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

The exposure of concrete to high temperatures, such as in a fire, leads to physical and chemical changes, which may cause deterioration of mechanical properties, cracking and spalling. This paper presents a critical review of microstructural changes in concrete exposed to high temperature. The transformations developed in the cement paste, aggregates and interfacial transition zone were studied, as well as the experimental techniques of microanalysis presented in recent related researches. Lastly, a critical analysis of experimental results from literature was performed. It was verified that microstructural changes are related to concrete properties and the heating process. The experimental techniques has a potential use for assessment of thermally damaged concrete, however, these techniques must be applied simultaneously and specific methods must be established.

Keywords:
microstructure; concrete; concrete structures; high temperatures

Authorship

B. Fernandes

Departamento de Estruturas, Unicamp, Campinas, SP, Brasil. fernandes.brn@gmail.comUnicampBrazilCampinas, SP, BrazilDepartamento de Estruturas, Unicamp, Campinas, SP, Brasil. fernandes.brn@gmail.com

A. M. Gil

itt Performance, UNISINOS, São Leopoldo, RS, Brasil. augustomg@unisinos.br, fabriciolb@unisinos.br, bftutikian@unisinos.brUNISINOSBrazilSão Leopoldo, RS, Brazilitt Performance, UNISINOS, São Leopoldo, RS, Brasil. augustomg@unisinos.br, fabriciolb@unisinos.br, bftutikian@unisinos.br

F. L. Bolina

B. F. Tutikian

SCIMAGO INSTITUTIONS RANKINGS

Departamento de Estruturas, Unicamp, Campinas, SP, Brasil. fernandes.brn@gmail.comUnicampBrazilCampinas, SP, BrazilDepartamento de Estruturas, Unicamp, Campinas, SP, Brasil. fernandes.brn@gmail.com

Figures | Tables

Figures (11)
Tables (2)

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Figure 1
Thermal incompatibility between aggregate and hydrated cement paste (adapted [⁶[6] Fédération internationale du béton - FIB. fib Bulletin 38: Fire design of concrete structures - materials, structures and modelling, 2007, 106 p.])

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Figure 2
Micrograph of transition zone of ordinary concrete subjected to 550 ºC (adapted [⁹[9] ANNEREL, E.; TAERWE, L. Revealing the temperature history in concrete after fire exposure by microscopic analysis. Cement and Concrete Research, v. 39, n. 12, 2009, p. 1239-1249.])

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Figure 3
Changes in concrete subjected to 1200 ºC (adaptaed [³⁶[36] ARIOZ, O. Retained properties of concrete exposed to high temperatures: Size effect. Fire and Materials, v. 33, n. 5, 2009, p. 211-222.])

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Figure 4
Micrographs of cement paste at ambiente temperature (a), 300 ºC (b), 500 ºC (c) e 900 ºC (d) (adapted [¹⁹[19] LIM, S.; MONDAL, P. Micro- and nano-scale characterization to study the thermal degradation of cement-based materials. Materials Characterization , v. 92, 2014, p. 15-25.])

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Figure 5
Diffractograms identifying portlandite behaviour (adapted [¹⁸[18] HANDOO, S.K.; AGARWAL, S.; AGARWAL, S.K. Physicochemical, mineralogical, and morphological characteristics of concrete exposed to elevated temperatures. Cement and Concrete Research , v. 32, n. 7, 2002, p. 1009-1018.])

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Figure 6
Diffractograms of cement paste heated up to 800 ºC (adapted [¹⁷[17] PENG, G.F.; HUANG, Z.S. Change in microstructure of hardened cement paste subjected to elevated temperatures. Construction and Building Materials , v. 22, n. 4, 2008, p. 593-599.])

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Figure 7
Diffractograms of cement paste heated at different temperatures (adapted [³⁷[37] KIM, K.Y.; YUN, T.S.; PARK, K.P. Evaluation of pore structures and cracking in cement paste exposed to elevated temperatures by X-ray computed tomography. Cement and Concrete Research , v. 50, 2013, p. 34-40.])

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Figure 8
Diffractograms of cement paste heated up to 800 ºC (adapted [³⁸[38] WANG, G.; ZHANG, C.; ZHANG, B.; LI, Q.; SHUI, Z. Study on the high-temperature behavior and rehydration characteristics of hardened cement paste. Fire and Materials , v. 39, n. 5, 2015, p. 741-750.])

