12. TESTING OF CEMENT PART 1.

Transcription

1 Chaper 12-Tesing of Cemen Par TESTING OF CEMENT PART Densiy The densiy is he fundamenal physical characerisic of he maerial. Densiy is defined by mass of a uni volume of a maerial subsance, expressed as kilograms per cubic mere. = m Vh where is densiy in kg.m -3 (g.cm -3 ) m mass of he maerial sample in kg (g) V h volume of he specimen in m 3 (cm 3 ) The mass can be deerminae by scale (usually analyic balance), o deermine volume of loose maerial is more difficul. For deerminaion of cemen densiy he pycnomeric mehod is used Deerminaion of Densiy by Pycnomeric Mehod. Pycnomeric mehod is indirec mehod; he measuring of volume is subsiued by several weighing of maerial in pycnomeer. Pycnomeer is glass (or meal) bole wih a igh fiing sopper having a small hole in is cenre. The hole in he sopper allows excess liquid o escape and he volume of he liquid in he pycnomeer is always he same. Densiy by pycnomery is calculae from basic formula: = m m k + m4 m 3 where m is mass of he sample of he esed maerial (m = m 2 m 1 ) m 1 mass of dry empy pycnomeer including sopper m 2 mass of dry pycnomeer wih sample and sopper m 3 mass of closed pycnomeer wih sample and measuring liquid m 4 mass of he closed pycnomeer wih measuring liquid k densiy of measuring liquid a esed emperaure Noe: Measuring liquid could no be waer in case of measuring cemen densiy! Usually is used alcohol. Tesing procedure weigh mass of he empy pycnomeer wih sopper - m 1 fill he pycnomeer wih measuring liquid. Replace sopper carefully, allowing excess liquid o escape hrough he hole in he sopper. Make sure here are no bubbles. Dry ouside and weigh m 4 fill he dry, empy pycnomeer abou 1/3 full of he sample. Closed i and weigh again m 2 page 59

2 Building Maerials 1- Tesing Mehods add measuring liquid o he sample. Fill pycnomeer abou 2/3 full. Mix up wih cauion and boil he pyknomeer for 2 hours. Afer cooling refill wih he liquid, closed he pycnomeer and weigh - m 3 calculae he mass of he sample from formula: m = m 2 - m 1 coun he densiy from he basic formula. Fig.:29 Derivaion of he formula for densiy deermined pycnomeric mehod where m k is mass of liquid, volume of which was pushed up by volume of he solid maerial 12.2 Fineness Sandard EN describes wo mehods of deermining he fineness of cemen: sieving mehod air permeabiliy mehod ( Blaine) Sieving Mehod This mehod serves only o demonsrae he presence of coarse cemen paricles. This mehod is primarily suied o checking and conrolling producion process. The fineness of cemen is measured by sieving i on sandard sieves. The proporion of cemen of which he grain sizes are larger han he specified mesh size is hus deermined Air Permeabiliy Mehod ( Blaine Mehod ) The fineness of cemen is measured as specific surface. Specific surface is expressed as he oal surface area in square meres of all he cemen paricles in one kilogram of cemen. The higher he specific surface is, he finer cemen will be. Principle of air permeabiliy mehod is in observing he ime aken for a fixed quaniy of air o flow hrough compaced cemen bed of specified dimension and porosiy. Under sandardised condiions he specific surface of cemen is proporional o where is he ime for given quaniy of air o flow hrough he compaced cemen bed. The number and size range of individual pores in he specified bed are deermined by he cemen paricle size disribuion which also deermined he ime for he specified air flow. The mehod is comparaive raher han absolue and herefore a reference sample of known specific surface is required for calibraion of he apparaus. page 6

3 Chaper 12-Tesing of Cemen Par 1 A bed of cemen is prepared in special permeabiliy cell and have exac porosiy e =,5 weigh a quaniy of cemen. The weigh of he cemen is calculaed from m 1 =,5 V [ g] where is he densiy of he cemen [g.cm -3 ] V volume of he cemen bed [cm 3 ] Specific surface S is expressed as K S = 3 e (1 e),1η 2 1 [ cm.g ] where K e is he apparaus consan porosiy of he bed he measured ime [s] densiy of cemen [g.cm -3 ] η he viscosiy of air a he es emperaure aken from Tab.:27 The apparaus consan is deerminae by measuring permeabiliy of reference cemen of known specific surface. The procedure repeas hree imes for hree samples of cemen bed. For each sample is calculaed consan K from formula: K = S (1 e) e 3,1η where S is he specific surface of he reference cemen [cm 2.g -1 ] densiy of he reference cemen [g.cm -3 ] η measured ime [s] air viscosiy a he es emperaure [Pa.s] Wih he specified porosiy of e =,5 K = 1,414 S,1η The mean of hree values of K is he consan K for he apparaus. page 61

4 Building Maerials 1- Tesing Mehods Fig.:3 Blaine apparaus MANOMETER CONICAL SOCKET STOPCOCK PERMEABILITY CELL PLUNGER ETCHED LINES COMPACTED CEMENT BED PERFORATED DISC RUBBER BULB Tesing procedure Place he perforaed disc on he ledge a he boom of he cell and place on i a new filer paper disc. Place he weighed quaniy of cemen, m 1, in he cell. Place a second new filer paper disc on he levelled cemen. Inser he plunger and press i genly bu firmly unil he lower face of he cap is in conac wih he cell. Slowly wihdraw he plunger, roae i hrough 9 and press once again. The bed is now compaced and ready for he permeabiliy es. Tes is performed on he Blaine apparaus (see Fig.:3). I is pracically manomeer in he U-ube form. One arm of he manomeer is provided a he op wih conical socke o form an airigh fi wih he conical surface of he cell. The same arm has four eched lines M 1 o M 4 and T-join, which lead o an airigh sopcock beyond which is aached aspiraion rubber bulb. Manomeer is filled o he level of he lowes eched line wih non-volaile, non-hygroscopic liquid of low viscosiy and densiy (such as dibuylphhalae or ligh mineral oil). Inser he conical surface of he cell ino he socke a he op of he manomeer. Open he sopcock and wih genle aspiraion raise he level of he manomeer liquid o ha of he highes eched line. Close he sopcock and he manomeer liquid will begins o flow. Sar he imer as he liquid reaches he second eched line and sop i when he liquid reaches he hird eched line. Record he ime,, and he emperaure, T. The procedure repeas hree imes Calculae hree values of he specific surface and he mean of hem. page 62

