The retention performance of concrete is highly influenced by external parameters such as cement type, water content, materials, temperature and so on which sometimes appears to be a problem for ready-mixed concrete producers. The influences of the molecular structure and functional groups of PCE superplasticizers on the retention performance in terms of external changes were studied. In the course of our investigations we focussed on the slump-loss-controlling agent with release compound (SLCA) and a common PCE with shorter polyethylene oxide chains. It was found that the retention ratio of the SLCA was much less affected by changes of temperature and mixing time, but the retention ratio of both superplasticizers was influenced by change of w/c. Superplasticizer SLCA with an additional release compound showed a much higher adsorption increase over time than the common selected PCE. The importance of the chemical structure of polycarboxylated superplasticizer to the retention stability could be related to the adsorption mechanism. At the same time a lower retardation effect on the setting time could be observed for the SLCA superplasticizer.

The use of polycarboxylate (PC)- and polyether (PE)-based superplasticizers often generates segregation, inadequate flowability or similar problems due to the incompatibility between the cements and admixtures used. In light of the widely varying composition of these admixtures, not all cement- and superplasticizer-related factors which could affect compatibility have been defined to date. In this study, therefore, rheological trials were conducted with a rotational viscometer and adsorption tests were conducted in a total organic carbon (TOC) analyzer to explore the compatibility between different PC - PE admixtures and cements employed in a variety of compositions and additions. Three admixtures (PC1, PC2, and PC3) with different carboxylate (CA) and polyether (PE) group contents were used, along with seven standard cements whose chemical and mineralogical compositions and active additions varied. The structural characteristic of the admixtures affecting compatibility most intensely was found to be the carboxylate (CA) to polyether (PE) group ratio. In cements with no active additions, characteristics such as fineness and the C3A to calcium sulphate and C3S to C3A ratios were also observed to have marked effect on compatibility. On the other hand, in cements with limestone or fly ash additions, no fundamental differences were identified with respect to a standard CEM I 42.5R cement in terms of admixture compatiblity. In calcium aluminate cement (CAC) the fluidizing effect of polycarboxylate superplasticizers led to very significant declines in yield stress.

Self-consolidated concrete (SCC) is increasingly being used for both precast and ready mixed concrete applications. For ready mixed concrete, slump flow retention becomes a concern when the concrete is transported for long distance, and when delays in placing the concrete occur due to unexpected traffic problems or incomplete jobsite preparations. In this study, the performance of a special multifunctional superplasticizer is discussed that can enable SCC mixtures to have slump flow retention up to two hours without any significant extended setting properties and delay in strength gain. Furthermore, during the period of extended slump-flow, the SCC demonstrates rheological properties adequate to ensure segregation resistance once the concrete has been placed, as well as good moisture tolerance. This capability provided by the special superplasticizer formulation is expected to significantly reduce quality control operations and facilitate the successful production and placement of self-consolidating ready mixed concrete by imparting an appropriate amount of thixotropy to the SCC mixture without compromising suitable flow properties.

In low-water/binder-ratio concrete such as high-strength concrete (HSC) or self-compacting concrete (SCC), concrete workability decreases due to the high viscosity of the concrete as a result of its mixture components and proportion. It is considered that a reduction in concrete viscosity is significantly advantageous for placement of HSC or SCC. In this study, the authors add viscosity reducing type superplasticizers to the formulation of low-water/binder-ratio concrete. As a result, it is found that viscosity reducing type superplasticizers can reduce the viscosity of cement paste in concrete; moreover, the time to achieve a 500 mm (19.7 in.) slumpflow (an index of concrete workability) can be reduced. Accordingly, it is confirmed that application of viscosity-reducing superplasticizers can effectively improve the workability of HSC or SCC.

Lignosulfonate-based air-entraining (AE) water-reducing agents have been used in various concrete structures for over 50 years. Polycarboxylate-based superplasticizers, which are the main superplasticizers in use today, have been on the market for 20 years and have recently been applied to various kinds of concrete structures. Therefore, it is important to know the difference that these three dispersants (lignosulfonate-based (LG), B-naphthalenesulfonate-based (BNS), and polycarboxylate-based (PC)) have on concrete durability. The authors, using superplasticizers containing each dispersant, studied the properties of concrete at a w/c of 0.50 up to the age of 20 years. This paper discusses the experimental results up to the age of 3 years following standard curing and artificial sea water curing, and under normal external exposure and exposure in a splash zone. As a result, no major difference has been observed in the effect on properties of the hardened concrete between PC and BNS, dispersants in superplasticizers. In addition, the authors consider that concrete incorporating PC-based superplasticizer or BNS-based superplasticizer has equal durability to that of concrete incorporating an AE waterreducing agent, most of which is in service over the long term.