Reuse of water purification sludge as raw material in cement production

The feasibility of partial replacement of siliceous raw material for cement production with water purification sludge (WPS) was investigated by X-ray diffraction, free-lime analysis, compressive strength testing and toxicity characteristics leaching procedure (TCLP). It is found that WPS has no negative effects on the consumption of free lime and the formation of clinker minerals. The samples with WPS from 4 to 10 wt.% have higher 3 days and 7 days strengths than the control. After 28 days, however, only WPS replacements <7% increased the strength of samples. It is noteworthy that heavy metals in WPS were almost completely incorporated into the clinkers, and up to 28 days the heavy metals were not detected in the leachates. From the above results of clinker minerals, compressive strength and leaching tests, it can be concluded that WPS has the potential to be utilized as an alternative raw material in cement production.     

Rheological and hydration characterization of calcium sulfoaluminate cement pastes

Calcium sulfoaluminate (CSA) cements are currently receiving a lot of attention because their manufacture produces less CO₂ than ordinary Portland cement (OPC). However, it is essential to understand all parameters which may affect the hydration processes. This work deals with the study of the effect of several parameters, such as superplasticizer (SP), gypsum contents (10, 20 and 30 wt.%) and w/c ratio (0.4 and 0.5), on the properties of CSA pastes during early hydration. This characterization has been performed through rheological studies, Rietveld quantitative phase analysis of measured X-ray diffraction patterns, thermal analysis and mercury porosimetry for pastes, and by compressive strength measurements for mortars. The effect of the used SP on the rheological properties has been established. Its addition makes little difference to the amount of ettringite formed but strongly decreases the large pore fraction in the pastes. Furthermore, the SP role on compressive strength is variable, as it increases the values for mortars containing 30 wt.% gypsum but decreases the strengths for mortars containing 10 wt.% gypsum.     

Chemical activation of calcium aluminate cement composites cured at elevated temperature

The influence of sodium sulfate, as an activator, on the hydration of calcium aluminate cement (CAC)–fly ash (FA)–silica fume (SF) composites was investigated. Different mixes of CAC with 20% pozzolans (20% FA, 20% SF and 10% FA + 10% SF) were prepared and hydrated at 38 °C for up to 28 days. The hydration products were investigated by XRD, DSC and SEM. The results showed that sodium sulfate accelerated the hydration reactions of calcium aluminate cement as well as the reactions of FA and SF with CAH₁₀ and C₂AH₈ to form the strätlingite (C₂ASH₈). The later reactions prevent the strength loss by preventing the conversion of CAH₁₀ and C₂AH₈ to the cubic C₃AH₆ phase. The acceleration effect of Na₂SO₄ on the reactivity of fly ash was more pronounced than on the reactivity of silica fume with respect to reaction with CAH₁₀ and C₂AH₈ phases.     

Thaumasite formation in limestone filler cements exposed to sodium sulphate solution at 20 °C

This paper presents a microstructural analysis of mortars made with OPC (C₃A=6%) and two SRPCs (C₃A < 2% and C₃S=40% and 74%) containing 20% of limestone filler. Specimens analysed were immersed in Na₂SO₄ solution (5% w/w or 0.352 M) with pH control during two years at 20 ± 2 °C. The evolution of attack was determined using XRD semi-quantitative analysis on the material obtained by wearing in layers by millimetre to millimetre of the specimens. Complementary SEM and EDS studies were carried out to confirm the presence of thaumasite. Results show that OPC and high-C₃S SRPC containing 20% limestone filler were found to be more susceptible to sulphate attack than the corresponding plain cement. The attack was characterised by the inward front leading first to the formation of ettringite, later formation of gypsum and finally thaumasite formation, when the decalcification of the mortar lead to the breakdown of C–S–H, providing the required silica. The reaction sequence in Portland limestone cements is essentially the same as in plain Portland cements. The main change is that thaumasite is formed at later stages with decomposition of the ettringite formed during the firsts stage of attack. In SRPC with low C₃S, the attack was limited to the first millimetres and the thaumasite was not detected.     

Carbonation of ternary building cementing materials

The carbonation processes of ettringite and calcium aluminate hydrates phases developed by hydration of calcium aluminate cement, fly ash and calcium sulphate ternary mixtures have been studied. The hydrated samples were submitted to 4% of CO₂ in a carbonation chamber, and were analysed, previous carbonation and after 14 and 90 days of carbonation time, by infrared spectroscopy and X-ray diffraction; the developed morphology was performed with the 14 days carbonated samples. The results evidenced that ettringite reacts with CO₂ after 14 days of exposition time and evolves totally at 90 days; the developed hydrated phases C₃AH₆ in samples with major CAC content, also reacts with CO₂. Due to carbonation, calcium carbonate – mainly vaterite but also aragonite-, depending on the initial formulation, aluminium hydroxide and gypsum were detected.     