5 Chaper 12-Tesing of Cemen Par 1 Tab.:27 Viscosiy of air and,1η Temperaure [ C] Air viscosiy η [Pa.s],1η linear inerpolaion can be used for he deerminaion of he inermediae values 12.3 Deerminaion of Seing Time The seing ime is deermined by observing he peneraion of needle ino cemen pase of sandard consisence unil i reaches a specified value. The laboraory shall be mainained a a emperaure of 2 ± 2 C and a relaive humidiy of no less han 65 % Sandard Consisence Tes Cemen pase of sandard consisence has a specified resisance o peneraion by a sandard plunger. The waer required for such a pase is deermined by rial peneraions of pases wih differen waer conens. Conen of waer is expressed as percenage by mass of he cemen. Vica apparaus (see Fig.:31) wih he plunger is used for he es. The plunger shall be of noncorrodible meal in he form of a righ cylinder of 5 ± 1mm effecive lengh and of 1, ±,5 mm diameer. The oal mass of moving pars shall be 3 ± 1 g. Par of he Vica apparaus is he mould from hard rubber (of runcaed conical form) on he glass base-plae. Procedure calibrae he Vica apparaus by lowering he plunger o res on he base-plae o be used and adjusing he poiner o read zero on he scale. Raise he plunger o he sand-by posiion. weigh 5 g of cemen (o he neares 1g). Weigh a quaniy of waer (disilled or deionized), e.g. 125 g, in he mixer bowl or measure he waer from he graduaed cylinder ino he mixer bowl. ad he cemen carefully o he waer in order o avoid loss of waer or cemen. The ime of addiion shall be no less han 5 s nor more han 1 s. Noe he ime of compleion of he addiion as zero ime, from which laer measuremens of ime shall be made. sar he mixer immediaely and run a low speed. sop he machine afer 9 s for 15 s during which remove wih a suiable scraper any pase adhering o he bowl ouside he mixing zone and reurn i o he mix. Resar he machine and run a low speed for furher 9 s. The oal mixer running ime shall be 3 min. page 63

6 Building Maerials 1- Tesing Mehods ransfer he pase immediaely o he mould and fill i o excess. Remove he excess genly and make a smooh upper surface immediaely afer levelling he pase, ransfer he mould and base-plae o he Vica apparaus and posiion i cenrally under he plunger. Lower he plunger genly unil i is in conac wih he pase. Pause in ha posiion for beween 1s and 2s. Than release he moving par quickly and allow he plunger o penerae verically ino he cenre of he pase. The release of he plunger shall occur 4 min afer zero ime. Read he scale when peneraion has ceased or 3 s afer he release of he plunger, whichever is he earlier. record he scale reading, which indicaes he disance beween he boom face of he plunger and he base plae. Clean he plunger immediaely afer each peneraion. repea he es wih pases conaining differen waer conens unil one is found o produce a disance beween plunger and base-plae of 6 ± 1 mm. Record he waer conen of ha pase o he neares,5% as he waer for sandard consisence. Fig.:31 Vica apparaus wih plunger and needle PLUNGER FOR STANDARD CONSISTENCE NEEDLE VICAT APPARATUS WITH HARD RUBBER MOULD Seing Time Tes Cemen pase of sandard consisence is used for his es. Vica apparaus is used, bu he plunger is replaced by he seel needle in he form of a righ cylinder of effecive lengh 5 ± 1 mm and diameer 1,13 ±,5 mm. The oal mass of moving par is 3±1 g. Procedure calibraion of Vica apparaus wih he needle is he same as for he apparaus wih he plunger. mould, filled by pase of sandard consisence and base plae ransfer o he Vica apparaus. procedure of peneraion is he same as by using plunger. page 64

7 Chaper 12-Tesing of Cemen Par 1 repea he peneraion es on he same specimen a convenienly spaced posiion, no less han 1 mm from he rim of he mould or from each oher, a convenienly spaced inervals of ime, e.g. a 1 min inervals. clean he Vica needle afer each peneraion iniial seing ime is ime measured from zero a which disance beween he needle and he base-plae is 4 ± 1 mm. Record i o he neares 5 min. final seing ime is ime measured from zero a which he needle firs peneraes only,5 mm ino he specimen Auomaic seing ime machines are commercially available and may be used provided ha hey can be shown o give he same es resuls as he specified apparaus and procedure. Vocabulary cemen pase coarse densiy final seing ime fine fineness iniial seing ime mesh mould porosiy seing ime sieving specific surface sandard consisence es specimen o harden hardening ime o se cemenová kaše hrubý husoa konec uhnuí jemný jemnos mleí počáek uhnuí sío forma porozia, mezerovios dobya uhnuí prosévání měrný povrch normální husoa zkušební vzorek, zkušební ěleso vrdnou doba vrdnuí uhnou doba uhnuí page 65