scholarly journals Increasing the crack resistance of high-strength self-compacting concrete

2021 ◽  
Vol 1 (1(57)) ◽  
pp. 17-24
Author(s):  
Vyacheslav Troуan ◽  
Bogdan Kindras
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Silica Fume ◽  
Critical Stress ◽  
High Strength ◽  
Critical Stress Intensity Factor ◽  
Self Compacting Concrete ◽  
Mineral Additive ◽  
Mineral Additives ◽  
Positive Effect

The object of research is high-strength self-compacting concrete, which does not require additional vibration during laying. One of the most problematic issues of high-strength self-compacting concretes is increased cracking, associated with large shrinkage deformations of such concretes and their fragile destruction. A decrease in shrinkage deformations of concrete was established when part of the cement was replaced to mineral additives. This effect is explained by a decrease of the cement content and, accordingly, a decrease of the chemical component of the autogenous shrinkage of concrete, and an increase of the adsorptive binding of capillary moisture by mineral additives, with reduces the physical drying shrinkage of concrete. In this case, the type and dispersion of the used mineral additive can affect to the shrinkage deformations of concrete. A significant decrease in shrinkage deformations when using metakaolin is explained by an increase the amount of ettringite as a result of the reaction of active metakaolin Al2O3 with two-water gypsum of cement. It was found that the replacement of cement to 10 % of mineral additives leads to a decrease in the value of the critical stress intensity factor (SIF), which is compensated by a decrease of the fragility of concrete fracture (an increase of the area of microplastic deformations). At the same time, the type of mineral additive used does not affect to the value of the critical stress intensity factor, but significantly affects to the fragility of fracture of concrete samples. The introduction of 10 % mineral additives (to replace cement) had a positive effect on the retention of flow of self-compacting concrete mixes; the best results according to this criterion were observed when using silica fume, fly ash and limestone. All mineral modifiers, except for silica fume, led to a decrease of the compressive strength of high-strength concretes on all terms of hardening. In the case of the tensile strength of concrete at bending and splitting, with the introduction of silica fume, metakaolin and fly ash, a positive effect was observed compared to the base composition without additives. Comprehensive accounting of the results obtained will allow a reasonable approach to the design of high-strength self-compacting concretes with increased crack resistance.

scholarly journals Studies of Fracture Toughness in Concretes Containing Fly Ash and Silica Fume in the First 28 Days of Curing

Materials ◽  
2021 ◽  
Vol 14 (2) ◽  
pp. 319
Author(s):  
Grzegorz Ludwik Golewski ◽  
Damian Marek Gil
Keyword(s):  
Fracture Toughness ◽  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Fly Ash ◽  
Critical Stress ◽  
Critical Stress Intensity Factor ◽  
Early Age ◽  
Strength Parameters ◽  
Cement Binder ◽  
Mineral Additives

This paper presents the results of the fracture toughness of concretes containing two mineral additives. During the tests, the method of loading the specimens according to Mode I fracture was used. The research included an evaluation of mechanical parameters of concrete containing noncondensed silica fume (SF) in an amount of 10% and siliceous fly ash (FA) in the following amounts: 0%, 10% and 20%. The experiments were carried out on mature specimens, i.e., after 28 days of curing and specimens at an early age, i.e., after 3 and 7 days of curing. In the course of experiments, the effect of adding SF to the value of the critical stress intensity factor—KIcS in FA concretes in different periods of curing were evaluated. In addition, the basic strength parameters of concrete composites, i.e., compressive strength—fcm and splitting tensile strength—fctm, were measured. A novelty in the presented research is the evaluation of the fracture toughness of concretes with two mineral additives, assessed at an early age. During the tests, the structures of all composites and the nature of macroscopic crack propagation were also assessed. A modern and useful digital image correlation (DIC) technique was used to assess macroscopic cracks. Based on the conducted research, it was found the application of SF to FA concretes contributes to a significant increase in the fracture toughness of these materials at an early age. Moreover, on the basis of the obtained test results, it was found that the values of the critical stress intensity factor of analyzed concretes were convergent qualitatively with their strength parameters. It also has been demonstrated that in the first 28 days of concrete curing, the preferred solution is to replace cement with SF in the amount of 10% or to use a cement binder substitution with a combination of additives in proportions 10% SF + 10% FA. On the other hand, the composition of mineral additives in proportions 10% SF + 20% FA has a negative effect on the fracture mechanics parameters of concretes at an early age. Based on the analysis of the results of microstructural tests and the evaluation of the propagation of macroscopic cracks, it was established that along with the substitution of the cement binder with the combination of mineral additives, the composition of the cement matrix in these composites changes, which implies a different, i.e., quasi-plastic, behavior in the process of damage and destruction of the material.

Fracture of monolayer germanene: A molecular dynamics study

2018 ◽  
Vol 32 (22) ◽  
pp. 1850241 ◽  
Author(s):  
Minh-Quy Le
Keyword(s):  
Molecular Dynamics ◽  
Stress Intensity Factor ◽  
Tensile Strength ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Critical Stress ◽  
Axial Strain ◽  
Critical Stress Intensity Factor ◽  
Monolayer Graphene ◽  
Fracture Properties

Molecular dynamics simulations with Tersoff potential were performed to study the fracture properties of monolayer germanene at 300 K. The two-dimensional (2D) Young’s modulus, 2D tensile strength and axial strain at the tensile strength of pristine monolayer germanene are about 36.0 and 37.5 N/m; 5.1 and 4.6 N/m; 21.4 and 15.9%, in the zigzag and armchair directions, respectively. Griffith theory was applied to compute the critical stress intensity factor. Compared to monolayer graphene, the critical stress intensity factor of monolayer germanene is much smaller. Fracture pattern and effects of the initial crack length on the fracture properties are also studied. Results are useful for future design and applications of this 2D material.

Probing the Critical Stress Intensity Factor for Slip Transfer across Grain Boundaries by Subgranular Indentation Alfonso

2000 ◽  
Vol 649 ◽  
Author(s):  
H.W. Ngan ◽  
Y.L. Chiu
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Critical Stress ◽  
Critical Stress Intensity Factor ◽  
Square Root ◽  
Slip Transfer ◽  
Macroscopic Deformation

ABSTRACTBy analysing the relevant results in the literature, we have found that, when indentation is made on a subgranular level, the hardness varies roughly inversely with the square root of the distance between the indent and the grain boundary. This effect is analogous to the Hall-Petch effect for macroscopic deformation.

Stress Intensity at the Initiation of Instability by R Curve

2014 ◽  
Vol 592-594 ◽  
pp. 1160-1164 ◽  
Author(s):  
S. Sundaresan ◽  
B. Nageswara Rao
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Critical Stress ◽  
Mouth Opening ◽  
Compact Tension ◽  
Critical Stress Intensity Factor ◽  
Pressure Vessels ◽  
Crack Mouth Opening Displacement ◽  
Opening Displacement

The life expectancy or failure of aerospace pressure vessels is evaluated by the critical stress intensity determined by the crack growth resistance curve of a material. Load versus crack mouth opening displacement data is generated from the Compact Tension specimens made from the weld joints of maraging steel rocket motor segments. The steps involved to generate critical stress intensity factor is explained. A power law is adopted to model the crack extension in terms of stress intensity factor and determine the maximum failure load of weld specimens. Maximum failure loads of CT specimens obtained by test and analysis are presented.

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