Ceramic wastes as alternative raw materials for Portland cement clinker production

The cement industry has for some time been seeking procedures that would effectively reduce the high energy and environmental costs of cement manufacture. One such procedure is the use of alternative materials as partial replacements for fuel, raw materials or even clinker. The present study explores the reactivity and burnability of cement raw mixes containing fired red or white ceramic wall tile wastes and combinations of the two as alternative raw materials.The results showed that the new raw mixes containing this kind of waste to be technically viable, and to have higher reactivity and burnability than a conventional mix, providing that the particle size of the waste used is lower than 90 μm. The mineralogical composition and distribution in the experimental clinker prepared were comparable to the properties of the clinker manufactured with conventional raw materials. Due to the presence of oxides such as ZnO, ZrO₂ and B₂O₃ in tile glazing, the content of these oxides was higher in clinker made with such waste. The mix of red and white ceramic wall tile waste was found to perform equally or better than each type of waste separately, a promising indication that separation of the two would be unnecessary for the purpose described above.     

Waste ammunition as secondary mineralizing raw material in Portland cement production

This paper presents a laboratory scale simulation that aims to investigate the possibility of partially substituting ordinary cement raw mix with waste ammunition materials (WAM), originated from a shooting range in Athens, Greece, in Portland cement clinker production. One reference and twelve modified mixtures, containing 0.5%, 1.0%, 1.5% and 2.0% w/w of three blends of corresponding types of waste ammunition materials, were examined. It was concluded that the three used WAM blends, improve remarkably the burnability of the cement raw mixture, even though in a different extent, without affecting considerably the hydration rate and the cement properties. In spite of the high volatile matter in the WAM, primarily due to high levels of lead present, incorporation degree of the heavy metals present in the WAM blends in the mineralogical clinker compounds was rather high during the sintering process. Leaching tests showed that the heavy metal concentrations in the leachates were kept low.     

Use of recycled glass as a raw material in the manufacture of Portland cement

Scrap glass is a solid waste from daily recycling. Most of the waste glass is sodium-lime-silicate glass which has, more or less, similar chemical compositions to clay, a raw material in cement manufacturing. Therefore, we utilize the solid waste in cement raw mix by replacing part of the clayey component. In this study, the effects of the glass in cement raw mix on clinker burning were investigated. The experimental results show that the addition of the glass into cement raw mix (1) results in the formation of more liquid phase between 950°C to 1250°C compared with conventional raw meals; (2) decreases C₃S content in the clinker; and (3) increases NC₈A₃ content, which leads to flash setting and poor strength development of the cement. Therefore, it is necessary to increase the SG value [SG=SO₃?100%/(1.292 K₂O+0.85 Na₂O)] of the clinker when the glass is present in the raw mix.     

Red mud addition in the raw meal for the production of Portland cement clinker

The aim of the present research work was to investigate the possibility of adding red mud, an alkaline leaching waste, which is obtained from bauxite during the Bayer process for alumina production, in the raw meal for the production of Portland cement clinker. For that reason, two samples of raw meals were prepared: one with ordinary raw materials, as a reference sample ((PC)Ref), and another with 3.5% red mud ((PC)R/M). The effect on the reactivity of the raw mix was evaluated on the basis of the unreacted lime content in samples sintered at 1350, 1400 and 1450 degrees C. Subsequently, the clinkers were produced by sintering the two raw meals at 1450 degrees C. The results of chemical and mineralogical analyses as well as the microscopic examination showed that the use of the red mud did not affect the mineralogical characteristics of the so produced Portland cement clinker. Furthermore, both clinkers were tested by determining the grindability, setting time, compressive strength and expansibility. The hydration products were examined by XRD analysis at 2, 7, 28 and 90 days. The results of the physico-mechanical tests showed that the addition of the red mud did not negatively affect the quality of the produced cement.     

