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International Concrete Abstracts Portal

Showing 1-5 of 38 Abstracts search results

Document: 

SP302-19

Date: 

June 1, 2015

Author(s):

Dirk Lowke and Christoph Gehlen

Publication:

Symposium Papers

Volume:

302

Abstract:

The effect of pore solution composition on zeta potential and superplasticizer adsorption has been investigated experimentally. The investigations were conducted on highly concentrated suspensions, containing quartz flour, limestone flour, cement and combinations of these materials. Furthermore cement-limestone suspensions with different types of cements and a varying ratio of cement to limestone were investigated. The results show that the zeta potential is significantly determined by pore solution. In a pore solution of highly concentrated cement suspensions the zeta potential can be characterized by the ratio of calcium to sulfate concentration. Furthermore it was shown that the superplasticizer adsorption is affected the zeta potential. At higher, more positive zeta potentials the superplasticizer molecules are more likely adsorbed onto the solid surfaces. Moreover, superplasticizer adsorption in limestone-cement suspensions is predominantly controlled by the composition of pore solution rather than the ratio of cement to limestone flour. If the ion concentration of the pore solution is artificially kept constant, the polymer adsorption is almost constant independent of the cement to limestone ratio in the suspension.

DOI:

10.14359/51688099


Document: 

SP302-05

Date: 

June 1, 2015

Author(s):

Manuel Ilg and Johann Plank

Publication:

Symposium Papers

Volume:

302

Abstract:

Polycondensates and polycarboxylates are known to be effective superplasticizers. Here, the synthesis of a novel, brown coal based superplasticizer by grafting acrylic acid (AA) and 2-acrylamido-2-tert.butyl sulfonic acid (ATBS) onto the alkali soluble components of brown coal (lignite) as backbone using free radical copolymerization technique is described. Furthermore, an ATBS-acrylic acid copolymer was synthesized to investigate the influence of the graft chains on the performance of the lignite copolymer. Successful grafting was confirmed by size exclusion chromatography (SEC) and comparison of the adsorbed layer thicknesses of the brown coal substrate and the grafted product. The dispersing performance of the graft copolymer was probed via mini slump tests and compared with that of BNS. Additionally, slump flow retention and sulfate tolerance were determined. It was found that the graft copolymer possesses higher dispersion effectiveness than BNS and exhibits high sulfate tolerance.

DOI:

10.14359/51688085


Document: 

SP302-15

Date: 

June 1, 2015

Author(s):

Johannes Paas, Maike W. Müller, and Johann Plank

Publication:

Symposium Papers

Volume:

302

Abstract:

Macromonomers for MPEG type of PCEs are produced through esterification of methacrylic acid (MAA) with methoxypoly(ethylene glycol) (MPEG) yielding the MPEG-MAA ester. However, PEG impurities present in MPEG may lead to MAA diester (PEG-di-MAA) formation. Such diester can cause crosslinking of the PCE polymer which might reduce its dispersing power. To investigate this effect, MPEG-MAA macromonomers containing 0 – 20 wt. % of PEG-di-MAA diester were used in PCE synthesis. It was found that when the PEG-di-MAA content in the macromonomer exceeds 2 wt. %, then dispersing effectiveness starts to decrease and the solution viscosity of the PCE increases. Surprisingly, incorporation of the diester into the PCE polymer does not occur randomly. Instead, two distinct species of crosslinked PCE molecules (Mw ~ 300.000 and ~ 3 mio g/mol) are formed within the first minutes of copolymerization. Apparently, the crosslinked PCE species counteract the dispersing effect of the main product.

DOI:

10.14359/51688095


Document: 

SP302-14

Date: 

June 1, 2015

Author(s):

Xiao Liu, Ziming Wang, Jie Zhu, Ming Zhao, Wei Liu, and Dongjie Yin

Publication:

Symposium Papers

Volume:

302

Abstract:

A polycarboxylate superplasticizer (PCE) with a novel star-shaped structure was prepared through copolymerization of acrylic acid (AA), isobutenyl polyethylene glycol (IPEG), and star-shaped polymerizable active center by an esterification between polyol and AA. In the first esterification step, the esterification rate reached more than 95% with the catalyst/polyol ratio of 0.07:1, inhibitor/AA ratio of 0.04:1 (or 0.011:1), water-carrying agent dosage of 70g and esterification time of 7 hours. In the second polymerization step, the highest fluidity of cement paste was achieved at the initiator/AA/IPEG ratio of 0.28: 3.3: 1. Infrared spectroscopy (IR) and 1H Nuclear magnetic resonance (1H NMR) measurements were used for structural characterization, and the spectral results confirmed the product’s star-shaped structure. Furthermore, this star-shaped PCE exhibited higher energy efficiency than the conventional comb-shaped PCE, indicated by its excellent paste fluidity and adsorption behavior in cement paste.

DOI:

10.14359/51688094


Document: 

SP302-10

Date: 

June 1, 2015

Author(s):

S. Mantellato; Q. Mehmeti; L. Ceni; M. Palacios; and R.J. Flatt

Publication:

Symposium Papers

Volume:

302

Abstract:

One of the essential problems of superplasticized concrete is the loss of fluidity over time. To limit this problem one must improve the compatibility of superplasticizers and cement. This is not a trivial task as cement contains phases with different responses to superplasticizers in the first hours of hydration. In the present work, the role of the polymer structure on the flow loss over time on superplasticized cement pastes has been studied. For this, we have correlated the impact of different molecular structures on the adsorption degree and ionic solution composition with the rheological properties of fresh cement pastes. The results revealed a high excess of aluminium in the aqueous solution. This could be due to aluminum complexation by the polymer or a poisoning of ettringite growth complemented by a stabilization of nano-sized ettringite particles. In addition, except for one of the studied polymers, the flow loss seems to decrease abruptly when the concentration of carboxylate ions in solution drops below a critical value (0.7-1.2 µeq/g).

DOI:

10.14359/51688090


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