International Concrete Abstracts Portal

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.

One-pack hybrid admixture (HSP) combining high fluidity, viscosity-reducing property, and shrinkage-reducing capability for high strength concrete with a target strength of 60 to 150 MPa was developed and examined. HSP showed high fluidity and viscosity-reducing performance, as well as excellent autogenous shrinkage-reducing effect to achieve a reduction in the autogenous shrinkage of 21 to 44% with respect to that of concrete containing a conventional high-range water-reducing admixture. HSP was therefore found to be a simple and effective solution to shrinkage problems for a wide range of high strength concretes.

The interactions between six commercial cements and three types of plasticizers, namely naphthalene sulfonate formaldehyde condensate (SNF), lignosulfonate (LS) and polyacrylate grafted with polyether (PA) are investigated using cement paste. PA was found to be the most efficient plasticizer of the three tested even though it was found to present lower adsorption onto cement than SNF and LS. SNF and LS brought about comparable results. PA was observed to induce flow gain of pastes within 2 hours of rheological measurements, while pastes made with SNF and LS exhibited flow loss as a function of time. The adsorption characteristics were found to depend on the plasticizer type. The plasticizer saturation dosages were, moreover, found to depend on cement surface area (Blaine fineness), amount of cubic C3A and soluble sulfates.

A combination of ground granulated blast furnace slag, fly ash and calcium hydroxide has been used to immobilize acid nuclear wastes in the form of a hardened system in the absence of any aggregate. An aqueous solution of NaOH (19 M) was used for two purposes: first, to neutralize the acid waste and to transform it in a very basic system (pH>13); second, to activate the hardening of the binder. Due to the liquid-solid ratio lower than 0.70, the fresh mixture is relatively stiff. Superplasticizers based on sulfonated naphthalene and melamine or acrylic polycarboxylate do not work to fluidify this system. D-Sorbitol as well as other alditols are very effective in terms of higher workability and lower workability loss of this cementitious system. Surprisingly this chemical admixture increases the compressive strength of this cementitious grout at both early and longer ages at a given waterbinder ratio. The properties of this cementitious system in the absence and in the presence of D-sorbitol as chemical admixture (0.2-0.5% by weight of binder) have been studied in the form of workability of the fresh mixture, early and later compressive strength, leachability by water and X-ray diffraction analysis of the hydrated products of the hardened system.

The relationship between the number of individual functional groups present in lignosulfonate molecular structures and the performance of lignosulfonates in fresh cement pastes was investigated. Lignosulfonate fractions from three different pulping processes (sulfite, sulfate and organosolv) were included in this study. The dispersing, set-retarding and air-entraining effects of these fractions in ordinary Portland cement pastes were studied. Elemental composition, methoxyl and sulfonate group contents were determined analytically. An algorithm was developed to generate model molecular structures representing individual lignosulfonate fractions. Each model structure was based on the results of the chemical analysis, the model structural segment typical of each particular lignin and additional literature data. The numbers of sulfonate, carboxyl, phenolic hydroxyl, aliphatic hydroxyl and methoxyl groups in each proposed molecular structure were determined. The numbers of C-C and C-O-C inter-unit bonds in each molecule were calculated as well. Correlations between selected functional group counts and the dispersing, set- retarding and air-entraining effects of lignosulfonates were determined. For the dispersing effect, methoxyl was the most positively correlated and carboxyl was the most negatively correlated group. Sulfonate had a very low correlation with the dispersing effect. For the set-retarding effect, the C-C inter-unit bond was the most positively correlated and sulfonate was the most negatively correlated. For the air-entraining effect, carboxyl was the most positively correlated and aliphatic hydroxyl was the most negatively correlated group. A low correlation was found between sulfonate and the air-entraining effect. The results are interpreted from the perspective of cement hydration processes and the implications on the understanding of lignosulfonate interactions with cement-water systems are discussed.