Crack Initiation of Alkali-Activated Slag Based Composites with Graphite Filler

2018 ◽  
Vol 761 ◽  
pp. 57-60
Author(s):  
Hana Šimonová ◽  
Libor Topolář ◽  
Pavel Rovnaník ◽  
Pavel Schmid ◽  
Zbyněk Keršner
Keyword(s):  
Crack Initiation ◽  
Crack Propagation ◽  
Building Materials ◽  
Crack Opening ◽  
Graphite Powder ◽  
Unstable Crack ◽  
Alkali Activated Slag ◽  
Fracture Tests ◽  
Activated Slag ◽  
Alkali Activated

The alkali-activated slag is an alternative building material to ordinary Portland cement based materials. This type of material is effective in reducing CO2 emissions and energy consumption. Addition of graphite powder increases its electric conductivity, hence, introducing new functionality to building materials such as self-sensing and self-heating properties. In this study, the effect of graphite filler on the crack initiation of alkali-activated slag composite is investigated. The graphite powder was added in the amount of 5, 10 and 15% with respect to the slag mass. Beam specimens with an initial stress concentrator were tested in three-point bending at the age of 28 days. The load versus crack mouth crack opening displacement (F–CMOD) diagrams were recorded during the fracture tests and subsequently evaluated using the Double-K fracture model. This model allows the quantification of two different levels of crack propagation: initiation, which corresponds to the beginning of stable crack growth, and the level of unstable crack propagation. The course of fracture tests was also monitored by acoustic emission (AE) method.

Differences in Electrical Properties of Portland Cement and Alkali-Activated Slag Mortars

2018 ◽  
Vol 276 ◽  
pp. 15-20 ◽  
Author(s):  
Pavel Rovnaník ◽  
Maria Míková ◽  
Ivo Kusák ◽  
Patrik Bayer
Keyword(s):  
Electrical Properties ◽  
Portland Cement ◽  
Building Materials ◽  
Elevated Temperatures ◽  
Sodium Ions ◽  
Alkali Activated Slag ◽  
Self Heating ◽  
Chemical Attack ◽  
Activated Slag ◽  
Alkali Activated

Alkali-activated slag is known as a building material for more than sixty years and is considered an alternative to Portland cement based binders. Compared to Portland cement it exhibits some superior properties such as higher resistance against chemical attack and exposure to elevated temperatures. Aluminosilicate binders are generally electrical insulators; however, electrical properties of building materials gain the importance in the new field of applications such as self-sensing or self-heating materials. This paper brings a comparison of the electrical properties, especially resistance and capacitance, between Portland cement and alkali-activated slag mortars. The measurements revealed that alkali-activated slag shows enhanced conducting properties due to the presence of mobile hydrated sodium ions and metallic iron microparticles.

scholarly journals Components of the Fracture Response of Alkali-Activated Slag Composites with Steel Microfibers

2019 ◽  
Vol 9 (9) ◽  
pp. 1754 ◽  
Author(s):  
Hana Šimonová ◽  
Petr Frantík ◽  
Zbyněk Keršner ◽  
Pavel Schmid ◽  
Pavel Rovnaník
Keyword(s):  
Mouth Opening ◽  
Crack Mouth Opening Displacement ◽  
Model Parameters ◽  
Crack Model ◽  
Mechanical Fracture ◽  
Alkali Activated Slag ◽  
Fracture Parameters ◽  
Fracture Tests ◽  
Activated Slag ◽  
Alkali Activated

Knowledge of the mechanical and primarily fracture parameters of composites with a brittle matrix is essential for the quantification of their resistance to crack initiation and growth, and also for the specification of material model parameters employed for the simulation of the quasi-brittle behavior of structures made from this type of composite. Therefore, the main target of this paper is to quantify the mechanical fracture parameters of alkali-activated slag composites with steel microfibers and the contribution of the matrix to their fracture response. The first alkali-activated slag composite was a reference version without fibers; the others incorporated steel microfibers amounting to 5, 10, 15 and 20% by weight of the slag. Prism specimens with an initial central edge notch were used to perform the three-point bending fracture tests. Load vs. displacement (deflection at midspan) and load vs. crack mouth opening displacement diagrams were recorded during the fracture tests. The obtained diagrams were employed as inputs for parameter identification, the aim of which was to transfer the fracture test response data to the desired material parameters. Values were also determined for fracture parameters using the effective crack model, work-of-fracture method and double-K fracture model. All investigated mechanical fracture parameters were improved by the addition of steel microfibers to the alkali-activated matrix. Based on the obtained results, the addition of 10 to 15% of microfibers by weight is optimal from the point of view of the enhancement of the fracture parameters of alkali-activated slag composite.

