Increase In Open Porosity Research Articles

Formulating Geopolymer Mortars through Construction and Demolition Waste (CDW) Recycling: A Comprehensive Case Study

The overall amount of construction and demolition waste (CDW) is steadily increasing due to urbanization-related phenomena in metropolitan cities. Only a small fraction is recycled to produce new concrete, a practice that would avoid the exploitation of natural aggregates. Furthermore, the Portland cement production process causes the release of high values of CO2 emissions into the atmosphere, increasing the global warming potential. For these reasons, materials alternative to ordinary Portland cement (OPC) are becoming more and more widespread, such as alkali-activated materials, which, when used with recycled aggregates, could become environmentally friendly substitutes for traditional concrete. During this study, various mix designs were formulated for alkali-activated metakaolin mortars containing recycled concrete aggregates. Their properties in the fresh and hardened states were analyzed. The main problem encountered was the presence of the adhered mortar layer on the recycled concrete aggregate. This layer not only caused a detrimental effect deriving from the increase in open porosity but also activated competitive reactions which partially compromised the alkali activation of metakaolin. All these phenomena deteriorated the final compressive strength of the composites containing recycled aggregates, which after 28 days, was around 20 MPa for samples with 12.5% of replacement of natural aggregate and 15 MPa for those with 25% of replacement, corresponding to a reduction of 35% and 50% compared to the standard sample without replacement, respectively.

Effect of Salt Mist Ageing on the Physical and Mechanical Properties of Two Ignimbrites from the Canary Islands (Spain).

The aim of this research work is to study the effect of salt mist ageing on the physico-mechanical properties of two ignimbrites from the Canary Islands (Spain). Due to their insular nature and extensive coastlines, these regions are highly susceptible to atmospheric salt aerosols, which is a significant weathering agent for building materials. The ignimbrites analysed are marketed under the names "Azul Lomo Tomás de León" and "Marrón de Abades" and are widely used as building stones. Petrographic, mineralogical and chemical properties were obtained via polarisation microscopy, X-ray diffraction and X-ray fluorescence. The samples were subjected to 60 cycles of a salt mist environment, following relevant European standards. Scanning electron microscopy images of the specimens were analysed along with physical properties, including apparent density, open porosity, water absorption, colourimetry and ultrasound propagation velocity, initially and after every 20 cycles, allowing us to assess their evolution during the ageing test. Mechanical properties were evaluated using uniaxial compressive strength and flexural strength under concentrated load tests on two groups of specimens: one unaged and the other subjected to 60 ageing cycles. With the exception of apparent density, the other properties show a decrease between 5% and 30%. However, open porosity increases and is one of the properties most affected by the ageing test.

Laboratorial Study of the Combined Effect of SO2 and High-Temperature Ageing on the Physical and Mechanical Properties of Encostinha Marble, a Portuguese Stone

ABSTRACT The effects of SO2, high temperature (600°C) and cooling type (slow and rapid) were investigated in this study as decay factors of a building stone (Encostinha Marble). Changes in colour, gloss, apparent density, open porosity, capillary water absorption and ultrasonic pulse velocity were assessed, complemented with SEM observations and XRD analysis. SO2 did not significantly react with the marble; no neoformed products were identified and only superficial changes were registered. Specimens became darker and duller. The increase in size of pre-existing microcracks and the development of new ones caused by high temperature, with a consequent increase in open porosity, was the main cause of the marked degradation of physical and mechanical properties. The cooling type was also shown to influence the physical and mechanical characteristics of the marble. A more pronounced increase in open porosity and capillary water absorption in specimens cooled by total immersion in tap water was observed. This increase was not in line with the corresponding decrease in ultrasonic parameter values.