Effects of Mo on microstructure of as-cast 28 wt.% Cr–2.6 wt.% C–(0–10) wt.% Mo irons

Microstructures of as-cast 28 wt.% Cr–2.6 wt.% C irons containing (0–10) wt.% Mo with the Cr/C ratio of about 10 were studied and related to hardness. The experimental irons were cast into dry sand molds. Microstructural investigation was performed by light microscopy, X-ray diffractometry, scanning electron microscopy, transmission electron microscopy and energy-dispersive X-ray spectrometry. It was found that the iron with about 10 wt.% Mo was eutectic/peritectic, whereas the others with less Mo content were hypoeutectic. The matrix in all irons was austenite, partly transformed to martensite during cooling. Mo addition promoted the formation of M₂₃C₆ and M₆C. At 1 wt.% Mo, multiple eutectic carbides including M₇C₃, M₂₃C₆ and M₆C were observed. M₂₃C₆ existed as a transition zone between eutectic M₇C₃ and M₆C, indicating a carbide transition as M₇C₃(M_2.3C) → M₂₃C₆(M_3.8C) → M₆C. At 6 wt.% Mo, multiple eutectic carbides including M₇C₃ and M₂₃C₆ were observed together with fine cellular/lamellar M₆C aggregates. In the iron with 10 wt.% Mo, only eutectic/peritectic M₂₃C₆ and M₆C were found without M₇C₃. Mo distribution to all carbides has been determined to be increased from ca. 0.4 to 0.7 in mass fraction as the Mo content in the irons was increased. On the other hand, Cr distribution to all carbides is quite constant as ca. 0.6 in mass fraction. Mo addition increased Vickers macro-hardness of the irons from 495 up to 674 HV₃₀. High Mo content as solid-solution in the matrix and the formation of M₆C or M₂₃C₆ aggregates were the main reasons for hardness increase, indicating potentially improved wear performance of the irons with Mo addition.     

Strength of deformation processed Cu–Fe–Ag in situ composites

Three Cu–Fe–Ag in situ composites, i.e. Cu–14 wt.%Fe–1 wt.%Ag, Cu–14 wt.%Fe–3 wt.%Ag and Cu–11 wt.%Fe–6 wt.%Ag, were prepared by cast and drawn process. Strength of the composites was investigated in detail. The results show that the presence of Ag can refine the primary Fe dendrites, leading to much higher strength of Cu–Fe–Ag composites, which reached 1578 and 1357 MPa for Cu–14Fe–3Ag and Cu–11Fe–6Ag respectively at η = 6.1, however that of the same processed Cu–12 wt.% Fe is only 978 MPa. Strength of Cu–Fe–Ag can be expressed as σ = 1319 × λ^− 1 / 2 + 57 × C_Fe–M^1 / 2 + Δσ_Ag, where λ is filament spacing, C_Fe–M is the Fe content in the matrix and Δσ_Ag is strengthening effect of Ag in the matrix. As Ag content is lower, Δσ_Ag = 100 × C_Ag ^1 / 2 and as it is near or beyond 6 wt.%, Δσ_Ag should be determined by specific experiment due to a second-stage work hardening of the matrix. The calculated strength of Cu–Fe–Ag composites fits the experimental results well.     

Carbonation of ternary building cementing materials

The carbonation processes of ettringite and calcium aluminate hydrates phases developed by hydration of calcium aluminate cement, fly ash and calcium sulphate ternary mixtures have been studied. The hydrated samples were submitted to 4% of CO₂ in a carbonation chamber, and were analysed, previous carbonation and after 14 and 90 days of carbonation time, by infrared spectroscopy and X-ray diffraction; the developed morphology was performed with the 14 days carbonated samples. The results evidenced that ettringite reacts with CO₂ after 14 days of exposition time and evolves totally at 90 days; the developed hydrated phases C₃AH₆ in samples with major CAC content, also reacts with CO₂. Due to carbonation, calcium carbonate – mainly vaterite but also aragonite-, depending on the initial formulation, aluminium hydroxide and gypsum were detected.     

