The entire Wikipedia article for concrete, with every e removed

Concrt

From Wikipdia, th fr ncyclopdia This articl is about th construction matrial. For othr uss, s Concrt (disambiguation). Not to b confusd with cmnt, grout, mortar, or plastr.

This articl nds additional citations for vrification. Plas hlp improv this articl by adding citations to rliabl sourcs. Unsourcd matrial may b challngd and rmovd. Find sourcs: "Concrt" – nws · nwspaprs · books · scholar · JSTOR (July 2022) (Larn how and whn to rmov this tmplat mssag) A singl concrt block, as usd for construction

Concrt is a composit matrial composd of aggrgat bondd togthr with a fluid cmnt that curs ovr tim. Concrt is th scond-most-usd substanc in th world aftr watr,[1] and is th most widly usd building matrial.[2] Its usag worldwid, ton for ton, is twic that of stl, wood, plastics, and aluminium combind.[citation ndd]

Whn aggrgat is mixd with dry Portland cmnt and watr, th mixtur forms a fluid slurry that is asily pourd and moldd into shap. Th cmnt racts with th watr through a procss calld concrt hydration[3] that hardns it ovr svral hours to form a hard matrix that binds th matrials togthr into a durabl ston-lik matrial that has many uss.[4] This tim allows concrt to not only b cast in forms, but also to hav a varity of toold procsss prformd. Th hydration procss is xothrmic, which mans ambint tmpratur plays a significant rol in how long it taks concrt to st. Oftn, additivs (such as pozzolans or suprplasticizrs) ar includd in th mixtur to improv th physical proprtis of th wt mix, dlay or acclrat th curing tim, or othrwis chang th finishd matrial. Most concrt is pourd with rinforcing matrials (such as stl rbar) mbddd to provid tnsil strngth, yilding rinforcd concrt.

In th past, lim basd cmnt bindrs, such as lim putty, wr oftn usd but somtims with othr hydraulic cmnts, (watr rsistant) such as a calcium aluminat cmnt or with Portland cmnt to form Portland cmnt concrt (namd for its visual rsmblanc to Portland ston).[5][6] Many othr non-cmntitious typs of concrt xist with othr mthods of binding aggrgat togthr, including asphalt concrt with a bitumn bindr, which is frquntly usd for road surfacs, and polymr concrts that us polymrs as a bindr. Concrt is distinct from mortar. Whras concrt is itslf a building matrial, mortar is a bonding agnt that typically holds bricks, tils and othr masonry units togthr.[7] Grout is anothr matrial associatd with concrt and cmnt. It dos not contain coars aggrgats and is usually ithr pourabl or thixotropic, and is usd to fill gaps btwn masonry componnts or coars aggrgat which has alrady bn put in plac. Som mthods of concrt manufactur and rpair involv pumping grout into th gaps to mak up a solid mass in situ.

Th word concrt coms from th Latin word "concrtus" (maning compact or condnsd),[8] th prfct passiv participl of "concrscr", from "con-" (togthr) and "crscr" (to grow).

Mayan concrt at th ruins of Uxmal (850-925 A.D.) is rfrncd in Incidnts of Travl in th Yucatán by John L. Stphns. "Th roof is flat and had bn covrd with cmnt". "Th floors wr cmnt, in som placs hard, but, by long xposur, brokn, and now crumbling undr th ft." "But throughout th wall was solid, and consisting of larg stons imbddd in mortar, almost as hard as rock."

Small-scal production of concrt-lik matrials was pionrd by th Nabatan tradrs who occupid and controlld a sris of oass and dvlopd a small mpir in th rgions of southrn Syria and northrn Jordan from th 4th cntury BC. Thy discovrd th advantags of hydraulic lim, with som slf-cmnting proprtis, by 700 BC. Thy built kilns to supply mortar for th construction of rubbl masonry houss, concrt floors, and undrground watrproof cistrns. Thy kpt th cistrns scrt as ths nabld th Nabataans to thriv in th dsrt.[9] Som of ths structurs surviv to this day.[9]

Extrior of th Roman Panthon, finishd 128 AD, th largst unrinforcd concrt dom in th world.[10] Intrior of th Panthon dom, sn from bnath. Th concrt for th coffrd dom was laid on moulds, mountd on tmporary scaffolding. Opus camnticium xposd in a charactristic Roman arch. In contrast to modrn concrt structurs, th concrt usd in Roman buildings was usually covrd with brick or ston.

In th Ancint Egyptian and latr Roman ras, buildrs discovrd that adding volcanic ash to lim allowd th mix to st undrwatr. Thy discovrd th pozzolanic raction. Concrt floors wr found in th royal palac of Tiryns, Grc, which dats roughly to 1400-1200 BC.[11][12] Lim mortars wr usd in Grc, such as in Crt and Cyprus, in 800 BC. Th Assyrian Jrwan Aquduct (688 BC) mad us of watrproof concrt.[13] Concrt was usd for construction in many ancint structurs.[14]

Th Romans usd concrt xtnsivly from 300 BC to 476 AD.[15] During th Roman Empir, Roman concrt (or opus camnticium) was mad from quicklim, pozzolana and an aggrgat of pumic. Its widsprad us in many Roman structurs, a ky vnt in th history of architctur trmd th Roman architctural rvolution, frd Roman construction from th rstrictions of ston and brick matrials. It nabld rvolutionary nw dsigns in trms of both structural complxity and dimnsion.[16] Th Colossum in Rom was built largly of concrt, and th Panthon has th world's largst unrinforcd concrt dom.[17]

Concrt, as th Romans knw it, was a nw and rvolutionary matrial. Laid in th shap of archs, vaults and doms, it quickly hardnd into a rigid mass, fr from many of th intrnal thrusts and strains that troubld th buildrs of similar structurs in ston or brick.[18]

Modrn tsts show that opus camnticium had as much comprssiv strngth as modrn Portland-cmnt concrt (ca. 200 kg/cm2 [20 MPa; 2,800 psi]).[19] Howvr, du to th absnc of rinforcmnt, its tnsil strngth was far lowr than modrn rinforcd concrt, and its mod of application also diffrd:[20]

Modrn structural concrt diffrs from Roman concrt in two important dtails. First, its mix consistncy is fluid and homognous, allowing it to b pourd into forms rathr than rquiring hand-layring togthr with th placmnt of aggrgat, which, in Roman practic, oftn consistd of rubbl. Scond, intgral rinforcing stl givs modrn concrt assmblis grat strngth in tnsion, whras Roman concrt could dpnd only upon th strngth of th concrt bonding to rsist tnsion.[21]

Th long-trm durability of Roman concrt structurs has bn found to b du to its us of pyroclastic (volcanic) rock and ash, whrby th crystallization of strätlingit (a spcific and complx calcium aluminosilicat hydrat)[22] and th coalscnc of this and similar calcium–aluminium-silicat–hydrat cmnting bindrs hlpd giv th concrt a gratr dgr of fractur rsistanc vn in sismically activ nvironmnts.[23] Roman concrt is significantly mor rsistant to rosion by sawatr than modrn concrt; it usd pyroclastic matrials which ract with sawatr to form Al-tobrmorit crystals ovr tim.[24][25]

Th widsprad us of concrt in many Roman structurs nsurd that many surviv to th prsnt day. Th Baths of Caracalla in Rom ar just on xampl. Many Roman aquducts and bridgs, such as th magnificnt Pont du Gard in southrn Franc, hav masonry cladding on a concrt cor, as dos th dom of th Panthon. Middl Ags

Aftr th Roman Empir, th us of burnd lim and pozzolana was gratly rducd. Low kiln tmpraturs in th burning of lim, lack of pozzolana, and poor mixing all contributd to a dclin in th quality of concrt and mortar. From th 11th cntury, th incrasd us of ston in church and castl construction ld to an incrasd dmand for mortar. Quality bgan to improv in th 12th cntury through bttr grinding and siving. Mdival lim mortars and concrts wr non-hydraulic and wr usd for binding masonry, "harting" (binding rubbl masonry cors) and foundations. Bartholomaus Anglicus in his D propritatibus rrum (1240) dscribs th making of mortar. In an English translation from 1397, it rads "lym ... is a ston brnt; by mdlyng throf with sond and watr smnt is mad". From th 14th cntury, th quality of mortar was again xcllnt, but only from th 17th cntury was pozzolana commonly addd.[26]

