MPa Flexural Strength Research Articles

Biochar as carbon sequestration material combines with sewage sludge incineration ash to prepare lightweight concrete

Sewage sludge incineration ash (SSIA) is a solid waste containing heavy metal pollutants, which could be recovered as construction material via cement solidification. Biochar, as a carbon sequestration material, has properties of water absorption, metals immobilization, electron donor, etc. This study produced lightweight concrete (LC) with the ratio of SSIA to Portland cement being 1:1 (w/w), and incorporated peanut shell biochar produced at 500℃ and 700℃ pyrolysis (BC500, BC700) with addition rates of 1–5 %. Both BC500 and BC700 increased the mechanical properties of the LC at their optimal addition rates, i.e., 5 % BC500 and 3 % BC700 respectively, achieved 10.8 MPa and 11.1 MPa compressive strength, 2.1 MPa and 2.8 MPa flexural strength, being much higher than the control (6.2 MPa compressive strength and 1.35 MPa flexural strength). Biochar also significantly enhanced the water resistance of LC by 56.3 % (BC500) and 60.4 % (BC700). Instrumental analysis (TGA, XRD, SEM-EDS and heat flow) revealed that the alkaline and porous biochar promoted and prolonged the hydration reactions with forming more cementitious materials such as calcium silicate hydrate and ettringite. Biochar simultaneously strengthened the metals immobilization in LC including Cr, Cu, Zn, Mn, As and Cd, especially it acted as electron donor to reduce Cr(VI) into Cr(III) with less toxicity and mobility. Based on leaching test, it was confirmed that converting 1-ton biomass into biochar and incorporating into SSIA-based FC could achieve 541 and 980 kg CO2eq carbon sequestration for BC500 and BC700 respectively.

Comparison between Synthetic and Biodegradable Polymer Matrices on the Development of Quartzite Waste-Based Artificial Stone

The development of artificial stone from the agglutination of polymeric resin using industrial wastes can be a viable alternative from a technical, economic, and sustainable point of view. The main objective of the present work was to evaluate the physical, mechanical, and structural properties of artificial stones based on quartzite waste added into a synthetic, epoxy, or biodegradable polyurethane polymer matrix. Artificial stone plates were produced through the vacuum vibration and compression method, using 85 wt% of quartzite waste. The material was manufactured under the following conditions: 3 MPa compaction pressure and 90 and 80 °C curing temperature. The samples were characterized to evaluate physical and mechanical parameters and microstructure properties. As a result, the artificial stone plates developed obtained ≤0.16% water absorption, ≤0.38% porosity, and 26.96 and 10.7 MPa flexural strength (epoxy and polyurethane resin, respectively). A wear test established both artificial quartzite stone with epoxy resin (AS-EP) and vegetable polyurethane resin (AS-PU) high traffic materials. Hard body impact resistance classified AS-EP as a low height material and AS-PU as a very high height material. The petrographic slides analysis revealed that AS-EP has the best load distribution. We concluded the feasibility of manufacturing artificial stone, which would minimize the environmental impacts that would be caused by this waste disposal. We concluded that the production of artificial rock shows the potential and that it also helps to reduce environmental impacts.

Effect of chemical treatment and fiber loading on various properties of Bauhinia vahlii bast fibers/acrylonitrile butadiene styrene composites for automotive body parts

AbstractCurrently, automobile industries are paying more attention on fabricating light weight materials for making vehicle body parts. So lots of research work is been carried out on natural fibers owing to their light weight and eco‐friendly nature. In this current research, composites were fabricated by reinforcing treated Bauhinia vahlii bast fiber (BV) fibers with Acrylonitrile butadiene styrene (ABS) thermoplastic polymer for making light weight automobile parts. Various properties like static and dynamic mechanical properties, thermal as well as morphological properties were studied. To get a better compatibility with ABS matrix, surfaces of fibers were treated with various chemicals. An enhancement in mechanical properties was noticed with the increase in treated BV fiber loading till optimum (23 wt%) thereafter declines. The highest mechanical properties obtained at optimum fiber loading was recorded as 68.94 MPa of tensile strength, 7.02 GPa of young's modulus, 95.27 MPa of flexural strength and 33.25 kJ/m2 of impact strength. Thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), and scanning electron microscopy (SEM) was used for analysis. Overall, the results show that reinforcing ABS matrix with BV filler improves the characteristics of the manufactured composite materials effectively. It was found that composites fabricated from 23 wt% fiber content shows superior static and dynamic mechanical properties as well as thermal properties as compared with other fabricated composites and can be used for making lightweight automobile parts.