High-volume natural volcanic pozzolan and limestone powder as partial replacements for portland cement in self-compacting and sustainable concrete

A laboratory study demonstrates that high volume, 45% by mass replacement of portland cement (OPC) with 30% finely-ground basaltic ash from Saudi Arabia (NP) and 15% limestone powder (LS) produces concrete with good workability, high 28-day compressive strength (39 MPa), excellent one year strength (57 MPa), and very high resistance to chloride penetration. Conventional OPC is produced by intergrinding 95% portland clinker and 5% gypsum, and its clinker factor (CF) thus equals 0.95. With 30% NP and 15% LS portland clinker replacement, the CF of the blended ternary PC equals 0.52 so that 48% CO₂ emissions could be avoided, while enhancing strength development and durability in the resulting self-compacting concrete (SCC). Petrographic and scanning electron microscopy (SEM) investigations of the crushed NP and finely-ground NP in the concretes provide new insights into the heterogeneous fine-scale cementitious hydration products associated with basaltic ash-portland cement reactions.     

Fabrication and properties of mechanically alloyed and Ni activated sintered W matrix composites reinforced with Y2O3 and TiB2 particles

Microstructural and physical properties of W–1 wt.% Ni matrix composites reinforced with Y₂O₃ and TiB₂ particles produced via mechanical alloying and sintering at 1400 °C for 1 h under Ar, H₂ gas flowing conditions were investigated. XRD patterns of the sintered samples revealed the presence of W, Ni and TiB₂ phases, whereas W₂B and NiTi phases were detected in the samples containing 4 wt.% and 5 wt.% TiB₂. Relative density value of W–1 wt.% Ni sample was measured as 97%, which decreased to 95.4% with the addition of 0.5 wt.% Y₂O₃. Relative density values varied between 95.4% and 97.3% for the sintered samples containing varying TiB₂ between 1 wt.% and 5 wt.%. Average W grain size in the sintered samples decreased with the addition of Y₂O₃ and TiB₂ particles, from 5.38 μm in the W–1 wt.% Ni sample to 0.8 μm in the W–1 wt.% Ni sample containing 0.5 wt.% Y₂O₃ and 5 wt.% TiB₂ particles. Vickers microhardness values varied between 4.53 GPa and 8.54 GPa. The sample with the composition of W–1 wt.% Ni/0.5 wt.% Y₂O₃ and 5 wt.% TiB₂ had a relative density value of about 95.7% and hardness value of 8.54 GPa after sintering at 1400 °C for 1 h.     

Properties of low temperature belite cements made from aluminosilicate wastes by hydrothermal method

The aim of this study is the synthesis at low temperature (1000 °C) of reactive belite cement, rich in reactive C₂S phases (α′_L and/or β-C₂S), starting from aluminosilicate wastes (oil well drilling mud and hydraulic dam sludge) and hydraulic lime dust recovered from bagging workshops. A hydrothermal treatment of the raw cement mixture was performed in an alkaline solution of KOH (0.6 M), with heating at 100 °C for 4 h under atmospheric pressure and continuous agitation. The burning of the hydrothermal mixture at 1000 °C produced reactive belite cements containing between 79% and 86% of C₂S (α′_L and/or β polymorphs), the rest being C₁₂A₇ (5–8%), C₄AF (7–11%) and free lime (2%). The cements were characterized by X-ray Fluorescence (XRF), X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), microprobe, and laser granulometry. The hardening evolution of belite cement pastes and mortars was followed by thermo-gravimetric analysis (TGA), setting time and compressive strength. The results showed a rapid production of hydrates (C–S–H/C–A–S–H, calcium aluminate hydrates and portlandite), with a fast setting time (reaction of C₁₂A₇) and compressive strength evolution that led to these cements being classified in the 32.5 category according to EN 197-1.     

Microstructure and mechanical properties of in situ TiC and Nd2O3 particles reinforced Ti–4.5 wt.%Si alloy composites

(TiC + Nd₂O₃)/Ti–4.5 wt.%Si composites were in situ synthesized by a non-consumable arc-melting technology. The phases in the composites were identified by X-ray diffraction. Microstructures of the composites were observed by optical microscope and scanning electron microscope. The composite contains four phases: TiC, Nd₂O₃, Ti₅Si₃ and Ti. The TiC and Nd₂O₃ particles with dendritic and near-equiaxed shapes are well distributed in Ti–4.5 wt.%Si alloy matrix, and the fine Nd₂O₃ particles exist in the network Ti + Ti₅Si₃ eutectic cells and Ti matrix of the composites. The hardness and compressive strength of the composites are markedly higher than that of Ti–4.5 wt.%Si alloy. When the TiC content is fixed as 10 wt.% in the composites, the hardness is enhanced as the Nd₂O₃ content increases from 8 wt.% to 13 wt.%, but the compressive strength peaks at the Nd₂O₃ content of 8 wt.%.     

