二氧化碳腐蚀对油井水泥石抗压强度的影响(英文)

利用扫描电子显微镜、强度测试仪检测了不同条件下二氧化碳腐蚀油井水泥的产物、微观结构及抗压强度,研究了二氧化碳腐蚀油井水泥的机理及腐蚀对水泥强度的影响,分析和评价出了适合于大庆油田不同温度深井条件的水泥浆体系.结果表明:二氧化碳对油井水泥的腐蚀作用本质在于二氧化碳能够与水泥的水化产物发生化学作用,生成了各种不同晶体结构的CaCO3产物,使原有的水泥石微观结构遭到破坏,导致腐蚀后水泥石的强度下降;温度和二氧化碳分压增高;改善水泥石抗腐蚀能力应以有效改善水泥水化产物及微观结构为基础,添加抗腐蚀填充材料能有效改善水泥浆体系的抗腐蚀能力.     

二氧化碳对油井水泥石的腐蚀

在分析二氧碳(CO2)腐蚀水泥的化学作用过程的基础上,测量和分析了腐蚀水泥石的微观结构、抗压强度及渗透率.结果表明:CO2对水泥产生腐蚀作用的本质在于CO2能够与水泥的水化产物相作用生成各种不同晶体结构的CaCO3,破坏了水泥石的原有产物组成及结构,导致腐蚀后水泥石的抗压强度下降,渗透率增大.温度、CO2分压增高,腐蚀水泥石抗压强度降低,渗透率增大.添加抗腐蚀填充材料的水泥浆腐蚀后初期抗压强度有所降低,后期抗压强度具有不下降或上升趋势.实验设计的6号水泥浆具有较好的抗腐蚀效果.     

微硅对水泥石抗腐蚀性能影响的研究

石在酸性介质下的耐腐蚀性,本文在分析水泥石在含H2S和CO2条件下的腐蚀机理的基础上,通过实验证明微在油气开采中,地层构造中的H2S/CO2对水泥石产生碳化腐蚀,严重影响固井效果,为改善和提高水泥硅是一种良好的填充料,可提高水泥石的密实度,从而提高其抗压强度。对不同龄期的水泥石进行腐蚀,测试腐蚀后的抗压强度,分析比较纯水泥、微硅水泥的抗腐蚀性能;并利用金相显微镜和X-衍射图谱,观察分析微硅的抗腐蚀原因。     

二元溶剂体系对泡沫传输制备聚苯乙烯微球的影响

采用二氯甲烷（DCM）和丙酮（AC）组成二元溶剂体系,考察了二元溶剂体系对制备聚苯乙烯（PS）微球时泡沫的传输和微球性能的影响,并探讨了对应的作用机理。实验结果表明,随着AC质量分数的增加,体系的出泡温度升高,PS微球的平均粒径下降且粒径分布逐渐变窄,微球的结构由多孔逐渐演变为中空。这主要是由于AC对水具有一定的亲和性,会往连续相迁移,改变连续相的表面张力,并在油水界面形成一个AC/DCM的混合液膜层,该液膜层改变了溶剂挥发的过程,最终实现对微球粒径和结构的调控。     

油井水泥用微球型防腐蚀剂的合成及性能评价

为了减缓含CO2油气井固井水泥环的腐蚀破坏,延长井筒生产寿命,制备出一种聚合物微球型防腐蚀剂(PSAC),首先对其微观结构进行了表征,然后评价了其抗腐蚀性能,最后初步探讨了其抗腐蚀作用机理.结果表明,微球型防腐蚀剂(PSAC)具有纳米尺度且呈现核-壳结构;PSAC赋予油井水泥石非渗透特性,使得水泥石抗渗性和致密性提高,...     

短切纤维增强水泥基胶凝材料力学性能研究

为了改善油气井固井用硅酸盐水泥石的性能，通过测试水泥浆工程性能、水泥石力学性能及渗透性，结合SEM和XRD分析其微观结构及水化产物，探讨了两种纤维在增强水泥石力学性能方面的耐温耐久对比及作用机制。结果表明：1.0%的纤维对水泥浆工程性能促进效果最好；90℃下，玄武岩纤维耐温耐久性能较差，在水泥基体中被完全腐蚀，促进水泥水化产物及微裂缝的生成同时增强了水泥石强度，28 d后，水泥石抗压强度相比于空白样提高了16.71%；同龄期下，相比于空白样，耐碱玻璃纤维水泥石抗压强度降低了9.88%，抗折与抗拉强度分别提高了33.43%和23.17%，弹性模量降低了32.38%。表明耐碱玻璃纤维虽然一定程度上抑制了强度的发展，但其能够在水泥基体中稳定存在并能限制微裂缝的产生及扩展，拔出过程中消耗了大量能量，从而提高了水泥石的韧性。     

