蒸压加气混凝土孔结构及其对性能的影响研究进展

蒸压加气混凝土的主要特征是多孔性,其孔结构是影响性能的主要因素之一。简述了蒸压加气混凝土中孔的分类、特征以及表征方法,综述了国内外蒸压加气混凝土强度、吸水导湿、干燥收缩、热工性能、耐久性能等方面的最新研究进展,探讨了蒸压加气混凝土孔结构与性能之间的关系。最后阐述了蒸压加气混凝土孔结构与性能今后的研究方向和研究重点。     

蒸压加气混凝土孔结构表征的图像分析方法

采用数码相机采集图像.利用Matlab将加气混凝土砌块断面照片转化为灰度照片,并对照片进行去噪、直方图均衡化、二值化处理,采用图像分析法实现了对蒸压加气混凝土的宏观孔孔隙率、孔面积及其分布等孔结构特征的计量.分析结果表明,基于Matlab图像分析法可以对蒸压加气混凝土的孔结构进行初步的量化表征,但限于所采用数码相机的分辨率,该方法只适合表征蒸压加气混凝土中的宏观孔.通过改进程序分辨能力、相片拍摄技巧以及样品准备与处理方法可以大幅减小图像分析法的表征误差,提高方法的准确性.     

水热合成镍矿渣加气混凝土及其水化产物

采用蒸压工艺,以镍矿渣为主要原料制备加气混凝土砌块。研究了钙硅比和一种自制外加剂对加气混凝土性能的影响,采用X射线衍射仪、扫描电镜分析了镍矿渣加气混凝土分别在原料干混、水合预固化和蒸压养护后的物相变化。结果表明,随着钙硅比减小,砌块干密度和强度逐渐增加,强度在钙硅比为0.64附近时达到峰值。外加剂在镍矿渣加气混凝土浆体制备的过程中起到了改善粘度的作用,使砌块形成独立、细小的孔结构。原料的矿物相经水合预固化生成C-S-H凝胶相及AFt相,再经高温蒸压后两相减少同时生成硬石膏和扁平状的托勃莫来石相。     

钙硅比对固硫灰蒸压混凝土性能的影响

固硫灰中CaO含量一般高于粉煤灰而SiO_2含量则低于粉煤灰,因此粉煤灰加气混凝土的钙硅比不宜直接用于固硫灰加气混凝土。改变燃煤灰渣和石灰的相对含量以调节蒸压混凝土的钙硅比,并研究钙硅比对水化产物、干密度、抗压强度及干燥收缩性能的影响。结果显示,干密度随钙硅比增大而增大;存在某一钙硅比使其抗压强度最高且干缩性能最小。当设计固硫灰蒸压混凝土配合比时,为达到较高的力学性能,其钙硅比应高于粉煤灰加气混凝土。     

养护方式对磷渣加气混凝土性能的影响

利用磷渣的潜在活性,研制了以磷渣为原材料的加气混凝土。研究了标准养护和蒸压养护两种养护方式对磷渣加气混凝土体积密度、抗压强度、干燥收缩、抗冻性和导热系数等性能的影响。结果表明,与标准养护相比,蒸压养护可以降低磷渣加气混凝土的体积密度、干燥收缩值和导热系数,提高加气混凝土的抗冻性能。     

养护方式对磷渣加气混凝土性能的影响

利用磷渣的潜在活性，研制了以磷渣为原材料的加气混凝土。研究了标准养护和蒸压养护两种养护方式对磷渣加气混凝土体积密度、抗压强度、干燥收缩、抗冻性和导热系数等性能的影响。结果表明，与标准养护相比，蒸压养护可以降低磷渣加气混凝土的体积密度、干燥收缩值和导热系数，提高加气混凝土的抗冻性能。     

蒸压加气混凝土砌块施工质量控制措施

蒸压加气混凝土砌块是目前应用非常广泛的一种比较成熟的轻质墙体材料。但由于砌体块材具有明显的吸水率大(高达60%以上),散水性差及湿胀干缩等性能,容易造成装饰面层裂缝、空鼓、渗漏及发霉变质等缺陷,影响了工程质量和使用功能。本文主要介绍在汕头大学医学院第一附属医院三期工程蒸压加气混凝土砌块在砌筑前及施工中采取有效的质量控制措施,有效地控制了缺陷的发生,确保了工程质量。     

基于释放法蒸压加气混凝土板内钢筋自应力研究

为研究分析蒸压加气混凝土板中钢筋在高温蒸压过程产生的自应力及其对板受力性能的影响,试验采用分步释放法测自应力,通过对配置HPB300钢筋的蒸压加气混凝土板进行切割逐步释放板中钢筋的自应力,记录对比蒸压加气混凝土板受压侧和受拉侧在跨中及板端自应力值,给出自应力在板内分布规律及取值。分析自应力对板的开裂弯矩及承载能力的影响。试验结果表明:蒸压加气混凝土板受压区板端自应力约为跨中自应力值的56%;受拉区板端自应力约为跨中自应力值的84%,跨中受拉区自应力约为受压区自应力的54%;板端受拉区自应力约为受压区的83%,并分析其产生及分布机理。此外,自应力也提高了板的抗裂能力,其中对开裂弯矩有较大影响,自应力所抵抗的开裂弯矩约为理论开裂弯矩值的65.7%。合理计算自应力可以有效利用蒸压加气混凝土板的抗裂和承载能力,对蒸压加气混凝土板的推广与发展有重要的理论价值和现实意义。     

基于孔结构的蒸压加气混凝土的冻融循环耐久性试验研究

为证明混凝土的毛细吸水系数可以作为其抗冻性能的表现形式,本工作通过蒸压加气混凝土和普通混凝土的冻融循环试验,共三组试件:B07、B08、C40普通混凝土,分别对其进行吸水率和毛细吸水系数的测定以及5次、15次、30次冻融循环试验,研究孔结构对混凝土抗冻性能的影响,通过数据分析和微观分析得出的结果:孔的数量越多,毛细吸水系数越大,在相同冻融循环情况下质量损失率、强度损失率越大,抗冻性能越差,证明了这一说法的可行性,为混凝土的应用提供了可靠的性能研究理论.     

冲击载荷作用下蒸压加气混凝土动态力学性能研究

为了研究蒸压加气混凝土(AAC)在冲击载荷作用下的动态力学性能,对密度为425 kg/m~3和625 kg/m~3的试件进行了准静态力学测试和分离式Hopkinson压杆(SHPB)试验。针对蒸压加气混凝土这类低阻抗多孔介质材料试件内部应力不均匀和透射信号难采集的问题,采用波形整形器和半导体应变片对SHPB装置进行了改进,保证了试验的有效性。试验得到了不同应变速率下的力学参数,并在此基础上研究了蒸压加气混凝土的强度性能。结果表明:蒸压加气混凝土的抗压强度随应变速率和密度的增加而增大;蒸压加气混凝土的动态强度增长因子与平均应变率的自然对数成线性关系;在冲压状态下蒸压加气混凝土存在应变率敏感阈值,当应变率超过这个值时,试件的抗压强度将明显增加;随着平均应变率和密度的增加,蒸压加气混凝土的冲击韧性不断增加且冲击韧性指标与平均应变率的对数呈线性关系。     

Gas permeability and capillary porosity of self-compacting concrete

Self-compacting concrete (SCC) can be placed without any external compaction avoiding some health risks as well as environmental problems. In order to obtain its key properties, a large amount of fine particles and a new generation of superplasticizers can be used. Earlier research by means of mercury intrusion porosimetry, already pointed out an important difference in pore structure between SCC and traditional concrete (TC). Since the transport properties of concrete are strongly depending on its pore structure, the question rises to what extent the gas permeability of SCC gets affected by the change in mixture design. In this paper the gas permeability of 16 mixtures SCC and 4 mixtures TC are being evaluated with special attention to the difference between SCC and TC, and the influence of the following parameters: water/cement ratio, powder content, type of filler, fineness of the filler, type of aggregate and cement/powder ratio. It was concluded that the gas permeability of SCC is about 5 times lower than the gas permeability of TC. The parameter with the largest impact on the gas permeability seems to be the water content and secondly the powder content. The capillary porosity has been estimated and a rather good correlation has been found with the gas permeability.      

