掺粉煤灰水泥石孔结构与力学性能关系的研究

本文对水泥石强度和胶空比之间的关系进行了研究,提出了相应的函数关系式,认为用胶空比作为研究水泥石强度的表征参数较为合适,分析了凝胶体强度和胶空比在不同龄期对水泥石强度影响的大小。同时文中也分析了掺粉煤灰对水泥石胶空比和强度的影响。     

矿物掺合料对水泥基材料自收缩影响综述

过大的自收缩是造成混凝土早期开裂的主要因素之一,防治混凝土早期开裂对提高混凝土的耐久性至关重要,目前掺入矿物掺合料是减小混凝土自收缩的重要措施。介绍了水泥基材料自收缩理论,然后对比、分析和总结了不同矿物掺合料种类、掺量、细度、掺入方式和水胶比对不同龄期水泥基材料自收缩的影响,同时探究了其作用机理,对未来的相关研究和应用提出了展望。     

矿物掺合料对高性能混凝土自收缩影响及计算模型研究

为研究矿物掺合料对高性能混凝土自收缩的影响及其计算模型,采用混凝土自收缩无接触自动测试装置进行粉煤灰掺量及品质、粉煤灰与偏高岭土复掺及粉煤灰与矿渣复掺对高性能混凝土自收缩性能的影响。研究结果表明:随着粉煤灰掺量的增加,高性能混凝土的自收缩值随之下降;在同掺量下,提高粉煤灰的品质可降低高性能混凝土的自收缩值。在粉煤灰高性能混凝土中复掺偏高岭土会增大其自收缩值;粉煤灰与矿渣复掺可进一步降低高性能混凝土的自收缩值,且在复掺比例为1∶1时最佳。通过对现有混凝土自收缩计算模型与试验数据对比分析,提出高性能混凝土自收缩计算模型,该模型计算结果与试验结果吻合良好。     

Combined effect of mineral admixtures with superplasticizers on the fluidity of the blended cement paste

The new concrete often incorporates several organic and mineral admixtures which interact with the various constituents of the cements and cause some problems of hardness and workability. In the present study, limestone cement (C1) and pozzolanic cement (C2) were used to make cement paste with two types of superplasticizer; SP1 based on polynaphthalene sulphonate (PNS); and SP2 based on resins melamines (PRM). Marsh cone test was adopted to check the combined effects of the following factors on the fluidity namely the type of cement, the type and the dosage of the superplasticizer, the type and the replacement rate of the mineral admixture and the water–cement ratio (W/C). The results of this work show that limestone cement presents a high fluidity with low loss after 1 h relatively to the pozzolanic cement within the saturation proportioning. Superplasticizer SP1 constitutes an incompatibility case when it is mixed with cement containing high C₃A or alkali content such as C2 cement. Also, limestone powder is found to be the best mineral admixture when it replaces a part of cement, where more fluidity is exhibited caused by the dilution effect.     

Effects of mineral admixtures on the thermal expansion properties of hardened cement paste

Concrete is a heterogeneous composite material with multiple components that have different thermal expansion properties. Internal stresses are generated if the concrete is rapidly heated or cooled, causing cracking in the micro- or macro-scale. If the coefficient of thermal expansion (CTE) of hardened cement pastes (HCP) is adapted, the thermal stress caused by the mismatch of thermal expansion properties of the components can be mitigated. The effects of the commonly used mineral admixtures (fly ash, ground granulated blast furnace slag and silica fume) on the thermal expansion properties of HCP are investigated. The thermal dilation rates (TDR) of HCP in which Portland cement is partially replaced with mineral admixtures are tested with a dilatometer and the CTE are derived. Replacing Portland cement with mineral admixtures is found to lower the CTE of HCP, which is beneficial for mitigating the thermal mismatch between the HCP and the aggregates. The extent of this lowering effect increases with the increasing replacement proportions of mineral admixtures in the pastes. Through quantitative determination of the porosity and the amount of portlandite in the paste and microscopic observations, it is revealed that the effects of the mineral admixtures are mainly due to the change of the porosity and the amounts of hydration products in the pastes.     

汞压法对水泥浆和掺合料水泥浆孔隙分析

硬化后混凝土材料具有细观、微观多孔隙特征,即使配制良好的高性能混凝土,也含有微孔隙和微裂纹。混凝土内部孔隙率及孔径分布对混凝土材料的性质有重要影响,如强度、变形、容重、导热性、吸水性、抗渗性及耐久性等;而矿物掺合料可改变混凝土内部孔隙的分布,从而影响混凝土的性能;因此,对混凝土材料内部孔隙的研究也是混凝土微观研究的一个重要方面。     

Contribution of CNTs/CNFs morphology to reduction of autogenous shrinkage of Portland cement paste

