Effect of geothermal waste on strength and microstructure of alkali-activated slag cement mortars

Mortars of blast furnace slag replaced with 10% of a geothermal silica waste were cured for 90 days. The binder was activated by 6 wt.% Na₂O equivalent of NaOH and water glass. The presence of the silica enhanced the formation of hydration products as shown by nonevaporable water (NEW) results. Backscattered electron images indicated that the microstructures of blended slag had less porosity than those of neat slag mortars and the interfacial zone between aggregate and hydration products was dense and of homogeneous composition similar to the matrix of hydration products. The main hydration products were C-S-H and for NaOH a hydrotalcite type phase was found as finely intermixed with the C-S-H.     

Partial replacement of metakaolin with red ceramic waste in geopolymer

Metakaolin was incrementally replaced (33.3%, 50% and 66.6%) by red ceramic waste in geopolymer formulation to study the effect on geopolymerisation and its resultant properties. The geopolymer binders composed of two calcined aluminosilicates (viz. Metakaolin and Red ceramic waste), NaOH and sodium silicate. In the experimental compositions, metakaolin was replaced gradually up to 66.6% in the clay fraction, the Si/Al increased from 3.36 to 5.16 and Na/Al increased from 0.93 to 1.38. The FTIR spectroscopic studies of geopolymer pastes along with XRD analysis indicated that the red ceramic waste partly reacts with alkali and takes part in geopolymer formation. Replacement of 33.3% metakaolin by the red ceramic waste in geopolymer binder did not reduce the compressive strength with respect to the pure metakaolin geopolymer here. Additional replacement resulted in a drastic decrease in the compressive strength of the geopolymer binder. However, the compressive strength of geopolymer mortars revealed interesting synergy between the amount of binder and particle packing in the mortar. Despite having a lower amount of binder phase, mortars with 33% and 50% red ceramic waste exhibited maximum compressive strength values. This has been attributed to improved particle packing through incorporation of red ceramic waste particles.     

Investigation of mechanical and thermo-mechanical strength of ceramic foam filters (CFFs)

During aluminium production, the molten metal will always contain varying amounts of impurities, e.g., non-metallic inclusions, and for high-quality products removing such inclusions is essential. This can be achieved by filtration using ceramic foam filters (CFFs). However, these filters are highly brittle materials subjected to strong mechanical and thermo-mechanical stresses during transport and operation, which occasionally leads to failure of the filter material. In the present study, the compression strength of five different Al₂O₃-based CFFs was measured at room temperature and elevated temperature (compressed at 730 °C), as well as while submerged in molten aluminium with varying melt compositions (pure aluminium and an aluminium-magnesium alloy). The compression strengths at room temperature were established to be in the range of 1.19–2.09 MPa depending on the filter type tested. In the case of the CFFs compressed at elevated temperature, a reduction in compression strength in the range of 9.2–58.6% was established to exist depending on filter type and heating duration, except in three of the filter/duration-combinations tested. Compression of CFF samples submerged in molten aluminium led to an even further reduction in compression strength in the range of 42.6–69.4% depending on filter type and duration of exposure. With an exposure time of only 5 min, no difference in compression strength was observed between the two aluminium melts.     

Ageing of lime mortars with admixtures: Durability and strength assessment

Lime-based mortars modified with admixtures were prepared and subjected to different environments such as outdoor and indoor exposures, climatic chamber, SO₂-chamber, and freezing-thawing cycles. The influence that the different admixtures (water repellents, water retainers, polypropylene fibre and a viscosity modifier) had on the pore size distribution of the hardened specimens was assessed and related to the water absorption capacity, and hence to the durability. Ageing resistance and mechanical strengths improved when additives reduced the water intake and increased the air-content. High dosages of water repellents were necessary to enhance the durability, sodium oleate being the most effective additive to endure freezing processes. Also the low tested dosage of fibre, a water retainer (guar gum derivative), and a starch proved to be useful. SO₂ deposition caused the formation of calcium sulphite hemihydrate as the main degradation product. A very small amount of calcium sulphate dihydrate was observed. A crystal habit composed of acicular agglomerates of calcium sulphite hemihydrate was detected in SO₂ deposition on calcareous materials.     

