Analysis of cementitious building materials by synchrotron x-ray imaging

Cement manufacturing especially Portland Cement, the main component for the fabrication of concretes, is the most used building and construction material which has complex hierarchical microstructures. Quantitative characterization of cementitious materials microstructures is of paramount importance for assessing the performance and durability of the final products. To gain a deeper insight into the microstructures of building materials, synchrotron X-ray nano- and micro-tomography with an appropriate spatial resolution would help. we will report the analysis of porosity and the different components and phases of different types of cement pastes, regarding their hydration ages.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

4D Early Age Cement Hydration Analysis by Ptychographic X-ray Computed Tomography and Machine Learning Segmentation

Cement manufacturing is responsible for ~7% of the anthropogenic CO2 emissions and hence, decreasing the CO2 footprint, in a sustainable, safe and cost-effective way, is a top priority. To fully understand the binder main properties and to decrease their CO2 footprints, a sound description of their spatially resolved mineralogy is necessary. Developing this knowledge is very challenging as about half of the volume of hydrated cement is a nanocrystalline component, calcium silicate hydrate (C-S-H) gel. Furthermore, other poorly crystalline phases (e.g. iron siliceous hydrogarnet or silica oxide) coexist. Here, we have used ptychographic X-ray computed tomography (PXCT) for understanding the first days of cement hydration with the final goal to improve the mechanical strength performances of low-CO2 cements

Accuracy in Cement Hydration Investigations: Combined X-ray Microtomography and Powder Diffraction Analyses

Cement hydration is a very complex set of processes. The evolution of the crystalline phases during hydration can be accurately followed by X-ray powder diffraction data evaluated by the Rietveld method. However, accurate measurements of some microstructural features, including porosity and amorphous content developments, are more challenging. Here, we combine laboratory X-ray powder diffraction and computed microtomography ( CT) to better understand the results of the CT analyses. Two pastes with different water–cement ratios, 0.45 and 0.65, filled within capillaries of two sizes, = 0.5 and 1.0 mm, were analysed at 50 days of hydration. It was shown that within the spatial resolution of the measured CTs, ~2 m, the water capillary porosity was segmented within the hydrated component fraction. The unhydrated part could be accurately quantified within 2 vol% error. This work is a first step to accurately determining selected hydration features like the hydration degree of amorphous phases of supplementary cementitious materials within cement blends.This research has been supported by PID2019-104378RJ-I00 and PID2020-114650RB-I00 (Spanish Science Ministry) research grants, which are co-funded by ERDF. IRS is thankful for funding from PTA2019-017513–I

Phase and microstructure evolutions in LC3 binders by multi-technique approach including synchrotron microtomography

Limestone Calcined Clay Cements, LC3, are attracting a lot of attention as it is possible to reduce the clinker factor by 50%, which means a cement CO2 footprint reduction of 40%. This is compatible with maintaining the mechanical strength performances after one week, if the kaolinite contents of the raw clays are above ~40 wt%. Durability properties are also maintained or even enhanced. Here, it is used a multi-technique approach to understand the phase and microstructure developments. From the thermal analysis, partial limestone reactivity is proven. Chiefly, high-resolution synchrotron microtomography has been employed, for the first time in these systems, to characterize their microstructures. The measured total porosities, within our 1 lm spatial resolution (voxel size 0.32 lm), were 16.6, 10.0 and 2.4 vol% at 7, 8 and 60 days of hydration, respectively. Pore connectivity strongly decreases with hydration time due to the chemical reactions producing new phases filling the pores. The 6-connected porosity fractions were 92, 78, and 9% at 7, 8 and 60 days. The reactions filling the pores were investigated by Rietveld quantitative phase analysis and 27Al MAS-NMR.Financial support from research grant No. PID2019-104378RJI00 (Spanish Ministry) and No. UMA18-FEDERJA-095 (Junta de Andalucía and Universidad de Málaga), are gratefully acknowledged. SLS is thanked for granting beamtime at TOMCAT beamline. We also thank Dr. Olbinado (SLS) for her support during synchrotron data collection. Funding for open access charge: Universidad de Málaga/CBUA

Portland cement pastes analysed by synchrotron and laboratory X-ray imaging

Portland Cement (PC) is the most used construction material and the derived building materials have very complex hierarchical microstructures. Quantitative characterization of their microstructures is of paramount importance for assessing the performance and durability of the final products. As cement performance is controlled by its phase composition and microstructure, in particular, the pore network plays a critical role in the mechanical properties and durability. The chemical and hydration changes in PC binders affect their performances mainly because of the binding properties of the main component, the so-called C-S-H gel. Here, we analyse porosity in PC pastes using laboratory and synchrotron X-ray micro-tomography with different water to cement mass ratios (w/c) after 28 days of hydration. Monochromatic synchrotron X-ray microtomography is used for reference and the main aim is determining volume percentage of different components with focus on porosity. It will be shown, as expected, that higher amount of water (that increases fluidity of pastes) results in higher porosities at 28 days of hydration. Therefore, in the histogram and tomograms more pores, hydrated materials, and less anhydrous materials would appear with increasing w/c (see Figure 1). The excellent spatial resolution (and slightly better contrast) of synchrotron experiments serve as reference for data analysis. Despite 0.2-0.3 m voxel-sizes in all the used experimental setups (see Figure 2), the laboratory tomograms show some limitations that will be discussed. In this work, a two-steps approach is followed. Firstly, we will report the analysis of the histograms by classifying in the three types of components based on grey-levels: i) pores, ii) hydrated components; and iii) unreacted cement phases. Secondly, segmented pore contribution will be further analyzed and the results from laboratory tomograms will be compared with the reference values derived from synchrotron data.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

