Change in microstructure of hardened cement paste subjected to elevated temperatures

Peng, Gai Fei; Huang, Zhanwen

doi:10.1016/j.conbuildmat.2006.11.002

Cited by 290 publications

(134 citation statements)

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“…Although concrete is not flammable, when exposed to elevated temperatures it partially decomposes and loses its mechanical properties. [1][2][3] The second mostly discussed problem about Portland-cement concrete is spalling. This effect is mainly related to the build-up of the pore pressure in consequence of the vaporization of the physically/chemically bound water which results in tensile loading of the microstructure of heated concrete.…”

Section: Introductionmentioning

confidence: 99%

Effect of the aggregate type on the properties of alkali-activated slag subjected to high temperatures

Rovnanı́k¹

2015

Mater. Tehnol.

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High temperatures present a risk of destruction for most silicate-based construction materials. Although these materials are not flammable, they lose their properties due to a thermal decomposition. In contrast to ordinary Portland-cement-based materials, alkali-activated slag exhibits a better thermal stability when exposed to temperatures up to 1200°C. Due to its different porosity it is less susceptible to spalling. However, the properties of the composites after a high-temperature treatment depend also on the stability of the aggregates. The effects of two different types of the aggregate (quartz and chamotte) on the residual mechanical properties and microstructure of the alkali-activated slag mortars exposed to 200-1200°C is presented in this study. The results showed an improved mechanical performance of the thermally stable chamotte aggregate at temperatures above 600°C. a-quartz is transformed to b-quartz at 573°C, causing a volume instability and, consequently, a strength deterioration. Although chamotte also contains some quartz phase, the reaction of mullite with the alkalis from the matrix leads to the formation of albite and anorthite, making the material tougher and, thus, compensating the negative effect of quartz. Keywords: alkali-activated slag, high temperatures, chamotte, quartz, strength, microstructure Visoke temperature so tveganje za razpad ve~ine gradbenih materialov, ki temeljijo na silikatih.^eprav ti materiali niso vnetljivi, izgubijo svoje lastnosti zaradi termi~ne razgradnje. Nasprotno od materialov, ki temeljijo na portland cementu, z alkalijo aktivirane`lindre izkazujejo bolj{o temperaturno obstojnost,~e so izpostavljene temperaturam do 1200°C. Zaradi razli~ne poroznosti so manj ob~utljive za pojav lu{~enja. Vendar pa so lastnosti kompozita po visokotemperaturni obdelavi odvisne tudi od stabilnosti agregatov. V {tudiji so predstavljeni vplivi dveh razli~nih vrst agregatov (kremen in {amota) na preostale mehanske lastnosti in mikrostrukturo malte iz z alkalijo aktivirane`lindre, izpostavljene temperaturam 200-1200°C. Rezultati so pokazali izbolj{ane mehanske lastnosti toplotno stabilnega {amotnega agregata pri temperaturah nad 600°C. a-kremen se transformira pri 573°C v b-kremen, kar povzro~i volumensko nestabilnost in posledi~no poslab{anje trdnosti.^eprav {amot vsebuje nekaj kremenove faze, reagiranje mulita z alkalijami iz osnove povzro~i nastanek albita in anortita, ki povzro~ita, da material postane bolj`ilav in s tem kompenzira negativni vpliv kremena.

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Section: Introductionmentioning

confidence: 99%

Effect of the aggregate type on the properties of alkali-activated slag subjected to high temperatures

Rovnanı́k¹

2015

Mater. Tehnol.

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“…With rising temperature, a negligible and limited strength loss was observed at 300˚C and 450˚C then the strength loss markedly increases at the higher temperatures. This indicates that beyond the critical temperature of 450˚C the decomposition of C-S-H markedly progresses [13]. Figure 6 illustrates the FTIR spectra of cement paste fired at 300˚C -750˚C.…”

Section: Resultsmentioning

confidence: 99%

“…According to Peng et al, it is difficult to differentiate between the peaks of C 2 S and C 3 S in XRD diagrams of cement pastes exposed to high temperatures. Hence, peaks of C 2 S and C 3 S can be used to [13]. Figure 9 illustrates the SEM micrographs of cement paste fired at 300˚C -750˚C.…”

Section: Resultsmentioning

confidence: 99%

“…According to Heikal, C-S-H gel dehydrates in the temperature range of 100˚C -400˚C and transforms to C 2 S and C 3 S at 800˚C [24]. According to Peng, C-S-H gel started to decompose at 560˚C and transforms to C 2 S and C 3 S at 800˚C [13].…”

Section: ) Estimation Of the Dehydration Mechanisms And Kinetics Formentioning

confidence: 99%

“…The first category investigates the degree of deterioration on the mechanical properties of concrete exposed to high temperatures and evaluates the fire damaged concrete by using nondestructive tools such as ultrasonic and resonance vibration techniques [3] [4]. The influence of high temperatures on the mechan- 3) The coarsening of pore structure due to void formation as a result of loss of bound water [13], 4) The pore pressure effects due to buildup of vapor pressure inside closed pores [14] and, 5) Cracking that develops as a result of the rehydration of lime [15].…”

Section: Introductionmentioning

confidence: 99%

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Effect of High Temperatures on the Microstructure of Cement Paste

Tantawy¹

2017

MSCE

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The microstructural and compositional changes within the cement paste exposed to high temperatures were monitored by XRD, FTIR, TGA/DTA and SEM techniques to understand the nature of decomposition of C-S-H gel and the associated physicomechanical properties of thermally damaged cement paste. OPC paste (w/c ratio 0.27) was hydrated for 28 days then fired up to 750˚C for 2 hours (heating rate 10˚C/min). The relative mass percent of calcium hydrates and portlandite was estimated by calculations derived from TGA results. Beyond 450˚C, the percentage of portlandite sharply diminishes and C-S-H progressively decomposes into C 2 S and C 3 S until complete loss of calcium hydrates content occurs at 750˚C. An increase of the total porosity, severe loss in mechanical strength and propagation of harmful cracks occurs. The thermal shock as a result of cooling of the heated cement paste and the rehydration of lime enhance the propagation of harmful cracks.

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Study on the high‐temperature behavior and rehydration characteristics of hardened cement paste

Wang

Zhang

et al. 2014

Fire and Materials

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Summary The high‐temperature behavior and rehydration characteristics of the hardened cement paste and their mechanisms have been studied in this paper. X‐ray diffraction and thermogravimetry are used to establish the effect of elevated temperatures on the mineralogical changes that occurred in the hardened cement paste. The change of microstructure was characterized by scanning electron microscopy. The results showed that with the temperature increased, the compressive strength of hardened cement paste first increased and then decreased. According to micromeasurements, at 400°C, the porosity and average pore diameter of hardened cement paste increased slightly, while at 800°C, the porosity and average pore diameter of hardened cement paste increased sharply. When hardened cement paste was cured after exposing to 400°C, its pore structure and phase composition had no change, while when hardened cement paste was cured after exposing to 800°C, there are new hydration products, and its pore structure may be finer, but it cannot fully recover to the original state. Copyright © 2014 John Wiley & Sons, Ltd.

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Change in microstructure of hardened cement paste subjected to elevated temperatures

Cited by 290 publications

References 3 publications

Effect of the aggregate type on the properties of alkali-activated slag subjected to high temperatures

Effect of the aggregate type on the properties of alkali-activated slag subjected to high temperatures

Effect of High Temperatures on the Microstructure of Cement Paste

Study on the high‐temperature behavior and rehydration characteristics of hardened cement paste

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