Effect of high volume tile ceramic wastes on resistance of geopolymer mortars to abrasion and freezing-thawing cycles: Experimental and deep learning modelling

Utilizing industrial and agriculture waste materials to produce a green and sustainable mortar have widely investigated and assessed based on the mechanical and durability properties. Herein, the abrasion and freezing-thawing resistance of fly ash (FA)-ground blast furnace slag (GBFS) based geopolymer mortars incorporating high content of tile ceramic wastes (TCWs) have been evaluated experimentally and mathematically using artificial neural network (ANN). A relatively dilute (4 M) alkaline solution was used to activate the ternary blend. The TCWs was maintained as a relatively large percentage of the total binder, i.e. 50%, 60% and 70%. Once the casting process was complete, curing of the samples was performed at 27 °C. These then underwent testing at day 1, day 3, day 7 and day 28 to provide durability data for various specimen ages. Tests encompassed exposure to abrasion, ability to withstand cyclic freeze-thawing and wet-drying, and permeability to water. Investigations to establish the impact of the high TCWs proportion on the generation of sodium aluminium, calcium aluminium and calcium silicate hydrate (N, C-A-S-H) gels, respectively, included X-ray diffraction, scanning electron microscopy and Fourier-transform infrared spectroscopy. The large percentage of TCWs (70%) generated GPMs that had a minimal effect on the environment and which, by day 28, evidenced a compressive strength above 35 MPa. Augmenting the GBFS and FA content promoted the capacity to withstand freeze-thawing cycles and enhanced durability. Improved performance was also observed in scenarios associated with abrasion resistance. In addition, the proposed models proved their accuracy in which MSE, MAPE, SI were less than 1.93, while R2 of greater than 0.9 confirmed the closeness between predicted and actual results. Substitution of TCWs and FA for GBFS additionally reduced landfill problems of ceramic wastes and achieved the sustainability aims.     

The effect of recycled concrete aggregate properties on the bond strength between RCA concrete and steel reinforcement

The purpose of this study was to investigate the influence that replacing natural coarse aggregate with recycled concrete aggregate (RCA) has on concrete bond strength with reinforcing steel. Two sources of RCA were used along with one natural aggregate source. Numerous aggregate properties were measured for all aggregate sources. Two types of concrete mixture proportions were developed replacing 100% of the natural aggregate with RCA. The first type maintained the same water–cement ratios while the second type was designed to achieve the same compressive strengths. Beam-end specimens were tested to determine the relative bond strength of RCA and natural aggregate concrete. On average, natural aggregate concrete specimens had bond strengths that were 9 to 19% higher than the equivalent RCA specimens. Bond strength and the aggregate crushing value seemed to correlate well for all concrete types.     

Phase composition,microstructure, and properties of ceramic tile prepared using ceramic polishing waste as raw material

Polished ceramic products are currently the most popular in architectural decoration, but a significant amount of ceramic polishing waste (CPW) is produced during the preparation process. Determining how to handle the CPW is a pressing task for enterprises. This work investigated the feasibility of recycling CPW in porcelain tile, and its influence on the phase composition, microstructure, and properties of the ceramic body. The CPW was found to have a similar composition to the traditional ceramics and worked as a flux. The SiC within CPW began to decompose into SiO₂ with CO₂ generation at about 1100°C, resulting in a porous structure. Microstructure observation indicated that a high CPW sample produced sufficient liquid phase when fired at temperatures ≤1100°C, which was not only beneficial for mullite growth but also for matrix densification by the viscous flow mechanism. But a high-content CPW caused the body to foam or even expand at temperatures >1100°C, thus significantly reducing mechanical properties. Finally, a series of porcelain tiles were successfully prepared with a CPW content of ≤30 wt% at a firing temperature of 1125-1200°C. The results of this study are considered to be valuable for the utilization of CPW.     

Waste recycling of coal fly ash: A novel approach to prepare hierarchically porous coal fly ash/Al2O3 ceramic composite with high porosity and high strength templated by emulsion-assisted self-assembly

The coal fly ash (CFA) produced from coal-fired power generation is classified as a common solid waste; thus, improving the recovery and utilization rate of CFA is highly desirable. In this study, a novel strategy using CFA and Al₂O₃ as raw materials, to prepare hierarchically porous ceramic composites that serve as potential candidates for future building materials is developed. In this process, the well-developed self-assembly method in which an anionic modifier is used to prepare hydrophobic powders that form an attractive oil/water network via electrostatic interactions, thereby yielding honeycomb-like structures. In order to explore the mechanism of preparation, five samples with different mixture ratios of alumina and CFA were prepared according to 1: 0, 2: 1, 1: 1, 1: 2, and 0: 1 (Alumina: CFA). Compared with the sample prepared with pure CFA, the as-prepared CFA/Al₂O₃ composite exhibited both superior porosity and high mechanical property. When the porosity is as high as 73 ± 0.17%, the compressive strength is as high as 80.9 ± 3.4mpa (alumina: CFA = 1:1). As the porosity decreases to 49.3 ± 0.7%, the compressive strength reaches 159.33 ± 36.89mpa (alumina: CFA = 1:2). Moreover, this work obtains the highest compressive strength-porosity related B-value in comparison to previously reported CFA-based composites and provides a new insight into the effective recycling of CFA and offers a novel approach to prepare CFA/Al₂O₃ composite with excellent overall mechanical properties.     

