Concrete with Highly Active Rice Husk Ash

1　IntroductionForengineering ,economicandecologicalbenefits ,theuseofpozzolanicandcementitiousmaterials ,suchasgranulatedblast furnaceslag ,flyash ,silicafumeandnaturalpozzolan ,inthecementandconcreteindustryhasrisengreatlyfromthemiddleofthelastcenturyan…     

高活性稻壳灰混凝土的强度特性和孔结构研究

研究了高活性稻壳灰混凝土的强度特性和孔结构，结果表明，随着混凝土中稻壳灰掺量的增加，混凝土的强度明显提高，龄期为7d和28d获得较高的强度提高率。稻壳灰替代水泥掺入混凝土后，能明显的改善孔结构，孔隙明显细化，小于20nm的无害孔明显增多。混凝土中Ca(OH)2的减少和孔结构的改善是稻壳灰混凝土强度提高的主要原因。     

Hydraulicity of Wet-milling Ultra-fine Grouting Cement

The physical and mechanical properties of wet-milling ultra-fine grouting cement were studied,and its microstructure was abserted through modern instrwnentation analysis such as scanning electronic micoscoty (SEM),X-ray diffraction and Hg-intrusion micromeritics ,The experimertal results indicate that wet-milling ultra-fine cement possesses high rheological properties and groutability,It can be filles densely in cracks of rock and hydrate fully,which may endow hydrated cemetnt with high mechanical strength Main hydration products of wetmilling ultra-fine cement are poorly crystalline G-S-H(I),acicular AFt and plank-shape Ca(OH)2,The dense crystal-netwonk structure can be formed in the rock gaps filled with cement psate ,but some weak regions exist owing to Ca(OH)2,The features of micro-pore structure of hydrated wet-milling ultra-fine cement are few big harmful pores,abundant harmless micro pores and little most possible pore radius.     

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…     

活性稻壳灰对混凝土强度和耐久性能的影响

研究了高火山灰活性稻壳灰对混凝土强度和耐久性能的影响。结果表明：混凝土中掺加稻壳灰后强度提高，且高水胶比时强度提高率更大；同时，混凝土的抗盐酸溶液的侵蚀能力、抗碳化和抗渗性能也得到改善。其主要原因可归结为：稻壳灰的掺入降低了混凝土的实际水胶比，促进了水泥的水化，使混凝土中有更多的C—S—H凝胶生成，并减少了混凝土中羟钙石的数量，降低了混凝土细孔的平均尺寸，使得混凝土的结构更加密实。     

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…     

Principle and method of optimization design for soft soil stabilizer

A stabilized soil structure formation model was introduced. In order to form compact stabilized soil structure, cementitious hydrates were needed to wrap and bind the soil aggregates. Meanwhile, expansible hydrates were needed to squeeze and fill the pores, especially the pores in the aggregates. The experimental results show that the influences of various chemical characteristic factors of soil on the strength of the stabilized soil are boiled down, for the influence on the concentration of Ca(OH)₂ in the pore solution of the stabilized soil, and the amount of CSH generated by cement. Finally an optimization design method is proposed, with which the stabilizer can be designed according to characteristics of soil samples. Funded by the National Natural Science Foundation of China(No. 50278007)     

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.     

Pore Size Distribution of High Performance Metakaolin Concrete

The Compressive strength, porosity and pore size distribution of high performance metakaolin (MK) concrete were investigated. Concretes containing 0,5%,10% and 20% metakaolin were prepared at a water/cementitious material ratio (W/C) of 0.30.In parallel, concrete mixtures with the replacement of cement by 20% fly ash or 5 and 10% silica fume were prepared for comparison.The specimens were cured in water at 27℃ for 3 to 90 days .The results show that at the early age of curing(3 days and 7 days),metakaolin re-placements increase the compressine strength ,but silica fume replacement slightly reduces the compressine strength.At the age of and after 28 days ,the compressive strength of the concrete with metakaolin and silica fume replace-ment increases.A strong reduction in the total porosity and average pore diameter were observed in the conctete with MK 20% and 10% in the first 7 days.     

A Comparative Study on the Pozzolanic Activity between Nano-SiO2 and Silica Fume

The pozzolanic activity of nano-SiO2 and silica fume was comparatirely stndied by X-ray diffraction （ XRD ） , differential scanning calorimetry （DSC）, scanning electron micrascopy （SEM） and the compressive , bond and bending streugths of hardened paste and concrete were also measured. Results indicate that the compressive strength development of the paste made from Ca（OH）2 and nano-SiO2, the reaction rate of Ca（ OH）2 with nano- SiO2 and the velocity of C-S-H gel formation from Ca （ OH）2 with nano-SiO2 showed marked increases over those of Ca（ OH）2 with silica fume. Furthermore, the bond strength at the interface between aggregate and hardened cement paste, and the bending strength of concrete incorporated with 3% .NS increased more than those with SF, especially at early ages. To sum up, the pozzolanic activity of nano-SiO2 was much greater than that of silica fume. The results suggest that with a small amount of nano-SiO2, the Ca（ OH）2 crystal at the interface between hardened cement paste and aggregate at early ages may be effectively absorbed in high performance concrete.     

Modificatin of ITZ Structure and Properties of Regenerated Concrete

1Introduction Increasingattentionispaidtotheinvestigationand applicationofregeneratedconcrete(RC)forthesustain abledevelopmentofsociety[13].TheRCispreparedwith demolitionwasteconcreteoroldconcreteastherecycled aggregate(RA).RAcontainsacertainamountofhard enedcementmortar,someofwhichhaveaformofinde pendentlumps,andothersadhereontothesurfaceofnat uralaggregate.SinceRAhasagreaterporosityanda higherwaterabsorptioncapacitythannaturalaggregate,whichhasagreaterinfluenceontheperformanceofRC;conse…     

Early hydration of composite cement with thermal activated coal gangue

Composite cement samples were prepared by mixing clinker, gypsum with burnt coal gangues which was calcined at various temperatures. The mechanical strength and Ca(OH)₂ content in the cement paste were tested, and the paste composition and microstructure were analyzed by thermogravimetry-differential thermal analysis (TG-DSC), X-ray diffraction(XRD), scanning electronic microscopy (SEM) and pore structure analysis. Results demonstrate that the thermal activated coal gangue could accelerate the early hydration of cement clinker obviously, which promotes the gangue hydration itself. The early hydrated products of the cement are C-S-H gel, Ca(OH)₂ and AFt. The cement with 30% (in mass) the gangue exhibits higher mechanical strength, and among all the cement samples the one with the gangue burnt at 700 °C displays the highest hydration rate, mechanical strength, the most gel pores and the lowest total porosity.     

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.     

纳米SiO2和纳米CaCO3增强混凝土强度的试验研究

为了研究纳米SiO2、纳米CaCO3对混凝土力学性能的影响,进行了混凝土抗压强度和抗劈裂强度试验.纳米SiO2以0.5%,1.0%,2.0%,3.0%,纳米CaCO3以1.0%,3.0%等量取代水泥,标准养护7,28,78,128 d后进行混凝土强度测试.结果表明:纳米SiO2以3%等量取代时可以加速混凝土中C-S-H凝胶在水化早期和二次水化反应中的形成,从而提高混凝土的抗压和劈裂强度,从经济的角度考虑纳米SiO2的最优掺量为2%;纳米CaCO3可以吸收Ca(OH)2,促进水化碳铝酸钙的生成而提高混凝土的强度,其最优掺量为3%.     

Influence of flux additives on iron ore oxidized pellets

Six additives, i.e., limestone, lime, magnesite, magnesia, dolomite and light-burned-dolomite, were added for investigating their influences on the pellet quality. For green balls, adding lime and light-burned-dolomite makes the wet drop strength decrease firstly, and then increase with further increase of additive dosage. Ca(OH)₂ affects the bentonite properties at the beginning, but the binding property of Ca(OH)₂ will be main when the dosage is higher. The other four additives decrease the drop strength for their disadvantageous physical properties. For preheated pellets, no mater what kind of additive is added, the compressive strength will be decreased because of unmineralized additives. For roasted pellets, calcium additives can form binding phase of calcium-ferrite, and suitable liquid phase will improve recrystallization of hematite, but excessive liquid will destroy the structure of pellets, so the compressive strength of pellet increases firstly and then drops. When adding magnesium additives, the strength will be decreased because of the oxidation of magnetite retarded by MgO.     

