Hydration Properties of Eco-Cement Pastes from Waste Sludge Ash Clinkers

Abstract

Three types of hydraulic cements have been developed by incorporating sludge ash from a primary sewage treatment plant and a water purification plant, as well as slag from steelworks (ferrate), as a partial replacement for clay, silica, alumina, and iron oxide in raw cement meal. The raw meal for the pre-determined recipes was prepared by heating it to 1400 °C for 6 hr in a clinkerization process, using a simulated incinerator and smelter. The major components of ordinary Portland cement, C₃S, C₂S, C₃A, and C₄AF, were all found in the clinkers. Of the three types of eco-cements, the eco-cement A paste was most similar to ordinary Portland cement in terms of composition and compressive strength development, while the eco-cement B paste showed early strength development. The differential thermal analysis species analyses indicated that the hydrates in the eco-cement pastes were mainly calcium hydroxide and CSH gels, like those found in ordinary Portland cement paste. Moreover, the degree of hydration, as determined by nuclear magnetic resonance, increased in all eco-cement pastes with an increasing curing age. The results indicate that it indeed is feasible to use sludge ash and ferrate to replace up to 20% of the mineral components of raw materials for cement.     

Latent hydraulic reactivity of blended cement incorporating slag made from municipal solid waste incinerator fly ash

The reactivity of cement pastes made by blending Portland cement with slag from municipal solid waste incinerator (MSWI) fly ash was investigated to assess the potential of recycling MSWI fly ash slag. The slag, prepared by melting MSWI fly ash at 1400 degrees C for 30 min, was pulverized and ground, then blended with ordinary Portland cement (OPC), using various substitution levels to make slag-blended cement (SBC). The pozzolanic reactivity of the ecocement was then characterized by determining variations in the compressive strength, degree of hydration, microstructure, speciation, and mineralogical crystalline phases. The results suggest that the strength of the pastes at an early age decreased with increasing substitution levels, whereas the strength at a later age of the tested pastes (with substitution levels less than 10%) outperformed OPC paste because of typical SBC properties. The development of strength at a later age was also confirmed by X-ray diffraction and scanning electron microscopy techniques. This implies that active silica (Si) and alumina (Al) react with the hydration product, calcium hydroxide (Ca(OH)2), to form calcium silicate hydrate (C-S-H), which contributed to strength development at a later age by the filling up of pores in the SBC pastes. The pozzolanic activity of the SBC pastes indicates that it is suitable for use as a substitute for OPC in blended cement.     

Latent Hydraulic Reactivity of Blended Cement Incorporating Slag Made from Municipal Solid Waste Incinerator Fly Ash

Abstract

The reactivity of cement pastes made by blending Portland cement with slag from municipal solid waste incinerator (MSWI) fly ash was investigated to assess the potential of recycling MSWI fly ash slag. The slag, prepared by melting MSWI fly ash at 1400 °C for 30 min, was pulverized and ground, then blended with ordinary Portland cement (OPC), using various substitution levels to make slag-blended cement (SBC). The pozzolanic reactivity of the ecocement was then characterized by determining variations in the compressive strength, degree of hydration, microstructure, speciation, and mineralogical crystalline phases. The results suggest that the strength of the pastes at an early age decreased with increasing substitution levels, whereas the strength at a later age of the tested pastes (with substitution levels less than 10%) outperformed OPC paste because of typical SBC properties. The development of strength at a later age was also confirmed by X-ray diffraction and scanning electron microscopy techniques. This implies that active silica (Si) and alumina (Al) react with the hydration product, calcium hydroxide (Ca(OH)₂), to form calcium silicate hydrate (C-S-H), which contributed to strength development at a later age by the filling up of pores in the SBC pastes. The pozzolanic activity of the SBC pastes indicates that it is suitable for use as a substitute for OPC in blended cement.     

Characterization of eco-cement paste produced from waste sludges

In this study, marble sludge, sewage sludge, drinking water treatment plant sludge, and basic oxygen furnace sludge were used as replacements for limestone, sand, clay, and iron slag, respectively, as the raw materials for the production of cement in order to produce eco-cement. It was found that it is feasible to use marble sludge to replace up to 50% of the limestone and also that other materials can serve as total replacements for the raw materials typically used in the production of cement. The major components of Portland cement were all found in eco-cement clinkers. The eco-cement was confirmed to produce calcium hydroxide and calcium silicate hydrates during the hydration process, increasing densification with the curing age. The compressive strength (S_c) and microstructural evaluations conducted at 28 d revealed the usefulness of eco-cement. It was observed that the S_c data correlated linearly with the pore volume (P) data at 28 d. The proposed model equation could be represented as S_c = 178-461P (correlation coefficient, R² = 0.96). Two parameters, the large capillary pore volume and the medium capillary pore volume, were evaluated using multiple regression analysis.     

