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Frontiers of Structural and Civil Engineering

Front. Struct. Civ. Eng.    2017, Vol. 11 Issue (2) : 158-168     https://doi.org/10.1007/s11709-016-0374-6
RESEARCH ARTICLE |
Experimental study on behavior of mortar-aggregate interface after elevated temperatures
Wan WANG, Jianzhuang XIAO(), Shiying XU, Chunhui WANG
Department of Structural Engineering, Tongji University, Shanghai 200092, China
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Abstract

A push-out test program was designed and conducted to study the meso-scale behavior of mortar-aggregate interface for concrete after elevated temperatures ranging from 20°C to 600°C with the concept of modeled concrete (MC) and modeled recycled aggregate concrete (MRAC). The MCs and MRACs were designed with different strength grade of mortar and were exposed to different elevated temperatures. Following that the specimens were cooled to room temperature and push-out tests were conducted. Failure process and mechanical behaviors were analyzed based on failure modes, residual load-displacement curves, residual peak loads and peak displacements. It is found that failure modes significantly depended on specimen type, the elevated temperature and the strength grade of mortar. For MC, major cracks started to propagate along the initial cracks caused by elevated temperatures at about 80% of residual peak load. For MRAC, the cracks appeared at a lower level of load with the increasing elevated temperatures. The cracks connected with each other, formed a failure face and the specimens were split into several parts suddenly when reaching the residual peak load. Residual load-displacement curves of different specimens had similarities in shape. Besides, effect of temperatures and strength grade of mortar on residual peak load and peak displacement were analyzed. For MC and MRAC with higher strength of new hardened mortar, the residual peak load kept constant when the temperature is lower than 400°C and dropped by 43.5% on average at 600°C. For MRAC with lower strength of new hardened mortar, the residual peak load began to reduce when the temperatures exceeded 200°C and reduced by 27.4% and 60.8% respectively at 400°C and 600°C. The properties of recycled aggregate concrete (RAC) may be more sensitive to elevated temperatures than those of natural aggregate concrete (NAC) due to the fact that the interfacial properties of RAC are lower than those of NAC, and are deteriorated at lower temperatures.

Keywords mortar-aggregate interface      push-out test      elevated temperatures      modeled concrete (MC)      modeled recycled aggregate concrete (MRAC)     
Corresponding Authors: Jianzhuang XIAO   
Online First Date: 07 April 2017    Issue Date: 19 May 2017
 Cite this article:   
Wan WANG,Jianzhuang XIAO,Shiying XU, et al. Experimental study on behavior of mortar-aggregate interface after elevated temperatures[J]. Front. Struct. Civ. Eng., 2017, 11(2): 158-168.
 URL:  
http://journal.hep.com.cn/fsce/EN/10.1007/s11709-016-0374-6
http://journal.hep.com.cn/fsce/EN/Y2017/V11/I2/158
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Wan WANG
Jianzhuang XIAO
Shiying XU
Chunhui WANG
Fig.1  Schematics of MC and MRAC. (a) MC; (b) MRAC
Fig.2  Geometric dimensions of MC (a) and MRAC(b)
strength gradew/c ratiomass (kg/m3)
watercementsand
M200.55160290.9584.73
M300.45160355.6565.32
M400.35190542.9400.10
Tab.1  Mix proportions of mortar
strength gradew/c ratiocompressive strength (MPa)elastic modulus (MPa)
M200.5526.8124065.91
M300.4539.3128030.69
M400.3547.3626738.75
Tab.2  Mechanical properties of mortar
Fig.3  MRCA
Fig.4  Casting MRAC
Fig.5  Measurement and loading system. (a) Photo; (b) schematic diagram
Fig.6  Failure modes of MC at ambient temperature. (a) MC-M40; (b) MC-M30; (c) MC-M20
Fig.7  Failure modes of MC after 200°C elevated temperatures. (a) MC-M40; (b) MC-M30; (c) MC-M20
Fig.8  Failure modes of MC after 400°C elevated temperatures. (a) MC-M40; (b) MC-M30; (c) MC-M20
Fig.9  Failure mode of MC after 600°C elevated temperatures. (a) M40; (b) M30; (c) M20
Fig.10  Failure modes of MRAC-M40 after different temperatures. (a) MRAC-M40-20; (b) MRAC-M40-200; (c) MRAC-M40-400; (d) MRAC-M40-600
Fig.11  Failure modes of MRAC-M30 after different temperatures. (a) MRAC-M30-20; (b) MRAC-M30-200; (c) MRAC-M30-400; (d) MRAC-M30-60
Fig.12  Failure modes of MRAC-M20 after different temperatures. (a) MRAC-M20-20; (b) MRAC-M20-200; (c) MRAC-M20-400; (d) MRAC-M20-600
Fig.13  Residual load-displacement curves of MC. (a) MC-M20; (b) MC-M30; (c) MC-M40
Fig.14  Residual load-displacement curves of MRAC. (a) MRAC-M20; (b) MRAC-M30; (c) MRAC-M40
elevated
temperature
decrease percentage of residual peak load
MC-M20MC-M30MC-M40MRAC-M20MRAC-M30MRAC-M40
400°C0.4%0.3%-2.3%35.5%19.7%-4.4%
600°C38.6%35.9%49.9%74.6%46.9%49.6%
Tab.3  Decreasing percentage of residual peak load after elevated temperatures
Fig.15  Simplified residual load-displacement curve
Fig.16  Residual peak load of MC and MRAC
Fig.17  Peak displacement of MC and MRAC
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