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This study presents a new approach towards the production of sol-gel silica-coated Bi2O3/Gd2O3 cement additives towards the improvement of early mechanical performance and radiation attenuation. Two types of silica coatings, which varied in synthesis method and morphology, were used to coat Bi2O3/Gd2O3 structures and evaluated as a cement filler in Portland cement pastes. Isothermal calorimetry studies and early strength evaluations confirmed that both proposed coating types can overcome retarded cement hydration process, attributed to Bi2O3 presence, resulting in improved one day compressive strength by 300% and 251% (depending on coating method) when compared to paste containing pristine Bi2O3 and Gd2O3 particles. Moreover, depending on the type of chosen coating type, various rheological performances of cement pastes can be achieved. Thanks to the proposed combination of materials, both gamma-rays and slow neutron attenuation in cement pastes can be simultaneously improved. The introduction of silica coating resulted in an increment of the gamma-ray and neutron shielding thanks to the increased probability of radiation interaction. Along with the positive early age effects of the synthesized structures, the 28 day mechanical performance of cement pastes was not suppressed, and was found to be comparable to that of the control specimen. As an outcome, silica-coated structures can be successfully used in radiation-shielding cement-based composites, e.g. with demanding early age performances. [ABSTRACT FROM AUTHOR]

Abstract This study aims to investigate the effects of carbon nanotubes and carbon nanotube-silica core-shell structures, on the behaviour of cement pastes exposed to high temperature (300, 450 and 600 ° C). Pristine multi-walled carbon nanotubes (MWCNTs) were coated with a solid nanosilica (NS) shell, to form a core-shell nanostructure (MWCNT/NS). The cement pastes were incorporated with three different nanomaterial contents equal to 0.125, 0.25 and 0.5 wt.-% of cement. The results demonstrate that incorporation of an optimum amount (0.125 wt.-%) of MWCNT/NSs, is much more beneficial than the incorporation of MWCNTs, for improving the properties of unheated and heated cement pastes. Silica shell improves the binding ability between cement matrices and nanotubes, which is reflected in specimens' compressive strength retention, as well as in decreased micro-cracking. However, exceeding the optimum amount of MWCNTs and MWCNT/NSs can lead to an agglomeration of nanomaterial, thus decreasing the thermal resistance of cement pastes. Graphical abstract Image 1 Highlights • Proposal of a green method of carbon nanotube-nanosilica (MWCNT/NS) core shell structure synthesis. • The use of MWCNT/NSs is more beneficial than the use of pristine MWCNTs, for compressive strength improvement. • MWCNT/NS structures present better mechanical and microstructural performance under elevated temperature. • Incorporation of MWNCT and MWCNT/NS decreases the cracking of specimens under elevated temperature. [ABSTRACT FROM AUTHOR]

This study investigates the effects of Fe 3 O 4 and Fe 3 O 4 /SiO 2 nanoparticle admixtures on the behavior of cement mortars exposed to elevated temperatures. Pristine nanoparticles of magnetite (Fe 3 O 4 ) were coated with a solid silica shell (via the Stöber method), to form a core-shell nanostructure (Fe 3 O 4 /SiO 2 ). The cement mortars were incorporated with an optimized ratio of 3 wt% Fe 3 O 4 and 5 wt% of Fe 3 O 4 /SiO 2 admixture. The specimens were exposed to elevated temperatures of 200, 300, 450, 600 and 800 °C. After cooling, the mass loss and flexural and compressive strengths of the specimens were determined. The results demonstrated that the presence of magnetite-silica (Fe 3 O 4 /SiO 2 ) nanostructures is much more beneficial for improving the thermal resistance of cement mortars than pristine Fe 3 O 4 nanoparticles. The silica (SiO 2 ) shell in the nanoparticles improves residual compressive strength and prevents crack extension in cement mortars exposed to elevated temperatures. The investigations undertaken in this study were supported by optical and scanning electron microscopic studies. [ABSTRACT FROM AUTHOR]

