基于低场核磁共振研究掺加磷石膏对水泥硬化体孔结构的影响

磷石膏是生产工业磷酸等的副产物,通常,磷石膏在水泥水化硬化中可起缓凝作用。本文基于低场核磁共振法这一无损检测方法,研究磷石膏的掺入对水泥在水化硬化过程中引起的早期孔结构的变化。结果表明,随着磷石膏的加入,水泥硬化体中的孔径分布逐渐向较小尺寸的方向进行发展;水泥硬化体的最可几半径不仅随养护龄期的增加而逐渐降低,随磷石膏掺量的增加而逐渐增加。基于分形理论研究了在该过程中水泥硬化体的孔径分布的变化,结果表明,其分形维数随养护龄期的增加而逐渐降低,随磷石膏掺量的增加而逐渐降低。     

利用超声波法对再生胶凝材料早期水化性能的研究

采用化学结合水含量测试法研究了水泥不同水灰比在不同水化龄期的水化程度,以及硬化浆体在650℃高温处理后的脱水程度,进而利用超声波波速法对脱水相的再水化过程进行连续监测,结果表明再生胶凝材料(脱水相)具有和水泥类似的水化过程,但水化放热多,水化速度和凝结时间快。     

氯离子对无机聚合物和硅酸盐水泥水化特性和硬化浆体性能的影响

研究了内掺氯离子对无机聚合物和硅酸盐水泥基本性能的影响,以及其硬化浆体对氯离子的固化特性及机理分析。结果表明:氯离子引入对无机聚合物及硅酸盐水泥的标准稠度用水量影响不大,对无机聚合物有缓凝作用,对硅酸盐水泥有促凝作用;氯离子对无机聚合物胶砂的抗压强度影响不明显,能提高硅酸盐水泥胶砂的早期抗压强度,但都能降低两种胶凝材料的抗折强度;内掺氯离子不改变无机聚合物和硅酸盐水泥的水化特性,但会改变放热峰的峰值及出峰时间;当水胶比一定时,无机聚合物与硅酸盐水泥硬化浆体对氯离子的固化能力总体的变化趋势表现为随龄期的增加而提高,随NaCl掺量的增加而下降,无机聚合物对氯离子的固化率低于硅酸盐水泥硬化浆体的原因是没有形成Friedel′s盐,仅仅由水化形成的C-S-H凝胶吸附氯离子。     

聚合物水泥基复合防水涂料料浆稳定性的研究

聚合物水泥基防水涂料是由水泥和聚合物乳液复合而成的双组分涂料。涂料中水泥遇水即发生水化,其水化所产生的电解质离子对聚合物乳液的稳定性有一定的影响。同时随着水分的逸失,聚合物颗粒逐渐胶接成膜。因此要求配制聚合物水泥基防水涂料的乳液与水泥具有良好的相容性。本文阐述了料浆的稳定性,分析了乳液和外加剂两个方面对料浆稳定性的影响。     

聚合物水泥基防水涂料的影响因素分析

聚合物水泥基防水涂料是由水泥和聚合物乳液复合而成的双组份涂料。涂料中水泥遇水即发生水化,其水化所产生的电解质离子对聚合物乳液的稳定性有一定的影响。同时随着水分的遗失,聚合物颗粒逐渐胶接成膜。分析了聚合物水泥基防水涂料防水机理和影响因素。     

无损检测法评判早龄期混凝土内部结构特征的研究

综合利用超声波、冲击回波、探地雷达等手段研究了凝结硬化早期混凝土内部的结构特征。超声波、应力波和电磁波波速以及介电常数等技术指标可以很好地反映早龄期混凝土内部结构特征的变化规律。受到水泥水化作用的影响,在前28d里,超声波、应力波和电磁波3种波速增长趋势以及介电常数下降的趋势都很明显,但随着水泥水化作用的减缓上述性质的变化也趋缓。预留试块抗压强度试验结果表明:3种无损检测手段相结合可以更加全面准确地反映早龄期混凝土结构特征。     

高铝水泥和硅酸盐水泥复合体系凝结硬化性能的试验研究

采用自动维卡仪、超声波测试仪和水化量热仪对高铝水泥和硅酸盐水泥复合体系的凝结硬化性能进行了研究。复合水泥系统的贯入深度曲线、超声波传播速度曲线以及水化放热速率和放热量曲线具有良好的相关性。不同测试方法的结合使用,可以为自流平砂浆产品的配方开发和质量控制提供必要的技术依据。     

赤泥-熟料体系的水化过程

采用常规的化学分析方法对赤泥-熟料体系水化过程中液相钙离子溶出、结合水以及水化样品含Ca(OH)2随龄期的变化的跟踪测定结果表明:赤泥-熟料体系的水化硬化过程中赤泥中的组分与硅酸盐水泥水化后放出的氢氧化钙之间发生了火山灰反应;600℃加热处理对赤泥产生明显的活化作用.     