Influence of Superplasticizer Quantity on Formation of Micro-Cracks during Setting and Hardening of Concretes by Acoustic Emission Method

2015 ◽  
Vol 1124 ◽  
pp. 219-224 ◽  
Author(s):  
Libor Topolář ◽  
Kristýna Timcakova ◽  
Petr Misák
Keyword(s):  
Acoustic Emission ◽  
Building Materials ◽  
Material Behaviour ◽  
Emission Method ◽  
Alkali Activated Slag ◽  
Volumetric Expansion ◽  
Hardening Process ◽  
Micro Cracks ◽  
Activated Slag ◽  
Alkali Activated

The acoustic emission phenomenon is directly associated with nucleation of cracks in building materials, therefore the changes result from the volumetric expansion causing formation micro and macro cracking in structure, which we can recognize. The main aim of the article is to compare four ways of curing alkali activated slag mortars by method of acoustic emission. A comprehension of microstructure−performance relationships is the key to true understanding of material behaviour. The results obtained in the laboratory are useful to understand the various stages of micro-cracking activity during the hardening process in quasi-brittle materials such as alkali activated slag mortars and extend them for general practice

Electrical Properties of Alkali-Activated Slag Mortar with Carbon Fibres

2017 ◽  
Vol 908 ◽  
pp. 100-105 ◽  
Author(s):  
Pavel Rovnaník ◽  
Maria Míková ◽  
Ivo Kusák
Keyword(s):  
Mechanical Properties ◽  
Electrical Properties ◽  
Building Materials ◽  
Specific Conductivity ◽  
Carbon Fibres ◽  
Alkali Activated Slag ◽  
Order Of Magnitude ◽  
Activated Slag ◽  
Mixing Water ◽  
Alkali Activated

Building materials with enhanced electrical properties gain the importance in the new field of applications such as self-sensing or self-heating materials. In this paper, 3 mm long carbon fibres were used as a conductive admixture to alkali-activated slag mortar in order to reduce its resistivity. The amount of carbon fibres was ranging from 0.5 to 4.0% of the slag mass and the effect of the conductive admixture on the mechanical properties, electrical impedance, specific conductivity, and microstructure of alkali-activated slag composite was investigated. Only 0.5% of carbon fibres caused a significant decrease in impedance of alkali-activated slag composite and the addition of 4% reduced the impedance by one order of magnitude for low AC frequencies. However, due to problematic dispersion and higher demand of mixing water, the mechanical properties were deteriorated, especially at higher content of carbon fibres.

scholarly journals Flexural Fatigue Life Reliability of Alkali-Activated Slag Concrete Freeze-Thaw Damage in Cold Areas

2021 ◽  
Vol 2021 ◽  
pp. 1-20
Author(s):  
Bin Chen ◽  
Jun Wang
Keyword(s):  
Fatigue Life ◽  
Building Materials ◽  
Fatigue Properties ◽  
Test Results ◽  
Distribution Fitting ◽  
Flexural Fatigue ◽  
Alkali Activated Slag ◽  
Freeze Thaw ◽  
Activated Slag ◽  
Alkali Activated

