Shrinkage and Expansive Strain of Concrete with Fly Ash and Expansive Agent

The effects of fly ash and MgO-type expansive agent on the shrinkage and expan-sive strain of concrete with high magnesia cement were investigated. The results show that high volumes of fly ash may reduce the shrinkage strain of concrete and inhibit the expansive strain of concrete with MgO-type expansive agent, but can not eliminate the shrinkage of concrete. MgO-type expansive agent may produce expansive strain and compensate the shrinkage strain of concrete, re-lieve the cracking risk, but the hydration product of magnesia tends to get together in paste and pro-duce expansive cracking of concrete with high magnesia content according to SEM observation.

Applied technique of the cemented fill with fly ash and fine-sands

Traditional stabilization of backfilling material is done by using Portland cement. However, the high price of cement forced mining engineer s to seek cheaper binding materials. Fly ash, which is the indus- trial wast e from thermal power plant, possess the potential activity of jellification, and can b e used in cemented fill as a partial substitute for cement to reduce the fill co s t. Tests were done during the past few years in Xinqiao Pyrite Mine and Phoenix Copper Mine to determine the technology parameters and the suitable content of f ly ash. Specimens with different cement/fly/ash tailings (sands) ratios were tes ted to obtain the strength values of the fill mass based on the analyses of both the chemical composition and physical and mechanical properties of fly ash . The compressive strength of specimens with a ratio of 1∶2∶8 (cement to fly ash to tailings ) can reach 2 MPa after 90 d curing, totally meeting the requiremen t of artificial pillar and reducing the fill cost by 20%-30%.

Cement-fly Ash Stabilization of Cold In-place Recycled (CIR) Asphalt Pavement Mixtures for Road Bases or Subbases

For lack of laboratory and field performance data on stabilization of reclaimed asphalt pavement （RAP） aggregate and stabilized soil （S） for road bases and subbases construction, the influences of RAP/S ratio, cement and fly ash content, modifying agent （MA） on the compact, unconfined compressive strength, indirect tensile strength and water stability of the CIR mixtures were investigated. The experimental results showed that the maximum dry density and the optimum moisture content of the mixture changed significantly with the RAP/S ratio and cement-fly ash content. Unconfined compressive strength, indirect tensile strength and water stability were improved significantly by the addition of MA, and the water stability was improved by nearly 20% on average. Scanning electron microscopy（SEM） images indicated that MA accelerated the hydration of cement-fly ash system. Needle-like AFt and fibrous C-S-H gel were observed in the mixtures, which resulted in the cementation effect among the CIR mixture particles and a more compact microstructure. All these could be the cause of high strength of the CIR mixtures with MA.

Research on the influence of the fly ash on the concrete carbonation

The influence of fly ash on the fresh properties, mechanical properties and carbonation properties were studied in this paper. The performance of a kind of curing agent which was applied to the hardened concrete surface was evaluated. Incorporating large volume of fly ash will risk the concrete carbonation. The curing agent could prevent the concrete carbonation, and the mechanism was explained.

矿渣基地聚物流态盾构固化土的性能研究

为实现对地下工程中的高含水率盾构土资源化利用,探究地聚物材料固化盾构土的可行性,本文采用矿渣基地聚物固化盾构土,通过研究碱激发剂模数、矿物配比、碱激发剂掺量、温度对不同种类盾构固化土无侧限抗压强度和工程性能的影响规律,确定固化土配合比设计,在此基础之上研究地聚物掺量对固化土水稳性的影响,并采用SEM对盾构固化土进行微观分析,揭示其固化机制。结果表明,在试验拟定的水固比下,两种不同土质流态盾构固化土均有良好的力学性能和工程性能,矿渣基地聚物产生了无定形凝胶,增强了土壤颗粒之间的胶结及密实度,其中固化剂掺量为干土质量22%的盾构固化土在标养条件下的28 d无侧限抗压强度可达5.38 MPa, 40℃条件下可达8.08 MPa,水稳系数达0.98。

低强度流态填筑材料配合比设计方法比较

低强度流态填筑材料具有匀质性较好、施工性能优异、强度低且可控、经济成本较低等特点,因组成材料与现场情况结合紧密、变化多样、表现形式较多,通过对流态粉煤灰水泥混合料和预拌流态固化土两种低强度流态填筑材料配合比设计方法的研究,可以发现配合比设计思路和方法的灵活性与多样性。

型钢水泥土复合搅拌桩用新型水泥土研究

论文以阜宁县棚户区改造(湖畔景苑)EPC工程总承包项目现场素填土、粉质黏土、淤泥质粉质黏土作为试验材料,通过掺加固化剂和设计要求的15%水泥进行了无侧限抗压强度试验。试验结果表明,掺加14%固化剂即可达到设计指标要求,且结果优于15%掺量的水泥,采用固化剂替换部分水泥进行土体固化经济效益显著。

