Examining the potential of calcined oyster shell waste as additive in high volume slag cement Ali Naqi a , Salman Siddique a , Hyeong-Ki Kim b , Jeong Gook Jang a,⇑ a Division of Architecture and Urban Design, Institute of Urban Science, Incheon National University, 119 Academy-ro, Yeonsu-gu, Incheon 22012, Republic of Korea b School of Architecture, Chosun University, 309 Pilmun-daero, Dong-gu, Gwangju 61452, Republic of Korea highlights  Calcined oyster shell (COS) waste was utilized as an additive for high volume slag cement binder.  Addition of COS had a positive effect on strength development of high volume slag cement binder.  COS increased the percentage of Ca 2+ leading to higher cumulative heat evolution.  Incorporation of COS refined the pore structure of high volume slag cement binder.  Increased degree of hydration and mean chain length was observed for binder mixes containing COS powder. article info Article history: Received 4 July 2019 Received in revised form 11 September 2019 Accepted 14 September 2019 Keywords: High volume slag cement Calcined oyster shell powder Heat of hydration 29 Si nuclear magnetic resonance Thermal gravimetric analysis abstract The present study investigates the effect of calcined waste oyster shell powder as additive on the fresh, hardened and microstructural properties of high volume slag cement. The results provide that addition of calcined oyster shell powder enhanced the early age compressive strength. The hydration of calcined oys- ter shell powder resulted in additional portlandite formation during the initial reaction stage. The obser- vations drawn from porosity measurements indicated that calcined oyster shell powder decreased the porosity of binder matrix at early and elongated duration of curing. Furthermore, by 29 Si NMR it was observed that the hydration of high volume slag cement was also benefited by calcined oyster shell pow- der as indicated by increased degree of hydration and chain length. However, excess addition of calcined oyster shell powder caused decreased compressive strength development. Considering the results, calcined oyster shell powder can be used as additive in high volume slag cement. Ó 2019 Elsevier Ltd. All rights reserved. 1. Introduction In the past few decades, the ecological and environmental awareness regarding high CO 2 footprint of cement industry has ushered the utilization of various industrial by-products as mineral admixtures. In many concrete applications, mineral admixtures have been used to replace more than 50% of total cement [1,2]. The utilization of many industrial by-products such as fly ash, blast furnace slag and rice husk ash as mineral admixtures reduces the environmental impact of concrete production. It also provides a sustainable reuse channel for these solid industrial by-products. Furthermore, the utilization of mineral admixtures can improve strength and durability performance of environmentally friendly concrete. Blast furnace slag (BFS) from the iron industry is one of the most economical and widely used mineral admixture to produce envi- ronmentally friendly concrete. Many studies reported an increase in compactness and improvements in concrete microstructure and durability against chemical ingress on the utilization of BFS. The improved durability characteristics of concrete containing BFS make it suitable for construction work in aggressive environ- ments. In previous years, studies have been carried out to incorpo- rate high volume of BFS as a cementitious material in concrete. Yazıci [3] studied the effect of three different curing conditions (standard, steam and autoclave) on strength development of high volume slag concrete. The author reported that under standard curing conditions, high volume slag in concrete causes large reduc- tions in compressive strength and early age strength development [3]. However, steam and autoclave curing can restrict large reduc- tions in compressive strength [3]. Sethy et al. [4] developed self- compacting concrete that contained 30–90% slag as a binder. They reported that the reactivity of slag contributed to the strength https://doi.org/10.1016/j.conbuildmat.2019.116973 0950-0618/Ó 2019 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail address: jangjg@inu.ac.kr (J.G. Jang). Construction and Building Materials 230 (2020) 116973 Contents lists available at ScienceDirect Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat