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International Concrete Abstracts Portal

Showing 1-5 of 17 Abstracts search results

Document: 

SP222-08

Date: 

May 1, 2004

Author(s):

D. Hardjito, S. E. Wallah, D. M. J. Sumajouw, and B. V. Rangan

Publication:

Symposium Papers

Volume:

222

Abstract:

This paper presents the effect of mixture composition on the compressive strength of fly ash-based geopolymer concrete. Test results show that water-to-sodium oxide (H2O-to-Na2O) molar ratio and the water-to-geopolymer solids ratio by mass influence the compressive strength of fly ash-based geopolymer concrete. The compressive strength decreases when these ratios increase. However, the sodium oxide-to-silicon oxide (Na2O-to-SiO2) molar ratio of the geopolymer mixture does not have any significant effect on the compressive strength within the range of 0.095 and of 0.120 of this ratio.

DOI:

10.14359/13308


Document: 

SP222-16

Date: 

May 1, 2004

Author(s):

J. J. Young, B. J. Balcom, T. W. Bremner, M. D. A. Thomas, and K. Deka

Publication:

Symposium Papers

Volume:

222

Abstract:

Magnetic Resonance Imaging (MRI) is a nondestructive technique that can be used to spatially resolve distributions of certain nuclei. Lithium is a relatively sensitive nucleus for MRI. Therefore, it is possible to directly measure the distribution of lithium in cement based materials. Lithium salts are used in concrete to suppress alkali-silica reaction. The MRI relaxation parameters associated with lithium in cement-based materials are relatively short by traditional MRI standards. Due to the short relaxation parameters, special MRI measurement techniques and hardware considerations had to be developed in order to quantify lithium distributions in cement based materials. MRI has the potential to play an important role in concrete technology. While this method has been developed for laboratory studies, measurements could be made on cores extracted from existing concrete structures.

DOI:

10.14359/13316


Document: 

SP222-07

Date: 

May 1, 2004

Author(s):

B. G. Petersen, K. Reknes, and K. Olavesen

Publication:

Symposium Papers

Volume:

222

Abstract:

Lignosulphonate is a widely used plasticizing admixture in concrete. It is well documented that different qualities of this material give different performance in concrete. Depending on what kind of concrete that is needed, workability can be controlled by adding different amounts or qualities of the lignosulphonate. This investigation compares the adsorption of lignosulphonate on three different portland cements, to the rheological properties of cement pastes made from the same cements. The adsorption isotherms were calculated from depletion experiments. A rheometer with bob-cup geometry was used to measure the rheological properties of the cement pastes. The plasticizing effect of lignosulphonates in cement paste slurries was confirmed. Recent advances have given a novel lignosulphonate with superplasticizer performance. This investigation demonstrates these improved properties achieved by this novel lignosulphonate by determining the differences in adsorption of the different lignosulphonates, on cements with different chemical characteristics.

DOI:

10.14359/13307


Document: 

SP222-06

Date: 

May 1, 2004

Author(s):

M. Collepardi, J. J. 0goumah Olagot, D. Salvioni, and D. Sorrentino

Publication:

Symposium Papers

Volume:

222

Abstract:

Delayed ettringite formation (DEF) occurs at late ages and the related heterogeneous expansion in a hardened concrete can produce cracking and spalling. There are two different types of DEF depending on the sulphate source: DEF caused by external sulphate attack (ESA) or internal sulphate attack (ISA). In the present paper only ISA-related DEF is studied with reference to the following three parameters: a) the sulfate content in the clinker phase of the cement; b) the curing temperature; c) the presence of preliminary cracks in concrete specimens. Concretes manufactured at room temperature (20°C) do not show any form of DEF-related expansion independently of the SO3 content of the clinker (1—2%) or the portland cement (2-4%). On the other hand, concretes steam-cured at 90°C and then kept under water show significant expansion related to DEF provided that the SO3 con-tent of the portland cement is relatively high (> 4%). The higher SO3 content in the clinker phases (> 2%) or the presence of preexisting cracks accelerates the DEF-related expansion. Deposition of ettringite fiber crystals occurs in the preexisting cracks or within the new microcracks. Curing at temperatures lower than 80°C, preferably lower than 70°C, is strongly recommended to avoid DEF-related risk. Blended cements with a lower SO3 content should be used in case this limit in curing temperature cannot be safely ensured.

DOI:

10.14359/13306


Document: 

SP222-12

Date: 

May 1, 2004

Author(s):

K. Yamada, H. Nakanishi, S. Tamaki, M. Yaguchi, M. Kinoshita, and S. Okazawa

Publication:

Symposium Papers

Volume:

222

Abstract:

The working mechanism of a polycarboxylate superplasticizer (PC) which is a new generation of superplasticizer (NSP) is investigated. This NSP shows a shrinkage reducing effect as well as a water reducing effect with adequate slump retention in a wide range of water cement ratio by introducing a shrinkage-reducing component (SRC) into the molecular structure. Superplasticizers have been thought to be adsorbed on cement hydrates and to show their particle dispersing effects by modifying the inter-particle potentials. On the other hand, shrinkage reducing agents of the organic type have been thought to exist at the interface between the aqueous and the pore phases in hardened cement paste and to show their shrinkage reducing effects by reducing the surface tension, which occasionally results in the degradation of freezing and thawing (F/T) resistance. In this study, the mechanisms of NSP are discussed. By building a SRC into the molecular structure, the entrained air system is expected to be controlled successfully compared to traditional shrinkage-reducing agents (SRA) and so the degradation of F/T resistance can be avoided. With the progress of hydration, SRC is released from NSP and the surface tensions decreases, which results in the reduction of drying shrinkage.

DOI:

10.14359/13312


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