Characterization of interfacial transition zone in concrete prepared with carbonated modeled recycled concrete aggregates

Treatment by accelerated carbonation has been widely studied to enhance the quality of recycled concrete aggregates (RCA) and hence the performance of new concrete produced with the RCA. This is often ascribed to the densification of RCA. This study investigated the influence of carbonation treatment of modeled RCA on the interface between the carbonated RCA and new cement mortar/paste using frictional (shear) and tensile bond tests, microhardness, X-ray diffraction (XRD), thermal analysis (TGA), and scanning electron microscope (SEM). It was found that carbonation treatment resulted in massive calcite precipitating on the surface of RCA, which further reacted with the aluminate species of the new cement to form the monocarbonate (Mc), and served as nucleation sites for the grow of C-S-H on the surface of RCA. These led to local densification around the surface of the carbonated RCA, resulting in a slight reduction of the porosity at the innermost part of ITZ and improved microhardness of ITZ. Moreover, the chemical bonds provided a superior adhesion of the carbonated RCA with the new cement pastes. This improved the bond strengths between the carbonated RCA and the new cement mortar.

Influence of the storage conditions on the dimensional changes of heat-cured mortars

Karen Scrivener

Some cementitious materials cured at elevated temperature may expand on subsequent exposure to moisture. Concern has been expressed as to the relevance of small laboratory specimens to field concretes, in particular due to the potential leaching of ions into the storage solution. The work presented here aims at investigating this effect. Mortars cured at elevated temperature in identical fashion were subsequently stored at 90-100% relative humidity (RH) and in water, a LiOH solution, and KOH solutions of various concentrations. The largest and most rapid expansion occurred with mortars immersed in water. The samples stored at 90-100% RH expanded more slowly. Expansion was even slower when subsequent storage was in LiOH or KOH solutions. The same samples were studied by scanning electron microscopy (SEM) and X-ray diffraction (XRD). These techniques indicated that ettringite had formed over time in all samples, with little apparent relation to the degree of expansion. The composition of the C-S-H gel changed over time, differently for the different storage conditions. © 2001 Elsevier Science Ltd.

2001

The origin of early age expansions induced in cementitious materials containing shrinkage reducing admixtures

Patrick Juilland, Barbara Lothenbach, Karen Scrivener

Studies on the early-age shrinkage behavior of cement pastes, mortars, and concretes containing shrinkage reducing admixtures (SRAs) have indicated these mixtures frequently exhibit an expansion shortly after setting. While the magnitude of the expansion has been noted to be a function of the chemistry of the cement and the admixture dosage: the cause of the expansion is not clearly understood. This investigation uses measurements of autogenous deformation, X-ray diffraction, pore solution analysis, thermogravimetry, and scanning electron microscopy to study the early-age properties and describe the mechanism of the expansion in OPC pastes made with and without SRA. The composition of the pore solution indicates that the presence of the SRA increases the portlandite oversaturation level in solution which can result in higher crystallization stresses which could lead to an expansion. This observation is supported by deformation calculations for the systems examined. (C) 2010 Elsevier Ltd. All rights reserved.

2011

Synthesis, crystal growth and physical properties of the frustrated spin ladder material BiCu2PO6

Shuang Wang

In recent years quantum antiferromagnets with an intrinsically disordered (“spin liquid”) ground state and an energy gap in the spin excitation spectrum have received a great deal of attention. In search for new experimental realizations of spin-ladder and related models, we have embarked upon a new interesting family of low-dimensional materials with the general formula BiCu2AO6 (A = P, V and As). Among them, BiCu2PO6 shows a structure where Cu spins appear to form a two-leg zigzag ladder, which is believed to be a valuable model of a quantum magnet. However, for detailed studies of quantum magnetism, single crystals are indispensible. Therefore, in this thesis, synthesis and characterization of the newly-discovered spin ladder material BiCu2PO6 (BCPO) and its derivatives in the form of powder and single crystal are presented. Polycrystalline samples of Bi(Cu1-xZnx)2PO6 (x= 0.01, 0.02, 0.03, 0.04, 0.05 and 1), Bi1-y(Ca, Sr, La )yCu2PO6 (y = 0.15, 0.5 and 1) and BiCu2(P1-zVz)O6 (z = 1) were synthesized in this work. The solid state synthesis reactions, phase purity and thermal properties of the samples, substitution solubility, and preliminary magnetic susceptibility have been studied by thermal analysis (TG-DTA), X-ray powder diffraction (XRD), and Scanning Electron Microscope (SEM) as well as DC magnetization measurements, respectively. The BiCu2PO6 structure shows a remarkable chemical flexibility and interesting substitution effects. For detailed studies of the magnetic properties, well characterized large single crystals are indispensable. Thus in this thesis, a number of single crystal growth experiments have been performed using the Travelling Solvent Floating Zone method (TSFZ). Under the elaborated crystal growth conditions (growth rate of ~1 mm/h, gas mixture of 20% O2 in Argon, total 3 pressure (6~6.5 bar), high quality cm -size single crystals of Bi(Cu1-xZnx)2PO6 (x = 0, 0.01, 0.03, 0.05) have been successfully grown for the first time. For these crystals phase purity, crystal morphology/orientation, defect density, chemical composition distribution, crystal structure (room temperature and 1.5 K) and single crystal quality were thoroughly studied based on X-ray and neutron powder diffraction, optical and scanning electron microscopy, X-ray/neutron Laue diffraction, ICP-OES/X-ray fluorescence and two-axis neutron diffraction. Moreover, the specific heat Cp (H,T), AC susceptibility χ(H,T) and DC magnetization M(H,T) measurements on well-characterized single crystal samples of the undoped BCPO and 5% Zn-doped BCPO with the field applied along main crystallographic axes were performed in order to study the unique low temperature magnetic behaviour exhibited in this system, such as anisotropy of the magnetic properties, impurity-induced magnetism by the substitution of non-2+ magnetic cations (e.g. Zn ) and frustration. The magnetic phase diagram (H-T) under low field has been constructed. Further results obtained by close collaborators, based on the measurements made on single crystal samples grown in this thesis, including field-induced quantum phase transitions, NMR, Raman studies are attached directly at the end of this thesis.

EPFL2013

Synthesis, crystal growth and physical properties of the frustrated spin ladder material BiCu2PO6

Shuang Wang

EPFL2013