1 34 th Cement and Concrete Science Conference Paper Number 198 14-17 September 2014 University of Sheffield The Alumino-Silicate Chain Structure of C-S-H Phase in High-Volume Volcanic Natural Pozzolan-Portland Cement Blended Systems A. Sassani, L. Turanli and C. Meral* Department of Civil Engineering, Middle East Technical University (METU) A.H. Emwas Advanced Nanofabrication Imaging and Characterization, King Abdullah University of Science and Technology (KAUST) ABSTRACT Partial replacement of portland cement (PC) with supplementary cementitious materials (SCMs) may result in an altered C-S-H structure in the hydrated cement paste. Amongst the SCMs, volcanic natural pozzolans (VNPs) constitute an important category. This research focuses on identifying the variations in the C-S-H structure of the hydrated high-volume VNP-PC blended systems through various techniques. There are two main groups of VNPs that do not require heat treatment: volcanic glasses (VG) and volcanic tuffs (VT). Three VNPs, perlite (a VG), a feldspar-containing VT and a zeolite-rich VT were selected to represent the two aforementioned groups. Selected VNPs were first characterized by 27 Al- and 29 Si- NMR spectroscopy. Then, 50VNP-50PC paste samples were prepared and aged at sealed containers for 7 months. A white PC was selected for the experiments. The silicate and alumino-silicate species present in the VNP-PC pastes were investigated by 29 Si and 27 Al NMR. XRD was used to identify the crystalline phases, such as AFt, AFm and Ca(OH)2, within the hydration products. Obtained results on the hydrated pastes were compared with the available data in the relevant literature. The tendency to form polysilicate species and the Al substitution for Si were higher in VNP-PC systems to different extents. 1. INTRODUCTION The structure of C-S-H and other product phases generated through the hydration of artificial/byproduct SCMs have been the subject of numerous studies. Extensive research has been conducted on fly ash [1–5], blast furnace slag [4–9] and silica fume [10–12]. Despite the abundance of natural pozzolans [13], and the long time they have been used [14], the micro- and nano-structure of natural pozzolan- containing cementitious systems have not received as much attention as by-product SCMs, the exceptions being calcined clay minerals : Kaolinite, Illite and Montmorillonite [15] and KOH-activated Metakaolin [16]. Only limited microstructural studies by XRD and SEM have been performed [12,17–19]. In order to thoroughly represent volcanic natural pozzolans (VNPs) found in Turkey, three pozzolans were chosen from three different regions: Perlite rock from quarry in Erzincan province was chosen to represent volcanic- glass-based natural pozzolans. Perlite is found in gray, black, light green and brown colors; the Perlite used in this research was in light gray color. Two tuffs were chosen to represent tuff- based natural pozzolans: (1) a yellowish zeolite- rich volcanic tuff from a quarry in Balikesir- Bigadic; (2) a Greenish-gray feldspar-rich volcanic tuff from a quarry in Isparta region. Hereinafter we refer to these two tuffs as tuff-1 and tuff-2 respectively and Perlite rock from Erzincan province will be simply called perlite. White portland cement (WPC) was used to make the neat PC as well as PC-VNP blended pastes. Super white 52.5/85 Portland cement (TS 21 BPÇ 52.5 R) was received from Çimsa cement group. The limited content of iron based compounds in the WPC allowed a smoother data analysis. The VNP-PC pastes were made by replacing 50% of WPC by VNP. 1:1 blends of pozzolan and WPC were made for each of the selected VNPs separately. The pastes were mixed in a glass beaker with water-to-solid ratio of 0.5. Then, they were cast into 15 ml plastic tubes, sealed and kept in room temperature (20-23 ᵒC) for seven months. In this paper the hydrated neat WPC, WPC-tuff-1, WPC-tuff-2 and WPC-