International Concrete Abstracts Portal

Showing 1-5 of 34 Abstracts search results

Document: 

SP288

Date: 

October 1, 2012

Author(s):

Editor: V.M. Malhotra

Publication:

Symposium Papers

Volume:

288

Abstract:

This CD contains 33 papers presented at the Tenth International Conference of Superplasticizers and Other Chemical Admixtures in Concrete held in Prague, Czech Republic, in October 2012. Topics include Synthesis, Characterization, and Dispersing Performance of a Novel Cycloaliphatic Superplasticizer; Compatibility between Polycarboxylate and Viscosity-Modifying Admixtures in Cement Pastes; Aspects of Gypsum-Free Portland Cement; A Novel Type of PCE Possessing Silyl Functionalities; and much more. Note: The individual papers are also available. Please click on the following link to view the papers available, or call 248.848.3800 to order. SP-288

DOI:

10.14359/51684135


Document: 

SP288-30

Date: 

September 14, 2012

Author(s):

Alex Lange, Tsuyoshi Hirata, and Johann Plank

Publication:

Symposium Papers

Volume:

288

Abstract:

The working mechanism for cement dispersion of an isoprenyloxy ether-based polycarboxylate superplasticizer (PCE-A) and of several PCEs based on MPEG-ester (PCE-B0, PCE-B1, PCE-B2) or APEG-ether monomers (PCE-C) was investigated via cement paste flow testing and measurement of hydrodynamic radius of solved PCE mole¬cules, adsorption isotherm, adsorption rate and zeta potential. Using “mini slump” test method it was found that the isoprenyloxy ether – acrylic acid copolymer (PCE-A) exhibits the highest water reduction, followed by the methacrylic acid – MPEG – 1100 – methac¬rylate copolymer (PCE-B2), whereas the methacrylic acid – MPEG – 250 – methacrylate copolymer (PCE-B0) required a very high dosage. Further experiments revealed that in cement pore solution, the conformation of PCE-A is star-like; while PCE-B0, PCE-B1 and PCE-B2 show a worm like conformation with flexible backbone and PCE-C exhibits a rod like structure possessing high rigidity. PCE-B2 disperses cement mainly via strong steric repulsion instigated by the long side chain. Based on adsorption and zeta potential data obtained it is proposed that PCE-A, PCE-B0, PCE-B1 and PCE-C disperse cement not only by steric repulsion originating from adsorbed PCE, but also by electrostatic and/or steric repulsion owed to non-adsorbed PCE molecules present in the pore solution. Especially PCE-B0 was found to require a dosage substantially beyond its saturation adsorption. This suggests that free PCE dissolved in the pore solution may provide the main contribution to cement dispersion. Consequently, a new type of dispersion mechanism which originates from dissolved PCE molecules exercising a “lubricating” effect between cement particles is postulated for PCE-B0.

DOI:

10.14359/51684246


Document: 

SP288-31

Date: 

September 14, 2012

Author(s):

Fatma Saidat, Michel Mouret, and Martin Cyr

Publication:

Symposium Papers

Volume:

288

Abstract:

Metakaolin (MK) comes from the calcination of kaolinite at temperatures ranging from 700°C (1292°F) to 850°C (1562°F). The resulting dehydroxylation of kaolinite produces an amorphous material (metakaolin) that is usually very reactive in alkaline media such as cement-based materials. However, the reactivity generally takes effect after a few days, so poor short-term performance is obtained, which is a disadvantage in cases where the concrete needs to be rapidly stripped of its formwork. The aim of this work was to test different chemical activators for metakaolin, in order to obtain short-term strength similar to that obtained without metakaolin. Twelve activators were selected and tested in mortars at different concentrations, using two modes of intro¬duction (in solution and in solid form). Four cements were used in the experiments (2 CEM I and 2 CEM II). Workability and compressive strength tests were carried out (at 16 h, 24 h, 48 h, 7 d, and 28 d). The results show disparities in the efficiency of the activation. Products very active at early ages often led to a decrease in strength at 28 days of age, compared to activator-free mixtures.

DOI:

10.14359/51684247


Document: 

SP288-28

Date: 

September 14, 2012

Author(s):

Serina Ng and Johann Plank

Publication:

Symposium Papers

Volume:

288

Abstract:

The negative impact of sodium montmorillonite clay on dispersion effective¬ness of two polycarboxylates consisting of methacrylate acid: MPEG methacrylate ester at molar ratios of 6:1 and 1.5:1 was investigated. When 1% by weight of cement (bwoc) of clay was present, cement spreads decreased by up to 60% while PCE sorption soared to ~ 400 mg/g clay (~ 100 times higher than on Portland cement). The PCEs mainly undergo chemisorption by intercalation between the alumosilicate layers via their poly(ethylene oxide) side chains. Additionally, to a minor extent (~ 15%), adsorption via electrostatic attraction to the positively charged clay surfaces takes place. Polyglycols can be effectively used as a sacrificial agent to protect PCEs possessing high grafting density from the nega¬tive effects of clay, while more anionic PCEs benefit, however to a certain extent only, from the addition of highly anionic polyelectrolytes such as poly(methacrylic acid).

DOI:

10.14359/51684244


Document: 

SP288-29

Date: 

September 14, 2012

Author(s):

Ilina Kondofersky-Mintova and Johann Plank

Publication:

Symposium Papers

Volume:

288

Abstract:

The fundamental interactions between polycarboxylate superplasticizers (PCEs), multi-walled carbon nanotubes (MWCNTs), Ca2+ ions and cement were investigated. Two commercial samples of MWCNTs were characterized by SEM and TEM imaging. It was found that only one sample contained mostly individual, non-agglomerated CNTs which were used in further tests. The MWCNT sample reduced cement paste flowability, but increased 28 day compressive strength by ~ 20% and tensile strength by 26%. The rela¬tively modest increase can be attributed to agglomeration of individual CNTs into large bundles (Ø ~ 900 nm, 3.51 × 10–5 in.). Agglomeration is caused by adsorption of Ca2+ ions onto the initially negatively charged surfaces of CNTs. This way, Ca2+ ions present in every cement pore solution impede maximal dispersion of CNTs in the cementitious matrix, thus limiting their potential application as nano reinforcement for concrete.

DOI:

10.14359/51684245


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