Microstructural and thermochemical properties of Al/AlN/CuAl2 composite prepared by a combination of combustion synthesis and spark plasma sintering

A combination of combustion synthesis (CS) and spark plasma sintering (SPS) technology was employed in the fabrication of Al/AlN/CuAl₂ dense composites. Al/AlN/CuAl₂ composite powders in which a portion of the AlN was present in macro- and nanofiber forms were prepared by combustion of Al–Cu–5 wt.% (C₂F₄)_n, under a nitrogen atmosphere. The resulting composite powders were then subjected to consolidation by SPS at a dwell temperature level of 1500 °C, mechanical pressure of 60 MPa, and a non-isothermal heating time of 10 min. It is found that the actual thermal conductivity of Al/AlN/CuAl₂ composites fabricated with 5 wt.% (C₂F₄)_n is much higher than that of materials prepared in the absence (C₂F₄)_n. Maximum thermal conductivity (320 W/m K) was recorded for the samples prepared from an 0.8Al–0.2Cu–5 wt.% (C₂F₄)_n mixture. The influence of (C₂F₄)_n on the growth mechanism of AlN fibers and thermal conductivity of composite samples is discussed in light of the experimental data.     

Synthesis of partial stabilized cement–gypsum as new dental retrograde filling material

The study describes the sol–gel synthesis of a new dental retrograde filling material partial stabilized cement (PSC)–gypsum by adding different weight percentage of gypsum (25% PSC + 75% gypsum, 50% PSC + 50% gypsum and 75% PSC + 25% gypsum) to the PSC. The crystalline phase and hydration products of PSC–gypsum were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis. The handling properties such as setting time, viscosity, tensile strength, porosity and pH, were also studied. The XRD and microstructure analysis demonstrated the formation of hydroxyapatite and removal of calcium dihydrate during its immersion in simulated body fluid (SBF) on day 10 for 75% PSC + 25% gypsum. The developed PSC–gypsum not only improved the setting time but also greatly reduced the viscosity, which is very essential for endodontic surgery. The cytotoxic and cell proliferation studies indicated that the synthesized material is highly biocompatible. The increased alkaline pH of the PSC–gypsum also had a remarkable antibacterial activity.     

Formulation of mortars with nano-SiO2 and nano-TiO2 for degradation of pollutants in buildings

This paper reports on the design of cement mortars that use nano-SiO₂ (nS) and nano-TiO₂ (nT) particles, aiming to improve the durability of traditional building materials while giving new functionalities (aerial decontamination of pollutants). Samples with 0–2 wt.% nS, 0–20 wt.% nT, 0.45–7 wt.% superplasticizer (SP) and 0.45–0.58 water/binder weight ratio were prepared. The formulations of mortars were defined according to rheology and flow table measurements, then showing suitable workability. The temperature of hydration, compressive strength, water absorption, and photocatalytic degradation of pollutants (NO_x and Orange II dye) were also evaluated. In general, the rheological behavior and the temperature of hydration changed in distinct levels, depending on the dosage and type of nanoadditives, but nT influenced more significantly the results. However, such differences were not identified on the compressive strength and water absorption. In addition, NO_x photocatalytic degradation up to 1 h under solar light ranged from 65% to 80%, while Orange II degradation after 9 h under visible light changed from 18% to 50%.     

Chemical activation of calcium aluminate cement composites cured at elevated temperature

The influence of sodium sulfate, as an activator, on the hydration of calcium aluminate cement (CAC)–fly ash (FA)–silica fume (SF) composites was investigated. Different mixes of CAC with 20% pozzolans (20% FA, 20% SF and 10% FA + 10% SF) were prepared and hydrated at 38 °C for up to 28 days. The hydration products were investigated by XRD, DSC and SEM. The results showed that sodium sulfate accelerated the hydration reactions of calcium aluminate cement as well as the reactions of FA and SF with CAH₁₀ and C₂AH₈ to form the strätlingite (C₂ASH₈). The later reactions prevent the strength loss by preventing the conversion of CAH₁₀ and C₂AH₈ to the cubic C₃AH₆ phase. The acceleration effect of Na₂SO₄ on the reactivity of fly ash was more pronounced than on the reactivity of silica fume with respect to reaction with CAH₁₀ and C₂AH₈ phases.     

