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Home > Publications > International Concrete Abstracts Portal
Showing 1-5 of 50 Abstracts search results
Document:
SP173-40
Date:
September 1, 1997
Author(s):
A. Macias and S. Goni
Publication:
Symposium Papers
Volume:
173
Abstract:
A deflocculation test based on the method proposed by A. Verhasselt and J. Pairon has been applied to different mixes of cement-admixtures in order tc distinguish quickly between plasticizer and superplasticizer. The admixtures used were commercial products containing different proportions of lignosulphonates (L), sulphonated naphthalene formaldehydecondensate (SNF) and sulphonated melamine formaldehyde condensate (SMF). Three different cements were employed: a low tricalcium aluminate (C3 A = 2.5 %), a high alkali content (Na2 O equivalent = 0.95%) and a high fineness Portland cement (S.A. Blaine = 5002 cm2/gr). In addition, the minimum active dosage of superplasticizer was calculated. The influence of the type of cement in the minimum active dosage is clearly shown by the results obtained through this method.
DOI:
10.14359/6214
SP173-41
Liang Wenquan, Lian Huizhen, He Zhen and Li Yajie
Polybasic organic phosphate and lignosulphonate were combined in appropriate proportions to be a kind of high-range retarder-plasticizer(KM) for use of higher temperatures. Various retarders have been used in ordinary concrete and roller-compacted concrete(RCC)for testing under 45 “C and 25% relative humidity. Rheology and time of setting of fresh concrete and mechanical properties of hardened concrete, allowance of exposure time of bond between two construction layers of RCC,etc. were investigated. Simulated testing for Three Gorges Project was also carried out by testing a t the Development General Co. and the Testing Center of Gezhouba group.
10.14359/6215
SP173-42
D. B. Stokes, H. H. Wang and S. Diamond
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.
10.14359/6216
SP173-43
G. Ferrari, T. Cerulli, P. Clemente and M. Dragoni
In the present paper a new analytical method for measuring the adsorption of naphthalene sulfonate formaldehyde condensate superplasticizers (NSFC) onto cement is described. By this method, based on the application of Gel Permeation Chromatography (GPC), it is possible to estimate the selective adsorption of the different components of these admixtures (P-naphthalene sulfonate, naphthalene disulfonates, polymer fraction). The results indicate that P-naphthalene sulfonate and naphthalene disulfonates are not substantially adsorbed onto the cement particles, independently on the cement used and the dosage of admixture. The polymeric fractions are adsorbed at different extent according to the dosage of superplasticizer and the cement used. Adsorption tests with two NSFC samples of different molecular weight indicate that the high molecular weight polymer fractions are preferably adsorbed over the low molecular weight fractions. The adsorption isotherms of the polymeric fraction of NSFC superplasticizers with different cements indicate that the saturation dosage depends on the chemical composition, the particle size and the specific surface area of the cements. Moreover, these results indicate that the NSFC polymer fraction is totally adsorbed on different cements up to a certain dosage of superplasticizer. This critical value seems to be related with the minimum dosage of superplasticizer to reach the optimum fluidity of cement mixtures. This observation could be put in relation with the preferred adsorption of the higher molecular weight fractions on NSFC, which exhibit a better superplasticizing effect.
10.14359/6217
SP173-44
H. Wang, K. Eubanks, B. Fitch, C. Manissero and F. Marin
This paper describes the development and applications of several lithium-based chemical admixtures for set control of cementitious-based construction and building materials. Comparative evaluations show the effect of these admixtures on the set time of (1) calcium aluminate cement; (2) portland cement; and (3) blended systems of calcium aluminate cement and portland cement. General information is provided to address the principles of material selection, dosage rate and application of cementitious systems.
10.14359/6218
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