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Figura 9
Diffractograms of cement paste after heating (adapted [¹⁹[19] LIM, S.; MONDAL, P. Micro- and nano-scale characterization to study the thermal degradation of cement-based materials. Materials Characterization , v. 92, 2014, p. 15-25.])

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Figure 10
Total porosity of cement paste (adapted [¹⁵[15] ZHANG, Q.; YE, G.; KOENDERS, E. Investigation of the structure of heated Portland cement paste by using various techniques. Construction and Building Materials, v. 38, 2013, p. 1040-1050.])

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Figura 11
Color change as a function of temperature (adapted [⁸[8] HAGER, I. Colour Change in Heated Concrete, Fire Technology, v. 50, n. 4, 2013, p. 945-958.])

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Table 1
Non-destructive testing applied to fire damaged concrete (adapted [¹⁰[10] COLOMBO, M.; FELICETTI, R. New NDT techniques for the assessment of fire-damaged concrete structures, Fire Safety Journal, v. 42, n. 6-7, 2007, p. 461-472.])

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Tabela 2
Summary of research that used microanalysis techniques

Figure 1 Thermal incompatibility between aggregate and hydrated cement paste (adapted [⁶[6] Fédération internationale du béton - FIB. fib Bulletin 38: Fire design of concrete structures - materials, structures and modelling, 2007, 106 p.])

Figure 2 Micrograph of transition zone of ordinary concrete subjected to 550 ºC (adapted [⁹[9] ANNEREL, E.; TAERWE, L. Revealing the temperature history in concrete after fire exposure by microscopic analysis. Cement and Concrete Research, v. 39, n. 12, 2009, p. 1239-1249.])

Figure 3 Changes in concrete subjected to 1200 ºC (adaptaed [³⁶[36] ARIOZ, O. Retained properties of concrete exposed to high temperatures: Size effect. Fire and Materials, v. 33, n. 5, 2009, p. 211-222.])

Figure 4 Micrographs of cement paste at ambiente temperature (a), 300 ºC (b), 500 ºC (c) e 900 ºC (d) (adapted [¹⁹[19] LIM, S.; MONDAL, P. Micro- and nano-scale characterization to study the thermal degradation of cement-based materials. Materials Characterization , v. 92, 2014, p. 15-25.])

Figure 5 Diffractograms identifying portlandite behaviour (adapted [¹⁸[18] HANDOO, S.K.; AGARWAL, S.; AGARWAL, S.K. Physicochemical, mineralogical, and morphological characteristics of concrete exposed to elevated temperatures. Cement and Concrete Research , v. 32, n. 7, 2002, p. 1009-1018.])

Figure 6 Diffractograms of cement paste heated up to 800 ºC (adapted [¹⁷[17] PENG, G.F.; HUANG, Z.S. Change in microstructure of hardened cement paste subjected to elevated temperatures. Construction and Building Materials , v. 22, n. 4, 2008, p. 593-599.])

Figure 7 Diffractograms of cement paste heated at different temperatures (adapted [³⁷[37] KIM, K.Y.; YUN, T.S.; PARK, K.P. Evaluation of pore structures and cracking in cement paste exposed to elevated temperatures by X-ray computed tomography. Cement and Concrete Research , v. 50, 2013, p. 34-40.])

Figure 8 Diffractograms of cement paste heated up to 800 ºC (adapted [³⁸[38] WANG, G.; ZHANG, C.; ZHANG, B.; LI, Q.; SHUI, Z. Study on the high-temperature behavior and rehydration characteristics of hardened cement paste. Fire and Materials , v. 39, n. 5, 2015, p. 741-750.])

Figura 9 Diffractograms of cement paste after heating (adapted [¹⁹[19] LIM, S.; MONDAL, P. Micro- and nano-scale characterization to study the thermal degradation of cement-based materials. Materials Characterization , v. 92, 2014, p. 15-25.])

Figure 10 Total porosity of cement paste (adapted [¹⁵[15] ZHANG, Q.; YE, G.; KOENDERS, E. Investigation of the structure of heated Portland cement paste by using various techniques. Construction and Building Materials, v. 38, 2013, p. 1040-1050.])

Figura 11 Color change as a function of temperature (adapted [⁸[8] HAGER, I. Colour Change in Heated Concrete, Fire Technology, v. 50, n. 4, 2013, p. 945-958.])

