高温条件下超高性能水泥基复合材料水化放热研究

超高性能水泥基复合材料组分复杂,高温养护会使水泥基材料水化过程发生显著变化,其早期水化、硬化及微结构形成机理仍存在众多疑惑.本文利用等温量热仪对不同水灰比、不同养护温度、不同矿物掺合料下的超高性能水泥基复合材料的水化放热过程进行研究.试验结果表明,减小水灰比、提高养护温度都将促进超高性能水泥基复合材料的水化放热进程;此外,硅灰的掺入能明显促进水化,但粉煤灰却有着延缓的作用.     

低水胶比水泥浆体的力学性能与水泥石微结构

随着工程对混凝土强度和耐久性要求的提高,混凝土材料的水胶比不断降低。低水胶比条件下,水泥基材料的力学性能、胶凝材料水化程度及孔结构特征变化规律可能出现新的特点。设计水胶比为0.13～0.21的低水胶比水泥浆体,采用标准养护和高温蒸养两种养护制度,研究了硬化浆体力学性能、水化程度和水化产物微结构变化规律。结果表明:低水胶比条件下,水泥硬化浆体的抗折强度随水胶比降低持续提升,抗压强度先提升后下降;存在极限水胶比使胶凝材料体系强度达到最高,极限水胶比取决于硬化浆体的孔隙变化规律,也受到养护温度的影响;水胶比高于0.15时,水泥水化程度与水胶比呈现严格线性;降低水胶比可有效细化毛细孔,降低硬化浆体的孔隙率;但极低的水胶比和高温蒸养会使大孔出现粗化。低水胶比条件下,硬化浆体的孔结构决定其力学性能,水泥的水化程度只起到辅助作用。     

低热硅酸盐水泥高温强度特性及其机理研究

低热硅酸盐水泥具有高温下强度稳定增长的特性，本文以硅酸盐水泥和低热硅酸盐水泥互为对比，研究了在水泥砂浆成型之后直接进行热养护(50～80℃)和标准养护1 d后再进行热养护两种情况下的强度发展和水泥浆体的物相组成、孔隙发展、微观形貌特征。结果表明：高温条件下水泥强度损伤行为源于水化后期的微结构劣化，但这一行为与水化初期受热密切相关，低热硅酸盐水泥在高温下较低的水化速率使其水化产物更均匀、密实，浆体的孔结构不随温度的升高以及受热方式的改变出现明显劣化，因此其强度在高温下仍能保持稳定增长；硅酸盐水泥后期由高温引发的钙矾石分解并没有直接导致强度倒缩，但水化初期过高的水化速率使水泥浆体出现更多的孔洞和缺陷，加速了后期由高温引起的单硫型水化硫铝酸钙(AFm)、Ca(OH)₂析出与生长，且诱发浆体孔隙率增大。     

高温养护下粉煤灰效应机理研究

大体积混凝土施工过程中,为降低水化热而采用大量的粉煤灰替代水泥,故对高掺量粉煤灰水泥的水化硬化机理进行深入系统的研究具有重要的意义.以大掺量粉煤灰胶凝材料硬化浆体为研究对象,结合XRD、FTIR、NMR等测试分析,研究高养护制度下粉煤灰掺量对其水化相C-S-H凝胶硅氧四面体聚合程度的影响规律.结果表明:高温养护的硬化浆体,其水化相C-S-H凝胶硅氧四面体聚合程度和Al原子取代Si原子的程度,在各个养护龄期始终高于常温养护的硬化浆体.     

温度匹配养护对大掺量矿物掺合料混凝土抗压强度及早期水化性能的影响

大体积混凝土由于胶凝材料水化放热,其内部温升对混凝土强度发展规律有很大影响.采用温度匹配养护和标准养护两种不同的养护方式,研究了单掺40％粉煤灰、单掺50％矿粉以及复掺30％粉煤灰和20％矿粉三种大掺量矿物掺合料混凝土与纯水泥、单掺20％粉煤灰两种普通混凝土在不同温度养护条件下的抗压强度差异,并对胶凝材料水化早期的浆体进行了扫描电镜和化学结合水测试.结果 表明:与纯水泥混凝土相比,温度匹配养护对大掺量矿物掺合料混凝土早期强度发展的促进作用要显著得多,且大掺量矿物掺合料混凝土温度匹配养护方式下的各龄期强度均比标准养护方式下的要高,然而纯水泥混凝土温度匹配养护条件下的后期强度却要低于标准养护条件下的后期强度.温度匹配养护方式下较高的早期水化温度显著加速了大掺量矿物掺合料混凝土的水化反应进程,从而使大掺量矿物掺合料混凝土的早期强度提高.     