Pozzolanic reactivity of the synthetic slag from municipal solid waste incinerator cyclone ash and scrubber ash

This study investigates the pozzolanic reactions and compressive strength of the blended cement manufactured using synthetic slag obtained from municipal solid waste incinerator (MSWI) cyclone ash and scrubber ash as partial replacement of portland cement. The synthetic slag was made by co-melting the MSWI scrubber ash and cyclone ash mixtures at 1400 degrees C for 30 min. Following pulverization, the different types of slag were blended with cement as cement replacement at ratios ranging from 10 to 40 wt %. The synthetic slag thus obtained was quantified, and the characteristics of the slag-blended cement pastes were examined. These characteristics included the pozzolanic activity, compressive strength, hydration activity, crystal phases, species, and microstructure at various ages. The 90-day compressive strength developed by slag-blended cement pastes with 10 and 20 wt % of the cement replaced by the synthetic slag outperformed ordinary portland cement by 1-7 MPa. X-ray diffraction species analyses indicated that the hydrates in the slag-blended cement pastes were mainly portlandite, the calcium silicate hydrate gels, and calcium aluminate hydrate salts, similar to those found in ordinary portland cement paste. Differential thermal and thermogravimetric analysis also indicated that the slag reacted with portlandite to form calcium silicate hydrate gels.     

基于响应面法的污泥快速固化效能综合影响

针对现有污泥固化技术存在的固化养护时间长、低温条件下固化效能低等问题。研究提出污泥快速（3d）固化技术，采用响应曲面分析方法，重点考察了石灰、组分A、硅酸盐水泥、粉煤灰和温度等5因素对固化效能的综合影响，研究结果表明，石灰、组分A、硅酸盐水泥、粉煤灰和养护温度等因素对3d固化体的无侧限抗压强度和含水率的线性效应显著，石灰和组分A、石灰和养护温度对无侧限抗压强度的交互影响显著，石灰和粉煤灰、组分A和养护温度、硅酸盐水泥和粉煤灰对含水率的交互影响显著；得出了5因素对固化体3d无侧限抗压强度和含水率影响的定量模型，可对污泥快速固化进行优化和预测；并利用XRD和SED对污泥固化块的化学成分和微观结构进行了分析。     

基于响应面法的污泥快速固化效能综合影响简

针对现有污泥固化技术存在的固化养护时间长、低温条件下固化效能低等问题。研究提出污泥快速（3 d）固化技术，采用响应曲面分析方法，重点考察了石灰、组分A、硅酸盐水泥、粉煤灰和温度等5因素对固化效能的综合影响，研究结果表明，石灰、组分A、硅酸盐水泥、粉煤灰和养护温度等因素对3 d固化体的无侧限抗压强度和含水率的线性效应显著，石灰和组分A、石灰和养护温度对无侧限抗压强度的交互影响显著，石灰和粉煤灰、组分A和养护温度、硅酸盐水泥和粉煤灰对含水率的交互影响显著；得出了5因素对固化体3 d无侧限抗压强度和含水率影响的定量模型，可对污泥快速固化进行优化和预测；并利用XRD和SED对污泥固化块的化学成分和微观结构进行了分析。     

Fluidized-bed-combustion ash for the solidification and stabilization of a metal-hydroxide sludge

Fluidized-bed-combustion (FBC) ash is a by-product from a developing technology for coal-fired power plants that will economically reduce air emissions to meet requirements of the Clean Air Act. FBC ash has physical and chemical properties similar to Portland cement, but only has moderate success as a pozzolan in concrete applications due to low compressive strengths. However, FBC ash has proven effective for use as a binder for the solidification and stabilization (S/S) of metal-bearing sludges. Physical and chemical characterization procedures were used to analyze FBC ash and a metal-bearing sludge obtained from a hazardous waste treatment facility to develop 12 different S/S mix designs. The mix designs consist of four binder designs to evaluate sludge-to-binder ratios of approximately 0, 0.5, and 1. Portland cement is used as a control binder to compare unconfined compressive strengths and Toxicity Characteristic Leaching Procedure (TCLP) analyses from different ratios of the FBC ash streams: fly ash, char, and spent bed material (SBM). Compressive strengths ranging from 84 lbs per square inch (psi) to 298 psi were obtained from various mix designs containing different sludge-to-ash ratios cured for 28 days. All the mix designs passed the TCLP. Recoveries from leaching for each metal were less than 5% for most mix designs. Results of unconfined compressive strengths, TCLP, and percent recovery calculations indicate that the mix design containing approximately a 1:1 ratio of fly ash to char-and-sludge is the best mix design for the S/S of the metal-bearing sludge.     

固体废弃物对新拌水泥浆体密实度与强度的影响

研究固体废弃物(石灰石粉、粉煤灰、赤泥和矿渣)作掺合料颗粒体系与新拌浆体填充密实性能的关系;分析了在水胶比为0.3时,以上4种固体废弃物以不同比例等质量取代水泥的净浆强度。实验结果表明,石灰石粉、粉煤灰、赤泥作为掺合料,能够改善胶凝材料的颗粒级配,填充新拌水泥浆体中的孔隙,使浆体更为密实,并且对其净浆的强度有利。     

Influence of thermally activated paper sludge on the behaviour of blended cements subjected to saline and non-saline environments

Background, aim and scope  One of the problems to affect Portland cement matrices is low resistance to aggressive agents, due principally to the presence of a high content of portlandite in the hydrated cements. Pozzolanic materials have played an important role in the improving the durability of cement-based materials for decades. This work studies the behaviour of cement mortar matrices blended with 10% calcined paper sludge (source for metakaolinite) and exposed to different environmental conditions (saline and non-saline environments) after 6 and 12 months of exposure. Materials and methods  Two cements were studied: an ordinary Portland cement (CEM 1, 42.5R), acting as reference cement, and a blended cement formulated by mixing 90% (by mass) of CEM 1, 42.5R with 10% (by mass) of paper sludge calcined at 700°C for 2 h. The specimens were exposed 1 year to saline and non-saline environments. All the mineralogy samples were studied through X-ray diffraction and scanning electron microscopy (SEM) equipped with an energy dispersive X-ray analyser. The in-depth study on ionic mobility was performed on samples subjected to natural exposure (coast and tableland) for 6 and 12 months. Results  Portland cement was composed of quartz, calcite, calcium hydroxide and tobermorite gels. The pozzolanic cement (10% calcined paper sludge) is of the same composition but a high calcite concentration and barium carbonate. SEM analysis from coastline show deposits of variable composition. The deposits are identified on the surface of different mineral components. The minerals from tableland are much fractured, i.e. calcite and feldspars. Inside the fractures, the deposits and the ions are located and trapped superficially. Discussion  SEM analysis of control cement Portland and 10% calcined paper sludge shows deposits on quartz and calcite with a very high concentration of Pb, Zn, Cl and barium sulphate. A very porous aspect is due to the presence of the different aggregate types. This porous configuration permits retention of the ion environment. The pozzolanic cement in environments subject to the saline mist favours the retention and transport of ions observed. Something similar also happens with the increase in exposure to outdoor weather. Non-saline samples show temperature changes (ice or thaw cycles). Barium retention is kept on the surface in fracture lines by the gelification processes. In general, it may be inferred that an increase in exposure time increases the diffusion of ions towards test piece interiors. The chemical composition profiles show that the ions present different penetration speeds. Conclusions  The results indicate the better vulnerability of pozzolanic cements from calcined paper sludge in saline and non-saline environments. The cements with a 10% addition of calcined paper sludge favour retention and transport of ion has been observed. Recommendations and perspectives  Today, projects are centred on a new recycling line for industrial waste of this kind, with special attention on its incorporation in cement manufacture as a pozzolanic material, setting the most appropriate activation conditions of the mineralogical compound in this waste (kaolinite and metakaolinite) and taking them as a starting point for this project. The use of pozzolanic cement with 10% addition of calcined paper sludge is a system which favours ionic retention.     

