Alkali activation of a slag at ambient and elevated temperatures

Strength development of alkali activated slag (AAS) mortars, activated using alkali hydroxide and sodium silicate, was investigated at room and elevated temperatures. Heat evolution at room temperature was measured using isothermal calorimetry. Important differences were observed between critical activation parameters. Heat cured specimens gain strength rapidly, humid oven conditions being favorable, but given sufficient time room temperature curing yields comparable strengths. Both activators are needed for high strength at room temperature, NaOH solution is more critical and its concentration greatly influences strength. At 80 °C however, sodium silicate is essential and even sufficient. KOH is more effective than NaOH at 80 °C, but not at room temperature. Lower water-to-slag ratios give higher strength at early ages. AAS hydration evolves less heat than Portland cement hydration. Time to significant strength gain of mixtures can be predicted using their time and heat evolution at setting. Twenty eight-day strength of AAS mortars is roughly related to total evolved heat and increases nearly linearly with the amount of NaOH activator for fixed water glass content.     

Gas-storage ice grown from water containing microbubbles

Gas-storage ice is the ice that contains various functional gas pores, and can be produced by freezing water in which a desired gas is dissolved. In this conventional method, however, the gas content in the ice is limited by the gas solubility in water. To overcome this limitation, we developed a method to produce gas-storage ice from water in which microbubbles of a desired gas are dispersed, and then obtained images of the structural features of pores formed in the ice prepared using this microbubble method. The images clarified the interaction between a microbubble arriving at an ice–water interface and an existing pore already formed in the ice. The air content in ice prepared using the microbubble method was higher than that prepared using the conventional method, and was about three times higher than the solubility of air in water.     

不同含水率混凝土遭受常温至-190℃间冻融循环作用的抗压强度试验研究

通过不同含水率混凝土的常温至-190℃间冻融循环作用试验,探讨混凝土含水率对其超低温冻融循环作用下的受力性能影响。结果表明,不同含水率混凝土的受力性能存在明显差异。经历超低温冻融循环作用的混凝土抗压强度随其含水率的增大,上下限温度时均逐渐提高。但随冻融循环作用次数的增加,上限温度时总是呈减小态势,而下限温度时则与之完全不同、且与混凝土含水率密切相关。其超低温相对抗压强度增量随混凝土含水率的变化趋势,与未经历冻融循环作用时相同但相比均较大。依据试验与已有的研究结果,给出的经历超低温冻融循环作用的混凝土相对抗压强度增量拟合公式可用于液化天然气储罐类的超低温混凝土结构设计。     

Pore structure of mortars with cellulose ether additions – Mercury intrusion porosimetry study

In this study, multi-cycle mercury intrusion porosimetry (MIP) was employed to study the pore structure of model tile adhesive mortars containing different types (Methyl Cellulose, Hydroxyethyl- and Hydroxypropyl-Methyl Cellulose) and different dosages (0.3%, 0.8%) of cellulose ethers (CE). The two cycles of mercury intrusion and extrusion allowed resolving not only the total porosity of the mortar, but also the interconnected porosity of the matrix. Different application scenarios were tested: application on a substrate with no water absorption (plastic mold), on a moderately absorbing substrate (cement–fiber board) and on a substrate with high absorption (concrete slabs). These conditions allowed for determining the influence of different moisture regimes on the pore structure of the mortars. Finally, tensile adhesion strength tests with different open times were performed. It was observed that the addition of CE did not considerably affect the capillary and gel pores of the matrix. At the same time, it led to a substantial increase of the total porosity due to the entrainment of air, with slightly increasing size of entrained air voids at higher CE addition rates. A very pronounced coarsening of the porosity could be observed when mortars where applied on a substrate with high water absorption. An improvement in tensile adhesion strength respect to the reference mortar was observed thanks to CE addition, in particular for longer open times.     

Impurity and surface condition effects on pore formation at Al2O3/FeAl interfaces

Abstract

Interfacial pores are commonly observed at the scale/alloy interface in NiAl and FeAl alloys after high temperature oxidation. The pores are often an order of magnitude larger than the oxide grains, and many are formed during the initial stage of oxidation. In order to better understand the development of these pores, the effects of pre-oxidation surface condition and surface impurities on pore formation at the oxide/alloy interface in Fe–40at%Al are investigated. Surface conditions included polishing to 4000 grit with SiC and polishing to 1 µm with diamond suspension. Surface impurities included a number of nitrate salts dissolved in water. Pore number distribution in each case was determined and related to the treatment effects. Testing was also performed on an Hf-containing Fe–40Al to evaluate the effect of adding a reactive element. It was found that surface roughness and the presence of impurities, even residues from water drops, increased the number of interfacial pores. Hf addition made the alloy more resistant to pore formation, but large pores developed under heavy salt deposits.     