Th Canal du Midi was built using concrt in 1670.[27] Industrial ra Smaton's Towr in Dvon, England Prhaps th gratst stp forward in th modrn us of concrt was Smaton's Towr, built by British nginr John Smaton in Dvon, England, btwn 1756 and 1759. This third Eddyston Lighthous pionrd th us of hydraulic lim in concrt, using pbbls and powdrd brick as aggrgat.[28]

A mthod for producing Portland cmnt was dvlopd in England and patntd by Josph Aspdin in 1824.[29] Aspdin chos th nam for its similarity to Portland ston, which was quarrid on th Isl of Portland in Dorst, England. His son William continud dvlopmnts into th 1840s, arning him rcognition for th dvlopmnt of "modrn" Portland cmnt.[30]

Rinforcd concrt was invntd in 1849 by Josph Monir.[31] and th first rinforcd concrt hous was built by François Coignt[32] in 1853. Th first concrt rinforcd bridg was dsignd and built by Josph Monir in 1875.[33]

Prstrssd concrt and post-tnsiond concrt wr pionrd by Eugèn Fryssint, a Frnch structural and civil nginr. Concrt componnts or structurs ar comprssd by tndon cabls during, or aftr, thir fabrication in ordr to strngthn thm against tnsil forcs dvloping whn put in srvic. Fryssint patntd th tchniqu on 2 Octobr 1928.[34]

Concrt is an artificial composit matrial, comprising a matrix of cmntitious bindr (typically Portland cmnt past or asphalt) and a disprsd phas or "fillr" of aggrgat (typically a rocky matrial, loos stons, and sand). Th bindr "glus" th fillr togthr to form a synthtic conglomrat.[35] Many typs of concrt ar availabl, dtrmind by th formulations of bindrs and th typs of aggrgat usd to suit th application of th nginrd matrial. Ths variabls dtrmin strngth and dnsity, as wll as chmical and thrmal rsistanc of th finishd product. Cross sction of a concrt railway slpr blow a rail

Construction aggrgats consist of larg chunks of matrial in a concrt mix, gnrally a coars gravl or crushd rocks such as limston, or granit, along with finr matrials such as sand.

Cmnt past, most commonly mad of Portland cmnt, is th most prvalnt kind of concrt bindr. For cmntitious bindrs, watr is mixd with th dry cmnt powdr and aggrgat, which producs a smi-liquid slurry (past) that can b shapd, typically by pouring it into a form. Th concrt solidifis and hardns through a chmical procss calld hydration. Th watr racts with th cmnt, which bonds th othr componnts togthr, crating a robust, ston-lik matrial. Othr cmntitious matrials, such as fly ash and slag cmnt, ar somtims addd—ithr pr-blndd with th cmnt or dirctly as a concrt componnt—and bcom a part of th bindr for th aggrgat.[36] Fly ash and slag can nhanc som proprtis of concrt such as frsh proprtis and durability.[36] Altrnativly, othr matrials can also b usd as a concrt bindr: th most prvalnt substitut is asphalt, which is usd as th bindr in asphalt concrt.

Admixturs ar addd to modify th cur rat or proprtis of th matrial. Minral admixturs us rcycld matrials as concrt ingrdints. Conspicuous matrials includ fly ash, a by-product of coal-fird powr plants; ground granulatd blast furnac slag, a by-product of stlmaking; and silica fum, a by-product of industrial lctric arc furnacs.

Structurs mploying Portland cmnt concrt usually includ stl rinforcmnt bcaus this typ of concrt can b formulatd with high comprssiv strngth, but always has lowr tnsil strngth. Thrfor, it is usually rinforcd with matrials that ar strong in tnsion, typically stl rbar.

Th mix dsign dpnds on th typ of structur bing built, how th concrt is mixd and dlivrd, and how it is placd to form th structur.

Portland cmnt is th most common typ of cmnt in gnral usag. It is a basic ingrdint of concrt, mortar, and many plastrs.[37] British masonry workr Josph Aspdin patntd Portland cmnt in 1824. It was namd bcaus of th similarity of its color to Portland limston, quarrid from th English Isl of Portland and usd xtnsivly in London architctur. It consists of a mixtur of calcium silicats (alit, blit), aluminats and frrits—compounds which combin calcium, silicon, aluminium and iron in forms which will ract with watr. Portland cmnt and similar matrials ar mad by hating limston (a sourc of calcium) with clay or shal (a sourc of silicon, aluminium and iron) and grinding this product (calld clinkr) with a sourc of sulfat (most commonly gypsum).

In modrn cmnt kilns, many advancd faturs ar usd to lowr th ful consumption pr ton of clinkr producd. Cmnt kilns ar xtrmly larg, complx, and inhrntly dusty industrial installations, and hav missions which must b controlld. Of th various ingrdints usd to produc a givn quantity of concrt, th cmnt is th most nrgtically xpnsiv. Evn complx and fficint kilns rquir 3.3 to 3.6 gigajouls of nrgy to produc a ton of clinkr and thn grind it into cmnt. Many kilns can b fuld with difficult-to-dispos-of wasts, th most common bing usd tirs. Th xtrmly high tmpraturs and long priods of tim at thos tmpraturs allows cmnt kilns to fficintly and compltly burn vn difficult-to-us fuls.[38]

Combining watr with a cmntitious matrial forms a cmnt past by th procss of hydration. Th cmnt past glus th aggrgat togthr, fills voids within it, and maks it flow mor frly.[39]

As statd by Abrams' law, a lowr watr-to-cmnt ratio yilds a strongr, mor durabl concrt, whras mor watr givs a frr-flowing concrt with a highr slump.[40] Impur watr usd to mak concrt can caus problms whn stting or in causing prmatur failur of th structur.[41]

Portland cmnt consists of fiv major compounds of calcium silicats and aluminats ranging from 5 to 50% in wight, which all undrgo hydration to contribut to final matrial's strngth. Thus, th hydration of cmnt involvs many ractions, oftn occurring at th sam tim. As th ractions procd, th products of th cmnt hydration procss gradually bond togthr th individual sand and gravl particls and othr componnts of th concrt to form a solid mass.[42] Hydration of tricalcium silicat

Du to th natur of th chmical bonds cratd in ths ractions and th final charactristics of th hardnd cmnt past formd, th procss of cmnt hydration is considrd irrvrsibl.[43] Aggrgats Main articl: Construction aggrgat Crushd ston aggrgats Fin and coars aggrgats mak up th bulk of a concrt mixtur. Sand, natural gravl, and crushd ston ar usd mainly for this purpos. Rcycld aggrgats (from construction, dmolition, and xcavation wast) ar incrasingly usd as partial rplacmnts for natural aggrgats, whil a numbr of manufacturd aggrgats, including air-coold blast furnac slag and bottom ash ar also prmittd.

Th siz distribution of th aggrgat dtrmins how much bindr is rquird. Aggrgat with a vry vn siz distribution has th biggst gaps whras adding aggrgat with smallr particls tnds to fill ths gaps. Th bindr must fill th gaps btwn th aggrgat as wll as past th surfacs of th aggrgat togthr, and is typically th most xpnsiv componnt. Thus, variation in sizs of th aggrgat rducs th cost of concrt.[44] Th aggrgat is narly always strongr than th bindr, so its us dos not ngativly affct th strngth of th concrt.

Rdistribution of aggrgats aftr compaction oftn crats non-homognity du to th influnc of vibration. This can lad to strngth gradints.[45]

Dcorativ stons such as quartzit, small rivr stons or crushd glass ar somtims addd to th surfac of concrt for a dcorativ "xposd aggrgat" finish, popular among landscap dsignrs.

Admixturs ar matrials in th form of powdr or fluids that ar addd to th concrt to giv it crtain charactristics not obtainabl with plain concrt mixs. Admixturs ar dfind as additions "mad as th concrt mix is bing prpard".[46] Th most common admixturs ar rtardrs and acclrators. In normal us, admixtur dosags ar lss than 5% by mass of cmnt and ar addd to th concrt at th tim of batching/mixing.[47] (S § Production blow.) Th common typs of admixturs[48] ar as follows:

Acclrators spd up th hydration (hardning) of th concrt. Typical matrials usd ar calcium chlorid, calcium nitrat and sodium nitrat. Howvr, us of chlorids may caus corrosion in stl rinforcing and is prohibitd in som countris, so that nitrats may b favord, vn though thy ar lss ffctiv than th chlorid salt. Acclrating admixturs ar spcially usful for modifying th proprtis of concrt in cold wathr.

