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International Concrete Abstracts Portal

Showing 1-5 of 38 Abstracts search results

Document: 

SP302-04

Date: 

June 1, 2015

Author(s):

David Platel; Jean-Marc Suau; Clement Chosson; and Yves Matter

Publication:

Symposium Papers

Volume:

302

Abstract:

For the Ready Mix Concrete mix design, the initial workability depends on the chemical composition of the Polycarboxylate Ether (PCE). Up to now the use of best PCE can achieve 2 hours of slump retention. However, a tendency to segregate is observed when over-dosage is made, due to water reduction capability of PCEs. An approach is to use also a combination of a water-reducing agent and a retarding agent which has the main disadvantage to delay the setting time and consequently the early strength of the concrete. This paper demonstrates the possibility to boost the performance of currently used PCEs. The new slump retention additive that we developed allows a significant increase of the slump retention while maintaining the initial fluidity without impacting the water reduction ability. The homogeneity of the concrete is also controlled by using this additive. On top of that, the combination between this new product and a standard water-reducting PCE is made at commonly used dosage.

DOI:

10.14359/51688084


Document: 

SP302-21

Date: 

June 1, 2015

Author(s):

Anatoly I. Vovk

Publication:

Symposium Papers

Volume:

302

Abstract:

In many countries there are regions with very cold winter climate. To provide for year-round building and construction works antifreezing admixtures must be used. When suitable technology and high performance antifreezing admixtures have been used, ready mix concrete may be delivered and placed at temperature as low as -25 °C. The transfer from “summer” concrete mix to “winter” one implies the addition of optimal amount of antifreezing admixture. In principal, both separate superplasticizer and antifreezing admixture dosing and usage of blended (combined) admixture is possible. In Russia the usage of blended plasticizing-antifreezing admixtures is predominant historically. The prime blended admixtures on the base of sodium formate didn’t freeze down to -15 oC and allowed secure concrete hardening with dosages about 10% of commercial product. At present day such admixtures are unsuitable neither by the dosage level (danger of ASR) nor by the freezing-point. The method for elaboration of blended antifreezing admixture (BAFA) with extreme freezing-point was developed. These admixtures allow building and construction works at a temperature as low as -25 oC with dosages about 1-1.3% for PCE-based admixtures and 1.8-2.2% for PNS-based admixtures. It is important that these dosages ensure superplasticizing effect. Non-chloride non-plasticizing admixture with freezing-point below -40 oC was developed also. The kinetic of concrete strengthening at various temperature regimes has been thoroughly studied.

DOI:

10.14359/51688103


Document: 

SP302-08

Date: 

June 1, 2015

Author(s):

Shinji Tamaki; Kazuhide Saito; Kazuhisa Okada; Daiki Atarashi; and Etsuo Sakai

Publication:

Symposium Papers

Volume:

302

Abstract:

Several studies have been pursued in Japan on developing concrete using high volume blast-furnace slag cement for reducing CO2 emissions arising from calcination of cement. However, when using high volume blast-furnace slag cement, various problems are encountered, such as decreased fluidity retention ability caused by the reduction of admixture dosage and decreased strength enhancement. In this paper, the authors focus on the adsorption properties of polycarboxylate ether superplasticizers and the properties of hardened concrete that incorporates a component of high volume blast-furnace slag cement, and discuss the development of a new type of superplasticizer through molecular design and optimization of the admixture composition. The admixture improved the fluidity and properties of hardened concrete using slag cement containing more than 60% blast-furnace slag.

DOI:

10.14359/51688088


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: 

SP302-03

Date: 

June 1, 2015

Author(s):

Wolfram Schmidt; Sarah Peters; and Hans-Carsten Kühne

Publication:

Symposium Papers

Volume:

302

Abstract:

Polysaccharides modify the rheological properties of cement based systems. Depending upon their chemistry, molecular architecture, and adsorption tendency, they have different modes of action. Some polysaccharides like diutan gum have strong effect on the fluid phase; others like starch strongly interact with particles. This paper presents effects of diutan gum and starches in presence of polycarboxylates. Rheometric investigations with varied particle volume fractions and increasing coarse aggregate diameters were conducted. The results show that starches have stronger influence on the rheology at high particle volume fractions than diutan gum. At lower particle volume fractions this trend is inverted. Experiments with aggregates sizes up to 16 mm (0.63 in.) indicate that stabilizing agent influences on the effects of aggregates on yield stress were small; however up to 1.0 mm (0.04 in.), a significant effect on the plastic viscosity could be observed, which levelled off at larger diameters.

DOI:

10.14359/51688083


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