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The impact of novel supplementary cementitious materials (SCMs) on the phase assemblage and the pore structure in cement pastes was studied and linked to their impact on the compressive strength in mortar. The composite cements analysed had a composition of 78 wt.% Portland cement, 18 wt.% SCM and 4 wt.% limestone filler, and the samples were cured sealed for 91 days at 20°C. The investigated SCMs comprise natural materials such as clays and volcanic rocks (rhyolite and hyaloclastite), and industrial products such as fly ash, slag, oil shale ash, bio-fuel ash or bio-coal fly ash. The results revealed that all the SCMs except oil shale ash contribute to the phase assemblage in a similar way, when clinker is replaced with 18 wt.% SCM. The pore structure of the different cement pastes was similar. Even when the composite cement pastes showed a higher total intruded pore volume compared to the Portland cement paste sample, these samples showed higher compressive strength. This indicates that total intruded porosity is not the only contribution to strength.

This study explored composite cements consisting of Portland clinker, two pozzolans (alumina-silica gel in carbonated Recycled Concrete Paste (cRCP) and metakaolin), and calcium carbonate. The rapid reactivity of alumina-silica gel resulted in full reaction within 28 days, while metakaolin exhibited slower reactivity. cRCP played a significant role in strength development between 1 and 7 days, with metakaolin becoming prominent thereafter. The combination of materials preserved their distinct characteristics. Early hydration was mainly influenced by clinker and cRCP, leading to high early compressive strength. After alumina-silica gel dissolved, metakaolin forms a microstructure, reducing porosity and allowing for continued strength improvement over time. The pozzolans did not hinder their respective reactions, and calcium carbonate from cRCP stabilized ettringite content, similar to limestone-calcined clay systems. This study's findings offer insights for developing multi-component cement with cRCP and calcined clays, resulting in higher strength and reduced CO2 footprint compared to calcined clay-limestone cements. [ABSTRACT FROM AUTHOR]

Deep neural networks (DNNs) have recently become one of the most often used soft computational tools for numerical analysis. The huge success of DNNs in the field of image processing is associated with the use of convolutional neural networks (CNNs). CNNs, thanks to their characteristic structure, allow for the effective extraction of multi-layer features. In this paper, the application of CNNs to one of the important soil-structure interaction (SSI) problems, i.e., the analysis of vibrations transmission from the free-field next to a building to the building foundation, is presented in the case of mine-induced vibrations. To achieve this, the dataset from in-situ experimental measurements, containing 1D ground acceleration records, was converted into 2D spectrogram images using either Fourier transform or continuous wavelet transform. Next, these images were used as input for a pre-trained CNN. The output is a ratio of maximal vibration values recorded simultaneously on the building foundation and on the ground. Therefore, the last layer of the CNN had to be changed from a classification to a regression one. The obtained results indicate the suitability of CNN for the analyzed problem. [ABSTRACT FROM AUTHOR]

In this work, an approach towards a carbon-neutral cement industry using carbon dioxide mineralisation of recycled concrete paste is investigated. It focuses on the effect of temperature on the enforced carbonation of cement paste. The enforced carbonation is a rapid process at ambient temperature, which is further accelerated at elevated temperatures. Moreover, the extent of the reaction is increased when the temperature rises. The carbonation reaction is divided into two kinetic stages. During the first stage, the carbonation kinetics is controlled by the availability of carbon dioxide that increases at higher temperatures. During the second stage, the reaction kinetics is controlled by the dissolution of the hydrates. Increased temperature accelerates this process by increasing the undersaturation level of the dissolving phases. The main carbonation products are calcium carbonate and an alumina–silica gel. The increasing temperature has a limited impact on these phases, and the differences come mainly from the different degrees of carbonation. [ABSTRACT FROM AUTHOR]

CO2 curing of fresh concrete is one of the solutions allowing direct carbon sequestration within the construction industry. Additionally, it enhances the early mechanical performance when comparing to traditional hydration curing. Temperature of carbonation curing has pronounced impact on both reactions involved in hardening of Portland cement: carbonation and hydration. Both reactions are accelerated with rising temperature, while the formed products and resulting microstructure are altered. Higher curing temperature promotes the precipitation of silica gel and C-S-H phase with reduced Ca/Si ratio. Furthermore, alumina and sulfate distributions among the reaction products are different. Temperature of carbonation curing has a distinct impact on the cement paste hydration after carbonation curing. The high curing temperature results in a densification of the matrix which limits further reaction progress, compared to the samples cured at lower temperatures. During the post hydration, calcium deficient system changes into C-S-H phase with higher Ca/Si and eventually portlandite. [ABSTRACT FROM AUTHOR]