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固井质量的好坏直接影响到钻井质量的好坏，并且会严重影响到油气井的产能和生产寿命。
因此，针对固井质量影响因素的系统分析研究十分必要。
1 影响固井质量的因素分析固井质量的影响因素从存在主义的角度来分析，分为客观因素和主观因素两大类型。
客观上的影响因素由于其本身的客观存在性以及不可调节性，在一定程度上导致了固井质量难以提高；主观上的影响因素与客观因素正相反，它具有可控制可调节的特征，可以通过一定的手段措施来提高固井质量。
1.1 影响固井质量的客观因素影响固井质量的客观因素主要有一下几个方面：（1）地层复杂在钻井过程中，如果裸眼井段正好钻遇岩性复杂的地层，例如膏盐层，或者是发育有大量断裂裂缝的地层，则会严重影响到井壁的稳定性。
在这种情况下，为了保证井壁的稳定性，会在固井前对钻井液性能进行调整。
这种类型的井，井眼状况普遍较差，顶替效率不高，二界面交接质量差。
（2）井轨迹复杂井轨迹比较复杂的井，例如S型井，由于井身轨迹比较复杂，扶正器的数量不能满足下套管的需求，套管很难剧中，从而造成井段间隙过小或过大，进而导致层间封隔或有效顶替难以实现。
（3）地层压力紊乱部分开发井受长期注水开采的影响，导致地层压力紊乱，井段上下高压低压交替出现，安全密度窗口狭窄，注替排量低。
对这种类型的井进行固井作业，固井质量往往不高，钻井液顶替效率普遍较差。
1.2 影响固井质量的主观因素影响固井质量的主观因素主要有一下几个方面：（1）设计缺陷完井设计存在设计缺陷，没有根据地质条件，油藏特征以及采油工程等方面对固井质量可能存在的影响进行设计，缺乏石油勘探开发所应有的整体认识。
因此，不具有针对性的完井设计是影响固井质量的主观因素之一。
（2）环节协作问题固井作业是一项系统性很强的多学科综合应用的作业，在整个勘探开发过程中，每一个环节都会对固井质量产生影响。
石油公司出于自身的经济利益的考虑，对每口钻井的投入成本都有比较严格的限制，从而导致每个环节因造价要求而产生的矛盾层层堆积，最后留给固井环节。
The Impact of Technological Advancementson the EnvironmentIn today's rapidly evolving world, technological advancements have become a ubiquitous force, shaping the way we live, work, and interact with the environment. While these advancements have brought remarkable conveniences and efficiencies, their impact on the environment is a complex and multifaceted issue that deserves careful consideration. On the one hand, technological progress has opened new doors for environmental protection and sustainability. For instance, renewable energy technologies such as solar and wind power have become increasingly viable and affordable, reducing our dependency on fossil fuels and mitigating greenhouse gas emissions. Additionally, advancements in energy efficiency and conservation techniques have enabled us to use resources more efficiently, reducing waste and pollution.Furthermore, technological advancements havefacilitated better monitoring and management of environmental resources. Remote sensing and data analytics tools allow us to track changes in ecosystems, identifythreats to biodiversity, and develop targeted conservation strategies. These technologies also enable more precise agriculture practices, such as precision farming, which can reduce the use of chemicals and maximize crop yields while minimizing environmental impact.However, the environmental costs of technological progress are also significant. The manufacturing and disposal of electronic devices and other technological products often involve the use of harmful materials and generate significant waste. The rapid obsolescence of technology also leads to a constant stream of discarded devices, creating an ever-growing e-waste problem thatposes a threat to soil, water, and air quality.Moreover, the increasing demand for technological products often drives resource extraction and deforestation, leading to habitat loss and biodiversity decline. Theenergy-intensive nature of many technological processes, such as mining and manufacturing, also contributes to greenhouse gas emissions and climate change.It is evident that the impact of technological advancements on the environment is not straightforward.While they offer promising solutions for environmental protection and sustainability, they also present significant challenges and risks. Therefore, it is crucial to approach technological progress with a balanced perspective, considering both its benefits and drawbacks. Policies and regulations can play a crucial role in guiding the development of environmentally friendly technologies. Governments and industries should prioritize research and development in renewable energy, energy efficiency, and waste reduction technologies. At the same time, they should enforce strict environmental standards for the manufacturing and disposal of technological products, ensuring that these activities do not harm the environment.In conclusion, technological advancements have a profound impact on the environment, both positive and negative. As we continue to develop and adopt new technologies, it is essential to remain mindful of their environmental implications and take proactive measures to mitigate any potential harm. By doing so, we can harnessthe power of technology to create a more sustainable and environmentally friendly future.**技术进步对环境的影响**在当今这个快速发展的世界里，技术进步已经成为无处不在的力量，塑造着我们生活、工作和与环境互动的方式。
高中英语阅读理解高难度单项选择题50题1. In the classic novel, the word "obscure" was used to describe the situation, but its meaning is closest to:A. clearB. confusingC. simpleD. obvious答案：B。
本题考查词汇理解。
“obscure”意为“模糊的，费解的”，A 选项“clear”表示“清晰的”；C 选项“simple”表示“简单的”；D 选项“obvious”表示“明显的”，都与“obscure”意思不同，B 选项“confusing”表示“令人困惑的”，与“obscure”意思相近。
2. When the character mentioned "perplexity" in the story, it refers to:A. happinessB. sadnessC. confusionD. anger答案：C。
“perplexity”意为“困惑，迷惘”，A 选项“happiness”是“幸福”；B 选项“sadness”是“悲伤”；D 选项“anger”是“愤怒”，都不符合“perplexity”的意思，C 选项“confusion”意思是“混乱，困惑”，与“perplexity”意思相近。
3. The phrase "elusive concept" in the classic work means:A. easy to understandB. difficult to catch or defineC. common and familiarD. simple and clear答案：B。
“elusive”有“难以捉摸的，难以理解的”之意，“elusive concept”指“难以捉摸的概念”，A 选项“easy to understand”表示“容易理解”；C 选项“common and familiar”表示“常见且熟悉”；D 选项“simple and clear”表示“简单清晰”，都不符合“elusive concept”的意思，B 选项“difficult to catch or define”意思是“难以抓住或定义”，符合题意。
高一英语阅读理解干扰项辨析单选题40题1. The story said that the man was very tall. But in fact, he was just of average height. This is an example of _____.A. stealing the conceptB. creating something out of nothingC. partial generalizationD. none of the above答案：A。
本题中，原文说男人很高，但实际是中等身高，这属于偷换概念，选项A 正确。
选项B 无中生有指的是文中根本没有提及的内容，这里并非这种情况。
选项C 以偏概全是指用局部的情况代表整体，本题也不符合。
2. The text mentioned that the girl liked apples. But the option said she loved all fruits. This is a kind of _____.A. stealing the conceptB. creating something out of nothingC. partial generalizationD. none of the above答案：C。
文中说女孩喜欢苹果，选项说她喜欢所有水果，这是以喜欢苹果这一部分来概括喜欢所有水果，属于以偏概全，选项 C 正确。
选项 A 偷换概念不符合，选项B 无中生有也不对。
3. The passage described the event happened in the morning. But one option claimed it occurred at night. This is _____.A. stealing the conceptB. creating something out of nothingC. partial generalizationD. none of the above答案：A。
试卷类型：A 山东新高考联合质量测评9月联考试题高三英语本卷满分150分，考试时间120分钟注意事项：1．答题前，考生先将自己的学校、姓名、班级、座号、考号填涂在相应位置。
2．选择题答案必须使用2B铅笔（按填涂样例）正确填涂：非选择题答案必须使用0.5毫米黑色签字笔书写，绘图时，可用2B铅笔作答，字体工整、笔迹清楚。
3．请按照题号在各题目的答题区域内作答，超出答题区域书写的答案无效，在草稿纸、试题卷上答题无效。
保持卡面清洁，不折叠、不破损。
第一部分听力（共两节，满分30分）做题时，先将答案标在试卷上。
录音内容结束后，你将有两分钟的时间将试卷上的答案转涂到答题纸上。
第一节（共5 小题；每小题1.5分，满分7.5分）听下面5段对话。
每段对话后有一个小题，从题中所给的A、B、C三个选项中选出最佳选项。
听完每段对话后，你都有10秒钟的时间来回答有关小题和阅读下一小题。
每段对话仅读一遍。
1．What will the speakers eat tonight?A．Italian food. B．Indian food. C．Chinese food.2．What does the man want to do?A．Invite Janet to the gym after work. B．Become a member of the gym.C．Take exercise every morning.3．How many cups of ingredients will the woman need in total?A．Six cups. B．Five cups. C．Four cups.4．Where does the conversation most likely take place?A．At home. B．In the office. C．In a restaurant.5．What is the man’s suggestion?A．Booking tickets in advance. B．Sitting at the back.C．Arriving early.第二节（共15小题；每小题1.5分，满分22.5分）听下面5段对话或独白。
