粉煤灰表面改性及其对水泥浆体强度和自收缩的影响

研究了白云石对Ⅲ级粉煤灰表面改性,并测定了掺改性粉煤灰水泥浆体的自收缩和抗压强度.利用X射线衍射、扫描电镜和能谱分析等测试方法对经950℃煅烧1 h后改性粉煤灰的物相结构和化学组成进行了表征,通过背散射扫描电镜观察和压汞试验研究了掺改性粉煤灰水泥浆体的微观结构.结果表明:改性粉煤灰颗粒表面生成了具有水化活性的β-C2S...     

复掺粉煤灰和硅灰复合水泥浆体的干燥收缩研究

以复掺粉煤灰、硅灰的复合水泥浆体为研究对象,研究了复合水泥浆体的干燥收缩的变化规律.结合TG-DSC、孔结构测定、IR等现代化测试方法,研究了复合水泥浆体的结构、组成与干缩性能的关系.结果表明:当粉煤灰和硅灰总掺量为40％,而其中的硅灰掺量为0～10％,粉煤灰掺量为30％ ～ 40％时,其干燥收缩均小于纯水泥浆体.     

矿物外加剂及测试方法对硬化水泥浆体自收缩值的影响

分别采用两种不同试验方法对比研究了单掺粉煤灰、硅灰和矿渣微粉这三种常用的矿物外加剂(即水泥混合材)对水泥浆体早期自收缩的影响。研究结果表明,单掺粉煤灰、硅灰和矿渣微粉后,硬化水泥浆体的自收缩值分别随其掺量的增加而减小、增大和增大。本文分析研究了这三种常用的矿物外加剂对硬化水泥浆体自收缩产生影响的原因,并对比分析了本试验采用的两种试验方法,发现波纹管法更能准确地测量水泥浆体的早期自收缩,参照现行行业标准JC/T313-1982测试无法正确地反映硬化水泥浆体更早期的收缩现象。     

三元复合水泥浆体水化进程及其与干缩的关系

采用选择性溶解法和非蒸发水法分别测量了粉煤灰-硅灰和水泥的反应程度;通过复合浆体中有效水胶比的计算和非线性拟合的方法,得出复合浆体中水泥的反应程度,研究了粉煤灰-硅灰-水泥三元体系中矿物掺合料对水泥水化程度的影响.根据矿物掺合料和水泥的反应程度数据,并结合强度数据分析了复合水泥浆体干燥收缩的规律.研究发现:在相同龄期,随着硅灰的逐渐增多,粉煤灰的逐渐减少,复合浆体的干燥收缩逐渐增大;在不同龄期,复合浆体的干燥收缩值随着龄期的延长,干燥收缩曲线由陡逐渐变得平缓;当粉煤灰和硅灰总掺量为50％,而其中的硅灰为5％时,可以得到干燥收缩较小,抗压强度较高的三元复合水泥浆体.     

水泥-硅灰/粉煤灰体系强度、收缩性能与微观结构研究

为研究硅灰及粉煤灰对不同养护龄期的水泥浆体强度及收缩性能的影响,以水胶比为0.29的水泥浆体为基体,设计制备了五种硅灰及粉煤灰掺量的复合水泥浆体,借助量热仪和压汞仪测试表征了不同复合水泥浆体的水化放热特性以及孔结构组成,分析了水化放热量、孔隙率等参数随硅灰和粉煤灰掺量增加的变化规律,建立了复合浆体抗压强度与孔结构以及水化特性与收缩应变之间的量化关系。结果表明,掺入粉煤灰会大幅降低水泥净浆早期抗压强度,但对减小自收缩应变和干缩应变极为有利。掺入硅灰能明显提高净浆3 d抗压强度,但当硅灰掺量超过10%(质量分数)后,净浆3 d自收缩应变及28 d干缩应变增加极为明显。掺入硅灰会使水泥水化诱导期开始和结束的时间提前,还会增加水化反应级数和各阶段的反应速率常数值,导致水泥-硅灰复合浆体的水化放热总量和放热速率相较于水泥-粉煤灰体系大幅增加。粉煤灰和硅灰的掺入均能有效细化水泥浆体内部孔结构,提高凝胶孔比例,大幅降低大孔比例。复合浆体的72 h水化放热总量和3 d自收缩应变呈现正相关关系,而孔隙率和抗压强度呈现明显的负相关关系。     

熟料细度对粉煤灰水泥浆体强度和自收缩的影响

通过实验室球磨机制备出比表面积分别为280m2/kg、370m2/kg和670m2/kg的3种水泥熟料,与不同掺量的粉煤灰配制成不同颗粒级配的粉煤灰水泥,并测试了粉煤灰水泥浆体的抗压强度、自收缩、孔隙率和显微结构。结果表明：提高熟料细度能在很大程度上降低粉煤灰水泥浆体的孔隙率并提高复合水泥浆体早期抗压强度;粉煤灰的掺入降低了水泥体系的自收缩,提高了粉煤灰水泥浆体的体积稳定性;粉煤灰水泥浆体背散射图像表明,提高熟料细度可显著减少粉煤灰水泥浆体中未水化的水泥颗粒含量,并在一定程度上减少未水化粉煤灰颗粒含量。     