硫酸盐侵蚀对不同养护制度UHPC水化产物微结构的影响

采用29Si和27Al MAS NMR、XRD、SEM等测试技术研究了硫酸盐侵蚀对不同养护制度的超高性能混凝土(UHPC)水化产物微结构的影响.结果表明:标准养护和80 ℃高温蒸汽养护条件下,UHPC水化产物主要为C-S-H、Ca(OH)2、AFt、AFm和TAH;210 ℃、2 MPa蒸压养护8 h后,水化产物主要为tobermorite、Ca(OH)2和TAH.硫酸盐侵蚀对不同养护制度的UHPC抗压强度和水化产物微结构的影响微弱,但可促进210 ℃蒸压养护的UHPC胶凝浆体中TAH向AFm和AFt的转化.同时硫酸盐侵蚀180 d时,C-S-H凝胶MCL和Al[4]/Si略有降低,但降低幅度较小,UHPC具有良好的抗硫酸盐侵蚀能力.     

硫氰酸钠与聚羧酸减水剂复配对水泥水化的影响研究

采用硫氰酸钠(SN)对普通聚羧酸减水剂(PC)进行复配改性,旨在开发一种低温、早强型聚羧酸减水剂.对比测试了PC与PC +SN对水泥胶砂与混凝土在低温(5℃)和常温(20℃)两种养护温度下强度发展的影响,通过对水泥水化热与水泥浆体化学结合水、水化产物、微结构与孔结构的测试,分析了SN早强剂对水泥浆体早期水化性能的影响.结果表明:在养护温度5℃时,掺入PC +SN的水泥胶砂1d、3d、7d、28 d强度较掺PC比,分别提高了138.5％、48.3％、51.2％、17.2％,掺入PC +SN的混凝土1d、3d、7d、28 d强度分别增长了182.1％、35.2％、34.9％、31％,而20 ℃条件养护时PC +SN的早强效果并不显著;PC复配SN早强剂后,增加了水泥早期水化放热速率与放热量,提高了水泥的水化程度,且浆体的水化产物数量增多,孔隙率降低,孔径减小,从而有利于混凝土早期强度的提高.     

养护制度对超高性能混凝土抗高温爆裂性能的影响EI北大核心CSCD

采用4种不同养护制度(20℃水养、热水养护、干热养护和热水-干热组合养护)制备超高性能混凝土(UHPC),测定其高温爆裂行为,并结合多种微观测试技术,对UHPC的微观结构进行分析。结果表明:组合养护能够明显改善UHPC的抗高温爆裂性能,且当先进行90℃热水预养护2 d,再进行250℃干热养护3 d时,混凝土的高温爆裂现象完全被抑制。明显不同于通常的掺加聚丙烯纤维抑制爆裂的是,热水-干热组合养护是一种新的抑制爆裂方法。其机理是内部游离水的减量化机理,即:组合养护可使UHPC内部建立一种高温蒸汽环境,有效促进水泥水化、激活掺合料的火山灰活性,导致许多致密的水化产物得以生成,同时消耗大量混凝土内部游离水,使得制备出的UHPC在高温加热过程中所能形成的蒸汽压较低,不足以引发高温爆裂。     

养护制度对超高性能混凝土抗高温爆裂性能的影响

采用4种不同养护制度(20℃水养、热水养护、干热养护和热水-干热组合养护)制备超高性能混凝土(UHPC),测定其高温爆裂行为,并结合多种微观测试技术,对UHPC的微观结构进行分析。结果表明:组合养护能够明显改善UHPC的抗高温爆裂性能,且当先进行90℃热水预养护2 d,再进行250℃干热养护3 d时,混凝土的高温爆裂现象完全被抑制。明显不同于通常的掺加聚丙烯纤维抑制爆裂的是,热水-干热组合养护是一种新的抑制爆裂方法。其机理是内部游离水的减量化机理,即:组合养护可使UHPC内部建立一种高温蒸汽环境,有效促进水泥水化、激活掺合料的火山灰活性,导致许多致密的水化产物得以生成,同时消耗大量混凝土内部游离水,使得制备出的UHPC在高温加热过程中所能形成的蒸汽压较低,不足以引发高温爆裂。     

