Dry Readymix AAC in a Cement Plant

8/17/2019 Dry Readymix AAC in a Cement Plant

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CEMENG MINI AND TINY AAC BLOCKS PLANTS:

“AAC DRY READY MIX “ IS THE BASIS

D S Venkatesh, Freelance Industrial Consultant

Mob: 093428!9"0 #$%ail: ds&enkatesh40'(%ail)co%

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1.0 What is AAC?

AAC is lightweight autoclaved aerated concrete which is completely cured, inertand stable form of calcium silicate hydrate. It is a structural material, approximatelyone quarter the weight of conventional concrete, composed of minute cells whichgive the material light weight and high thermal insulation properties. It is availableas blocks and pre-cast reinforced units, i.e. floors, roofs, walls and lintels.

here are at present !" AAC manufacturing units in India operating on standalonebasis. #ome of the cement plants have added AAC blocks to their product portfolio.$owever, AAC has not penetrated into smaller towns and cities, mainly, due to itshigher cost visa a vis locally manufactured conventional concrete masonry blocks,in spite of its several techno economic advantages for the %uildings ConstructionIndustry. %eing a green product, use of AAC would pave way for conservingdepleting high cost &atural 'iver sand (manufactured sand.

2.0 Materials required for manufacture of AAC:

)aterials for AAC vary with manufacturer and location specific. he constituentmaterials for AAC are specified in A#) C*!+. hey include some or all of thefollowing fine silica sand Class / fly ash hydraulic cements calcined limegypsum expansive agents such as finely ground aluminum powder or paste andmixing water.


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Autoclaved aerated concrete is actually hydrated calcium silicate. AAC is producedout of a mix of quart0 sand and(or pulveri0ed fly ash 12/A3, lime, cement,gypsum(anhydrite, water and aluminum and is hardened by steam-curing inautoclaves.

he silica is obtained from silica sand, fly ash 12/A3, crushed silica rock and(or stone. It is possible to obtain silica as a by-product from other processes, e.g.foundry sand or burgee from glass grinding, provided the levels of alkalis or other impurities are not too high. he calcium is obtained from quick lime,hydrated lime and cement. he gypsum is used as a catalyst and for optimi0ingthe properties of AAC. Careful regulation of the amount of aluminum powder gives accurate control of the density of the final product.

3.0 Limitation on Availabilit and cost of Materials:

The cost of AAC predominantly depends upon the cost of input material constituents .In India, AAC is either sand based or pulverized fuel ash based. AsSand is getting costly day by day, substitute industrial waste materials areincreasingly used for partial or full replacement of Sand for effecting economy inthe construction industry. Availability of fly ash is limited to thermal plants /captiveunits and remote locations away from the maret.

AAC being multi-constituent, not all raw materials would be available at any specificlocation, limiting spread of AAC manufacturing units across the country. %esides,the transportation (distribution costs to consuming centre pose additional restraint.

3.0 What is the solution4 !roduce AAC "r #ead Mi$.

he existing AAC units and Cement plants can add AAC Dry Ready mix to their product portfolio. AAC 5ry 'eady mix is proportioned blend of siliceous materials,calcined lime, cement and gypsum that can be made available in dry powder formof requisite fineness 6ust like Cement or 'eady mix mortar in packed bags.

!any )ini and iny AAC %locks 2lants can be set up across the country to meetlocal needs. 7ach of these units will use AAC 5ry 'eady mix as 8starting 8 point ,make a slurry with water, mix the expansive agent and cast the blocks .#team curegreen blocks in autoclaves to produce the finished product vi0 AAC %locks.

o economi0e production costs, instead of natural sand(manufactured sand,substitute waste materials from other industries have been partially used up tocopper slag 1"9:3, ;ranulated %last furnace #lag 1


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%.0 AAC "r #ead mi$ &roduction in Cement !lants:

)ost of the cement plants in India face the problem of utili0ation of marginal and lowgrade lime stones from their quarries unless they resort to beneficiation techniqueswhich may not be always profitable. hese marginal and low grade lime stones can

be put to better use to produce AAC 5ry 'eady mix. According to &C% &orms,limestone with :Cao ?9@?? and :#iB *B-* are classified as marginal, whereaslimestone with :Ca !-?9 and :#iB*-B9 are classified as low grade.