Study on mechanism of strength weakening of concrete subjected to microwaves in microwave-assisted concrete recycling

This paper explores the multi-field distribution in concrete by coupling of the electromagnetics, heat transfer and solid mechanics in COMSOL Multiphysics software under microwave irradiation. The numerical model is validated by the temperature data captured from the experiment. The physicochemical reactions in mortar and aggregate during heating and evolution of surface cracks are further investigated by the tests. The results show that when the radiation effect is considered above 100 °C, the simulated temperature profile is in alignment with the experimental one. The hot spots formed by heating exist at surface edges and in aggregate area on the cross section. The maximum tensile stress and compressive stress appear at the boundary on the cross section. Although the stress in aggregate is greater than that in mortar, it maintains in the elastic deformation stage, whereas mortar will undergo the plastic strain with the strain over 0.04%, approximately rheological behavior. In the first 100 s of heating, the migration and evaporation of water and the dehydration of hydration products are the main factors of strength degradation of concrete, which is manifested by the generation and propagation of cracks and the decrease in density. The initial position of visible cracks has a lot to do with the path of moisture migration. The surface cracks have been coalesced over stress relief caused by the increase in open porosity after heating for 150 s. The pore pressure induced by moisture migration and thermal stress caused by temperature gradient initiate more internal cracks. This paper can provide reference and insight for effective strength weakening of concrete exposed to microwaves so as to make its weakened mechanical properties can work to recovery of high-quality aggregate after mechanical crushing.

Study of keto-hydrazide crosslinking effect in acrylic latex applied to Portland cements with respect to physical properties

Polymer-modified Portland-based composites are of interest for specific applications, in reason of their properties. There are different types of commercial additives and waste polymer-based materials applied to cement-based composites, however, their impacts on the environment are debatable. This work has prepared new acrylic latex additives with and without keto-hydrazide crosslinking from standardly available low-cost raw monomers. The influence of their incorporation into Portland cement-based fine-grained mortars has been investigated. The obtained results indicate that the highest effect on heat flow evolution changes has been detected in the case of latexes without crosslinking. The incorporation of both latex types into produced cement composites resulted in a significant increase in open porosity connected with the gradual decrease in mechanical resistance, especially the compressive strength. On the other hand, an important mitigation of liquid water transport properties of latex-modified composites has been achieved, and such properties can be tuned according to the used latex type and its concentration. The developed latex cement-based composites may find utilization as special materials for structures or products for water-loaded constructions or in areas with high concentrations of water-soluble salts or other pollutants.

Laboratorial Simulation for Assessing the Performance of Slates as Construction Materials in Cold Climates

This paper presents the results of a laboratory simulation of a subarctic climate carried out in climatic chamber. Realistic daily and seasonal cycles of temperature of a regular subarctic continental climate without dry seasons (Dfc) were simulated and the physical/mechanical properties and performance of the slates were assessed. The slate was selected because of its use as cladding and roofing material in cold regions. Mechanical performances before and after Dfc climate simulation were evaluated through point load index, uniaxial compression, flexural strength and anchor rupture load. A decrease in these mechanical features between 9 and 50% with respect to the initial strengths has been registered. Other physical parameters such as apparent density, open porosity and water absorption were evaluated. The tests showed an increase in open porosity (+72%) and a decrease in bulk density (−0.7%). The results highlighted a predominantly physical decay and mechanical performance decreasing with a relevant lowering in strength without the detection of chemical–mineralogical alterations. Moreover, artificial sun exposure reproduced the weak solar radiation that characterizes the Dfc climate. This was carried out to assess the aesthetic characteristics of the slate, since discoloration under sun exposure was supposed to occur but the slates did not exhibit substantial color changes.

Silicon carbide microfiltration membranes for oil-water separation: Pore structure-dependent wettability matters