粉煤灰掺量对硬化水泥净浆长期溶蚀性能的影响

为了分析长期处于软水环境下粉煤灰对水泥基材料溶蚀特性及其溶蚀过程的影响,以单掺粉煤灰的复合水泥浆体薄片试件为研究对象,开展不同粉煤灰掺量的水泥复合浆体浸泡在去离子水长达两年的溶蚀实验,并通过饱水-干燥称重、SEM/EDS、XRD等测试,分析溶蚀过程中复合水泥浆体薄片试件的孔隙率、微观结构、钙硅比及物相组成等参数的变化规律,揭示粉煤灰对水泥浆体溶蚀特性的影响及其抗溶蚀性能的改善机理.结果表明,在水泥浆体中合理掺加粉煤灰可有效地改善其微观结构及物相组成,减缓水泥浆体的微观结构劣化和溶蚀进程,提高其在去离子水中的抗溶蚀性能,掺入40％ 粉煤灰的复合水泥浆体在去离子水中具有最佳的抗溶蚀性能.     

矿物超细粉对水泥浆体化学收缩的影响研究

通过笔者自行设计的化学收缩测量装置分别对掺硅灰、磨细矿渣、超细粉煤灰的水泥浆体化学收缩进行了测定。结果表明，硅灰的掺入增大了水泥浆的化学收缩；磨细矿渣的掺入使水泥浆体的化学收缩稍有增长，但不十分明显；而超细粉煤灰则可以较好地抑制水泥浆体的化学收缩。对掺矿物掺合料的水泥浆体强度的测试结果从另一个角度论证了化学收缩是由水化引起的，即水化程度的大小反映了化学收缩的大小。     

水泥基材料受限开裂敏感性研究

介绍了水泥基材料受限收缩的试验方法与影响水泥基材料收缩的因素,采用限制收缩中的轴向约束试验方法,研究了不同矿物掺合料和水胶比的水泥基材料受限开裂敏感性.结果表明较大的水胶比、较高的磨细矿渣和硅灰掺量会增大水泥浆体的开裂敏感性,粉煤灰对水泥浆体的限制收缩开裂敏感性具有降低作用.     

水泥浆体早期收缩的试验研究

开发了一套采用高精度LVDT位移传感器测定水泥浆体长度变化的仪器,并用该仪器对不同水灰比和不同混合材的水泥浆体的收缩行为进行了研究。结果表明,该仪器能够准确、连续地测量水泥浆体终凝后的自收缩和干燥收缩的发展过程。早期自收缩和干燥收缩随着水灰比降低而明显增加,在20℃相对湿度50%的环境下,水泥浆体的自收缩占干燥收缩的10%左右;掺粉煤灰可以少量降低水泥浆体的自收缩和干燥收缩,而掺入石灰石和矿渣则不同程度的增大了水泥浆体早期收缩率。     

矿物掺和料与再生骨料对水泥强度和收缩性能的影响

矿物掺和料与再生骨料应用于水泥制品中是废弃物资源化利用的重要途径。为了研究矿物掺和料与再生骨料对水泥强度和收缩性能的影响,设计不同掺和料掺合比例与再生骨料取代率,进行不同龄期的强度、干燥收缩和早期自收缩测试。结果表明,粉煤灰降低水泥强度,而矿粉可提高水泥后期强度;粉煤灰和矿粉对水泥的干燥收缩有抑制作用,但对水泥早期自收缩有促进作用;再生骨料能够提高水泥强度,而对水泥的收缩性能无明显影响。     

The influences of siliceous waste on blended cement properties

The influences of siliceous waste on the properties of fly ash and blast furnace slag cement were studied, and its optimum mixing amount in blended cement was determined. The strength, setting time, resistance to chemical attack, dry shrinkage, and impermeability of blended cement mixed with siliceous waste were also investigated by different experiments. The measurement of pore size distribution for hardened cement pastes made by Poremaster-60 was recorded and analyzed in this article.     

Biomass fly ash in concrete: Mixture proportioning and mechanical properties

ASTM C 618 prohibits use of biomass fly ashes in concrete. This document compares the properties of biomass fly ashes from cofired (herbaceous with coal), pure wood combustion and blended (pure wood fly ash blended with coal fly ash) to those of coal fly ash in concrete. The results illustrate that with 25% replacement (wt%) of cement by fly ash, the compressive strength (one day to one year) and the flexure strength (at 56th day curing) of cofired and blended biomass fly ash concrete is statistically equal to that of two coal fly ash concrete in this investigation (at 95% confidence interval). This implies that biomass fly ash with co-firing concentration within the concentration interest to commercial coal-biomass co-firing operations at power plants and blended biomass fly ash within a certain blending ratio should be considered in concrete.     