Utilization of steel slag for Portland cement clinker production

The aim of the present research work is to investigate the possibility of adding steel slag, a by-product of the conversion of iron to steel process, in the raw meal for the production of Portland cement clinker. Two samples of raw meals were prepared, one with ordinary raw materials, as a reference sample ((PC)(Ref)), and another with 10.5% steel slag ((PC)(S/S)). Both raw meals were sintered at 1450 degrees C. The results of chemical and mineralogical analyses as well as the microscopic examination showed that the use of the steel slag did not affect the mineralogical characteristics of the so produced Portland cement clinker. Furthermore, both clinkers were tested by determining the grindability, setting times, compressive strengths and soundness. The hydration products were examined by XRD analysis at 2, 7, 28 and 90 days. The results of the physico-mechanical tests showed that the addition of the steel slag did not negatively affect the quality of the produced cement.     

Investigation into the stabilization/solidification performance of Portland cement through cement clinker phases

This research studied the influence of individual heavy metal on the hydration reactions of major cement clinker phases in order to investigate the performance of cement based stabilization/solidification (S/S) system. Tricalcium silicate (C3S) and tricalcium aluminate (C3A) had been mixed with individual heavy metal hydroxide including Zn(OH)2, Pb(OH)2 and Cu(OH)2, respectively. The influences of these heavy metal hydroxides on the hydration of C3S and C3A have been characterized by X-ray diffraction (XRD) and differential scanning calorimetry-thermogravimetry (DSC-TG). A mixture of Zn(OH)2, Pb(OH)2 and Cu(OH)2 was blended with Portland cement (PC) and evaluated through compressive strength and dynamic leach test. XRD and DSC-TG data show that all the heavy metal hydroxides (Zn(OH)2, Pb(OH)2 and Cu(OH)2) have detrimental effects on the hydration of C3A, but only Zn(OH)2 does to the C3S at early curing ages which can completely inhibit the hydration of C3S due to the formation of CaO(Zn(OH)2).2H2O. Cu6Al2O8CO(3).12H2O, Pb2Al4O4(CO3)(4).7H2O and Zn6Al2O8CO(3).12H2O are formed in all the samples containing C3A in the presence of metal hydroxides. After adding CaSO4 into C3A, the detrimental effect of heavy metals increases due to the coating effect of both calcium aluminate sulphates and heavy metal aluminate carbonates. The influence of heavy metal hydroxide on the hydration of C3S and C3A can be used to predict the S/S performance of Portland cement.     

Utilization of municipal solid waste incineration ash in Portland cement clinker

Municipal solid waste incineration (MSWI) ash is used in part as raw materials for cement clinker production by taking advantage of the high contents of SiO₂, Al₂O₃, and CaO. It is necessary for environmental reasons to establish a material utilization system for the incineration waste ash residue instead of disposing these ashes into landfill. The aim of this paper is to study the feasibility of replacing clinker raw materials by waste ash residue for cement clinker production. MSWI bottom ash and MSWI fly ash are the main types of ashes being evaluated. The ashes were mixed into raw mixture with different portions of ash residue to produce cement clinker in a laboratory furnace at approximately 1400°C. X-ray diffraction and X-ray florescence techniques were used to analyze the phase chemistry and chemical composition of clinkers in order to compare these ash-based clinkers with commercial Portland cement clinker.     

Utilization of ferroalumina as raw material in the production of Ordinary Portland Cement

Red mud (RM), the digestion by-product of bauxite processing from “Aluminum Hellas”, was dewatered by means of a filter press. The filtrand with water content from 28 to 32 wt% was named ferroalumina (FA). In order to utilize it as a raw material in the production of Ordinary Portland Cement (OPC), mixtures were prepared with limestone, sandstone and 1, 3 and 5 wt% FA addition, respectively. The design of the mixtures was based on the cement's compositional indexes LSF, AM and SM. Burnability tests showed that less than 1 wt% free lime can be obtained in all cases for firing at 1450 °C, except for the mixture with 1 wt% FA addition, which requires 1550 °C. XRD analysis and optical microscopy examination showed that FA addition did not affect the mineralogical phases of the produced clinkers. The characterisation of the produced Portland cements indicated that differences on surface area, water requirement and setting time are negligible. Compressive strength results after 28 days of curing varies from 55 to 63 MPa, which ranks the produced cements in CEM I 42.5N category. More specifically, the cements with FA addition due to their relatively high 2-day strengths (>20 MPa) can be ranked in CEM I 52.5N category. Addition of FA increases the amount of water-soluble chromium proportionally to the amount of total chromium to the mixture; however, conversion of total Cr to hexavalent Cr remains practically constant, in the range of 32–35 wt%. The results indicate that FA can be used as raw material in the production of OPC up to 5 wt% according to the chemical composition of the other raw materials.     

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.     

The utilization of recycled concrete aggregate to produce controlled low-strength materials without using Portland cement

This paper reports the results of an experimental study that investigated the feasibility of using fine and coarse recycled concrete aggregate (RCA) with slag or fly ash to produce Controlled Low-Strength Materials (CLSM). The main objective was to produce CLSM using only recycled and by-product materials without the need to add Portland cement. In addition to the hydraulic activity of slag and high-calcium fly ash (HCFA), their pozzolanic reaction was activated by the alkalis and calcium hydroxide present in the residual paste of the RCA. Preliminary tests showed mixtures with slag to have 7-day compressive strengths 70% higher than mixtures with fly ash.Two types of CLSM with slag were investigated in further detail: one with fine and the other with fine/coarse RCA. The results showed that the developed CLSMs are suitable for a wide range of applications particularly those requiring structural support and fast hardening.     

Utilization of flotation wastes of copper slag as raw material in cement production

Copper slag wastes, even if treated via processes such as flotation for metal recovery, still contain heavy metals with hazardous properties posing environmental risks for disposal. This study reports the potential use of flotation waste of a copper slag (FWCS) as iron source in the production of Portland cement clinker. The FWCS appears a suitable raw material as iron source containing >59% Fe(2)O(3) mainly in the form of fayalite (Fe(2)SiO(4)) and magnetite (Fe(3)O(4)). The clinker products obtained using the FWCS from the industrial scale trial operations over a 4-month period were characterised for the conformity of its chemical composition and the physico-mechanical performance of the resultant cement products was evaluated. The data collected for the clinker products produced using an iron ore, which is currently used as the cement raw material were also included for comparison. The results have shown that the chemical compositions of all the clinker products including those of FWCS are typical of a Portland cement clinker. The mechanical performance of the standard mortars prepared from the FWCS clinkers were found to be similar to those from the iron ore clinkers with the desired specifications for the industrial cements e.g. CEM I type cements. Furthermore, the leachability tests (TCLP and SPLP) have revealed that the mortar samples obtained from the FWCS clinkers present no environmental problems while the FWCS could act as the potential source of heavy metal contamination. These findings suggest that flotation wastes of copper slag (FWCS) can be readily utilised as cement raw material due to its availability in large quantities at low cost with the further significant benefits for waste management/environmental practices of the FWCS and the reduced production and processing costs for cement raw materials.     

Incorporation of waste materials into portland cement clinker synthesized from natural raw materials

For every ton of portland cement that is manufactured, approximately half a ton of carbon dioxide is released from calcining limestone. One method of reducing the carbon dioxide from portland cement production is to reduce or eliminate the use of limestone through replacement with calcium oxide-bearing waste materials. In this study, portland cement clinker was synthesized using minimal limestone content and maximal waste material content, specifically fly ash and blast furnace slag. The synthetic cements were characterized using X-ray diffraction, scanning electron microscopy, and isothermal calorimetry. Results show that portland cement clinker can be successfully synthesized from a maximam of 27.5% fly ash and 35% slag. The synthetic cements possessed early-age hydration behavior similar to a commercial Type I/II portland cement. However, the presence of sulfur impurities contained in waste materials significantly affected phase formation in portland cement clinker.

