Contents lists available at ScienceDirect Applied Radiation and Isotopes journal homepage: www.elsevier.com/locate/apradiso Enhancement of thermal neutron shielding of cement mortar by using borosilicate glass powder Bo-Kil Jang a , Jun-Cheol Lee b , Ji-Hyun Kim a , Chul-Woo Chung a, ⁎ a Pukyong National University, Nam-gu, Busan 48513, Republic of Korea b Kyungpook National University, Buk-gu, Daegu 41566, Republic of Korea ARTICLE INFO Keywords: Borosilicate glass powder Pozzolanic reaction Compressive strength Neutron shielding ABSTRACT Concrete has been used as a traditional biological shielding material. High hydrogen content in concrete also effectively attenuates high-energy fast neutrons. However, concrete does not have strong protection against thermal neutrons because of the lack of boron compound. In this research, boron was added in the form of borosilicate glass powder to increase the neutron shielding property of cement mortar. Borosilicate glass powder was chosen in order to have beneficial pozzolanic activity and to avoid deleterious expansion caused by an alkali–silica reaction. According to the experimental results, borosilicate glass powder with an average particle size of 13 μm showed pozzolanic activity. The replacement of borosilicate glass powder with cement caused a slight increase in the 28-day compressive strength. However, the incorporation of borosilicate glass powder resulted in higher thermal neutron shielding capability. Thus, borosilicate glass powder can be used as a good mineral additive for various radiation shielding purposes. 1. Introduction Concrete has been considered as one of the promising biological shielding materials. Concrete is effective for shielding gamma radiation because of its dense, complex, and heterogeneous microstructure, and the use of high-density aggregates can effectively increase gamma ray shielding capability (Mehta and Monteiro, 2006). In addition, Davis (1972) reported that high hydrogen content associated with free water (capillary pore solution), physically adsorbed water within calcium silicate hydrate layers, and chemically bound water in the structure of calcium silicate hydrate in concrete effectively attenuate high-energy fast neutrons. Thus, concrete can be a very good neutron moderator if there is a method to protect against thermal neutrons because concrete does not contain any boron compounds that have high neutron capture cross section in its structure (Rinard, 1991). Therefore, it is necessary to include some amount of boron compounds in concrete to increase its efficiency as a biological shielding material. One of the easiest ways to add boron compound in concrete is to use boric acid and borax. These materials are not known to be compatible with portland cement whose major reaction is based on silicate polymerization that occurs at high pH environment. These materials cause set delay and strength loss of concrete (Davraz, 2015; Olgun et al., 2007; Targan et al., 2002; Volkman and Bussolini, 1992) and thus making it meaningless to add them for thermal neutron protection of concrete. Boron carbide can be used as an alternative material (Kharita et al., 2011), but it is very expensive; moreover, its particle size distribution either for cement replacement or for aggregate replacement is difficult to control because of its high hardness. The objective of this research is to use borosilicate glass for thermal neutron shielding. Borosilicate glass is a material with very low thermal expansion property. Typical examples are Schott by Duran or Pyrex by Corning. It contains up to 13 wt% of boron trioxide (B 2 O 3 ), and thus can show excellent thermal neutron shielding performance when it is added to the cement-based material. Hence, borosilicate glass has been used as a medium for immobilizing various types of radioactive wastes (Alton et al., 2002; McCloy et al., 2012; Mishra et al., 2008; Tomar et al., 2005). However, borosilicate glass is an amorphous silica and is known to cause an alkali–silica reaction that causes deleterious expan- sion and cracking in concrete when it is added in the form of fine aggregate. Thus, the size of the borosilicate glass needs to be controlled to avoid such problems. Shao et al. (2000) reported that incorporation of a soda-lime glass with a particle size of less than 150 μm did not show the alkali–silica reaction. They also showed that smaller-sized waste lime glass (75 and 38 μm) had less expansion than plain cement mortar. Zhu and Byars (2004) reported that there is a critical particle size for colored waste glass to be used as aggregate; pessimum size for amber and green color glass was 0.6 and 1.18 mm for flint color glass. Shayan and Xu (2004) http://dx.doi.org/10.1016/j.apradiso.2017.01.047 Received 19 August 2016; Received in revised form 16 January 2017; Accepted 27 January 2017 ⁎ Corresponding author. Tel.: 82-51-629-6084, fax: 82-51-629-7084. E-mail address: cwchung@pknu.ac.kr (C.-W. Chung). Applied Radiation and Isotopes 123 (2017) 1–5 Available online 06 February 2017 0969-8043/ © 2017 Elsevier Ltd. All rights reserved. MARK