Recently, the recycling ofwaste glass has become aworldwide issue in the reduction ofwaste and energy consumption.Waste glass can be utilized in construction materials, and understanding its effects on material properties is crucial in developing advanced materials. In this study, recycled crushed and expanded glasses are used as lightweight aggregates for concrete, and their relation to the material characteristics and properties is investigated using several approaches. Lightweight concrete specimens containing only crushed and expanded waste glass as fine aggregates are produced, and their pore and structural characteristics are examined using image-based methods, such as scanning electron microscopy (SEM), X-ray computed tomography (CT) and automated image analysis (RapidAir). The thermal properties of the materials are measured using both Hot Disk and ISOMET devices to enhance measurement accuracy. Mechanical properties are also evaluated and the correlation between material characteristics and properties is evaluated. As a control group, a concrete specimen with natural fine sand is prepared, and its characteristics are compared with those of the specimens containing crushed and expanded waste glass aggregates. The obtained results support the usability of crushed and expanded waste glass aggregates as alternative lightweight aggregates. [ABSTRACT FROM AUTHOR]

The scope of the study is to test the influence of nanocomposite silica-titania (mSiO 2 /TiO 2 ) core-shell structures on the mechanical and bactericidal properties of cement mortars. Nanocomposites are widely applied in many fields of science however, cement-based composites are mainly modified with single type of nanostructures. The goal of the presented work is to obtain a nanocomposite which exhibits the positive properties of both nanomaterials, while diminishing the negative impacts of each of the nanomaterials applied separately. The study shows that application of silica-titania (mSiO 2 /TiO 2 ) core-shell nanostructures simultaneously demonstrated the properties of nanosilica and titanium dioxide and thus the nanomaterial behaved not only as a filler to improve the microstructure and activator to promote pozzolanic reaction, but also exhibited self-cleaning and bactericidal properties when exposed to UV light. The observed improvement of compressive strength was caused by the presence of nanosilica (acting as a core) while titanium dioxide (shell) exhibits photocatalytic activity. [ABSTRACT FROM AUTHOR]

In recent years utilization of solid waste in building materials has gathered spectacular attention. One material with potential applications, especially in cement-based composites, is waste glass. The aim of this study was to evaluate the possibility of manufacturing sustainable cement mortars with the use of nanosilica (NS) and brown soda-lime waste glass (WG) fine aggregate. The mechanical and thermal properties of cement mortars containing WG aggregate and nanosilica, were analyzed in terms of waste glass and nanosilica content. Ordinary fine aggregate (river sand) was replaced with WG fine aggregate at a ratio of 100% by weight. Moreover, 0, 1 and 3 wt% of NS was incorporated to cement mortar. The experiment revealed that the presence of WG fine aggregate significantly decreased the thermal conductivity of the cement mortars and that furthermore, the sorptivity coefficient decreased. The study has shown that WG fine aggregate can be a successful substitute for natural fine sand without leading to mechanical deterioration and by significantly improving thermal properties of cement mortars. Additionally, the incorporation of nanosilica (especially in higher contents – 3 wt%) leads to a further decrement in thermal conductivity and sorptivity and improves compressive strength. [ABSTRACT FROM AUTHOR]

In this contribution the effect of nanosilica (NS) on the behavior of cement mortars containing quartz aggregate and two types of heavyweight aggregates (magnetite and barite) exposed to elevated temperature will be investigated. The cement mortars have been modified with nanosilica in quantities of 1%, 2%, 3%, 4% and 5% (by weight of cement). The samples were exposed to the elevated temperatures of 200 °C, 400 °C, 600 °C and 800 °C, respectively. The mass loss, flexural and compressive strength of the cooled specimens were determined. Additionally, by means of scanning electron microscopy (SEM) and optical microscopy the structure defects have been determined. The results clearly demonstrate that there is an optimal nanosilica content, in the cement mortar containing quartz and magnetite aggregate, improving the thermal resistance and preventing the crack extension (especially in the range of 200–400 °C). However, the study has also shown that cement mortars containing barite aggregate tend to crack and exhibit spalling as a result of low thermal resistance of the aggregate. [ABSTRACT FROM AUTHOR]

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]