活化煤矸石/粉煤灰水泥水化过程及性能差异

用水化热、热分析、化学结合水量、压汞法和扫描电镜研究了20℃养护条件下硅酸盐水泥和活化煤矸石/粉煤灰硅酸盐水泥的水化过程、硬化浆体孔结构和微观结构,并研究了浆体抗压强度和收缩值随龄期的发展规律.结果表明:与粉煤灰相比,活化煤矸石较大的比表面积及其所含有的多孔或致密的惰性物质,使其对水泥熟料水化的早期稀释效应有所削弱,也使其后期火山灰反应对水泥熟料和活化煤矸石混合材整体水化程度的提高幅度有所下降,并且活化煤矸石硅酸盐水泥水化1 a后其硬化浆体的毛细孔含量高于粉煤灰硅酸盐水泥,其抗压强度和收缩值则低于粉煤灰硅酸盐水泥.     

水泥-双掺料胶凝体系碾压混凝土孔结构试验研究

将磨细水淬矿渣与石灰石粉按一定比例混合制成双掺料,利用扫描电镜、压汞测孔技术研究了水泥-双掺料胶凝体系水化硬化浆体的密实度和孔结构发展规律,同时进行大掺量双掺料碾压混凝土强度及抗渗性随龄期变化试验。结果表明,随着水化龄期的增长,双掺料与粉煤灰相似,具有优化浆体孔结构的作用,硬化浆体无害孔比例明显增加,浆体密实度改善,混凝土强度及抗渗性能均有显著提高。     

用白云石生产氯氧镁水泥的新工艺

以安徽凤阳白云石为原料,在实验室进行了煅烧、水化和强度试验,用正交试验法确定了白云石的最佳煅烧温度和保温时间,借助X射线衍射、扫描电镜、红外光谱、差热分析等测试手段,研究了白云石的分解和轻烧白云石的水化硬化过程,给出了白云石中MgCO3分解率的定义,依据测试结果提出了轻烧白云石的水化硬化机理。结果表明,轻烧白云石可代替菱苦土用于氯氧镁水泥制品的生产。     

聚合物改性硫铝酸盐水泥修补砂浆的耐硫酸盐腐蚀性研究

以快硬硫铝酸盐水泥为基材,利用聚合物乳液对其改性用来制备混凝土修补材料,研究了聚合物乳液的引入对修补砂浆的耐化学腐蚀性能的影响.     

硫铝水泥和胶乳对水泥乳化沥青砂浆低温硬化性能的影响

通过分析水泥乳化沥青砂浆(CA砂浆)冬季低温病害的产生原因,研究了硫铝酸盐水泥、胶乳对CA砂浆低温凝结和灌注质量的影响。结果表明,低温导致CA砂浆超长缓凝,使体系稳定性变差,并引起泌水和揭板起皮等病害;掺入硫铝水泥能加快CA砂浆的低温凝结过程,随替代量增加,凝结时间逐渐缩短;随温度升高,胶乳水泥流态体系可搅拌时间呈降低趋势,选用低温稠化性能合适的的胶乳,可改善新拌CA砂浆的低温均匀稳定性;复掺10%硫铝水泥和8%胶乳的CA砂浆在24h的强度和膨胀率符合要求,在实测0.5~7.7℃的低温环境中,揭板检查CA砂浆断面均匀、表面平整无起皮,符合上道要求。     

