coarse & A ; mulcts

Fergran coarse feriron mulcts

Iron shooting

Lead shooting Non structural

Typical criterion concrete comparing

Typical cement content

kg/mA?

330+

200-400

360

350

300

400

500

330

Typical free w/c ( +s/plasticiser )

A

0.5

0.7-0.45

0.45

0.45

0.45

0.43

0.34

0.5

Typical denseness

kg/mA?

3500

4000

4400

5200

5300

5900

8600

2300-2400

28-day strength ( 100 mm regular hexahedron )

Mpa

20-30

20-40

70.0+

80.0+

45-55

30-40

20

30-40

Indirect tensile strength 200 ten 100 millimeter cyl. )

Mpa

2.7

4.0

5.0

5.2

6.0 ( Eastern Time )

4.5

N/A

3.5

Young modulus

Grade point average

20

20-35

40

50

50-60 ( est )

70 ( Eastern Time )

N/A

20-30

Flexural strength

Mpa

3.7

6.0

6.0+

8.5

N/A

6.5

N/A

5.5

Dry shrinking

%

0.04

0.04

Similar

Similar

0.03 ( Eastern Time )

0.02

N/A

0.04

Thermal conduction

W/mk

1.1

Similar

2.5 ( est. )

2.5 ( est. )

25-30 ( est )

33

N/A

1.9

Coefficient of additive enlargement

A

22 ( Height )

10

N/A

N/A

12 ( Eastern Time )

12.5

N/A

8-15

5. High denseness concrete application and jobs encountered.

5.1 Applications of high denseness concretes.

Although HDC can be used for assorted applications ( ballast blocks in domestic lavation machines, radiation shielding, span counterbalances, hospital x-ray shielding, coating of pipes, under H2O grapevine covering, submerged constructions such as under H2O tunnels and for bank vault protecting ) , the treatment will concentrate on the chief usage of HDC in building of a additive gas pedal.

HDC was used for the 60 mA? additive gas pedal installation located in the cellar of a infirmary as a shield against radiation generated by the additive gas pedal, which uses high strength X raies to kill malignant neoplastic disease cells in patients without damaging healthy tissue. Radiation can be harmful to hospital forces and the populace if non contained in a shielded environment.

HDC was used in the walls, ceiling and foundation. A sum of 85 mA? HDC with a denseness of 4800 kg/mA? was used. The steel support consisted of 11 dozenss placed in both waies at 300 millimeter Centres. To accomplish the needed concrete denseness to absorb the radiation a combination of high-density sums steel shooting ( all right sum ) and hematite iron-ore ( harsh sum ) was used. The usage of high denseness sums increased the cost for 40 Mpa concrete from about R370.00 to R7 600.00 per three-dimensional meter of concrete in 1996. ( A. Balogh, 1996 )

Figure 1: North/South subdivision through additive gas pedal room. ( A. Balogh, 1996 )

5.2 Problems encountered.

5.2.1 Limited infinite.

The bing cellar had a floor to floor tallness of about 4.8 m. The needed tallness totalled 5.4 m ( 3.9 m for the gas pedal and 1.5 m for the normal weight concrete slab ) . Due to the tallness of the bing cellar the concrete thickness was changed from about 1.525 m to 600 millimeters by using HDC. Cost analyses determined that HDC was more economical than a combination of normal weight concrete and lead shielding.

The bing infirmary exterior cellar wall was non designed to back up the extra weight of HDC. The design was alterations so that the walls and ceiling of the gas pedal room be free standing. Large beam subdivisions were incorporated in the ceiling within the needed thickness by concentrating reenforcing steel in beam strips. The beams acted as cantilevers from the gas pedal room to the exterior cellar wall. ( A. Balogh, 1996 )

5.2.2 Mix design.

The location of the gas pedal required an like an expert combined high-density sum mix to see that the needed denseness for the HDC mix is obtained, be pump-able and be placed without segregation. Access to the gas pedal room was limited to a 600 millimeter gap bored in the side walk. All the needed research lab trials related to the HDC mix design was tested to set up the suitableness of the mix related to the denseness, strength and workability, where after the mix design was all right tuned and a trail mix pumped and placed in the foundation of the gas pedal room. ( A. Balogh, 1996 )

5.2.3 Materials bringing.

The concrete trucks presenting the HDC could merely be load to 30 % of their capacity because of the weight of the HDC. The bringing point every bit good as the concrete pump was straight in forepart of the chief entryway were the entree hole was bored. Al concrete bringings were scheduled for early Saturday forenoons to understate intervention with traffic and visitants. ( A. Balogh, 1996 )

5.2.4 Concrete arrangement.

To guarantee that the undertaking was complete in the contract period all mistakes that would necessitate the remotion and replacing of the HDC was avoided at all cost. All workers were instructed non to over vibrate the HDC after being placed, to guarantee segregation did non take topographic point.

The formwork was stripped after obtaining strengths of 30 Mpa. ( A. Balogh, 1996 )

6. Decisions.

HDC can be used for assorted types of building undertakings ( ballast blocks in domestic lavation machines, radiation shielding, span counterbalances, hospital x-ray shielding, coating of pipes, under H2O grapevine covering, submerged constructions such as under H2O tunnels and for bank vault protecting ) and although more expensive, it has its rightful topographic point in building.

HDC requires no extra or particular equipment, works or blending techniques.

Quality monitoring should take topographic point from design phase through to the production phase and particular quality control measures must be in topographic point. Changes or supplements to standard specifications must be in topographic point to stipulate the needed densenesss and other belongingss.

Aggregate handiness every bit good as the chemical composing of the intended sum to be used must be confirmed before planing research lab mixes prior to the building stage.

The cost deduction in utilizing HDC must be verified earlier building as it is non a inexpensive general trade good.