he high silica content marginal and low grade limestone can be burnt invertical shaft kilns located at the quarry itself, employing mix of rice husk and (or coal as fuel. he burnt output would be a mix of burnt lime un burnt limestone,and fuel ash acceptable in AAC production. 'ice husk ash contains around +" :- 9 : amorphous silica, a rich silica substitute. he particle si0e of the cement isabout !" microns .'$A is finer than cement having very small particle si0e of B"microns , so much so that it fills the interstices in between the cement in the

aggregate. hat is where the strength and density comes from. And that is whyit can reduce the amount of cement in the concrete mix. ther constituents vi0Cement Clinker and gypsum are readily available in the plant.

7xisting cement plants can thus produce AAC 5ry 'eady )ix economically.Cemeng employs a 2#'; )ill functioning in open circuit to grind the raw mixconstituents comprising proportioned amounts of clinker, burnt and un burntlimestone, fly ash and gypsum. Additives as required may be simultaneously addedto enhance the property of mix if required. he AAC 5ry ready mix can be packedin paper bags and sold, 6ust like cement or ready mortar. Alternatively, the plant canemploy mini silos for transport to site and stored.

'.0 Cemen( Mini and )in AAC *loc+s &lants:

".* AAC 'eady )ix is the basis for Cemeng )ini and iny AAC %locks plants. Ahori0ontal drum reversible concrete mixer converts AAC dry ready mix with additionof water into slurry of required consistency. &ext, Aluminum powder is added andmixed. Immediate discharge is carried out into the moulds for casting the %locks.his is a batch mixer and thus most appropriate for the 6ob. he reversible mixer canbe completely emptied before taking up the next batch.


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Conventional ,teel *o$ Mould and -Wet cuttin( of /reen ca+e to *loc+s

".B he si0e of the wet cake is generally *BB9x*B*9x99. wo alternatives areconsidered for the mould conventional steel box arrangement or 8/leximouldD8=etD cutting of green cake is resorted in case of exclusive production of smaller blocks. =et cutting is carried out by a one-way or two-way =ire cutting machine.$owever, other AAC products with or without reinforcement necessarily require 85ryDmilling of cured cakes for profiling. 8/leximould 8 is employed when 85ryD milling of cured cakes is resorted.

".! Autoclaving is steam curing at high temperature and pressure, and required toachieve the desired structural properties and dimensional stability. he chemical

reactions that produce the final calcium silicate hydrate structure takes place in theautoclave. he process takes about eight to *B hours under a pressure of about *


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reservoir is directly mounted on the top of the autoclave and concentrated solar heatreceive is employed with linear acrylic /resnel lens box. he thermal oil is kept incontinuous circulation via a pump and the required heat exchange coil is submergedwithin the water reservoir of the autoclave.

Conventional Autoclave ith "ouble door arran(ement ote: /reen bloc+s stac+ed horiontal or vertical

".# Cemeng Autoclaves are $novel% in concept and construction suitable for steamcuring of wide variety of concrete products. It is primarily an underground rectangular shaped longitudinal tunnel constructed from &CC and refractory lined.The base of the tunnel serves as water reservoir and has embedded heat e'changer arrangement. Two (uic opening doors are provided one at each end of autoclave. !obile mold trays carrying the caes are loaded or unloaded by means of a )ib hoist and winch mechanism. *ot thermic fluid flows through the heat e'changer to generate re(uired steam. Solar heat is employed to heat the thermic fluid.

Cemen( -le$imold for castin( (reen ca+es

+se of $le'imold% for casting the green cae and $after-cutting% of autoclaved caewould be highly productive with underground autoclaves. The ready slurry is poured


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directly into the le'imold that is lowered into the autoclave. re-curing is within theautoclave as also steam curing subse(uently. This reduces the au'iliary transfer e(uipment and also process time.

he steam cured AAC block can be directly transported to the marketing yards

economically than cut to si0e small blocks and after-cutting can be carried out by the#tockiest or at the Construction site itself.