ANALYSIS OF BUILDING MATERIALS BY SYNCHROTRON X-RAY IMAGING

Building materials have complex hierarchical microstructures. The largest components are coarse aggregates with dimensions larger than a few centimetres and the smallest ones are the calcium silicate hydrate (C-S-H) gel nanoparticles with sizes smaller than 5 nm. To fully understand the main properties of cement binders and optimize their performances, a sound description of their spatially-resolved contents is compulsory. Furthermore, cement manufacturing is responsible for about 7% of the anthropogenic CO2 emissions and hence, to decrease the CO2 footprint, in a sustainable and cost-effective way, is a top priority. To gain a deeper insight into the microstructures of building materials, synchrotron X-ray ptychographic nanotomography and absorption-based microtomography have been employed. Here we will present three examples of our approach blending quantitative powder diffraction with synchrotron X-ray imaging. Firstly, we will show our comparative work on belite and Portland cement pastes cured at varying temperatures [1]. Synchrotron tomographic data taken at TOMCAT allowed understanding the different hydrating behaviour of both cements. Secondly, ptychographic nanotomographic data taken at cSAXS showed the hydration of CaAl2O4 with curing temperature [2]. Ptychographic data have permitted to characterise the conversion of the aluminate hydrates which is key for durability. The very good contrast in the electron density tomograms will be discussed as well as the porosity induced after the conversion reactions. Finally, we will report our work on Portland cements [3]. The densities and spatial distribution of calcium silicate hydrate (C-S-H) gel and amorphous iron-siliceous hydrogarnet components will be described.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech. BIA2017-82391-R UMA18-FEDERJA-09

Quantitative analysis of cementitious materials by X-ray ptychographic nanotomography

Cement manufacturing is responsible for ~7% of the anthropogenic CO2 emissions and hence, decreasing the CO2 footprint, in a sustainable, safe, and cost-effective way, is a top priority. It is also key to develop more durable binders as the estimated world concrete stock is 315 Gt which currently results in ~0.3 Gt/yr of concrete demolition waste (CDW). Moreover, models under development predict a skyrocketing increase of CDW to 20–40 Gt/yr by 2100. This amount could not be easily reprocessed as aggregates for new concretes as such volumes would be more than two times the predicted need. Furthermore, concretes have very complex hierarchical microstructures. The largest components are coarse aggregates with dimensions bigger than a few centimetres and the smallest ones are amorphous components and the calcium silicate hydrate gel with nanoparticle sizes smaller than a few nanometres. To fully understand the properties of current and new cement binders and to optimize their performances, a sound description of their spatially-resolved contents is compulsory. However, there is not a tomographic technique that can cover the spatial range of heterogeneity and features of concretes and mortars. This can only be attained within a multitechnique approach overlapping the spatial scales in order to build an accurate picture of the different microstructural features. Here, we have employed far-field and near-field synchrotron X-ray ptychographic nanotomographies to gain a deeper insight into the submicrometer microstructures of Portland cement binders. With these techniques, the available fields of view range from 40 to 300 um with a true spatial resolution evolving between ~50to~300 nm. It is explicitly acknowledged here that other techniques like X-ray synchrotron microtomography are necessary to develop the whole picture accessing to larger fields of view albeit with poorer spatial resolution and without the quantitativeness in the reconstructed electron densities

Accuracy in cement hydration investigations: Combined X-ray microtomography and powder diffraction analyses

Cements are multi-phase materials that can be well understood using a multi-technique approach. Furthermore, the hydration of cement pastes is a very complex set of processes. In this work, we focus on the accuracy of the results of the laboratory computed tomography (µCT) analysis by quantifying three sets of components based on their attenuations: porosity, hydration products (HP) and unhydrated cement phases (UHP), and comparing with laboratory X-ray powder diffraction data (LXRPD).Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

4D nanoimaging of early age cement hydration.

Despite a century of research, our understanding of cement dissolution and precipitation processes at early ages is very limited. This is due to the lack of methods that can image these processes with enough spatial resolution, contrast and field of view. Here, we adapt near-field ptychographic nanotomography to in situ visualise the hydration of commercial Portland cement in a record-thick capillary. At 19 h, porous C-S-H gel shell, thickness of 500 nm, covers every alite grain enclosing a water gap. The spatial dissolution rate of small alite grains in the acceleration period, ∼100 nm/h, is approximately four times faster than that of large alite grains in the deceleration stage, ∼25 nm/h. Etch-pit development has also been mapped out. This work is complemented by laboratory and synchrotron microtomographies, allowing to measure the particle size distributionswith time. 4D nanoimagingwill allow mechanistically study dissolution-precipitation processes including the roles of accelerators and superplasticizers.Financial support from PID2019-104378RJ-I00 research grant, which is co-funded by FEDER, is gratefully acknowledged. ToScA (United Kingdom) is gratefully acknowledged for awarding Jim Elliott Award to Shiva Shirani, I.R.S. is thankful for funding from PTA2019-017513–I