Air ntraining agnts add and ntrain tiny air bubbls in th concrt, which rducs damag during frz-thaw cycls, incrasing durability. Howvr, ntraind air ntails a tradoff with strngth, as ach 1% of air may dcras comprssiv strngth by 5%.[49] If too much air bcoms trappd in th concrt as a rsult of th mixing procss, dfoamrs can b usd to ncourag th air bubbl to agglomrat, ris to th surfac of th wt concrt and thn disprs.

Bonding agnts ar usd to crat a bond btwn old and nw concrt (typically a typ of polymr) with wid tmpratur tolranc and corrosion rsistanc. Corrosion inhibitors ar usd to minimiz th corrosion of stl and stl bars in concrt.

Crystallin admixturs ar typically addd during batching of th concrt to lowr prmability. Th raction taks plac whn xposd to watr and un-hydratd cmnt particls to form insolubl ndl-shapd crystals, which fill capillary pors and micro-cracks in th concrt to block pathways for watr and watrborn contaminats. Concrt with crystallin admixtur can xpct to slf-sal as constant xposur to watr will continuously initiat crystallization to nsur prmannt watrproof protction.

Pigmnts can b usd to chang th color of concrt, for asthtics. Plasticizrs incras th workability of plastic, or "frsh", concrt, allowing it to b placd mor asily, with lss consolidating ffort. A typical plasticizr is lignosulfonat. Plasticizrs can b usd to rduc th watr contnt of a concrt whil maintaining workability and ar somtims calld watr-rducrs du to this us. Such tratmnt improvs its strngth and durability charactristics.

Suprplasticizrs (also calld high-rang watr-rducrs) ar a class of plasticizrs that hav fwr dltrious ffcts and can b usd to incras workability mor than is practical with traditional plasticizrs. Suprplasticizrs ar usd to incras comprssiv strngth. It incrass th workability of th concrt and lowrs th nd for watr contnt by 15–30%.

Pumping aids improv pumpability, thickn th past and rduc sparation and blding. Rtardrs slow th hydration of concrt and ar usd in larg or difficult pours whr partial stting is undsirabl bfor compltion of th pour. Typical polyol rtardrs ar sugar, sucros, sodium gluconat, glucos, citric acid, and tartaric acid.

Minral admixturs and blndd cmnts Componnts of cmnt: comparison of chmical and physical charactristics[a][50][51][52] Proprty Portland cmnt Silicous[b] fly ash Calcarous[c] fly ash Slag cmnt Silica fum Proportion by mass (%) SiO2 21.9 52 35 35 85–97 Al2O3 6.9 23 18 12 — F2O3 3 11 6 1 — CaO 63 5 21 40 < 1 MgO 2.5 — — — — SO3 1.7 — — — — Spcific surfac (m2/kg)[d] 370 420 420 400 15,000 – 30,000 Spcific gravity 3.15 2.38 2.65 2.94 2.22 Gnral purpos Primary bindr Cmnt rplacmnt Cmnt rplacmnt Cmnt rplacmnt Proprty nhancr

Valus shown ar approximat: thos of a spcific matrial may vary.

Inorganic matrials that hav pozzolanic or latnt hydraulic proprtis, ths vry fin-graind matrials ar addd to th concrt mix to improv th proprtis of concrt (minral admixturs),[47] or as a rplacmnt for Portland cmnt (blndd cmnts).[53] Products which incorporat limston, fly ash, blast furnac slag, and othr usful matrials with pozzolanic proprtis into th mix, ar bing tstd and usd. Ths dvlopmnts ar vr growing in rlvanc to minimiz th impacts causd by cmnt us, notorious for bing on of th largst producrs (at about 5 to 10%) of global grnhous gas missions.[54] Th us of altrnativ matrials also is capabl of lowring costs, improving concrt proprtis, and rcycling wasts, th latst bing rlvant for circular conomy aspcts of th construction industry, whos dmand is vr growing with gratr impacts on raw matrial xtraction, wast gnration and landfill practics.

Fly ash: A by-product of coal-fird lctric gnrating plants, it is usd to partially rplac Portland cmnt (by up to 60% by mass). Th proprtis of fly ash dpnd on th typ of coal burnt. In gnral, silicous fly ash is pozzolanic, whil calcarous fly ash has latnt hydraulic proprtis.[55] Ground granulatd blast furnac slag (GGBFS or GGBS): A by-product of stl production is usd to partially rplac Portland cmnt (by up to 80% by mass). It has latnt hydraulic proprtis.[56]

Silica fum: A by-product of th production of silicon and frrosilicon alloys. Silica fum is similar to fly ash, but has a particl siz 100 tims smallr. This rsults in a highr surfac-to-volum ratio and a much fastr pozzolanic raction. Silica fum is usd to incras strngth and durability of concrt, but gnrally rquirs th us of suprplasticizrs for workability.[5

High ractivity mtakaolin (HRM): Mtakaolin producs concrt with strngth and durability similar to concrt mad with silica fum. Whil silica fum is usually dark gray or black in color, high-ractivity mtakaolin is usually bright whit in color, making it th prfrrd choic for architctural concrt whr apparanc is important.

Carbon nanofibrs can b addd to concrt to nhanc comprssiv strngth and gain a highr Young's modulus, and also to improv th lctrical proprtis rquird for strain monitoring, damag valuation and slf-halth monitoring of concrt. Carbon fibr has many advantags in trms of mchanical and lctrical proprtis (.g., highr strngth) and slf-monitoring bhavior du to th high tnsil strngth and high lctrical conductivity.[58]

Carbon products hav bn addd to mak concrt lctrically conductiv, for dicing purposs.[59]

Nw rsarch from Japan's Univrsity of Kitakyushu shows that a washd and drid rcycld mix of usd diaprs can b an nvironmntal solution to producing lss landfill and using lss sand in concrt production. A modl hom was built in Indonsia to tst th strngth and durability of th nw diapr-cmnt composit.

Concrt production is th procss of mixing togthr th various ingrdints—watr, aggrgat, cmnt, and any additivs—to produc concrt. Concrt production is tim-snsitiv. Onc th ingrdints ar mixd, workrs must put th concrt in plac bfor it hardns. In modrn usag, most concrt production taks plac in a larg typ of industrial facility calld a concrt plant, or oftn a batch plant. Th usual mthod of placmnt is casting in formwork, which holds th mix in shap until it has st nough to hold its shap unaidd.

In gnral usag, concrt plants com in two main typs, rady mix plants and cntral mix plants. A rady-mix plant mixs all th ingrdints xcpt watr, whil a cntral mix plant mixs all th ingrdints including watr. A cntral-mix plant offrs mor accurat control of th concrt quality through bttr masurmnts of th amount of watr addd, but must b placd closr to th work sit whr th concrt will b usd, sinc hydration bgins at th plant.

A concrt plant consists of larg storag hopprs for various ractiv ingrdints lik cmnt, storag for bulk ingrdints lik aggrgat and watr, mchanisms for th addition of various additivs and amndmnts, machinry to accuratly wigh, mov, and mix som or all of thos ingrdints, and facilitis to dispns th mixd concrt, oftn to a concrt mixr truck.

Modrn concrt is usually prpard as a viscous fluid, so that it may b pourd into forms, which ar containrs rctd in th fild to giv th concrt its dsird shap. Concrt formwork can b prpard in svral ways, such as slip forming and stl plat construction. Altrnativly, concrt can b mixd into dryr, non-fluid forms and usd in factory sttings to manufactur prcast concrt products.

A wid varity of quipmnt is usd for procssing concrt, from hand tools to havy industrial machinry. Whichvr quipmnt buildrs us, howvr, th objctiv is to produc th dsird building matrial; ingrdints must b proprly mixd, placd, shapd, and rtaind within tim constraints. Any intrruption in pouring th concrt can caus th initially placd matrial to bgin to st bfor th nxt batch is addd on top. This crats a horizontal plan of waknss calld a cold joint btwn th two batchs.[60] Onc th mix is whr it should b, th curing procss must b controlld to nsur that th concrt attains th dsird attributs. During concrt prparation, various tchnical dtails may affct th quality and natur of th product.