• The effects of micro-Bi 2 O 3 and nano-Bi 2 O 3 powders were compared. • Incorporation of high dosage of nano-Bi 2 O 3 results in lower strength loss when compared to micro-Bi 2 O 3. • Addition of both Bi 2 O 3 powders enhances the gamma-ray shielding capability of pastes. • Addition of nano-Bi 2 O 3 improved the slow neutron attenuation ability of cement pastes. • Both Bi 2 O 3 powders are effective in producing lead-free cementitious composites with improved shielding properties. This study presents a comparison of the effects of micro-Bi 2 O 3 and nano-Bi 2 O 3 powders on the mechanical, microstructural and gamma / neutron shielding properties of Portland cement pastes. Cement pastes with various ratios of cement (up to 30 wt-%) replaced with Bi 2 O 3 micro and nanoparticles were prepared. Consistency, compressive strength, water accessible porosity and mercury intrusion porosimetry tests were performed, in order to characterize their engineering properties. In addition, experimental and theoretical evaluations of γ-ray and neutron shielding properties were performed. The results showed that the incorporation of Bi 2 O 3 powders gradually leads to a decline in cement pastes' compressive strength and an increase in their porosity, as the amount of powder is increased. However, the deterioration rate varies depending of type of powder used, in favor of nano-Bi 2 O 3. Gamma attenuation tests results indicate that the addition of Bi 2 O 3 powders enhances the shielding capability of pastes, in the energy range of interest (0.08–2.614 MeV). However, the effects of particle size on γ-ray attenuation are negligible in that energy range. Slow neutron attenuation study showed that the addition of nano-Bi 2 O 3 improved the shielding ability of cement pastes, with enhancements ranging between 15.3% and 25.5% for samples with 5 and 30 wt-% nano-Bi 2 O 3 , respectively. In conclusion, this study shows that the addition of nano or micro-Bi 2 O 3 is effective in producing lead-free cementitious composites with improved γ-ray and neutron shielding properties. Unlike gamma shielding, nano-sized Bi 2 O 3 has a better ability to attenuate neutrons, in comparison to their micro-sized counterparts. [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 presents the results of an experimental investigation of the effects of nanosilica (NS) on the strength development, transport properties, thermal conductivity, air-void, and pore characteristics of lightweight aggregate concrete (LWAC), with an oven-dry density <1000 kg/m3. Four types of concrete mixtures, containing 0 wt.%, 1 wt.%, 2 wt.%, and 4 wt.% of NS were prepared. The development of flexural and compressive strengths was determined for up to 90 days of curing. In addition, transport properties and microstructural properties were determined, with the use of RapidAir, mercury intrusion porosimetry (MIP), and scanning electron microscopy (SEM) techniques. The experimental results showed that NS has remarkable effects on the mechanical and transport properties of LWACs, even in small dosages. A significant improvement in strength and a reduction of transport properties, in specimens with an increased NS content, was observed. However, the positive effects of NS were more pronounced when a higher amount was incorporated into the mixtures (>1 wt.%). NS contributed to compaction of the LWAC matrix and a modification of the air-void system, by increasing the amount of solid content and refining the fine pore structure, which translated to a noticeable improvement in mechanical and transport properties. On the other hand, NS decreased the consistency, while increasing the viscosity of the fresh mixture. An increment of superplasticizer (SP), along with a decrement of stabilizer (ST) dosages, are thus required. [ABSTRACT FROM AUTHOR]

• Magnesite was used as a precursor for synthesizing alkali-activated binder. • Magnesite was activated by sodium hydroxide, silicate and aluminate. • Adding lead glass sludge enhanced the polymerization of magnesium silicate hydrate. • Magnesite based binder recorded 28-day compressive strength of 9–53 MPa. • The prepared binder showed high efficiency in the stabilization of Pb inside sludge. The present paper focuses on synthesizing an alkali-activated binder, in which magnesium carbonate (MC) was the only precursor. MC was individually activated with sodium hydroxide (NaOH), sodium silicate (Na 2 SiO 3) and sodium aluminate (NaAlO 2). Increasing Na 2 O content (as NaOH) up to 10 wt% enhanced the compressive strength slightly. At constant Na 2 O content (10 wt%), the sample activated by (Na 2 SiO 3) recorded the highest compressive strength. Although the hardened mixture activated by NaAlO 2 showed the higher compressive strength compared to NaOH-activated sample, it still recorded strength lower than Na 2 SiO 3 -activated-mixture. XRD, TG/DTG, FTIR, and SEM techniques indicated that phase composition depends mainly on the Na 2 O source. 29Si MAS-NMR spectroscopy verified the formation of magnesium silicate hydrate with Q1, Q2, and Q3 silicate connectivity, when MC was activated with Na 2 SiO 3. Incorporating lead glass sludge (LGS) as a silicate source, enhances the formation of a cross-like silicate chain (Q3) coinciding with an improvement of the compressive strength and a retardation of Pb-leachability. As proved by 27Al MAS-NMR, Al inside hydrotalcite phase, formed within NaAlO 2 -activated-MC, has six coordination bonds. Activating MC with NaOH produces magnesium hydroxide (Mg(OH) 2) and thermonatrite Na 2 CO 3 ·H 2 O phases. Owing to the diversity of the hydration products, a wide range of 90-day compressive strengths (9–53 MPa) was recorded. A preliminary result showed that the CO 2 -emission generates from optimum mixture containing 30 wt% LGS is lower than resulted from Portland cement manufacturing. [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]