Studying the application of alkali-activated slag concrete for roads in cold areas is of great significance for promoting and developing green building materials. In this study, the effect of freeze-thaw damage on the flexural fatigue properties of alkali-activated slag concrete was studied and the fatigue life of alkali-activated slag concrete with various degrees of damage after freeze-thaw cycles was studied through a three-point flexural test. The results show that the flexural fatigue life decreases with freeze-thaw cycles from 0 to 150 times. Through a distribution fitting test and K-S test results, the flexural fatigue life followed both the two-parameter and three-parameter Weibull distributions. Between them, the three-parameter Weibull distribution fitting had a higher accuracy and better test results. The results of the reliability analysis show that the curves of alkali-activated slag concrete samples with various degrees of freeze-thaw damage for various failure probabilities have good correlation under different stresses, and the correlation correlations were greater than 0.81. The flexural fatigue life of alkali-activated slag concrete samples with various degrees of freeze-thaw damage was more sensitive to freeze-thaw damage under high stresses. It is suggested that the fatigue design of alkali-activated slag concrete should consider the adverse effects of cold areas, and the reliability should be improved accordingly.

scholarly journals Electrical and Self-Sensing Properties of Alkali-Activated Slag Composite with Graphite Filler

Materials ◽  
2019 ◽  
Vol 12 (10) ◽  
pp. 1616 ◽  
Author(s):  
Pavel Rovnaník ◽  
Ivo Kusák ◽  
Patrik Bayer ◽  
Pavel Schmid ◽  
Lukáš Fiala
Keyword(s):  
Mechanical Properties ◽  
Electrical Properties ◽  
Compressive Loading ◽  
Conductive Filler ◽  
Graphite Powder ◽  
Alkali Activated Slag ◽  
Sensing Properties ◽  
Activated Slag ◽  
Conductive Properties ◽  
Alkali Activated

The electrical properties of concrete are gaining their importance for the application in building construction. In this study, graphite powder was added to alkali-activated slag mortar as an electrically conductive filler in order to enhance the mortar’s conductive properties. The amount of graphite ranged from 1% to 30% of the slag mass. The effect of the graphite powder on the resistivity, capacitance, mechanical properties, and microstructure of the composite was investigated. Selected mixtures were then used for the testing of self-sensing properties under compressive loading. The results show that the addition of an amount of graphite equal to up to 10% of the slag mass improved the electrical properties of the alkali-activated slag. Higher amounts of filler did not provide any further improvement in electrical properties at lower AC frequencies but caused a strong deterioration in mechanical properties. The best self-sensing properties were achieved for the mixture with 10 wt% of graphite, but only at low compressive stresses of up to 6 MPa.

Crack Initiation and Length Change in Modified Alkali Activated Slag Mortars

CONCREEP 10 ◽  
2015 ◽  
Author(s):  
V. Bílek ◽  
I. Havlíková ◽  
L. Topolář ◽  
P. Schmid ◽  
H. Šimonová ◽  
...  
Keyword(s):  
Crack Initiation ◽  
Length Change ◽  
Alkali Activated Slag ◽  
Activated Slag ◽  
Alkali Activated

scholarly journals Experimental and numerical analysis of the fracture response of alkali-activated slag-based materials

2020 ◽  
Vol 323 ◽  
pp. 01006
Author(s):  
Martin Lipowczan ◽  
David Lehký ◽  
Hana Šimonová ◽  
Barbara Kucharczyková
Keyword(s):  
Crack Model ◽  
Fracture Test ◽  
Mechanical Fracture ◽  
Alkali Activated Slag ◽  
Fine Grained ◽  
Shrinkage Reducing Admixture ◽  
Edge Notch ◽  
Fracture Tests ◽  
Activated Slag ◽  
Alkali Activated

The paper deals with the experimental and numerical determination of mechanical fracture parameters of fine-grained composites based on the alkali-activated slag (AAS) at different ages of hardening. Two AAS composites, which differed only in the presence of shrinkage reducing admixture, were studied. The prismatic specimens with the nominal dimensions of 40 × 40 × 160 mm and initial central edge notch were subjected to fracture tests in a three-point bending configuration. The results of the fracture tests in the form load F versus deflection d diagrams were used as input data for the identification of parameters via the inverse analysis based on the artificial neural network whose aim is to transfer the fracture test response data to the desired material parameters. The modulus of elasticity, tensile strength, and fracture energy values were identified and subsequently compared with values obtained based on the direct fracture test evaluation using the effective crack model and work-of-fracture method.

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