Dsign mix ratios ar dcidd by an nginr aftr analyzing th proprtis of th spcific ingrdints bing usd. Instad of using a 'nominal mix' of 1 part cmnt, 2 parts sand, and 4 parts aggrgat (th scond xampl from abov), a civil nginr will custom-dsign a concrt mix to xactly mt th rquirmnts of th sit and conditions, stting matrial ratios and oftn dsigning an admixtur packag to fin-tun th proprtis or incras th prformanc nvlop of th mix. Dsign-mix concrt can hav vry broad spcifications that cannot b mt with mor basic nominal mixs, but th involvmnt of th nginr oftn incrass th cost of th concrt mix.

Concrt Mixs ar primarily dividd into nominal mix, standard mix and dsign mix. Nominal mix ratios ar givn in volum of Cmnt : Sand : Aggrgat {\displaystyl {\txt{Cmnt : Sand : Aggrgat}}}. Nominal mixs ar a simpl, fast way of gtting a basic ida of th proprtis of th finishd concrt without having to prform tsting in advanc.

Various govrning bodis (such as British Standards) dfin nominal mix ratios into a numbr of grads, usually ranging from lowr comprssiv strngth to highr comprssiv strngth. Th grads usually indicat th 28-day cub strngth.[61]

Thorough mixing is ssntial to produc uniform, high-quality concrt. Sparat past mixing has shown that th mixing of cmnt and watr into a past bfor combining ths matrials with aggrgats can incras th comprssiv strngth of th rsulting concrt.[62] Th past is gnrally mixd in a high-spd, shar-typ mixr at a w/c (watr to cmnt ratio) of 0.30 to 0.45 by mass. Th cmnt past prmix may includ admixturs such as acclrators or rtardrs, suprplasticizrs, pigmnts, or silica fum. Th prmixd past is thn blndd with aggrgats and any rmaining batch watr and final mixing is compltd in convntional concrt mixing quipmnt.[63]

Workability is th ability of a frsh (plastic) concrt mix to fill th form/mold proprly with th dsird work (pouring, pumping, sprading, tamping, vibration) and without rducing th concrt's quality. Workability dpnds on watr contnt, aggrgat (shap and siz distribution), cmntitious contnt and ag (lvl of hydration) and can b modifid by adding chmical admixturs, lik suprplasticizr. Raising th watr contnt or adding chmical admixturs incrass concrt workability. Excssiv watr lads to incrasd blding or sgrgation of aggrgats (whn th cmnt and aggrgats start to sparat), with th rsulting concrt having rducd quality. Changs in gradation can also affct workability of th concrt, although a wid rang of gradation can b usd for various applications.[64][65] An undsirabl gradation can man using a larg aggrgat that is too larg for th siz of th formwork, or which has too fw smallr aggrgat grads to srv to fill th gaps btwn th largr grads, or using too littl or too much sand for th sam rason, or using too littl watr, or too much cmnt, or vn using jaggd crushd ston instad of smoothr round aggrgat such as pbbls. Any combination of ths factors and othrs may rsult in a mix which is too harsh, i.., which dos not flow or sprad out smoothly, is difficult to gt into th formwork, and which is difficult to surfac finish.[66]

Workability can b masurd by th concrt slump tst, a simpl masur of th plasticity of a frsh batch of concrt following th ASTM C 143 or EN 12350-2 tst standards. Slump is normally masurd by filling an "Abrams con" with a sampl from a frsh batch of concrt. Th con is placd with th wid nd down onto a lvl, non-absorptiv surfac. It is thn filld in thr layrs of qual volum, with ach layr bing tampd with a stl rod to consolidat th layr. Whn th con is carfully liftd off, th nclosd matrial slumps a crtain amount, owing to gravity. A rlativly dry sampl slumps vry littl, having a slump valu of on or two inchs (25 or 50 mm) out of on foot (300 mm). A rlativly wt concrt sampl may slump as much as ight inchs. Workability can also b masurd by th flow tabl tst.

Slump can b incrasd by addition of chmical admixturs such as plasticizr or suprplasticizr without changing th watr-cmnt ratio.[67] Som othr admixturs, spcially air-ntraining admixtur, can incras th slump of a mix.

High-flow concrt, lik slf-consolidating concrt, is tstd by othr flow-masuring mthods. On of ths mthods includs placing th con on th narrow nd and obsrving how th mix flows through th con whil it is gradually liftd.

Aftr mixing, concrt is a fluid and can b pumpd to th location whr ndd. Curing A concrt slab bing kpt hydratd during watr curing by submrsion (ponding) Maintaining optimal conditions for cmnt hydration Concrt must b kpt moist during curing in ordr to achiv optimal strngth and durability.[68] During curing hydration occurs, allowing calcium-silicat hydrat (C-S-H) to form. Ovr 90% of a mix's final strngth is typically rachd within four wks, with th rmaining 10% achivd ovr yars or vn dcads.[69] Th convrsion of calcium hydroxid in th concrt into calcium carbonat from absorption of CO2 ovr svral dcads furthr strngthns th concrt and maks it mor rsistant to damag. This carbonation raction, howvr, lowrs th pH of th cmnt por solution and can corrod th rinforcmnt bars.

Hydration and hardning of concrt during th first thr days is critical. Abnormally fast drying and shrinkag du to factors such as vaporation from wind during placmnt may lad to incrasd tnsil strsss at a tim whn it has not yt gaind sufficint strngth, rsulting in gratr shrinkag cracking. Th arly strngth of th concrt can b incrasd if it is kpt damp during th curing procss. Minimizing strss prior to curing minimizs cracking. High-arly-strngth concrt is dsignd to hydrat fastr, oftn by incrasd us of cmnt that incrass shrinkag and cracking. Th strngth of concrt changs (incrass) for up to thr yars. It dpnds on cross-sction dimnsion of lmnts and conditions of structur xploitation.[70] Addition of short-cut polymr fibrs can improv (rduc) shrinkag-inducd strsss during curing and incras arly and ultimat comprssion strngth.[71]

Proprly curing concrt lads to incrasd strngth and lowr prmability and avoids cracking whr th surfac dris out prmaturly. Car must also b takn to avoid frzing or ovrhating du to th xothrmic stting of cmnt. Impropr curing can caus scaling, rducd strngth, poor abrasion rsistanc and cracking. Curing tchniqus avoiding watr loss by vaporation

During th curing priod, concrt is idally maintaind at controlld tmpratur and humidity. To nsur full hydration during curing, concrt slabs ar oftn sprayd with "curing compounds" that crat a watr-rtaining film ovr th concrt. Typical films ar mad of wax or rlatd hydrophobic compounds. Aftr th concrt is sufficintly curd, th film is allowd to abrad from th concrt through normal us.[72]

Traditional conditions for curing involv spraying or ponding th concrt surfac with watr. Th adjacnt pictur shows on of many ways to achiv this, ponding—submrging stting concrt in watr and wrapping in plastic to prvnt dhydration. Additional common curing mthods includ wt burlap and plastic shting covring th frsh concrt.

For highr-strngth applications, acclratd curing tchniqus may b applid to th concrt. A common tchniqu involvs hating th pourd concrt with stam, which srvs to both kp it damp and rais th tmpratur so that th hydration procss procds mor quickly and mor thoroughly.

Asphalt concrt (commonly calld asphalt,[73] blacktop, or pavmnt in North Amrica, and tarmac, bitumn macadam, or rolld asphalt in th Unitd Kingdom and th Rpublic of Irland) is a composit matrial commonly usd to surfac roads, parking lots, airports, as wll as th cor of mbankmnt dams.[74] Asphalt mixturs hav bn usd in pavmnt construction sinc th bginning of th twntith cntury.[75] It consists of minral aggrgat bound togthr with asphalt, laid in layrs, and compactd. Th procss was rfind and nhancd by Blgian invntor and U.S. immigrant Edward D Smdt.[76]

Th trms asphalt (or asphaltic) concrt, bituminous asphalt concrt, and bituminous mixtur ar typically usd only in nginring and construction documnts, which dfin concrt as any composit matrial composd of minral aggrgat adhrd with a bindr. Th abbrviation, AC, is somtims usd for asphalt concrt but can also dnot asphalt contnt or asphalt cmnt, rfrring to th liquid asphalt portion of th composit matrial.

Graphn nhancd concrts ar standard dsigns of concrt mixs, xcpt that during th cmnt-mixing or production procss, a small amount of chmically nginrd graphn (typically < 0.5% by wight) is addd.[77][78] Ths nhancd graphn concrts ar dsignd around th concrt application.