Table 1 Non-destructive testing applied to fire damaged concrete (adapted [¹⁰[10] COLOMBO, M.; FELICETTI, R. New NDT techniques for the assessment of fire-damaged concrete structures, Fire Safety Journal, v. 42, n. 6-7, 2007, p. 461-472.])

Concrete cover analysis	Point-by-point analysis of small samples	Special techniques
Hammer tapping	Small-scale mechanical testing	Ultrasonic Pulse Velocity (UPV)
Schmidt rebound hammer	Differential thermal analysis (DTA)	Impact echo
Windsor probe	Thermogravimetric analysis (TGA)	Sonic tomography
CAPO test	Dilatometry (TMA)	Modal analysis of surface waves (MASW)
BRE internal fracture	Thermoluminescence	Electric resistivity
	Porosimetry
	Colorimetry
	Petrographic analysis
	Chemical analysis

Tabela 2 Summary of research that used microanalysis techniques

Author [Reference]	Year	Sample type*	T. max (ºC)	SEM**	XRD**	MIP**	DTA/ TGA**	COL**	PET**	Others
Rostásy, Weiβ e Wiedemann [41]	1980	Lab.	900			X
Piasta, Sawicz e Rudzinski [42]	1984	Lab.	800		X	X	X			Infrared spectroscopy
Chan, Peng e Chan [43]	1996	Lab.	1200			X
Saad et al. [44]	1996	Lab.	600		X
Lin, Lin e Powers-Couche [45]	1996	Lab.	900	X
Luo, Sun e Chan [46]	2000	Lab.	800			X
Short, Purkiss e Guise [47]	2001	Lab.	700					X
Poon et al. [48]	2001	Lab.	800			X
Handoo, Agarwal e Agarwal [18]	2002	Lab.	1000	X	X		X
Castellote et al. [30]	2004	Lab.	620			X	X			Neutron diffraction
Alarcon-Ruiz et al.[49]	2005	Lab.	800				X
Georgali e Tsakiridis [2]	2005	Est.	-						X
Lima [20]	2005	Lab.	900	X	X		X			Dilatometry
Wang, Wu e Wang [50]	2005	Lab.	500	X
Wendt [51]	2006	Lab.	900					X
Peng e Huang [17]	2008	Lab.	800	X	X	X
Biolzi, Cattaneo e Rosati [52]	2008	Lab.	750	X		X
Annerel e Taerwe [9]	2009	Lab.	550	X				X		Fluorescent Microscope
Arioz [36]	2009	Lab.	1200	X
Fall e Samb [53]	2009	Lab.	600	X		X	X			Capillary Absorption
Sousa [23]	2009	Lab.	600	X
Menéndez e Vega [54]	2009	Est.	-	X	X		X
Annerel e Taerwe [14]	2011	Lab.	100					X
Britez [25]	2011	Est.	-		X		X
Ruschel [39]	2011	Est.	-		X
Ibrahim, Hamid e Taha [55]	2012	Lab.	700	X	X		X			BET
Hager [8]	2013	Lab.	800				X	X
Akca e Zihnioğlu [56]	2013	Lab.	900	X		X	X
Heap et al. [57]	2013	Lab.	1000	X	X		X
Heikal et al. [58]	2013	Lab.	800	X	X
Zhang, Ye e Koenders [15]	2013	Lab.	1000	X	X					Nitrogen Adsorption
Kim, Yun e Park [37]	2013	Lab.	1000	X	X					X-ray Computed Tomography
Carré, Hager e Perlot [16]	2014	Lab.	1000					X
Lim e Mondal [19]	2014	Lab.	1000	X	X		X			Atomic Force Microscopy
Wang et al. [38]	2014	Lab.	800	X	X	X	X

*Lab. = Amostra confecionada em laboratório; Est. = Amostra retirada de elemento estrutural ** MEV = Microscopia Eletrônica de Varredura; DRX = Difração de Raios X; PIM = Porosimetria por Intrusão de Mercúrio; DTA = Análise Térmica Diferencial; TGA = Termogravimetria; COL = Colorimetria e PET = Petrografia

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

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[TFN1] *Lab. = Amostra confecionada em laboratório; Est. = Amostra retirada de elemento estrutural ** MEV = Microscopia Eletrônica de Varredura; DRX = Difração de Raios X; PIM = Porosimetria por Intrusão de Mercúrio; DTA = Análise Térmica Diferencial; TGA = Termogravimetria; COL = Colorimetria e PET = Petrografia