海河交汇区水泥搅拌桩加固技术初探

本文依托珠海隧道工程,针对超深欠固结淤泥地层,进行一系列不同配比、施工工艺、水灰比和QC-固化剂比例条件下的水泥搅拌桩加固试桩试验,系统研究了多种参数影响下辅道、明挖基坑和海域浅覆土加固试桩的成桩效果,发现掺入固化剂可获得更好的成桩效果和更优良的抗压性能。经加固处理的芯样其强度大部分在1~3 MPa,部分芯样强度可高达5 MPa,且桩身更为连续和完整。在其他参数相同的条件下,QC-固化剂占比高的芯样具有更好的完整性和强度,而水灰比对成桩效果及抗压强度的影响不大,四搅和两搅的施工工艺在单点土体切削次数达到20次或以上时,其对成桩效果和强度的影响无明显区别。最后对加固后的软土开展了微观电镜扫描试验,对比分析了经QC-固化剂与纯水泥固化剂加固后生成晶体对土体孔隙的填充现象,发现QC-固化剂对土体孔隙具有更好的填充效果。本水泥搅拌桩加固试桩试验在珠海海河交汇区软弱地层取得了较好的加固效果,可为沿海地区类似地质条件下的地基处理提供参考。

硅灰及粉煤灰对海水拌养硅酸盐水泥性能影响

研究了在20℃、50℃养护温度下单掺及混掺硅灰与粉煤灰对海水拌养硅酸盐水泥性能的影响。通过测试基体抗压强度、物理性能、基体氯离子结合率及pH值,采用XRD及SEM分析基体水化产物及微观形貌。研究结果表明:硅灰对海水拌养硅酸盐水泥强度有促进作用,提高水泥基体密实度,增加化学收缩,降低水泥基体pH值,削弱Cl^(-)固化作用,改善水泥基体微观结构;粉煤灰对海水拌养硅酸盐水泥早期强度产生不利影响,但对其后期强度有促进作用,能小幅改善基体密实度,但对化学收缩、pH及Cl^(-)固化作用没有产生显著影响。粉煤灰能促进Friedel′s盐的生成,并对水泥基体微观结构产生小幅不利影响。提高养护温度能促进硅酸盐水泥抗压强度的形成,并对水泥基体微观结构有改善作用。

高性能海相淤泥固化剂在工程中的应用

针对在珠海、南沙、中山、福州等沿海区域的海相流塑状淤沙,以及水泥搅拌桩不成桩、成桩强度不高、成桩不均匀、取芯不完整等这一难题,成功研制出一种海相淤泥质土专用固化剂,较好地解决了这个问题。该固化剂在珠海市某建筑工地开展了试桩试验,试桩结果表明,桩身整体成桩均匀,芯样连续、完整、牢固、坚硬,搅拌均匀,呈短柱状,局部成块,28d无侧限抗压强度均大于设计强度,满足设计要求。

Effect of temperature on the hydration process and strength development in blends of Portland cement and activated coal gangue or fly ash

This paper describes the results of an investigation into the effect of the variation of curing temperatures between 0 and 60 °C on the hydration process,pore structure variation,and compressive strength development of activated coal gangue-cement blend(ACGC) . Hardened ACGC pastes cured for hydration periods from 1 to 360 d were examined using the non-evaporable water method,thermal analysis,mercury intrusion porosimetry,and mechanical testing. To evaluate the specific effect of activated coal gangue(ACG) as a supplementary cementing material(SCM) ,a fly ash-cement blend(FAC) was used as a control. Results show that raising the curing temperature accelerates pozzolanic reactions involving the SCMs,increasing the degree of hydration of the cement blends,and hence increasing the rate of improvement in strength. The effect of curing temperature on FAC is greater than that on ACGC. The pore structure of the hardened cement paste is improved by increasing the curing temperature up to 40 °C,but when the curing temperature reaches 60 °C,the changing nature of the pore structure leads to a decrease in strength. The correlation between compressive strength and the degree of hydration and porosity is linear in nature.

Effects of seeding nucleation agent on geopolymerization process of fly-ash geopolymer

Geopolymer, an inorganic aluminosilicate material activated by alkaline medium solution, can perform as an inorganic adhesive. The geopolymer technology has a viability to substitute traditional concrete made of portland cement （PC） because replacing PC with fly ash leads to reduced carbon dioxide emissions from cement productions and reduced materials cost. Although fly ash geopolymer stimulates sustainability, it is slow geopolymerization reaction poses a challenge for construction technology in term of practicality. The development of increasing geopolymerization reaction rate of the geopolymer is needed. The purpose of this study is to evaluate seeding nucleation agents （NA） of fly ash geopolymer that can accelerate polymerization reactions such that the geopolymer can be widely used in the construction industry. Results from the present study indicate that the use of NA （i.e., Ca（OH）2） can be potentially used to increase geopolymerization reaction rate and improve performance characteristics of the fly ash geopolymer product.

