Morphology and Properties in Blended Cements with Ceramic Wastes as a Pozzolanic Material

This paper describes the research run on ceramic materials, and more specifically fired clay roof tiles, ground to a fineness suitable for use as an active replacement for portland cements (PCs). The utilization of waste products from calcined clay roof tiles as a pozzolanic material in the cement manufacture is studied. One of the first materials used as pozzolans in the history was thermal-treated clay, a material similar to the calcined clay precast elements. For this study, the materials selected are clay products that have been eliminated for different reasons: a wrong temperature inside the kiln, dimensional and mechanical failures, and durability loss. The results showed that these products have good pozzolanic properties; at an early age, the pozzolanic activity was found to be higher than fly ash, although it was lower than silica fume. The morphology of clay tile–PC pastes are similar to the morphology of the pastes containing other pozzolanic materials. Hydrated calcium aluminate products are generated when the preparation method yields less compact pastes with a greater voids' volume to accommodate these products. The hydrated calcium aluminate phases were analyzed using scanning electronic microscopy and X-ray diffraction techniques.     

Influence of metakaolin on the properties of mortar and concrete: A review

Supplementary cementing materials (SCM) have become an integral part of high strength and high performance concrete mix design. These may be naturally occurring materials, industrial wastes, or byproducts or the ones requiring less energy to manufacture. Some of the commonly used supplementary cementing materials are fly ash, silica fume (SF), granulated blast furnace slag (GGBS), rice husk ash (RHA) and metakaolin (MK), etc. Metakaolin is obtained by the calcination of kaolinite. It is being used very commonly as pozzolanic material in mortar and concrete, and has exhibited considerable influence in enhancing the mechanical and durability properties of mortar and concrete. This paper presents an overview of the work carried out on the use of MK as partial replacement of cement in mortar and concrete. Properties reported in this paper are the fresh mortar/concrete properties, mechanical and durability properties.     

Calcined oil sands fine tailings as a supplementary cementing material for concrete

In recent years, metakaolin (MK) has received considerable attention, as a high-performance pozzolanic supplementary cementing material for use in concrete. MK is produced by calcining kaolinite at temperatures between 600 and 1000 °C. In the province of Alberta, Canada, the oil sand mining industry produces millions of cubic metres of oil sand tailings that could become a major source of MK. This paper summarizes the behaviour of calcined fine tailings (CFT) as a supplementary cementing material in high-performance concrete and compares its performance to that of MK and silica fume (SF). It was found that CFT has excellent pozzolanic activity in concrete, making it an environmentally friendly and potentially cost effective supplement.     

The effect of temperature on the rate of sulfate attack of Portland cement blended mortars in Na2SO4 solution

Sulfate attack on Portland cement and Portland blended cement concretes is a well-researched field. However, the effect of varying temperature on the rate of sulfate attack requires further attention. This laboratory experiment studied temperatures of 23 °C, 10 °C, 5 °C, and 1 °C. Both Portland and Portland limestone cements were studied in combination with several supplementary cementing materials. The mortar bars were submerged in 5% Na2SO4 (33,800 ppm SO₄^2 −) solution for 15–30 months. At higher temperatures the supplementary cementing materials, particularly the fly ashes, greatly improved the resistance to external sulfate attack. At lower temperatures the metakaolin improved the resistance to sulfate attack; the fly ashes had little to no effect on the low-temperature sulfate resistance. The alterations to sulfate resistance are attributed to: dilution of Portland cement in the presence of supplementary cementing materials; additional nucleation sites provided by finely ground SCMs; and the pozzolanic and hydraulic reactions of the SCMs.     