Bactria such as Bacillus pasturii, Bacillus psudofirmus, Bacillus cohnii, Sporosarcina pasturi, and Arthrobactr crystallopoits incras th comprssion strngth of concrt through thir biomass. Howvr som forms of bactria can also b concrt-dstroying.[79] Bacillus sp. CT-5. can rduc corrosion of rinforcmnt in rinforcd concrt by up to four tims. Sporosarcina pasturii rducs watr and chlorid prmability. B. pasturii incrass rsistanc to acid.[80] Bacillus pasturii and B. spharicuscan induc calcium carbonat prcipitation in th surfac of cracks, adding comprssion strngth.[81]

Nanoconcrt (also splld "nano concrt"' or "nano-concrt") is a class of matrials that contains Portland cmnt particls that ar no gratr than 100 μm[82] and particls of silica no gratr than 500 μm, which fill voids that would othrwis occur in normal concrt, thrby substantially incrasing th matrial's strngth.[citation ndd] It is widly usd in foot and highway bridgs whr high flxural and comprssiv strngth ar indicatd.[81]

Prvious concrt is a mix of spcially gradd coars aggrgat, cmnt, watr, and littl-to-no fin aggrgats. This concrt is also known as "no-fins" or porous concrt. Mixing th ingrdints in a carfully controlld procss crats a past that coats and bonds th aggrgat particls. Th hardnd concrt contains intrconnctd air voids totaling approximatly 15 to 25 prcnt. Watr runs through th voids in th pavmnt to th soil undrnath. Air ntrainmnt admixturs ar oftn usd in frz-thaw climats to minimiz th possibility of frost damag. Prvious concrt also prmits rainwatr to filtr through roads and parking lots, to rcharg aquifrs, instad of contributing to runoff and flooding.[83]

Polymr concrts ar mixturs of aggrgat and any of various polymrs and may b rinforcd. Th cmnt is costlir than lim-basd cmnts, but polymr concrts nvrthlss hav advantags; thy hav significant tnsil strngth vn without rinforcmnt, and thy ar largly imprvious to watr. Polymr concrts ar frquntly usd for th rpair and construction of othr applications, such as drains.

Volcanic concrt substituts volcanic rock for th limston that is burnd to form clinkr. It consums a similar amount of nrgy, but dos not dirctly mit carbon as a byproduct.[84] Volcanic rock/ash ar usd as supplmntary cmntitious matrials in concrt to improv th rsistanc to sulfat, chlorid and alkali silica raction du to por rfinmnt.[85] Also, thy ar gnrally cost ffctiv in comparison to othr aggrgats,[86] good for smi and light wight concrts,[86] and good for thrmal and acoustic insulation.[86]

Pyroclastic matrials, such as pumic, scoria, and ashs ar formd from cooling magma during xplosiv volcanic ruptions. Thy ar usd as supplmntary cmntitious matrials (SCM) or as aggrgats for cmnts and concrts.[87] Thy hav bn xtnsivly usd sinc ancint tims to produc matrials for building applications. For xampl, pumic and othr volcanic glasss wr addd as a natural pozzolanic matrial for mortars and plastrs during th construction of th Villa San Marco in th Roman priod (89 BC – 79 AD), which rmain on of th bst-prsrvd otium villa of th Bay of Napls in Italy.[88]

Wast light is form of polymr modifid concrt. Th spcific polymr admixtur allows th rplacmnt of all th traditional aggrgats (gravl, sand, ston) by any mixtur of solid wast matrials in th grain siz of 3–10 mm to form a low-comprssiv-strngth (3–20 N/mm2) product[89] for road and building construction. On cubic mtr of wast light concrt contains 1.1–1.3 m3 of shrddd wast and no othr aggrgats.

Sulfur concrt is a spcial concrt that uss sulfur as a bindr and dos not rquir cmnt or watr.

Concrt has rlativly high comprssiv strngth, but much lowr tnsil strngth.[90] Thrfor, it is usually rinforcd with matrials that ar strong in tnsion (oftn stl). Th lasticity of concrt is rlativly constant at low strss lvls but starts dcrasing at highr strss lvls as matrix cracking dvlops. Concrt has a vry low cofficint of thrmal xpansion and shrinks as it maturs. All concrt structurs crack to som xtnt, du to shrinkag and tnsion. Concrt that is subjctd to long-duration forcs is pron to crp.

Tsts can b prformd to nsur that th proprtis of concrt corrspond to spcifications for th application. Comprssion tsting of a concrt cylindr

Th ingrdints affct th strngths of th matrial. Concrt strngth valus ar usually spcifid as th lowr-bound comprssiv strngth of ithr a cylindrical or cubic spcimn as dtrmind by standard tst procdurs.

Th strngths of concrt is dictatd by its function. Vry low-strngth—14 MPa (2,000 psi) or lss—concrt may b usd whn th concrt must b lightwight.[91] Lightwight concrt is oftn achivd by adding air, foams, or lightwight aggrgats, with th sid ffct that th strngth is rducd. For most routin uss, 20 to 32 MPa (2,900 to 4,600 psi) concrt is oftn usd. 40 MPa (5,800 psi) concrt is radily commrcially availabl as a mor durabl, although mor xpnsiv, option. Highr-strngth concrt is oftn usd for largr civil projcts.[92] Strngths abov 40 MPa (5,800 psi) ar oftn usd for spcific building lmnts. For xampl, th lowr floor columns of high-ris concrt buildings may us concrt of 80 MPa (11,600 psi) or mor, to kp th siz of th columns small. Bridgs may us long bams of high-strngth concrt to lowr th numbr of spans rquird.[93][94] Occasionally, othr structural nds may rquir high-strngth concrt. If a structur must b vry rigid, concrt of vry high strngth may b spcifid, vn much strongr than is rquird to bar th srvic loads. Strngths as high as 130 MPa (18,900 psi) hav bn usd commrcially for ths rasons.[93]

Th cmnt producd for making concrt accounts for about 8% of worldwid CO2 missions pr yar (compard to, .g., global aviation at 1.9%).[95][96] Th two largst sourcs of CO2 ar producd by th cmnt manufacturing procss, arising from (1) th dcarbonation raction of limston in th cmnt kiln (T ≈ 950 °C), and (2) from th combustion of fossil ful to rach th sintring tmpratur (T ≈ 1450 °C) of cmnt clinkr in th kiln. Th nrgy rquird for xtracting, crushing, and mixing th raw matrials (construction aggrgats usd in th concrt production, and also limston and clay fding th cmnt kiln) is lowr. Enrgy rquirmnt for transportation of rady-mix concrt is also lowr bcaus it is producd narby th construction sit from local rsourcs, typically manufacturd within 100 kilomtrs of th job sit.[97] Th ovrall mbodid nrgy of concrt at roughly 1 to 1.5 mgajouls pr kilogram is thrfor lowr than for many structural and construction matrials.[98]

Onc in plac, concrt offrs a grat nrgy fficincy ovr th liftim of a building.[99] Concrt walls lak air far lss than thos mad of wood frams.[100] Air lakag accounts for a larg prcntag of nrgy loss from a hom. Th thrmal mass proprtis of concrt incras th fficincy of both rsidntial and commrcial buildings. By storing and rlasing th nrgy ndd for hating or cooling, concrt's thrmal mass dlivrs yar-round bnfits by rducing tmpratur swings insid and minimizing hating and cooling costs.[101] Whil insulation rducs nrgy loss through th building nvlop, thrmal mass uss walls to stor and rlas nrgy. Modrn concrt wall systms us both xtrnal insulation and thrmal mass to crat an nrgy-fficint building. Insulating concrt forms (ICFs) ar hollow blocks or panls mad of ithr insulating foam or rastra that ar stackd to form th shap of th walls of a building and thn filld with rinforcd concrt to crat th structur.

Concrt buildings ar mor rsistant to fir than thos constructd using stl frams, sinc concrt has lowr hat conductivity than stl and can thus last longr undr th sam fir conditions. Concrt is somtims usd as a fir protction for stl frams, for th sam ffct as abov. Concrt as a fir shild, for xampl Fondu fyr, can also b usd in xtrm nvironmnts lik a missil launch pad.

Options for non-combustibl construction includ floors, cilings and roofs mad of cast-in-plac and hollow-cor prcast concrt. For walls, concrt masonry tchnology and Insulating Concrt Forms (ICFs) ar additional options. ICFs ar hollow blocks or panls mad of firproof insulating foam that ar stackd to form th shap of th walls of a building and thn filld with rinforcd concrt to crat th structur.