The Strength and Thermal Properties of Concrete containing Water Absorptive Aggregate from Well-Graded Bottom Ash (BA) as Partial Sand Replacement

Bottom ash (BA) is a hazardous waste material from power plant. The well-graded BA can be a good sand replacement material in concrete. This study presents strength and thermal properties of concrete containing high calcium and water absorptive fine aggregate from well-graded BA as partial sand replacement (control mix (CM) 0%, BM5: 5%, BM10: 10%, BM15: 15%, and BM20: 20%). The workability of fresh concrete mixes was tested via slump test. The strength of the hardened concrete was assessed based on compressive strength, split tensile strength, and flexural strength. The thermal property was evaluated based on thermal conductivity test. The optimization of these model parameters was conducted via I-Optimal design. The workability of concrete mixes was reduced with an increase of well-graded BA due to high water absorption effect. The compressive strengths of all mixes reached more than 50% on 28th curing days with maximum strength by BM15 (49.0 MPa). The split tensile strengths showed one quadratic curve combining all mixes with maximum strength reached by BM10 (2.7 MPa). The flexural strength has slow growth exponential pattern with maximum strength by BM20 (6.0 MPA). The thermal conductivity values were steadily increased up to BM15 (2.44 W/mK) and reduced at BM20 (2.15 W/mK). The well-graded BA proportions (5 to 20%) were not showing any significant effect on the thermal properties. The optimised model of compressive strength has the highest accuracy with percentage errors below 5% compared to other parameters. The optimal well-graded BA as sand replacement material was BM10 giving 47 MPa compressive strength, 2.7 MPa split tensile strength, 5.3 MPa flexural strength, and 2.1152 W/mK thermal conductivity. The highest positive correlation coefficients were obtained between compressive strength and thermal conductivity (R2: 0.921). Thus, the well-graded BA improved the strength properties providing a sustainable supply in concrete technology.

Mechanical and thermal analysis of coir fiber reinforced jute/bamboo hybrid epoxy composites

AbstractIn this current research study, nine different combinations of coir, jute, and bamboo reinforced epoxy composites were fabricated using casting technique. These composites were employed to mechanical tests such as flexural and impact tests, and analyzed the thermal stability through Thermogravimetric analysis (TGA) and Differential Scanning Calorimetry (DSC). Moreover, the thermal conductivity and surface morphology was also studied for hybrid composites. The hybridization of more than one fiber with epoxy matrix resulted in better mechanical and thermal properties as compared to individual reinforcements, and this statement is agreed with the present research work as well as the research works reported in the literature. The hybrid composite with the maximum amount of jute fibers reinforcement with bamboo fiber (B2C0J8) exhibited maximum flexural and impact strengths of 92.521 MPa and 82.4 kJ/m2 respectively, which is due to the higher modulus and energy‐absorbing behavior of jute fibers, also it was an advantage of coir fibers absence having lower modulus and strength values. In thermal conductivity analysis, the marginal variations of values were observed with different volume fractions of fibers, and the maximum conductivity (0.317 W/m‐K) was obtained for B2C8J Composite having only coir and bamboo fiber reinforcements with epoxy matrix. The Thermogravimetric analysis results reveal that all nine types of hybrid composites possess nearly equal thermal stability, and slight variations in degradation temperatures were observed in the thermographs. The B2C1J7 hybrid composite was recommended for better mechanical and thermal properties, where it has 89.06 MPa of flexural strength, 78.6 kJ/m2 of impact strength, 0.233 W/m‐K of thermal conductivity and exhibited better surface morphology.

Obtaining High Mechanical Properties Polyamide - Continuous Carbon Fiber Reinforced Thermoplastic Composites with Infrared Heating

Nowadays, additive manufacturing is being used in various industries such as automotive, aviation and space, medical applications, etc. Although additive manufacturing methods offer more freedom in design and manufacturing, they usually have low production speed and mechanical properties. Continuous carbon fiber reinforced thermoplastic (CFRTP) composites are one of the investigated methods in the literature to increase the mechanical properties of the additively manufactured parts. This study utilized a production line based upon the melt impregnation method to obtain continuous carbon fiber reinforced thermoplastic filaments using polyamide and continuous carbon fibers. In the printing process, an infrared heat source was utilized to further increase the mechanical properties by improving the interlaminar bonding. The mechanical properties of the printed parts were measured using three-point bending tests. A significant increase was observed in flexural modulus of elasticity and flexural strength with infrared heaters at low printing speeds. A maximum value of 418.99 MPa flexural strength and 52.15 GPa flexural modulus was achieved.

