Influence of admixtures on the plastic shrinkage cracking of concrete
| dc.contributor.advisor | Combrinck, Riaan | en_ZA |
| dc.contributor.author | Le Roux, Burgert Daniel | en_ZA |
| dc.contributor.other | Stellenbosch University. Faculty of engineering. Dept. of Civil Engineering. | en_ZA |
| dc.date.accessioned | 2016-03-09T14:31:52Z | |
| dc.date.available | 2016-03-09T14:31:52Z | |
| dc.date.issued | 2016-03 | |
| dc.description | Thesis (MEng)--Stellenbosch University, 2016. | en_ZA |
| dc.description.abstract | ENGLISH ABSTRACT: Plastic shrinkage cracking (PSC) is a well-known form of cracking in concrete at early ages and causes major concerns with regard to durability and aesthetical appearance of concrete structures. PSC is mainly attributed to tensile stresses arising in concrete due to a combination of capillary pressure and restraints provided by reinforcement and formwork. Concrete elements with large exposed surfaces, sited in areas with high evaporation rates, are prone to PSC. Although the phenomenological behaviour of PSC is well documented for normal concrete, the addition of admixtures to modern day concrete has resulted in unexpected and uncommon PSC behaviour. Therefore, the main objectives of this study are to determine both the phenomenological and fundamental influences of a wide range of admixtures at different dosages on the PSC of concrete. Crack area measurements are used to determine the phenomenological influence of admixtures while measurement of surface tension, capillary pressure, bleeding, setting time, evaporation, shrinkage, and settlement are used to investigate the fundamental influences of admixtures. The experimental tests were conducted in a climate chamber with an ambient temperature of 40 °C, relative humidity of 10 % and a wind speed of 20.2 km/h. The associated admixtures include a minimum and maximum dosage of a glucose based retarder, calcium chloride based accelerator, chloride free air entraining agent, lignosulphonate plasticiser, shrinkage reducing admixture (SRA), poly carboxylate ethers (PCE) based super-plasticiser, and a sulphonated melamine formaldehyde (SMF) based super-plasticiser. A high flow concrete mix is used to accommodate the respective super-plasticisers whereas a conventional concrete mix is used to accommodate the remaining admixtures. The influences of admixtures on PSC are determined by comparing the experimental results of mixes containing admixtures to a corresponding reference mix devoid from admixtures. The addition of the associated admixtures at different dosages altogether display a reduction in the severity of PSC compared to the reference mixes. The different dosage limits of the retarder and SMF-based super-plasticiser displayed a similar reduction in the severity of PSC. The addition of air entrainer, SRA and PCE-based super-plasticiser progressively reduced the severity of PSC since a higher dosage corresponds to a more profound reduction in cracking. Lastly, the minimum dosage of plasticiser and accelerator respectively exhibited a more substantial reduction in the severity of PSC compared to the maximum dosage. The associated phenomenological behaviour of admixtures is explained by referring to the underlying fundamental influences. Differences in the severity of PSC are mainly attributed to a reduction in surface tension and shrinkage with increasing content of the associated admixtures. | en_ZA |
| dc.description.abstract | AFRIKAANSE OPSOMMING: Plastiese krimp krake (PKK) is ‘n bekende vorm van krake wat ontstaan gedurende die eerste paar ure nadat beton gegiet is. PKK het ‘n nadelige gevolg aangaande die estetiese voorkoms van strukture en kan moontlik probleme veroorsaak in verband met die duursaamheid van beton. PKK word hoofsaaklik toegeskryf aan trekspannings wat voortspruit in beton as gevolg van kapilêre druk wat ontstaan weens hoë verdamping van samestellende water in die beton meng. Beton konfigurasies met ‘n groot oppervlakte wat blootgestel is aan verdamping is hoofsaaklik vatbaar vir die ontstaan van PKK. Die tipiese gedrag van PKK in beton is goed gedokumenteer alhoewel die invloed van bymiddels dikwels lei tot ongewone gedrag. Die doel van die studie is om die fenomenologiese - en fundamentele invloed van bymiddels op die plastiese krimp gedrag van beton te bepaal. Die fenomenologiese invloed van bymiddels is vasgestel deur die uitvoer van kraak area toetse terwyl die oppervlakspanning, kapilêre druk, bloei, set tye, verdamping, krimp en versakking van beton onderskeidelik gemeet is om die fundamentele invloed van bymiddels te onsersoek. Die voorgenome toetse was uitgevoer in klimaat-beheerde toestande om ‘n hoë tempo van verdamping te bewerkstellig. Die verskeie toetse was blootgestel aan uiterste toestande vir verdamping met ‘n temperatuur van 40 °C, ‘n relatiewe humiditeit van 10 % en ‘n windspoed van 20.2 km/h. Die fenomenologiese - en fundamentele invloed van die volgende bymiddels is ondersoek in die studie: glukose-gebaseerde vertrager, klasium chloried versneller, “chloride free air entrainer”, “poly carboxylate ethers (PCE) based super-plasticiser”, “sulphonated melamine formaldehyde (SMF) based super-plasticiser”, “lignosulphonate based plasticiser” asook ‘n krimp-verlagende bymiddel. ‘n Hoë vloei beton meng is gebruik om die verskeie super-plastiseerders te akkommodeer terwyl ‘n konvensionele beton meng gebruik is om die oorblywende bymiddels te akkommodeer. Die fenomenologiese - en fundamentele gedrag van die menge wat bymiddels bevat is vergelyk met ‘n verwysings mengsel wat geen bymiddels bevat nie om sodoende die invloed van die verskeie bymiddels vas te stel. Die toevoer van die voorgenome bymiddels het ‘n algehele afname in PKK tot gevolg gehad. Die toevoer van beide ‘n hoë en lae dosis van die vertrager asook die “SMF based super-plasticiser” het ‘n soortgelyke afname in PKK opgelewer. Die krimp-verlagende bymiddel, “air entrainer” asook die “PCE based super-plasticiser” het ‘n progressiewe mate van afname in PKK tot gevolg gehad. Die toevoegging van die minimum dosis van beide plastiseerder en versneller het ‘n meer noemenswaardige afname in PKK opgelwer in vergelyking met die toevoegging van ‘n ooreenstemmende maksimum dosis. Die voorgenome fenomenologiese gedrag van die verskeie menge is verklaar deur te verwys na die onderliggende fundamentele gedrag. Die verskil in fenomenologiese gedrag is hoofsaaklik toegeskryf aan die verlaging van oppervlakspanning en krimp weens die toevoer van die verskeie bymiddels. | af_ZA |
| dc.format.extent | xv, 158 pages : illustrations | en_ZA |
| dc.identifier.uri | http://hdl.handle.net/10019.1/98544 | |
| dc.language.iso | en_ZA | en_ZA |
| dc.publisher | Stellenbosch : Stellenbosch University | en_ZA |
| dc.rights.holder | Stellenbosch University | |
| dc.subject | Concrete -- Detorioration | en_ZA |
| dc.subject | Concrete -- Cracking | en_ZA |
| dc.subject | Concrete -- Plastic properties | en_ZA |
| dc.subject | UCTD | en_ZA |
| dc.subject | Concrete -- Expansion and contraction | en_ZA |
| dc.subject | Concrete -- Additives | en_ZA |
| dc.title | Influence of admixtures on the plastic shrinkage cracking of concrete | en_ZA |
| dc.type | Thesis | en_ZA |