PEMFC catalyst layers: the role of micropores and mesopores on water sorption and fuel cell activity

The effects of carbon microstructure and ionomer loading on water vapor sorption and retention in catalyst layers (CLs) of PEM fuel cells are investigated using dynamic vapor sorption. Catalyst layers based on Ketjen Black and Vulcan XC-72 carbon blacks, which possess distinctly different surface areas, pore volumes, and microporosities, are studied. It is found that pores <20 nm diameter facilitate water uptake by capillary condensation in the intermediate range of relative humidities. A broad pore size distribution (PSD) is found to enhance water retention in Ketjen Black-based CLs whereas the narrower mesoporous PSD of Vulcan CLs is shown to have an enhanced water repelling action. Water vapor sorption and retention properties of CLs are correlated to electrochemical properties and fuel cell performance. Water sorption enhances electrochemical properties such as the electrochemically active surface area (ESA), double layer capacitance and proton conductivity, particularly when the ionomer content is very low. The hydrophilic properties of a CL on the anode and the cathode are adjusted by choosing the PSD of carbon and the ionomer content. It is shown that a reduction of ionomer content on either cathode or anode of an MEA does not necessarily have a significant detrimental effect on the MEA performance compared to the standard 30 wt % ionomer MEA. Under operation in air and high relative humidity, a cathode with a narrow pore size distribution and low ionomer content is shown to be beneficial due to its low water retention properties. In dry operating conditions, adequate ionomer content on the cathode is crucial, whereas it can be reduced on the anode without a significant impact on fuel cell performance.     

孔结构对泡沫混凝土性能的影响与控制技术

泡沫混凝土是我国水泥基建筑材料的重要组成部分,分析了孔结构的分类及其对泡沫混凝土的强度、耐久性、保温系数等宏观性能的影响,发现泡沫混凝土的宏观性能与孔结构密切相关。总结了泡沫混凝土孔结构的控制技术,发现水灰比、矿物掺合料等的加入都会影响孔的形成。在此基础上,提出加强对建立孔结构与宏观性能之间的理论模型、孔结构与宏观性能间关系的适用范围、孔的定量控制等方面的研究。     

中空桔瓣型超细纤维/水性聚氨酯合成革的制备及性能

以聚酯-聚酰胺6(PET-PA6)中空桔瓣型超细纤维非织造布为基布,以水性聚氨酯(WPU)膜为聚合物涂层,经干法移膜技术得到了中空桔瓣型超细纤维/水性聚氨酯(PET-PA6/WPU)合成革,实现了超纤革的绿色化制备。通过场发射扫描电镜(FESEM)等测试手段表征了PET-PA6中空桔瓣型超细纤维非织造布的结构性能,系统研究了发泡倍率对WPU膜形态结构和性能的影响规律,分析了PET-PA6/WPU合成革的结构、透气透湿和物理力学性能。结果表明:PET-PA6中空桔瓣型超细纤维非织造布裂离后单根纤维的直径介于2.2~5.5μm之间,且其性能满足纺织品合成革用非织造基布的使用要求。当发泡倍率为100%时,所制备WPU膜为致密无孔结构,透气量和透湿率分别为14.72L/(m~2·s)和3 686.84g/(m~2·24h)。随着发泡倍率的增加,所制备WPU膜具有通透型泡孔和有孔表面,平均孔径、透气量和透湿率均依次增大。其中,当发泡倍率为250%时,WPU膜的透气量和透湿率分别达到169.43L/(m~2·s)和5 209.09g/(m~2·24h)。所制备的PET-PA6/WPU超纤革为三层复合结构,包括基布层、发泡层和面层,且其透气量为0.45L/(m~2·s),断裂强力为纵向138.40N、横向96.60N,断裂伸长率为纵向72.70%、横向101.80%,撕裂强力为纵向63.20N、横向88.20N,剥离强力为水解前15.86N、水解后15.61N,褶皱回复角为纵向149.30°、横向151.80°,均优于同类型的海岛针织合成革和真皮,同时透湿率高达1 673.8g/(m~2·24h),接近于真皮。     