Compatibility between superplasticizer admixtures and cements with mineral additionsOlga Burgos-Montes a ,Marta Palacios b ,Patricia Rivilla a ,Francisca Puertas a ,⇑a Eduardo Torroja Institute for Construction Sciences (IETcc-CSIC),Serrano Galvache,4,Madrid 28033,Spain bInstitute of Building Materials,ETH Zurich,Schafmattstrasse 6,8093Zurich,Switzerlanda r t i c l e i n f o Article history:Received 26April 2011Received in revised form 13December 2011Accepted 23December 2011Available online 31January 2012Keywords:Compatibility CementsSuperplasticizers admixtures Limestone Fly ash Silica fumea b s t r a c tThe incorporation of mineral additions to Portland cement reduces the amount of clinker required in cement manufacture improving the eco-efficiency of this process.They also impact rheology and it may affect the interaction between superplasticizers and cements.The presented study explores the effect of limestone,fly ash and silica fume on Portland cement and the interaction of these additions with naphthalene (PNS)-,melamine (PMS)-,lignosulfonate (LS)-and polycarboxylate (PCE)-based admixtures.The adsorption isotherms,zeta potentials and rheological behaviour of the blended cements were found and compared to the same parameters in non-blended cement.The results showed that cement–super-plasticizers compatibility was altered by the physical (specific surface)and chemical (surface charge)characteristics of the mineral additions studied.Ó2011Elsevier Ltd.All rights reserved.1.IntroductionThe incorporation of mineral additions to Portland cement re-duces the amount of clinker required in cement manufacture improving the eco-efficiency of this process by lowering both greenhouse gas emissions and energy consumption [1].These additions also enhance mainly the long-term strength and durabi-lity of the material obtained.Additions may be natural materials (limestone,pozzolans,schist)or industrial by-products (vitreous granulated blast furnace slag,fly ash or silica fume)with pozzola-nic or hydraulic properties [2,3].Limestone-blended cements have been widely studied.In terms of durability,permeability and strength,they are similar to non-blended cements,while exhibiting high compressive strength when small amounts of limestone are added [4–7].A final material with the desired properties can only be obtained,however,when the limestone used complies with certain quality,content,and particle size and fineness requirements [8,9].These characteristics allow the better packing of particles obtaining more compact and hence less porous structures [10].The use of fly ash in cement compositions is very common because it raises product strength and reduces alkali silica reaction-induced expansion [11–14].Fly ash fineness determines theproperties of the end material,which is more fluid and less porous than non-blended cement pastes [15–18].In light of its very fine particle size,silica fume has been studied as an addition to densify cement paste.As cements made with this addition exhibit higher compressive strength than non-blended materials,it is used to manufacture high-strength concrete [19–21].Moreover,it has been observed to act not only as filler or poz-zolanic material,but also to improve the cement paste–aggregate interface,which contributes to further improving mortar and con-crete strength.Its incorporation also affects fresh cement flowabil-ity,however,substantially raising the water demand,and its high early age hydration reactivity increases the heat of hydration and consequently intensifies total shrinkage [22–25].Cement paste,mortar and concrete microstructure,and in particular the homogeneity,density and porosity of the reaction products,must be closely monitored to attain the desired properties in the hardened material.Fresh cement paste rheology is regarded to be closely associated with the development of mortar and concrete microstructure [26].Given the direct impact of the presence of mineral additions on such microstructure,and consequently behaviour rheology,an understanding of blended cement behaviour in this regard is imperative.As a rule,the incorporation of mineral additions raises yield stress and to a lesser extent,plastic viscosity,especially in silica fume-blended cements [27–29].The fresh characteristics of concrete made with Portland ce-ment and rheology can be modified and controlled with super-plasticizers.Achieving the steepest decline in the water–cement0950-0618/$-see front matter Ó2011Elsevier Ltd.All rights reserved.doi:10.1016/j.conbuildmat.2011.12.092Corresponding author.Tel.:+34913020440x206;fax:+34913020700.E-mail address:puertasf@ietcc.csic.es (F.Puertas).ratio,greatest workability and decreasing the viscosity and the yield stress is,however,contingent upon the compatibility between the admixture chosen and the cement used.The presence of mineral additions such as limestone,fly ash and silica fume may affect the interaction between the superplasticizer and the cement. The performance of additions could be also influenced by admix-tures.Conventional superplasticizers such as naphthalene(PNS)-, melamine(PMS)-or lignosulfonate(LS)-based disperse the particles due to a electrosteric mechanism while the PCE form a steric obstacle to any direct inter-particle contact[35–41].The compatibility of mineral additons with,and affinity for,a given admixture must therefore be determined[3,30–34].The studies of limestone-blended cements and the superplasti-cizers have focused primarily on PCE admixtures[42–45]. Magarotto et al.[43]and Banfill[44]determined the importance of the molecular weight and the structure of the PCE on the rheological behaviour and the water-reduction of the limestone-blended cement.Mikanovic and Jolicoeur[46]studied the relation-ship between particle–superplasticizer interactions,rheology and paste stability on the one hand,and blending,sedimentation and consolidation on the other.Theirfindings showed that the mecha-nisms involved in superplasticizer action on limestone and cement type I varied depending on whether the admixture was PCE or PNS. They also observed that while the dispersion effect of the two was similar in water–limestone pastes,the presence of Ca(OH)2 improved the effectiveness of PCE.The use offly ash has been reported to improve cement rheol-ogy and lower the dose of superplasticizer needed(PCE and PMS) to obtain the desired reological properties[45,47].Due to the nearly spherical shape and the size offly ash particles,these ce-ment pastes demand a lower concentration of admixture than limestone blended cements[45].Silica fume blended cements behave differently from other blended cements due to the mineral surface[48]of this addition. The use of silica fume reduces paste workability.The improvement in reological properties depends on the type of superplasticizer. The PMS dose needed by silica fume-containing cements is similar to the dose required by cement type I to induce the same reological behaviour[47–49].The molecular architectures of the PCE are crit-ical to the dispersion of the silica fume particles[48].Despite the importance of admixture compatibility,the interac-tions between blended cements and superplasticizers have been scantly studied,and the interactions between limestone,fly ash and silica fume particles and superplasticizers have barely been re-searched at all.The present study aimed to establish the effect of mineral addi-tions on fresh type II Portland cement pastes containing limestone (CEM II/B-L),fly ash(CEM II/B-V)and silica fume(CEM II/A-D),and to determine the compatibility between these additions and four superplasticizers:naphthalene(PNS),melamine(PMS),lignosul-phonate(LS)and polycarboxylate(PCE)polymers.The control used throughout was non-blended CEM I52.5-R.2.Materials and methods2.1.MaterialsThe characteristics of the commercial CEM I52.5R Portland cement used are given in Table1.The three type II cements studied were prepared in the laboratory: CEM II/B-L,containing(30wt%)limestone,CEM II/B-V,containing(30wt%)fly ash and CEM II/A-D,containing(10wt%)silica fume.The cement constituents were blended in a turbula mixer for2h.The chemical composition and specific surface of these blended-cements are given in Table1.Table2lists the chemical composi-tion and B.E.T.specific surface of the mineral additions.Four commercial superplasticizers were used:a lignosulphonate(LS)derivative, a naphthalene-based compound(PNS),a melamine-based material(PMS)and a polycarboxylate superplasticizing admixture(PCE).The physical–chemical charac-teristics of the admixtures are given in Table3.2.2.Methods2.2.1.Adsorption isothermsAdmixture adsorption isotherms were determined for cements and mineral additions.The suspensions were prepared as described by Perche[50].The admix-tures were dissolved in water and40g of each solution were mixed with20g of cement.The dosage ranged from0to40mg of polymer/g of cement for LS,PNS and PMS and from0to2.5mg of polymer/g of cement for the PCE.The suspen-sions were stirred magnetically for30min at25°C and subsequently centrifuged for3min to separate the supernatant from the solid.The amount of admixture present in the supernatant was determined with a SHIMADZU TOC-VCSH/CSN to-tal organic carbon analyzer.The amount of admixture consumed was obtained as the difference between the amount initially added and the quantity remaining in the supernatant.Table1Chemicals composition(wt%),Blaine and BET specific