Prediction of strength parameters of FRP-confined concrete

This research deals with the prediction of compressive strength and crushing strain of FRP-confined concrete using neural networks and regression models. Basic information on neural networks and the types of neural networks most suitable for the analysis of experimental results are given. A set of experimental data, covering a large range of parameters, for the training and testing of neural networks is used. The prediction models based on neural network are presented. The influence of raw and the non-dimensional group of variables on compressive strength and crushing strain of FRP-confined concrete is studied through sensitivity analysis, which provided a basis for the development of a new regression based model. The neural networks based model gave high prediction accuracy and the results demonstrated that the use of neural networks in assessing the compressive strength and crushing strain of FRP-confined concrete is both practical and beneficial.     

Mechanical properties of cement-treated aggregate material – A review

Cement-treated aggregate material (CTAM) is a traditional material applied in road bases and sub-bases. Its mixture proportioning design method applied in the last decades is tentative, time-consuming and cost-effective. There is no advanced technique to design the mixture proportioning of CTAM so far. Therefore, the problem of designing a CTAM mixture is the lack of an effective procedure that allows predicting its mechanical properties from mixture parameters like the mix composition and the characteristics of components. For cement concrete and asphalt concrete such prediction techniques already exist.This paper herein reviews the influence of mixture variables on the mechanical properties of CTAM. These properties include the unconfined compressive strength (UCS), the tensile strength and the elastic modulus. It was found that the UCS is normally taken as an important quality indicator of CTAM. Variables influencing the UCS, such as cement content, curing time, degree of compaction and so on, play different roles to determine the performance of CTAM. Models to predict the tensile strength and the elastic modulus are always correlated to the UCS. Evidence may be given that prediction models for the mechanical properties of CTAM may be established on basis of mixture parameters.     

Production of biopolymer composites by particle bonding

This paper describes a new technology to produce biopolymer composites at room temperature. During the process, micrometer-scale raw material is coated with zein that has strong adhesive property, which is then compressed to form a rigid material. Since this technology does not require purification of the raw materials, various types of compounds can be used as component materials. The coating of particles with zein makes use of the unique property of zein in aqueous ethanol solution. Zein molecules adsorb to the surface of hydrophilic particles when the ethanol content of solvent mixture increases. Formation of aggregates is followed to form large agglomerates. Removal of solvents from the agglomerates yields the final product. Biopolymer composites thus formed showed a broad range of compressive strengths depending on the hardness of the starting raw material used as a base component.     

Synthesis of low-temperature calcium sulfoaluminate-belite cements from industrial wastes and their hydration: Comparative studies between lignite fly ash and bottom ash

The aim of this research was to study the production of calcium sulfoaluminate-belite (CŜAB) cement from industrial waste materials via hydrothermal-calcination process. Lignite fly ash and bottom ash were used as starting materials for comparison. Other waste materials viz., Al-rich sludge and flue gas desulfurization gypsum were also key players in raw mixes for the synthesis of CŜAB cement. For lignite fly ash as a starting material, mixed phases between ye'elimite and larnite were obtained, whereas for lignite bottom ash as starting material, only ye'elimite was obtained The hydration reaction was studied in terms of heat evolution, setting time, compressive strength and hydration product formation with various gypsum contents. The results showed a rapid formation of ettringite as a main hydration product mixed with calcium silicate hydrate, monosulfate and strätlingite phases as minority, with a fast final setting time of 24–26 min and high early compressive strength of 16.0 and 18.0 MPa in 1 day for CŜAB cements made of fly ash and bottom ash, respectively.     

Mathematical model for the prediction of cement compressive strength at the ages of 7 and 28 days within 24 hours

In this study 450 cement mortar cubes were cast from 50 different cement samples taken from 9 different cement factories, to develop a mathematical model that can predict Portland cement compressive strength at ages 7 and 28 days within 24 hours only. This is in order to save time and expense, that is lost in waiting for such a long period, and for quality control assurance for both produced cement (in cement factories), and concrete mixes in constructions. In addition, attention has been made on the right choice of variables of the cement itself (phase composition and fineness). In addition, an attempt has been made to use other variables that are believed to affect compressive strength of Portland cement as the minor oxides MgO, SO₃ and soundness. Other variables obtained from chemical analysis of the cement as LOI, IR, and LSF were also included in the model. The most important thing in this study is to get use of the concept of using early age strength to predict Portland cement strength at later ages for the first time. An attempt was made to combine both accelerated strength testing (as an early strength and UPV of cement mortar specimens), with the characteristics of the cement mentioned above, in predicting the compressive strength of cement. It was found that the accelerated strength yields good and high correlation with the compressive strength of cement, especially at the age of 28 days. In this work too, the importance of the ultrasonic pulse velocity (UPV) and mortar density were evident and the usefulness of using these variables in predicting the compressive strength of the cement was proved (because of fixing most of the factors affecting this property). Thus, it is possible to have good results that can be used in the prediction of compressive strength of cement. It was found that using each of the accelerated compressive strength f_acc, UPV and density of the mortar cubes yielded high correlation with the compressive strength than any of the other variables. Different combinations of variables were introduced into the model, in order to choose the variables that can significantly predict the cement compressive strength. In this work, it was possible to obtain a model that can predict the cement strength with standard errors of only 1.887 and 1.904 MPa and coefficients of correlation of 0.903 and 0.928, for cement strengths at 7 and 28 days respectively.     