利用不同造孔剂制备Al2O3多孔陶瓷

以炭黑和自制的PS微球（聚苯乙烯微球）、PMMA微球（聚甲基丙稀酸甲酯微球）为造孔剂制备氧化铝多孔陶瓷,通过SEM和其他方法对其强度、密度、外观形貌进行比较。结果表明,用PS微球与PMMA微球为造孔剂的多孔陶瓷在强度、气孔率等这些方面对多孔陶瓷的影响相近,炭黑对多孔陶瓷的各方面影响最大,以炭黑为造孔剂的多孔陶瓷比以PS微球与PMMA微球为造孔剂的多孔陶瓷的强度大、但是气孔率的稳定性差且不易控制。     

碱矿渣水泥石碳化产物研究

碱矿渣水泥水化产物不同于硅酸盐水泥,会产生不同的碳化行为.以水玻璃与NaOH为碱组分制备碱矿渣水泥石,采用X-射线衍射(XRD)、红外光谱(FF-IR)与综合热分析(TG-DSC)研究了碱矿渣水泥石的碳化产物.结果表明:碱矿渣水泥石碳化生成的CaCO3的存在形式主要为方解石,球霰石和文石含量较少,随碳化龄期延长,文石与球霰石含量增加;以模数1.0～1.5的水玻璃为碱组分的碱矿渣水泥石碳化后,出现钠的碳酸盐结晶相;碱矿渣水泥石碳化脱钙后生成富硅的C-S-H凝胶,C-S-H凝胶的聚合度增加.     

基于颗粒级配技术的防腐水泥浆体系的室内研究

基于颗粒级配技术用不同粒度的砂及微细水泥对G级水泥进行复配,研制了防腐水泥浆,对防腐水泥石和G级水泥石进行H_2S腐蚀对比研究,测定水泥石外观、腐蚀深度和抗压强度的变化,通过扫描电镜、X-衍射分析了水泥石腐蚀后的微观结构与成分。结果表明,通过颗粒级配技术复配的防腐水泥浆体系能够明显地改善水泥石的抗腐蚀性能。     

有序大孔二氧化硅微球的制备研究

采用乳液聚合法合成了单分散改性聚苯乙烯（PS）乳胶粒,利用PS乳胶粒自组装制得胶体晶体（“蛋白石”）微球,通过溶胶-凝胶模板法制备了有序大孔SiO2（“反蛋白石”）微球,通过SEM对改性PS乳胶粒、胶体晶体微球和有序大孔SiO2微球表面形貌进行了表征。结果表明,改性PS乳胶粒呈单分散性,粒径为317 nm;胶体晶体微球表面PS乳胶粒排列有序;有序大孔SiO2微球表面呈有序多孔,其孔呈六边形,孔径分布均一,约为200 nm。     

Prediction of diffusivity of concrete based on simple analytic equations

Proposed is a simple analytic model that can predict realistically the diffusivities of concrete and mortar. The basic concept of the model comes from the relation between the diffusivities and the microstructure of concrete. The microstructure that affects the diffusivity includes the interfacial transition zone (ITZ) between aggregates and cement pastes as well as the microstructure of cement paste itself. The general effective media (GEM) equation was introduced to derive the diffusivity of cement paste. The effective diffusivity of concrete is derived on the basis of the composite sphere assemblage model, which considers the diffusivities of both ITZ and cement paste. The main parameters in the proposed model are the microstructural properties of cement paste such as capillary porosity and pore structure parameter, solid phase diffusivity, aggregate volume fraction, and interfacial zone properties. To validate the proposed model, many series of concrete and mortar specimens have been tested to measure the diffusivities. The major test variables include the water-to-binder ratios, the types and amount of mineral admixtures on the diffusivities. The effects of compressive strength, water-to-binder ratio, and mineral admixtures have been investigated comprehensively. The comparison of the proposed theory with the test data exhibits reasonably good correlation. The proposed model allows more accurate prediction of diffusion process and, thus, more realistic durability design of concrete structures.     

Modelling relationships between permeability and cement paste pore microstructures

Pore size distribution and the interconnectivity of cement paste pores have a strong influence on permeability. A computer network model has been developed to simulate flow through the pore microstructure cement paste. Network models have been successfully applied to predicting permeabilities of geological materials including rocks and soils but have not been specifically developed in the area of cement and concrete. The network model presented in this paper is used to obtain further insight into how pore size distributions of cement paste microstructures influences permeability. The model accounts for variations in pore microstructure by using a two-dimensional network of tubes with different log-normal size distributions.     

预湿水泥浆颗粒内养护材料对混凝土早期自收缩及抗压强度的影响

制备不同粒径和水灰比的水泥浆颗粒作为低水灰比混凝土内养护材料.以最佳内养护水灰比原则,设计了使用三种水灰比分别为0.6、0.7和0.8的同粒径水泥浆颗粒等体积取代砂子的混凝土.研究了不同水灰比水泥浆颗粒对混凝土早期自收缩、抗压强度和内部微结构的影响.结果表明:颗粒吸水率与其水灰比正相关、与其粒径负相关;预湿水泥浆颗粒可显著降低混凝土早期的自收缩,颗粒水灰比越大,自收缩降低效果越明显;但是掺入水泥浆颗粒也会降低混凝土的抗压强度,颗粒水灰比越高抗压强度降低越多,应用中应优化选择预湿颗粒的水灰比;水泥浆颗粒作为高性能混凝土内养护材料,可改善微观界面的孔隙结构,提高界面的密实性,减少混凝土早期的收缩和开裂.     