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水泥生料中有机碳测定方法研究

采用K2Cr2O7容量法测定水泥生料中有机碳的方法,先以碳酸盐岩国家一级标准物质样品(GBW07135)进行条件试验,结果与标准值相符后再进行生料样品的测定。结果表明,在180℃下持续沸腾25~30 min,有机碳回收率最高;该方法测定结果与元素分析仪和TOC分析仪的测定结果相关性较高,相关系数分别为0.992 6和0.997 7;该法测得的新型干法窑和立窑生料有机碳的95%置信区间分别为0.17%~0.25%和4.36%~7.48%。由于成本低,操作简便,K2Cr2O7容量法是廉价、快速并且精确测定生料有机碳的首选方法。     

Susceptibility of Portland cement and blended cement concretes to plastic shrinkage cracking

The market share of different types of blended cements is increasing year by year. Generally, blended cements are ground to higher fineness and exhibit a slower development of mechanical properties compared to Ordinary Portland Cement (OPC), which might affect the concrete performance in terms of shrinkage cracking at early ages.In this paper, the performance of concretes made with different cement types is compared according to the ASTM C1579-13 standard for plastic shrinkage cracking. The cracking behavior was further correlated to the deformations of both unrestrained and restrained specimens measured by a 3D image correlation system. The main factors influencing the cracking behavior were discussed based on poromechanics. It is concluded that the bulk modulus evolution has a dominant effect on controlling the plastic shrinkage cracking. Concretes made of more reactive cements, in particular with higher clinker content, are less susceptible to plastic shrinkage cracking. For cements with the same clinker content, increasing the cement fineness reduces the risk of plastic shrinkage cracking.     

Examination of the jarosite-alunite precipitate addition in the raw meal for the production of sulfoaluminate cement clinker

The aim of the present research work was to investigate the possibility of adding a jarosite-alunite chemical precipitate, a waste product of a new hydrometallurgical process developed to treat economically low-grade nickel oxides ores, in the raw meal for the production of sulfoaluminate cement clinker. For that reason, two samples of raw meals were prepared, one contained 20% gypsum, as a reference sample ((SAC)Ref) and another with 11.31% jarosite-alunite precipitate ((SAC)J/A). Both raw meals were sintered at 1300 degrees C. The results of chemical and mineralogical analyses as well as the microscopic examination showed that the use of the jarosite-alunite precipitate did not affect the mineralogical characteristics of the so produced sulfoaluminate cement clinker and there was confirmed the formation of the sulfoaluminate phase (C4A3S), the most typical phase of this cement type. Furthermore, both clinkers were tested by determining the grindability, setting time, compressive strength and expansibility. The hydration products were examined by XRD analysis at 2, 7, 28 and 90 days. The results of the physico-mechanical tests showed that the addition of jarosite-alunite precipitate did not negatively affect the quality of the produced cement.     

Characterisation of ground hydrated Portland cement-based mortar as an additive to alkali-activated slag cement

The sustainable development of cement manufacturing requires extension of the raw material base, including large-tonnage waste. Hydrated mortar waste is a promising mineral resource for the production of Portland cements and alternative binders, such as alkali-activated slag cement. The influences of ground-hydrated mortar aged for 3 months on the properties of alkali-activated slag fresh and hardened pastes were performed. The results show that the properties are dependent on the concentration (2.5–60%), cement:sand ratio (1:1–3) and fineness (200–600 m²/kg) of the ground hydrated mortar; the alkali activator (sodium carbonate and sodium silicate); and the curing conditions (normal conditions and steam curing). The fresh paste properties that we considered in this study included the water requirement and the setting time; the hardened paste properties we considered were the water absorption, the density, and the compressive strength after 2, 7, 14, 28, 180 and 360 days of ageing. The ground hydrated mortar improved the early strength and the long-term strength of the alkali-activated slag paste and replaced the slag up to 50%. The factors that affecting the strength of the alkali-activated slag cement with ground hydrated mortar as an additive were, in order of influence, alkali activator type > curing conditions > cement:sand ratio > ground-hydrated mortar fineness.     

Recycling petroleum coke in blended cement mortar to produce lightweight material for Impact Noise Reduction

This work introduces a new way to use low-cost petroleum (pet) coke as lightweight aggregate in cement mortars to make sound barriers. The feasibility of adding pet coke in cement matrix was investigated: an in-depth characterization of as-received coke and the new lightweight mortar was made. The acoustic behaviour herein was assessed by constructing a large dimension mortar slab (made of cement and coke as aggregate) used as floor covering and measuring, according to the procedure described in international standards, the impact noise pressure level over the range of frequencies 100–5000 Hz. Impact Noise Reduction (INR) was also obtained and the results were compared to the ones experimentally obtained from a control mortar slab (made of cement and sand). Results showed that coke addition leads to a decrease in mechanical properties of resultant mortars, this is principally due to an increase of the porosity (∼60%). A gradual increase of impact noise insulation was observed in lightweight floor covering from middle to higher frequencies tested, reaching, within this range, a remarkable improvement of sound insulation compared to control slab (∼14 dB).     

Recycling petroleum coke in blended cement mortar to produce lightweight material for Impact Noise Reduction

This work introduces a new way to use low-cost petroleum (pet) coke as lightweight aggregate in cement mortars to make sound barriers. The feasibility of adding pet coke in cement matrix was investigated: an in-depth characterization of as-received coke and the new lightweight mortar was made. The acoustic behaviour herein was assessed by constructing a large dimension mortar slab (made of cement and coke as aggregate) used as floor covering and measuring, according to the procedure described in international standards, the impact noise pressure level over the range of frequencies 100–5000 Hz. Impact Noise Reduction (INR) was also obtained and the results were compared to the ones experimentally obtained from a control mortar slab (made of cement and sand). Results showed that coke addition leads to a decrease in mechanical properties of resultant mortars, this is principally due to an increase of the porosity (～60%). A gradual increase of impact noise insulation was observed in lightweight floor covering from middle to higher frequencies tested, reaching, within this range, a remarkable improvement of sound insulation compared to control slab (～14 dB).     

Potential use of pyrite cinders as raw material in cement production: Results of industrial scale trial operations

Pyrite cinders, which are the waste products of sulphuric acid manufacturing plants, contain hazardous heavy metals with potential environmental risks for disposal. In this study, the potential use of pyrite cinders (PyCs) as iron source in the production of Portland cement clinker was demonstrated at the industrial scale. The chemical and mineralogical analyses of the PyC sample used in this study have revealed that it is essentially a suitable raw material for use as iron source since it contains >87% Fe₂O₃ mainly in the form of hematite (Fe₂O₃) and magnetite (Fe₃O₄). The samples of the clinkers produced from PyC in the industrial scale trial operation of 6 months were tested for the conformity of their chemical composition and the physico-mechanical performance of the resultant cement products. The data were compared with the clinker products of the iron ore, which is used as the raw material for the production Portland cement clinker in the plant. The chemical compositions of all the clinker products of PyC appeared to conform to those of the iron ore clinker, and hence, a Portland cement clinker. The mechanical performance of the mortars prepared from the PyC clinker was found to be consistent with those of the industrial cements e.g. CEM I type cements. It can be inferred from the leachability tests (TCLP and SPLP) that PyC could be a potential source of heavy metal pollution while the mortar samples obtained from the PyC clinkers present no environmental problems. These findings suggest that the waste pyrite cinders can be readily used as iron source for the production of Portland cement. The availability of PyC in large quantities at low cost provides further significant benefits for the management/environmental practices of these wastes and for the reduction of mining and processing costs of cement raw materials.