碱激发水泥的类型与特点(英文)

基于所含胶凝组份的成分,可以将碱激发水泥分成5种类型:1)碱激发矿渣水泥;2)碱激发波特兰复合水泥;3)碱激发火山灰水泥;4)碱激发石灰-火山灰/矿渣水泥;5)碱激发铝酸钙复合水泥,每种类型碱激发水泥包含几种胶凝体系。综述了这5种碱激发水泥的成分和特征。     

偏高岭土-水泥基材料力学性能研究进展

在配制水泥基材料过程中,利用活性材料替代部分水泥,可提高基体的力学和耐久性能,同时还可减少水泥用量,对节能减排有重大帮助.近年来偏高岭土(MK)活性材料开始受到广泛关注和研究,其对水泥基材料性能的影响研究也有重大进展.主要综述了MK对水泥基材料力学性能的影响研究进展,主要包括含杂质煅烧高龄粘土以及纯MK对砂浆和混凝土的早期和后期力学性能影响,MK与石灰石粉(LF)复掺对水泥基材料力学性能以及MK对超高性能混凝土(UHPC)的力学性能影响,最后对MK-水泥基材料的未来研究方向进行了展望.     

Performance of volcanic ash and pumice based blended cement concrete in mixed sulfate environment

The deterioration of concrete structures due to the presence of mixed sulfate in soils, groundwater and marine environments is a well-known phenomenon. The use of blended cements incorporating supplementary cementing materials and cements with low C₃A content is becoming common in such aggressive environments. This paper presents the results of an investigation on the performance of 12 volcanic ash (VA) and finely ground volcanic pumice (VP) based ASTM Type I and Type V (low C₃A) blended cement concrete mixtures with varying immersion period of up to 48 months in environments characterized by the presence of mixed magnesium-sodium sulfates. The concrete mixtures comprise a combination of two Portland cements (Type I and Type V) and four VA/VP based blended cements with two water-to-binder ratio of 0.35 and 0.45. Background experiments (in addition to strength and fresh properties) including X-ray diffraction (XRD), Differential scanning calorimetry (DSC), mercury intrusion porosimetry (MIP) and rapid chloride permeability (RCP) were conducted on all concrete mixtures to determine phase composition, pozzolanic activity, porosity and chloride ion resistance. Deterioration of concrete due to mixed sulfate attack and corrosion of reinforcing steel were evaluated by assessing concrete weight loss and measuring corrosion potentials and polarization resistance at periodic intervals throughout the immersion period of 48 months. Plain (Type I/V) cement concretes, irrespective of their C₃A content performed better in terms of deterioration and corrosion resistance compared to Type I/V VA/VP based blended cement concrete mixtures in mixed sulfate environment.     

Mineral phases formation on the pozzolan/lime/water system

In Spain, the paper industry recycles large amounts of waste paper in the new paper production process. Paper sludge thermal activation (calcination at 700 °C for 2 h) is an environment-friendly alternative source for metakaolinite (MK) to be used for the manufacture of blended cements or cement based materials.This paper could contribute to standardization of the use of new pozzolanic products in cement based materials and its use mixed with saturated lime dissolution. In this process are obtained zeolite, CSH gel, hydrotalcite-like compounds, hydrated aluminate tetracalcium and stratlingite.These materials are formed in different times of pozzolanic reaction.     

活化煤矸石细粉-水泥复合胶凝材料水化性能研究

主要采用XRD、DTA/TG、SEM、MIP及等温微量量热仪研究了华新硅酸盐水泥以及掺有活化煤矸石细粉水泥胶凝体体系的水化性能和微观结构,试验证明煅烧后的煤矸石具有火山灰活性。掺有活化煤矸石细粉的水泥浆体结构较疏松,孔隙较多,但随着龄期的增长,浆体结构变得越来紧密,其主要的水化产物亦为水化硅酸钙凝胶、钙矾石和Ca(OH)2晶体。     

Mineralogical Evolution of Kaolin‐Based Drinking Water Treatment Waste for Use as Pozzolanic Material. The Effect of Activation Temperature