不同矿物掺合料对改性硫氧镁水泥性能影响的研究

为探究矿物掺合料对改性硫氧镁水泥的影响及作用机理,分别将不同掺量的粉煤灰、矿粉掺入改性硫氧镁水泥中,对其力学性能、耐水性和耐酸性进行测试,并结合X射线衍射和扫描电镜对其物相组成及微观形貌进行表征和分析。研究结果表明:粉煤灰的掺入会提高改性硫氧镁水泥的3 d强度,但后期强度有所下降,当粉煤灰掺量大于20%(质量分数)时,其28 d抗压强度相较于基准组损失了14.7%;掺入矿粉对改性硫氧镁水泥的前期强度影响较小,并导致后期强度下降,当矿粉掺量为30%~40%(质量分数)时,水泥的28 d强度损失率高达17.3%。适量的粉煤灰与矿粉均能够提升改性硫氧镁水泥的耐水性和耐硫酸腐蚀性,其中水泥的耐硫酸腐蚀性随着粉煤灰掺量的增加而增强,耐硫酸腐蚀效果最好时矿粉掺量为20%。     

碱-磷渣-粉煤灰胶凝材料的性能与硬化浆体结构

为充分利用磷渣和粉煤灰两种工业废渣生产高性能胶凝材料,研究了不同磷渣/粉煤灰配合比的碱-磷渣-粉煤灰胶凝材料性能,并用扫描电子显微镜和压汞仪分析了硬化浆体的细观结构和孔结构.结果表明:碱-磷渣-粉煤灰胶凝材料的凝结时间正常,在粉煤灰掺量为0～30 %(质量分数)范围内,随粉煤灰的掺量的增加,碱-磷渣-粉煤灰胶凝材料的凝结时间略有延长.与普通硅酸盐水泥相比,碱-磷渣胶凝材料的抗压强度较高,其3d和28d抗压强度分别可达到30.9MPa和98.8MPa,但其抗折强度相对较低.掺加粉煤灰后碱胶凝材料的抗压强度降低,而抗折强度提高.碱-磷渣-粉煤灰胶凝材料的耐蚀性和抗冻性能均显著优于硅酸盐水泥,其干缩比硅酸盐水泥的大.用部分粉煤灰取代磷渣粉可一定程度减小干缩.碱-磷渣-粉煤灰胶凝材料硬化浆体的结构非常致密,其孔隙率和平均孔径均小于普通硅酸盐水泥硬化浆体.     

Improvement of the durability of glass fiber reinforced cement using blended cement matrix

Blended cements prepared with two fly ashes were used as matrices in glass fiber reinforced cement (GRC) composites in an attempt to improve their durability. The hydrated matrices from the two blended cements investigated here had similar strength and composition. Both fly ashes reduced the Ca(OH)₂ content to the same extent but in both cases the pH level was only slightly reduced compared to the portland cement matrix. In spite of these similarities, the GRC prepared with one fly ash showed considerable improvement in durability while the other one had only a small positive effect. SEM observations indicated that the improved durability in one case was associated with modification in the microstructure of the hydration products deposited in between the glass filaments, resulting in a much more open structure compared to that of portland cement matrix or the other blended cement. It is therefore suggested that the potential of the blended cement matrix to improve the durability of GRC is associated with its ability to modify the microstructure of the paste at the glass interface. This characteristic is not necessarily related to the overall composition of the blended cement matrix and to the reactivity of fly ash with Ca(OH)₂.     

Hydration of fly ash-portland cements

Hydration products of fly ash-portland cements were studied with x-ray diffraction (XRD), differential thermal analysis (DTA) and scanning electron microscopy (SEM) as part of a continuing research effort to understand the pozzolanic activity of fly ashes. It was found that the amount of calcium hydroxide crystals in the cement pastes is diminished due to the addition of fly ash to the cement. Ettringite was produced in the early age, and the consumption of sulfate by the formation of ettringite was accelerated by the addition of fly ash. A partial conversion of ettringite to monosulfate within the first 7 days of hydration in the fly ash-portland cement pastes, but the formation of ettringite continued to form up to at least 28 days of hydration in the pastes without fly ash. Examination of the fly ash bearing pastes showed, in all cases, varying amounts of calcium hydroxide and unreacted portland cement, with minor quartz and gehlenite hydrate. It appears that hydration reactions actually occur in the fly ash cement pastes more or less on a particle-by-particle basis.     

Durability of biomass fly ash concrete: Freezing and thawing and rapid chloride permeability tests

Strict interpretation of ASTM C 618 excludes non-coal fly ashes, such as biomass fly ashes from addition in concrete. Biomass fly ash in this investigation includes (1) cofired fly ash from burning biomass with coal; (2) wood fly ash and (3) blended fly ash (wood fly ash mixing with coal fly ash). A set of experiments conducted on concrete from pure cement and cement with fly ash provide basic data to assess the effects of several biomass fly ashes on the performances of freezing and thawing (F-T) and rapid chloride permeability test (RCPT). The F-T tests indicate that all fly ash concrete has statistically equal or less weight loss than the pure cement concrete (control). The RCPT illustrate that all kinds of fly ash concrete have lower chloride permeability than the pure cement control concrete.