The effects of nanomaterials on microstructures of sludge ash cement paste

To broaden the beneficial reuse of sewage sludge, small amounts of nanomaterial were considered as additives to evaluate influences of nanomaterials on microstructures of sludge cement paste. Paste specimens were manufactured using different mix designs and cured for various ages. Tests such as scanning electron microscope, X-ray diffraction, transmission electron microscope, and mercury intrusion porosimetry were then performed. Results obtained indicated that the quantities of crystallization in hydrates rose with the increased amounts of nanomaterial added. Moreover, nanomaterial additives could make crystallizations denser, pore sizes smaller, and the number of pores decreased. Consequently, the strength of sludge cement paste became better as more amounts of nanomaterial were added.     

Fly and bottom ashes from biomass combustion as cement replacing components in mortars production: Rheological behaviour of the pastes and materials compression strength

In the present research mortar pastes obtained by replacing a commercial cement with the equivalent mass of 5, 10, 20 and 30 wt.% of fly ash or bottom ash from fir chips combustion, were prepared and rheologically characterized. It was observed that the presence of ash modifies their rheological behaviour with respect to the reference blend due to the presence, in the ashes, of KCl and K₂SO₄ which cause precipitation of gypsum and portlandite during the first hydration stages of the pastes. Hydrated materials containing 5 wt.% of ash display compression strength and absorption at 28 d of same magnitude as the reference composition; conversely, progressive increase of ash cause a continuous decline of materials performances. Conversely, samples tested after 180 d display a marked decline of compression strength, as a consequence of potassium elution and consequent alkali-silica reaction against materials under curing.     

A Modified Power Law Representation of the Pasquill-Gifford Dispersion Coefficients

Abstract

To broaden the beneficial reuse of sewage sludge, small amounts of nanomaterial were considered as additives to evaluate influences of nanomaterials on microstructures of sludge cement paste. Paste specimens were manufactured using different mix designs and cured for various ages. Tests such as scanning electron microscope, X-ray diffraction, transmission electron microscope, and mercury intrusion porosimetry were then performed. Results obtained indicated that the quantities of crystallization in hydrates rose with the increased amounts of nanomaterial added. Moreover, nanomaterial additives could make crystallizations denser, pore sizes smaller, and the number of pores decreased. Consequently, the strength of sludge cement paste became better as more amounts of nanomaterial were added.     

污泥焚烧灰固化处理技术研究

研究了硅酸盐水泥、高铝水泥、高岭土和β-萘系减水剂在污泥焚烧灰固化技术中的应用效果。考察了污泥焚烧灰固化块(以下简称固化块)的抗压强度,测定了固化块的重金属浸出毒性,并采用X射线衍射(XRD)和扫描电镜(SEM)分析固化块组成和微观结构。结果表明,4种物质对提高固化块的抗压强度均具有较好的效果,硅酸盐水泥、高铝水泥、高岭土和β-萘系减水剂的适宜掺量分别为10、30、20、1.0g(以100g污泥焚烧灰中掺加的质量计)。XRD和SEM分析结果显示,经固化处理后制得的固化块结构密实,存在石英(SiO2)、水化硅铝酸钙(CaAl2Si2O8)和水化硅酸铝钙(Ca2Al2SiO7)等物质,其中水化硅铝酸钙等凝胶物质有利于提高固化块的抗压强度。     

Possible reuse of Egyptian controlled cement dust

Possibilities for the reuse of controlled cement dust, collected from the hopper of the electrostatic precipitators installed on the different cement kilns of two of the three biggest companies for Portland cement production located to the south of Cairo, have been investigated. Twenty-one factors representing the physical properties and mineral and chemical composition of the cement dust were estimated and discussed. The results have been compared with the corresponding figures of three Portland cement companies in the United Arab Emirates and also with the British Standard Requirements of ordinary Portland cement. The study found that the cement dust can be reused after some feasible treatments, such as increasing the fineness and tricalcium silicate ratio and decreasing its alkalinity. Consequently, in this circumstance, pollution prevention at source is proving to be a boon as it can not only bring down pollution levels but also add to the companies' profits through efficient use of resources.     

