In this paper, the influence of different setting regulators on the performances of an inorganic acid based alkali-free accelerator was analysed. Setting time and compressive strength development were determined on clinker samples added with b-hemihydrate or anhydrite and admixed with the alkalifree accelerator. It was found that the lower is the setting regulator instantaneous dissolution rate, the shorter is the final set and the higher the compressive strength development (therefore the more efficient is the accelerator). In order to understand this phenomenon, physical (hydration temperature profile), chemical (TG and XRD), morphological (ESEM-FEG and specific surface area measurements) analyses were carried out on paste samples added with the accelerator.

The interaction between CEM I type cements and PolyCarboxylates with PolyEthyleneOxide side chains superplasticizers was examined to clarify the origin of incompatibility problems. Particular care was devoted to the possible role of a competition between sulphates and superplasticizer in these issues. Both laboratory and industrial cements were examined so as to analyze the influence of set regulator amount and/or nature, and of alkali level. The study mainly focused on the ionic composition of the aqueous solution, the consumption isotherms of the superplasticizers and the rheology of cement grouts. The results showed a major influence of the alkali sulphates of the clinker: the higher the latter, the higher the concentration of sulphates in the aqueous solution and the lower the superplasticizer consumption. The yield stress was correlated to superplasticizer consumption: it decreased when the consumption increased. On the other hand, the amount and nature of the set regulator appeared to induce a second order effect on the aqueous phase composition and on the superplasticizer consumption.

Different types of superplasticizers have been widely used over the past few decades in order to produce a more fluid or very high strength and durable concrete. These chemical admixtures interfere with the various physico-chemical processes occurring in early cement paste. In this paper we present results from a study on the influence of superplasticizers on pure tricalciumaluminate hydration in presence of gypsum. The suspensions hydration has been investigated by conductimetry, isothermal calorimetry and total organic carbon analysis of the liquid phase. The time taken for ettringite formation has been determined without superplasticizer and in presence of three different types of superplasticizers: polynaphtalene sulfonates (PNS), polycarboxylate-polyox (PCP) and diphosphonate terminated polyoxyethylene. Whereas diphosphonate terminated polyoxyethylene does not seem to modify tricalcium aluminate hydration carried out in presence of gypsum, PCP and even more PNS slow down ettringite formation. This effect seems to be largely due to a decrease of the C3A dissolution rate and might be connected to an adsorption of PCP. or PNS observed from the early C3A hydration. Such an adsorption does not happen with diphosphonate terminated polyoxyethylene superplasticizer. Moreover the presence of PCP superplasticizer causes a decrease in the size of the ettringite crystals formed.

The adsorption of sodium lignosulphonate onto cement was investigated. The cement has either been pre-hydrated or hydrated with the lignosulphonate present. The pre-hydrated cement particles grow with time, thus a larger surface is created and the plateaus in the adsorption isotherms increase. With lignosulphonate present there is hardly any growth of new surface. It is found that, a lignosulphonate that adsorbs strongly to the surface causes, less retardation than weakly adsorbed lignosulphonates. This can be explained by different interactions with the different minerals present.

Aggregate shape, texture, and grading have been known to have a significant effect on the rheological performance of fresh concrete. Moreover, while the optimization of aggregate selection can provide both technical and economical benefits, the availability of materials and construction operations can often dictate the use and proportioning of certain aggregate sources, such as manufactured sands, which can adversely impact the rheology of cementitious mixtures. The use of certain chemical admixtures has been found to often minimize the need to increase cement and water contents in order to overcome the loss of workability that can accompany aggregate sources which feature flat, elongated, angular, and rough particles. In this study, a wide range of natural and manufactured sands, characterized for gradation, mineralogy, shape, texture, and cleanliness, are evaluated for their effect on mortar rheology, with and without a viscosifying-type chemical admixture. While associations between aggregate characteristics and their impact of mortar rheology may not be readily evident, the ability of this class of admixture can be shown to mitigate the rheological effect of certain sands, and in some cases allow for optimizing the mixture to lower paste contents.