再生砂对砂浆的施工和易性及抗压强度的影响

将湖北襄阳地区的建筑垃圾粉碎筛分得到再生砂,以再生砂部分或全部取代建筑砂浆中的天然砂,用粉煤灰作为掺加料,制作再生砂浆,研究再生砂对砂浆和易性及抗压强度的影响.在砂浆流动性基本相同的情况下,随再生砂掺量增加,砂浆的用水量明显增大、保水性趋于提高.再生砂浆在再生砂取代量为40%时获得良好的骨料级配,强度提高.     

Effect of binder content on the performance of alkali-activated slag concretes

This paper assesses the mechanical and durability performance of concretes produced using alkali silicate-activated ground granulated blast furnace slag as sole binder. Alkali-activated concretes are formulated with 300, 400 and 500 kg slag per m³ of fresh concrete, and their performance is compared with reference concretes produced using Portland cement (OPCC). Regardless of the binder content, the alkali-activated slag concretes (AASC) develop higher compressive strength than the comparable reference concretes. A higher binder content leads to increased strength in both AASC and OPCC at 28 days. However, at 90 days, the performance penalty for low binder content is more significant in the OPCC than AASC samples. Permeability, water sorption and carbonation resistance properties are also improved at higher binder contents. By controlling mix design parameters, it is possible to produce AASC with mechanical strength and durability comparable to conventional Portland cement concretes.     

Effect of SNNWS content on the microstructure and properties of SNNWS/Si-C-N ceramic composites via PIP

Si-C-N ceramic composites containing well distributed silicon nitride nanowires (SNNWs) were fabricated by die-pressing and precursor infiltration and pyrolysis process at a low temperature. The structure, composition, mechanical and thermophysical properties of the composites were investigated. The results show that the composites consisted of amorphous SiCN, α-Si₃N₄ and α-cristobaslite. The composites with different contents of SNNWs possessed a density of 2.02–2.07 g cm^?3 and open porosity of 7.9–9.9%. SNNWs can effectively restrain the contraction of matrix with a decrease by 25% in linear shrinkage. The composites with 3 wt% SNNWs owned the highest flexural strength (83.7 MPa) and elastic modulus (54.0 GPa) at room temperature, which increase by 13.2% and 62.3% respectively, compared with pure SiCN ceramics. The SNNWs displayed good reinforcement function at high temperature due to the fact that the composites with 7 wt% SNNWs had a 96.8% retention rate of bending strength at 1200 °C. The composites had relatively low coefficient of thermal expansion and thermal diffusivity which were less than 2.2 × 10^?6 K^?1 and 0.62 mm² s^?1, respectively.     

Preparation and characterization of ceramic nanofiltration membrane prepared from hazardous industrial waste

Kiln rollers, which are widely used in ceramic tiles production, are usually subjected to surface grinding to remove the contaminations. The resulted fine powder is considered useless waste and a hazardous source of environmental pollution particularly as it contains health-threatening fine free silica. In the present paper, the grind waste from kiln rollers was reused as raw material in the fabrication of nanofiltration ceramic membrane. The samples of produced ceramic membranes were formed into disks by adding 15% (by weight) organic binder solution with 2% concentration, then pressed at 35 MPa, dried and fired at temperatures range from 1100°C to 1300°C for 1 hour soaking time. It was found that the best firing temperature to produce nanofiltration ceramic membrane is 1250°C, where the ceramic membrane provides high removal of turbidity and high monovalent, divalent, and trivalent salts separation percentage.     