南京城市污泥发酵苏云金杆菌培养基成分优化

研究南京江心州污水处理厂污泥作为原料发酵生产苏云金杆菌(Bacillus thringiensis)的可行性,并与常规的工业发酵黄豆粉培养基发酵B.thringiensis做比较,结果表明,以固形物含量3%的污泥为基质发酵B.thringiensis,其菌体数及芽孢数只有108个/mL,而工业发酵黄豆粉培养基发酵B.thringiensis菌体数及芽孢数为109个/mL。优化污泥发酵生产苏云金杆菌培养基成分,将污泥与不同量的黄豆粉复配作基质发酵B.thringiensis,结果发现,在污泥中添加15 g/L黄豆粉可基本满足工业发酵生产的需要,发酵72 h获得的B.thringiensis细胞总数及芽孢数均在109个/mL以上。以黄粉虫作试虫的生物毒性实验表明,复配后的基质与工业发酵黄豆粉培养基生产的B.thringiensis孢晶混合液的毒性相当。     

城市河涌受污染底泥的固化/稳定化处理

为了给河涌疏浚底泥的资源化提供技术支持,以广州市车陂涌表层受污染底泥为研究对象,用水泥、石灰、粉煤灰、膨润土等材料对底泥进行固化/稳定化处理实验。通过无侧限抗压强度、污染物在模拟自然条件下(中性)的释放特征、毒性浸出实验(酸性条件)对固化/稳定化处理效果进行综合分析。结果表明:经合适的处理后,固化体抗压强度能高于300 kPa;固化体自然条件下重金属的释放量明显减少,固化/稳定化处理能够有效减缓和减少固化体的二次污染;毒性浸出实验结果表明,河涌底泥经固化/稳定化处理后其重金属浸出能力显著降低。     

A comparison between sludge ash and fly ash on the improvement in soft soil

In this study, the strength of soft cohesive subgrade soil was improved by applying sewage sludge ash as a soil stabilizer. Test results obtained were compared with earlier tests conducted on soil samples treated with fly ash. Five different proportions of sludge ash and fly ash were mixed with soft cohesive soil, and tests such as pH value, compaction, California bearing ratio, unconfined compressive strength (UCS), and triaxial compression were performed to understand soil strength improvement because of the addition of both ashes. Results indicate that pH values increase with extending curing age for soil with sludge ash added. The UCS of sludge ash/soil were 1.4-2 times better than untreated soil. However, compressive strength of sludge ash/soil was 20-30 kPa less than fly ash/soil. The bearing capacities for both fly ash/soil and sludge ash/soil were five to six times and four times, respectively, higher than the original capacity. Moreover, the cohesive parameter of shear strength rose with increased amounts of either ash added. Friction angle, however, decreased with increased amounts of either ash. Consequently, results show that sewage sludge ash can potentially replace fly ash in the improvement of the soft cohesive soil.     

垃圾焚烧飞灰浸出特性及固化试验的研究

垃圾焚烧飞灰残留有重金属元素和二恶英等物质而被认为是危险废物,必须对之进行稳定化处理.通过试验研究分析了国内首家自主开发成功的广东省东莞市某回转窑垃圾焚烧发电厂垃圾焚烧飞灰的化学成分及矿物组成,研究了飞灰的浸出毒性,考察了水泥固化焚烧飞灰的效果,并与熔融/玻璃固化进行了比较.研究表明,该焚烧飞灰中重金属Cd的浸出毒性严重超标,并且随pH值的减小而增大,水泥固化效果随龄期的增大而更加显著.熔融/玻璃固化的效果优于水泥固化,但其经济性有待提高.     

Preparation and characterization of green bricks using pharmaceutical industrial wastes

This paper reports on recycling of industrial wastes (three pharmaceutical industrial sludges) into environmental friendly value-added materials. Stabilization/Solidification (S/S or bricks) process was applied to make a safer way for the utilization of pharmaceutical waste. The additives in this study include binders (cement, lime and bentonite) and strengthening material (pulverized fuel ash (PFA), silica fume and quarry dust) was used at different compositions. Bricks were cured for 28 days, and the following analysis-like compressive strength, leachability of heavy metals, mineralogical phase identity by X-ray diffraction (XRD) spectroscopy, Fourier transform infrared spectroscopy (FTIR) and thermal behaviour by thermogravimetric-differential thermal analysis (TG-DTA) had done. All the bricks were observed to achieve the standard compressive strength as required for construction according to BIS standards. Metal concentration in the leachate has reached the dischargeable limits according to Brazilian standards. Results of this study demonstrate that production of bricks is a promising and achievable productive use of pharmaceutical sludge.