In this experimental study, carbon nanotubes (CNTs) and carbon nanofibers (CNFs) were dispersed by intensive sonication in water in the presence of superplasticizer and subsequently mixed with Portland cement with water/ cement ratios varying between 0.3 and 0.4. The autogenous shrinkage in the fresh stage was investigated. The CNTs and CNFs were characterized by high resolution scanning electron microscopy (SEM) and the hydrated pastes were studied by X-ray diffraction and SEM. The results showed a reduction of the autogenous shrinkage by 50% for pastes containing small amounts (0.01 wt%) of nanomaterials. Higher additions appeared to be less effective. The highest reduction of shrinkage was observed for carbon nanofibers which were long, rather straight and had diameters of around 200 nm. The result showed that the addition of nanomaterials accelerated the hydration processes especially in the early stages of hydration. The effect was the most pronounced in the case of functionalized nanotubes. The proposed mechanism resulting in the reduction of the autogenous shrinkage was a combination of nano-reinforcing effects, alterations of hydration and microstructure of the hydrated matrix.     

基于大掺量矿物掺合料的混凝土制备及孔结构研究

通过单掺及二元复掺钢渣和矿渣微粉,研究了矿物掺合料的最大掺量及对混凝土力学性能和孔结构的影响.结果表明,单掺钢渣微粉的最大掺量为30%,二元复掺钢渣与矿渣微粉(质量比为1∶1)的最大掺量为40%时,可制备出符合C40等级要求的大掺量矿物掺合料混凝土;矿物掺合料的加入可以有效降低混凝土的孔隙率,同时显著降低混凝土中有害大孔数量和水化后期的中值孔径.     

矿物掺合料对干粉砂浆物理性能及孔结构的影响

研究了石灰石、矿渣和粉煤灰3种矿物掺合料分别对干粉砂浆的工作性能和力学性能的影响,并探讨了掺有掺合料时干粉砂浆的宏观力学性能和其微观孔结构之间的关系。结果表明:粉煤灰在掺量小于30%时能够提高砂浆的流动度,但掺量再继续增大时,砂浆流动度反而下降;掺入矿渣粉略能提高砂浆的流动度;石灰石粉在一定程度上降低砂浆流动度;同时石灰石粉能够提高砂浆的保水率,而矿渣粉和粉煤灰却降低砂浆的保水率。随着石灰石、矿渣和粉煤灰掺量的增加,砂浆28 d强度均有不同程度的降低,影响顺序为石灰石>粉煤灰>矿渣;与空白样相比,内掺占水泥质量50%的石灰石粉和矿渣粉时,28 d砂浆硬化体的总孔隙率分别增加10.2%、7.7%,而掺等量粉煤灰时总孔隙率则基本不变。以石灰石替代50%的水泥时,28 d砂浆硬化体中d>100 nm的多害孔增加24.0%,而以粉煤灰替代50%的水泥时,砂浆中多害孔基本不变,以等量的矿渣粉替代时d>100 nm的多害孔减少6.5%。     

矿物掺合料对混凝土塑性收缩裂缝的影响

针对高胶凝材料用量泵送混凝土早期塑性收缩开裂现象普遍存在并导致混凝土结构耐久性衰减的问题,进行了掺合料对混凝土早期塑性开裂的影响效果比对试验,研究了花岗岩石粉、粉煤灰对混凝土工作性、抗压强度、早期塑性抗裂性能的影响规律,结果表明:掺合料品种、掺量对混凝土早期塑性开裂性能影响差异显著,15%~20%掺量的粉煤灰或15%掺量的花岗岩石粉能有效降低混凝土早期开裂风险。     

水泥和矿物掺合料与减水剂相容性问题的研究

不同水泥与外加剂之间相容性存在差异,这是毫无疑义的,矿物掺合料作为混凝土中的组分之一,也存在着与水泥共同作为胶凝材料时与高效减水剂的相容性问题.研究两种新型高效减水剂与水泥和3种矿物掺合料的相容性,并就矿物掺合料的合理掺量和复合使用问题进行了初步讨论.     

低水胶比下矿物掺合料对净浆流动性与流变性能的影响

研究了矿物掺合料种类及掺量对低水胶比水泥浆流动性以及流变性能的影响.试验结果表明:在低水胶比条件下,矿粉和粉煤灰可以有效提高浆体流动性,随着掺量的增加,流动度增大;而硅灰作用相反.掺30%矿渣可降低浆体的屈服应力与塑性黏度,改善浆体的流变性能;而掺10%硅灰增大了浆体屈服应力及塑性黏度.     

Strength and corrosion properties of Portland cement mortar and concrete with mineral admixtures

This work aims to validate the design assumptions by the California Department of Transportation in order to better define the strategies used to design concrete structures with adequate corrosion mitigation and thus a “maintenance-free” service life. To this end, various laboratory tests were conducted to investigate the compressive strength of and chloride diffusivity in mortar and concrete samples with cement partially replaced by various minerals (class F and class N fly ash, ultra-fine fly ash, silica fume, metakaolin, and ground granulated blast-furnace slag), the porosity of mineral concretes, the freeze–thaw resistance of mineral mortars in the presence of deicers, and the effect of supplementary cementitious materials on the chloride binding and chemistry of the pore solution in mortar.     