Electron microscopy of oxidized silicon nitride

The effect of oxidation at 1000 and 1400° C on the internal structure of reaction sintered silicon nitride has been examined by high voltage electron microscopy. The formation of a sheath region of amorphous silica around internal pores has been observed after oxidation at both temperatures. The frequency of occurrence of these regions is higher after oxidation at 1000° C, which is consistent with weight gain experiments. The effects of oxidation on strength are discussed. The main effect of the amorphous silica regions is probably in founding off internal pores, effectively increasing the surface energy and so increasing strength. Another factor is the formation at 1000 and 1400° C of an oxidized surface layer (containing crystalline silica) [1, 2] leading to an increase in room temperature strength after oxidation at 1000° C. Removal of this layer produces a further increase in strength (∼15%) showing that the oxidation has a greater beneficial effect on the internal structure.     

SiO2/环氧树脂基纳米复合材料的室温和低温力学性能

利用溶胶-凝胶法制备了SiO₂/环氧树脂基复合材料,研究了材料的室温与低温(77 K)下的力学性能。结果表明,适量SiO₂的引入提高了室温与低温下材料的拉伸强度、断裂伸长率和冲击强度,即SiO₂含量在2%时可同时起到增强、增韧作用。采用扫描电镜(SEM)和透射电镜 (TEM)分别对复合材料的断口形貌和高温焚烧后残留物纳米颗粒进行了观察。还利用动态力学分析(DMA)研究了二氧化硅的引入对复合材料的影响。      

Effect of aggregates and water contents on the properties of magnesium phospho-silicate cement

Properties of magnesium phospho-silicate cement (MPSC) mortars with different fine aggregates, and different water contents were investigated in the present work. Three types of fine aggregates, natural sand, dead burnt magnesia and alumina particles were used. Two types of hard burnt magnesia powder with MgO content 89.51 and 71.50 wt.% were used as binder. Compressive strength of MPSC mortar with different water/binder ratios were determined at ages of 1, 3, 7, and 24 h. The 3, 7, and 28 day compressive strength and modulus of elasticity were also tested. It was found that the compressive strength of MPSC mortar decreases with the increase of sand content, regardless of sand type. However, the strength reduction of MPSC mortars formed with magnesia and alumina sand was much smaller than that of mortars formed with natural sand. Moreover, in spite of the raw materials, compressive strength and elastic modulus of MPSC decreased with the increase of water/binder ratio at all ages. The hydrate products were analysed by XRD and TG-DTA, and the porosity of MPSC mortar was analysed by MIP. Results showed total porosity increased with the increase of water content. The content of hydrate product of MPSC, phosphate hexahydrate, also increased with the increase of water content. However, it seems that the change of mechanical properties of MPSC is mainly controlled by increase of total porosity which was determined by water content.     

Influence of cement kiln dust on the physical properties of calcium lime mortars

This work investigates the influence of cement kiln dust (CKD) on the properties of mortars made with a non-hydraulic binder of high available-lime content (calcium lime—CL), in order to further recycle industrial waste. Physical properties of CKD-CL90 mortars with increasing CKD content were compared to those of feebly-hydraulic lime (NHL2) and CL90 mortars. This paper concludes that, despite the CKD in this study being partially inert, the abundant reactive, free lime provided by the CL90 binder has enabled formation of hydration products. The strength development, rising proportionally to the amount of CKD when addition is over 5%, and the reduction in porosity/suction of the CKD/CL90 mixes, support the occurrence of hydraulic set. The high alkalinity of the CKD/CL90 system; the high specific surface of the CKD particles and the presence of amorphous reactive silica further support the presence of hydraulic set. Results evidenced that CKD addition significantly increased the mortar’s water demand simultaneously enhancing compressive strength and bulk density, and decreasing porosity and capillary suction. These effects can be ascribed to both the gain of packing density induced by the CKD particles, and the formation of hydration phases within pores and the space originally filled with water. Finally, this work concludes that the physical properties of CKD/CL mortars including at least 20%CKD are comparable to those of feebly hydraulic lime mixes, however, fracturing by shrinkage (due to high water demand) and damage related to sulphur, chlorine and alkali content need to be investigated before CKD/CL mixes are advised for application.     