Research on the electrical conductivity and mechanical properties of copper slag multiphase nano-modified electrically conductive cementitious composite

Electrically conductive cementitious composite (ECCC) features structural material functions, electrical conductivity, and piezoresistivity properties broadly applied in snow melting, electromagnetic shielding, cathodic protection system, and structural health monitoring (SHM). Nano-graphite is an ideal ECCC functional filler since its ability to fill molecular pores, reduce concrete shrinkage and significantly improve their electrical conductivity. However, nano-graphite is high-cost and its excessive amounts can lead to particle agglomeration. Therefore, copper slag (CS) can partially replace NG to beneficially reuse the waste by-products and save energy for protecting the environment. Nevertheless, a single blend of fillers hardly exploits the potential mechanical and conductive properties. Consequently, different activation methods were adopted to obtain desirable dispersion and performances. This paper explored the influences of chemical alkali excitation, ultrasonic vibration, and combined activation on copper slag and nano-graphite wrapped ECCC. Experimental results from a total of 387 ECCC specimens with 16 design ratios demonstrated that the combined treatment of alkali excitation and ultrasonic vibration was superior to any single treatment. The optimal samples based on 3 wt% ratio of NG and 60 wt% of copper slag activated with combined treatment exhibited 44.55 MPa compressive strength, 6.65 MPa flexural strength, and 8180 Ω·cm electrical resistance. Lastly, an SEM was conducted to analyze the microstructure of the mixture and ECCC and a schematic diagram was proposed.

Wear Properties and Post-Moisture Absorption Mechanical Behavior of Kenaf/Banana-Fiber-Reinforced Epoxy Composites

The contribution of natural lignocellulosic fibers to the reduction in wear damage in polymer resins is of interest, especially when two of these fibers can combine their respective effects. Wear properties of hybrid kenaf/banana epoxy composites have been investigated using three different total amount of fibers, 20, 30 and 40 wt.%, at loading forces up to 30 N and to sliding distances of up to 75 m. This demonstrated that the introduction of the highest level of fibers proved the most suitable for consistency of results and containment of wear with increasing load, as was also found from the morphological evaluation of wear degradation using scanning electron microscopy (SEM). Subsequently, tensile, flexural and impact properties of as-received and post-water-saturation hybrid composites were examined. The tests revealed a limited reduction in tensile and flexural strength, not exceeding 10% of the initial values, which were very high compared to similar materials, almost reaching 140 MPa for tensile strength and exceeding 170 MPa for flexural strength. In contrast, a higher standard deviation of values was found for impact strength, although the decrease in average values was only slightly above 10%. The results suggest the availability of these hybrids for wear-resisting applications in high-moisture environments, and the even more limited water absorption conferred by banana fibers added to kenaf ones.

High strength metakaolin/epoxy hybrid geopolymers: Synthesis, characterization and mechanical properties

Inorganic/organic hybrid geopolymers were synthesized by using metakaolin (MK) and solid organic components comprising an epoxy resin - diglycidyl ether of bisphenol A (DGEBA), and a hardener - dicyandiamide (DICY). In this study, solid organics were chosen to obtain a homogeneous mix upon co-milling all the solid precursors viz. MK, DGEBA and DICY in a planetary ball mill prior to geopolymerisation. Inorganic/organic hybrid geopolymers synthesized were then characterized for thermal, structural and mechanical properties. Thermogravimetric analysis (TG-DTG) revealed that hybrid geopolymers restricted the degradation of organics (~72% and ~79% organics loss corresponding to 10 mass% and 20 mass% DGEBA addition, respectively) compared to their milled counterparts (~95% and ~100% organics loss corresponding to 10 mass% and 20 mass% DGEBA addition, respectively) suggesting strong inorganic/organic interactions. This was substantiated by structural characterization via X-ray diffraction (XRD) and Fourier-transform infrared (FTIR) spectroscopy. Major changes in DGEBA peak positions (FTIR) and disappearance of DICY peaks (XRD, FTIR) corroborated the MK-DGEBA-DICY reactions during geopolymerisation. Microstructural studies (scanning electron microscopy and transmission electron microscopy) coupled with elemental line scan and area maps, confirmed the homogeneous distribution of organics into the inorganic geopolymer matrix with no phase separation. Incorporating 20 mass% epoxy resulted in improved compressive strength from ~20.2 MPa to ~50.6 MPa (2.5 times superior vis-à-vis only MK-based geopolymer) and higher flexural strength of 5.4 MPa. The significantly enhanced mechanical properties of hybrid geopolymers were indicative of effective inorganic/organic interactions.