钴离子和氢离子共掺杂聚苯胺的形貌可控制备与电化学性能

利用氧化聚合法制备钴离子(Co~(2+))和氢离子(H~+)共掺杂聚苯胺(PCoH),系统研究了Co~(2+)/苯胺(An)摩尔比、质子酸的种类和溶剂中水/乙醇体积比对PCoH的形貌和电化学性能的影响。结果表明,随着Co~(2+)/An摩尔比的提高,PCoH由无定形团聚态转变为纳米纤维结构。质子酸为盐酸(HCl)时,PCoH具有疏松规整的短棒结构,内部孔径分布规整,电化学性能最佳。溶剂中加入乙醇有助于PCoH聚合过程中生长出形貌均匀的纳米纤毛结构,并表现出优异的电化学性能,但过量的乙醇会增大PCoH的阻抗。当Co~(2+)/An摩尔比为2∶1,HCl为质子酸,溶剂中水/乙醇体积比为1∶1时,PCoH具有最大的比电容为374 F/g,经1000次循环后,仍保留85.2%的初始比电容,表现出良好的循环稳定性。     

Influence of limestone powder used as filler in SCC on hydration and microstructure of cement pastes

In recent years, self-compacting concrete (SCC) has gained wide application in the construction industry. As for high performance concrete (HPC) and traditional concrete (TC), the microstructural properties of SCC are the main factors, which determine the material properties, i.e. the mechanical properties, transport properties and the durability behaviour.In order to investigate the development of the microstructure of SCC, the microstructural parameters of the paste including porosity, pore size distribution and phase distribution are determined by means of mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM). The thermogravimetric analysis (TGA) and the derivative thermogravimetric analysis (DTG) are used to identify the phase constituents. These parameters as studied for self-compacting concrete are compared with high performance concrete and traditional concrete. The specimens of self-compacting cement paste (SCCP) are made with water/binder ratio 0.41 and 0.48, the high performance cement paste (HPCP) with w/c 0.33 and traditional cement paste (TCP) with w/c 0.48. The measurements are performed at different hydration stages, i.e. at 1, 3, 7, 14, 28 and 56 days.The result of this research shows that the pore structure, including the total pore volume, pore size distribution and critical pore diameter, in the SCCP is very similar to that of HPCP. The fact that limestone powder does not participate in the chemical reaction was confirmed both from thermal analysis and BSE image analysis.     

聚丙烯接枝聚乙二醇改性聚丙烯微孔膜

以聚丙烯接枝聚乙二醇(PP-g-PEG)对聚丙烯共混改性,通过单向拉伸工艺制备亲水性聚丙烯微孔膜。使用压汞仪、扫描电镜、Gurley值和水蒸气透过率表征微孔膜的孔结构和透过性能,研究PP-g-PEG含量、PEG接枝率及链长对微孔膜孔结构、水蒸汽透过率及锂电池性能的影响。结果表明,对于接枝率为0.78%的PP-g-PEG,随着添加剂PP-g-PEG含量增加,微孔膜孔隙率和微孔尺寸下降,反映孔道结构的曲挠度及喉孔比上升;微孔膜孔结构与亲水性的综合作用导致水蒸气透过率在PP-g-PEG含量为2.5%时达到最大值。PP-g-PEG含量为2.5%和5.0%的微孔膜组装的锂电池具有较低的电荷转移电阻和较高的充放电比容量,电池性能优于未改性微孔膜组装的电池。提高PEG接枝率使得改性微孔膜孔结构有所变差,但是水蒸气透过率提高,组装电池的性能也更好。长PEG侧链PP-g-PEG对微孔膜孔结构的破坏程度大于短PEG侧链PP-g-PEG,导致组装电池的性能变差。