surface of Portland cements. L.O.I.:loss on ignition.I.R.:insoluble residue.S S BET.Specific Surface Area determined by B.E.T.wt%CEM I52.5R CEM II/B-L CEM II/B-V CEM II/A-D L.O.I. 2.3514.83 3.58 2.56SiO220.5113.4528.4432.58Al2O3 5.37 3.5314.11 4.25Fe2O3 2.10 1.54 2.93 1.76MnO0.020.010.020.02MgO 3.86 2.79 2.93 3.13CaO57.0557.4940.7948.47Na2O0.640.560.550.64K2O 1.44 1.02 1.44 1.23TiO20.160.120.450.14P2O50.130.120.450.12SO3 6.37 6.16 4.33 5.09I.R.0.26 1.48 2.00 2.33CaO free 1.270.100.930.96Blaine(m2/kg)501.7524472.1559.0S S BET(m2/g) 1.22 2.11 1.53 2.98Table2Chemicals composition(wt%),Blaine and BET specific surface of mineral additions.wt%L CV HSL.O.I.43.56 6.76 3.96 SiO20.3446.3294.29 Al2O30.0431.010.24 Fe2O30.11 4.500.11 MnO0.010.050.02 MgO0.93 1.290.24 CaO54.56 4.900.46 Na2O0.360.340.11 K2O– 1.340.37 TiO20.01 1.53–P2O50.080.980.05 SO3–0.980.15 Si react.036.492.7 S S BET(m2/g) 4.38 2.7020.29 Dv(l m)1 1.714.70.31214.736.210.48Table3Physical and chemical characteristics of superplasticizers.Admixture LS PNS PMS PCESolid content(%)40.139.641.940.9 M w(Da)39,230136,99578,82859,596 Mn16,91525,695731535,923 Viscosity(mPa.s)24.2851.1131.50118.20 %C37.0843.7818.6551.67 %S 5.919.1310.650.30 %H 4.89 4.53 3.988.14 %N 1.460.8022.170.17 Na(ppm)41,84031,40055,2802820 K(ppm)3903400.210pH88.58 4.5O.Burgos-Montes et al./Construction and Building Materials31(2012)300–3093012.2.2.Effect of superplasticizers on the zeta potential of cements and additions suspensionsThe effect of different dosages of four superplasticizers (LS,PNS,PMS and PCE)on the zeta potential of the suspensions of non-blended and blended cements as well as on suspensions additions was obtained on a Colloidal Dynamics AcoustosizerIIs.The zeta potential values were determined using the Smoluchowski approxima-tion.Thirty grams of each cement and addition were suspended in 160g of water.The suspensions were stirred magnetically for 15min,subsequently dispersed with a sonicator for 5min and finally mixed by magnetic stirring for a further 5min.They were then placed in a measuring cell to determine the zeta potential after this 25-min contact between material and water.The superplasticizers were added to the cement suspensions with an automatic titrator at a rate of 0–20mg polymer/g bin-der and to the addition suspensions at 0–40mg polymer/g addition.The zeta poten-tial values were corrected for the presence of the background solution.2.2.3.Rheological behaviourYield stress was evaluated for the cement pastes with a Haake Rheowin Pro RV1rotational viscometer fitted with a roughened cylindrical rotor.The inner cylinder has of 37and 55mm of diameter and height,respectively,and the outer cylinder has 44and 70mm of diameter and height,respectively.In both cylinders the height of the grooves is 1mm.The cement pastes were prepared by mixing 100g of ce-ment and 45ml of water for 3min in a mechanical blade stirrer.Superplasticizer doses ranging from 0to 8mg of polymer per g of cement were added with the mixing water.The cement paste rheology test consisted of exposure to pre-shear stress at 100s À1for 1min,after which the rotor speed was reduced to 0s À1,subsequently ramped up to 100s À1in 12min and then lowered to 0s À1,likewise in 12min.The cement cycles obtained in the rheological tests exhibited virtually no hystere-sis,an indication that the binder pastes were perfectly floc-free (Fig.1).All the rheo-logical curves followed the same pattern,with the decline in shear rate conforming to the Bingham equation (Eq.(1)),in which the y -intercept defines the yield stress and the slope of the fitted line,paste plastic viscositys ¼s 0þg Ãðc Þð1ÞTable 4Experimental admixture adsorption on cements in the adsorption plateau values.Cement Admixtures Experimental adsorption mg polymer/g bindermg polymer/m 2binder CEM ILS 14.2811.70PNS 10.078.25PMS 11.539.45PC 0.620.50CEMII/BLLS 18.278.66PNS 9.56 4.53PMS 16.357.75PC 0.650.31CEMII/BVLS 10.867.10PNS 11.087.24PMS 17.8411.66PC 0.730.48CEMII/ADLS 22.107.42PNS 13.63 4.57PMS 20.01 6.71PC0.850.29302O.Burgos-Montes et al./Construction and Building Materials 31(2012)300–3093.Results and discussion3.1.Control cement(CEM I52.5R)Cement paste behaviour is conditioned by the physical–chemi-cal interaction between the particles and the medium.The inclu-sion of superplasticizers,which are adsorbed onto the particles, preventsflocculation and water entrapment in theflocs,reducing the amount of water needed to obtain similarfluidity in the pastes. However admixture effectiveness depends on its compatibility and affinity with the cement and mineral addition particles.This calls for a detailed study of the surface interaction between these poly-mers and the various types of particles comprising the cements.The behaviour of the non-blended cement in the presence of the four superplasticizers is shown in the adsorption isotherms in Fig.2a.Admixture adsorption on the cement exhibited exponential behaviour,linear at low concentrations of the admixture,followed by a plateau adsorption period in which the inclusion of larger amounts of superplasticizer led to no further consumption by the cement.The traditional admixtures had high adsorption values for CEM I:14.28,11.53and10.07mg of admixture/g of cement for LS,PMS and PNS,respectively(see Table4).These values are in keeping with the molecular weight of the admixtures(see Ta-ble3),for adsorption was most intense in the superplasticizer with the lowest molecular weight(LS),and least intense in the polymer with the highest(PNS).Molecular weight may be also related to the radious of gyration of the polymer in the solution.Many stud-ies[3,30,37,51]determine that the PCE-based admixture exhibited a substantially larger radius of gyration therefore larger thickness of the polymer layer than the other polymers,required signifi-cantly smaller dosages to reach the adsorption.The adsorption pla-teau value of PCE corresponds to0.62mg of admixture/g of cement.Information on both superplasticizer adsorption and the varia-tion in the charge on particle surfaces were obtained by studying the variation in the zeta potential of the particles with the amountTable5Experimental admixture adsorption on additions in adsorption plateau values.Addition Admixtures Experimental adsorptionmg polymer/ g addition mg polymer/ m2additionLime LS14.77 3.37PNS––PMS 6.06 1.38PC0.910.21Fly ash LS13.44 4.98PNS––PMS10.67 3.95PC0.300.11Silica fume LS33.21 1.64PNS––PMS19.950.98PC0.780.04O.Burgos-Montes et al./Construction and Building Materials31(2012)300–309303of admixture included(Fig.2b).The slightly positive(+0.5mV)zeta potential of the cement particles favoured adsorption of the anion group-bearing superplasticizers.The main effect of traditional superplasticizers LS,PMS and PNS induce the dispersion of cement particles by an electrosteric mechanism favouring mutual repul-sion and hinderingflocculation[3,31].Taking into account of the zeta potential values observed in Fig.2b,the PMS have the highest electrical contribution followed by PNS and,lastly,LS.This pro-gression concurred of concentration of percentage of sulphur in the admixture(see Table3)that corresponds to the number of RÀSOÀ3groups originally present in the sulphonates and the poly-mer molecules directly involved in adsorption.The PCE-based admixtures,in turn,induced a steric obstacle to any direct inter-particle contact[3,51].The zeta potential values of close to0for the PCE admixture showed that the electrostatic contribution to the cement particle stability will be negligible.The preparation of cement pastes,mortars and concretes calls for high concentrations of solids.Therefore,in addition to the interactions between the particles and admixtures studied,others, such as particle–particle or particle–admixture–particle interac-tions,take place in these products.In this connection,Fig.3shows the results of the yield stress of the cement pastes with and with-out superplasticizers to determine their rheological behaviour.In the non-blended CEM I cement pastes,the inclusion of superplas-ticizers reduced yield stress,i.e.,inter-floc interaction,since these polymers stabilized the particles,hindering their agglomeration. Here also,the behaviour of the PCE-based admixture deviated sig-nificantly from the pattern