Influence of the void ratio of cellular concrete on the corrosion of steel reinforcement

The objective of this study was to understand whether voids intensify the triggering of reinforcement corrosion in cellular concrete, for slabs with light specific masses. The methodology was based on four tests: visual inspection, corrosion potential, electrical resistivity, and mass loss. In relation to the L1 family, the L2 and L3 families (higher air content) were shown to be more susceptible to reinforcement corrosion and mass loss from the steel bars in 90% of cases. However, the behavior of some slabs indicates the possibility of the process being asymptomatic with regard to staining, considering that the influence of the cover on the corrosion of the steel bars was verified

KINETICS OF RHEOLOGICAL CHARACTERISTICS OF FOAM CONCRETE MIXTURE

The results of experimental studies are presented, the purpose of which was to study the influence of variable formulation and technological factors on the rheological characteristics of the foam concrete mixture, in particular, the structural strength. This is preceded by an analysis of the process of structure formation of cellular concrete. As a result, it is shown that the properties of cellular concrete are determined by the nature of the distribution of the solid component. The structure of the solid phase is formed at the earliest stages of the formation of cellular products and depends on the rheological characteristics of the mortar and cellular mixture. In the technology of cellular concrete, it is important to synchronize the processes of pore formation and the growth of plastic (structural) strength, which is also associated with a change in the rheological properties of the mixture. Using the methods of mathematical statistics, the influence of the content of the filler in the mixture with cement, the content of the complex additive, and the effect of mechanical chemical activation on the kinetics of the plastic strength of the foam concrete mixture were studied. The kinetic dependences of the plastic strength of the foam concrete mixture in the range of 6 ... 24 hours from the moment of manufacture have been constructed. Each of the 15 curves is maximized by a 3rd-degree polynomial. Based on the obtained dependences, they are differentiated between the first and second derivatives. As a result, the equations of the speed and intensity (acceleration) of the plastic strength of the foam concrete mixture were obtained. According to the results of the previous experiment, carried out according to a three-factor plan, a 4-factor plan was synthesized, in which the aging period of the foam concrete mixture was taken as the fourth factor. The calculated theoretical values of the characteristics of the structural strength of the foam concrete mixture were entered into the matrix. As a result, mathematical models of plastic strength, speed, and intensity of plastic strength of the foam concrete mixture were calculated and the influence of variable factors studied on the isosurfaces of these properties was visualized. The analysis of these dependencies made it possible to determine the characteristic recipe and technological conditions for obtaining a foam concrete mixture with the required values of plastic strength.

Applicability of X-ray computed tomography for concrete cellular structure analysis

Nowadays, the researchers of materials sciences area, use direct and indirect methods such as microscopy, porosimetry, etc. for studying structural characteristics of materials. X-ray computed tomography is among one of the modern and widely used research analytical methods that provides 3D images of solid materials without any preliminary preparation, such as crashing of sample, and violation of its structural integrity. To demonstrate the potential possibilities of X-ray computed tomography, in this research matrices with cellular structure using portland cement-based cellular concrete was studied as an example. The study showed that the pore structure of cellular concrete is dominated by capillary pores with a diameter of up to 200 um. The majority of pores did not exceed 1.6 mm in diameter, that formed during the foaming process. The calculated average size of the volumetric distribution of air voids was 0.95 mm. About 80% of large pores of a cellular concrete specimen with an average size of about 1 mm determines high porosity of the composite which is consistent with its average density values. The study of interpore structure partition using X-ray computed tomography allows for evaluation the difference in thickness from 10 um to 0.6 mm in the zones of “confluence” of large pores. The porosity of cement matrix, including individual pores with sizes from -30 to 250 um, was about 16.5%. The cement matrix is dominated by the products of cement hydration with capillary and “gel” pores. There are few nonreacted cement particles that are evenly distributed throughout the volume of the composite. To obtain more complete information about the structure of cellular concrete or any other composite, it is necessary to perform complex studies applying not only X-ray computer tomography technique, also scanning electron microscopy for evaluation of chemical analysis to identify mineral phases present and correlate them with absorption intensity of X-ray radiation on tomographic images.