玄武岩纤维增强地质聚合物混凝土的动态本构模型

以矿渣与粉煤灰为原材料制备玄武岩纤维增强地质聚合物混凝土(BFRGC),采用φ100mm分离式霍普金森压杆(SHPB)装置对BFRGC进行了冲击压缩试验,并对SHPB试验过程中的波形整形技术展开了研究,以此来提高材料SHPB试验的精度。通过SHPB试验,获得了BFRGC在10s-1―102s-1应变率范围内的应力-应变曲线,分析了BFRGC的强度和变形性能,并建立了BFRGC的率型非线性粘弹性本构模型。通过试验对模型进行验证,模型曲线与试验曲线吻合良好,该文建立的率型本构模型可以较为准确地描述BFRGC的动态力学行为。     

Sequentially Generated Second Order Quasi D-Optimal Designs for Experiments With Mixture and Process Variables

Second order designs for experiments with mixture and process variables are proposed. They are constructed on the basis of continuous D-optimal designs by use of a three-stage procedure for sequentially generating optimal designs. The determinants of the information matrices of the designs obtained are very near to those of continuous D-optimal designs. Tables of discrete quasi D-optimal designs for q + r ≤ 7 are given, where q is the number of mixture components and r is the number of process variables. The experimenter can choose the number of trials N within the interval k ≤ N ≤ min(2k, k + 20), where k is the number of model coefficients. An application of the proposed designs in an investigation of truck tire properties is given.     

Red mud addition in the raw meal for the production of Portland cement clinker

The aim of the present research work was to investigate the possibility of adding red mud, an alkaline leaching waste, which is obtained from bauxite during the Bayer process for alumina production, in the raw meal for the production of Portland cement clinker. For that reason, two samples of raw meals were prepared: one with ordinary raw materials, as a reference sample ((PC)Ref), and another with 3.5% red mud ((PC)R/M). The effect on the reactivity of the raw mix was evaluated on the basis of the unreacted lime content in samples sintered at 1350, 1400 and 1450 degrees C. Subsequently, the clinkers were produced by sintering the two raw meals at 1450 degrees C. The results of chemical and mineralogical analyses as well as the microscopic examination showed that the use of the red mud did not affect the mineralogical characteristics of the so produced Portland cement clinker. Furthermore, both clinkers were tested by determining the grindability, setting time, compressive strength and expansibility. The hydration products were examined by XRD analysis at 2, 7, 28 and 90 days. The results of the physico-mechanical tests showed that the addition of the red mud did not negatively affect the quality of the produced cement.     

Design development of aggregates cooling systems for hot weather concreting

Using hot aggregates, in concrete production, results in a drop in compressive strength of the produced concrete. Various methods have been proposed for cooling concrete aggregates. This paper proposes new two designs for aggregates cooling systems for various production rate demands. Conveyor system for small to moderate production rates and rotating drum for high production rates. Simulation of the heat flow during the cooling process over the conveyor and through the drum are analyzed with the objective of understanding the effect of the various design parameters and achieving minimum cooling time with the least possible power. Finite element models for the new designs are proposed and discussed. The results of the finite element analysis of the new designs are presented for various initial conditions and cooling rates.     

基于最大似然原理的电厂混煤均匀性确定

采用传统采样分析法对电厂混煤混合均匀性进行评估存在较大困难。将掺混原煤看作是各种成分符合不同概率分布的混合物,在原煤掺混而成的混煤中,某种成分的概率分布由原煤该成分分布、混合比例以及颗粒混合状态共同决定。以挥发分作为示踪成分,考察了掺混过程中挥发分概率分布的变化,在给定原煤挥发分分布和混煤挥发分样本集的情况下,采用最大似然原理对混煤中各种原煤掺混比例和标准差进行估计,进而对混合状态进行评估。研究表明,掺混模型对实际掺混系统的预测结果与原煤消耗量的统计数据吻合良好;多工况仿真实验也表明,掺混系统混合质量越差,模型的预测精度越高。     

掺CWCPM的砂浆强度灰色关联分析及预测模型的建立

为提高建筑垃圾砖粉活性,将其与粉煤灰、矿粉、激发剂复合形成建筑垃圾复合粉体材料(Construction waste composite powder materials,以下简称CWCPM)。从宏观和微观两方面研究了CWCPM对砂浆力学性能的影响,并采用灰色关联分析及多元回归分析理论,研究了水灰比、CWCPM掺量与砂浆强度的关联性,建立了砂浆抗压强度与水灰比、CWCPM掺量、龄期之间的定量关系模型。结果表明,CWCPM降低了砂浆早期强度,而其合理的颗粒级配及二次水化反应提高了砂浆后期强度;其中CWCPM掺量为抗压强度的准优因素,抗折强度受水灰比的影响较大;多元回归模型对砂浆抗压强度的预测精度较高,为CWCPM的有效利用提供了理论依据。     

The construction of robust mixture‐process experimental designs via genetic algorithm

Mixture experiments with the presence of process variables are commonly encountered in the manufacturing industry. The experimenter who plans to conduct mixture experiments in which a process involves the combination of machines, methods, and other resources will try to find condition of design factors which make the product/process insensitive or robust to the variability transmitted into the response variable. We propose the genetic algorithm (GA) for generating robust mixture‐process experimental designs involving control and noise variables. When the noise variables, which are extremely difficult to control or not routinely controlled during the manufacturing process and may change without warning, are considered in a mixture experiment, we propose the robust design setting. When considering a robust design, the design that has a lower and flatter faction of design space curves for all levels of the controllable process variables at varying noise interaction is preferable. We evaluate the designs with respect to these criteria for both the mean model and the slope model. The evaluation demonstrates that the proposed GA designs are robust to the contribution of the interactions involving the noise variables.     

环氧树脂-混凝土的早龄期压缩性能

环氧树脂-混凝土是混合环氧树脂、固化剂和骨料后养护成型的一种新型聚合物混凝土,早期强度增长快是其优异性能之一。本文通过对不同养护龄期的环氧树脂-混凝土进行单轴压缩试验,研究其早龄期压缩性能。试验结果表明,在养护龄期的最初24 h内环氧树脂-混凝土压缩强度迅速增大,养护24 h的压缩强度达50.3 MPa。基于环氧树脂-混凝土的强度增长机制和养护72 h后压缩强度趋于稳定的现象,建立了一种基于环氧树脂n级固化反应的环氧树脂-混凝土早龄期压缩强度预测模型,该模型比普通水泥混凝土经典的CEB-FIP、ACI 209强度预测模型具有更好的预测效果。基于压缩强度预测和实验结果,建立了考虑龄期的环氧树脂-混凝土单轴压缩本构模型,该模型能较好地预测环氧树脂-混凝土早龄期压缩应力-应变关系。      

Production and properties of foamed reservoir sludge inorganic polymers

The feasibility of using reservoir sludge as a raw material in the production of foamed inorganic polymers with different densities is investigated in this work. Reservoir sludge is first crushed, ground down and then calcined at the temperature of 850 °C for 6 h to become calcined reservoir sludge (CRS) powders. A mixture of 30% blast furnace slag and 70% CRS powders is alkali-activated by mixing with different alkaline activating solutions of water, sodium hydroxide and sodium silicate. The viscosities and compressive strengths of the resulting inorganic binders are measured and compared with each other. Furthermore, the inorganic binder paste that has the maximum compressive strength and best workability is mixed with various amounts of preformed air bubbles to produce foamed reservoir sludge inorganic polymer (FRSIP) specimens with different densities. The effects of density on the water absorption, pore size distribution, compressive strength, bending strength and transmission loss of the FRSIP specimens are evaluated.     

Effect of Moisture and Temperature on the Compressive Failure of CCF300/QY8911 Unidirectional Laminates

CCF300/BMI composites are relevant materials for supersonic aircraft due to their high specific properties. However in aeronautical applications, the composites are exposed to severe environmental conditions, and it is known that hot and humid environments can degrade some aspects of the material performance especially the compressive strength. In this paper, the effect of moisture and temperature on the compressive failure of unidirectional CCF300 carbon fiber reinforced bismaleimide(BMI) matrix composites were studied. Also scanning electron microscope (SEM) was employed for fractographic investigations. It is observed that the plastic deformations at the fiber/matrix and interlaminar interface as well as residual stresses lower the compressive strength of the material. The failure of specimens tested in hot and wet conditions always occurs as a result of out-of-plane microbuckling that is attributed to the reduction of matrix strength. In addition, the fiber microbuckling model, fiber kinking model and combined model were employed for the compressive strength prediction of the UD CCF300/QY8911 composites subjected to different environment conditions. The comparison was done between these models. Results show that the combined model is more suitable for the compressive strength prediction of CCF300/QY8911 composite systems when suffering severe environment conditions.     