recorded for the traditional polymers, due to the differences in their stabilization mechanisms.Similar observations have been reported by other authors,who found that at least twice as much PNS as PCE was needed to achieve similar yield stress values[33,7,51].Yield stress was observed to decline rapidly by as much as90%at low dosages of PCE(lower that 2mg PCE/g cement),whereas much larger amounts of the other admixtures were required to obtain a significant difference in these values.Behaviour was observed to be linear in the presence of tra-ditional admixtures up to values of6mg of admixture/g of cement, while concentrations of8mg of admixture/g of cement were needed to lower the yield stress.The steepest such reduction was obtained with PNS(82%),followed by PMS(44%)andfinally LS(22%).3.2.Effect of limestone(CEM II/B-L)The inclusion of30%limestone in cement pastes(Fig.4a)raised LS and PMS adsorption,indicating that these admixtures had a greater affinity for CEM II/BL than for CEM I,while PNS and PCE be-haved in much the same way in the limestone blend as in the non-blended cement.The presence of mineral additions changes the physical–chemical properties of the cement and its behaviour in terms of superplasticizer adsorption according to the values shown in Table4on admixture adsorption in the plateau region(in mg of admixture/g of cement).Since these adsorption plateau values were closely related to the physical characteristics of the cement, however,adsorption was also found per m2of particle.This param-eter defines the amount of admixture adsorbed per particle area, i.e.,the affinity of the polymer molecules for the particle studied, irrespective of the specific surface of the material(see results in Table5).Table6Theoretical and normalize adsorption plateau data.Cement Admixtures Theoretical adsorption Normalize adsorptionmg polymer/g binder mg polymer/m2binder mg polymer/g binder mg polymer/m2binderCEMII/BL LS14.439.20 1.270.94PNS––––PMS9.897.03 1.65 1.10PC0.700.410.920.75CEMII/BV LS14.039.680.770.73PNS––––PMS11.727.80 1.58 1.50PC0.520.38 1.40 1.25CEMII/AD LS16.1710.69 1.370.69PNS––––PMS12.378.60 1.620.78PC0.640.45 1.340.64304O.Burgos-Montes et al./Construction and Building Materials31(2012)300–309Adsorption analysis of the mineral additions revealed,firstly, that due to the dispersion of the addition particles in the presence of PNS,the solid particles could not be separated from the superna-tant.Consequently,the amount of free admixture present in the li-quid,i.e.,not adsorbed onto the addition particles,could not be quantified for this admixture.Superplasticizer adsorption on lime-stone was similar to its adsorption on limestone-blended cement: the highest consumption was observed for LS,followed by PMS and PCE,in that order(Fig.4b).The amount of admixture consumed by the limestone particles was similar to the value observed for CEM II/B-L cement,although the amount of polymer adsorbed onto the surface was substantially lower:i.e.,affinity was much smaller for limestone than for cement particles.Nonetheless,the presence of thefiller led to a higher total consumption of admixture as a result of its greater specific surface(See Table5).Mikanovic and Jolicoeur [46]observed that twice as much PNS as PCE was adsorbed and that adsorption of both polymers was twice as high on cement as on limestone particles.Table6gives the theoretical adsorption data in both mg of admixture/g of cement and mg of admixture/m2of cement,given the proportions of each component in the blend and their adsorp-tion plateau,assuming that the cement and addition particles did not interact.The normalize adsorption has been calculated by the comparation of the theoretical and experimental data,in order to determine the existence or otherwise of synergies between the addition and the cement.This exercise showed that adding lime-stone to the cement led to greater consumption of traditional admixture,in particular PMS,per gram of cement,whereas the amount of PCE consumed was similar with and absence of the addition.The surface adsorption rate(mg of admixture/m2of ce-ment)was lower in LS and PCE after the inclusion of limestone, however,while for PMS this parameter was essentially unaffected by the addition.The variations in the zeta potential of cement CEM II/B-L (blended with limestone)in the presence of superplasticizers are shown in Fig.4c and d.Initially,the cement containing limestone behaved very much like the unadditioned material,with PMS affording the greatest electrostatic contribution to stabilization. Limestone particle behaviour was the outcome of a high zeta po-tential(+13mV),which favoured the adsorption of the negatively charged(with values of overÀ20mV)traditional admixtures.Of these,PMS had the highest negative charge.The adsorption of the PCE superplasticizer leads to zeta potential values close to0 (À2mV),in the limestone particles.The cement pastes containing limestone exhibited only slightly higher yield stress than the control(Fig.5a).Their rheological behaviour in the presence of the superplasticizers was more dis-tinctly differentiated,however.The yield stress values for the lime-stone cement were observed to decline with even very small quantities of superplasticizer.PNS proved to be the most effective traditional admixture,for at concentrations of6mg/g of cement, the value dipped to17.5Pa,whereas8mg of PMS/g of cementO.Burgos-Montes et al./Construction and Building Materials31(2012)300–309305were required to attain similar levels.Admixture LS lowered yield stress least effectively.To1.6mg of PCE/g of cement the yield stress has reduced in a78%for limestone cement whereas a53% for non blended cement.PCE was more effective in CEM II/B-L than in the control cement,with a steeper decline in yield stress ob-served at low dosages of the admixture lower that2mg PCE/g cement.Fig.5b shows the normalized yield stress values for the lime-stone-blended cement with respect to the control non-blended ce-ment.Values of less than1denote a decline in yield stress,i.e.,an improvement in paste rheological properties.The addition of lime-stone induced higher yield stress values when the admixture dos-age was low or non-existent.At values of8mg of admixture/g of cement(the optimal concentration found for CEM I),however, the limestone cement pastes exhibited better rheological proper-ties than the non-blended material.3.3.Effect offly ash(CEM II/B-V)The adsorption isotherms for superplasticizers on cement con-tainingfly ash(Fig.6a)showed that LS consumption was much lower than in the control cement,while a striking rise was ob-served in PMS consumption(11.66mg of PMS/g of cement).Actual adsorption was greater than forecast in the theoretical calculations (Table6),an indication of the existence of interaction between the cement andfly ash particles.The difference between the calculated and experimental data was higher here than for limestone-blended cement,with normalized adsorption values of nearly1.6and1.4 for PMS and PCE,respectively.Moreover,the addition offly ash to the cement led to the adsorption of more admixture molecules per unit of area.In other words,PMS and PCE consumption was greater both overall(per gram of cement)as on the surface(per m2of particle surface area).The adsorption of superplasticizers onfly ash particles confirmed that PMS was consumed more inten-sely than on limestone particles,with values close to thefindings recorded for LS(Fig.6b).The amount of admixture consumed per unit area was generally higher than in the limestone cement,in particular for PMS,for which the values doubled the limestone blendfigures.In contrast,PCE was adsorbed less profusely onfly ash than on limestone.The variations in the zeta potential with the amount of admix-ture are shown in Fig.6c.CEM II/B-V behaved in much the same way as the cements discussed above,except that slightly higher zeta potential values were recorded in the presence of PMS,which is consistent with the more intense consumption of this admixture observed on the adsorption isotherms.Fly ash particles,with a zeta potential of+2.5mV(see Fig.6d),favour polymer adsorption.The zeta potential was lower than found for the limestone particles, however,which translated into lower zeta potential