再生粗骨料取代率对碎卵石混凝土抗压性能影响研究

设计制作了再生粗骨料取代率r=0％、30％、50％、70％、100％的碎卵石混凝土立方体及棱柱体试件,在不同龄期下对其进行抗压试验.研究了五种再生粗骨料取代率下,不同龄期的混凝土立方体抗压强度以及棱柱体抗压强度的变化趋势.结果表明:在龄期为3 d和7 d情况下,r=30％时混凝土的抗压强度较r=0％时无显著变化;当r>...     

Durability and micro-structure of reactive powder concrete

Durability of traditional reactive powder concrete (RPC) with rich cement and high volume of fly-ash reactive powder concrete (FRPC) were studied. The X-diffraction and scanning electron microscope (SEM) measurement was imployed to analyze the microstructure. The results show that both types of RPC have higher compressive strength, less volume shrinkage ratio and better carbonation-, chloride-, freezing-resistances than the conventional concrete. The results of X-diffraction indicate that they basically have C-S-H as the main composition without Ca(OH)₂ crystal and ettringite. SEM results show that hydration products of FRPC is mainly III-C-S-H which is piled up closely like densely arranged stone body and it has very compacted structure, in addition, Ca/Si ratio of C-S-H gel is lower than 1.5.     

Effect of straw mixing amount on mechanical properties of admixture-adding hollow block

The bonding mechanism between straw and concrete was analyzed through testing the compressive strength and flexural strength of hollow block, with different straw amount and different dosage and types of admixtures. The test results show that the mechanical properties of hollow blocks reduced after adding straws, and the more straws was added, the more hollow block density decreased. But adding Al₂(SO₄)₃ and CaCl₂ could improve the dense degree between rice straw and concrete. And when the proportion of straw mixing amount was 10%, the flexural strength of the early strength agent (2% Al₂(SO₄)₃, CaCl₂) added hollow block reached as maximal as 3.1 MPa, while the compressive strength was 9.1 MPa, consisting with the strength grade of common concrete hollow block MU7.5.     

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.     

Laboratory investigation on mechanisms of stress wave propagations in porous media

A number of porous models having the similar statistical characteristics of pores and physical properties with natural sandstones have been produced using reactive powder concrete (RPC) and polystyrenes. Spit-Hopkinson-Pressure -Bar tests and CT scans have been carried out on the models with the various porosities to probe the performance of wave propagations and the responses of pores and the matrix during wave propagations. It is shown that porosities significantly influence wave propagations. For an identical impact strain rate, the greater the porosity is, the larger the amplitude of the reflected wave appears, the more the peak in the reflected wave presents, and the smaller the amplitude of the transmitted wave turns out. A single peak emerges in the reflected wave when the porosity falls down to 5%. The larger the impact strain rate, the much remarkable the phenomena. The energy-dissipated ratio of porous models, i.e., W _J /W _I , linearly increases with the increment of porosities. The ratio is sensitive to the impact strain rate. Differences in the performance of wave propagations and energy dissipation result from the varied mechanisms that pores response to impacts. For the porosity less than 10%, the mechanism appears to be a process fracturing the matrix to generate new surfaces or pores. Energy has primarily been dissipated in creating new surfaces or pores. No apparent pore deformation takes place. The impact strain rate takes little effect on pore geometry. For the porosity of 15% or more, the mechanism works depending on the impact strain rate. When a low impact strain rate applies, the mechanism still appears to crack the matrix to generate surfaces or pores, but the amount is lower as compared to the case with a low porosity. If a large impact stain rate applies, the mechanism combines both fracturing the matrix and deforming the pores, with the deforming pores predominating. The vast majority of energy has been dissipated to deform pores. Only high porosity and impact strain rate can bring significant deformation to the pores. The proposed eccentricity of pores is capable of characterizing the geometry of pores and its change during wave propagations. Supported by the Natural Sciences & Engineering Research Council of Canada (PGS-D2-2006), the National Basic Research Program of China (“973” Project) (Grant No. 2002CB412705), and the New Century Excellent Talents Program of the Ministry of Education of China (NCET-05-0215)