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International Concrete Abstracts Portal

Showing 1-5 of 50 Abstracts search results

Document: 

SP173-46

Date: 

September 1, 1997

Author(s):

Giovanni Ticozelli, Danilo Galbiati and Angelo Pasqualini

Publication:

Symposium Papers

Volume:

173

Abstract:

New world record of altitude transportation of concrete (532 m) reached on the 2nd June 1994 in Riva de1 Garda Hydroelectric Power Plant. The requirement involved the construction of a new piezometric well and intake conduit and the replacing of the existing surface penstock with a new one built underground to reduce environmental impact. Two parallel tunnels were excavated: one for Ledro - Garda lakes location, the other for transporting penstock’s metal elements. The self supporting metal pipe (0 2, 30 mm, thickness 23 mm) has been blocked for all its length (790 m) by filling of the ring space between the excavation wall and the piping with 5.000 m2 of concrete. In order to reduce environmental impact it was decided to pump concrete from the l owe r end from an excavated chamber nearby the Powerhouse. The record level: 532 m (vertical) and 790 m (total length) widely exceeded the former one (432 m) obtained in 1985 in Spanish ESTANGENTO SALLENTE Power Plant.

DOI:

10.14359/6220


Document: 

SP173-42

Date: 

September 1, 1997

Author(s):

D. B. Stokes, H. H. Wang and S. Diamond

Publication:

Symposium Papers

Volume:

173

Abstract:

This paper describes the effect of a lithium nitrate-based admixture on the hydroxide ion concentration of the pore solution of hydrating pastes made from portland cement and water. No significant increase in the hydroxide ion concentration results from using this admixture in the mix, which is thus different than any published study with any other lithium compound. It has been reported that underdosing with lithium salts can increase the expansion due to ASR. The authors propose that this is mainly due to increases in hydroxide concentration observed with other lithium salts and therefore this admixture will not show such an effect. Mortar bar tests with the new admixture verify the hypothesis that the lithium nitrate-based admixture does not increase expansion at any dose. This is then a much safer admixture to use in the field with respect to risk from damaging ASR expansions. It is also much safer to handle than lithium hydroxide-based admixtures since solutions of lithium nitrate are much closer to neutral pH than lithium hydroxide solutions.

DOI:

10.14359/6216


Document: 

SP173-17

Date: 

September 1, 1997

Author(s):

Toshiyoshi Goto, Akira Yoshino and Shinzou Nishibayashi

Publication:

Symposium Papers

Volume:

173

Abstract:

Recently in Japan, foamed cement paste and foamed mortar have frequently been used as embankment material on soft ground because of their low unit weight, flowability, and ease of strength control. Conventional uses of these foamed materials include grouting for tunnel voids and for securing pipelines in tunnels. Since each material for foamed cement milk and foamed mortar have a different specific gravity, segregation can occur during mixing, pumping and placing. The mixture proportions of these foamed mixtures is very important, and are usually determined by trial and error. The authors carried out experiments on the rheological properties of cement past, mortar, foamed cement milk and foamed mortar. Compressive strength of these materials were also examined. Obtained results are as follows.(l)Plastic viscosity of foamed cement pastes or mortars are as same as that of cement pastes or mortars. (2)Yield value of foamed mixture decreases with addition of foam less than 30% by volume, and decrease with addition of foam more than 40%. (3)Relation between plastic viscosity and yield value is almost the same as mixtures without foam.(4)Compressive strength of foamed mixtures decreases with increase of foam content , and the tendency is apparent in lower w/c.

DOI:

10.14359/6191


Document: 

SP173-21

Date: 

September 1, 1997

Author(s):

S. Kakuta

Publication:

Symposium Papers

Volume:

173

Abstract:

The fluidity of self compacting concrete is influenced by the fluidity of the composed mortar. This paper discusses the rheological estimation of the fluidity of highly-flowing mortars with superplasticizers. The character of the fine aggregate is considered the most effective factor on mortar fluidity. The applicability of the viscosity equation proposed by Mori and Ototake for condensed suspension liquids to highly-flowing mortar is discussed. Mortars were tested with different volume concentration of fine aggregate suspended in highly-flowing paste. The result from rheological test using a Brookfield type viscometer indicated good agreement with the equation. Provided that the fluidity of the mortar behaves as a Bingham fluid, it can be estimated by plastic viscosity and yield value. These rheological tests were applied to two types of highly-flowing mortars composed of self-compacting concrete mixtures ranging from 60 ~ 70 cm of slumping flow value. The effects of the fine aggregate fluctuated with differences in water content, sand content and sand grading of the basic mortar. Test result showed that the character of the sand remarkably affects the 5uidity of highly-flowing mortar.

DOI:

10.14359/6195


Document: 

SP173-12

Date: 

September 1, 1997

Author(s):

V. Fernon, A. Vichot, N. Le Goanvic, P. Colombet, F. Corazza and U. Costa

Publication:

Symposium Papers

Volume:

173

Abstract:

The ability of tricalcium aluminate hydration products to absorb polynaphthalene sulfonates (PNS) has been studied by reacting a small excess of saturated lime solution, containing various amounts of PNS, with an aqueous solution of sodium aluminate. Using X-ray diffraction, infrared spectroscopy and transmission electron microscopy, it is shown that well defined organomineral intercalation compounds result from the reaction. They can be described as layered double hydroxides where part of the hydroxyl groups have been replaced by the PNS anions. The consequences of the formation of such compounds upon the rheological characteristics in the early hydration period of portland cement is discussed. Emphasis is laid on the fact that the absorptive behavior of calcium aluminate hydrates in the presence of superplasticizers is not at the origin of the occasionally observed abnormal early stiffening. This point is illustrated by the investigation of cases of practical interest, based in particular on the analysis of the pore fluid composition in fresh mortars and pastes.

DOI:

10.14359/6186


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