脱硫石膏对大掺量粉煤灰-矿渣粉干混砂浆性能的影响

针对大掺量粉煤灰、矿渣粉导致干混砂浆早期强度和后期强度较低的问题,研究脱硫石膏对该干混砂浆性能的影响;采用X射线衍射、扫描电镜及孔结构分析等手段进行微观机理讨论。结果表明,在大掺量粉煤灰矿粉干混砂浆中掺加占胶凝材料总质量6%～8%的脱硫石膏,对和易性无不良影响,并可显著提高浆体的抗压强度及拉伸粘结强度,收缩率降低10%以上,并改善抗碳化能力,使砂浆体积更稳定;脱硫石膏对粉煤灰及矿渣粉起到激发硫酸盐和碱性的双重作用,并在一定程度上促进水泥水化;胶凝材料的水化产物改善砂浆浆体内部结构,使砂浆浆体中的孔隙大大减少。     

Camphene-based freeze-cast ZrO2 foam with high compressive strength

Highly porous zirconia ceramic bodies with interconnected pores were fabricated by freeze-casting technique using camphene-based slurries. The pore volume fraction and pore size are controllable by adjusting the initial solid content in the mixed slurries. The pores are replicas of connected dendrites of frozen camphene, which sublimed during room temperature drying. As the solid content was increased from 10 to 20 vol.%, the compressive strength was significantly increased from 19 ± 2 to 58 ± 3 MPa, and the examined porosity was decreased from 81.5 to 66.5%. This technique is considered potentially useful in producing novel porous ceramics, and introduces a new application field of freeze-casting.     

二元Al-Li合金的低温力学性能

本文研究了纯 Al,Al-ILi 和 Al-2.5Li 合金力学性能与实验温度的关系。结果表明,这些合金在低温下有很显著的增强增韧现象,但屈服强度变化较小,加工硬化能力显著提高;时效温度与 Al-2.5Li 合金低温力学性能改善无关,低温断裂前比室温时需经历更大的形变。     

Effect of fly ash fineness on compressive strength and pore size of blended cement paste

This paper presents an experimental investigation on the effect of fly ash fineness on compressive strength, porosity, and pore size distribution of hardened cement pastes. Class F fly ash with two fineness, an original fly ash and a classified fly ash, with median particle size of 19.1 and 6.4 μm respectively were used to partially replace portland cement at 0%, 20%, and 40% by weight. The water to binder ratio (w/b) of 0.35 was used for all the blended cement paste mixes.Test results indicated that the blended cement paste with classified fly ash produced paste with higher compressive strength than that with original fly ash. The porosity and pore size of blended cement paste was significantly affected by the replacement of fly ash and its fineness. The replacement of portland cement by original fly ash increased the porosity but decreased the average pore size of the paste. The measured gel porosity (5.7–10 nm) increased with an increase in the fly ash content. The incorporation of classified fly ash decreased the porosity and average pore size of the paste as compared to that with ordinary fly ash. The total porosity and capillary pores decreased while the gel pore increased as a result of the addition of finer fly ash at all replacement levels.     

Performance of blended metakaolin/blastfurnace slag alkali-activated mortars

This paper studies the effect of silicate content on the mechanical and durability-related properties of metakaolin (MK) and metakaolin/blastfurnace slag (BFS) alkaline activated mortars. A reference mortar based on the alkaline activated MK was compared to 60/40 MK/BFS mortars containing different SiO₂/Na₂O molar ratios in the activator. The properties assessed were compressive strength, porosity (water saturation), porosity and pore size distribution by Mercury Intrusion Porosimetry (MIP) and water capillary sorption. The microstructure was assessed using SEM and x-ray computerized micro-tomography (μ-CT). Results show that the addition of BFS significantly alters the microstructure of alkali-activated mortars, promoting a reduction of porosity and capillary sorption. In addition, an optimum SiO₂/Na₂O molar ratio in the activator is required to produce better durability mortars, which however do not necessarily present the highest mechanical strength.     

二氧化硅/ 聚酰亚胺纳米杂化薄膜室温及低温力学性能

利用溶胶-凝胶技术制备了不同SiO₂ 含量的二氧化硅/ 聚酰亚胺(SiO₂ / PI) 纳米杂化薄膜。采用红外光谱( IR) 和扫描电镜(SEM) 手段对该体系的分子结构和断裂形貌进行了表征, 研究了聚酰亚胺薄膜室温和低温(77K) 力学性能。结果表明: 室温和低温(77 K) 下, SiO₂ / PI 杂化薄膜的拉伸强度开始时均随SiO₂ 含量的增加而增加, 在含量为3 %时达到最大值, 低温下杂化薄膜的拉伸强度明显高于室温。室温下, 杂化薄膜的断裂伸长率在含量为3 %时达到最大值, 而低温(77 K) 下, 薄膜的断裂伸长率的变化没有呈现明显的规律性。      