After4cuttin( of autoclaved AAC

7xisting granite(stone cutting and polishing units at different cities in the marketing0one can be #tockiest and effectively used to saw cut and trim the AAC %locks torequired si0e(dimensions. It is always possible to saw cut the large si0e AAC %lockto required smaller units at the Construction site. Any broken pieces can be used aslightweight filler, thus nothing is wasted.

5.0 Conclusion:

6ver *uildin( materials &lant has to ta+e (reen sustainabilit initiatives7

*ein( a (reen &roduct8 use of AAC ould &ave a for conservin( de&letin( hi(h cost natural river sand 9manufactured sand.AAC "r #ead mi$ can bereadil added to &roduct &ortfolio of e$istin( lar(er ca&acit AAC &lants and Cement &lants. AAC "r #ead mi$ forms the basis for settin( of Mini and )in AAC *loc+s &lants in smaller tons and cities ide across ndia8com&etin( ith conventional concrete masonr bloc+s. AAC *loc+s can savetime and labor8 Cement and ,and durin( construction.

ote: 6ntre&reneurs can retain the author as )echnical Consultant for detailed en(ineerin( services from conce&t to commissionin( and trial runs.

*e+erences:0 Silica and calcium )oined in premium products


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1y Sandy *erod it and 2uarry 3ec 0456 pages 67 8 6#7 1ric manufacture in a Cement lant by 3 S 9enatesh,

Cemtec :ngineering, and Secunderabad. Indian Cement &eview !ay 0454, ages IC&-04 toIC&-7"

;$


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C Dr *ead Mi6 can be used +or 1roduction o+ cellular concrete blocks7CC, In this

case, -e e5ui1 additionall a +oa% (enerator) *est o+ the e5ui1%ent are sa%e)

utocla&in( is o1tional, but, desirable to reduce -orkin( in&entor)

.aste to .ealth is 1ossible in case o+ reect +lakes +ro% Shahabad /ile .orks, -here

these are a&ailable in hea1s +ro% abandoned stone 5uarries) nl coarse (rindin( isneeded and this can re1lace sand in the %i6)

Si%ilarl, Cudu11a Slab .orks result in -asted broken tiles) Si%ilar treat%ent is

re5uired)

Sodiu% ;ercarbonate is a dr (ranulated +or% o+ hdro(en 1ero6ide)

ust addin( -ater and %i6in(, aerated concrete can be 1oured into %oulds) /he

concrete e61ands in about 2 hours and attains re5uisite (reen stren(th) Final stren(th is

achie&ed in 28 das) CFC also e%1los snthetic +ibres in its ra- %i6) /he ad&anta(e is

that no se1arate +oa% %i6er is re5uired) /he %ain concern is the e6tent o+ hei(ht o+

raisin( in the %oulds) n e6cess %aterial has to be re%o&ed +or recclin() 7@indl note

that the read %i6 is added to 1redeter%ined 5uantit o+ -ater -hile %i6in() /his is

nothin( but (as concrete and not con&entional +oa% concrete) #ither a %onoscre- 1u%1

or 1eristaltic 1u%1 can be e%1loed to trans+er the slurr to the %oulds)

---)Saradabrickindustr)co% ruche$k9'ahoo)co)in

---)1rolicon)co% >an(kok

http://www.saradabrickindustry.com/mailto:[email protected]://www.prolicon.com/http://www.prolicon.com/mailto:[email protected]://www.prolicon.com/http://www.saradabrickindustry.com/


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Mini Silo for site.

What type of moulds do we employ? The moulds may be a rectangular steel frame for height

equal to the depth of block and has removable steel sheet partitions placed within. The mould

is placed on clean ground. A mobile trolley will distribute the mied slurry manually. After waiting for !" hours# the intermediate steel sheet partitions are removed. $ach block is lifted

manually and stacked.

Alternatively# moulds with removable sidewalls are mounted over a trolley . The Trolley

mould is preferred when wet wire cutting is employed. When the green block is ready# the

sides are dismantled and the trolley moved for wire cutting. The wire cut loaded trolleys are

shifted to Autoclave section. %f necessary# manual loading of cut blocks above one set of wirecut blocks can be done to effectively employ use of autoclaves.

