For the Ready Mix Concrete mix design, the initial workability depends on the chemical composition of the Polycarboxylate Ether (PCE). Up to now the use of best PCE can achieve 2 hours of slump retention. However, a tendency to segregate is observed when over-dosage is made, due to water reduction capability of PCEs. An approach is to use also a combination of a water-reducing agent and a retarding agent which has the main disadvantage to delay the setting time and consequently the early strength of the concrete. This paper demonstrates the possibility to boost the performance of currently used PCEs. The new slump retention additive that we developed allows a significant increase of the slump retention while maintaining the initial fluidity without impacting the water reduction ability. The homogeneity of the concrete is also controlled by using this additive. On top of that, the combination between this new product and a standard water-reducting PCE is made at commonly used dosage.

Several studies have been pursued in Japan on developing concrete using high volume blast-furnace slag cement for reducing CO2 emissions arising from calcination of cement. However, when using high volume blast-furnace slag cement, various problems are encountered, such as decreased fluidity retention ability caused by the reduction of admixture dosage and decreased strength enhancement. In this paper, the authors focus on the adsorption properties of polycarboxylate ether superplasticizers and the properties of hardened concrete that incorporates a component of high volume blast-furnace slag cement, and discuss the development of a new type of superplasticizer through molecular design and optimization of the admixture composition. The admixture improved the fluidity and properties of hardened concrete using slag cement containing more than 60% blast-furnace slag.

Viscosity-modifying admixtures (VMA) are often introduced in the formulation of modern factory-made mortars in order to prevent segregation and to improve the homogeneity and workability of cement-based system. Among VMAs, organic admixtures, and more especially polysaccharides such as cellulose ethers (CE), are widely used, since they improve both rheological property and water retention capacity of the mortars. The present study examines the influence of chemical composition and structure of guar gum derivatives on water retention capacity (WR) and rheological behavior of fresh state Portland-based mortars. The investigation was also completed by adsorption isotherms. For this, original guar gum, HydroxyProplyl Guars (HPG) and hydrophobically modified HPGs were selected. The effect of the molar substitution (MSHP) and the degree of substitution (DSAC) was investigated. The results highlight that chemical composition of HPGs has a remarkable effect on fresh state properties of mortars. The original guar gum does not impact both WR and rheological behavior. Increasing MSHP leads to an improvement of the WR and the stability of mortars while the hydrophobic units further enhance WR and lead to a decrease in the yield stress and an increase in the resistance to the flow of admixed mortars.

The microstructure of MPEG-type polycarboxylate (PCE) copolymers, i.e. the distribution of side chains along the main chain was investigated via 13C NMR spectroscopy and the effect on the interaction with cement was determined. For this purpose, two series of polycarboxylate samples (one series synthesized by radical copolymerization, the other one via grafting/esterification) at molar ratios of –COO– to side chain of 2 to 10 were compared. The 13C NMR spectra suggest that the copolymerized PCEs possess a gradient-like distribution of side chains along the main chain while the grafted PCEs exhibit a statistical (random) repartition. Owed to those microstructural differences the grafted PCE copolymers show a tendency to adsorb in lower amount on cement. The reason is that in the copolymerized PCEs, large blocks of –COO– groups are present which exhibit high affinity to the surface of cement and therefore promote adsorption.

Superplasticizers are often used in conjunction with other additives and this can produce either an adverse or synergistic effect on rheology and setting properties of cementitious systems. These effects can be enhanced when temperatures are increased due to environmental changes or induced temperature as in hydrothermal curing. This research focuses on the compatibilities of different types of superplasticizer either sulfonated naphthalene or polycarboxylate based in combination with a lignosulphonate or hydroxycarboxylic acid type retarder. Rheological measurements were made using a rotational viscometer at temperatures from 25°C (77°F) to 120°C (248°F) under pressure, and plastic viscosity and yield point determined based on the Bingham Plastic model though in almost all cases it was noted that the Power Law or more so the Herschel-Buckley model gives a better fit. Zeta potential was used to characterize particle surface interactions to understand synergy of additive combinations. Setting properties, investigated using conduction calorimetry, were observed to be dominated by retarder response.