Formulation of nanocellulosic fibres and particle fillers, and their mono and hybrid reinforced polymer composites

Finite element analysis was used to formulate novel models of both mono and hybrid nanocomposites, and, also to predict their flexural properties. This study also formulated the optimal combination mix ratio of fibres and matrix of the flexural properties for use in different applications. The predicted properties were verified using the experimental method. This study found that the flexural properties of all the composites depicted an increase with fibre additions up to a certain optimum point, beyond which they began to fall gradually with further fibre additions. There was also evidence of transverse matrix fracture in rice husk nanoparticle-reinforced epoxy resin composites’ flexural stiffness graphs. Moreover, it was found that the increases in flexural properties of mono composites were about two times lower in magnitude than hybrid composites. With regards to the formulation of optimal combination mix ratio of fibres and matrices for different applications, it was noted that the optimal combination mix ratio of fibres to the matrix for applications where all the flexural properties were maximized was 4:1. Moreover, the optimal combination mix ratio of fibres to the matrix for applications where the flexural properties were minimized was 1:2. Furthermore, the optimal combination mix ratio of fibres to the matrix for applications with a target of 10 MPa flexural strength properties and 10 GPa for flexural stiffness properties was 2:3.

Use of luminescent-glass aggregates for the production of decorative architectural mortar

This work aims to study the feasibility of applying luminescent material on transparent recycled glass aggregate (RG) for the production of decorative architectural mortar. The luminescent-glass aggregate (LGA) was prepared by coating mixtures of luminescent powder and transparent adhesive paint on the surface of RG with different particle sizes (2.36∼5 mm and 5∼10 mm), and their impact on the properties of architecture luminescent-glass mortars (ALM) was studied. The results indicated that the ALM possessed 27–30 MPa compressive strength and 6–7 MPa flexural strength meeting most architectural and building applications. The 28-day compressive strength of ALM was lower than that of the control sample (GA without luminescence) due to the retarded cement hydration caused by the adhesive paint. However, ALM performed better in terms of shrinkage and resistance to alkali-silica reaction in particular with larger size of LGA, because the presence of a coated layer of luminescent powder can prevent the contact between silica and alkaline phase. Most importantly, the luminescent surface emitted yellowish-green light (glow) and maintained an appropriate brightness for 8 h in a dark environment.

Experimental Investigation of Engineering Properties of Iron-Based Binary and Ternary Pozzolanic Supplementary Cementitious Materials

