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 They can be described as layered double hydroxides where part of the hydroxyl groups have been replaced by the PNS anions.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.

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.

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.

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.

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.