Microstructure and tensile strength of PM304 composite

PM304 composite comprising NiCr (80/20) matrix (60 wt.%) combined with Cr₂O₃ (20 wt.%), Ag (10 wt.%) and eutectic BaF₂/CaF₂ (10 wt.%) as solid self-lubricants additives has been successfully prepared by mechanical alloying and powder metallurgy. The sintered PM304 samples were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDXS). The density of PM304 composite sintered at 1100 °C was 7.3 g/cm³, and the mean tensile strength 47 MPa. The size of Cr₂O₃, BaF₂/CaF₂ particles was less than 1 μm, and that of Ag particles below 5 μm. Fracture morphology indicates that the fracture of PM304 is mainly along Ni80Cr20 grains.     

Controlling ettringite formation in FBC fly ash geopolymer concrete

Fluidized bed coal combstion (FBC) is extensively used in small self-generation power plants. The fly ash obtained from this FBC process contains high quantity of calcium and sulfate compounds which hinders its use in the construction industry. In addition, its reactivity is low and additional source material or additive is, therefore, needed to increase the reaction. This research studied the use of Al(OH)₃ and high concentrations of NaOH to control ettringite formation in the FBC fly ash geopolymer. Two replacement levels of 2.5 wt.% and 5.0 wt.% of Al(OH)₃ and three NaOH concentrations of 10, 12 and 15 M were used in the study. Results indicated that the NaOH concentration affected the ettringite formation and strength of the FBC geopolymer. No ettringite was formed at high NaOH concentration of 15 M which helped the dissolution of calcium sulfate and formed the additional calcium hydroxide. The subsequent pozzolanic reaction led to strength gain of the geopolymer. For 15 M NaOH, the addition of 2.5 wt.% Al(OH)₃ promoted the reaction and formed a dense matrix of alumino silicate compound. Relatively high 7-day compressive strength of 30 MPa was obtained.     

Low-firing of BiSbO4 microwave dielectric ceramic with V2O5–CuO addition

Effects of 1.0 wt.% V₂O₅–CuO mixture addition on the sintering behavior, phase composition and microwave dielectric properties of BiSbO₄ ceramics have been investigated. BiSbO₄ ceramics can be well densified below temperature about 930 °C with 1.0 wt.% V₂O₅–CuO mixtures addition with different ratios of CuO to V₂O₅. The formation of BiVO₄ phase and substitution of Cu²⁺ can explain the decrease of sintering temperature. Dense BiSbO₄ ceramics sintered at 930 °C for 2 h exhibited good microwave dielectric properties with permittivity between 19 and 20.5, Qf values between 19,000 and 40,000 GHz and temperature coefficient of resonant frequency shifting between ?71.5 ppm °C^?1 and ?77.8 ppm °C^?1. BiSbO₄ ceramics could be a candidate for microwave application and low temperature co-fired ceramics technology.     

Osteoblast interaction with laser cladded HA and SiO2-HA coatings on Ti–6Al–4V

In order to improve the bioactivity and biocompatibility of titanium endosseous implants, the morphology and composition of the surfaces were modified. Polished Ti–6Al–4V substrates were coated by a laser cladding process with different precursors: 100 wt.% HA and 25 wt.% SiO₂-HA. X-ray diffraction of the laser processed samples showed the presence of CaTiO₃, Ca₃(PO₄)₂, and Ca₂SiO₄ phases within the coatings. From in vitro studies, it was observed that compared to the unmodified substrate all laser cladded samples presented improved cellular interactions and bioactivity. The samples processed with 25 wt.% SiO₂-HA precursor showed a significantly higher HA precipitation after immersion in simulated body fluid than 100 wt.% HA precursor and titanium substrates. The in vitro biocompatibility of the laser cladded coatings and titanium substrate was investigated by culturing of mouse MC3T3-E1 pre-osteoblast cell line and analyzing the cell viability, cell proliferation, and cell morphology. A significantly higher cell attachment and proliferation rate were observed for both laser cladded 100 wt.% HA and 25 wt.% SiO₂-HA samples. Compared to 100 wt.% HA sample, 25 wt.% SiO₂-HA samples presented a slightly improved cellular interaction due to the addition of SiO₂. The staining of the actin filaments showed that the laser cladded samples induced a normal cytoskeleton and well-developed focal adhesion contacts. Scanning electron microscopic image of the cell cultured samples revealed better cell attachment and spreading for 25 wt.% SiO₂-HA and 100 wt.% HA coatings than titanium substrate. These results suggest that the laser cladding process improves the bioactivity and biocompatibility of titanium. The observed biological improvements are mainly due to the coating induced changes in surface chemistry and surface morphology.