Effect of pozzolanic reaction products on alkali-silica reaction

1 IntroductionThe use of fly ashto control the expansion dueto al-kali-silica reaction (ASR) is well established and a num-ber of reviews have been published recently[1-4]. Howflyash brings about this reductionin expansionis not yet un-derstood although a number of theories have been put for-ward to explain its action. For controlling mechanism,they put more emphasis onthe adsorption andresort of al-kali by supplementary cementing material (SCM) , formore acidity oxide in SCM,and the secon…     

Mechanical property and microstructure of alkali-activated Yellow River sediment-coal slime ash composites

This work focuses on the production of a new composite material using Yellow River sediment and coal slime ash via alkali-activating method. XRD, FTIR and SEM/EDS were used to characterize the alkali-activated products and microstructure of the composite material. Compressive strength was tested to characterize the mechanical property of the composite material. It is found that the compressive strength of the Yellow River sediment-coal slime ash composites increases as the added Ca(OH)₂ content grows. The compressive strength increases fast in the early stage but slowly after 28 days. The strength of the composites can be significantly improved via the addition of small amount of NaOH and gypsum. The products (C-S-H, ettringite and CaCO₃), especially C-S-H, make much contribution to the enhancement of strength. The highest strength of the composites can reach 14.4 MPa after 90 days curing with 5% Ca(OH)₂, 0.2% NaOH and 7.5% gypsum. The improved properties of the composites show great potential of utilizing Yellow River sediment for inexpensive construction materials.     

Comparison of hydration properties between cement-GGBS-fly ash blended binder and cement-GGBS-steel slag blended binder

The hydration properties of cement-GGBS-fly ash blended binder and cement-GGBS-steel slag blended binder were compared. The experimental results show that the hydration rate of cement-GGBS- steel slag blended binder is higher than that of cement-GGBS-fly ash blended binder within 28 days, but lower than the latter after 28 days. The hydration of cement-GGBS-steel slag blended binder tends to produce more Ca（OH）2 than the hydration of cement-GGBS-fly ash blended binder, especially at late ages. Cement-GGBS- steel slag mortar exhibits higher strength than cement-GGBS-fly ash mortar within 28 days, but at late ages, it exhibits similar compressive strength with eement-GGBS-fly ash mortar and even slightly lower bending strength than cement-GGBS-fly ash mortar. Cement-GGBS-steel slag paste has finer early pore structure but coarser late pore structure than cement-GGBS-fly ash paste. Cement-GGBS-steel slag paste can get satisfied late pore structure and cement-GGBS-steel slag mortar can get satisfied late strength as compared with pure cement paste and pure cement mortar, respectively.     

Activation of rejected fly ash using flue gas desulphurization (FGD) sludge

Low-grade fly ash (rejected fly ash, rFA), a significant portion of the pulverized fuel ash (PFA) produced from coal-fired power plants and rejected from the ash classifying process, remains unused due to its high carbon content and large particle size (>45 μm). But it is thought that the rejected ash may have potential uses in chemical stabilization solidification (S/S) processes which need relatively lower strengths and a lower chemical reactivity. Flue Gas Desulphurisation (FGD) sludge is a by-product of air pollution control equipment in coal fired power plants whose chemical composition is mainly gypsum. As there is no effective usage of both of these two materials, it is of interest to research on the possible activation of rFA using FGD. This paper presents experimental results of a study on the properties of rFA activated by the FGD in rFA-cement pastes. Different percentages of FGD were added into the mix to study the effects of the FGD on the reaction of the rFA blended cement pastes. The results show that FGD takes effect as an activator only at late curing ages. Adding Ca(OH)₂ enhances the effect of FGD on activating the hydration of rFA. Also, 10% FGD by weight of rFA is the optimal addition in the rFA-cement pastes. The results of the compressive strength measurements correlate well with the porosity results. QIAO Xiu-chen : Born in 1973 Funded by the Research Grants Council of Hong Kong (Project No. PolyU 5056/00E)     

中热水泥-粉煤灰体系的贫钙问题

为了提高水工大体积混凝土中的粉煤灰掺量,研究了中热水泥 粉煤灰体系的贫钙问题.通过抗折和抗压强度试验研究了粉煤灰掺量对中热水泥-粉煤灰体系的强度的影响，通过水化率测定和XRD分析研究了中热水泥-粉煤灰体系的水化特性.结果表明：在强度实验中，粉煤灰存在一个允许掺量，这个掺量随着养护龄期的增长而提高0.3 d和28 d时，允许掺量小于10%， 而在3.5a时，允许掺量高达65%以上；体系中粉煤灰的水化速率很慢，粉煤灰明显降低了体系中的Ca(OH)₂，随着粉煤灰掺量增加和龄期延长，Ca(OH)₂减少.在中热水泥-粉煤灰体系中并不存在贫钙问题.     