Sinterability,microstructure and compressive strength of porous glass-ceramics from metallurgical silicon slag and waste glass

Porous glass-ceramics have been prepared by the direct sintering of powder mixtures of metallurgical silicon slag and waste glass. The thermal behavior of silicon slag was examined by differential thermal analysis and thermogravimetry to clarify the foaming mechanism of porous glass-ceramics. The mass loss of silicon slag below 700 °C was attributed to the oxidation of amorphous carbon from residual metallurgical coke in the silicon slag, and the mass gain above 800 °C to the passive oxidation of silicon carbide. The porosity of sintered glass-ceramics was characterized in terms of the apparent density and pore size. By simply adjusting the content of waste glass and sintering parameters (i.e. temperature, time and heating rate), the apparent density changed from 0.4 g/cm³ to 0.5 g/cm³, and the pore size from 0.7 mm to 1.4 mm. In addition to the existing crystalline phases in the silicon slag, the gehlenite phase appeared in the sintered glass-ceramics. The compressive strength of porous glass-ceramics firstly increased and then decreased with the sintering temperature, reaching a maximal value of 1.8 MPa at 750 °C. The mechanical strength was primarily influenced by the crystallinity of glass-ceramics and the interfaces between the crystalline phases and the glassy matrix. These sintered porous glass-ceramics exhibit superior properties such as light-weight, heat-insulation and sound-absorption, and could found their potential applications in the construction decoration.     

The preparation of LPVCS with high ceramic yield and low oxygen content

ABSTRACT

As by-products produced by the synthesis of polycarbosilane, RLPS and dimethyldivinylsilane (DVS) can synthesise vinyl-containing liquid polycarbosilane (LPVCS) via hydrosilylation reaction. The structure, thermal curing performance and pyrolysis performance of PVCS are characterised by means of the analysis means such as FT-IR, GPC and TG, etc. According to the result, the structure of PVCS is affected by the different synthesised temperatures and different proportions of introduced DVS. And LPVCS that contains Si–H and –CH=CH₂ groups is synthesised under the control of reaction condition. Cross-linking solidity is available at 350°C in an inert atmosphere, and the total ceramic yield of LPVCS is 42.5%. The oxygen content of the pyrolysed product is just about 2.0% after heating in 1000°C, which is a suitable precursor polymer for SiC-based composite.     

The effect of high temperature on the residual mechanical performance of concrete made with recycled ceramic coarse aggregates

This paper presents an experimental study on the residual mechanical properties of concrete with recycled ceramic coarse aggregate (RCCA) after exposure to elevated temperatures. Four concrete mixes were produced: a control concrete and three concrete mixes with replacement ratios of 20, 50 and 100% of natural aggregate (NA) by RCCA. The specimens were subjected to temperatures of 200, 400 and 600°C, for a period of 60 min. After cooling down to room temperature, the following concrete properties were evaluated: (i) compressive strength; (ii) splitting tensile strength; (iii) modulus of elasticity; (iv) ultrasonic pulse velocity (UPV); and (v) water absorption by immersion. At ambient temperature, as expected, the replacement of NA by RCCA resulted in a performance reduction of concrete. After exposure to elevated temperature, in general, the results obtained indicated an improvement of the residual relative mechanical properties of the mixes with RCCA, particularly after exposure to 400 and 600°C. However, exposure to the highest temperature (600°C) tended to cause spalling in concrete mixes containing RCCA. Significant linear correlations were observed between the residual compressive strength of all concrete mixes and both the UPV and the water absorption by immersion. Copyright © 2014 John Wiley & Sons, Ltd.     

An economic and environment friendly way of recycling boron carbide waste to prepare B4C/Al composite ceramic

Recently, with the rapid growth of sapphire wafer applications, boron carbide as abrasive, has shown an increasing demand. Great amounts of boron carbide waste (low purity and small grain size with D₅₀ ≈ 1 μm) are therefore produced during the production of boron carbide abrasives and barely recovered and utilized. This paper is aimed at developing an economic and environment friendly process to recycle the boron carbide waste through adding a certain amount of Al powder to prepare B₄C/Al composite ceramic. Prior to the sintering process, samples were firstly mixed with different Al powder and then pelleted and dehydrated. The effects of the pelletizing factors on performances of the pellets and the ceramics were optimized as binder hydroxypropyl methylcellulose addition 0.4%, pelleting pressure 30 MPa, Al addition 9 wt%, sintering time 90 minutes. Under these conditions, the apparent porosity, bulk density, compressive strength and flexural strength of the sintered B₄C/Al are 19.08%, 1.84 g/cm³, 246.88 MPa and 71.10 MPa respectively. Al addition can not only attribute to the low-temperature liquid sintering and densification of the product, but also generation of some stable phases including AlB₁₂, AlB₁₂C₂ and Al₃BC, which in turn increase the performance of the ceramic composite.     

