Utilization of weathered phosphogypsum as set retarder in Portland cement

In this study, usability of weathered phosphogypsum (PG) from residue areas as set retarder in Portland cement was investigated. The effects on the setting and mechanical properties of PG added in ratios 1, 3, 5, 7, 10, and 12.5 wt.% to Portland cements were studied and compared with a Portland cement containing natural gypsum (NG). It was found that PG can be used in place of NG for Portland cement according to Turkish standards. The highest 28-day compressive strength was found in the sample with 3 wt.% PG.     

Hospital waste ashes in Portland cement mortars

Nowadays, most concretes incorporate mineral additions such as pozzolans, fly ash, silica fume, blast furnace slag, and calcareous filler among others. Although the technological and economical benefits were the main reasons for the use of mineral additions, the prevention of environmental contamination by means of proper waste disposal becomes a priority. The chance of incorporating hospital waste ashes in Portland cement-based materials is presented here. Ash characterization was performed by chemical analysis, X-ray diffraction, radioactive material detection, and fineness and density tests. Conduction calorimetry and setting time tests were developed on pastes including ash contents from 0% to 100%. Mortars were prepared including ash contents up to 50% of cement. The results of setting time, temperature development, flexural and compressive strengths, water absorption, density, and leachability are analyzed. Results indicate that Portland cement systems could become an alternative for the disposal of this type of ashes.     

Preparation of hardened tiles from waste phosphogypsum by a new intermittent pressing hydration

The solid waste phosphogypsum (PG), as the sole-raw material, was processed into hardened tiles with favorable mechanical strength by a novel intermittent pressing hydration process. First, the raw PG with dihydrate gypsum was dehydrated into semi-hydrate gypsum. The dehydrated PG was granulated with water, press-formed, and then immersed in water under intermittent pressing. Using the optimal granulation humidity of 35%, pressing pressure of 20 MPa, pressing frequency of once per 2 min and total times of 24, PG hardened tiles with bending strength of 18.9 MPa was obtained. It was revealed that the dehydrated PG was hydrated into the dense dihydrate gypsum crystals under the action of intermittent pressing, which contributed to the high mechanical strength of the tiles. The hardened tile has the potential to be a new-type wall material and its application may help to solve PG׳s environmental risk.     

Waste fuels: their effect on Portland cement clinker

Nowadays, different kinds of industrial wastes are increasingly used in the clinkering process by the cement industry, with the aim of taking advantage of their energy content or confining unsuitable substances. This work evaluates the physicochemical characteristics of the clinkers obtained after incorporating three different wastes in different proportions: two of them with energetic capacity—trade marked waste fuel and waste carbon of petroleum—and the third that would be confined—pyrolitic carbon.The fusion temperature of the mixtures, the differential thermal analysis and the thermogravimetric analysis (DTA/TG) during clinkering and after hydration, the specific surface area at the same milling times, X-ray diffraction (XRD) and mechanical strength of the pastes elaborated with a water/cement 0.4 relation were analyzed. The results obtained were compared to those of the clinker obtained without additions.     

An investigation into the effect of various chemical and physical treatments of a South African phosphogypsum to render it suitable as a set retarder for cement

The work describes various physical and chemical treatments to eliminate the deleterious effects of impurities in phosphogypsum on the delayed setting time and impaired strength development behaviour of cement to which it was added as a set regulator. The physical treatments included washing, milling, and ultrasonic treatment of the material, while the chemical treatments dealt with acidic and basic additions to the phosphogypsum during the washing stage. It was found that chemical treatment with a milk of lime solution, which is often recommended in literature, was ineffective in reducing set retardation. Treatment with ammonium hydroxide or sulphuric acid was more effective in this regard. Intergrinding phosphogypsum with slaked lime improved its effectiveness in reducing set retardation, but the use of unslaked lime was less effective and also resulted in marked reductions in compressive strengths. A combined treatment of wet milling phosphogypsum with a lime slurry in a ball mall was derived from these experiments and is recommended for full-scale plant applications.     

Immobilization of chromium (VI) evaluated by binding isotherms for ground granulated blast furnace slag and ordinary Portland cement

The interaction mechanisms of the Cr(VI) ion in presence of GGBFS and OPC were evaluated by chromium binding isotherms and by pore solution analysis. The chromium in the final leaching solution was measured and the solid samples were investigated by SEM and by XRD. GGBFS was more efficient than OPC in fixing Cr ions at lower initial concentrations. However, from an initial Cr(VI) concentration of 2000 and 5000 mg/L, OPC was more efficient.

For an initial Cr(VI) concentration of 50 000 mg/L, around 145 mg Cr/g was fixed by OPC and only 8 and 55 mg Cr/g were fixed by GGBFS in alkaline and water-based immersion solutions, respectively. The Cr-bearing phases identified by XRD and SEM are: CaCrO₄ and CaCrO₄·2H₂O, C–S–H and calcium aluminate phases. The pore solution chemistry indicates that a value around 92% of chromium was retained by GGBFS and 87% by OPC.     

