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This Symposium Publication includes 37 papers selected from the conference that took place in Nice, France, in October 2000. Topics include effects of superplasticizers, interaction of admixtures with calcium aluminate cements, lignosulfates, admixtures for improving resistance to chemical attack, effects of admixtures on concrete shrinkage, and many more. Note: The individual papers are also available as .pdf downloads.. Please click on the following link to view the papers available, or call 248.848.3800 to order. SP195

Chemical admixtures play a central role in modern concrete materials and technologies. In conjunction with mineral additives such as silica fume, chemical admixtures have enabled major improvements in many of the properties of concrete, particularly, compressive strength and durability. Chemical admixtures have also assisted in developing new concrete technologies, for example, concrete pumping and self-leveling, underwater concreting and shotcreting. Chemical admixtures have further promoted the use of secondary industrial materials (blast furnace slag and fly ash) in cementitious systems, contributing to resource conservation and environmental sustainability. In the continuing quest for more cost-efficient and environmentally acceptable materials and technologies, it may thus be expected that chemical admixtures will continue to play an important role in future generations of concrete. Probing into the future, how will concrete chemical admixtures evolve in the coming decades? What trends can be anticipated in future developments and use of these admixtures ? What will be the driving influences for these developments? This paper addresses some of the issues that are considered relevant driving forces to promote changes in the use of currently available chemical admixtures, or in the development of new admixtures. The trends already apparent in cementitious materials and concrete applications provide a reasonable basis for proposing probable trends in the evolution of concrete admixtures into the 2 lSt Century.

The effects of Na2S04 addition to cement pastes containing PNS superplasticizer with different molecular weight were investigated in different parameters of cement pastes, such as the rheological properties, the adsorption of PNS superplaticizer, and the development of the heat of cement hydration. Na2S04 addition significantly improves the fluidity of cement pastes made with a low-alkali-cement and a high-molecular-weight PNS. On the contrary, Na2S04 addition to a high-alkali-cement has a negative effect on the fluidity of cement pastes in the presence of PNS superplasticizer. The effect of Na2S04 addition on the fluidity of cement pastes made with a low-molecular-weight PNS is relatively small. When sodium sulfate is added to the low-alkali cements in order to adjust the soluble alkali content, it is confirmed that the cement pastes containing the high-molecular-weight PNS have better fluidity than those containing the low- molecular-weight PNS. The Na2S04 addition reduces the amount of PNS adsorbed on cement particles and the effectiveness of Na2S04 in reducing the amount of PNS adsorbed is independent to the molecular weight of the PNS. The Na2S04 addition to low-alkali-cements retards cement hydration during induction period in the presence of a high-molecular-weight PNS and then accelerates it during the acceleration period. However, the Na2S04 addition to high-alkali-cements just accelerates cement hydration and this acceleration effect is not dependent to the molecular weight of PNS super-plasticizer.

Carboxylic acid ester superplasticizers (CAE) consist of polymers in which hydrophilic polyoxyethylene ester chains (CE) are grafted onto a main chain bearing carboxylic groups (CA). In the present work, CAE copolymers characterized by different molar carboxylic acid - carboxylic ester ratios (CAKE) were synthesized and evaluated as super-plasticizers by using two different cements. The efficiency of CAE copolymers as superplasticizers was found to be dependent on the carboxylic acid - carboxylic ester ratio (CAKE) and the optimum CA/CE value in order to attain the best flowability was different for the two cements. Adsorption measurements indicated an increase of adsorption onto both the cements by increasing CAKE. On the other hand, zeta potential of cement pastes was not substantially influenced by the addition of the different superplasticizers. The results of the present work seem to indicate that both adsorption and steric stabilization are the main factors which determine the performances of CAE as superplasticizers and that CA/CE is an important parameter influencing the cement/CAE superplasticizer compatibility.

The results presented and discussed are those of a study aimed at understanding how and why tint heterogeneities occur at the surface of concrete. In particular, the study involved laboratory tests on mortars which were aimed at examining the effect of the following parameters on the phenomenon of tint heterogeneity: W/C, super-plasticizer content, cement alkali content, mould type, and curing conditions. The results appear to show that two of the parameters aforementioned have a major influence on tint homogeneity: the homogeneity of the binder volume fraction distribution resulting from the use of super-plasticizers, and the absorption properties of the mould.