International Concrete Abstracts Portal

SP173 In October 1997, the Council for the Orginazation of CANMET/ACI Conferences in association with American Concrete Institute and several cement and concrete organizations in Italy sponsored the fifth conference on the subject in Rome, Italy. This conference was aimed at transferring technology in the fastmoving field of chemical admixtures. A total of more than 60 papers from more than 20 countries were received and reviewed by the ACI review panel and 49 were accepted for publication in the proceedings of the conference. The proceedings were published as ACI special publication SP-173.

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.

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.

The paper examines the rheological and mechanical behavior of super-plasticized microcement grouts to be used for the consolidation of porous systems (e.g. sand deposits, masonry walls of historical buildings). Five microcements were used: they differed in chemical composition of the clinker, type of mineral addition (natural pozzolan or silica fume), and particle size distribution. Three different super-plasticizing chemical admixtures - acrylic, naphtalene, and melamine based - were used, all with an active polymer content of 0.4% by mass of cement. The following properties of the grouts were investigated compressive strength, stability (bleeding test). fluidity (Marsh cone), The acrylic polymer proved to be more effective than the naphtalene and melamine based products in reducing the mixing water to produce a given initial fluidity. Furthermore, the grouts produced with this super-plasticizer displayed a lower fluidity loss with time. The performance of a specific mixture was also strongly dependent on the fineness of the binder and on the type of mineral addition. The compressive strength of the hardened grouts was primarily affected -especially at latter ages - by the water-binder ratio, independently of the type of super-plasticizer. None of the mixtures considered showed any significant bleeding. A limited number of injection tests in columns of dense sand were also performed. For a given water binder ratio, the groutability of a mixture was greatly improved using the acrylic based super-plasticizer in place of the melamine- and naphtalene-based products.

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.