Evaluation of time to shrinkage-induced crack initiation in OPC and slag cement matrices incorporating circulating fluidized bed combustion bottom ash Bang Yeon Lee a , Sang-Min Jeon b , Chang Geun Cho b , Hyeong-Ki Kim b,⇑ a School of Architecture, Chonnam National University, 77 Yongbong-ro, Buk-gu, Gwangju 61186, Republic of Korea b School of Architecture, Chosun University, 309 Pilmun-daero, Dong-gu, Gwangju, 61452, Republic of Korea highlights  CFBC bottom ash was used as an expansion agent in OPC and slag cement.  Cracking potential was evaluated by direct tensile and shrinkage tests.  Ash delayed cracking times due to its shrinkage compensation.  This cracking times varied with the drying condition rather than ash content. article info Article history: Received 2 March 2020 Received in revised form 5 May 2020 Accepted 8 May 2020 Available online 19 May 2020 Keywords: OPC Slag cement Circulating fluidized bed combustion Bottom ash Shrinkage Crack Tensile test abstract The effect of bottom ash produced from circulating fluidized bed combustion (CFBC) on the shrinkage- induced cracking potential of ordinary Portland cement (OPC) and slag cement mixtures were investi- gated by evaluating the time to crack initiation, predicted by comparing tensile strength obtained from direct tensile tests with shrinkage-induced stress obtained from shrinkage strain and elastic modulus results. Although replacing OPC and slag cement amounts with CFBC bottom ash delayed cracking times due to its shrinkage compensation, the effect varied with the drying condition. Therefore, for effective application of CFBC ash in cement mixtures, boundary conditions affecting drying rates need careful consideration. Ó 2020 Elsevier Ltd. All rights reserved. 1. Introduction In our previous papers, bottom ash obtained from a circulating fluidized bed combustion (CFBC) boiler was incorporated into ordi- nary Portland cement (OPC) and blast furnace slag blended cement [1]. The CFBC is an advanced power plant system compared to tra- ditional pulverized coal combustion (PCC) system, and it has sev- eral merits that include a high combustion efficiency while providing a reduction in pollution emissions, such as nitrogen oxide or sulfates [2]. Calcite powders are directly supplied to the boiler for desulfurization during coal combustion; therefore, the resulting ash has a very different chemical composition compared to that of ordinary ash from PCC boilers, and it contains higher pro- portions of free-lime (f-CaO) and anhydrite (CaSO 4 ) [3,4]. Due to the presence of these minerals, CFBC ash could be hydrated by itself within short time without any help of OPC [5] and can also serve as an activator for slag or PPC fly ash [6]. In our previous study [1], raw CFBC bottom ash that had not been previously treated (no sieving or grinding) was applied for OPC and slag cement. Binder was replaced with the CFBC bottom ash at percentage weights of 10 wt% and 20 wt% for pure IPC and at 50 wt% and 70 wt%, respectively, for slag powder blended cement. However, replacement with CFBC bottom ash caused a sig- nificant reduction in autogenous and dry shrinkages for the first two weeks in all mixtures, as the sulfate ions and f-CaO produced greater amounts of ettringite and portlandite, which can resist shrinkage. In addition, the use of greater amounts of CFBC bottom ash with pure OPC yielded an excessive formation of ettringite in water-cured mixtures, which caused more than 3,000 microstrains https://doi.org/10.1016/j.conbuildmat.2020.119507 0950-0618/Ó 2020 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail address: hyeongki@chosun.ac.kr (H.-K. Kim). Construction and Building Materials 257 (2020) 119507 Contents lists available at ScienceDirect Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat