A review of the hardened mechanical properties of self-compacting concrete

Data from more than 70 recent studies on the hardened mechanical properties of self-compacting concrete (SCC) have been analysed and correlated to produce comparisons with the properties of equivalent strength normally vibrated concrete (NVC).The significant scatter obtained in much of the data is a consequence of the wide range of materials and mixes used for SCC, but clear relationships have been obtained between cylinder and cube compressive strength, tensile and compressive strengths, and elastic modulus and compressive strength. It is also clear that limestone powder, a common addition to SCC mixes, makes a substantial contribution to strength gain.Bond strength of SCC to reinforcing and prestressing steel is similar to or higher than that of normally vibrated concrete. Variation of in situ properties in structural elements cast with SCC is similar to that with NVC, and the performance of the structural elements is largely as predicted by the measured material properties.The analysis has shown that sufficient data have been obtained to give confidence in the general behaviour of SCC, and future studies need only be focused on specific or confirmatory data for particular applications.     

Use of rice husk ash in sandcrete blocks for masonry units

Different mix proportions of sand, cement and rice husk ash (RHA) were studied for use in sandcrete blocks. Optimum water/(cement+RHA) ratios were determined at different mix proportions. Compressive strengths of various mix proportions at 7, 28 and 60 days were also determined. The optimum water/(cement+RHA) ratio increased with rice husk ash contents. Test results showed that up to 40% RHA could be added as a partial replacement for cement without any significant change in compressive strength at 60 days. Compressive strengths of various mix proportions were compared with British Statutory minimum compressive strengths of bricks for various walls and it was found that sandcrete blocks of 1∶5 mortar mixes with 40% RHA (by weight of cement) could be used in both load and non-load bearing walls.     

Effect of coarse aggregate blending on short-term mechanical properties of self compacting concrete

This investigation is mainly focused on finding the unit weight, compressive strength, modulus of elasticity (MOE) and splitting tensile strength (STS) of SCC mixes with different coarse aggregate blending (60:40 and 40:60) (20 mm and 10 mm) and coarse aggregate content (28% and 32%) and these properties were compared to a conventional concrete (CC). All SCC mixes had 35% replacement of cement with class F fly ash. The coarse aggregate blending did not affect the compressive strength of SCC mixes, but it affected the unit weight, MOE and STS of SCC mixes. A new parameter called coarse aggregate points (CAPs) has been introduced to study the effect of coarse aggregate blending in a particular coarse aggregate content on mechanical properties of SCC mixes. It is observed that for the given strength, SCC mixes with the same CAP value have shown similar mechanical properties. The measured MOE of all mixes were compared with ACI 363R and AASHTO LRFD/ACI 318 predicted equations. The measured STS of all mixes were compared with ACI 363R and CEB-FIP predicted equations.     

相关向量机及其在机械故障诊断中的应用研究进展

相关向量机是一种基于贝叶斯稀疏理论的新型机器学习算法,近年来被应用于多个行业,并得到了国内外学者的不断关注和研究,然而在机械故障诊断领域还未得到足够的重视。简述了相关向量机的特点,通过与支持向量机相比较,阐述了相关向量机的优缺点,综述和分析了近年来相关向量机的国内外研究现状,重点关注相关向量机在机械设备状态监测与故障诊断领域的研究进展。在此基础上,分析了相关向量机研究所存在的一些问题,并展望了相关向量机在机械故障诊断领域应用的未来方向。     

A double-loop relevant vector machine-based system reliability analysis method with Meta-IS idea and active learning strategy

This paper proposes a double-loop relevant vector machine (RVM) model for system reliability analysis. To reduce the computational load, an adaptive RVM is constructed, which is built by minority initial samples and K-folds clustering. The candidate sample pool constructed by this rough adaptive RVM model improves the computational efficiency. Based on the idea of active learning, another adaptive RVM is established. By combining two adaptive RVMs, the proposed model has the advantages of both active learning and importance sampling, which is called DLRVM. In this model, the failure probability is expressed as a product of the augmented failure probability and the correction factor. From the characteristics of RVM, this model under the Bayesian framework has significant generalization ability which avoids the limitations of many machine learning models. The accuracy and high efficiency are verified via four academic examples and an implicit engineering problem. The results also indicate that RVM is appropriate for system reliability analysis.     

Properties of self-compacting concrete prepared with recycled glass aggregate

The effects of recycled glass (RG) cullet on fresh and hardened properties of self-compacting concrete (SCC) were investigated. RG was used to replace river sand (in proportions of 10%, 20% and 30%), and 10 mm granite (5%, 10% and 15%) in making the SCC concrete mixes. Fly ash was used in the concrete mixes to suppress the potential alkali-silica reaction. The experimental results showed that the slump flow, blocking ratio, air content of the RG–SCC mixes increased with increasing recycled glass content. The compressive strength, tensile splitting strength and static modulus of elasticity of the RG–SCC mixes were decreased with an increase in recycled glass aggregate content. Moreover, the resistance to chloride ion penetration increased and the drying shrinkage of the RG–SCC mixes decreased when the recycled glass content increased. The results showed that it is feasible to produce SCC with recycled glass cullet.     

Signal compensation of AC MMW radiometer based on DCT and RVM

针对交流毫米波辐射信号丢失部分低频分量的缺陷,使用RVM算法在交流毫米波辐射信号的DCT变换域补偿出丢失的成分,再通过IDCT变换即可获得补偿的交流毫米波辐射信号。RVM使用贝叶斯方法推理,推广能力好,与支持向量机相比解更为稀疏,这些保证了RVM算法具有良好的预测能力。实验结果也显示本方法可以获得良好的补偿效果。     

Design of clay/cement mixtures for extruded building products

In this work, ternary mixes of sand, cement and kaolin are studied in order to design extruded building products with reduced environmental impact. Firstly, the amount of water required to reach the extrusion rheological criterion and the immersed mechanical strength are studied. Results lead to a compressive strength prediction tool (derived from Feret model) which provides the compressive strength of a given ternary mix. Then, the dimensional and immersion stabilities of ternary mixes are studied. It shows that for mixes containing more kaolin volume than cement volume, mechanical strength is largely influenced by the saturation state. Finally, collected data show that cement stabilized clay blocks and high content cement substitution concrete can be designed with clay/cement mixes.     

Modified water/cement ratio law for compressive strength of fly ash concretes

Experimental data are presented which suggest that the development of compressive strength of fly ash concretes can be explained by superposition of two independent mechanical pore-filling mechanisms in the cement—fly ash paste. It is also suggested that the traditional water/cement ratio law for ordinary Portland cement concretes can be applied to fly ash concretes, provided that a slight modification is introduced. This will be of assistance in the design of fly ash concrete mixes for compressive strength.     

Influence of curing time on the chloride penetration resistance of concrete containing rice husk ash: A technical and economical feasibility study

This study investigates the influence of the curing time on the chloride penetration behavior of concrete produced with different concentrations of rice husk ash. Compressive strength and chloride penetration at 91 days were assessed according to ASTM C1202. Concentrations of 10%, 20% and 30% of rice husk ash were used and the results were compared with a reference mix with 100% Portland cement and with two other binary mixes with 35% fly ash and 50% ground blast furnace slag. Increases in rice husk ash content produced lower Coulomb charge values. Longer curing times reduced Coulomb charges values for all mixes investigated. However, the extent of the effect of curing times on compressive strength and chloride penetration in concrete is related to the type of mineral addition, the concentration of the substitutions used, the w/b ratio and the curing time used. This behavior points at an optimal curing period for each type of binder to meet specific technical and economical criteria, namely durability and compressive strength specifications for the structure.     

Experimental and analytical study on fiber-kinking failure mode of laminated composites

Compressive behavior of composite materials has received significant attention in recent years. In the present work, a recently developed strain based fiber kinking model and stress based ones for unidirectional laminated composites are compared with experimental results. These models are implemented into a finite element code and the obtained results for glass/epoxy (Type C) ASNA 4197 unidirectional composites are presented and discussed in detail. Experimental investigations on compressive strength and kink band formation were also performed for several specimens with various dimensions and off-axis angles made of the same glass/epoxy prepreg composite material. A special compressive fixture was also fabricated in order to ensure that the specimens are in full contact with the loading machine elements and also to eliminate the potential bending moments.Comparison between the experimental and analytical results indicated that the proposed fiber kinking model and the developed code can be used to predict the compressive strength of laminated composites due to fiber kinking mode.     

Genetic algorithm-least squares support vector regression based predicting and optimizing model on carbon fiber composite integrated conductivity

Support vector machine (SVM), which is a new technology solving classification and regression, has been widely used in many fields. In this study, based on the integrated conductivity(including conductivity and tensile strength) data obtained by carbon fiber/ABS resin matrix composites experiment, a predicting and optimizing model using genetic algorithm-least squares support vector regression (GA-LSSVR) was developed. In this model, genetic algorithm (GA) was used to select and optimize parameters. The predicting results agreed with the experimental data well. By comparing with principal component analysis-genetic back propagation neural network (PCA-GABPNN) predicting model, it is found that GA-LSSVR model has demonstrated superior prediction and generalization performance in view of small sample size problem. Finally, an optimized district of performance parameters was obtained and verified by experiments. It concludes that GA-LSSVR modeling method provides a new promising theoretical method for material design.     

Compressive strength and chloride resistance of self-compacting concrete containing high level fly ash and silica fume

The influence of high-calcium fly ash and silica fume as a binary and ternary blended cement on compressive strength and chloride resistance of self-compacting concrete (SCC) were investigated in this study. High-calcium fly ash (40–70%) and silica fume (0–10%) were used to replace part of cement at 50, 60 and 70 wt.%. Compressive strength, density, volume of permeable pore space (voids) and water absorption of SCC were investigated. The total charge passed in coulombs was assessed in order to determine chloride resistance of SCC. The results show that binary blended cement with high level fly ash generally reduced the compressive strength of SCC at all test ages (3, 7, 28 and 90 days). However, ternary blended cement with fly ash and silica fume gained higher compressive strength after 7 days when compared to binary blended fly ash cement at the same replacement level. The compressive strength more than 60 MPa (high strength concrete) can be obtained when using high-calcium fly ash and silica fume as ternary blended cement. Fly ash decreased the charge passed of SCC and tends to decrease with increasing fly ash content, although the volume of permeable pore space (voids) and water absorption of SCC were increased. In addition when compared to binary blended cement at the same replacement level, the charge passed of SCC that containing ternary blended cement was lower than binary blended cement with fly ash only. This indicated that fly ash and silica fume can improve chloride resistance of SCC at high volume content of Portland cement replacement.     

Filling ability and plastic settlement of self-compacting concrete

The use of self-compacting concrete (SCC) facilitates the placing of concrete by eliminating the need for compaction by vibration. Given the highly flowable nature of such concrete, care is required to ensure excellent filling ability and adequate stability. This is especially important in deep structural members and wall clements where concrete can block the flow, segregate and exhibit bleeding and settlement which can result in local defects that can reduce mechanical properties, durability and quality of surface finish.This paper shows results of an investigation of fresh properties of self-compacting concrete, such as filling ability measured by slump flow and flow time (measured by Orimet) and plastic fresh settlement measured in a columin. The SCC mixes incorporated various combinations of fine inorganic powders and admixtures. The slump flow of all SCCs was greater than 580 mm and the time in which the slumping concrete reached 500 mm was less than 3 s. The flow time was less than 5 s. The results on SCCs were compared to a control mix. The compressive strength and splitting tensile strength of SCCs were also measured.The effects of water/powder ratio, slump and nature of the sand on the fresh settlement were also evaluated. The volume of coarse aggregate and the dosage of superplasticizer were kept constant. It can be concluded that the settlement of fresh self-compacting concrete increased with the increase in water/powder ratio and slump. The nature of sand influenced the maximum settlement.     

基于滑动平均与相关向量机的齿轮早期故障智能诊断

早期故障及时检测与预防维护具有很大的经济与安全意义,提出一种基于相关向量机(RVM)的智能故障诊断方法用于检测齿轮早期故障。首先,小波包变换与Fisher准则结合,自动确定最优分解层次,并在小波包树节点能量中提取出具有最大分类能力的全局最优特征;其次,RVM用于训练故障诊断模型;最后,在线监控过程中,对连续监测的特征值做滑动平均滤波,再输入到故障诊断模型。实验表明,该方法具有很高的分类精度,RVM模型比SVM模型更适合在线故障监测。     

Pseudo NLP Joint Spam Classification Technique for Big Data Cluster

Spam mail classification considered complex and error-prone task in the distributed computing environment. There are various available spam mail classification approaches such as the naive Bayesian classifier, logistic regression and support vector machine and decision tree, recursive neural network, and long short-term memory algorithms. However, they do not consider the document when analyzing spam mail content. These approaches use the bag-of-words method, which analyzes a large amount of text data and classifies features with the help of term frequency-inverse document frequency. Because there are many words in a document, these approaches consume a massive amount of resources and become infeasible when performing classification on multiple associated mail documents together. Thus, spam mail is not classified fully, and these approaches remain with loopholes. Thus, we propose a term frequency topic inverse document frequency model that considers the meaning of text data in a larger semantic unit by applying weights based on the document’s topic. Moreover, the proposed approach reduces the scarcity problem through a frequency topic-inverse document frequency in singular value decomposition model. Our proposed approach also reduces the dimensionality, which ultimately increases the strength of document classification. Experimental evaluations show that the proposed approach classifies spam mail documents with higher accuracy using individual document-independent processing computation. Comparative evaluations show that the proposed approach performs better than the logistic regression model in the distributed computing environment, with higher document word frequencies of 97.05%, 99.17% and 96.59%.     