This study reports on exhaustive scientific research into the influence of the activation temperature of inert waste from drinking water treatment plants for use as supplementary cementing material in cements. The effect of activation temperature on the mineralogy of the reactive products resulting from pozzolanic activity and on the evolution of the hydrated phases formed during the pozzolanic reaction at 28 d of curing was analyzed with the assistance of different instrumental techniques such as X‐ray fluorescence, X‐ray diffraction, thermogravimetric analysis, infrared spectroscopy, and scanning electron microscopy. The results show that all the activated products (based on metakaolinite) presented high pozzolanic activity at all ages of the reaction (up to 90 d), although 600°C at 2 h are the recommended ideal activation conditions from an energetic and economic viewpoint. The activation temperature (600°C–900°C for 2 h of retention) plays an important role in the reaction kinetics in activated drinking water waste/Ca(OH)₂ systems. The hydrated phases identified under these activation conditions were very similar, but with important differences in the crystalline aluminates phases content. Thus, the formation of stratlingite (C₂ASH₈) is favored at low temperatures (<800°C); whereas at higher temperatures (at 900°C), tetra calcium aluminate hydrate (C₄AH₁₃) appears as the only crystalline phase. Finally, this type of treatment of drinking water waste (based on kaolinite) is ideal to obtain future pozzolans based on recycled metakaoline, a product that is currently listed in international standards for the manufacture of commercial cements.     

Encapsulation of Sn(II) and Sn(IV) Chlorides in Composite Cements

The hydration of two high replacement composite cements (3:1 blast furnace slag:ordinary Portland cement (BFS:OPC), and 3:1 pulverized fuel ash:OPC (PFA:OPC)) with the addition of both SnCl₂ and SnCl₄ has been investigated and the results from X-ray diffraction (XRD) and scanning electron microscopy (SEM) with energy-dispersive spectroscopy (EDS) are presented. Adding 5% or 1% SnCl₂·2H₂O or SnCl₄·5H₂O to the mix water resulted in the formation of Friedel's salt, Ca₃Al₂O₆.CaCl₂·10H₂O, and calcium hydroxo-stannate CaSn(OH)₆, which also involved the consumption of calcium hydroxide. After 90 days hydration at lower levels of addition (i.e., 1%) there was no longer evidence for CaSn(OH)₆, indicating that it too had been consumed in the pozzolanic reaction due to the lack of calcium hydroxide present. Results from SEM and EDS showed that bright regions between the BFS or PFA grains were tin containing and they were incorporated into the hydrated cement matrix. The tin was, therefore, localized rather than spread throughout and intimately incorporated into the microstructure.     

Characterization by Multinuclear High-Resolution NMR of Hydration Products in Activated Blast-Furnace Slag Pastes

The effect of activators on the hydration of granulated blast-furnace slag (gbfs) was studied through compressive strength measurements, ²⁹Si, ²⁷Al, and ²³Na high-resolution nuclear magnetic resonance, and X-ray diffraction. Four different activations containing sodium hydroxide, sodium silicate, and/or calcium hydroxide (CH) were considered, at fixed amounts of alkali: 5% Na₂O, 5% Na₂O-2.5% CH, 5% Na₂O-7.5% SiO₂, and 5% Na₂O-2.5% CH-7.5% SiO₂. Silicate-activated gbfs cements have greater compressive strength than Portland cements over the whole period of study (1 yr). Also, silicate-free activated gbfs cements have poorer mechanical strength than silicate-activated cements. In fact, substantial structural differences were observed between hydration products in both kinds of activations. In silicate-activated pastes there exists an intimate mixture of C-S-H layers and AFm-like arrangements containing Al in octahedral sites bonded to the silicate layers, originated either from phase intergrowths or from a high density of Ca-Al incorporation in the interlayer spaces of C-S-H. In pastes obtained from silicate-free activation of gbfs there is a better chemical and structural definition among C-S-H and calcium aluminate hydrate domains (AFm and hydrogarnet).     