Effect of concrete mixing parameters on propagation of ultrasonic waves

An experimental study was conducted to evaluate the effect of concrete aggregate gradation, water–cement ratio, and curing time on measured ultrasonic wave velocity (UPV). 30 × 30 × 10 cm Portland cement concrete slabs were cast for ultrasonic evaluation, while 10 cm diameter by 20 cm height cylinders were cast for compressive strength evaluation The slabs and cylinders were prepared using Portland cement and limestone aggregate. Two slabs were cast from each combination of coarse aggregate gradations and water cement ratio (0.40, 0.45, 0.50, and 0.55). Four ASTM gradations were considered, ASTM No: 8, 67, 56, and 4. These gradations have nominal maximum aggregate size 25, 4.75, 19.3, and 12.5 mm, respectively.The ultrasonic equipment used in this study was the portable ultrasonic non-destructive digital indicating tester (PUNDIT) with a generator having an amplitude of 500 V producing 54 kHz waves. The time needed to transfer the signal between the transducers was recorded and used to calculate the signal velocity, which was used as a parameter in the evaluation. Ultrasonic measurements were performed at 3, 7, 28, and 90 days after concrete casting.The results of the analysis indicated that water–cement ratio was found to have a significant effect on UPV. The UPV was found to decrease with the increase of water cement ratio. Aggregate gradation was also found to have significant effect on UPV. In general, the larger the aggregate size used in preparing Portland cement concrete, the higher the measured velocity of ultrasonic waves. Also, UPV was found to be increased as concrete curing time increased. Concrete compressive strength was found to be significantly affected by water–cement ratio and coarse aggregate gradation. Lower water–cement ratio produced higher concrete strength. Also, the concrete compressive strength increased as maximum aggregate size decreased.     

快凝型聚合物水泥防水浆料的研究

研制了快凝型聚合物水泥防水浆料，分别考察了普通硅酸盐水泥、快凝快硬硫铝酸盐水泥、调凝剂、活性矿渣、乳液等对产品可施工时间、抗折强度、抗压强度、抗渗性、抗冻性、拉伸强度、断裂伸长率等性能的影响。试验表明，该产品具有可施工时间充裕、早期强度高、弹性好、粘结性好、抗渗性好的特点，可以满足对工期和性能均有较高要求的防水、防渗、堵漏场合的应用要求。     

快硬超早强混凝土的研究与工程应用

研究了使用双快水泥和缓凝剂配制混凝土的凝结硬化性能和强度性能。结果表明，这种混凝土具有凝结硬化速度快、凝结时间可调、早期强度高、后期强度稳定正常的特点，并已成功应用于工程实践。     

Micro-annulus generation under downhole conditions: Insights from three-dimensional staged finite element analysis of cement hardening and wellbore operations

A micro-annulus (MA) is defined as a high permeability zone or gap initiating/occurring at the casing-cement and cement-formation interfaces during the wellbore life span. An MA can significantly compromise wellbore integrity by establishing enhanced fluid flow pathways. This study uses a staged finite element approach to simulate wellbore integrity during various loading steps of wellbore operations under downhole conditions. Particular emphasis is placed on the processes of cement poro-elastic property evolution, volume variation, and pore pressure variation as part of the cement hardening step. The resulting state of stress during the life cycle of a typical injection well (i.e. hardening, completion, and injection) is analyzed to assess the onset and evolution of micro-annuli at various interfaces of the composite wellbore system under downhole conditions. The results show that cement shear failure is observed at the casing-cement interface during pressure testing (excessive wellbore pressure); and tensile debonding failure initiates at the cement-formation interface due to cement shrinkage during hardening and injection-related cooling (thermal cycling). Sensitivity analyses considering several parameters show that: (1) the degree of poro-elastic bulk shrinkage has significant implications for both shear and tensile failure initiation – the less the cement shrinks, the less likely the failure initiation is; (2) cement integrity increases with increasing depth; (3) cement pore pressure evolution has significant implications for tensile failure – if cement pore pressure decreases more, higher temperature differences can be sustained before an MA occurs; and (4) cement temperature fluctuations during hardening promote initiation of debonding failure. In summary, the results presented indicate that establishing downhole conditions to quantitatively analyze MA generation is necessary. The results are different compared to laboratory studies without considering/simulating downhole conditions. The knowledge from this study can raise the awareness of predicting and evaluating MA under downhole conditions and can be used to supplement and improve future laboratory experiments.     

Geo-environmental application of municipal solid waste incinerator ash stabilized with cement

The behavior of soluble salts contained in the municipal solid waste incinerator (MSWI) ash significantly affects the strength development and hardening reaction when stabilized with cement. The present study focuses on the compaction and strength behavior of mixed specimens of cement and MSWI ash. A series of indices such as unconfined compressive strength, split tensile strength, California bearing ratio (CBR) and pH value was examined. Prior to this, the specimens were cured for 7 d, 14 d, and 28 d. The test results depict that the maximum dry density (MDD) decreases and the optimum moisture content (OMC) increases with the addition of cement. The test results also reveal that the cement increases the strength of the mixed specimens. Thus, the combination of MSWI ash and cement can be used as a lightweight filling material in different structures like embankment and road construction.