Investigation of early growth of calcium hydroxide crystals in cement solution by soft X-ray transmission microscopy

Abstract

Research on cement hydration was performed at the full-field soft transmission X-ray microscope XM-1 located at beamline 6.1.2 at the Advanced Light Source (ALS) in Berkeley CA which is operated by the Center for X-ray Optics, Lawrence Berkeley National Laboratory, Berkeley, California. A series of works [1][2][3] has been conducted using this microscope for the insitu observation and qualitative analysis of through-solution hydration products and products of topochemical reactions, which form in cementitious aqueous solutions. This paper studies the precipitation of the calcium hydroxide (CH) crystals from the cement solution. The analysis of successive images of the hydration process provides critical quantitative information about the growth rate of calcium hydroxide (CH) crystals, the supersaturation ratio, and the kinetic and diffusion coefficients of the growth process.ASTM Type II portland cement and 6% 4 3 C A S admixture were mixed in aqueous solution and saturated with respect to CH and gypsum. The 4 3 C A S admixture was included in the experimental program because of the general research program on expansive cements, and adding 4 3 C A S to portland cement is an efficient method of generating ettringite and significant early-age expansion. The solution/solid materials ratio was 10 cm 3 /g, which is higher than the one existing in regular concrete and mortars; to compensate for this dilution, the solution was originally saturated with CH and gypsum. To allow sufficient transmission of the soft X-rays, a small droplet was taken from the supernatant solution and assembled in the sample holder, and then squeezed between two silicon nitride windows for the analysis. The X-ray optical setup of the microscope XM-1 is described elsewhere [2].In this experiment, a wavelength of 2.4 nm (516.6 eV) was used. The radiation transmitting the sample was detected using an X-ray CCD camera, with a resolution of 35 nm provided by

Diffusion-Controlled Anisotropic Growth of Stable and Metastable Crystal Polymorphs in the Phase-Field Crystal Model

“…A [16], is close to the present $1:7-2:7, while the ratio v 10 " 10 =v 0001 $ 2:8 observed for CaðOHÞ 2 (hexagonal but not hcp) [17] accords reasonably with our $2:4 for hcp; however, this agreement might be fortuitous.…”

Role of porosity on the stiffness and stability of (001) surface of the nanogranular C–S–H gel

“…In fact, the surface free energy obtained for a surface terminated with 3 layers of water is 0.10 J/m 2 , in good agreement with the experimental measurement of 0.09 J/m 2 [66][67].…”

Changes in portlandite morphology with solvent composition: Atomistic simulations and experiment

“…The identification of the low index [00.1] and [10.0] surfaces was expected as these surfaces are part of the hexagonal platelet shape reported as the morphology of naturally found portlandite minerals [28] and of portlandite grown in cementitious systems in the presence of sulfates [4,5,27]. The presence of the higher index [20.3] surface was more unexpected.…”

“…This indicates that the interaction of portlandite surfaces and surface steps with gypsum and C 3 A dissolution products might give some insight into the working mechanisms of the observed change in morphology. Harutyunyan et al, used soft X-ray techniques to observe the growth of CH near cement particles in a CH and C$ saturated solution [5]. The observed portlandite particles had a hexagonal platelet morphology with a aspect ratio of 2.5 to 2.7.…”