Mechanical Properties of Solid‐Sintered Porous Silicon Carbide Ceramics

The freeze‐drying combining solid sintering is a good method to fabricate porous SiC ceramics with good high temperature mechanical properties. Though SiC ceramics are sintered at a high temperature of 2150 °C, there are still large quantity of macropores generated by sublimating large ice crystals and micropores in the ceramic wall caused by small ice crystals sublimating, SiC particles stacking, and burning out of polyvinyl alcohol (PVA). The content of PVA affects the microstructure and strength. As increasing the content of PVA, the size of pores caused by sublimating the ice crystals decreases while both open porosity and room temperature strength increase. After being treated at a temperature of 1200 and 1500 °C, the ceramics exhibit good thermal shock damage resistance.     

混合型固化剂对环氧树脂室温和低温力学性能的影响

研究了一种刚性和柔性胺混合型固化剂（芳香胺DETD和聚醚胺D-400）固化环氧树脂浇铸体的力学性能、材料断裂表面的微观形貌和玻璃化转变温度等性能。结果表明:当D-400加入量占固化剂总量的40%时,其室温拉伸强度呈现最大值,为82.52 MPa,弹性模量为2.30 GPa,与未加D-400的体系相比分别提高了6.3%和14.4%,其低温冲击强度提高了14%。对冲击断面形貌进行扫描电子显微分析表明:D-400的加入致使断口形貌变得粗糙,抗开裂能力得到提高。热分析实验结果显示,体系的玻璃化转变温度随着D-400含量的增加而降低。此外,还探讨了环氧树脂体系低温增韧机制。      

Durability of class C fly ash belite cement in simulated sodium chloride radioactive liquid waste: influence of temperature

This work is a continuation of a previous durability study of class C fly ash belite cement (FABC-2-W) in simulated radioactive liquid waste (SRLW) that is very rich in sulphate salts. The same experimental methodology was applied in the present case, but with a SRLW rich in sodium chloride. The study was carried out by testing the flexural strength of mortars immersed in simulated radioactive liquid waste that was rich in chloride (0.5M), and demineralised water as a reference, at 20 and 40 degrees C over a period of 180 days. The reaction mechanism of chloride ions with the mortar was evaluated by scanning electron microscopy (SEM), porosity and pore-size distribution, and X-ray diffraction (XRD). The results showed that the FABC mortar was stable against simulated chloride radioactive liquid waste (SCRLW) attack at the two chosen temperatures. The enhancement of mechanical properties was a result of the formation of non-expansive Friedel's salt inside the pores; accordingly, the microstructure was refined.     

Resistance of class C fly ash belite cement to simulated sodium sulphate radioactive liquid waste attack

The resistance of class C fly ash belite cement (FABC-2-W) to concentrated sodium sulphate salts associated with low level wastes (LLW) and medium level wastes (MLW) is discussed. This study was carried out according to the Koch and Steinegger methodology by testing the flexural strength of mortars immersed in simulated radioactive liquid waste rich in sulphate (48,000 ppm) and demineralised water (used as a reference), at 20 degrees C and 40 degrees C over a period of 180 days. The reaction mechanisms of sulphate ion with the mortar was carried out through a microstructure study, which included the use of Scanning electron microscopy (SEM), porosity and pore-size distribution and X-ray diffraction (XRD). The results showed that the FABC mortar was stable against simulated sulphate radioactive liquid waste (SSRLW) attack at the two chosen temperatures. The enhancement of mechanical properties was a result of the formation of non-expansive ettringite inside the pores and an alkaline activation of the hydraulic activity of cement promoted by the ingress of sulphate. Accordingly, the microstructure was strongly refined.     

Influence of fired clay brick waste additions on the durability of mortars

The use of metakaolin is known to help improve properties of Portland cement-based mortars. The presumed similarities between the characteristics of metakaolin and those of a powdered (<45 μm) fired clay brick clean waste (CBW) led to the investigation of the effect on the durability of mortars of partial replacement (10, 25 and 40 wt.%) of Portland cement by CBW. Properties such as 28 and 90 days-compressive strength, water absorption, apparent porosity, absorption by capillarity, chloride retention, carbonation depth and sulphate resistance were evaluated. The CBW-containing cured mortars showed improved strength and density, as the result of combined physical and pozzolanic pore filling effect of added CBW. However, CBW-free mortar exhibited larger spreading and, being more porous, higher sulphate resistance and ability to absorb chlorides. Optimum performance was found for the 40 wt.% CBW mortar whose compressive strength can be up to 130% higher than that of the CBW-free mortar.