The wire cut green blocks are manually transferred into the autoclave chamber and stacked.

This would be the most economical way. &or quicker loading# trolley mould can beemployed. The trolley with blocks can be lowered into the autoclave. 'efore which#

additional blocks are manually stacked. (accum lifting of green blocks and cured blocks may be attempted to reduce manual handling to a certain etent.

rolley )ould

;as Concrete

he addition of powered aluminium or 0inc to the cement causes evolution of hydrogen gas onaddition of water. he powered metal is added to the cement in dry state in the ratio of **999. After thorough mixing in the dry state, water is mixed. his cause the evolution of gases and the processgoes on for an hour or so. his cement paste is filled in the moulds up to about *(! rddepth and soonafterwards, the paste fills the mould up to top and overflows. he excess paste is then struck off andthe paste allowed to set. he paste hardens to a mass having the innumerable small bubblessurrounded by cement. his concrete is quite impervious to water but has a high drying shrinkage. #oeach block or unit should be fully cured and dried, before being used to eliminate any subsequent


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shrinkage. he density of this concrete is about "9 to "9 kg(m ! and its strength is about *" to !9kg(cmB.

)ussian patent*

S+'STA,-$* invention relates to construction materials and can be used to produce non

autoclave# naturally setting composite foamed concrete. The dry miture for making foam

concrete contains# /* portland cement !0.012.345# mineral filler 30.010.0# microsilica 6.05.0#superplasticiser 0."0.1# water repellent 0.33.0# modifying 7eolite additive consisting of a

combination of 7eolite and multilayer and singlelayer nanotubes !.08.0# composite blowing

agent consisting of a dry gasforming agent and a dry foaming agent 0.00!0.82# polypropylene

fibre 0.13.2 kg per 3 m6. The dry miture includes a composite blowing agent which contains#/* a dry gasforming agent 20# a dry foaming agent 20# wherein the gasforming agent consists

of aluminium powder 9A93 60/ and 9A9! 10/# and the dry foaming agent used is dry

foaming agent :-'# protein foaming agent 'iopor# industrial abietic resin and sulphanolchloride.

$&&$-T* obtaining a dry miture with a longer shelf life# obtaining foam concrete from said

miture with improved physical and mechanical properties strength# frost resistance and

thermal conductivity.

The purpose of the invention is to provide a dry mi for the production of composite cellularconcrete with improved physical and mechanical performance�their characteristics# with alonger shelf life# with the ability to use directly on the construction site# with gradual smooth liftthe miture and uniform distribution of pores of the same si7e.

This ob;ect is achieved in that the dry mi for the production of aerated concrete# including

9ortland cement# mineral filler# silica fume# superplastici7er# fibre polypropylene# blowing agent

and water# further comprises modifying 7eolite additive consisting of a combination of 7eoliteand multilayer and singlelayer nanotubes# and a blowing agent is a comple composed of dry

blowing agent and foaming agent.

The obtained dry miture has the following ratio of components# /*


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Modifying 7eolite Supplement !#08#0

9olypropylene fiber 0.1 to 3.2 kg per 3m6

-omprehensive a blowing agent 0#00!0#82

)epellent 0.3 to 3.0

This comple contains a blowing agent# /*

>ry blowing agent 20

>ry blowing agent 20

%n turn# the blowing agent consists of aluminum powders brands 9A93 60/ and 9A9! 10/.

A large number of proprietary methods and agents are used to make cellular concrete but essentially they can bedivided into two groups* those using a chemical reaction and those relying on mi foaming to entrain air into

the concrete. The lightweight concrete made by gasification from a chemical reaction is called in this patent

application aerated concrete or Aerated -ellular -oncrete A--@. Since this process usually employs an

autoclave# it is also called Autoclaved -ellular -oncrete A--@. The lightweight concrete made by usingaqueous foams is called foamed concrete or aircrete.

The foamed concrete derived from aqueous foams is typically proportioned to achieve only low compressive

strengths as compared to A-- and only suitable for use in void fill and trench reinstatement# and thus the

material is largely disregarded for use in weightbearing and structural applications.

