Crack resistance of decorative composites

Abstract

The results of a study of crack resistance obtained during the development of fine-aggregate concrete for architectural elements are presented. The crack resistance study of 27 different proportions of compositions was carried out in accordance with DSTU B V.2.7-227: 2009 using experimental statistical modeling methods. Due to the fact that the method of initiating the initial crack in the samples changes the distribution of the technological fields of strain, the tests were carried out on two series of samples. The data obtained show that the crack sealing method changes the deformative-stressed state of the composite. So, crack resistance for one concrete composition can vary, from the conditions of the experiments, from 3 to 40 %. Based on the obtained values of the characteristics of the material, in particular, for the coefficient of technological impact on crack resistance, which describe the fields of these criteria in the coordinates of the factors of concrete composition, models were built. The results of the model are presented on 5 factor diagrams of the form “cubes squared”. An analysis of the constructed diagrams showed that the initial conditions for the organization of the structure of concrete determine its ability to resist the development of various types of cracks. During the introduction of finely dispersed fibers at an optimal dosage of fine sand grains (50 % in a sand mixture) and a slight replacement of cement with zeolite (from 2 to 3.4 %), it is possible to reduce the technological damage to the decorative composite, thereby improving crack resistance.

Estimation of the Probability of Cracking of Facade Coatings

“…Analysis of the literature [3][4][5] indicates that the currently existing methods for assessing the crack resistance of coatings are conditional and do not allow quantitatively assessing the parameters of their crack resistance. Lukuttsova [6] believes that the main reason for the appearance of cracks is the appearance in the material of general and local tensile deformations exceeding the ultimate tensile strength.…”

Dispersed-Reinforced Decorative Concrete: Influence of Composition Factors on Shrinkage Deformations

“…In turn, such concretes are made on high-level cement (grades 500 і 600) with the use of organic-mineral modifiers and certain granulometry of fillers [1][2][3][4], require an increase in binder content and low water-cement ratio. The increased cement content, low W/C, presence of high-level fine-dispersed additives and type of fillers contribute to the growth of deformations of the composite shrinkage, which on its part lead to the emergence and development of technological cracks, as well as the cracks appearance depends on the services, elastic modulus, material volume and geometric shape of products [1][2][5][6][7][8][9][10].…”

“…Сement system is characterized by large deformations of plastic shrinkage at micro-level, the least  at macro-level, because filler forms composite framework and perceives shrinkage. Also, the reason for the growth of shrinkage deformations, when concrete dries after 1st day of manufacture,  there are stresses in the material, caused by the action of capillary pressure in capillaries measuring  1000 Å [13], that, due to the limitation of volume compression of the solid skeleton, exceed the tensile strength of concrete, as a result, microcracks are formed [14] and, accordingly, embedded cracks develop in the cement system [9][10]. Shrinkage can also result in a peeling of the surface and deterioration of the decorative and operational characteristics of the material.…”