Influence of Fly Ash Addition on the Hydration of Portland Cement

Influence of fly ash addition on the hydrationof Portland cement clinker,particularly at the initial stage,has been studied on the basis of measured data obtained. Fly ash,considering its active components,was added as a partial replacement of Portland cement at different water/cementitious ratios. The hydration heat was measured in a controlled environmental room of 20 ℃. Both non-evaporable water content and mineral phase were investigated. Data indicate that the amount of fly ash involved in hydration reaction is little at initial stage while it becomes more after 7 d hydration. As hydration reaction is a continuous process,chemical stress results in the disruption of stable structure on the surface of fly ash consisting of Ca,O,Si,Al,C,etc. Additionally,surface of glass beads begins to lose smooth and reacts to blend in with the paste.

焚烧灰造粒水泥玻璃固化配方研究

本文报道了针对中低水平放射性焚烧灰处理的水泥玻璃固化配方研究结果。以一种自制磷酸盐材料作为硬化剂，以水玻璃为固化基质进行了固化剂配方研究，并进行了固化体的性能测定。研究结果表明，当水泥玻璃固化剂的配方为：硬化剂，30±3％（wt）；水玻璃，66％（wt）；水泥，3±0．3％（wt）；外加剂，l％（wt）时，所制得水泥玻璃固化体均匀密实，密度在1．8～2．5g/cm^3间，28d的抗压强度≥10MPa；对^85Sr和134^Cs，第42天的浸出率均≤1．5×10^-4cm/d。焚烧灰经过造粒水泥玻璃固化后，固化体的减容系数（焚烧灰造粒固化后固化体的体积与焚烧灰的体积比）为0．56，减容效果好，性能优于水泥固化体。

水泥搅拌饱和黄土强度影响因素试验研究

研究目的：水泥土搅拌桩加固软土地基能有效提高地基的承载力,减少和控制沉降量,但其强度大小及发挥程度受土质等因素影响较大。本文依托兰州至中川机场铁路建设项目水泥土搅拌桩处理饱和黄土地基工程,系统地研究和总结水泥与粉煤灰（简称“二灰”）掺入比、龄期、粉煤灰掺入量、水泥强度等级、有机质含量、搅拌均匀程度等因素对水泥搅拌饱和黄土强度特性的影响。研究结论：（1）水泥搅拌饱和黄土的强度随二灰掺入比、龄期的增大而增大,二灰掺入比从12%增加到20%,90 d龄期强度增长了0.9倍;（2）在二灰掺入总量一定的条件下,水泥搅拌饱和黄土强度随粉煤灰掺入量的增加而有所降低,粉煤灰与水泥的质量比为1∶2是比较经济合理的;（3）水泥强度等级从P.O 32.5提高到P.O 42.5,水泥搅拌饱和黄土的强度显著增长,90 d龄期时,P.O 42.5级水泥搅拌饱和黄土的强度高出P.O 32.5级水泥约40%~50%;（4）水泥搅拌饱和黄土的强度随土中有机质含量的增加而减小;（5）搅拌均匀程度对水泥搅拌饱和黄土强度的影响显著,当二灰掺入比一定时,搅拌均匀程度是影响水泥搅拌饱和黄土强度的关键因素,工程中须保证水泥搅拌土的均匀性,以提高水泥土搅拌桩加固饱和黄土地基的处理效果;（6）该研究结论可为高速铁路饱和黄土地基处理设计及施工参数选择提供依据及指导作用。

三峡工程三期围堰碾压混凝土试验研究

为了合理选择三峡工程三期上游横向围堰碾压混凝土设计和施工的各项参数,对碾压混凝土的力学、耐久、热学等性能进行了试验,同时对碾压混凝土层间处理方法和层面结合特性进行了探讨,提出了满足技术要求的推荐配合比。结果表明,极限拉伸值和抗渗标号,尤其是28d龄期,对碾压混凝土的配合比参数的选择起控制作用,胶凝材料用量对混凝土的绝热温升有较大影响。

泡沫混凝土

较全面地分析了泡沫混凝土的材料组成、搅拌时间及养护条件 。

粉煤灰混凝土强度增长规律初探

经过大量试验,初步探讨了粉煤灰掺量、胶水比、养护温度对混凝土28天强度的影响规律,建立的三元数学模型较好地描述了这一强度增长规律。对于粉煤灰混凝土的试配和现场施工,这一数学模型有积极的指导作用。

城市垃圾焚烧灰在地下深层搅拌桩中的应用

以城市垃圾焚烧灰为新材料,将其视为一种辅助性胶凝材料与水泥共用,利用水泥固化原理提供一种围护桩体,将此围护桩体应用于土木工程建设中。讨论传统城市垃圾的处理方法及其存在的弊端,并对城市垃圾焚烧灰所存在的价值作进一步的说明。

公路下伏采空区注浆处治泡沫轻质土新型材料试验研究

为解决西北部地区公路经过采空区采用常规水泥粉煤灰浆液注浆处治存在的问题,采用阴、阳离子型泡沫剂,对水泥粉煤灰浆液进行发泡改性,研制出一种新型泡沫轻质土注浆新材料。研究结果表明:泡沫轻质土新材料强度和密度随着水固比的减小而增大,随着水泥占固相比的增大而增大,随着泡沫溶液掺量增加而减小。提出了两种适用于公路一般路基、桥梁、隧道下伏采空区注浆处治的新型轻质注浆材料配比范围。