values in the presence of the admixtures.Despite this lower surface charge and the smaller specific surface infly ash particles,adsorption per unit of area was higher than in limestone(see Table5).Surface morphology and the adsorption sites available for the polymer may have changed the polymer adsorption configurations and thus effective surface coverage[44].The rheological behaviour of cement CEM II/B-V(Fig.7a)con-firmed the greater affinity offly ash particles for PMS observed ear-lier.The cement pastes with PMS and PNS exhibited a75%decline in the yield stress at dosages of6mg of admixture/g of cement.As in the preceding cases,LS accounted for the smallest decline in yield stress in cement pastes.Fig.7b shows that at low doses of admixture or in its absence,thefly ash-blended cement behaved like the CEM I cement under the same conditions,rheologically speaking.At concentrations of over1(for PCE)or over5(for the traditional polymers)mg of admixture/g of cement,however,con-siderable improvement was observed in yield stress.The greater affinity of thefly ash for the traditional admixtures observed on the adsorption isotherms translated into better rheological behav-iour in these pastes than in the limestone cement material.This same effect was reported by Artel and Garcia[45].Moreover,sig-nificant improvement was observed in the cement paste in the presence of PMS.3.4.Effect of silica fume(CEM II/A-D)Fig.8a and b shows the admixture adsorption isotherms on sil-ica fume-containing cement and silica fume particles.No adsorp-tion plateau was attained in any of the cases studied,due to the large specific surface of silica fume and the concomitantly high de-mand for admixture.CEMII/A-D consumed more LS and PMS than PNS and,as in the preceding cements,the behaviour exhibited by the PCE polymer was completely different.A comparison of the theoretical and experimental adsorption data revealed the exis-tence of interaction between the cement and silica fume particles, reflected in the higher consumption of admixture.The silica fume particle adsorption isotherms were practically linear(see Fig.8b). Silica fume was,moreover,the addition that consumed the great-est quantity of admixture(see Table5and Fig.8b)due to its high specific surface(Table2),five-and ten-fold larger than infly ash and limestone,respectively.That notwithstanding,in terms of admixture consumed per unit of area,silica fume was observed to have lower affinity for the admixture molecules although the306O.Burgos-Montes et al./Construction and Building Materials31(2012)300–309。
When writing an essay about history in English,it is important to follow a structured approach that includes an introduction,body paragraphs,and a conclusion.Here are some tips and a sample outline to help you craft a compelling historical essay.Introduction:Begin with a hook to engage the readers interest.Provide a brief overview of the historical event or period you will discuss.State your thesis,which should be a clear and concise statement of your argument or perspective.Body Paragraphs:Each paragraph should focus on a single aspect of the historical event or period.Start with a topic sentence that introduces the main idea of the paragraph.Provide evidence from primary and secondary sources to support your argument. Analyze the evidence,showing how it relates to your thesis.Use transitions to connect your ideas and maintain a logical flow.Conclusion:Summarize the main points of your essay.Restate your thesis in a new way,showing how your argument has been supported by the evidence.End with a closing thought that leaves a lasting impression on the reader.Sample Outline:Title:The Impact of the Industrial Revolution on SocietyI.IntroductionA.Hook:A quote or a vivid description of the changes brought by the Industrial Revolution.B.Brief overview of the Industrial Revolution.C.Thesis statement:The Industrial Revolution had a profound impact on society, transforming economies,creating new social classes,and altering the landscape of urban areas.II.Economic TransformationA.Topic sentence:The Industrial Revolution led to significant economic changes.B.Evidence:The shift from agrarian economies to industrial economies.C.Analysis:How these changes affected production,trade,and wealth distribution.III.Creation of Social ClassesA.Topic sentence:The Industrial Revolution created new social classes.B.Evidence:The emergence of the working class and the industrial bourgeoisie.C.Analysis:The role of these classes in shaping societal norms and values.IV.Urbanization and its EffectsA.Topic sentence:Urban areas expanded rapidly during the Industrial Revolution.B.Evidence:The growth of cities and the migration of people from rural to urban areas.C.Analysis:The impact of urbanization on living conditions,public health,and social dynamics.V.Technological InnovationsA.Topic sentence:Technological advancements were a key feature of the Industrial Revolution.B.Evidence:Examples of new machinery and processes.C.Analysis:The role of technology in driving economic and social change.VI.ConclusionA.Summary of the economic,social,and urban changes.B.Restated thesis:The Industrial Revolution was a transformative period that reshaped society in multiple ways.C.Closing thought:The lasting legacy of the Industrial Revolution and its relevance to modern society.Remember to cite your sources properly and use a consistent writing style throughout your essay.By following this structure and focusing on clear argumentation and evidence, you can write a compelling historical essay.。
小学上册英语第六单元测验卷(有答案)英语试题一、综合题(本题有100小题，每小题1分，共100分.每小题不选、错误，均不给分)1.The bird has bright _______ (鸟有鲜艳的_______).2.The cat is ___ (climbing) the shelf.3.The first human to reach the North Pole was ______ (阿蒙森).4.The __________ (城市与乡村) have different lifestyles.5.She is _______ (非常聪明).6. A ____ is a gentle creature that enjoys being around people.7. A ____ hops around and has big ears.8._______ can help clean the air.9.My sister plays ________ with her friends.10.I have a ________ for my birthday.11.This ________ (玩具) inspires me to be creative.12.I help my sister with her __________. (画画)13.I see a ___ (cloud/rainbow) above.14.The bobcat is a skilled _______ (猎手).15.The __________ (历史的叙述模式) shape our perceptions.16.She is ___ (laughing/sobbing) at the movie.17.The _____ (avocado) is creamy.18.What color do you get when you mix red and white?A. PinkB. PurpleC. OrangeD. Brown答案: A. Pink19.What do you call the sound made by a cat?A. BarkB. MeowC. RoarD. Tweet答案: B20.The _______ (金鱼) can come in various colors.21.The capital of Kyrgyzstan is __________.22.My ________ (姑姑) is getting married next month.23.My pet _____ loves to chase its tail.24.The _______ of an object can change based on its position.25.Electricity can create a ______.26. A _______ is a reaction that occurs in the atmosphere.27.I have a toy _______ that can make me smile.28.Which instrument has keys?A. GuitarB. ViolinC. PianoD. Drums答案: C29.The ______ has a unique call.30.The flower needs sunlight and ______.31.The chemical formula for glucose is ______.32.What do you call the act of watching something closely?A. ObservingB. ViewingC. GazingD. Glancing答案: A33. A reaction involving the transfer of electrons is called a ______ reaction.34.My cousin is a __________ (演员).35.The __________ (历史故事) can inspire future generations.36.The ______ (绿色技术) often utilizes plant resources.37.My dog loves to play with a ______ (球).38.My favorite sport is ______ (美式足球).39. A ________ (植物观察活动) encourages interest in nature.40. (Japanese) feudal system included samurai warriors. The ____41.The capital of Nepal is _____.42.The __________ (全球视野) broadens perspectives.43.We can ___ a movie night. (have)44.The flower pot is colorful and ______.45.Eclipses occur due to the alignment of the sun, moon, and ______.46.My _____ (姑姑) has a lovely collection of flower pots. 我姑姑有一个美丽的花盆收藏。
大学英语阅读试题及答案一、阅读理解（共20分）阅读下列短文，然后根据短文内容回答问题。