Both the pore size and surface properties of silicon carbide (SiC) membranes are demonstrated to significantly affect their separation efficiency when used for oily water treatment. However, the potential influences of open porosity together with the pore size of SiC membranes on their surface properties and oil-water separation performance have rarely been investigated. In this work, porous SiC ceramic membranes with tunable open porosity and pore size were purposely prepared and selected to systematically study the effect of pore structure-dependent wettability on the oil-water separation performance. The measured pure water flux of selected membranes as a function of open porosity (34–48%) and pore size (0.43–0.67 μm) was well-fitted by using a modified H-P equation. Interestingly, the hydrophilicity of SiC membranes was improved with the increase in open porosity and pore size, as evidenced by the gradually decreased dynamic water contact angle and underwater adhesion of oil droplets. Further, the open porosity of SiC membranes was found to contribute more to the improved surface wettability. As a result, the stable flux of SiC membranes in oil-in-water (O/W) emulsions was increased by 24% with the increased open porosity while the oil rejection rate remained above 90%. This work quantitatively reveals the contributions of the pore structure to the surface wettability of ceramic membranes, and thus provides an effective pathway to improve their performance in oil-water separation.

Use of Wood Waste as Aggregate in Mortars: An Experimental Study

The construction sector is one of the largest and most active in the world economy, being responsible for consumption of huge amounts of natural resources. Natural sand and gravel are the most important resources in construction, they are mainly used as aggregates, and its extraction often causes environmental damages. Bearing these considerations in mind, the wood waste has been used as partial replacement of natural sand in concrete and mortars to reduce the environmental burden of natural sand extraction. The aim of this paper is to characterize the physical and mechanical properties of natural hydraulic lime-based mortars proportioned with different percentages of wood wastes (0% to 30%) as replacement of natural sand. Thus, several specimens of mortar proportioned with wood wastes have been subjected to different experimental procedures, such as: workability, mechanical strength, water absorption and thermal conductivity. Results obtained showed that the incorporation of wood waste causes a reduction of mechanical resistance mostly due to the increase in open porosity, but on the other hand the thermal conductivity presents an improvement up to 83%. The results obtained are quite acceptable and encouraging for the follow-up studies using wood wastes as fine aggregate in mortars and, simultaneously, to improve the energy efficiency of buildings since this waste material contributes to obtain mortars with improved thermal performance.

Porous Ni-Cr-Mo-Cu alloys fabricated by elemental powder reactive synthesis

Fabrication of porous Ni-Cr-Mo-Cu alloys is available through Ni, Cr, Mo and Cu elemental powder reactive synthesis at the sintering temperature of 1150 °C. The pore structures, including swelling behavior, open porosity, pore size and viscous permeability of the porous Ni-Cr-Mo-Cu alloys are systematically investigated. The results revealed that the parameters of pore structure firstly increased, and then decreased with the increase of the sintering temperature. When the sintering temperature rose to 1000 °C, the volume expansion, open porosity and viscous permeability of porous Ni-Cr-Mo-Cu alloys reached the peak value of 8.0%, 41.6% and 17.2 μm2, respectively. In addition, it was confirmed that the pore structure evolution was based on three stages, that is, in the low temperature section before stearic acid decomposition, the formation of pores was initiated by the volatilization of pore-forming agent and the interstitial pores of green compact; when the temperature was lower than 1083 °C, the increase of open porosity was mainly due to the Kirkendall effect caused by solid partial diffusion; while, when the temperature is within the range of 1083 ∼ 1150 °C, the shrinkage behavior at high temperature and a small amount of metal solution formed by the unreacted Cu led to decrease in pore structure parameters.

Cu- and Zn-doped alkali activated mortar – Properties and durability in (bio)chemically aggressive wastewater environments

Metakaolin-based alkali activated mortars (AAM) - with and without CuSO4·5H2O and ZnO addition (mass ratio Mn+/solid binder 0.08% to 1.7%) - were casted and exposed within an extensive long-term field campaign over the period of 20 months to a sewer basin, strongly affected by biogenic acid corrosion. (Un-)exposed AAM were tested regarding their physicochemical and microstructural properties, bioreceptivity and overall durability. Metal addition led to a retarding effect during alkali-activation reaction, as well as to an increase in open porosity of up to 3.0% and corresponding lower compressive strength of up to 10.9%. Reduced microbial colonization and diversity were observed on AAM with Cu, while Zn addition led to increased biodiversity. We propose that the observed higher durability of Cu-doped AAM is due to antibacterial effects and associated reduction of biogenic acid production, superseding overall negative effects of metal-dosage on physical material properties. Observed lower durability of Zn-doped AAM was related to combined negative physicochemical and microbial effects.