Supplementary cementing materials in concrete: Part I: efficiency and design

Many solid industrial by-products such as siliceous and aluminous materials (fly ash, silica fume, slags, etc.) as well as some natural pozzolanic materials (volcanic tuffs, diatomaceous earth, etc.) may be characterized as supplementary cementing materials (SCM) as they exhibit cementitious and/or pozzolanic properties. Due to plenty of these materials and their large variations on physical and chemical composition, the development of a general design for their use in concrete is required. In this work, the concept of an efficiency factor is applied as a measure of the relative performance of SCM compared with Portland cement. Artificial materials of various compositions and some natural pozzolans were studied. Compressive strength and accelerated chloride penetration tests were performed. With regard to these characteristics, efficiency factors for these materials were calculated. A mix design strategy to fulfil any requirements for concrete strength and service lifetime was developed and it enables concrete performance to be accurately predicted.     

Use of recycled copper slag for blended cements

Copper slag is a by‐product generated during smelting to extract copper metal from the ore. The copper slag obtained may exhibit pozzolanic activity and may therefore be used in the manufacture of addition‐containing cements. In this paper the effect of the incorporation of the copper slag in cement is measured. Blends of copper slag with Portland cement generally possess properties equivalent to Portland cement containing fly ash, but very different to the silica fume incorporation. Copper slag and fly ash reduce the heat of hydration more effectively than silica fume in mortars. The replacement of 30% cement by copper slag reduces the flexural and compressive strength in a similar way to fly ash; however, after 28 days, the reduction is less than the percentage of substitution. Hydrated calcium aluminate phases were analysed using scanning electron microscopy (SEM) and X‐ray diffraction (XRD) techniques. The pozzolanic activity of copper slag is similar to that of fly ash and higher than silica fume. In the presence of low water/cement ratios, certain pozzolanic materials produce a very compact cement paste that limits the space available for hydration products, a determining factor in the formation of hydrated calcium aluminates. SEM was found to be a useful analytical technique when aluminates are formed and can be clearly detected by XRD. Copyright © 2008 Society of Chemical Industry     

Pozzolanic reactions of six principal clay minerals: Activation, reactivity assessments and technological effects

Six standard clays, before and after calcination at 3 or 4 temperatures and being mixed with Ca(OH)₂ [CH] in the presence of simulated cement pore solution, and with ordinary Portland cement, respectively, were studied in detail. Chemical compositions of most clays conform well to the requirement in ASTM C 618. Water demand of clay-containing mortar varies, depending on the crystal chemistry of raw clays, and on the specific surface area of calcined clays. Measurements of XRD background or alkali soluble Si are rapid methods in evaluation of the pozzolanic activity of clays. Compressive strength of mortars based on the raw clays is affected by structure of clays. Calcination increases the pozzolanic activity of clays and the compressive strength of the Portland cement — clay mortars. A close correlation exists between compressive strength of mortars and particle size distribution of the dehydroxylated clays. The most common reaction products of clay — CH mixtures are C-S-H² and C₄AH_x, while C₂ASH_j8 and C₃AH₆ were also detected with clays rich in Al.     

Recycling of silicomanganese slag as pozzolanic material in Portland cements: Basic and engineering properties

Correct use of SiMn slags requires a detailed knowledge of their properties, as chemical and mineralogical composition, pozzolanic activity, reaction kinetics, setting time, volume expansion and strength play important role in the final valorisation of SiMn slag as pozzolanic material. This kind of slag is formed mainly of SiO2 and CaO, followed by Al2O3 and MnO which sum is nearly 90%. Sulphites content of 0.42% was detected. The main crystalline compound identified in SiMn slag is akermanite.The results obtained show that SiMn slag blended cements do not show volume instability, the strength values are very close to the control mortar and they have a denser matrix. SiMn blended matrices fulfil standard specification requirements (chemical, physical and mechanical ones) and show that SiMn slag is suitable for blended cements manufacture.     