Modeling the linear elastic properties of Portland cement paste

The linear elastic moduli of cement paste are key parameters, along with the cement paste compressive and tensile strengths, for characterizing the mechanical response of mortar and concrete. Predicting these moduli is difficult, as these materials are random, complex, multi-scale composites. This paper describes how finite element procedures combined with knowledge of individual phase moduli are used, in combination with a cement paste microstructure development model, to quantitatively predict elastic moduli as a function of degree of hydration, as measured by loss on ignition. Comparison between model predictions and experimental results are good for degrees of hydration of 50% or greater, for a range of water : cement ratios. At early ages, the resolution of the typical 100³ digital microstructure is inadequate to give accurate results for the tenuous cement paste microstructure that exists at low degrees of hydration. Elastic computations were made on higher resolution microstructures, up to 400³, and compared to early age elastic moduli data. Increasing agreement with experiment was seen as the resolution increased, even when ignoring possible viscoelastic effects.     

Experimental study and numerical simulation on the formation of microstructure in cementitious materials at early age

The formation of microstructure in early age cement paste and concrete was examined with an ultrasonic experimental set-up. Research parameters included the influence of curing temperature (isothermal curing at 20, 30 and 40 °C), water/cement ratio (0.40, 0.45 and 0.55) and amount of aggregate. In parallel with the experiments, the cement hydration model HYMOSTRUC was utilized to simulate the formation of the microstructure. In this study, the cement paste was considered as a four-phase system consisting of water, unhydrated cement, hydration products and that part of the hydration product that causes the contact between the hydrating cement grains (so called “bridge volume”). A correlation has been found between the growth of bridge volume calculated with the model and the changes in the pulse velocity. It is believed that ultrasonic pulse velocity (UPV) measurements can represent a valuable tool to investigate the development of the microstructure at early age.     

Microstructure and composition of the hydrated cement paste of an 84 year old concrete bridge construction

The hydrated cement paste of an 84 year old reinforced concrete bridge construction has been examined for its composition and microstructure by means of chemical analysis, SEM, X-ray diffraction analysis and thermal analysis. The main hydration products are: calcium hydroxide, fibrous calcium-silicate-hydrate incorporated frequently with the calcium hydroxide into hexagonal plates, and calcium-aluminate-carbonate-hydrate. The properties of the almost completely hydrated cement paste have not been adversely affected even after more than 80 years.     

A gap-graded particle size distribution for blended cements: Analytical approach and experimental validation

To increase the packing density of blended cement paste, a gap-graded particle size distribution (PSD) was theoretically deduced and modified according to the wet density of actual paste. Then experiments were conducted to validate the hypothesis of improvement of the properties of blended cements by the gap-graded PSDs proposed. The experimental results show that the gap-graded PSD resulted in a decreased water requirement and an increased packing density of blended cement paste, and modified gap-graded PSDs gave further effects. The heat of hydration of gap-graded blended cement pastes released slowly in the first 24 h and increased rapidly afterward. The microstructure of gap-graded blended cements was much more homogeneous and denser than that of reference blended cement, therefore both early and late mechanical properties of low clinker gap-graded blended cements were improved significantly and even higher than those of Portland cement.     

Aggregate-cement paste transition zone properties affecting the salt-frost damage of high-performance concretes

The influence of the cement paste-aggregate interfacial transition zone (ITZ) on the frost durability of high-performance silica fume concrete (HPSFC) has been studied. Investigation was carried out on eight non-air-entrained concretes having water-to-binder (W/B) ratios of 0.3, 0.35 and 0.42 and different additions of condensed silica fume. Studies on the microstructure and composition of the cement paste have been made by means of environmental scanning electron microscope (ESEM)-BSE, ESEM-EDX and mercury intrusion porosimetry (MIP) analysis. The results showed that the transition zone initiates and accelerates damaging mechanisms by enhancing movement of the pore solution within the concrete during freezing and thawing cycles. Cracks filled with ettringite were primarily formed in the ITZ. The test concretes having good frost-deicing salt durability featured a narrow transition zone and a decreased Ca/Si atomic ratio in the transition zone compared to the bulk cement paste. Moderate additions of silica fume seemed to densify the microstructure of the ITZ.     

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。     

透水混凝土冻融剥蚀成因分析

为探究透水混凝土冻融剥蚀是否来自水泥浆体劣化,选取2.5~10.0 mm粒径骨料,制备了水灰比为0.31的透水混凝土及同水灰比的水泥石,测量二者冻融循环下质量、强度及透水混凝土相对动弹性模量变化。采用压汞法(MIP)测量水泥石冻融循环下孔结构特征参数及孔径分布变化,并通过扫描电镜(SEM)观察透水混凝土骨料水泥界面形貌演变。结果表明,在水冻与盐冻环境下透水混凝土宏观性能指标均有不同程度下降,骨料水泥界面产生裂缝并随冻融次数增加不断扩展,而水泥石强度、质量及微观孔隙结构均无明显变化。这表明透水混凝土冻融劣化与骨料水泥界面劣化相关。