Three dimensional characterization of micronized soybean seeds using X-ray microtomography

The efficacy of critical processing techniques, such as micronization, relies on the microstructural changes that take place in foods as they go through the various unit operations. X-ray microtomography or computed microtomograhy (μCT) can serve as a means to non-invasively and non-destructively characterize the complex structure of food matrices. Herein, high resolution X-ray μCT was used to visualize and quantify the effect of micronization or infrared (IR) treatment on the microstructure of soybeans at different micronization durations (60, 90, and 120 s), and initial moisture contents (12, 16, 20, and 24% wb). The study includes a quantitative and qualitative analysis of soybean microstructure using 2D and 3D images to assess total porosity, volumetric changes, bulk and particle densities, drying rate, and colour. All of these parameters showed significant changes as micronization time and initial moisture content increased. Although higher initial moisture contents (20 and 24%) improved volumetric expansion and total porosity of soybean kernels, formation of large surface cracks and darkening due to IR heating rendered 24% moisture content unsuitable. Soybeans with an initial moisture content of 20%, subjected to 90 s and 120 s of micronization showed comparable lightness L*values (63.23 ± 3.9 and 61.1 ± 4.1, respectively) to the unprocessed soybean (67.22). These beans also showed the minimal increase in open porosity (5.72–6.06%) but an appreciable increase in total porosity (9.8–11%) was noticed. The results of this study on microstructure and qualitative parameters of micronized soybeans could be used to further optimize the microwave assisted roasting and drying processes of beans and pulses.

Selected Properties of Clay-Ash Composite Containing Bottom Ash from Combustion of Wood - Coconut Shells Biomass

In this article, the influence of the addition of the bottom ash to clay on the selected physical and mechanical properties of ceramic composite are discussed. The biomass (80% wood with the addition of 20% coconut shells) was combustion in the fluidised-bed boiler. The tests were carried out on the samples, in which the contents of bottom ash in relation to clay ranged from 5 to 15%. The absorbability, open porosity, apparent density, compression strength and freeze resistance have been determined. The obtained test results indicate that the increase of this bottom ash in clay-ash composite causes the increase of open porosity, absorbability and compression strength, but a reduction in resistance against frost attract.

Natural hydraulic lime mortars - The effect of ceramic residues on physical and mechanical behaviour

In the past, it was common the use of ceramic residues as a pozzolan and/or aggregate in air lime mortars and concrete. Nowadays, incorporating ceramic residues in mortars is one of the ways to increase sustainability of the construction sector and introduce some benefits in the properties of those mortars.Ceramic residues were collected from several ceramic industries, namely from bricks, roof tiles and pots production, milled in laboratory and incorporated in natural hydraulic lime (NHL) mortars. Two distinct groups of mortars were prepared, with two different proportions, and samples were produced. A group with a volumetric proportion of one part of NHL and three parts of aggregate (1:3) and three different percentages of replacement of the aggregate by each of the residues (0, 20 and 40% in volume) and a second group with a volumetric proportion of one part of NHL and four parts of aggregate (1:4) and percentages of replacement of 0 and 30% were prepared. Their behaviour was analysed by determining its properties after 28 days of curing.The incorporation of ceramic residues in the NHL mortars led to an increase in open porosity, capillarity water absorption and water vapour permeability but also an increase in dynamic elasticity modulus and mechanical strengths. This increase was more significant for higher replacement percentages. The behaviour of these mortars seems appropriate for new construction renders and plasters but caution must be taken concerning moisture migration, namely when used in rehabilitation.