A. 短文一In recent years, the popularity of online courses has surged, with millions of students around the world taking advantageof the convenience and flexibility they offer. Online courses provide a wide range of subjects, from humanities to science, and are accessible to anyone with an internet connection. However, there are concerns about the quality of education that can be delivered through this medium.问题1： Why has the popularity of online courses increased in recent years?答案1： The popularity of online courses has increased due to the convenience and flexibility they offer, allowing millions of students to access a wide range of subjects through the internet.问题2： What are the concerns regarding online courses?答案2： There are concerns about the quality of educationthat can be delivered through online courses.B. 短文二The concept of a "smart city" is becoming more prevalent as technology advances. A smart city uses technology to improve the quality of life for its citizens, enhance sustainability, and facilitate efficient urban services. For example, smart traffic management systems can reduce congestion, while smart energy systems can optimize energy consumption.问题3： What is a smart city?答案3： A smart city is a city that uses technology to improve the quality of life for its citizens, enhance sustainability, and facilitate efficient urban services.问题4： What are some of the benefits of smart city technology?答案4： Benefits include improved quality of life, enhanced sustainability, and optimized energy consumption through efficient urban services like smart traffic and energy management systems.二、完形填空（共10分）阅读下面的短文，从短文后各题所给的选项中选出可以填入空白处的最佳选项。
Influence of cement and superplasticizers type and dosageon the fluidity of cement mortars—Part IS.Chandra*,J.Bjo ¨rnstro ¨mChalmers University of Technology,Civil Engineering Department,Applied Concrete Chemistry,41296Go ¨teborg,SwedenReceived 10January 2002;accepted 29April 2002AbstractConcrete quality is controlled by the flow behavior of cement paste,which is related to the dispersion of cement particles.Superplasticizers (SPs)provide the possibility of a better dispersion of cement particles,thereby producing paste of higher fluidity.With the development of high strength,high performance concrete,SPs are becoming indispensable.SPs are adsorbed on the cement particles.This adsorption is uneven and depends upon the clinker composition of cement and the type of SP used.This work is focused on the study of the influence of lignosulfonic acid (LS)-and melamine sulfonic acid (SMF)-based SPs on the fluidity of mortars made with ordinary Portland (OPC),low alkali (LAC)and white cement (WC)at different water to cement ratio.It is shown that LS are more effective than SMF in providing better fluidity.Further WC has given the highest fluidity among the cements used.It is attributed to the lower C 3A +C 4AF and alkali content,and higher SO 3content.D 2002Elsevier Science Ltd.All rights reserved.Keywords:Adsorption;Clinker mineral;Workability;Cement paste;High-range water reducers1.IntroductionThe properties of concrete are governed by its flow behavior,which is controlled by the dispersion of cement particles.It is widely known that better fluidity is achieved by the addition of superplasticizers (SPs).The role of SPs in concrete has therefore become increasingly important.For instance,the contribution of SP in the development of high strength concrete is remarkably larger than that of cement.The SPs are adsorbed on the cement particles,which deflocculate and separate,releasing trapped water from cement flocks.A variety of SPs have been developed and are available in the market.These belong to different basic groups,such as lignosulfonic acid (LS),melamine form-aldehyde sulfonic acid (SMF),naphthalene formaldehyde sulfonic acid (SNF)and polycarboxylic acid (CE).Apart from the SPs of different basic groups,there can also be differences in SPs from the same group depending upon their synthesis,which influences upon the molecular weight and chemical configuration.The problem,which is encoun-tered in the interpretation of results,very often is the non-availability of data,especially the molecular weight of SPs.Cements,on the other hand,vary in composition and fineness,which influence upon the hydration process and thereby on the flow behavior of cement paste.In this work,influence of different dosage of lignosulfonate and sulfo-nated melamine formaldehyde SPs,on the fluidity of mortars made with ordinary Portland cement (OPC),low alkali cement (LAC)and white cement (WC)has been studied.Possible mechanism of interaction is discussed.2.Materials and methods 2.1.CementsThree types of cements were used.OPC and LAC were supplied by Cementa,Sweden.WC was supplied by Aal-borg Portland Cement,Denmark.The properties are shown in Table 1.2.2.SPsLS,Cementa P40,was supplied by Cementa.SMF,Cementa Flyt 92M,was supplied by Cementa.0008-8846/02/$–see front matter D 2002Elsevier Science Ltd.All rights reserved.PII:S 0008-8846(02)00839-6*Corresponding author.Tel.:+46-3-1772-2301;fax:+46-3-1772-2853.E-mail address :jok@inoc.chalmers.se (S.Chandra).Cement and Concrete Research 32(2002)1605–1611Standard grade sands 1,2and 3was used.The mortars were made with 1:3cement to sand ratio,where equal part of each sand grade was mixed.Mortars were mixed in aHobart mixer.Fluidity was measured on the cement mortars made with different types of cements and SPs at different water to cement ratios.The dosage of SP mentioned in this study was calculated to the weight of cement.Flow was measured at 20°C by pull out spread of the mortar from a cone of top diameter 70mm,bottom diameter 100mm and height 60mm.The spread was the average of two perpen-dicularly crossing diameters.From the spread (F ),relativeflow area (A ˜)was calculated by Eq.(1)[1].A ~¼ðF =r 0Þ2À1ð1Þwhere r 0=50mm,bottom cone radius.Flow area and fresh density of mortars with OPC,LAC and WC with different dosage of LS (P40)and SMF (Cementa Flyt 92M)were measured at different water to cement ratios.Air content was calculated.Flow area andTable 1Composition and properties of the cements used:OPC,LAC,WCOPCLAC WC C 2S,%1322.825C 3S,%6455.763C 3A,%5 2.14C 4AF,%1013.11K 2O +Na 2O,% 1.60.50.3SO 3,%3.2 2.43–5Specific surface area,m 2/kg 337304410Density,kg/m 3320032103150*Data presented were supplied by themanufacturers.Fig.1.Relation between flow area (a),fresh density (b)and air content (c)for OPC,LAC and WC at different water to cementratio.Fig.2.Flow area (a),fresh density (b)and air content (c)with respect to water to cement ratio at different dosage of lignosulfonate SP,P40.For OPC.S.Chandra,J.Bjo ¨rnstro ¨m /Cement and Concrete Research 32(2002)1605–16111606fresh density data presented are based on triplicate measure-ments.The average standard deviation in determining flow area is 1.12and for the fresh density determinations 5.88.The results are shown in Figs.1–7.3.Results and discussionsThe results of the tests performed with three cements without SP are shown in Fig.1a–c .It is seen here that there is no significant difference on the fluidity of mortars up to 0.45water to cement ratio.At 0.50water to cement ratio,the fluidity of WC increased compared to the other cements,whereas the cement OPC and LAC have shown the same fluidity.High fluidity was marked at 0.60water to cementratio.Similar trends were observed with the fresh density upto 0.45water to cement ratio.At 0.50water to cement ratio,the fresh density of WC was slightly higher,while the air content was slightly lower than for the other two cements.This was due to better compaction of the mortar because of enhanced fluidity.Fig.2shows the results of mortars made with OPC and 0.3,0.5and 0.8wt.%of lignosulfonate (P40)SP.It is seen from Fig.2a–c that the addition of P40has increased the flow.However,an increase in the dosage from 0.3%to 0.5%did not result in a significant increase on the flow,marginal changes are,however,noted.At 0.8%P40,the flow was also similar to 0.3%and 0.5%,but has significantly increased at 0.6water to cement ratio.Substantial differ-ences on fresh density were observed up to 0.45water to cement ratio,exceeding,which no appreciable difference in the fresh density could be noticed.At 0.35water to cement ratio,the density of mortars with 0.3%and 0.5%P40areFig.3.Flow area (a),fresh density (b)and air content (c)with respect to water to cement ratio at different dosage of lignosulfonate SP,P40.ForLAC.Fig.4.Flow area (a),fresh density (b)and air content (c)with respect to water to cement ratio at different dosage of lignosulfonate SP,P40.For WC.S.Chandra,J.Bjo ¨rnstro ¨m /Cement and Concrete Research 32(2002)1605–16111607similar and lower than that obtained with 0.8%P40.This is in agreement with the air content,which is higher for 0.3%and 0.5%and lower for 0.8%P40.Increase in the density at 0.45water to cement ratio follows with lower air content.At 0.35water to cement ratio,the lower density and conse-quently higher air content is due to inadequate packing of the mortar in the pot during weighing for density deter-mination.With increase in the water to cement ratio to 0.50wettability increases,which provides better compaction,thereby density increases and air content decreases com-pared to with 0.35water to cement ratio.With further increase in the water to cement ratio,flowability increased but there is not so much decrease in the density as the mass was very cohesive and there was no bleeding.Because of this the air content is low and stable.Fig.3shows the influence of P40on LAC.It is seen from the figure that the flow of mortars with 0.3%,0.5%and 0.8%P40were similar.The density and air content have,however,some differences when the dosage increased to 0.8%com-pared to 0.3%and 0.5%.It is attributed to the increase incohesiveness of mortar with increased dose of P40.Fig.4shows the influence of P40on WC.It is seen from Fig.4a that there is no significant difference in the fluidity up to 0.40water to cement ratio for different doses of P40.At 0.45water to cement ratio,there is a substantial difference in fluidity between 0.3%and 0.5%.Whereas between 0.5%and 0.8%,there is practically no difference.There was no substantial difference in the densities and air content for the three dosages of P40at all the water to cement ratios (Fig.4b,c).It is,however,observed that,at 0.35water to cement ratio,the density was low and the air content was high.It is because of the inadequate fluidity and thereby bad compaction of the mass in the density measure-ments.At 0.40water to cement ratio,the density increased for the three dosages.With higher water to cementratios,Fig.5.Flow area (a),fresh density (b)and air content (c)with respect to water to cement ratio at different dosage of SMF SP,Flyt 92M.ForOPC.Fig.6.Flow area (a),fresh density (b)and air content (c)with respect to water to cement ratio at different dosage of SMF SP,Flyt 92M.For LAC.S.Chandra,J.Bjo ¨rnstro ¨m /Cement and Concrete Research 32(2002)1605–16111608the density decreased,as the fluidity increased.The air content decreased simultaneously.It was noted that the cohesiveness of the mixture increased with the increase in the P40dosages.Identical tests were performed with SMF (Flyt 92M)and three cements OPC,LAC and WC.Fig.5shows the influence of SMF on OPC.It is seen here that,with OPC,there is no difference in the flow,density and air content with increase in the dosages of SP (Fig.5a–c).Increase in the water to cement ratio increased the fluidity equally.Fig.6shows the influence of SMF on LAC.It is seen from Fig.6a that,with LAC,the fluidity increased with the increase in the water to cement ratio.It was higher for 0.8%compared to 0.3%and 0.5%.At 0.55and 0.60water to cement ratio,the fluidity increased more for 0.5%and 0.8%compared to 0.3%(Fig.6a).The density was lower for 0.3%.For 0.5%,it was almost constant up to 0.55water tocement ratio and then decreased at 0.60water to cementratio.At 0.8%SMF,there is a slight increase in the density at 0.4and 0.45water to cement ratio and then a decrease.This decrease in density is due to the increase in the fluidity (Fig.6b).The air content for 0.3%and 0.5%SMF was the same at all the water to cement ratios.It,however,decreased with 0.8%water to cement ratio up to 0.50,beyond which it became constant (Fig.6c).Fig.7shows the influence of SMF on WC.It is seen here that there is no appreciable difference on fluidity,density and air content with increasing dosage.The fluidity increased with increase in water to cement ratio (Fig.7a).But there was practically no difference in the density (Fig.7b).The air content decreased with the increase in the fluidity and exceeding 0.55water to cement ratio,there was practically no air in the mixture (Fig.7c).It shows that the increase in the dose of SMF does not increase the fluidity,0.3%can be translated as the optimum dose.WC cement has shown the highest fluidity compared to the other patibility of cements with LS and SMFThe fluidity of a cement paste is related to the hydration of the cement,which,in its turn,is connected with the cement composition and fineness.Cement particles contain several mineral phases of different reactivity,as well as a variety of chemical and structural defects.Their initial hydration will likely generate a surface with important variation in the surface charge density,both in size and magnitude.These localized surface charges promote floc-culation of hydrating cement particles,but they can be effectively neutralized and separated by the anionic charge of the SP molecules.The hydration of interstitial phases is affected by the concentration of Ca 2+,OH Àand SO 42Àions in the mixing water.The concentration of those ions depends upon the amounts of alkali sulfate,gypsum and free lime in the cement just after mixing with water,after that,it depends upon the hydration reaction of C 3S,alite.The hydration of interstitial phases is affected in particular by the lime–saturation ratio.Since small crystals of ettringite,which are produced in high concentration conditions,cover the unreacted interstitial phase,the hydration reaction rate slows down.On the contrary,in low ion concentration conditions,large amounts of ettringite are produced in the shape of large needles.In this case,the hydration of the interstitial phase continues to produce large amounts of ettringite,which causes the stiffness and pseudo-setting [2,3].A few points relevant in the interaction of SP with cements,which are sometimes overlooked,are worth men-tioning [4].First,the relative sizes of the particles in a cementitious system of SP molecules differ typically by two or three orders of magnitude;the average diameter of cement par-ticles are typically of 10m m,whereas the size of the SP molecules is of the order of a fewnanometers.Fig.7.Flow area (a),fresh density (b)and air content (c)with respect to water to cement ratio at different dosage of SMF SP,Flyt 92M.For WC.S.Chandra,J.Bjo ¨rnstro ¨m /Cement and Concrete Research 32(2002)1605–16111609Second,since the initial surface hydration of cement particles is extremely rapid(t1/2<1min),the action of SP molecules will mainly occur on the surface of the hydrated particles.Third,as complex chemical entities,SP molecules can themselves participate in chemical processes.3.2.Depletion effectAs the hydration reaction proceeds,the amount of free water decreases,and so does the distance between the hydration surfaces of the neighboring cement(hydrate) particles.As the interparticle volume becomes smaller,the concentration of SP molecules becomes higher,the concen-tration of SP molecules confined in this volume may create a substantial osmotic pressure effect.The latter would either tend to expel the SP molecules from the confined interpar-ticle volume or create a water flow to dilute the polymer molecules in that region.The first effect would lead to induce a particle–particle attraction,while the latter would induce additional particle–particle repulsion.The variation in lime saturation ratio with different water to cement ratio varies with the cement type used.The variation of the lime saturation ratio when using a lignin sulfonic acid based admixture is smaller than the variation observed when using no admixture or SMF.The reason is that lignin sulfonic acid based admixture binds up the Ca2+, and the concentration of Ca2+in the pore solution is therefore lowered.It is seen from the experiments that at up to0.55water to cement ratio there was not significant increase in the fluidity,but exceeding this,the fluidity increased substantially.It seems that,up to the water to cement ratio of0.55,the Ca2+were blocked by the LS, indicating the formation of an interlayer complex[5].With an increase in the water to cement ratio,more alite hydrates and thereby more Ca2+ions are produced.Lime saturation in the pore solution increases,poisoning the hydration process.Subsequently the fluidity increases.The admixture is not evenly adsorbed on cement par-ticles.It adsorbs more readily on C3A,C4AF than on C3S and C2S[6].Comparisons of SMF and LS have shown that SMF is even more unevenly adsorbed on the clinker minerals than LS is.The more even the adsorption of SMF,the higher the fluidity.The admixture is so unevenly adsorbed on cement containing much C3A+C4AF that the amount of admix-ture adsorbed on alite and belite is relatively decreased, thereby lowering the fluidity of the paste.The more even the adsorption of admixture on cement minerals,the higher the fluidity of the paste will be.Thus,the amount of the admixture adsorbed on the cement sometimes fluctuates greatly,as it depends on the mineral composi-tion of the clinker.In this work,the highest fluidity was observed with WC both for LS and SMF,followed by the cements LAC and OPC.The reason is the low C3A+C4AF and low alkali content of the WC.This agrees with the results reported by Hanna et al.