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This paper deals with the hygric characterization of early 20th century machine-made clay bricks, representative of great number of historical buildings in north-eastern Poland. Heritage buildings have a high potential for adaptive reuse, which is strictly connected with an urge for knowledge about the properties of these existing building envelopes. To better understand the hygric behavior of historic buildings, various experimental laboratory tests, including density, water absorption, compressive strength and freeze-thaw resistance, were conducted. In order to assess the microstructural characteristics of the tested bricks, mercury intrusion porosimetry (MIP) and X-ray micro-computed tomography (micro-CT) tests were performed. These tests were conducted on clay bricks from historic buildings, as well as on those that are currently being produced, in order to identify the relationship between the materials used in the past and the replacements produced presently. This paper addresses the lack of systematic application of existing standards for evaluating the state of the conservation of historic bricks and for establishing the specifications for replacement bricks. The results of conducted study and further research will be the basis for creating a historic materials database. It would be a useful tool for selecting bricks that correspond with the historically used materials and help to maintain homogenous structure of the restored buildings. [ABSTRACT FROM AUTHOR]

• 3D printable mortars containing different dosages of nanosilica (NS) were developed and evaluated. • NS accelerates significantly the setting and hardening of printable mortar, while reducing its open time. • Increment of yield stress, together with an increment in NS dosage, was found to have occurred. • Optimal NS dosage results in improvement of the compressive strength and pore structure. • Incorporation of NS in the mixture resulted in improved buildability and decrement in pore anisotropy. This study presents the experimental results of an investigation on the effects of nanosilica (NS) on the material characteristics of printable mortars used for additive manufacturing. Printable cement mortars based on Ordinary Portland Cement, limestone filler and silica sand were modified with different dosages of nanosilica (from 2% to 6% by weight of binder) and its influence on their hydration, rheological, mechanical and transport properties was assessed. The study showed that NS accelerates significantly the setting and hardening of printable mortar, while reducing its open time. Moreover, an increment of yield stress, together with an increment in NS dosage, was found to have occurred. The incorporation of an optimal NS dosage results in a noticeable increase in the compressive strength and alteration of the pore structure as determined by the MIP measurements. Moreover, transport properties of the produced mortar are significantly improved due to incorporation of NS. In addition to the microstructure refinement, Micro-CT and scanning electron microscopy (SEM) studies revealed that 3D printed mortars exhibit pore anisotropy in accordance with the printing direction. However, incorporation of NS in the mixture resulted in improved buildability, thus decreasing pore anisotropy. [ABSTRACT FROM AUTHOR]

Lightweight aggregate concrete (LWAC) has relatively larger porosity than conventional concrete, mainly due to the incorporation of porous lightweight aggregates. The types of used lightweight aggregates are critical in determining the physical properties of LWAC, and it is therefore important to examine their effects on the durable characteristics of the material. To perform comparative analysis, the concrete mixture designs with two theoretical density classes were developed. The mixture composition for each class was constant and the only variable parameter was the type of the used lightweight aggregates-expanded glass (Liaver®), expanded clay (Liapor®), and foam glass (Ecoglas®). Accordingly, their pore characteristics and durability-related properties, such as sorptivity, open water porosity, and water penetration depth, were examined. To understand these phenomena, the permeable characteristic, tortuosity, was also calculated using a numerical approach incorporating X-ray micro-computed tomography. The examined results confirm that the durability characteristics of LWAC are strongly affected by the used aggregate types and are highly correlated with their pore structures. In terms of permeable characteristics, expanded glass is the most beneficial material among the used particles, and the systematic approach in this study can be used to examine the durability characteristic of LWAC. • Lightweight concrete with different aggregates and density classes were produced. • The pore characteristics and tortuosity were examined using micro-CT imaging. • Durability of lightweight aggregate concrete is affected by the aggregate pores. • Among the used materials, expanded glass has beneficial permeable characteristics. • A proper lightweight aggregate needs to be selected for the purpose of the use. [ABSTRACT FROM AUTHOR]

• Lightweight aggregate concretes (LWACs) with a targeted density of 850 kg/m3, and 450 kg/m3 were developed. • Cement was replaced with 1, 2, 5 and 10% nanosilica (by mass of cement). • Shrinkage, transport, mechanical and microstructural (2D and 3D) properties of concretes were evaluated. • Nanosilica has a beneficial effect in improving the mechanical and transport properties of concretes. • Nanosilica significantly improves the pore characteristics of lightweight concretes. This work is aimed at characterizing the effects of nanosilica (NS) on the properties of lightweight aggregate concretes with different densities. Lightweight aggregate concrete (LWAC) and ultra-lightweight aggregate concrete (ULWAC) with targeted oven-dry densities of 850 kg/m3 and 450 kg/m3, respectively, were produced. The mixtures were modified by replacing cement with nanosilica, in concentrations of 1, 2, 5 and 10 wt-%. For comparison purposes, control specimens containing either cement alone or cement with silica fume (SF) were also produced. Their mechanical properties, including flexural and compressive strengths and transport characteristics, were evaluated by measuring the water accessible porosity and water absorption coefficients of the concretes. In addition, the thermal conductivity and drying shrinkage, being important parameters of lightweight concrete, were characterized. The pore structure characteristics of the concretes were assessed using 2D and 3D image analysis techniques; namely, using an automated air void analyser and micro-computed tomography (micro-CT), respectively. The experimental results show that NS has a significant effect on improving the mechanical and transport properties of lightweight concretes and that the efficiency of NS is much higher than that of SF. Moreover, depending on dosage, NS was found to have a negligible or decreasing influence on the drying shrinkage of concrete, after 28 days of curing. Microstructural studies confirmed that NS significantly affects the pore characteristics of concretes, thus resulting in concretes with denser and stronger microstructures. [ABSTRACT FROM AUTHOR]

The performance of vacuum insulation panels (VIPs) is strongly affected by several factors, such as panel thickness, design, quality of vacuum, and material type. In particular, the core materials inside VIPs significantly influence their overall performance. Despite their superior insulation performance, VIPs are limited in their widespread use as structural materials, because of their low material strength and the relatively expensive core materials. As an alternative core material that can compensate these limitations, foamed concrete, a type of lightweight concrete with very low density, can be used. In this study, two different types of foamed concrete were used as VIP core materials, with their effects on the thermal behavior of the VIPs having been evaluated using experimental and numerical methods. To confirm and generate numerical models for VIP analysis, micro-computed tomography (micro-CT) was utilized. The obtained results show that insulation effects increase effectively when panels with lightweight concrete are in a vacuum, and both foamed concrete types can be effectively used as VIP core materials. [ABSTRACT FROM AUTHOR]

This study aims to more accurately investigate the pore size distribution of air voids in cement-based materials. For this purpose, micro-computed tomography (micro-CT) images were used to describe the inner structure of target materials, without damaging them. Together with the data obtained and the imaging techniques used, the pore structures of the specimens were visualized in 3D, with the pore size distributions being investigated using a volume-based method. The chord-length distribution, another approach to describe heterogeneous pore characteristics, was computed from 3D micro-CT images and compared with the conventional method. A RapidAir 457, an automated air void analyzer, was also used as a reference, with the results obtained being quantitatively and qualitatively compared using several curve fitting algorithms. The correlation between the pore characteristics and the mechanical properties of the specimens was examined, with the results indicating that the pore size distribution described using chord-length distribution is more effective than the conventional volume-based method. The results obtained can be utilized to investigate and predict material properties. • Two methods (2D and 3D) of pore size distribution investigation of concretes were analyzed • Concretes with different air-entraining agent dosages were produced • X-ray micro-computed tomography (micro-CT) method has been applied to obtain a 3D volumetric images of concretes • The correlation between the pore characteristics and the mechanical properties of the specimens was examined • Chord-length distribution can be effectively used to describe pore size distribution in 3D by incorporating micro-CT. [ABSTRACT FROM AUTHOR]

Improving the thermal insulation properties of cement-based materials is the key to reducing energy loss and consumption in buildings. Lightweight cement-based composites can be used efficiently for this purpose, as a structural material with load bearing ability or as a non-structural one for thermal insulation. In this research, lightweight cement pastes containing fly ash and cement were prepared and tested. In these mixes, three different techniques for producing air voids inside the cement paste were used through the incorporation of aluminum powder (AL), air entraining agent (AA), and hollow microspheres (AS). Several experiments were carried out in order to examine the structural and physical characteristics of the cement composites, including dry density, compressive strength, porosity and absorption. A Hot Disk device was used to evaluate the thermal conductivity of different cement composites. In addition, X-ray micro-computed tomography (micro-CT) was adopted to investigate the microstructure of the air-entrained cement pastes and the spatial distribution of the voids inside pastes without destroying the specimens. The experimental results obtained showed that AS specimens with admixture of hollow microspheres can improve the compressive strength of cement composites compared to other air entraining admixtures at the same density level. It was also confirmed that the incorporation of aluminum powder creates large voids, which have a negative effect on specimens' strength and absorption. [ABSTRACT FROM AUTHOR]

This study investigates the addition of Poly-vinyl Alcohol (PVA) fibres and attapulgite nanoclay to alkali-activated materials (AAMs) with the aim of enhancing the mechanical performance and optimizing the printability and buildability of AAMs. The fresh properties of six mix formulations, including flowability, slump values, rheology, shape retention, and extrusion window, were evaluated. The best performing mixes, that exhibited optimal fresh properties, were 3D printed, and their mechanical performance, microstructure, and buildability were investigated. The addition of 1 wt.-% attapulgite nanoclay (i.e. A-1) showed the desirable fresh properties required for 3D printing, as well as providing sufficient mechanical reinforcement to the samples. The 3D printed A-1 samples showed an improved flexural and compressive strength by 43% and 20%, respectively, compared to both the casted and printed control mixes. Moreover, microstructure analysis, including SEM, Rapidair measurement, and micro-CT, provided evidence of the compatibility by showing the lowest pores anisotropy and mixture homogeneity, between attapulgite and AAMs. [Display omitted] • Poly-vinyl alcohol fibres and attapulgite nanoclay as additives for 3D printable alkali-activated materials • P0.25 and A-1alkali-activated composites were found to be the best performing sample for 3D printability and mechanical performance • The microstructure analysis showed the effectiveness of attapulgite and PVA fibres incorporation in filling the voids and crack bridging mechanisms [ABSTRACT FROM AUTHOR]