• Katoite (KT) binder is fabricated by mixing dolomite powder with sodium aluminate. • Both KT and unreacted dolomite powder completely decomposed at 1000 °C. • Thermally-exposed KT powder can be rehydrate to yield layered-double hydroxide. • Using silicate waste powder enhanced firing resistance but inhibit the rehydration. This study investigated the effect of red-clay brick and perlite wastes (RCBW and PW) on the performance and rehydration of katoite-based binder after exposure to elevated temperatures. The KT-binder was produced by combining dolomite waste with sodium aluminate. The exposure of KT binder to temperatures up to 1000 °C (CA-1000) caused a significant compressive strength loss associated with the decomposition of KTand other phases into mayenite, sodium aluminate, and lime. The CA-1000 acts as a one-part alkali-activated binder, as it can re-interact with water to yield a layered double hydroxide-based binder with 1-day compressive strength of 9.7 MPa and volume expansion of 160%. The individual inclusion of 50 wt% RCBW and PW improved the thermal resistance of the CA-binder but decreased its ability to rehydrate, as they hindered the reformation of sodium aluminate and mayenite through the formation of lower hydraulic calcium/sodium aluminosilicates. [ABSTRACT FROM AUTHOR]

Highlights • The characteristics and properties of lightweight aggregate concrete and foamed concrete with the same density levels were investigated based on image analysis. • SEM images confirmed that the solid structures of the matrix in foamed concrete are relatively denser than that of lightweight aggregate concrete. • The micro-CT images demonstrated that foamed concrete has larger porosity than lightweight aggregate concrete when the material density is similar. • The proper use of lightweight aggregate concrete can be more beneficial in terms of having a material with better mechanical performance by minimizing the loss of the insulation effect. Abstract Lightweight concrete is a special type of concrete with low density and advanced insulation, mainly produced using lightweight aggregates or a cellular matrix. Concrete material made of lightweight aggregates is called lightweight aggregate concrete, while material made from a cellular matrix is generally called foamed concrete because of the pores introduced by a foaming agent. Both lightweight concrete types have different characteristics due to their different compositions. In this study, the material properties and characteristics of these lightweight concretes were investigated and compared. A series of foamed and lightweight aggregate concrete specimens with the same density level were produced, with their mechanical and thermal properties being evaluated using sensitive measurement tools. X-ray micro-computed tomography (μ -CT) and scanning electron microscopy (SEM) were used to characterize each material, using image-based techniques. The results brought to light the details of each lightweight concrete, at the microstructural level, in regard to their material properties and showed that the properly designed lightweight aggregate concrete can be more beneficial in mechanical performance by minimizing the loss of the insulation. [ABSTRACT FROM AUTHOR]

[Display omitted] • Natural and calcined Halloysite clay additives were characterised. • Halloysite clay additives were incorporated to modify AAMs' printing properties. • Enhanced compatibility of calcined Halloysite clay additives in the AAMs was verified. • Buildability and mechanical properties were improved in CH-modified AAMs. This study investigates the effects of natural and calcined halloysite clay minerals ("NH" and "CH", respectively) on the performance of 3D printed alkali-activated materials (AAMs). Halloysite clay minerals are selected as they are low-cost and abundantly available. At first, different characterisation techniques were employed to characterise the NH and CH additives. Mechanical performance, extrusion window, and shape stability of several AAM formulations containing various dosages (0.5 wt% to 5 wt%) of the NH and CH additives were evaluated. The best-performing mixtures in terms of fresh and hardened properties namely, NH-1.5 and CH-1.5 mixtures (containing 1.5 wt% of NH and CH additives, respectively) were then selected for 3D printing. The results showed that the CH-1.5 mixture exhibited enhanced shape stability, buildability, and mechanical properties as compared to the control mixture. The flexural and compressive strengths of 3D printed CH-1.5 samples were 88% and 40%, respectively higher than those of the printed control samples. Using the CH-1.5 mixture, a twisted column with an intricate shape was printed to verify the suitability of the developed CH-modified AAM for the construction of complex structures. This study establishes the use of halloysite clay minerals as low-cost additives for enhancing the mechanical properties and printing performance of AAMs. [ABSTRACT FROM AUTHOR]