Sintering, crystallization and foaming of La2O3•SrO•5B2O3 glass powders: effect of the holding time

Sintering, crystallization and foaming of nano glass powders with composition La2O3•SrO•5B2O3 were studied by hot stage microscopy (HSM) and simultaneous thermal analysis (DTA-TG) under non-isothermal regime at 10°C/min and by optical contactless dilatometer under isothermal conditions at 700 °C up to 10 hours for different times. After the thermal treatments, specimens were characterized by gas pycnometry, X-ray Powder Diffraction (XRD) and Field Emission Scanning Electron Microscopes (FE-SEM).The results demonstrate that the densification completed before the crystallization process, thus forming well sintered samples. Then, during the phase formation gas is released, which leads to foaming process. After holding of 160 minutes at 700°C the degree of crystallization reached about 0.8 and the foaming stopped. The obtained sample had high closed porosity and quite intriguing structure composed of two fairly different crystal arrangements. The first was “sponge-like”, while the second was denser and consisted of “sheets”, 10-30 nm thick. The subsequent holding led to re-crystallization, formation of larger denser zones that reached even 10-15 µm and an increase in open porosity. These results highlight that in the case of sinter crystallization of nano powders, some intriguing features can be expected.

Using TiO2 nanoparticles as a SO2 catalyst in cement mortars

Titanium dioxide (TiO2) has been used in building materials to produce products that do not require major maintenance and also contribute to improve air quality and extend the life of buildings. Thus, this research evaluated the effects of incorporation of this substance into cement mortars in the process of degradation of sulfur dioxide (SO2), one of the largest atmospheric pollutants. Mortars were developed at a weight ratio of 1:3 (cement: sand), incorporating 2.5%, 5%, 7.5% and 10% of TiO2 relative to the cement weight. Mortars were evaluated in their fresh state (consistency and bulk density) and hardened (dry bulk density, water absorption by capillarity, open porosity and flexural and compressive strength). The samples were exposed to an accelerated aging SO2 (pollutant) chamber, then moistened and exposed to ultraviolet radiation. For this exposure of the samples, two Light Emitter Diodes (LEDs) with wavelengths covering the UV-A range were used: UV (380–420 nm) and blue (420–493 nm). Fourier Transform Infrared measurements were also performed in three stages, which were: (1) before contamination, (2) after SO2 contamination and (3) after radiation exposure. The nano TiO2 incorporation in the mortars contributed to the increase in open porosity and favored the increase in dry bulk density of mortars this was due to the filler effect. In addition, there was an increase in both the compressive strength and the flexural strength for mortars with addition, compared with the reference mortar. It can be concluded that the incorporation of TiO2 improved the physical, mechanical and photocatalytic properties, and enabled the decontamination of mortars due to the action of the SO2 pollutant.

New insight into the modification of pore structure in porous ceramics prepared from fly ash rich in CaO

AbstractPorous ceramics with high open porosity and good mechanical properties were successfully prepared from fly ash rich in CaO. An addition of 30–50wt.% dolomite decreased the average pore diameter from ∼11.79 μm to ∼2.82μm due to the decrease of viscosity with high dolomite addition, while there is an increase in open porosity from 48.63% to 53.23%. SEM results suggested that pores were firstly surrounded by glassy phase. With the addition of more than 30 wt.% of dolomite, pores were covered by loose structure. XRD results showed the changes in crystal phases of sintered ceramics, from anorthite sodian to alkaline basalt and then to calcium magnesium silicate. CaO and MgO from decomposed dolomite were proposed to be the main reason on modification closed pores to open ones. Except this, CO2 emission and crystalline water emission during sintering were also contributed to the formation of open pores in porous ceramics.

Experimental investigation on mode I fracture characteristics of granite after cyclic heating and cooling treatments