蒸养制度对预制桥面板混凝土强度与抗渗性的影响

为了获得预制桥面板的最佳蒸养制度,研究了蒸养温度、蒸养时间及蒸养后补充养护方式对复掺粉煤灰和矿粉配制的C55混凝土的强度和氯离子扩散系数的影响,并采用X-射线衍射仪(XRD)和扫描电子显微镜(SEM)分析了不同蒸养制度下胶凝材料浆体的物相组成和微结构。结果表明,蒸养温度的提高和蒸养时间的延长,对水泥的水化和浆体微结构形成有促进作用,提高了混凝土的脱模强度,但降低了混凝土的后期强度和抗氯离子渗透性能。混凝土蒸养后的补充湿润养护为未水化水泥和矿物掺合料的持续水化提供水化用水,有利于混凝土的后期强度增进和抗渗性提高。预制桥面板在55 ℃温度下蒸养6 h,蒸养后补充覆盖洒水养护7 d具有较好的综合性能。     

Insect antifeedant properties of anthranoids from the genusVismia

Vismiones and ferruginins, representatives of a new class of lypophilic anthranoids from the genusVismia were found to inhibit feeding in larvae of species ofSpodoptera, Heliothis, and inLocusta migratoria.     

Direct observation of freeze-thaw instability of latex coatings via high pressure freezing and cryogenic SEM

Despite its industrial importance, the subject of freeze-thaw (F/T) stability of latex coatings has not been studied extensively. There is also a lack of fundamental understanding about the process and the mechanisms through which a coating becomes destabilized. High pressure (2100 bar) freezing fixes the state of water-suspended particles of polymer binder and inorganic pigments without the growth of ice crystals during freezing that produce artifacts in direct imaging scanning electron microscopy (SEM) of fracture surfaces of frozen coatings. We show that by incorporating copolymerizable functional monomers, it is possible to achieve F/T stability in polymer latexes and in low-VOC paints, as judged by the microstructures revealed by the cryogenic SEM technique. Particle coalescence as well as pigment segregation in F/T unstable systems are visualized. In order to achieve F/T stability in paints, latex particles must not flocculate and should provide protection to inorganic pigment and extender particles. Because of the unique capabilities of the cryogenic SEM, we are able to separate the effects of freezing and thawing, and study the influence of the rate of freezing and thawing on F/T stability. Destabilization can be caused by either freezing or thawing. A slow freezing process is more detrimental to F/T stability than a fast freezing process; the latter actually preserves suspension stability during freezing. Presented at the 82nd Annual Meeting of the Federation of Societies for Coatings Technology, October 27–29, 2004 in Chicago, IL. Tied for first place in The John A. Gordon Best Paper Competition.     

Ethanol and (−)-α-Pinene: Attractant Kairomones for Bark and Ambrosia Beetles in the Southeastern US

In 2002–2004, we examined the flight responses of 49 species of native and exotic bark and ambrosia beetles (Coleoptera: Scolytidae and Platypodidae) to traps baited with ethanol and/or (−)-α-pinene in the southeastern US. Eight field trials were conducted in mature pine stands in Alabama, Florida, Georgia, North Carolina, and South Carolina. Funnel traps baited with ethanol lures (release rate, about 0.6 g/day at 25–28°C) were attractive to ten species of ambrosia beetles (Ambrosiodmus tachygraphus, Anisandrus sayi, Dryoxylon onoharaensum, Monarthrum mali, Xyleborinus saxesenii, Xyleborus affinis, Xyleborus ferrugineus, Xylosandrus compactus, Xylosandrus crassiusculus, and Xylosandrus germanus) and two species of bark beetles (Cryptocarenus heveae and Hypothenemus sp.). Traps baited with (−)-α-pinene lures (release rate, 2–6 g/day at 25–28°C) were attractive to five bark beetle species (Dendroctonus terebrans, Hylastes porculus, Hylastes salebrosus, Hylastes tenuis, and Ips grandicollis) and one platypodid ambrosia beetle species (Myoplatypus flavicornis). Ethanol enhanced responses of some species (Xyleborus pubescens, H. porculus, H. salebrosus, H. tenuis, and Pityophthorus cariniceps) to traps baited with (−)-α-pinene in some locations. (−)-α-Pinene interrupted the response of some ambrosia beetle species to traps baited with ethanol, but only the response of D. onoharaensum was interrupted consistently at most locations. Of 23 species of ambrosia beetles captured in our field trials, nine were exotic and accounted for 70–97% of total catches of ambrosia beetles. Our results provide support for the continued use of separate traps baited with ethanol alone and ethanol with (−)-α-pinene to detect and monitor common bark and ambrosia beetles from the southeastern region of the US.     