养护制度对粉煤灰复合水泥浆体干燥收缩及孔径分布的影响

将水泥试件在水中养护6天和13天后放入干燥养护箱中,测定其质量损失和干燥收缩。采用氮吸附方法测定不同龄期时的孔径分布。结果表明:粉煤灰复合水泥浆体,干燥收缩早期变化较为明显,随着龄期延长,变化逐渐变缓;水养时间延长,干燥收缩减小;不同水养时间养护后,粉煤灰复合水泥浆体4-40nm孔径体积含量减小,相应干燥收缩减小。     

Early age properties of cementitious materials by electrical resistivity measurement

Three cement pastes were prepared with the fixed water-binder ratio and different fly ash contents. The compression test and electrical resistivity measurement of the paste mixes were conducted during 48 h. The changes of the CH content and the non-evaporable water content in the cement-fly ash hydration systems with time were obtained by the thermal gravimetric analysis. The experimental results show that dilution effect of fly ash as micro-filler is dominant mechanism before 48 h, which appears to decrease in the CH content and the non-evaporable water content, also in compressive strength and electrical resistivity, with the increase of fly ash replacement. The relationships between CH content, non-evaporable water content and electrical resistivity show that electrical resistivity can be the indicators of hydration products CH and non-evaporable water. The correlation of the compressive strength f _c and the electrical resistivity ρ can be obtained as f _c =8.3429 ρ = 6.7088 for the period of 48 h. The early age compressive strength can then be predicted by electrical resistivity measurement.     

Assessment of curing efficiency and effect of moist curing on performance of fly ash concrete

This study was conducted to evaluate the sensitivity of compressive strength,water permeability and electrical resistance of near-surface layer concrete with different fly ash contents to curing conditions.It is shown that the sensitivity to curing condition and fly ash content descends in the following order:difference between internal and surface resistivity (ρ) at 28 days,water permeability and compressive strength;both of longer duration of moist curing and use of fly ash in concrete enhanced the water ...     

Synthesis and heavy metal immobilization behaviors of fly ash based gepolymer

Two aspects of studies were carried out: 1) synthesis of geopolymer by using fly ash and metakaolin; 2) Immobilization behaviors of fly ash based geopolymer in a presence of Pb and Cu ions. As for the synthesis of fly ash based geopolymer, 4 different fly ash content (10%, 30%, 50%, 70%) and 3 types of curing regimes (standard curing, steam curing and autoclave curing) were investigated to obtain the optimum synthesis condition based on the compressive and flexural strength. The experimental results show that geopolymer, containing 30% fly ash and synthesized at steam curing (80° for 8 h), exhibits higher mechanical strengths. The compressive and flexural strengths of fly ash based geopolymer reach 32.2 MPa and 7.15 MPa, respectively. Additionally, Infrared (IR) and X-ray diffraction (XRD) techniques were used to characterize the microstructure of the fly ash geopolymer. IR spectra shows that the absorptive band at 1086 cm⁻¹ shifts to lower wave number around 1033 cm⁻¹, and the 6-coordinated Al transforms into 4-coordination during the synthesis of fly ash based geopolymer. The resulting geopolymeric products were X-ray amorphous materials. As for immobilization of heavy metals, the leaching tests were employed to investigate the immobilization behaviors of the fly ash based geopolymer synthesized under the above optimum condition. The leaching tests showed that fly ash based geopolymer can effectively immobilize Cu and Pb heavy metal ions, and the immobilization efficiency reached 90% greater when heavy metals were incorporated in the fly ash geopolymer in the range of 0.1% to 0.3%. The Pb exhibits better immobilization efficiency than the Cu, especially in the case of large dosages of heavy metals.     

废弃粉煤灰火山灰活性的研究

通过对细粉煤灰与废弃粗粉煤灰在强度发展、水化程度、水化产物等方面的对比 ,发现粗粉煤灰在 90 d的强度发展和水化速度大于细粉煤灰。水灰比 ( W/ C)对粉煤灰尤其是粗粉煤灰的火山灰反应影响重大 ,随着水灰比的增加 ,掺粗粉煤灰样品的强度和水化程度都成倍增长。这主要是由于高水灰比有利于 Ca2 和粉煤灰中溶出的活性成分进入溶液参与反应。这可从扫描电镜 ( SEM)的测试结果得以证实     

复合浆体中粉煤灰和水泥水化反应程度的测定

采用盐酸选择溶解法测定粉煤灰的水化程度,再结合水化热法计算复合浆体中水泥的水化程度。试样结果表明,在水化早期粉煤灰仅作为惰性材料填充于复合浆体的孔隙中。随着粉煤灰掺量的增大,水泥的水化程度越高,单位体积中水化产物的总体数量仍为减少。     

In-situ monitoring the setting behavior of foamed concrete using ultrasonic pulse velocity method

The applicability of ultrasonic pulse velocity （UPV） method to in-situ monitor setting and hardening process of foamed concrete （FC） was systematically investigated. The UPVs of various FC pastes were automatically and continuously measured by a specially designed ultrasonic monitoring apparatus （UMA）. Ultrasonic tests were performed on FC mixtures with different density （300, 500, 800 and 1 000 kg/m3）, and different fly ash contents （0%, 20%, 40% and 60%）. The influence of curing temperatures （20, 40, 60 and 80~C） was also studied. The experimental results show that three characteristic stages can be clearly identified during the setting process of an arbitrary FC paste： dormant stage, acceleration stage, and deceleration stage. Wet density, fly ash content, and curing temperature have great impact on setting behavior. A stepwise increase of the wet density results in shorter dormant stage and larger final UPV. Hydration reaction rate is obviously promoted with an increase in curing temperature. However, the addition fly ash retards the microstn,lcture formation. To aid in comparing with the ultrasonic results, the consistence spread test and Vicat needle test （VNT） were also conducted. A correlation between ultrasonic and VNT results was also established to evaluate the initial and final setting time of the FC mixtures. Finally, certain ranges of UPV with reasonable widths were suggested for the initial and final setting time, respectively.     

化学激发剂对废弃粗粉煤灰火山灰活性的影响

通过研究不同化学激发剂对废弃粗粉煤灰-水泥系统的强度发展、水化程度、水化产物等的影响，发现掺入Na2SO4和K2SO4可以大幅提高废弃粗粉煤灰-水泥系统在早期和晚期的抗压强度，而掺入CaCl2和Ca(OH)2的效果则不明显，X射线衍射的测试结果也证明了这一点。由此说明化学激发废弃粗粉煤灰的火山灰活性重点在于提高系统的pH值。另外，水化程度测试的结果显示，化学激发剂对粗粉煤灰的促进作用主要集中在28d以前。     

Effect of limestone powder and fly ash on magnesium sulfate resistance of mortar

The effect of limestone powder and fly ash on magnesium sulfate resistance of mortar was studied by testing on the strength, expansion and hydration products of the specimens stored in MgSO₄ solution at certain periods. The experimental results show that the strength of mortar stored in MgSO₄ solution increases a little before 28 d, but decreases fast subsequently. The more the contents of limestone powder and fly ash, the less the strength losses. Mortar swells in the MgSO₄ solution with the soaking time. And the more the contents of limestone powder and fly ash, the less the expansion rate is. The expansion or strength loss of mortars results from the expansion of gypsum, as well as the loss of Ca(OH)₂ and other hydration products of cement. The magnesium sulfate resistance of the mortars containing limestone powder and fly ash is high.     

Influence of elevated curing temperature on the properties of cement paste and concrete at the same hydration degree

Three different curing temperatures(20 ℃, 40 ℃, and 60 ℃) were set, so that the nonevaporable water(w_n) contents of plain cement pastes cured at these three temperatures were measured to determine the hydration degree of cement. Tests were carried out to compare the pore structure and strength of cement paste, as well as the strength and permeability of concrete under different temperature curing conditions when their cements were cured to the same hydration degree. The experimental results show that either at a relatively low hydration degree(w_n=15%) or high hydration degree(w_n=16.5%), elevated curing temperature has little influence on the hydration products of cement paste, while it has a negative influence on the pore structure and compressive strength of cement paste. However, this negative effect is weaker at high hydration degree. The large capillary pore(100 nm) volumes of cement pastes remain almost the same at high hydration degree, regardless of curing temperatures. As for the concrete, elevated curing temperature also has negative influence on its compressive strength development, at both low hydration degree and high hydration degree. And this negative effect is stronger than that on cement paste's compressive strength at the same hydration degree. On the whole, elevated curing temperature has little influence on the resistance of concrete to chloride ion penetration.     

Effect of MSWI fly ash and incineration residues on cement performances

The activities of municipal solid waste incineration (MSWI) fly ash and incineration residues were studied contrastively, through the component analysis and the activity ratio tests. The mechanical properties, hydration mechanism and leaching toxicity of the hardened cement paste mixing with MSWI fly ash and incineration residues were investigated. The experimental results indicated that the active constituents (CaO+Al₂O₃+Fe₂O₃) in MSWI fly ash were higher than those in incineration residues. Therefore the activity ratio of MSWI fly ash was 43.58%, twice as much as that of incineration residues. Meanwhile, the hydration of cement was delayed by mixing with MSWI fly ash and incineration residues, which also reduced the cement strength markedly. By adding with exceeding 20% MSWI fly ash, the specimens expanded and microcracks appeared. The leaching toxicities of cement pasted mixed with MSWI fly ash and incineration residues were lower than the Chinese national standard. Accordingly the cement mixed by MSWI fly ash and incineration residues can be considered as the environment-friendly materials.     

Glass-ceramics made from arc-melting slag of waste incineration fly ash

Grate fly ash and fluidized bed fly ash mixed with glass cullet additive respectively were melted in the electronic arc-furnace. The product, arc-melting slag, was further treated by crushing, pressing and heat treatment in order to make the glass-ceramics. The crystallization behaviors of the produced glass-ceramics were examined by differential thermal analysis (DTA), X-ray diffractometry (XRD) and scanning electron microscopy (SEM). Results show that main crystalline phase of the glass-ceramics from grate fly ash is wollastonite (CaSiO₃) with small amount of diopside (Ca(Mg,Al)(Si,Al)₂O₆), and that from fluidized bed fly ash is diopside (Ca(Mg,Al)(Si,Al)₂O₆). It is found that the glass-ceramics sintered at 850 °C and 1 000 °C from grate fly ash and fluidized bed fly ash respectively have the optimal physical, mechanical and chemical characteristics. Glass-ceramics samples, produced from incinerator fly ash with desirable properties and the low leaching concentration of heavy metals, can be the substitute of nature materials such as marble, granite and porcelain tiles.     

Effect of magnesium on the C-S-H nanostructure evolution and aluminate phases transition in cement-slag blend

The microstructural study was conducted on cement and cement-slag pastes immersed in different concentrations of Mg(NO_3)_2 solutions utilizing ~(29)Si, ~(27)Al NMR spectroscopy and XRD techniques. The results show that the hydration of both the cement and cement-slag pastes is delayed when the pastes are cured in Mg(NO_3)_2 solutions as compared to the pastes cured in water. Moreover, Mg~(2+) ions also exhibit an decalcifying and dealuminizing effect on the C-A-S-H in cement and cement-slag pastes, and thereby decrease Ca/Si and Al[4]/Si ratios of the C-A-S-H. The dealuminization of C-A-S-H is mitigated for cement-slag paste as compared to pure cement paste. The depolymerized calcium and aluminum ions from C-A-S-H gel mainly enter the pore solution to maintain the pH value and form Al~[6] in TAH, respectively. On the other hand, Mg~(2+) ions exert an impact on the intra-transition between Al~[6] species, from AFm and hydrogarnet to hydrotalcite-like phase. NO_3~-ions are interstratified in the layered Mg-Al structure and formed nitrated hydrotalcite-like phase(Mg_(1-x)Al_x(OH)_2(NO_3)_x·nH_2O). Results from both ~(27)Al NMR and XRD data show that ettringite seems not to react with Mg~(2+) ions.     

Microstructure and Composition of Hydration Products of Ordinary Portland Cement with Ground Steel-making Slag

1　IntroductionSteel makingslagisthewasteofsteel makingindus tryandnearlysixteenmilliontonssteel makingslagisproducedinChinaperyear[1] .Justasflyashandblastfurnaceslag ,itisoneofthreekindsofdominantindustrywastesinourcountry .Eventhoughsteel makingslagce menthasdevelopedformorethantwentyyearsinCh ina[2 ,3 ] ,comparedwithothertwowastes ,thestudyandap plicationonsteel makingslagincementandconcreteareinsufficientyet.Moststeel makingslagcementsarepre paredbyinter grindingprocess ,sotheparticlesiz…     

Influence of CG With High Content of Metallic Particles as a Cement Admixture on Cement Strength

1　IntroductionCopperresidueisanindustrialby productdis chargedbycopperrefineries ,butitusuallycontainssomeusefulmetals .Forexamplecopperresiduecontains 4 %to5 %copper ,1.0 1g tgold ,2 4g tsilverand 4 2 %magne tite ,alltheseexceedthecontentforacomprehensiveutili zation .Inordertoextracttheseusefulmetals ,thecoolingtechnologyofremovingresidueisintroducedbyslowlycooling (4 8h)sothatsomemetallicionsgrow .Afteronemoreflotationforcopperandmagneticbyextractionofiron ,thedischargedresidueiscalledcopp…