Compressive strength and microstructural analysis of fly ash/palm oil fuel ash based geopolymer mortar

This paper presents the effects and adaptability of palm oil fuel ash (POFA) as a replacement material in fly ash (FA) based geopolymer mortar from the aspect of microstructural and compressive strength. The geopolymers developed were synthesized with a combination of sodium hydroxide and sodium silicate as activator and POFA and FA as high silica–alumina resources. The development of compressive strength of POFA/FA based geopolymers was investigated using X-ray florescence (XRF), X-ray diffraction (XRD), Fourier transform infrared (FTIR), and field emission scanning electron microscopy (FESEM). It was observed that the particle shapes and surface area of POFA and FA as well as chemical composition affects the density and compressive strength of the mortars. The increment in the percentages of POFA increased the silica/alumina (SiO₂/Al₂O₃) ratio and that resulted in reduction of the early compressive strength of the geopolymer and delayed the geopolymerization process.     

Properties of binary and ternary blended cement mortars containing palm oil fuel ash and metakaolin

Abstract

This paper has investigated the properties of mortars made from binary and ternary blends of metakaolin (MK), palm oil fuel ash (POFA), and ordinary Portland cement (OPC). A total of 17 different mortar mixtures were produced. The OPC in the mixtures was partially replaced by MK, POFA, or a combination of MK and POFA at different replacement levels of (0–30%) by weight of the binder. At the fresh state, the flow (workability) of mortar mixtures was determined, while at the hardened state, the compressive strength and porosity at the ages of 7, 28, and 90 days were evaluated. The results showed that the flow of mortar is boosted with the combined use of MK and POFA compared to when MK is separately used. Besides, improvement in low early compressive strength development and reduction in high porosity from use of POFA occurred with the addition of up to 10% MK content. Therefore, the combination of POFA and MK could be used as a supplementary cementitious material to produce cement-based material of higher quality than OPC.     

Shrinkage and strength of alkaline activated ground steel slag/ultrafine palm oil fuel ash pastes and mortars

This study evaluated the contributions of steel slag and activators ratio to the shrinkage of the alkali-activated ground steel slag (G)/ultrafine palm oil fuel ash (U) or AAGU pastes and mortars. The base materials were combined such that G/U+G varied from 0 to 0.8 (pastes) and 0–0.6 (mortars) with the use of 10M-NaOH_aq and Na₂SiO_3aq (Ms = SiO₂/Na₂O of 3.3) as activators whose ratios (Na₂SiO_3aq/10M NaOH_aq) were varied as 1.0/1.0 and 2.5/1.0. The findings revealed that steel slag reduced the AAGU shrinkage through pore-refinement, elimination of microcracks, and improvement in the microstructural density and strength. The changing of Na₂SiO₃/10NaOH ratio in the synthesis of AAGU products from 2.5 to 1.0 slightly reduced the shrinkage through the modification of amorphousity and nature of the products (C-A-S-H/C-S-H). The maximum 90-day slag-free AAGU paste and mortar shrinkages were 60.80 × 10³ με and 11.82 × 10³ με but reduced to 25.88 × 10³ and 2.71 × 10³ με, respectively as G/(U+G) = 0.4 in AAGU_0.4.     

拉应力对玻璃纤维增强聚合物基复合材料介电强度的影响

在拉应力条件下, 测试了聚合物基体和单向玻璃纤维增强聚合物基复合材料的介电强度, 探索了聚合物基体和玻璃纤维/聚合物复合材料的介电强度与拉应力的关系, 提出并证明了聚合物基体的介电强度与拉应力呈负指数关系, 复合材料中纤维与基体的界面是影响材料介电强度的主要因素。     

Influence of treated palm oil fuel ash on compressive properties and chloride resistance of engineered cementitious composites

