International Concrete Abstracts Portal

The resistance to a 0.5% sulfuric acid solution of six different concrete compositions with and without addition of polymer was investigated. Four different polymer types were used: a styrene-acrylic ester polymer, an acrylic polymer, a styrene butadiene polymer and a vinylcopolymer. The different concrete compositions were tested on a testing apparatus for accelerated degradation tests. The test procedure consists of an alternated submersion in a 0.5 % sulfuric acid solution and drying in air of the test cylinders (0 230 mm, height 70 mm). After each cycle, the concrete cylinders were brushed with rotary brushes to remove the weakly adhering concrete particles. Concrete degradation was measured by the change in radius of the cylinders after each cycle. The measurements were performed before and after brushing in order to determine the swelling of the cylinders due to sulfate attack formation of gypsum and ettringite- as well as the decrease of the radius due to material loss caused by brushing. The concrete composition with blast furnace slag cement showed the best resistance to the sulfuric acid attack. Comparing the four different polymer types, addition of styrene-acrylic ester increased the resistance of the concrete the most. The addition of the acrylic and the styrene butadiene caused a decreased resistance of the concrete compared to the composition without polymer addition.

A new generation of complex modifiers for concrete on organo-mineral basis have recently appeared on the Russian construction market. These powder type modifiers with bulk weight around 800 kg/ m3 consist of a mineral part - silica fume (SF) or its combination with fly ash (FA), and an organic part - superplasticizer (SP) or its combination with setting regulator (SR) . Effects of the modifiers on the structural parameters of cement paste and concrete - porosity, phase composition, hydration degree, compressive strength and permeability - were studied. Four types of modifiers with mineral to organic parts in the ratio of 10: 1 were used. The modifiers had different mineral parts: the first consists of pure SF (100%); the second and third of a combination of SF and FA (70:30) and (50:50) respectively; and the fourth of pure FA (100%). The organic part of the modifiers comprises SP on the basis of naphtalen-sulfoacid and formaldehyde polycondensate. Cement paste structure was studied by several methods. A combination of different methods enabled porosity on overmolecular, submicroscopic, microscopic and macroscopic levels to be defined. Peculiarities of cement paste structure provided by the four different types of modifiers were revealed. The influence of silica fume and fly ash proportion on cement paste porosity and phase composition, as well as on compressive strength and permeability of concrete was investigated. It was concluded that the key factor that controls a modifier’s efficiency is the proportion of silica fume in its mineral part. However, at replacements of up to 50% silica fume by fly ash, the efficiency of a modifier remains rather high.

Superplasticizers are key components to enhance greatly the workability of concrete. A new carboxylic acid-based copolymer was synthesized and evaluated as a superplasticizer. This copolymer was prepared from methacrylic acid and 2-acrylamido-2-methylpropane sulfonic acid through free radical polymerization. The test results on cement pastes indicate that this copolymer could uniformly disperse the cement particles and improve the fluidity of the system. Compared to the commercially available naphthalene-based superplasticizer, the polymer requires less amount to achieve the same mini-slump value, and provides longer slump retention time. Thus the synthesized resin has a potential to become a superplasticizer. Finally, the workability and compressive strength of concrete with this new admixture were also tested, and compared with that of the commercial superplasticizers.

Shrinkage-reducing admixtures currently available in the market serve for controlling cracks occurring in concrete due to reduction in the shrinkage stresses from drying by relieving the surface tension of free water in concrete. However, it is generally believed that freezing and thawing resistance of concrete would be decreased when shrinkage-reducing admixture is used, and presumably this can cause problems in cold and snowy regions, In this study, analytical examinations were carried out by focusing attention on the molecular structure of a shrinkage-reducing admixture and methods of its application for the purpose of improving freezing and thawing resistance of concrete. As the result, it was found that freezing and thawing resistance could be improved if concrete is mixed with delayed adding method of shrinkage-reducing admixture.

The oxygen diffusion coefficient through hydrophobic cement-based materials fully immersed in water was determined by potentiostatic measurements on concrete and by the use of a diffusion cell on cement pastes and mortars. The results obtained show that very high oxygen diffusion occurs through cement paste, mortar and concrete made with hydrophobic admixture as opposed to negligible diffusion through the reference cement matrix without admixture. Moreover, the oxygen diffusion coefficients measured through hydrophobic cement matrices immersed in water were comparable with those reported in literature for unsaturated cement materials in air. These experimental results appear to confirm that oxygen dissolved in water directly diffuses as a gaseous phase through the empty pores of a hydrophobic cement matrix. This could explain the severe corrosion of steel reinforcement embedded in cracked hydrophobic concrete immersed in an aqueous chloride solution observed in a previous work.