矿物掺合料和外加剂对超细水泥流变性能的影响

采用旋转黏度计和流动度仪分别研究了超细粉煤灰、硅灰、MgO膨胀剂、羟丙基甲基纤维素醚和黄原胶、聚羧酸系减水剂和萘系减水剂对超细水泥流变性能的影响规律.结果表明,W/C=0.6时超细水泥浆体的屈服应力和塑性黏度分别为1 1.32 Pa和1522x10-2Pa·s,掺加20％超细粉煤灰后屈服应力和塑性黏度分别增大为18.6...     

矿物掺合料和化学外加剂对胶凝材料浆体的流变参数的影响

基于最优化方法,给出使用同轴双圆柱流变仪来获取胶凝材料浆体的Bingham流变参数的途径;探究五种矿物掺合料(粉煤灰、矿渣粉、硅灰、石英粉、粉煤灰微珠)和两种化学外加剂(减水剂与引气剂)对胶凝材料浆体流变参数的影响。研究结果表明:矿物掺合料等体积替代水泥相对于等质量替代水泥,对降低浆体的屈服应力和塑性黏度有利。粉煤灰可降低浆体的屈服应力和塑性黏度;矿渣粉和石英粉可降低高水胶比浆体的屈服应力和塑性黏度,但增大低水胶比浆体的屈服应力和塑性黏度;硅灰可显著提升浆体的屈服应力;粉煤灰微珠可降低浆体的塑性黏度但增大其屈服应力。减水剂可降低浆体的屈服应力和塑性黏度;引气剂可降低浆体的塑性黏度。矿物掺合料和化学外加剂对胶凝材料浆体的Bingham流变参数的影响,取决于水胶比、矿物掺合料或化学外加剂的掺量、矿物掺合料颗粒粒径、粒形和水化活性等因素,因此使得胶凝材料浆体的流变参数随着矿物掺合料和化学外加剂种类和掺量的变化,表现出非线性特征。     

-3℃养护条件下矿物掺合料对混凝土强度和孔隙结构的影响研究

为了研究不同养护条件下矿物掺合料对混凝土强度和孔隙结构的影响,进行-3℃和标准养护条件下,复掺粉煤灰、矿粉和硅灰对混凝土抗压强度、孔隙结构的试验。结果表明:与标准养护相比,在-3℃养护条件下,矿物掺合料的掺入对混凝土抗压强度有下降趋势,但对其孔径均有优化作用。基准组、复掺10%粉煤灰+10%矿粉+1%硅灰组、复掺10%粉煤灰+10%矿粉+3%硅灰组,28 d龄期标准养护下出现细小孔的频率是负温养护1.122~1.259倍,56 d龄期标准养护下出现细小孔的频率是负温养护1.108~1.180倍,矿物掺合料对混凝土硬化含气量和平均气泡间距均有改善作用,在标准养护条件下的优化作用明显优于负温养护条件。     

浅谈混凝土外加剂对水泥的适应性

介绍了外加剂在不同水泥中的应用效果 ,并就外加剂对水泥的适应性的影响进行了分析 ,提出了解决外加剂对水泥适应性的改进方法 ,以使外加剂能够得到更加广泛的应用     

Strength and drying shrinkage properties of self-compacting concretes incorporating multi-system blended mineral admixtures

Drying shrinkage can be a major reason for the deterioration of concrete structures. The contraction of the material is normally hindered by either internal or external restraints so that tensile stresses are induced. These stresses may exceed the tensile strength and cause concrete to crack. The present study investigated compressive strength and particularly drying shrinkage properties of self-compacting concretes containing binary, ternary, and quaternary blends of Portland cement, fly ash (FA), ground granulated blast furnace slag (GGBFS), silica fume (SF), and metakaolin (MK). For this purpose, a total of 65 self-compacting concrete (SCC) mixtures were prepared at two different water to binder ratios. It was observed that drying shrinkage lessened with the use of FA, GGBFS, and MK while incorporation of SF increased the drying shrinkage.     

粉煤灰对水泥浆体化学收缩的影响

水泥水化反应引起的化学收缩会引起砂浆及混凝土的体积变化，可能会导致收缩裂缝的产生。粉煤灰的掺入在一定程度上可减少化学收缩。本文通过一些试验研究所得数据论证了随粉煤灰掺量的增多，化学收缩随之减小，而随细度增加，水泥浆体化学收缩随之略有增大。并通过强度检测验证了测定的化学收缩可间接反映水泥的水化程度。     

颗粒级配对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280、370和670 m2/kg三种不同细度的水泥,与不同掺量矿粉配制成不同颗粒级配的复合水泥,并进行了复合水泥干粉压实体孔隙率、复合水泥浆体的抗压强度、孔隙率、自收缩和BSEM测试。结果表明:随着水泥细度的增加,压实体的孔隙率逐渐增大。细水泥对复合水泥浆体早期孔隙的细化效果显著,提高了大掺量矿渣复合水泥浆体早期强度。矿粉的掺入减小了复合水泥体系的自收缩,矿粉掺量越大,水泥浆体自收缩越小。