The influence of palm oil fuel ash (POFA) inclusion on the compressive properties and chloride resistance of engineered cementitious composites (ECC) were experimentally investigated. In the material development, pozzolanic reactivity of POFA, direct tensile test and matrix fracture test were performed for evaluating the performance of ECC with POFA. Different ECC mixes with varying POFA content and water–binder ratios were used. The results show that the use of POFA should be helpful for achieving strain-hardening behavior by enhancing the fracture toughness and interfacial bond between matrix and PVA fiber. Moreover, at 28 and 90 days, increasing the POFA/cement ratio up to 0.2 led to an increase in the compressive strength of the ECC. The ECC mix with 1.2 POFA–cement ratio achieved a compressive strength of 30 MPa at 28 days, which is within the normal range of concrete strength for many applications. In addition, the test results show that mechanically pre-loaded POFA–ECC specimens exposed to chloride solution remain durable. The results also indicated strong evidence of self-healing of micro-cracked POFA–ECC specimens, which can still carry considerable flexural load. The rapid chloride permeability test reveal that the total charge passed was gradually reduced with the inclusion of higher amount of POFA. The results presented in this study provide a preliminary database for the durability of cracked and uncracked POFA–ECCs under chloride environment or/and combined mechanical loading.     

热残余应力对考虑微观孔隙碳纤维增强环氧树脂复合材料横向拉伸性能的影响

为研究由于材料固化产生的热残余应力对碳纤维增强环氧树脂复合材料横向拉伸性能预测结果的影响,发展了一种基于摄动算法的纤维和孔洞随机分布代表性体积单元（RVE）生成方法,建立更加接近真实材料微观结构的RVE模型。通过施加周期性边界条件,并赋予组分（纤维、基体和界面）材料本构关系,进而实现温度和机械荷载下模型的热残余应力和损伤失效分析。从结果中发现,材料固化过程会在纤维之间产生残余压应力,在模型孔隙周围产生沿加载方向的残余拉应力。所建立不含孔隙RVE模型的失效均是由于界面脱黏引起,材料固化在纤维之间产生的残余压应力会增加模型的预测强度。含有孔隙的RVE模型失效起始于孔隙周围的基体中,而材料固化在模型孔隙周围产生的热残余拉应力对含孔隙RVE模型预测的失效强度有降低作用。对于具有不同孔隙尺寸的RVE模型,模型的失效强度随着孔隙尺寸的增加而不断降低,但是热残余应力减弱了孔隙尺寸对模型预测结果的降低作用。对于具有不同长宽比椭圆形孔隙的RVE模型,热残余应力增加了孔隙长宽比对模型强度的降低作用。      

孔隙微观特征对碳纤维/环氧树脂复合材料横向拉伸强度的影响

通过有限元方法研究了相同孔隙率下孔隙的分布、尺寸和形状等微观特征对碳纤维增强环氧树脂复合材料单向板横向拉伸强度的影响。首先使用Matlab对复合材料微观图像进行处理,提取孔隙的半径分布。然后通过C++编写多种孔隙随机分布算法,包括可以生成不同分布孔隙、不同尺寸孔隙以及不同形状孔隙的随机分布算法。最后通过Python参数化生成代表性体积单元（RVE）,用有限元方法研究相同孔隙率下孔隙的分布、尺寸和形状对碳纤维/环氧树脂复合材料单向板横向拉伸强度的影响。研究结果显示,孔隙率相同时,碳纤维/环氧树脂复合材料的孔隙形状对横向弹性模量的影响较大,孔隙尺寸和形状对横向拉伸强度有较大的影响。     

PVA短纤维和粉煤灰对地聚合物基复合材料流变学行为和弯曲性能的影响

利用自行研制的活塞式挤压流变仪研究了掺加聚乙烯醇(PVA)短纤维和粉煤灰的地聚合物浆体在挤压过程中的流变学特性,在此基础上通过单轴挤压机成功制备出宽厚比=12.5∶1.0的短纤维增强地聚合物基复合材料。利用MTS电液侍服机系统研究了各种纤维和粉煤灰掺量的地聚合物基复合材料的弯曲行为。采用扫描电镜(SEM)研究了地聚合物基复合材料中纤维的分布、取向、纤维-基体间界面,以及弯曲实验后试样断裂面上的纤维伸出长度、纤维尖端断裂形貌和纤维表面组织,从细观和微观角度探讨各种地聚合物基复合材料微观结构和弯曲破坏机制。结果表明：PVA短纤维的加入改变了地聚合物浆体的破坏模式,由脆性破坏变为延性破坏;对于不掺或掺加少量粉煤灰(≤10%)的地聚合物基复合材料弯曲强度高,但延性小,当粉煤灰的掺加量≥30%时,地聚合物基复合材料的弯曲强度显著下降,但延性增大。     