[7].However,a comparison with the fineness shows a contradiction.The fineness of WC is the highest, yet it has shown the highest fluidity.This may be due to the fact that C3A+C4AF and the alkali are very low and the sulfate content is high.Because of the competitive adsorp-tion between SP and SO3,most of the SP remained in the solution,poisoning the hydration process so much that the fineness became insignificant.It has been reported that the extent of adsorption is influenced more by the sulfate content than by the fineness.In high sulfate content cement,adsorption of SP is less than in low sulfate content cement[8].Similar results have been reported by Simard et al.[9].3.3.Influence of alkali contentIn the absence of SP,cements containing high levels of alkali(e.g.,Na2SO4or K2SO4)will usually exhibit poorer rheological behaviors than cements having low alkali contents,other conditions being the same.Also,the water reduction with admixtures will be more readily achieved with LAC[7,10].Several effects may be promoted by the alkalis,namely:flocculation of cement(or other)fine particles induced by the electrolytes,formation of new hydrates containing alkali ions(e.g.,syngenite)or increase in the reactivity of mineral phases(particularly C3A).WC has shown the highest fluidity followed by LAC and OPC.One of the reasons for this is due to its low alkali content.In the presence of SP,it was found that the addition of alkali sulfates(Na2SO4)can lead to improvements in the rheological properties of cement paste[11,12].While the results shown may not be generalized,they are consistent with the concepts of SO42À/SP competition.The presence of SO42Àions leads to a decreased absorption of the SP, leaving more of the latter available on the solution phase for paste fluidification;the fluidity of the paste increases, accordingly,with the amount of Na2SO4added.In another study Andersson et al.[12]further reported that the adsorption of SP was reverted by addition of potassium hydroxide(KOH).3.4.Influence of water to cement ratioThe water to cement ratio controls the concentration of ions in the pore solution.At low water to cement ratio, the surface of interstitial phases especially of C3A and C4AF is adsorbing the SP;thus,very little SP is in the pore solution.But with an increase in the water to cement ratio,more alite hydrates and thereby more Ca2+ions are produced.Lime saturation in the pore solution in-creases,poisoning the hydration process.Subsequently, the fluidity increases.It has been observed in the experiments that,up to a water to cement ratio of0.45,there was no significantS.Chandra,J.Bjo¨rnstro¨m/Cement and Concrete Research32(2002)1605–1611 1610increase in the fluidity,but when it exceeded0.45,there was substantial increase in the fluidity.3.5.Fresh density and air contentFresh density is a measure of compactness.Generally,it is low at0.35water to cement ratio,while the air content is high.It is due to the bad compaction because of inadequate fluidity.At0.40–0.45water to cement ratio,the fluidity increases,thereby the density increases due to better com-paction.But,at higher water to cement ratios,the density decreases gradually.The air content also decreases gradually with the increase in fluidity.The decrease in density is due to decrease in the solid content in the mass as the water to cement ratio is increased,a dilution effect.Sometimes,the density is high observed at high water to cement ratios,it is due to mortar segregation.4.ConclusionsThe addition of a LS-based SP resulted in higher fluidity of the mortar compared to when a SMF-based SP was used. This is because the variation of lime saturation rate in the case of LS is smaller than that in the case of SMF.Further SMF is much more unevenly adsorbed than LS on the clinker minerals of cement.Higher fluidity was observed with WC for both LS and SMF than in the case of LAC and OPC cements.This is attributed to the lower C3A+C4AF and alkali content and higher sulfate content in WC com-pared to the LAC and OPC.WC has a particle size distribution with a large amount of fine material.This should have given a low fluidity in the mortar but the observations showed the opposite.The reason may be that the C3A+C4AF and alkali content was so low and sulfate content so high that much of the SP remained in the solution.When it adsorbed on alite and belite,it poisoned the hydration process so much that the fineness did not play a significant role.Many factors are influencing the fluidity and hydration process of the cement paste some of these factors may also have synergistic effects.This makes a theory based on one parameter irrelevant,and it makes it difficult to point out one parameter,which is responsible to produce a particular property.AcknowledgmentsThis work has received financial support from the Knowledge Foundation(KK-stiftelsen,Stockholm),which is gratefully acknowledged.References[1]H.Okamura,K.Ozawa,S.Matsuo,K.Shimokawa,Evaluation ofsuperplasticizers for self compacting concrete with mortar test,JCA Proc.Cem.Concr.48(1994)374–379.[2]H.Uchikawa,S.Uchida,K.Ogawa,S.Hanehara,Influence ofCaSO4Á2H2O,CaSO4Á1/2H2O,and CaSO4on the initial hydration of clinker with different burning temperature,Cem.Concr.Res.14 (1984)645–656.[3]H.Uchikawa,Hydration of cement and structure formation and pro-perty of cement paste in the presence of organic admixture,Confer-ence in Tribute to Micheline Moranville Regourd at Beton Canada Conference,Sherbrooke,Canada,1994,pp.63–117.[4]C.Jolicouer,M.A.Simard,Admixture–cement interactions:phenom-enology and physico-chemical concepts,pos.20 (2/3)(1998)87–102.[5]V.S.Ramachandran,F.R.Feldman,Effect of calcium lignosulfonateon tricalcium aluminate and its hydration products,Mater.Struct.5 (1972)67–76.[6]H.Uchikawa,S.Hanehara,T.Shirasaka,D.Sawaki,Effect of admix-ture on hydration of cement,absorptive behavior of admixture,and fluidity and setting of fresh cement paste,Cem.Concr.Res.22(1992) 1115–1129.[7]E.Hanna,K.Luke,D.Perraton,P.C.Aitcin,Rheological behavior ofPortland cement in the presence of a superplasticizer,in:V.M.Malho-tra(Ed.),Proc.3rd Int.Conf.,Superplasticizer and other Chemical Admixtures in Concrete,ACI SP vol.119,1989,pp.171–188. [8]T.Nawa,H.Eguchi,Effect of cement characteristics on the fluidity ofcement paste containing chemical admixture,9th Int.Cong.Chem.Cem.IV,New Delhi,India,(1999)597–603.[9]M.A.Simard,P.C.Nkinamubanzi,C.Jolicouer,D.Perraton,P.C.Aitcin,Calorimetry,rheology and compressive strength of superplas-ticized cement paste,Cem.Concr.Res.23(1993)939–950. [10]V.Dodson,Concrete admixtures,Van Nostrand Reinhold,NewYork,1990.[11]T.Nawa,H.Eguchi,Y.Fukaya,Effects of alkali sulfates on therheological behavior of cement pastes containing superplasticizers, superplasticizers and other chemical admixtures in concrete,in: V.M.Malhotra(Ed.),Proc.4th CANMET/ACI Int Conf.,ACI SP vol.119,1989,pp.405–424.[12]P.J.Andersson,A.Kumar,D.M.Roy,D.Wolfe-Confer,The effects ofcalcium sulphate concentration on the adsorption of a superplasticizer on a cement;methods,Zeta potential and adsorption studies,Cem.Concr.Res.16(1986)255–259.S.Chandra,J.Bjo¨rnstro¨m/Cement and Concrete Research32(2002)1605–16111611。