Concrt also provids good rsistanc against xtrnally applid forcs such as high winds, hurricans, and tornados owing to its latral stiffnss, which rsults in minimal horizontal movmnt. Howvr, this stiffnss can work against crtain typs of concrt structurs, particularly whr a rlativly highr flxing structur is rquird to rsist mor xtrm forcs.

As discussd abov, concrt is vry strong in comprssion, but wak in tnsion. Largr arthquaks can gnrat vry larg shar loads on structurs. Ths shar loads subjct th structur to both tnsil and comprssional loads. Concrt structurs without rinforcmnt, lik othr unrinforcd masonry structurs, can fail during svr arthquak shaking. Unrinforcd masonry structurs constitut on of th largst arthquak risks globally.[102] Ths risks can b rducd through sismic rtrofitting of at-risk buildings, (.g. school buildings in Istanbul, Turky).[103]

Concrt is on of th most durabl building matrials. It provids suprior fir rsistanc compard with woodn construction and gains strngth ovr tim. Structurs mad of concrt can hav a long srvic lif.[104] Concrt is usd mor than any othr artificial matrial in th world.[105] As of 2006, about 7.5 billion cubic mtrs of concrt ar mad ach yar, mor than on cubic mtr for vry prson on Earth.[106]

Th us of rinforcmnt, in th form of iron was introducd in th 1850s by Frnch industrialist François Coignt, and it was not until th 1880s that Grman civil nginr G. A. Wayss usd stl as rinforcmnt. Concrt is a rlativly brittl matrial that is strong undr comprssion but lss in tnsion. Plain, unrinforcd concrt is unsuitabl for many structurs as it is rlativly poor at withstanding strsss inducd by vibrations, wind loading, and so on. Hnc, to incras its ovrall strngth, stl rods, wirs, msh or cabls can b mbddd in concrt bfor it is st. This rinforcmnt, oftn known as rbar, rsists tnsil forcs.[108]

Rinforcd concrt (RC) is a vrsatil composit and on of th most widly usd matrials in modrn construction. It is mad up of diffrnt constitunt matrials with vry diffrnt proprtis that complmnt ach othr. In th cas of rinforcd concrt, th componnt matrials ar almost always concrt and stl. Ths two matrials form a strong bond togthr and ar abl to rsist a varity of applid forcs, ffctivly acting as a singl structural lmnt.[109]

Rinforcd concrt can b prcast or cast-in-plac (in situ) concrt, and is usd in a wid rang of applications such as; slab, wall, bam, column, foundation, and fram construction. Rinforcmnt is gnrally placd in aras of th concrt that ar likly to b subjct to tnsion, such as th lowr portion of bams. Usually, thr is a minimum of 50 mm covr, both abov and blow th stl rinforcmnt, to rsist spalling and corrosion which can lad to structural instability.[108] Othr typs of non-stl rinforcmnt, such as Fibr-rinforcd concrts ar usd for spcializd applications, prdominatly as a mans of controlling cracking.[109]

Prcast concrt is concrt which is cast in on plac for us lswhr and is a mobil matrial. Th largst part of prcast production is carrid out in th works of spcialist supplirs, although in som instancs, du to conomic and gographical factors, scal of product or difficulty of accss, th lmnts ar cast on or adjacnt to th construction sit.[110] Prcasting offrs considrabl advantags bcaus it is carrid out in a controlld nvironmnt, protctd from th lmnts, but th downsid of this is th contribution to grnhous gas mission from transportation to th construction sit.[109]

Prfrrd dimnsion schms xist, with lmnts of trid and tstd dsigns availabl from a catalogu. Major savings in tim rsult from manufactur of structural lmnts apart from th sris of vnts which dtrmin ovrall duration of th construction, known by planning nginrs as th 'critical path'.

Availability of Laboratory facilitis capabl of th rquird control tsts, many bing crtifid for spcific tsting in accordanc with National Standards. Equipmnt with capability suitd to spcific typs of production such as strssing bds with appropriat capacity, moulds and machinry ddicatd to particular products.

Arial photo of rconstruction at Taum Sauk (Missouri) pumpd storag facility in lat Novmbr 2009. Aftr th original rsrvoir faild, th nw rsrvoir was mad of rollr-compactd concrt.

Du to cmnt's xothrmic chmical raction whil stting up, larg concrt structurs such as dams, navigation locks, larg mat foundations, and larg brakwatrs gnrat xcssiv hat during hydration and associatd xpansion. To mitigat ths ffcts, post-cooling[111] is commonly applid during construction. An arly xampl at Hoovr Dam usd a ntwork of pips btwn vrtical concrt placmnts to circulat cooling watr during th curing procss to avoid damaging ovrhating. Similar systms ar still usd; dpnding on volum of th pour, th concrt mix usd, and ambint air tmpratur, th cooling procss may last for many months aftr th concrt is placd. Various mthods also ar usd to pr-cool th concrt mix in mass concrt structurs.[111]

Anothr approach to mass concrt structurs that minimizs cmnt's thrmal by-product is th us of rollr-compactd concrt, which uss a dry mix which has a much lowr cooling rquirmnt than convntional wt placmnt. It is dpositd in thick layrs as a smi-dry matrial thn rollr compactd into a dns, strong mass.

Raw concrt surfacs tnd to b porous and hav a rlativly unintrsting apparanc. Many finishs can b applid to improv th apparanc and prsrv th surfac against staining, watr pntration, and frzing.

Exampls of improvd apparanc includ stampd concrt whr th wt concrt has a pattrn imprssd on th surfac, to giv a pavd, cobbld or brick-lik ffct, and may b accompanid with coloration. Anothr popular ffct for flooring and tabl tops is polishd concrt whr th concrt is polishd optically flat with diamond abrasivs and sald with polymrs or othr salants.

Othr finishs can b achivd with chisling, or mor convntional tchniqus such as painting or covring it with othr matrials.

Prstrssd concrt is a form of rinforcd concrt that builds in comprssiv strsss during construction to oppos tnsil strsss xprincd in us. This can gratly rduc th wight of bams or slabs, by bttr distributing th strsss in th structur to mak optimal us of th rinforcmnt. For xampl, a horizontal bam tnds to sag. Prstrssd rinforcmnt along th bottom of th bam countracts this. In pr-tnsiond concrt, th prstrssing is achivd by using stl or polymr tndons or bars that ar subjctd to a tnsil forc prior to casting, or for post-tnsiond concrt, aftr casting.

Prtnsiond concrt is almost always prcast, and contains stl wirs (tndons) that ar hld in tnsion whil th concrt is placd and sts around thm. Post-tnsiond concrt has ducts through it. Aftr th concrt has gaind strngth, tndons ar pulld through th ducts and strssd. Th ducts ar thn filld with grout. Bridgs built in this way hav xprincd considrabl corrosion of th tndons, so xtrnal post-tnsioning may now b usd in which th tndons run along th outr surfac of th concrt.

Mor than 55,000 mils (89,000 km) of highways in th Unitd Stats ar pavd with this matrial. Rinforcd concrt, prstrssd concrt and prcast concrt ar th most widly usd typs of concrt functional xtnsions in modrn days. For mor information s Brutalist architctur.

Onc mixd, concrt is typically transportd to th plac whr it is intndd to bcom a structural itm. Various mthods of transportation and placmnt ar usd dpnding on th distancs involv, quantity ndd, and othr dtails of application. Larg amounts ar oftn transportd by truck, pourd fr undr gravity or through a trmi, or pumpd through a pip. Smallr amounts may b carrid in a skip (a mtal containr which can b tiltd or opnd to rlas th contnts, usually transportd by cran or hoist), or whlbarrow, or carrid in toggl bags for manual placmnt undrwatr.

Extrm wathr conditions (xtrm hat or cold; windy conditions, and humidity variations) can significantly altr th quality of concrt. Many prcautions ar obsrvd in cold wathr placmnt.[113] Low tmpraturs significantly slow th chmical ractions involvd in hydration of cmnt, thus affcting th strngth dvlopmnt. Prvnting frzing is th most important prcaution, as formation of ic crystals can caus damag to th crystallin structur of th hydratd cmnt past. If th surfac of th concrt pour is insulatd from th outsid tmpraturs, th hat of hydration will prvnt frzing.

Th minimum strngth bfor xposing concrt to xtrm cold is 500 psi (3.4 MPa). CSA A 23.1 spcifid a comprssiv strngth of 7.0 MPa to b considrd saf for xposur to frzing.