Effect of surface oxidation treatment on the tribological performance of carbon fiber reinforced polyimide composites

The effect of ozone surface treatment of carbon fibers (CF) on the tensile strength and tribological properties of carbon fiber reinforced polyimide (CF/PI) composite was investigated. Experimental results revealed that the tensile strength of ozone and air oxidation treated CF reinforced PI composite was improved compared with that of untreated composite. Compared with the untreated and air‐oxidated CF/PI composite, the ozone treated composite had the lowest friction coefficient and specific wear rate under given applied load and reciprocating sliding frequency. Ozone treatment effectively improved the interfacial adhesion between CF and PI. The strong interfacial adhesion of the composite made CF not easy to detach from the PI matrix, and prevented the rubbing‐off of PI, accordingly improved the friction and wear properties of the composite.     

石墨表面TiC涂层对高定向石墨/Cu复合材料热导率和抗弯强度的影响

以高温盐浴法对天然鳞片石墨粉体(GF)进行表面TiC镀层处理,然后采用真空热压烧结法制备TiCGF/Cu复合材料,研究了粉体表面涂层和GF体积分数对复合材料微观结构、热导率及抗弯强度的影响。系列测试结果表明:随着GF体积分数的降低以及粉体表面TiC镀层的形成,TiC-GF/Cu复合材料平行于GF片层方向的热导率有所降低,抗弯强度有所提升。其中在GF的体积分数占TiC-GF/Cu复合材料70%时,这种变化最为明显,平行于GF片层方向的TiC-GF/Cu复合材料热导率下降幅度最大,从676W/(m·K)下降到526 W/(m·K)。同时,TiC-GF/Cu复合材料的微观结构进一步说明,GF表面的TiC涂层对GF/Cu复合材料的断裂模型起着重要的作用。     

Influence of boron carbide content on the microstructure,tensile strength and fracture behavior of boron carbide reinforced aluminum metal matrix composites

In the present work, an indigenously developed low cost modified stir casting technique is developed for the processing of 6061 Al‐B₄C composites containing high‐volume fraction of boron carbide particles (up to 20 vol. %). The influence of varying reinforcement content on the spatial distribution of boron carbide in the aluminum matrix is qualitatively characterized using scanning electron microscope. At a lower volume fraction of reinforcement, wide particle free zone and large interparticle spacing were observed in the matrix while the composite with high reinforcement content displayed relatively homogeneous and discrete particle distribution. X‐ray diffraction analysis confirms the presence of only aluminum and boron carbide diffraction peaks, indicating that no significant reaction occurs during composite processing. The tensile behavior of composites revealed that strength and ductility are influenced by varying particulate content. The quantitative analysis of strengthening mechanism in the casted composites showed that higher volume fraction of boron carbide lead to larger values of thermal dislocation strengthening, grain size and strain gradient strengthening. The morphology of fracture surfaces reveals the presence of dimple network and the average size of dimples gradually decreases with the increase in particulate content, which indicates the co‐existence of ductile and brittle fracture.     

Influence of tableting forces and lubricant concentration on the adhesion strength in complex layer tablets

The strength of adhesion in complex two-layer tablets is assessed using statistical methods with respect to the applied tableting forces for the first layer and for applying the second layer on the first, as well as regarding the fraction of the lubricant. These results, obtained on a single-punch tablet press, are compared with the results for three-layer tablets produced on a rotary press at production scale. The strongest negative influence on adhesion strength was exerted by the amount of lubricant in the central layer. As expected, compression forces for central-layer tableting also had a negative effect, whereas the compression forces for complex layer tableting exerted a positive effect on layer adhesion. The validity of the derived model equation was proved by experiments: It was shown that the adhesion strength in complex layer tablets produced in production scale can be predicted from laboratory-scale experiments. This makes optimization of the formulation and parameter settings at an early stage of development possible.