International Concrete Abstracts Portal

This Symposium Publication includes 30 papers selected from a conference that took place in Seville, Spain, in October 2009. Topics include Use of a Supplemental Agent to Improve Flowability of Ultra-High Performance Concrete; Performance of Superplasticizers in Blended Cement Systems; and Multifunctional Chemical Admixture to Reduce Quality Control Requirements of Self-Consolidated Concrete. Note: The individual papers are also available. Please click on the following link to view the papers available, or call 248.848.3800 to order. SP-262

Total Organic Carbon (TOC) measurement of cementitious pore solutions for quantification of (super)plasticizer adsorption was reviewed in this study with a system of two Polycarboxylate Ethers (PCE) and one Naphtalene Sulfonate polymer (BNS) in combination with 3 different cements. The influence of pore solution salt concentrations as well as different methods for pore solution extraction on the measured amount total organic carbon have been investigated. Adsorption measurements in paste, mortar and concrete systems are compared and conclusions are drawn by summarizing and interpreting the results obtained in the studies.

The hydration of tricalcium silicate (C3S), the major component of portland cement, determines setting and strength of concrete. Setting of portland cement pastes (that is, concretes) is strongly affected by the use of superplasticizers (SP). As it is commonly agreed, the hydration of C3S proceeds through a dissolution precipitation process. Thus, the present study investigates the dissolution behavior of C3S in dependence of SP addition. Dissolution experiments are carried out at paste conditions (w/C3S = 0.5) and at high liquid-solid ratio (w/C3S = 50). It is shown that in the presence of SP the ionic concentrations in the solution are shifted to lower calcium and higher silicon values. The reason might be a varied degree of C3S hydration, complex formation, or shifted ion concentrations due to the presence of ions introduced by SP addition (that is, Na). Additionally, calorimetric analysis clearly shows that in the presence of SP the dissolution heat of C3S is increased. It is concluded that in the presence of SP the dissolution of C3S is not diminished but rather unchanged or even increased.

Concretes with portland cement in the presence of fly ash or beneficiated fly ash (BFA) all at a slump of about 240 mm (9.4 in.) were made. Fly ash or BFA was used as mineral addition replacing 20% of portland cement in both plain and superplasticized concretes with or without shrinkage-reducing admixtures (SRA). The 28-day compressive strength of the superplasticized and plain concretes without mineral addition were higher than those of the corresponding concretes with fly ash and lower than that with BFA. Drying shrinkage of specimens exposed to a dry environment with relative humidity of 50% up to 4 months was measured. In the presence of fly ash the drying shrinkage decreased by about 15% with respect to the corresponding plain concretes without fly ash. In the presence of a superplasticizer and/or a SRA there was further reduction in dry shrinkage of fly ash mixtures. The drying shrinkage of concretes, where portland cement was replaced by BFA was lower than that of the corresponding concretes with fly ash. Even in the presence of superplasticizer and/or SRA a further reduction of drying shrinkage of BFA concretes was found. In fly ash or BFA concrete mixtures, and more significantly in the presence of superplasticizer and/or SRA, the cracking in restrained slabs was reduced in terms of both the number and the width of cracks.

Recently, concrete workability has become regarded as much more important because of large demands for high -strength concrete with high unit powder content and unstable quality of concrete materials. The new hyper-branched polymer was developed to provide better workability with much lower plastic viscosity of the mortar than the conventional polycarboxylate type superplasticizers. In this study, further workability improvement for a longer periods was investigated to provide better workability to the construction job site. The higher density of ethylene oxide (EO) chains adsorbed on cement surfaces was found to provide a more stable dispersion state that leads to lower viscosity of the dispersion system. However, the cement dispersion states might change with time generally due to the cement hydration process, so that the viscosity of the mortar or the concrete tends to become higher although the fluidity is maintainable. Thus, new additional EO chains were thought to be required with time on the hydrated cement surfaces to maintain a stable dispersion state. Based on this hypothesis, theoretically required EO chains were calculated and it was possible to maintain the mortar viscosity utilizing new hyper-branched polymer and hydrolysis type polymer.