Concrt may b placd and curd undrwatr. Car must b takn in th placmnt mthod to prvnt washing out th cmnt. Undrwatr placmnt mthods includ th trmi, pumping, skip placmnt, manual placmnt using toggl bags, and bagwork.[115]

Groutd aggrgat is an altrnativ mthod of forming a concrt mass undrwatr, whr th forms ar filld with coars aggrgat and th voids thn compltly filld with pumpd grout.[115]

Concrt roads ar mor ful fficint to driv on,[116] mor rflctiv and last significantly longr than othr paving surfacs, yt hav a much smallr markt shar than othr paving solutions. Modrn-paving mthods and dsign practics hav changd th conomics of concrt paving, so that a wll-dsignd and placd concrt pavmnt will b lss xpnsiv on initial costs and significantly lss xpnsiv ovr th lif cycl. Anothr major bnfit is that prvious concrt can b usd, which liminats th nd to plac storm drains nar th road, and rducing th nd for slightly slopd roadway to hlp rainwatr to run off. No longr rquiring discarding rainwatr through us of drains also mans that lss lctricity is ndd (mor pumping is othrwis ndd in th watr-distribution systm), and no rainwatr gts pollutd as it no longr mixs with pollutd watr. Rathr, it is immdiatly absorbd by th ground.[citation ndd]

A major componnt of concrt is cmnt, a fin powdr usd mainly to bind sand and coarsr aggrgats togthr in concrt. Although a varity of cmnt typs xist, th most common is "Portland cmnt", which is producd by mixing clinkr with smallr quantitis of othr additivs such as gypsum and ground limston. Th production of clinkr, th main constitunt of cmnt, is rsponsibl for th bulk of th sctor's grnhous gas missions, including both nrgy intnsity and procss missions.[117]

Th cmnt industry is on of th thr primary producrs of carbon dioxid, a major grnhous gas – th othr two bing nrgy production and transportation industris. On avrag, vry tonn of cmnt producd rlass on tonn of CO2 into th atmosphr. Pionr cmnt manufacturrs hav claimd to rach lowr carbon intnsitis, with 590 kg of CO2q pr tonn of cmnt producd.[118] Th missions ar du to combustion and calcination procsss,[119] which roughly account for 40% and 60% of th grnhous gass, rspctivly. Considring that cmnt is only a fraction of th constitunts of concrt, it is stimatd that a tonn of concrt is rsponsibl for mitting about 100–200 kg of CO2.[120][121] Evry yar mor than 10 billion tonns of concrt ar usd worldwid.[121] In th coming yars, larg quantitis of concrt will continu to b usd, and th mitigation of CO2 missions from th sctor will b vn mor critical.

Concrt is usd to crat hard surfacs that contribut to surfac runoff, which can caus havy soil rosion, watr pollution, and flooding, but convrsly can b usd to divrt, dam, and control flooding. Concrt dust rlasd by building dmolition and natural disastrs can b a major sourc of dangrous air pollution. Concrt is a contributor to th urban hat island ffct, though lss so than asphalt.

Rducing th cmnt clinkr contnt might hav positiv ffcts on th nvironmntal lif-cycl assssmnt of concrt. Som rsarch work on rducing th cmnt clinkr contnt in concrt has alrady bn carrid out. Howvr, thr xist diffrnt rsarch stratgis. Oftn rplacmnt of som clinkr for larg amounts of slag or fly ash was invstigatd basd on convntional concrt tchnology. This could lad to a wast of scarc raw matrials such as slag and fly ash. Th aim of othr rsarch activitis is th fficint us of cmnt and ractiv matrials lik slag and fly ash in concrt basd on a modifid mix dsign approach.[122]

An nvironmntal invstigation found that th mbodid carbon of a prcast concrt facad can b rducd by 50% whn using th prsntd fibr rinforcd high prformanc concrt in plac of typical rinforcd concrt cladding.[123]

Studis hav bn conductd about commrcialization of low-carbon concrts. Lif cycl assssmnt (LCA) of low-carbon concrt was invstigatd according to th ground granulatd blast-furnac slag (GGBS) and fly ash (FA) rplacmnt ratios. Global warming potntial (GWP) of GGBS dcrasd by 1.1 kg CO2 q/m3, whil FA dcrasd by 17.3 kg CO2 q/m3 whn th minral admixtur rplacmnt ratio was incrasd by 10%. This study also compard th comprssiv strngth proprtis of binary blndd low-carbon concrt according to th rplacmnt ratios, and th applicabl rang of mixing proportions was drivd.[124]

High-prformanc building matrials will b particularly important for nhancing rsilinc, including for flood dfnss and critical-infrastructur protction. Risks to infrastructur and citis posd by xtrm wathr vnts ar spcially srious for thos placs xposd to flood and hurrican damag, but also whr rsidnts nd protction from xtrm summr tmpraturs. Traditional concrt can com undr strain whn xposd to humidity and highr concntrations of atmosphric CO2. Whil concrt is likly to rmain important in applications whr th nvironmnt is challnging, novl, smartr and mor adaptabl matrials ar also ndd.[121][126]

Grinding of concrt can produc hazardous dust. Exposur to cmnt dust can lad to issus such as silicosis, kidny disas, skin irritation and similar ffcts. Th U.S. National Institut for Occupational Safty and Halth in th Unitd Stats rcommnds attaching local xhaust vntilation shrouds to lctric concrt grindrs to control th sprad of this dust. In addition, th Occupational Safty and Halth Administration (OSHA) has placd mor stringnt rgulations on companis whos workrs rgularly com into contact with silica dust. An updatd silica rul, which OSHA put into ffct 23 Sptmbr 2017 for construction companis, rstrictd th amount of brathabl crystallin silica workrs could lgally com into contact with to 50 micro grams pr cubic mtr of air pr 8-hour workday. That sam rul wnt into ffct 23 Jun 2018 for gnral industry, hydraulic fracturing and maritim. That dadlin was xtndd to 23 Jun 2021 for nginring controls in th hydraulic fracturing industry. Companis which fail to mt th tightnd safty rgulations can fac financial chargs and xtnsiv pnaltis. Th prsnc of som substancs in concrt, including usful and unwantd additivs, can caus halth concrns du to toxicity and radioactivity. Frsh concrt (bfor curing is complt) is highly alkalin and must b handld with propr protctiv quipmnt.

Th Tunkhannock Viaduct in northastrn Pnnsylvania opnd in 1915 and is still in rgular us today

Concrt can b damagd by many procsss, such as th xpansion of corrosion products of th stl rinforcmnt bars, frzing of trappd watr, fir or radiant hat, aggrgat xpansion, sa watr ffcts, bactrial corrosion, laching, rosion by fast-flowing watr, physical damag and chmical damag (from carbonatation, chlorids, sulfats and distillat watr).[128] Th micro fungi Asprgillus altrnaria and Cladosporium wr abl to grow on sampls of concrt usd as a radioactiv wast barrir in th Chrnobyl ractor; laching aluminium, iron, calcium, and silicon.[129]

Concrt may b considrd wast according to th Europan Commission dcision of 2014/955/EU for th List of Wast undr th cods: 17 (construction and dmolition wasts, including xcavatd soil from contaminatd sits) 01 (concrt, bricks, tils and cramics), 01 (concrt), and 17.01.06* (mixturs of, sparat fractions of concrt, bricks, tils and cramics containing hazardous substancs), and 17.01.07 (mixturs of, sparat fractions of concrt, bricks, tils and cramics othr than thos mntiond in 17.01.06).[130] It is stimatd that in 2018 th Europan Union gnratd 371,910 thousand tons of minral wast from construction and dmolition, and clos to 4% of this quantity is considrd hazardous. Grmany, Franc and th Unitd Kingdom wr th top thr pollutrs with 86,412 thousand tons, 68,976 and 68,732 thousand tons of construction wast gnration, rspctivly.[131]

Currntly, thr is not an End-of-Wast critria for concrt matrials in th EU. Howvr, diffrnt sctors hav bn proposing altrnativs for concrt wast and r purposing it as a scondary raw matrial in various applications, including concrt manufacturing itslf.[132]

Rus of blocks in original form, or by cutting into smallr blocks, has vn lss nvironmntal impact; howvr, only a limitd markt currntly xists. Improvd building dsigns that allow for slab rus and building transformation without dmolition could incras this us. Hollow cor concrt slabs ar asy to dismantl and th span is normally constant, making thm good for rus.[127]

Othr cass of r-us ar possibl with pr-cast concrt pics: through slctiv dmolition, such pics can b disassmbld and collctd for furthr us in othr building sits. Studis show that back-building and rmounting plans for building units (i.., r-us of pr-fabricatd concrt) is an altrnativ for a kind of construction which protcts rsourcs and savs nrgy. Espcially long-living, durabl, nrgy-intnsiv building matrials, such as concrt, can b kpt in th lif-cycl longr through rcycling. Prfabricatd constructions ar th prrquisits for constructions ncssarily capabl of bing takn apart. In th cas of optimal application in th building carcass, savings in costs ar stimatd in 26%, a lucrativ complmnt to nw building mthods. Howvr, this dpnds on svral courss to b st.[133] Th viability of this altrnativ has to b studid as th logistics associatd with transporting havy pics of concrt can impact th opration financially and also incras th carbon footprint of th projct. Also, vr changing rgulations on nw buildings worldwid may rquir highr quality standards for construction lmnts and inhibit th us of old lmnts which may b classifid as obsolt.

