Synthesis and Structural Characterization of CSH-Phases in the Range of C/S = 0.41 - 1.66 at Temperatures of the Tobermorite Xonotlite Crossover

Andrea Hartmann,David Schulenberg,Josef-Christian Buhl

doi:10.4236/msce.2015.311006

Andrea Hartmann, David Schulenberg + Show 1 more

Open Access

https://doi.org/10.4236/msce.2015.311006

Copy DOI

Abstract

Calcium-Silicate-Hydrate-phases (CSH-phases) are important binding agents of building materials. The synthesis of CSH phases and their structural characterization was done to investigate the crystallization in dependence of an increasing CaO/SiO2 ratio (C/S ratios) from 0.41 up to 1.66 at temperatures in the crossover region of tobermorite to xonotlite (180℃ and 230℃). Parallel runs with the same C/S ratio but on the one hand with constant mass of quartz and variation of lime and on the other hand under reverse conditions (constant mass of lime but variable amounts of quartz) were performed at both temperatures. The aim was to clarify the connections of crystallization mechanism and kinetics of phase formation with structure, crystallinity and morphology of the CSH’s in the mentioned C/S ratio for both temperatures in the tobermorite-xonotlite crossover region. The parallel experiments with different mass ratios of the educts are important to study the influence of time evaluation of supersaturation within the solution under the peculiarities of the retrograde solubility of lime but accelerated solubility of quartz. The products were characterized by XRD, SEM/EDX, FTIR and 29Si MAS NMR spectroscopy (using the Q-site nomenclature [1]). The experiments could clarify some important connections of crystallization process and the reaction pathway.

Highlights

Calcium-Silicate-Hydrate-phases (CSH-phases) are important binding agents in building materials, like concrete and limesand stone
Our knowledge on certain structural features connected with temperature dependent phase transitions and crystallization process from the 14 tobermorites to the 11 phase and to xonotlite in structural relation to wollastonite types can be further mentioned here beside many other questions on this broad field of CSH-phases. In this sense the present work investigates CSH crystallization in view of two special points: Firstly we investigate the temperature interval of the crossover reaction from tobermorite to xonotlite to get more information on structure-temperature relations of both CSH’s during this process step
The amount of quartz decreases with increasing C/S ratio

Summary

Introduction

Calcium-Silicate-Hydrate-phases (CSH-phases) are important binding agents in building materials, like concrete and limesand stone. The crystallization of CSH-phases depends on the C/S ratio of the educts, the reaction temperature and the reaction time. These parameters influence the formation of structure type, crystallinity and crystal morphology of the CSH-phases, e.g. in limesand stone, in the free pore space between the quartz cores. CaO (calcinated lime) is obtained by calcination of carbonate (CaCO3) at 900°C Reaction of the latter with water leads to the formation of portlandite (Ca(OH)). Ca-rich phases crystallize at first during the hydrothermal process, e.g. α-C2SH, followed by the amorphous gel-like CSH-II [5]-[7]. Mörtel (1980) described the following crystallization steps of the formation of CSH-phases [2]:

Objectives

Methods

Results

Conclusion