Calcium sulfoaluminate cement blended with OPC: A potential binder to encapsulate low-level radioactive slurries of complex chemistry

Investigations were carried out in order to solidify in cement a low-level radioactive waste of complex chemistry obtained by mixing two process streams, a slurry produced by ultra-filtration and an evaporator concentrate with a salinity of 600 gxL^− 1. Direct cementation with Portland cement (OPC) was not possible due to a very long setting time of cement resulting from borates and phosphates contained in the waste. According to a classical approach, this difficulty could be solved by pre-treating the waste to reduce adverse cement–waste interactions. A two-stage process was defined, including precipitation of phosphates and sulfates at 60 °C by adding calcium and barium hydroxide to the waste stream, and encapsulation with a blend of OPC and calcium aluminate cement (CAC) to convert borates into calcium quadriboroaluminate. The material obtained with a 30% waste loading complied with specifications. However, the pre-treatment step made the process complex and costly. A new alternative was then developed: the direct encapsulation of the waste with a blend of OPC and calcium sulfoaluminate cement (CS̄̄A) at room temperature. Setting inhibition was suppressed, which probably resulted from the fact that, when hydrating, CS̄̄A cement formed significant amounts of ettringite and calcium monosulfoaluminate hydrate which incorporated borates into their structure. As a consequence, the waste loading could be increased to 56% while keeping acceptable properties at the laboratory scale.     

磷石膏制水泥缓凝剂工艺述评

简要叙述了磷石膏利用的基本概况 ,介绍了几种各具特色的磷石膏制水泥缓凝剂的生产工艺流程 ,以及作者的实验流程     

阿利特—硫铝酸盐水泥与硅酸盐水泥复合性能的研究

研究了阿利特－硫铝酸盐水泥与硅酸盐水泥复合所制备的水泥的性能。结果表明,复合后水泥的强度性能优于单一品种水泥的性能;凝结时间则由复合体中占比例较多的一种水泥所控制。     

磷石膏联产水泥,硫酸烧成工艺的热耗分析

通过热工标定，对磷石膏制酸联产水泥的中空窑煅烧工艺熟料烧成热耗进行了分析，结果表明其热效率为42％～45％，达到或超过了相同生产能力的普通水泥五级旋风预热器窑热效率水平，且系统简单，操作控制可靠，因而具有较强的生命力。当前的重要工作为进一步优化系统设计与生产管理，确保系统长周期稳定、优质地运转。经热工分析预测，煅烧磷石膏生料的预热器窑工艺熟料烧成热耗为1500×4．18～1550×4．18kJ／kg·熟料，理论SO2浓度10．5％～10．8％，与中空窑比较，热耗降低10％～15％、SO2气浓提高约1％。系统存在的研究课题为预热器漏风、烟气中CO2、H2O（g）对处于悬浮状态的还原剂──焦炭粉末稳定性的影响等。     

水淬矿渣微细粉配制水泥的研究

研究了水淬矿渣的特性,检测了不同细度、掺量的矿渣微粉与Ｐ·Ⅰ熟料或Ｐ·Ｏ配制的Ｐ·Ｓ或复合硅酸盐水泥的性质。认为矿渣与熟料分别粉磨然后混拌在技术上是可行的,适宜的矿渣细度、掺量与熟料或Ｐ·Ｏ可配制成系列Ｐ·Ｓ或复合硅酸盐水泥。     

磷石膏的微量组分及其对水泥凝结、水化和硬化的影响

借助差热分析、热失重、X射线衍射和扫描电镜等测试手段,分析了磷石膏的微量组分,研究了磷石膏对硅酸盐水泥物理性能及水化过程和水化产物的影响,进而探讨了磷石膏对水泥单矿物的水化作用机理。     

The influence of municipal solid waste incinerator fly ash slag blended in cement pastes

This study investigates the effect of mixing Type I, Type II, and Belite cements with municipal solid waste incinerator (MSWI) fly ash slag-blended cement (FASBC). The experimental results showed that a 10-40% slag replacement of by caused an increase in the initial and the final setting time. The toxicity characteristic leaching procedure (TCLP) results show that the heavy metal content met the Environmental Protection Administration (EPA) regulatory limits. From the results, it can be seen that the effect of the replacement of 10-40% of the cement by slag caused an increase in the initial and final setting time. Compressive strength results indicate that the slag-blended cement (SBC) pastes had slower compressive strength development in the early stages, but this strength obviously increased at later ages. Variations in the Portland cements can affect early strength development but have no significant effect on the degree of hydration at later ages. MSWI slag gives a relatively slower increase in early strength but may show a greater degree of reaction at later ages.     