The autoclaved cellular concrete uses significant amounts of 9ortland cement and lime calcium hydroide@. %t

is well known that production of 9ortland cement and lime emits carbon dioide# which contributes to global

warming. igh temperature


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d. Adding at least one foaming agent near the end of miing

e. 9ouring the miture of step d@ into a mold and allowing it to foam# epand# set# and

harden

f. )emoving the hardened body from the mold

g. :ptionally cutting and shaping the hardened body

h. -uring the geopolymer composite cellular concrete products at room temperature or at

higher temperatures

The dry constituents described above# ecept for the micron


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&oaming agents

The fifth ingredient in a B--- composition according to one embodiment of the presentinvention is a foaming agent. 'ubbles are made by adding at least one foaming agent to the

B--- slurry usually near the end of the miing process. -hemical reaction of a foaming agent

with the alkaline activator solution generates gas which forms bubbles cells@ and thus thecellular structure within the geopolymer paste. $amples of foaming agents include aluminum

powder# &eSi powders# 7inc# hydrogen peroide# alkali peroides such as sodium peroide#

alkali perborates# and alkali and alkaliearth hypochlorites such as sodium or calcium

hypochlorite.

%n one embodiment of the present invention# aluminum powder may be used due to its efficiency

in volumetric epansion and its low cost. %n one embodiment of the present invention# aluminum

powders may have particle si7es of about 10 microns or less# in other embodiments of the presentinvention of about 60 microns or less# and in other embodiments of the present invention of

about 32 microns or less. )eaction of aluminum powder with alkaline solution in the B---

composition gives off hydrogen which epands the paste until a desirable volume is reached.

ydrogen is a volatile gas and is replaced rapidly by air. Addition of aluminum powder may befrom about 0.03 to about 0.2 wt./ of a B--- composition to produce geopolymer composite

cellular concrete with a density ranging from about 200 to about 3500 kg


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Slag, Fly ash and low grade limestone rejects from quarry can be ground together to form a

composite raw mix . Portland Pozolana Cement PPC based on fly ash and Portland Slag Cement

based on Slag can be combined to form a ternary mixture can be employed along with dry foaming agent to form dry composite mix. he ad!antage is sand is not required. "oreo!er, low grade

limestone powder can be added at the factory stage. he foaming agent can be powder and this

would be a ready mix just add water and mix in a regular mixer and cast the bloc#s and other elements. $o necessity for autocla!e curing. %utocla!e curing will reduce the curing time and wor#

in progress in!entory.

?o o+ >locks 1er cu%:!00 %% 6 200%%6

00%% "0%% 200%% 22"%%

83 "" 4 3! ?osAcu%

0 " 20 22)" k(Ablock

40 !0 80 CC >locks, *sAblock

"" 82 08 Si1ore6 *sAblock

Cellular concrete %asonr units ha&e o&ertaken con&entional concrete %asonr units in &ie- o+

resultin( ad&anta(es in construction costs and 1ro&idin( ther%al and +ire resistin( abilities) In

s1ite, con&entional %asonr units are still bein( used to a lar(e e6tent) Conser&ation o+ natural

sand or %anu+actured sand and ce%ent to reduce carbon e%issions is the need o+ the hour, and

-e ha&e to (o B(reen in e&er construction as1ect) /he 5uantu% o+ sand re5uired 1er %asonr

unit is hi(h -hereas less than hal+ 5uantit is re5uired in case o+ CC or C cellular blocks)

Sand can alto(ether be re1laced b +l ash thus sa&in( considerable costs and ecolo(ical balance)

Co%1ared to CC >locks, C >locks +urther sa&e on Ce%ent thus (oin( %ore B(reen)

In all cases, the need +or re1lacin( nor%al ce%ent b s1ecial ce%ents %ust be e%1hasied to

achie&e +urther econo%) lkali acti&ated sla( ce%ent, lkali acti&ated +l ash ce%ent, or lkali

acti&ated sla( and +l ash ce%ent are e%er(in( as better re1lace%ent o1tions to con&entional

;C, ;SC or ;;C ce%ents) /hese ;ortland Ce%ent +ree cellular concrete blocks are -hat is

described in this article)

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Dry Readymix AAC in a Cement Plant

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