The influence of selected new generation Admixtures on the workability, air-voids parameters and frost-resistance of self compacting concrete

Abstract The influence of a new generation superplasticizer (SP) type, air-entraining Admixture (AEA), viscosity modifying Admixture (VMA) and anti-foaming Admixture (AFA) on the air-content, workability of self-compacting concrete (SCC) is analyzed in the paper. The purpose of this study was to examine the influence of the Admixtures on porosity and pore size distribution of SCC at constant water on cement ratio, type and volume of aggregate and volume of cement paste. The compressive strength, frost resistance and durability coefficient (DF), parameters of the air-voids of hardened SCC are also investigated.

The influence of selected new generation Admixtures on the workability, air-voids parameters and frost-resistance of self compacting concrete

Abstract The influence of a new generation superplasticizer (SP) type, air-entraining Admixture (AEA), viscosity modifying Admixture (VMA) and anti-foaming Admixture (AFA) on the air-content, workability of self-compacting concrete (SCC) is analyzed in the paper. The purpose of this study was to examine the influence of the Admixtures on porosity and pore size distribution of SCC at constant water on cement ratio, type and volume of aggregate and volume of cement paste. The compressive strength, frost resistance and durability coefficient (DF), parameters of the air-voids of hardened SCC are also investigated.

influence of time addition of superplasticizers on the rheological properties of fresh cement pastes

It is well known that the fluidity and the fluidity loss of fresh cement pastes are affected by the kind and the time of addition of organic Admixtures. The influence of the time addition of two chemical Admixtures, namely, melamine formaldehyde sulfonate (MFS) and naphthalene formaldehyde sulfonate (NFS), on the rheological properties of ordinary Portland and sulfate-resisting cement pastes through the first 120 min of hydration was investigated. The Admixture addition was delayed by 0, 5, 10, 15, 20, and 25 min. Shear stress and apparent viscosity of the cement pastes were determined at different shear rates (3–146 s−1) and hydration times of 30, 60, 90, and 120 min. The concentration of Ca2+ and the combined water content of the cement pastes were determined after 120 min. Yield stress and plastic viscosity values were also determined by using the Bingham model. The results show that an increase in the addition time of the Admixture reduces the shear stress, the yield stress, and the plastic viscosity of the cement pastes at the early ages (15 min) as well as at later early ages (120 min). The optimum delaying time of Admixture addition is found to be 10–15 min. This time does not depend on the cement and superplasticizer type.

interaction between cement and chemical Admixture from the point of cement hydration absorption behaviour of Admixture and paste rheology

Chemical Admixtures can improve the properties of concrete. High performance concrete with high strength, superior fluidity, and self-compactibility can be realized mainly because of chemical Admixtures. Rheological properties of fresh concrete can be strongly affected by the combination of cement and chemical Admixture, method of Admixture addition, or the water-cement ratio. Problems in fluidity, such as stiffening and large slump-loss, occasionally happen under a particular combination of cement and Admixture. These phenomena are generally called incompatibilities between cement and chemical Admixtures. In this study, the interaction between cement and the chemical Admixture types lignin sulfonate, naphthalene sulfonate, melamine sulfonate, amino sulfonate, and polycarboxylate, together with the working factors and mechanisms, are discussed from the viewpoint of cement hydration. Although the polycarboxylate type superplasticizer was considered to have better compatibility in combination with different kinds of cement, the authors show that its compatibility is affected by the amount of alkaline sulfates in cement.

effect of Admixture on hydration of cement adsorptive behavior of Admixture and fluidity and setting of fresh cement paste

The adsorptive behavior of Admixtures and the hydration of cement in the presence of Admixtures were examined and the relationships of them with the physical properties of fresh cement paste including fluidity, variation of fluidity with time and setting time were discussed with the quantitative determination of organic Admixture adsorbed on the cement, and with the observation and determination of the surface microstructure and composition of polished clinker dipped in aqueous solution containing a specified quantity of Admixture by advanced method of surface analysis.

In order to prepare the same fluidity of fresh cement paste, mortar and concrete, the required amount of an easily adsorbed Admixture is larger than that of a hard adsorbed one. An Admixture having a functional group producing a complex salt with Ca2+ decreases the concentration of Ca2+ in liquid phase at early age and delays the saturation of Ca2+, which influences the morphology of hydrate produced, causes fluidity loss with time and delays the setting time of cement. The microstructural and compositional estimations of the adsorption layer of Admixture on the surface of clinker minerals by in-lens FESEM, ESCA-imaging, AES and AFM indicates that the Admixture is partially adsorbed to the interstitial phase in a thick layer, forming characteristic three dimensional surface structure.

Effect of Admixture on hydration of cement, adsorptive behavior of Admixture and fluidity and setting of fresh cement paste

The adsorptive behavior of Admixtures and the hydration of cement in the presence of Admixtures were examined and the relationships of them with the physical properties of fresh cement paste including fluidity, variation of fluidity with time and setting time were discussed with the quantitative determination of organic Admixture adsorbed on the cement, and with the observation and determination of the surface microstructure and composition of polished clinker dipped in aqueous solution containing a specified quantity of Admixture by advanced method of surface analysis.

In order to prepare the same fluidity of fresh cement paste, mortar and concrete, the required amount of an easily adsorbed Admixture is larger than that of a hard adsorbed one. An Admixture having a functional group producing a complex salt with Ca2+ decreases the concentration of Ca2+ in liquid phase at early age and delays the saturation of Ca2+, which influences the morphology of hydrate produced, causes fluidity loss with time and delays the setting time of cement. The microstructural and compositional estimations of the adsorption layer of Admixture on the surface of clinker minerals by in-lens FESEM, ESCA-imaging, AES and AFM indicates that the Admixture is partially adsorbed to the interstitial phase in a thick layer, forming characteristic three dimensional surface structure.