Mechanical and durability properties of ternary concretes containing silica fume and low reactivity blast furnace slag

In this study, the effect of incorporation of silica fume in enhancing strength development rate and durability characteristics of binary concretes containing a low reactivity slag has been investigated. Binary concretes studied included mixes containing slag at cement replacement levels of 15%, 30% and 50% and mixes containing silica fume at cement replacement levels of 2.5%, 5%, 7.5% and 10%. Ternary concretes included combinations of silica fume and slag at various cement replacement levels. The w/b ratio and total cementitious materials content were kept constant for all mixes at 0.38 and 420 kg/m³ respectively. Concrete mixes were evaluated for compressive strength, electrical resistance, chloride permeability (ASTM C1202 RCPT test) and chloride migration (AASHTO TP64 RCMT test), at various ages up to 180 days.The results show that simultaneous use of silica fume has only a moderate effect in improving the slow rate of strength gain of binary mixes containing low reactivity slag. However it improves their durability considerably. Using appropriate combination of low reactivity slag and silica fume, it is possible to obtain ternary mixes with 28 day strength comparable to the control mix and improve durability particularly in the long term. Ternary mixes also have the added advantage of reduced water demand.     

Long-term strength development of concrete in arid conditions

A long-term investigation into the development of the compressive strength of various concretes, subjected to Kuwait hot and arid environmental conditions is reported. The main parameters investigated included, w/c ratio, cement type and content, and admixture type and its dosage. Other parameters investigated included the effects of using different water curing periods, curing compounds, and casting season. Forty-seven different mixes were placed on the roof of the laboratory building and were exposed to the environment. Compression tests on 100 mm cubes were carried out over a period in excess of five years.The results generally showed that the compressive strength of the concrete increased with age. The gain in strength at 1800 days above that at 28 days varied considerably depending on the concrete constituents and curing procedure. Concretes made with white Portland cement achieved higher compressive strengths than those made with ordinary or sulphate resisting Portland cements. Also, the type and dosage of admixture influenced the compressive strength of concrete. An increase in the water-curing period was more effective in improving the 28-day compressive strength than the 1800-day strength. The use of curing compounds or silica fume appeared to influence the early age strength more than the long-term strength. Compression test results from selected mixes at the age of 10 years indicated that there was little or no increase in strength during the previous five years.     

自密实再生块体混凝土直剪性能试验研究

对29个尺寸为300 mm×300 mm×600 mm的自密实再生块体混凝土棱柱体试件开展直剪性能和单轴受压性能试验研究。探讨了废旧混凝土块体取代率及特征尺寸对自密实再生块体混凝土的直剪强度、抗压强度的影响,并进一步分析了自密实再生块体混凝土棱柱体的直剪强度与抗压强度之间的关系。试验表明:自密实再生块体混凝土内新混凝土与废旧混凝土粘结良好;当自密实再生块体混凝土中的自密实混凝土强度高于废旧混凝土块体强度时,试件的直剪性能会由于废旧混凝土块体的取代率的增加而劣化;特征尺寸比介于0.22~0.44时,块体的特征尺寸对自密实再生块体混凝土直剪强度和抗压强度的影响不明显,可以近似忽略;自密实再生块体混凝土的剪压比随废旧混凝土块体取代率和特征尺寸均无显著变化,其值近似为0.1。基于试验结果,提出了棱柱体自密实再生块体混凝土试件的直剪强度计算公式,建立了直剪强度测试值与抗压强度计算值之间的关系,计算结果与试验值吻合良好。     

Optimal water/cement ratios and strength characteristics of some local clay soils stabilized with cement

Two clay deposits from Lagos in Nigeria were used to develop cement-stabilized blocks. Crushing strengths were determined at the optimum water/cement ratios for different cement/clay-soil mixes which ranged from 5∶1 to 1∶15. The optimal cube crushing strength (Y ₂) decreased with increasing water/cement ratio (X) in a power relation as follows: Oregun Soil:Y ₂=16,329.29X ^?0.147. Alausa Soil:Y ₂=6,307.42X ^?0.580. Over 80% of the cube strength was developed by the fourteenth day (100% at 28 days). A comparison of the results with those of the British Statutory Minimum Compressive strength in bricks for various walls showed that the cement/clay soil mixes may be used for both load and non-load bearing walls of one or two storey houses.