Alkaline Activation of Metakaolin: Effect of Calcium Hydroxide in the Products of Reaction

The alkali activation of metakaolin (MK) leads to the production of high-mechanical-performance network-structure materials. Adding calcium hydroxide (Ca(OH)₂) to the raw MK produces a somewhat different reaction: a network structure and C-S-H gel form. In the present study, MK and (MK + Ca(OH)₂) mixes were activated with 5 M and 12 M NaOH solutions and cured at 45°C. A 5 M concentration, in the absence of Ca(OH)₂, did not produce MK activation within the test time. An activator concentration of 12 M resulted in complete activation and the formation of a network structure. When Ca(OH)₂ was present in the raw mix, a small amount of C-S-H gel formed.     

Characteristics of a thermally activated alumino-silicate pozzolanic material and its use in concrete

This paper presents the results of the physical and chemical properties of a thermally activated alumino-silicate material (MK), and deals with the properties of fresh and hardened concrete incorporating this material. The properties of fresh concrete investigated included workability, bleeding, setting time, and autogenous temperature rise. The properties of the hardened concrete investigated included compressive, splitting-tensile and flexural strengths, Young's modulus of elasticity, drying shrinkage, resistance to chloride-ion penetration, freezing and thawing, and saltscaling resistance. The properties of the MK concrete were also compared with those of the control portland cement concrete and the silica fume concrete.

The test results indicate that the MK material is highly pozzolanic and can be used as a supplementary cementing material to produce high-performance concrete. Although it requires a higher dosage of the superplasticizer and air-entraining admixture compared with that of the control concrete, the MK concrete can be produced with satisfactory slump, air content, and setting time. The concrete incorporating 10% MK had higher strength at all ages up to 180 days compared with the control concrete; in comparison with the silica fume concrete the MK concrete showed a faster strength development at early ages, but had lower strength after 28 days. At 28 days, the MK concrete had somewhat higher splitting-tensile and flexural strengths, Young's modulus of elasticity, and lower drying shrinkage compared with that of the control and the silica fume concretes. The resistance of the MK concrete to the chloride-ion penetration was significantly higher than that of the control concrete, but similar to that of the silica fume concrete. The MK concrete showed excellent performance in the freezing and thawing test. The performance of the MK concrete subjected to the de-icing salt scaling test was similar to that of the silica fume concrete, but marginally inferior to the control concrete.     

Property improvement of Portland cement by incorporating with metakaolin and slag

The physical and mechanical properties of Portland cement (PC) containing metakaolin (MK) or combination of MK and slag and the compatibility between such materials and superplasticizers were investigated in present study. After MK was incorporated into PC, the compressive strength of the blended cement was enhanced. However, the fluidity of MK blended cement became poorer than that of PC at the same dosage of superplasticizer and the same water/binder ratio. When both MK (10%) and ultra-fine slag (20% or 30%) were incorporated into PC together, not only the compressive strength of the blended cement was increased, but also the fluidity of the blended cement paste was improved comparing to MK blended cement. This indicates that ultra-fine slag can improve the physical and mechanical properties of MK blended cement. The physical and chemical effects of two mineral admixtures were also discussed.     

有替代硅酸盐水泥熟料的生产的选择吗?(英文)

人们一直在寻找CO2排放量低的水硬性胶凝材料,用它替代传统的以硅酸盐水泥熟料(Portland clinker,PC)为主的水泥。介绍了几种处于不同发展时期的新型非PC基的胶凝材料体系。目前大多数水泥生产商都尽可能多地用辅助性胶凝材料替代硅酸盐水泥熟料。火山灰材料具有低的水硬活性,它可使用高浓度碱金属溶液来激发,得到介于"地聚合物"和石灰激发火山灰胶凝材料间的复合胶凝材料。较远期可以期待基于贝利特、硫铝酸钙和铁铝酸钙矿物组成的水泥熟料,如拉法基公司的AetherTM已投入生产。更远的将来,不产生CO2的原材料,如硅酸镁等,可能使得水泥生产中实现CO2零排放,然而,这些胶凝材料的耐久性有待验证,用其配制的混凝土中钢筋锈蚀的防护是实际应用中的关键问题。