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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.

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 They can be described as layered double hydroxides where part of the hydroxyl groups have been replaced by the PNS anions.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

A consequence of drying shrinkage is intrinsic cracking due to some form of restraint. In thick sections of concrete, drying from the surface causes differential shrinkage and such internal restraint can be responsible for surface cracking because of the induced tensile stress. When thin drying concrete members are restrained externally, a time-dependent failure is likely unless drying shrinkage is minimised. Besides drying shrinkage, the potential for cracking depends on tensile creep and tensile strength or tensile strain capacity and such properties are not normally measured in the laboratory. The possible effects of chemical admixtures on the foregoing properties is also largely unknown. The current research is investigating the role of tensile creep in relieving the tensile stress induced by fully restraining the drying shrinkage of concrete with and without chemical and mineral admixtures. All the relevant properties contributing to the time-dependent strength are being measured using bobbin-shaped specimens previously developed for uniaxial creep determination. The present paper presents the findings for concretes with and without a plasticizer and a new shrinkage reducing admixture. While the plasticizer has little influence on properties, the shrinkage reducing admixture significantly lowers the strength, elastic modulus, free drying shrinkage and creep. When restrained from the age of seven days all the concretes failed between 4 and 13 days, the concrete with the shrinkage reducing admixture failing at the lowest stress but after the longest time.

An acrylic polymer was mixed with fine sand and cementitious binders. The mixtures were studied as rubber-like coating to protect reinforced concrete specimens. Three coatings (all with water-binder ratio of 0.50, polymer-binder ratio of 0.50 and sand-binder ratio of 2) were produced by changing the type of binder: portland cement, pozzolan-portland cement with metakaolin and slag-based cement. The coatings were applied to a porous concrete substrate with a water-cement ratio of 0.80. Preliminary tests on uncoated and coated concrete specimens were carried out to study the penetration of water, carbon dioxide, chloride, and sulphate ions. The resistance to penetration of these aggressive agents was very poor in the uncoated specimens and became as good as that of a watertight and durable concrete in the coated specimens. Coated beam specimens were kept for 24 months in three different environments (laboratory at 20°C and 60% R.H.; outdoors environment exposed to natural changes in temperature and relative humidity; under water) in order to examine the influence of the binder type on the bond strength and the flexibility of the coating in terms of ability to bridge the cracks of the concrete substrate. Bond strength of the coatings was substantially unchanged or improved by the exposure to the three different environments. Initial flexiiity of the coating was improved by the addition of metakaolin or slag. However, at later ages there was some flexibility loss, for coated concrete specimens exposed to water, when portland cement was used specially in the presence of mtakaolin. No flexibility loss was found in the polymer-cement coating in the presence of slag.

The authors have shown that it is possible to make a concrete with low-heat and high-strength by properly exploiting the potentials of the materials used. The high-range water-reducing air-entraining agent (AE) used played an important role. However, there was a need to reduce the slump loss. A new high-range water-reducing AE agent was developed for this purpose. The agent is a compound of a polycarboxylate type copolymer and a special polymetric surface active agent. This paper describes strength and heat properties of concrete with the developed agent. A moderate heat portland cement and a super-ground granulated blast-furnace slag were used. The test results showed that the newly-developed high-range water-reducing AE agent makes it possible to reduce the slump loss of concrete without losing the properties of low-heat and high-strength. However, it was found that the low-heat property of the developed concrete is lost when the concrete is proportioned to be flowable.