Effect of thermal exposure on the microstructure and strength of an alumina-silica ceramic fiber

The microstructure and mechanical properties of an alumina-silica ceramic fiber after thermal exposure at 1100–1300°C were investigated by X-ray diffraction, nuclear magnetic resonance, scanning electron microscopy, transmission electron microscopy analyses and room temperature tensile strength test. The results showed that the fiber was composed of γ-A1₂O₃ and amorphous SiO₂. A phase reaction of γ-A1₂O₃ and amorphous SiO₂ occurred when thermal exposure temperature exceeded 1150°C, and a new mullite phase formed. The grain size of the newly formed mullite increased with the increase of exposure temperature. Both the phase transition and grain growth of mullite had a significant impact on the mechanical properties of the fiber. Tensile strength of the fiber decreased slightly when thermal exposure temperature was below 1150°C, while the strength retention of the fiber decreased sharply to 65.36% as exposure temperature rose to 1200°C. A higher dispersion of tensile strength was also observed at higher exposure temperatures, as revealed by the Weibull statistical model.     

Influence of slag chemistry on the hydration of alkali-activated blast-furnace slag — Part I: Effect of MgO

The hydration and the microstructure of three alkali activated slags (AAS) with MgO contents between 8 and 13 wt.% are investigated. The slags were hydrated in the presence of two different alkaline activators, NaOH and Na₂SiO₃·5H₂O (WG). Higher MgO content of the slag resulted in a faster reaction and higher compressive strengths during the first days. The formation of C(− A)–S–H and of a hydrotalcite-like phase was observed in all samples by X-ray diffraction (XRD), thermal analysis (TGA) and scanning electron microscopy (SEM) techniques. Increasing the MgO content of the slag from 8 to 13% increased the amount of hydrotalcite and lowered the Al uptake by C–S–H resulting in 9% higher volume of the hydrates and a 50 to 80% increase of the compressive strength after 28 days and longer for WG activated slag pastes. For NaOH activated slags only a slight increase of the compressive strength was measured.     

Use of ceramic industry milling and glazing waste as an active addition in cement

The beneficial effects of pozzolans on cement manufacture have encouraged their use in that industry. Traditional natural pozzolan have become less available of late, however, due to a decline in quarrying intensity aimed at minimizing the impact on the landscape. At the same time, environmental policies pursue the reduction or elimination of spoil heaps by valorizing industrial waste and by‐products as raw materials, in keeping with the principles of the circular economy. The quest for new types of waste and by‐products with pozzolanic properties has consequently become a priority line of research. This study explored the valorization of one such by‐product, the ceramic sludge resulting from fired clay industry milling and glazing, as a component in new, more eco‐sustainable cements. The sludge was characterized physically, chemically, morphologically, and mineralogically to determine its suitability as a pozzolanic addition in cement. The findings showed that ceramic sludge consists in clustered particles ranging in size from 100 μm to 1 μm. SiO₂, Al₂O₃, and Fe₂O₃ together comprise over 70% of the total composition, while the reactive silica content is greater than the 25% required by the existing legislation. The predominant minerals are quartz, kaolinite, and muscovite, with some zircon. A study of pozzolanic reaction kinetics in the ceramic sludge/lime system revealed that over time this waste can fix lime, generating products such as calcium aluminate hydrates and C–S–H gels. The cements made with ceramic sludge proved to be standard‐compliant in terms of water demand, setting, drying shrinkage and mechanical strength.     

Evaluation of laboratory test method for determining the potential alkali contribution from aggregate and the ASR safety of the Three-Gorges dam concrete

The releasable alkali from granite, which was used in the Three-Gorges concrete dam project in China, and from gneiss and feldspar was estimated by extraction in distilled water and super-saturated Ca(OH)₂ solution. Results show that: i) the finer the particles and the higher the temperature, the greater and faster the release of alkali; ii) compared with extraction by distilled water, super-saturated Ca(OH)₂ solution had a stronger activation on feldspar than on granite and gneiss; iii) for the three rocks tested, thermal activation had the largest effect on gneiss and a lower and similar effect on granite and feldspar. For very fine particles, temperature had a similar effect on the release of alkali by all three rocks.Because the aggregate used in the Three-Gorges dam concrete is non-reactive and a low calcium fly ash was used in the concrete, ASR would not be an issue for the dam, despite the release of alkali from the aggregate into the concrete.