Evaluation of freeze-thaw damage on concrete material and prestressed concrete specimens Xiao-chuan Qin a , Shao-ping Meng a , Da-fu Cao b , Yong-ming Tu a,c,⇑ , Natalia Sabourova c , Niklas Grip c , Ulf Ohlsson c , Thomas Blanksvärd c , Gabriel Sas c , Lennart Elfgren c a School of Civil Engineering, Southeast University, No. 2 SiPaiLou, XuanWu District, Nanjing 210096, China b School of Civil Science and Engineering, Yangzhou University, No. 198 HuaYangXiLu, HanJiang District, Yangzhou 225127, China c Division of Structural Engineering, Luleå University of Technology, SE-971 87 Luleå, Sweden highlights  We study the microscopic and macroscopic freeze-thaw damage on concrete material.  We investigate the freeze-thaw prestress loss of the bonded and unbonded specimens.  Severe microscopic damages occur after 200 freeze-thaw cycles.  Prestress loss from the intact to the completed damaged status is about 5% of r con .  Influence of grouting on freeze-thaw prestress loss depends on grout damage status. article info Article history: Received 15 October 2015 Received in revised form 20 July 2016 Accepted 25 August 2016 Available online 1 September 2016 Keywords: Concrete structures Durability Assessment Deterioration Damage abstract The pore structure of the hardened concrete and the microscopic changes of a few selected pores throughout the freeze-thaw test were investigated by a method combining RapidAir and digital metallo- scope. Traditional tests were also performed to evaluate the macroscopic change caused by freeze-thaw cycles (FTCs). The investigation shows that the concrete material, of which the spacing factor is 0.405 mm and the air content is 2.38%, can still withstand more than 300 FTCs. Severe microscopic damages occurred after approximately 200 FTCs and the freeze-thaw damage were gradually aggravated after- wards. Prestress forces have a remarkable impact on the failure pattern under FTCs. It was further found that the compressive strength as an indicator is more reliable than the relative dynamic modulus of elas- ticity in evaluating the freeze-thaw damage on concrete material. In addition, the test and analysis show that the measured prestress losses of bonded specimen are larger than that of unbounded specimen under the attack of FTCs due to the duct grouting effect. The ultimate freeze-thaw prestress loss is about 5% of r con for both the bonded and unbonded specimens because the grouting cement paste will eventu- ally be completely destroyed. Ó 2016 Elsevier Ltd. All rights reserved. 1. Introduction Freeze-thaw cycles (FTCs) can cause severe deterioration in reinforced concrete structures and prestressed concrete structures due to the nature of porous structure in concrete material. The microscopic porous structure inside the concrete material makes it capable of absorbing and holding water [1]. As the ambient tem- perature drops below 0 °C, ice will form inside the pores of con- crete and the volume of water and ice mixture will increase, introducing pore pressure inside the porous concrete material. If the tensile stress in concrete caused by pore pressure exceeds the tensile strength of the pore structure, freeze-thaw induced micro-cracks will occur. Then, as the ambient temperature rises above 0 °C, more water will be absorbed into the pores and new micro-cracks. Therefore, freeze-thaw damage will be aggravated during the next freezing process [2–5]. In order to find out the freeze-thaw damage mechanism of con- crete material and to quantify this damage, experiments with the http://dx.doi.org/10.1016/j.conbuildmat.2016.08.098 0950-0618/Ó 2016 Elsevier Ltd. All rights reserved. ⇑ Corresponding author at: School of Civil Engineering, Southeast University, No. 2 SiPaiLou, XuanWu District, Nanjing 210096, China. E-mail addresses: qinxc@seu.edu.cn (X.-c. Qin), msp1960@vip.sina.com (S.-p. Meng), dfcao@yzu.edu.cn (D.-f. Cao), tuyongming@seu.edu.cn (Y.-m. Tu), natalia.sabourova@ltu.se (N. Sabourova), niklas.grip@ltu.se (N. Grip), ulf.ohlsson@ ltu.se (U. Ohlsson), thomas.blanksvard@ltu.se (T. Blanksvärd), gabriel.sas@ltu.se (G. Sas), lennart.elfgren@ltu.se (L. Elfgren). Construction and Building Materials 125 (2016) 892–904 Contents lists available at ScienceDirect Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat