Microstructure of concrete subjected to elevated temperatures: physico-chemical changes and analysis techniques

Fernandes, Bruno; Gil, Augusto Masiero; Bolina, Fabrício Longhi; Tutikian, Bernardo Fonseca

doi:10.1590/s1983-41952017000400004

Cited by 54 publications

(34 citation statements)

References 36 publications

(76 reference statements)

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“…In the temperature range up to 250 °C, the cement matrix is chemically and thermally stable. The main effect of heating at this temperature is the intensive evaporation of free water [ 28 ].…”

Section: Materials and Methodologymentioning

confidence: 99%

The Influence of Metakaolinite on the Development of Thermal Cracks in a Cement Matrix

Szeląg

2018

Materials

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In the paper the cluster cracks of cement paste that has been modified with metakaolinite was analyzed. The samples were loaded with an elevated temperature based on a thermal shock. To describe the crack structure, three stereological parameters were proposed to measure: (i) the cluster average area (A¯); (ii) the cluster average perimeter (L¯); and (iii) the crack average width (I¯). The computer image analysis was implemented in the study, and 4 series of samples were subjected to the examination. In two series, metakaolinite was used as a substitute for 10% of a cement’s mass. An assessment of the basic physico-mechanical characteristics of the cement matrix was also carried out. The structure of the cement paste was considered as a highly concentrated dispersion system, in which the interactions between the cement’s grains at the initial stage of the structure self-assembly affect the crack characteristics. The study has been supplemented with microstructural investigations using a scanning electron microscope and an X-ray microanalyzer. The conducted research indicated the direction of changes in the geometrical characteristics of thermal cracks if the technological variables of the material are subjected to modification. It was also confirmed that the cluster structures have fractal character and can be analyzed and observed on many levels of a structural heterogeneity.

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Section: Materials and Methodologymentioning

confidence: 99%

The Influence of Metakaolinite on the Development of Thermal Cracks in a Cement Matrix

Szeląg

2018

Materials

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“…This is attributable to the higher thermal expansion of carbonatic aggregates, as well as to the quartz crystal transition, which takes place at around 573 °C (low to high quartz), resulting in volume expansion [ 11 ]. In the case of calcareous aggregates, a temperature range of 700 °C to 900 °C seems to be disruptive, as a result of the decomposition of calcium carbonate; CaCO 3 decomposes into CaO (lime) and CO 2 (carbon dioxide) [ 2 , 5 , 13 ].…”

Section: Introductionmentioning

confidence: 99%

“…The thermal resistance of cement paste is governed by many factors, in which the most important are the water to cement (w/c) ratio, the C/S (calcium oxide/silicon dioxide ratio), as well as the quantity of portlandite (CH). A paste containing a low C/S ratio and thus a low CH content is more desirable for obtaining heat-resistant cement paste [ 3 , 9 , 13 ].…”

Section: Introductionmentioning

confidence: 99%

“…Firstly, the capillary and free water not influenced by the Van der Walls attraction forces, evaporate; afterward, the loss of physically and chemically combined water, associated with the C–S–H phase, occurs [ 3 , 13 ]. The C–S–H decomposition process starts at the very beginning of the heating process, resulting in a reduction of its volume, which turns to an increment in total porosity as well as a coarsening of the pore structure [ 2 , 13 ]. However, up to 300 °C, no dramatic changes in porosity are observed, but when the temperature exceeds 300 °C, the porosity increases significantly [ 13 ].…”

Section: Introductionmentioning

confidence: 99%

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The Influence of Nanomaterials on the Thermal Resistance of Cement-Based Composites—A Review

2018

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Exposure to elevated temperatures has detrimental effects on the properties of cementitious composites, leading to irreversible changes, up to total failure. Various methods have been used to suppress the deterioration of concrete under elevated temperature conditions. Recently, nanomaterials have been introduced as admixtures, which decrease the thermal degradation of cement-based composites after exposure to high temperatures. This paper presents a comprehensive review of recent developments related to the effects of nanoparticles on the thermal resistance of cementitious composites. The review provides an updated report on the effects of temperature on the properties of cement-based composites, as well as a detailed analysis of the available literature regarding the inclusion of nanomaterials and their effects on the thermal degradation of cementitious composites. The data from the studies reviewed indicate that the inclusion of nanoparticles in composites protects from strength loss, as well as contributing to a decrease in disruptive cracking, after thermal exposure. From all the nanomaterials presented, nanosilica has been studied the most extensively. However, there are other nanomaterials, such as carbon nanotubes, graphene oxide, nanoclays, nanoalumina or nano-iron oxides, that can be used to produce heat-resistant cementitious composites. Based on the data available, it can be concluded that the effects of nanomaterials have not been fully explored and that further investigations are required, so as to successfully utilize them in the production of heat-resistant cementitious composites.

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“…The micro-structural properties of concrete exposed to high temperatures potentiate chemical-physical reactions in materials generating different physical-mechanical characteristics 1,2 . When heated, the water vapor pressure within the concrete element increases, which then undergoes physical changes such as cracking and spalling 1,3 .…”

Section: Introductionmentioning

confidence: 99%

Durability of Concrete After Fire Through Accelerated Carbonation Tests

et al. 2019

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Degradation of mechanical properties and durability of reinforced concrete structures occur when they are subjected to fire situations, depending on the characteristics of the material, fire duration and the ways of fire extinguishing. Mechanical properties such as compressive strength, tensile strength and elasticity modulus are some examples of typically altered characteristics in concrete during high temperature exposure. Nevertheless, little is known about the advance of the carbonation front on fire-damaged concrete, which is a characteristic directly related to the durability of the structural system. For this purpose, the carbonation front was evaluated in specimens with characteristic strengths of 20 MPa and 35 MPa, subjected to high temperatures (200 °C, 500 ºC and 700 ºC) and different types of cooling (fast and slow). It was observed that the concrete durability is harmed by exposure to high temperatures and fast cooling. However, advance of the carbonation front was not verified in slow cooling situations.

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Microstructure of concrete subjected to elevated temperatures: physico-chemical changes and analysis techniques

Cited by 54 publications

References 36 publications

The Influence of Metakaolinite on the Development of Thermal Cracks in a Cement Matrix

The Influence of Metakaolinite on the Development of Thermal Cracks in a Cement Matrix

The Influence of Nanomaterials on the Thermal Resistance of Cement-Based Composites—A Review

Durability of Concrete After Fire Through Accelerated Carbonation Tests

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