The characteristic global warming potential of ordinary Portland cement (OPC) makes it a huge challenge for researchers to weigh its enormous use with potentially feasible engineering properties versus the environmental impacts. The formulation of sustainable, economical, and greener supplementary cementitious materials (SCMs) is an ongoing phenomenon, attracting the large-scale attention of industry/ academia. The formulation of ferrock by David Stone with low embodied energy, lower consumption of natural resources and minimal global warming potential has paved the way for the use of novel material comprising iron powder, pozzolans (pulverised fly ash (PFA) and metakaolin (MK) and lime exhibiting at par performance with OPC. However, a gap has been identified in its formulation, raising a further research question on how it will perform if PFA and MK are replaced by ground granulated blast furnace slag (GGBS) or other pozzolans like silica fume (SF) etc., with different mix ratios. Therefore, an endeavour has been made in this study to identify the engineering properties with sustainable use of modified binary and ternary pozzolans/ GGBS in place of 20% PFA in conventional ferrock. The conventional ferrock contains 8% MK and 20% PFA (as binary pozzolans), 60% iron powder, 12% lime and 2% oxalic acid (set 1). An effort has been made to formulate the different mixes of 10,20,30,40 and 50% by keeping 60% iron powder, 12% lime, 8% MK and 2% oxalic acid constant but replacing 20% PFA with 20% GGBS (set 2), with 10%PFA+10%GGBS (set 3) and with 10%PFA+10%SF (set 4). A target compressive strength of C32/40 or M40 concrete was selected for this study to achieve and compare results with the control mix (0% ferrock) and conventional ferrock during the experimental investigation of modified novel materials. 10-20% ratios of modified mixes exhibited the best performance and achieved the threshold strength of 60 MPa of high-strength cement concrete. Maximum compressive strength of 65 MPa was achieved by the 10% mix of set 2 (20% GGBS), followed by 20% mix ratios of set 3 (10%PFA+10%GGBS) and set 4 (10%PFA+10%SF), achieving 64 MPa. Whereas the 10% mix of the conventional ferrock (set1) reached 63 MPa strength, and the control mix with no ferrock gained 57 MPa strength at 56 days of curing. Overall, an increase of 2-13% compressive strength was observed with10- 30% mixes of all the SCMs; however, a decrease of 3-27% was observed with 40-50% use of SCMs. The use of iron powder increased the ductility of ferrock-based SCMs mixes and exhibited more flexural strength. Set 3 performed the best in exhibiting up to 5.8 MPa flexural strength, followed by set 4, set 2 and lastly, set 1 of conventional ferrock. 20% and 30% mix ratios exhibited flexural strength of more than 5% MPa, better than 10% and 40/ 50% mixes. The study supports the use of 10-20% ferrock-based SCMs for high-strength concrete and 10-50% for concrete mixes with a target strength of C32/40 or M40 to decrease the CO2 footprints of the construction industry significantly.

The Influence of the Material Structure on the Mechanical Properties of Geopolymer Composites Reinforced with Short Fibers Obtained with Additive Technologies.

Additive manufacturing technologies have a lot of potential advantages for construction application, including increasing geometrical construction flexibility, reducing labor costs, and improving efficiency and safety, and they are in line with the sustainable development policy. However, the full exploitation of additive manufacturing technology for ceramic materials is currently limited. A promising solution in these ranges seems to be geopolymers reinforced by short fibers, but their application requires a better understanding of the behavior of this group of materials. The main objective of the article is to investigate the influence of the microstructure of the material on the mechanical properties of the two types of geopolymer composites (flax and carbon-reinforced) and to compare two methods of production of geopolymer composites (casting and 3D printing). As raw material for the matrix, fly ash from the Skawina coal power plant (located at: Skawina, Lesser Poland, Poland) was used. The provided research includes mechanical properties, microstructure investigations with the use of scanning electron microscope (SEM), confocal microscopy, and atomic force microscope (AFM), chemical and mineralogical (XRD-X-ray diffraction, and XRF-X-ray fluorescence), analysis of bonding in the materials (FT-IR), and nuclear magnetic resonance spectroscopy analysis (NMR). The best mechanical properties were reached for the sample made by simulating 3D printing process for the composite reinforced by flax fibers (48.7 MPa for the compressive strength and 9.4 MPa for flexural strength). The FT-IR, XRF and XRD results show similar composition of all investigated materials. NMR confirms the presence of SiO4 and AlO4 tetrahedrons in a three-dimensional structure that is crucial for geopolymer structure. The microscopy observations show a better coherence of the geopolymer made in additive technology to the reinforcement and equal fiber distribution for all investigated materials. The results show the samples made by the additive technology had comparable, or better, properties with those made by a traditional casting method.

A new approach to the reuse of waste glass in the production of alkali-activated materials

The massive carbon footprint of cement manufacturing has provided great opportunities for research and development of eco-friendly alternative binders, geopolymers for instance. This research aims to maximise the waste uptake in the production of geopolymers by reusing glass waste as the auxiliary activator and fly ash/blast furnace slag blend as the aluminosilicate precursor. A filtration technique is utilised to assess the dissolution efficiency of glass waste powders in alkaline medium. The advantage of filtration compared with other methods includes its simplicity, accuracy, and availability to the research team. Compressive and flexural strength, X-ray diffraction, scanning electron microscopy, and Fourier-transform infrared spectroscopy are conducted. The binders illustrated up to 28 MPa compressive strength, 3.4 MPa flexural strength, and 2.9 GPa Elastic modulus after 7 days implying competitive properties to those synthesised by silicate-contained activators. The weight loss after dissolution confirmed glass waste participation in the hardening mechanism and geopolymerisation reactions. The microstructure is also an analogy to the conventional binders resulting in the benefits of durability.