Employing of some hyperbranched polyesteramides as new polymeric admixtures for cement

Hyperbranched polyesteramides (HBPA₁ and HBPA₂) were synthesized by the bulk polycondensation of maleic anhydride (MA_n) as an A₂ monomer with both of diisopropanolamine (DIPA) and diethanolamine (DEA), respectively, as B′B₂ monomer. The prepared polymers were analyzed with IR, GPC, ¹H NMR, TGA, and DSC. The hyperbranched polyesteramides were applied as polymeric admixtures in two different types of cement, namely ordinary Portland cement (OPC) and Portland limestone cement (PLC). Several parameters were studied to evaluate the action of HBPA₁ and HBPA₂ polymers as cement admixtures. Adding HBPA₁ and HBPA₂ decreased the water of consistency and increased the compressive strength with no effect on the chemical composition of the cement phases. The combined water content and bulk density displayed the same trend as compressive strength. The IR spectra of the formed phases for the mixed cement pastes with HBPA₁ and HBPA₂ illustrated increased intensities of the absorption bands than those of the pristine cement pastes. The SEM photos showed that the incorporation of HBPA₁ and HBPA₂ in cement phases affected the morphology and microstructure of the formed hydrates. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

磷石膏制水泥缓凝剂净化工艺

磷石膏制水泥缓凝剂是其综合利用的重要方法之一。分析了磷石膏中各类杂质对水泥缓凝剂性能的不利影响,介绍了磷石膏净化过程的几种工艺方法:物理水洗法、化学预处理法和干燥煅烧法,分析其净化效果。推荐针对不同杂质含量的磷石膏采用不同的净化组合工艺。     

Geochemical modeling of leaching of Ca, Mg, Al, and Pb from cementitious waste forms

Results from extraction tests on cement-waste samples were simulated with a thermodynamic equilibrium model using a consistent database, to which lead data were added. Subsequent diffusion tests were modeled by means of a 3D diffusive transport model combined with the geochemical model derived from the extraction tests.Modeling results of the leached major element concentrations for both uncarbonated and (partially) carbonated samples agreed well with the extraction test using the set of pure minerals and solid solutions present in the database. The observed decrease in Ca leaching with increasing carbonation level was qualitatively predicted. Simulations also revealed that Pb leaching is not controlled by dissolution/precipitation only. The addition of the calcite-cerrusite solid solution and adsorption reactions on amorphous Fe- and Al-oxides improved the predictions and are considered to control the Pb leaching during the extractions tests. The dynamic diffusive leaching tests were appropriately modeled for Na, K, Ca and Pb.     

Natural cement as the precursor of Portland cement: Methodology for its identification

When cements appeared in the 19th century, they took the place of traditional binding materials (lime, gypsum, and hydraulic lime) which had been used until that time. Early cements can be divided into two groups, natural and artificial (Portland) cements. Natural cements were introduced first, but their widespread usage was short-lived as they were quickly replaced by artificial cements (Portland), still the most important and predominant today. The main differences between natural and artificial cements arise during the manufacturing process. The final properties of the cements are greatly influenced by differences in the raw materials and burning temperatures employed.The aim of this paper is to assess the efficiency of traditional analytical techniques (petrographic microscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR)) used to differentiate natural and artificial cements.     

Comparison of radioactive transmission and mechanical properties of Portland cement and a modified cement with trommel sieve waste

In this study, it was aimed to stabilize trommel sieve waste (TSW) occurring during manufacture of borax from tincal. The effects of TSW added on the mechanical properties and radioactive transmission of modified cement prepared by adding TSW to clinker was investigated. The properties which TSW as additive caused the cement to gain were tested and compared with normal Portland cement.Measurements have been made to determine variation of mass attenuation coefficients of TSW and cement by using an extremely narrow-collimated-beam transmission method in the energy range 15.746-40.930 keV with X-ray transmission method. The characteristic Kα and Kβ X-rays of the different elements (Zr, Mo, Ag, In, Sb, Ba and Pr) passed through TSW and cement were detected with a high-resolution Si(Li) detector. Results are presented and discussed in this paper.     

Experimental limitations regarding the formation and characterization of uranium-mineral phases in concrete waste forms

Predicting the fate of low-level radioactive waste (LLW) requires understanding radionuclide-waste form interactions. Concrete encasement is one method being considered for containment of LLW. The formation of uranium-mineral phases has been investigated in simulated concrete pore fluids and waste forms. X-Ray diffraction analyses of uranium precipitates from concrete pore fluids suggest uranium salts and -silicates are solubility-limiting phases. Scanning electron microscopy-energy dispersive spectroscopic analyses of uranium-spiked concrete suggest that under conditions both under-saturated and over-saturated with respect to the formation of uranium phases, uranyl-oxyhydroxide phases precipitate within the initial two weeks. Uranyl-silicate phases form after approximately one month and uranyl-phosphate phases provide a significant contribution to uranium retention in concrete waste forms after two months. This investigation demonstrates the importance of 1) studying the interaction of uranium in the complete matrix (i.e., concrete matrix versus pore fluids) and 2) formation of uranium-mineral phases on the retention of uranium within concrete waste forms.     

改性硅酸盐复合水泥早期力学性能的初探及机理分析

通过设计正交试验探索掺磷铝酸盐水泥的改性硅酸盐复合水泥的力学性能,从石膏、磷铝酸盐水泥熟料、外加剂等因素调控,以改性后的硅酸盐复合水泥水化浆体的早期抗压强度为主要指标确定最佳方案,并与未改性的硅酸盐水泥强度作对比,并通过数据分析及XRD、SEM、孔结构分析等现代测试手段,解释改性硅酸盐复合水泥早期力学性能得以改善的机理。