Inadequate performance of concrete structures is often caused by deficient construction practices and lack of appropriate specifications for controlling concrete properties that are related to adequate performance during the expected service life of a structure. Work carried out for many years at the Civil Engineering Materials Unit (CEMU) of the University of Leeds has shown that the durability of concrete can be assessed effectively by measuring its permeability to gases, liquids, and ions. Paper presents the findings of a laboratory study of the properties of normal portland cement and fly ash-normal portland cement mortar and concrete mixtures that influence their oxygen and chloride-ion permeability. The study involves 28 mixtures incorporating the use of five chemically different superplasticizers and three water-cementitious materials ratios. Statistical models that relate compressive strength, porosity, pore-size distribution, and water-cementitious materials ratio to oxygen and chloride-ion permeability are presented.

Influence of an acrylic polymer on the rheology of mortars was investigated using a mixer in which the torque on the impeller shaft was continuously measured. The polymer was added to specific mortars either alone or in combination with aqueous solutions of sulfonated naphthalene formaldehyde condensate or sulfonated melamine formaldehyde condensate. Two cements were ground from two different clinkers to specific surfaces of 270 and 400 m 2/kg, respectively. The flow properties of these fresh mortars closely approximate the Bingham model, whatever the time after initial mixing may be. When used alone, the polymer decreases the plastic viscosity of the mortar. When used in combination with sulfonated melamine or naphthalene formaldehyde condensates, it decreases the yield value.

Various types of superplasticizer that maintain concrete slump for longer periods have been extensively investigated. A new type of superplasticizer with high-range water-reducing slump-maintaining capacities, composed of sulfonic acid polymer with methacrylic acid derivatives, has recently been developed. In this study, influence of cement type, concrete temperature, and pozzolans on properties of fresh and hardened concrete with this type of superplasticizer was investigated. Two reference superplasticizers were widely used naphthalene-based and amino sulfonic acid-based. A significant increase in water-reducing capacity to obtain the same consistency was observed at a much lower dosage. Absolute value of zeta potential of cement particles with the superplasticizer increased with elapsed time until 90 min after mixing, which explains the high-slump-retention capacity of the concrete. Plasticizing effects of superplasticizers were more pronounced for concretes with fly ash or blast furnace slag as blending agents. Concrete bleeding decreased slightly. Properties of hardened concrete, such as compressive strength and drying shrinkage, were at nearly the same level as those of concrete with naphthalene-based superplasticizer.

The corporate use of mineral admixtures, such as slag, silica fume, fly ash, and superplasticizer, in concrete is steadily rising for reasons of economy, enhanced strength, low heat generation, increased durability, and better rheological control. This study reports results of the influence of a cross-linked and NSF type of superplasticizer on the flow properties of blended cements. The cross-linked superplasticizer was comprised of polycarboxylic ether and cross-linked polymer, whereas the NSF type was a modified lignin, alkysulfonate, and polymer. In view of the difference in their molecular structures, their effect was studied on two types of cement: a normal portland cement and a moderate heat portland cement (belite-rich, low in C 3A), to which different proportions of slag, silica fume, and Class C and F fly ash were added to simulate binary and ternary blended cement compositions. Following a detailed chemical and mineralogical characterization of these blending components, the slump flow of 25 mortar blends were tested at a sand-binder ratio of 1.5, with the superplasticizer dosage varying from 2.5 to 3 percent by weight of cement. The water-binder ratio of these mixes ranged from 0.31 to 0.35. Marked differences in flow characteristics (determined by different methods) were recorded as a function of the cement type, blending component, and superplasticizer composition. Viscometric measurements made on the corresponding cement paste mixtures using a rheometer also exhibit pronounced differences in terms of their apparent viscosity. The possible superplasticizer interactions that occur in these blended cementitious systems are discussed. This study reiterates the cement-superplasticizer compatibility factor currently under intense discussion among researchers.

The rheological properties of fresh mortar and concrete were studied with five types of polysaccharide syrup added to either naphthalene or melamine sulfonate-based superplasticizer. The effects of the binary admixture system (superplasticizer and syrup) on the physicomechanical properties of the cementitious system, based on two types of cement (portland and pozzolan), were studied. The properties, studied at 25 and 40 C, were slump, loss of workability, setting time, and compressive and flexural strength. For one type of syrup added to the superplasticizer, synergistic effects were observed. In particular, it was demonstrated that, at 40 C, it is possible to increase the slump and reduce loss of workability using an admixture based on naphthalene sulfonate, plus Syrup G62 and melamine sulfonate, plus Syrup G62, compared to normal superplasticizer-retarding admixtures.