Rock in the geothermal reservoir is frequently subjected to cyclic heating and cooling, and fracture characteristics are closely related to the stable operation of Enhanced Geothermal Systems. To examine impacts of cyclic heating and cooling treatments on mode I fracture characteristics of granite, fracture tests of semi-circular bend specimens were conducted, acoustic emission (AE) events were monitored, and morphology characteristics of fracture surfaces were analyzed. Meanwhile, the open porosity was measured, and the scanning electron microscope (SEM) was applied to identify variations of microstructure in granite affected by cyclic treatments. Failure pattern and modifications of microstructure in treated granite specimens were discussed. Results indicated that cyclic treatments can lead to serious degradation in granite, manifested as the increase of open porosity, the decrease of fracture toughness and cumulative AE counts with both increasing temperature and cycles. The smoother post-peak stage in load-displacement curves and the prolonged active period of AE events of granite specimens after cyclic treatments implied the enhancement of ductility. Fractal dimensions of fracture surfaces exhibited evidently negative correlation with the brittleness index, which demonstrated that the enhanced ductility promotes the generation of rougher fracture surfaces. The failure pattern of treated granite specimens revealed that the propagation path of the main crack is strongly affected by the thermal cracks. SEM observations verified the increased, extended and deepened micro-cracks in granite after cyclic treatments, which can be attributed to the comprehensive effects of heating, rapid cooling, thermal cycling, and water-induced weakening.

Synthesis of SiOC using solvent-modified polymer precursors

Silicon oxycarbide ceramics are an important class of materials that can be modified to cover a wide range of microstructures and compositions during processing. This study focuses on a polysiloxane precursor to SiOC conversion when crosslinked in the presence of 0, 50, 100, and 200 vol% of 3-pentanone, n-heptane, or isobutylbenzene, relative to the volume of the polysiloxane. The solvent modified samples show a decrease in bulk density and an increase in open porosity. The addition of the solvents facilitates the formation of crystalline SiC, especially for 3-pentanone. The ability of the solvents to encourage SiC formation is directly related to the solvent molecular size, with smaller solvents being more likely to increase polymer chain entanglement and remain trapped within the polymer after drying and subsequently creating more C-C and Si-C bonds after pyrolysis. This work shows the unique function of solvents in modifying the SiOC microstructures and properties.

Mechanical and thermal properties of concrete suitable for radioactive waste disposal sites

Secondary casing as a part of a multi-barrier system serves to meet the safety requirements on the radioactive waste repositories. Such casing needs to be durable, radiation- and thermal resistant, with good mechanical properties; these requirements are fulfilled by concrete. However, the casing should also serve as a barrier limiting the leaching of radionuclides, in case of failure of primary package. This problem is addressed in the article by the addition of a sorption material (natural zeolite rock) in the concrete mixture. Mechanical and thermal properties of concrete containing different amount of natural zeolite rock are studied with the link to concrete porosity. The addition of natural zeolite is found to cause a decrease in thermal conductivity and specific heat capacity. Both compressive and flexural strength decrease as well when natural zeolite is added in the mixture, which correlates with the increase of open porosity of studied concrete mixtures.

Fabricating 3D printed orally disintegrating printlets using selective laser sintering

Selective laser sintering (SLS) is a three-dimensional printing (3DP) technology employed to manufacture plastic, metallic or ceramic objects. The aim of this study was to demonstrate the feasibility of using SLS to fabricate novel solid dosage forms with accelerated drug release properties, and with a view to create orally disintegrating formulations. Two polymers (hydroxypropyl methylcellulose (HPMC E5) and vinylpyrrolidone-vinyl acetate copolymer (Kollidon® VA 64)) were separately mixed with 5% paracetamol (used as a model drug) and 3% Candurin® Gold Sheen colorant; the powder mixes were subjected to SLS printing, resulting in the manufacture of printlets (3DP tablets). Modulating the SLS printing parameters altered the release characteristics of the printlets, with faster laser scanning speeds accelerating drug release from the HPMC formulations. The same trend was observed for the Kollidon® based printlets. At a laser scanning speed of 300 mm/s, the Kollidon® printlets exhibited orally disintegrating characteristics by completely dispersing in <4 s in a small volume of water. X-ray micro-CT analysis of these printlets indicated a reduction in their density and an increase in open porosity, therefore, confirming the unique disintegration behaviour of these formulations. The work reported here is the first to demonstrate the feasibility of SLS 3DP to fabricate printlets with accelerated drug release and orally disintegrating properties. This investigation has confirmed that SLS is amenable to the pharmaceutical research of modern medicine manufacture.