Concrt rcycling is an incrasingly common mthod for disposing of concrt structurs. Concrt dbris wr onc routinly shippd to landfills for disposal, but rcycling is incrasing du to improvd nvironmntal awarnss, govrnmntal laws and conomic bnfits.

Contrary to gnral blif, concrt rcovry is achivabl – concrt can b crushd and rusd as aggrgat in nw projcts.[127] Rcycling or rcovring concrt rducs natural rsourc xploitation and associatd transportation costs, and rducs wast landfill. Howvr, it has littl impact on rducing grnhous gas missions as most missions occur whn cmnt is mad, and cmnt alon cannot b rcycld. At prsnt, most rcovrd concrt is usd for road sub-bas and civil nginring projcts. From a sustainability viwpoint, ths rlativly low-grad uss currntly provid th optimal outcom.[134]

Th rcycling procss can b don in situ, with mobil plants, or in spcific rcycling units. Th input matrial can b rturnd concrt which is frsh (wt) from rady-mix trucks, production wast at a pr-cast production facility, or wast from construction and dmolition. Th most significant sourc is dmolition wast, prfrably pr-sortd from slctiv dmolition procsss.[127]

By far th most common mthod for rcycling dry and hardnd concrt involvs crushing. Mobil sortrs and crushrs ar oftn installd on construction sits to allow on-sit procssing. In othr situations, spcific procssing sits ar stablishd, which ar usually abl to produc highr quality aggrgat. Scrns ar usd to achiv dsird particl siz, and rmov dirt, forign particls and fin matrial from th coars aggrgat.[135][127]

Chlorid and sulfats ar undsird contaminants originatd from soil and wathring and can provok corrosion problms on aluminium and stl structurs.[135] Th final product, Rcycld Concrt Aggrgat (RCA), prsnts intrsting proprtis such as: angular shap, roughr surfac, lowr spcific gravity (20%), highr watr absorption, and pH gratr than 11 – this lvatd pH incrass th risk of alkali ractions.[127]

Th lowr dnsity of RCA usually Incrass projct fficincy and improv job cost – rcycld concrt aggrgats yild mor volum by wight (up to 15%).[134] Th physical proprtis of coars aggrgats mad from crushd dmolition concrt mak it th prfrrd matrial for applications such as road bas and sub-bas. This is bcaus rcycld aggrgats oftn hav bttr compaction proprtis and rquir lss cmnt for sub-bas uss. Furthrmor, it is gnrally chapr to obtain than virgin matrial.[127] Applications of rcycld concrt aggrgat

Th main commrcial applications of th final rcycld concrt aggrgat ar: Aggrgat bas cours (road bas), or th untratd aggrgats usd as foundation for roadway pavmnt, is th undrlying layr (undr pavmnt surfacing) which forms a structural foundation for paving. To this dat this has bn th most popular application for RCA du to tchnical-conomic aspcts.[136] Aggrgat for rady-mix concrt, by rplacing from 10 to 45% of th natural aggrgats in th concrt mix with a blnd of cmnt, sand and watr. Som concpt buildings ar showing th progrss of this fild. Bcaus th RCA itslf contains cmnt, th ratios of th mix hav to b adjustd to achiv dsird structural rquirmnts such as workability, strngth and watr absorption.[127]

Soil Stabilization, with th incorporation of rcycld aggrgat, lim, or fly ash into marginal quality subgrad matrial usd to nhanc th load baring capacity of that subgrad.[136]

Landscap Matrials: to promot grn architctur. To dat, rcycld concrt aggrgat has bn usd as bouldr/stackd rock walls, undrpass abutmnt structurs, rosion structurs, watr faturs, rtaining walls, and mor.[136]

Cradl-to-cradl challngs

Circularity of Concrt: Cradl-to-Cradl dsign

Th applications dvlopd for RCA so far ar not xhaustiv, and many mor uss ar to b dvlopd as rgulations, institutions and norms find ways to accommodat construction and dmolition wast as scondary raw matrials in a saf and conomic way. Howvr, considring th purpos of having a circularity of rsourcs in th concrt lif cycl, th only application of RCA that could b considrd as rcycling of concrt is th rplacmnt of natural aggrgats on concrt mixs. All th othr applications would fall undr th catgory of downcycling. It is stimatd that vn nar complt rcovry of concrt from construction and dmolition wast will only supply about 20% of total aggrgat nds in th dvlopd world.[127]

Th path towards circularity gos byond concrt tchnology itslf, dpnding on multilatral advancs in th cmnt industry, rsarch and dvlopmnt of altrnativ matrials, building dsign and managmnt, and dmolition as wll as conscious us of spacs in urban aras to rduc consumption. World rcords

Th world rcord for th largst concrt pour in a singl projct is th Thr Gorgs Dam in Hubi Provinc, China by th Thr Gorgs Corporation. Th amount of concrt usd in th construction of th dam is stimatd at 16 million cubic mtrs ovr 17 yars. Th prvious rcord was 12.3 million cubic mtrs hld by Itaipu hydropowr station in Brazil.[137][138][139]

Th world rcord for concrt pumping was st on 7 August 2009 during th construction of th Parbati Hydrolctric Projct, nar th villag of Suind, Himachal Pradsh, India, whn th concrt mix was pumpd through a vrtical hight of 715 m (2,346 ft).[140][141]

Th Polavaram dam works in Andhra Pradsh on 6 January 2019 ntrd th Guinnss World Rcords by pouring 32,100 cubic mtrs of concrt in 24 hours.[142] Th world rcord for th largst continuously pourd concrt raft was achivd in August 2007 in Abu Dhabi by contracting firm Al Habtoor-CCC Joint Vntur and th concrt supplir is Unibton Rady Mix.[143][144] Th pour (a part of th foundation for th Abu Dhabi's Landmark Towr) was 16,000 cubic mtrs of concrt pourd within a two-day priod.[145] Th prvious rcord, 13,200 cubic mtrs pourd in 54 hours dspit a svr tropical storm rquiring th sit to b covrd with tarpaulins to allow work to continu, was achivd in 1992 by joint Japans and South Koran consortiums Hazama Corporation and th Samsung C&T Corporation for th construction of th Ptronas Towrs in Kuala Lumpur, Malaysia.[146]

Th world rcord for largst continuously pourd concrt floor was compltd 8 Novmbr 1997, in Louisvill, Kntucky by dsign-build firm EXXCEL Projct Managmnt. Th monolithic placmnt consistd of 225,000 squar ft (20,900 m2) of concrt placd in 30 hours, finishd to a flatnss tolranc of FF 54.60 and a lvlnss tolranc of FL 43.83. This surpassd th prvious rcord by 50% in total volum and 7.5% in total ara.[147][148]

Th rcord for th largst continuously placd undrwatr concrt pour was compltd 18 Octobr 2010, in Nw Orlans, Louisiana by contractor C. J. Mahan Construction Company, LLC of Grov City, Ohio. Th placmnt consistd of 10,251 cubic yards of concrt placd in 58.5 hours using two concrt pumps and two ddicatd concrt batch plants. Upon curing, this placmnt allows th 50,180-squar-foot (4,662 m2) coffrdam to b dwatrd approximatly 26 ft (7.9 m) blow sa lvl to allow th construction of th Innr Harbor Navigation Canal Sill & Monolith Projct to b compltd in th dry.[149]