Methyl 2,4,6-decatrienoates Attract Stink Bugs and Tachinid Parasitoids

Halyomorpha halys (Stål) (Pentatomidae), called the brown marmorated stink bug (BMSB), is a newly invasive species in the eastern USA that is rapidly spreading from the original point of establishment in Allentown, PA. In its native range, the BMSB is reportedly attracted to methyl (E,E,Z)-2,4,6-decatrienoate, the male-produced pheromone of another pentatomid common in eastern Asia, Plautia stali Scott. In North America, Thyanta spp. are the only pentatomids known to produce methyl 2,4,6-decatrienoate [the (E,Z,Z)-isomer] as part of their pheromones. Methyl 2,4,6-decatrienoates were field-tested in Maryland to monitor the spread of the BMSB and to explore the possibility that Thyanta spp. are an alternate host for parasitic tachinid flies that use stink bug pheromones as host-finding kairomones. Here we report the first captures of adult and nymph BMSBs in traps baited with methyl (E,E,Z)-2,4,6-decatrienoate in central Maryland and present data verifying that the tachinid, Euclytia flava (Townsend), exploits methyl (E,Z,Z)-2,4,6-decatrienoate as a kairomone. We also report the unexpected finding that various isomers of methyl 2,4,6-decatrienoate attract Acrosternum hilare (Say), although this bug apparently does not produce methyl decatrienoates. Other stink bugs and tachinids native to North America were also attracted to methyl 2,4,6-decatrienoates. These data indicate there are Heteroptera in North America in addition to Thyanta spp. that probably use methyl 2,4,6-decatrienoates as pheromones. The evidence that some pentatomids exploit the pheromones of other true bugs as kairomones to find food or to congregate as a passive defense against tachinid parasitism is discussed.     

2007～2008年世界塑料工业进展

收集了2007年7月～2008年6月世界塑料工业的相关资料,介绍了2007～2008年国外塑料工业的发展情况,提供了世界塑料产量、消费量及全球各类树脂的需求量及产能情况.按通用热塑性树脂(聚乙烯、聚丙烯、聚苯乙烯、聚氯乙烯、ABS树脂)、工程塑料(尼龙、聚碳酸酯、聚甲醛、热塑性聚酯、聚苯醚)、特种工程塑料(聚苯·硫醚、液晶聚合物、聚醚醚酮)、通用热固性树脂(酚醛、聚氨酯、不饱和聚酯树脂、环氧树脂)不同品种的顺序,对树脂的产量、消费量、供需状况及合成工艺、产品应用开发、树脂品种的延伸及应用的进一步扩展等技术作了详细介绍.     

2005～2006年国外塑料工业进展

收集了2005年7月～2006年6月国外塑料工业的相关资料,介绍了2005—2006年国外塑料工业的发展情况。提供了世界塑料产量、消费量及全球各类树脂生产量以及各国塑料制品的进出口情况。作为对比,介绍了中国塑料的生产情况。按通用热塑性树脂（聚乙烯、聚丙烯、聚苯乙烯、聚氯乙烯、ABS树脂）、工程塑料（聚酰胺、聚碳酸酯、聚甲醛、热塑性聚酯、聚苯醚）、通用热固性树脂（酚醛、聚氨酯、不饱和树脂、环氧树脂）、特种工程塑料（聚苯硫醚、液晶聚合物、聚醚醚酮）的品种顺序,对树脂的产量、消费量、供需状况及合成工艺、产品开发、树脂品种的延伸及应用的扩展作了详细的介绍。