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International Concrete Abstracts Portal

Showing 1-5 of 40 Abstracts search results

Document: 

SP242-10

Date: 

April 1, 2007

Author(s):

J. Wolsiefer Sr.

Publication:

Symposium Papers

Volume:

242

Abstract:

The research goal of this project was to measure silica fume particle size distribution and conduct dispersion tests, using measured levels of ultrasound as a method to evaluate the relative agglomeration "strength" and de-agglomeration [dispersability] of the undensified and densified product forms of silica fume. Scanning Electron Microscopy (SEM) testing of silica fume samples was performed, showing combinations of individual particles (0.02 to 0.25µm) along with loose agglomerate clusters (25 to 120µm), which could not be quantified in size distribution analysis. A specially modified laser scattering particle size distribution analyzer, with a built in digitally controlled ultrasonic processor, was developed to measure particle size distribution statistics such as mean, medium and standard deviation. Ultrasonic energy levels were determined for complete de-agglomeration of undensified and densified material, which allows the measurement of the primary un-agglomerated material particle size. A test method was developed to evaluate the dispersability or relative agglomerate "strength" of the different silica fume forms by measuring the various particle size distributions, with and without ultrasound. Through the application of ultrasound, at specific energy levels and time periods, the relative agglomerate dispersability at different bulk density levels were determined. Mortar and shotcrete performance tests were conducted to evaluate the dispersability of different silica fume product forms, for different bulk loose density levels. The mortar laboratory evaluation tests included pozzolanic strength activity index ratios and electrical resistivity measurements. The test method’s ability to evaluate product dispersability and quality assurance was further verified through a field shotcrete test program, conducted with various bulk loose densities, measuring rebound percentages, thickness before bond break and compression strength.

DOI:

10.14359/18709


Document: 

SP242-28

Date: 

April 1, 2007

Author(s):

P. Termkhajornkit and T. Nawa

Publication:

Symposium Papers

Volume:

242

Abstract:

This paper describes the effect of fly ash on composition of C-S-H gel. The CaO/SiO2 ratio and chemical bonding water of C-S-H gel were estimated by the combination of the Rietveld analysis by XRD, the selective dissolution analysis and loss of ignition measurement. The results indicated that the CaO/SiO2 ratio of hydrate gel in fly ash-portland cement paste decreased as the hydration of fly ash proceeds, while the CaO/SiO2 ratio of C-S-H gel in portland cement paste did not vary with the progress of hydration. At the same amount of produced C-S-H gel, bonding water in C-S-H gel of paste prepared with 50% fly ash was higher than those of pastes prepared with of fly ash 25% and 0%. The corresponded results can be seen from decreasing of density of C-S-H gel when replacement ratio of fly ash increases. The bonding water in C-S-H gel decreases as its CaO/SiO2 ratio increases. The effect of chemical bonding water in C-S-H gel can be applied to modify the gel/space-strength model.

DOI:

10.14359/18727


Document: 

SP242-29

Date: 

April 1, 2007

Author(s):

J. Gotaszewski

Publication:

Symposium Papers

Volume:

242

Abstract:

The influence of fly ash, ground granulated blast furnace slag, and condensed silica fume on rheological properties of mortars with different cements and different new generation superplasticizers are presented and discussed. Rheological properties of these mortars were studied using Two-point workability test and these mortars can be considered as a model of concrete. The addition of mineral admixtures significantly influences rheological properties of mortars and the nature and range of this influence depend not only on the type, properties and content of mineral admixture but also on the properties of the cement and superplasticizer and interaction of these. The basic influence trends of mineral admixtures on rheology of mortars with polycarboxylate and polyeter superplasticizers are presented. It is concluded that the compatibility of cement and superplasticizer system should be selected taking into account presence and estimated dosage of given mineral admixture. The combined influence of given cement - mineral admixture - superplasticizer system on rheology of fresh concrete should be verified by means of experimentation. Two-point workability test made on mortars enables both selection of optimal cement - mineral admixture - superplasticizer system and collection of data for fresh concrete workability control.

DOI:

10.14359/18728


Document: 

SP242-27

Date: 

April 1, 2007

Author(s):

T. Horiguchi, T. Kikuchi, Y. Nakagawa, and K. Shimura

Publication:

Symposium Papers

Volume:

242

Abstract:

This research evaluated, from the ecological and economical points of view, the potential use of high volumes of incineration ash from sewage sludge in CLSM (Controlled Low Strength Materials). Moreover, a dust powder from crushed stone production is used as a fine aggregate. This new type of green CLSM will be a promising sustainable cementitious material for reducing CO2 emissions. In-situ early-age strength estimation of CLSM was proposed with applying simple cone penetration method (so-called YCP Test, Yamanaka Cone Penetration Test), which has been used for soil strength estimation. Test result showed that the YCP Test is found to be effective for estimating the in-situ early-age compressive strength of CLSM. Test results also showed the adequate strength development and reasonable flowability are confirmed if the mixture proportion is carefully selected. Although, the compressive strength decreases with increasing level of incineration ash, this strength reduction is easily compensated for increasing a small amount of cement content. From these tests results it is confirmed that a wide range of municipal solid waste is applicable for the materials of a new green CLSM.

DOI:

10.14359/18726


Document: 

SP242-17

Date: 

April 1, 2007

Author(s):

P.L. Ng, H.H.C. Wong, I.Y.T. Ng, and A.K.H. Kwan

Publication:

Symposium Papers

Volume:

242

Abstract:

This paper presents a long-term concrete shrinkage test on self-consolidating concrete (SCC) conducted at The University of Hong Kong. In this study, one normal concrete mixture with only portland cement and five SCC mixtures incorporating fly ash or both fly ash and silica fume were produced and tested for their shrinkage characteristics in the form of prismatic specimens. Fiber-optic sensors, which give stable and reliable measurements, were embedded into the prismatic concrete specimens to measure shrinkage strains. Compared with the normal concrete mixture, the autogenous shrinkage of the SCC mixtures included in this study is larger while the one-year drying shrinkage is smaller. Besides, lowering the water/cementitious materials ratio of a SCC mixture would increase its autogenous shrinkage but reduce its one-year shrinkage. Experimental results also reveal that replacement of cement by fly ash would reduce both autogenous and one-year shrinkage strains of SCC whereas replacement of cement by silica fume would increase both. Lastly, the shrinkage half-time of SCC is found to be longer than that of the normal concrete.

DOI:

10.14359/18716


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