The mechanical performance of the 3D printed composites produced with continuous carbon fiber reinforced filaments obtained via melt impregnation

Additive manufacturing of the continuous fiber-reinforced thermoplastic (CFRTP) composites with fused deposition modeling is an up-and-coming production method because of their exceptional mechanical properties, even though these values are still relatively low when compared with conventional thermoset products. In this respect, the additive manufacturing of continuous fiber-reinforced thermoplastic composites with high mechanical properties based on PLA thermoplastic polymer was investigated in this study. At the first stage, a polymer impregnation line was designed for manufacturing pre-preg forms of the continuous fiber-reinforced thermoplastic filaments with different fiber fractions. Afterward, standard tensile and three-point bending test specimens were printed with the fused deposition modeling (FDM) method using these filaments. Test results showed approximately 989 MPa tensile strength for pre-preg filaments. Maximum tensile strength of 544 MPa and maximum flexural strength of 310 MPa were achieved for CFRTP specimens with a 40% fiber fraction. In addition, scanning electron microscope (SEM) inspection showed a quite homogenous impregnation in both the filaments and the printed parts. Obtained results indicate that this manufacturing method could be a promising approach for printing CFRTP parts with improved mechanical properties.

Microwave cladding of NiCrSiC-5Al2O3 on austenitic stainless steel to improve cavitation erosion resistance

The current investigation aimed to study the cavitation erosion performance of the microwave synthesized NiCrSiC-5Al2O3 composite clad with a 900 W power multimode domestic microwave applicator of 2.45 GHz frequency. The clads were deposited on the austenitic grade stainless steel, namely AISI-316. The as-deposited composite clad’s microstructure, crystal structure, porosity, microhardness, and flexural strength were examined. Cavitation erosion study was done using the vibratory cavitation method at varying standoff distance (SOD)-(0.5 mm, 1 mm, 1.5 mm) and vibration amplitude (AMP)-(40 μm, 50 μm, 60 μm), keeping other parameters constant. The results had shown that the deposited NiCrSiC-5Al2O3 composite clad exhibited 1.20% porosity, 489.16 ± 47.95 HV0.3 microhardness, 264.91 ± 4.5 MPa flexural strength, and performed 3.5 times much better than the AISI-316 in terms of cavitation resistance. The least weight loss occurred at 1.5 mm SOD and 40 μm AMP, where the highest weight loss was observed at 0.5 mm SOD and 60 μm AMP. The erosion mechanism of the NiCrSiC-5Al2O3 composite clad surface was observed as plastic deformation followed by surface fatigue; the clad surface was eroded in the form of pits, craters, impingement marks, secondary cracks, and plastically deformed lips.

Alkali-Activated Mortars with Recycled Fines and Hemp as a Sand.

Nowadays, effective and eco-friendly ways of using waste materials that could replace natural resources (for example, sand) in the production of concrete composites are highly sought. The article presents the results of research on geopolymer composites produced from two types of waste materials—hemp and fine fractions recovered from recycled cement concrete, which were both used as a replacement for standard sand. A total of two research experiments were conducted. In the first experiment, geopolymer mortars were made using the standard sand, which was substituted with recycled fines, from 0% to 30% by weight. In the second study, geopolymers containing organic filler were designed, where the variables were (i) the amount of hemp and the percent of sand by volume (0%, 2.5%, and 5%) and(ii) the amount of hydrated lime and the percent of fly ash (by weight) (0%, 2%, and 4%) that were prepared. In both cases, the basic properties of the prepared composites were determined, including their flexural strength, compressive strength, volume density in a dry and saturated state, and water absorption by weight. Observations of the microstructure of the geopolymers using an electron and optical microscope were also conducted. The test results show that both materials (hemp and recycled fines) and the appropriate selection of the proportions of mortar components and can produce composites with better physical and mechanical properties compared to mortars made of only natural sand. The detailed results show that recycled fines (RF) can be a valuable substitute for natural sand. The presence of 30% recycled fines (by weight) as a replacement for natural sand in the alkali-activated mortar increased its compressive strength by 26% and its flexural strength by 9% compared to control composites (compared to composites made entirely of sand without its alternatives). The good dispersion of both materials in the geopolymer matrix probably contributed to filling of the pores and reducing the water absorption of the composites. The use of hemp as a sand substitute generally caused a decrease in the strength properties of geopolymer mortar, but satisfactory results were achieved with the substitution of 2.5% hemp (by volume) as a replacement for standard sand (40 MPa for compressive strength, and 6.3MPa for flexural strength). Both of these waste materials could be used as a substitute for natural sand and are examples of an eco-friendly and sustainable substitution to save natural, non-renewable resources.

