The main objective of this study is to investigate the possibility of utilizing nano/submicron sized boron mineral (colemanite) in Portland cement concrete. Colemanite was obtained from a mine in three different sizes as -3 mm (C-3m), 75 mu m (C-75 mu) and -45 mu m (C-45 mu), respectively. The C-3m was ground by mechanical milling process in a high-energy ball mill and then passed througha 25 mu m (C-25 mu) sieve in order to obtain a smaller size/nano sized particles. The material information of these powders was investigated by using laser size analyzer, optical microscopes, and scanning electron microscope analyses. The particle size was respectively reduced for the C-3m, C-75 mu, C-45 mu and C-25 mu and therefore its homogeneity was improved. Five different ratios of Portland cement were used as 0.5%, 1%, 2%, 3% and 5% (wt). For each of rations, the C-75 mu, the C-45 mu, the C-25 mu different particle size colemanite and control samples (0%, no addition) were evaluated and 15 cm x 15 cm x 15cm cubic samples were produced. The fine and coarse aggregates were natural conventional aggregates. As a result, the highest compressive strength and elastic modulus were obtained in case colemanite with sizes C-75 mu and the C-45 mu added into the concrete in ratios 3% and 5%; and colemanite with a size of C-25 mu added into the concrete in ratios 1% and 0.5%, respectively. Since the C-25 mu is close to the ideal size of the cement, it becomes a good adherence by high specific surface area. Nano particle materials are used for their high specific surface area which has a great impact on the hydration. This is the reason why findings it could be observed that C-75 mu and C-45 mu required to be added at high percentage to probably have a concrete with the same mechanical properties as for C-25 mu that required a small percentage of addition. (C) 2016 Elsevier Ltd. All rights reserved.