Production, Properties and Performance of Slag-Based, Geopolymer Foams

This paper demonstrates the transformation of the industrial residue (copper slag) of a Swedish mining and smelting company “Boliden”, through geopolymerization, into advanced building materials. The main objective of this experimental study is the assessment of the appropriate conditions for the preparation of alkali-activated slag-based geopolymer pastes with further foaming production, by aluminum powder addition. The alkaline-activating solution used was KOH, at a constant concentration (8 M). The effect of crucial operating parameters, such as S/L ratio (3.5–4.5 g/mL) and aluminum powder addition (0.12%–0.22%), on the geopolymer paste were studied, in order to achieve the optimum rheological conditions of the slurry. The physical properties of the materials were examined after the appropriate curing process (24 h at 70 °C), with density values ranging between 805 and 1100 kg/m3. The mechanical performance of the materials ranged between 1.28 and 2 MPa (compressive strength), and from 0.25 to 0.85 MPa (flexural strength), indicating the strong correlation of physical and mechanical properties. To assess the porosity and the size distribution of the voids, image processing techniques were applied on digital images of selected samples. According to these results, the synthesized materials exhibit similar, or even better, properties than the current concrete porous materials.

Fibre-reinforced lightweight engineered cementitious composites for 3D concrete printing

While the 3D printing technology for cementitious composites has developed rapidly, a combination of 3DP technology and lightweight engineered cementitious composites (LWECCs) could improve many aspects of the construction industry. In this study, a fibre-reinforced high-performance LWECC for extrusion-based printing was proposed. First, six LWECCs were prepared, incorporating two kinds of hollow glass microspheres (HGMs) in varying replacement ratios of fly ash (FA) at 60 wt%, 80 wt%, and 100 wt%. In addition, polyvinyl alcohol (PVA) fibre was introduced given its shrinkage resistance and improvement in printability performance. Thereafter, fresh property (slump loss and setting time), unconfined compression strength (UCS), and flexural strength experiments thoroughly investigated the optimised LWECC design, which was later calibrated for the printing procedure via a printability assessment, including extrudability and buildability. The UCS, flexural strength, and densities of the printed and cast specimens were compared. Lastly, a microstructural investigation using a scanning electron microscope described the reinforcement mechanism of PVA fibre upon the performance of the printed structures and HGMs. The addition of HGMs significantly improve the lightweight property that reaches a value at 1384 kg/m3 but inevitably negates mechanical properties. The printed LWECC obtains 33.6 MPa for UCS and 9.29 MPa for flexural strength. When the printed filament was perpendicular to loading direction, superior toughness was observed, creating a 63% and 40% increase for UCS and flexural strength, respectively.

Expansionless oxidation-bonded SiC microfiltration membrane by controlling the oxidation of SiC particle mixtures

ABSTRACT Oxidation bonding is a technique used to produce porous SiC ceramics at low temperatures. The oxidation behavior of SiC particles depends on various factors, including the oxidation environment, temperature, time, particle size, and impurities. The key properties required for a porous ceramic membrane are a controlled pore morphology, high strength, and high permeability. In this study, SiC powders with different particle sizes (0.55 and 7 μm) were used to fabricate porous ceramic membranes. First, the oxidation behavior of the SiC powders was evaluated. Then, the feasibility of using their mixture to create supports for microfiltration applications was analyzed. Through this study, not only were the ideal conditions for fabricating microfiltration supports quantified but also the conditions where specimens could be made with zero size change. Finally, a membrane fabricated from a powder mixture composed of 92% of the 7 μm powder and 8% of the 0.55 μm powder and sintered at 1450°C was proposed, which had a 37% porosity, 1.42 μm pore size, 49.6 MPa flexural strength, and L cm-2 min-1 bar-1 air permeability.