Modern technology ensures zinc die castings meet market needs

The zinc pressure die casting process is capable of producing complex accurate engieerring components at high production rates with considerable automation. However, market requirements are changing: designers are calling for better engineering properties and higher quality standards, while at the same component cost must be reduced and lead time on new components shortened. The paper considers two main ways in which these requirements are being met by the die casting industry.Firstly the engineering properties of die cast alloys are examined in comparison with those of other materials. This enables the most competitive material for a given application to be selected. More accurate and more widely based information is now available for many materials so that engineers can make properly calculated designs which use material in the most economic way. This can often mean eliminating some components entirely, by combining their functions into a simple complex shaped zinc pressure die casting: examples are given to illustrate these points.Secondly the paper considersrecent process improvements. Present knowledge of metal flow enables components to be made with thinner sections, with greater soundness and more predictability so that properties of the final product are improved and lead lines reduced. More recent developments in predicting and controlling the heat flow in the die are also described. These give better surfaces, higher accuracy and improved production rates as dies are pushed towards their thermal limits.A brief look at the future describes how the other factors such as lubricant and die surface effects are now being studied and how a complex model is being built up in which the combined effects of all the process variables will give the industry total process control.     

海工磷酸镁水泥基材料的制备及性能研究

选用海砂、海水制备了海工磷酸镁水泥基材料,研究了该材料的贮存性能,早期强度特性及抗海水侵蚀性能。结果显示磷酸镁水泥有着良好的贮存性能,原材料按一定方式存放360d后,水泥强度降低不超过5%,原材料存放1000d后,水泥强度降低不超过10%;所制备的海工磷酸镁水泥基材料,2h的抗压强度均达到28MPa以上,1d抗压强度已达52MPa以上,凝结时间在25min以内;所制备的海工磷酸镁水泥胶砂抗海水侵蚀性能良好。     

Compressive static strength model for impact damaged laminates

A simple analytical model for the prediction of the compressive strength of composite structures with Barely Visible Impact Damage (BVID) subject to static loading is presented. The model represents the complex damage morphology using circular approximations of the damage area and determines a critical interface for propagation of BVID. Results are compared with experimental values for static strength of a variety of examples reported in the literature. For impacts on the skin under a stiffener the model is accurate to within 5% of the reported experimental result. It is demonstrated how the model can be manipulated for use in laminate optimisation for improved damage tolerance.     

Evaluation of the performance of recycled textile fibres in the mechanical behaviour of a gypsum and cork composite material

Given the need for using more sustainable constructive solutions, an innovative composite material based on a combination of distinct industrial by-products is proposed aiming to reduce waste and energy consumption in the production of construction materials. The raw materials are thermal activated flue-gas desulphurization (FGD) gypsum, which acts as a binder, granulated cork as the aggregate and recycled textile fibres from used tyres intended to reinforce the material.This paper presents the results of the design of the composite mortar mixes, the characterization of the key physical properties (density, porosity and ultrasonic pulse velocity) and the mechanical validation based on uniaxial compressive tests and fracture energy tests. In the experimental campaign, the influence of the percentage of the raw materials in terms of gypsum mass, on the mechanical properties of the composite material was assessed.It was observed that the percentage of granulated cork decreases the compressive strength of the composite material but contributes to the increase in the compressive fracture energy. Besides, the recycled textile fibres play an important role in the mode I fracture process and in the fracture energy of the composite material, resulting in a considerable increase in the mode I fracture energy.     

Biological materials: Functional adaptations and bioinspired designs

Biological materials are typically multifunctional but many have evolved to optimize a chief mechanical function. These functions include impact or fracture resistance, armor and protection, sharp and cutting components, light weight for flight, or special nanomechanical/chemical extremities for reversible adhesive purposes. We illustrate these principles through examples from our own research as well as selected literature sources. We conduct this analysis connecting the structure (nano, micro, meso, and macro) to the mechanical properties important for a specific function. In particular, we address how biological systems respond and adapt to external mechanical stimuli. Biological materials can essentially be divided into mineralized and non-mineralized. In mineralized biological materials, the ceramics impart compressive strength, sharpness (cutting edges), and stiffness while the organic components impart tensile strength, toughness and ductility. Non-mineralized biological materials in general have higher tensile than compressive strength, since they are fibrous. Thus, the mineralized components operate optimally in compression and the organic components in tension. There is a trade-off between strength and toughness and the stiffness and density, with optimization. Mineralization provides load bearing capability (strength and stiffness) whereas the biopolymer constituents provide viscoelastic damping and toughness. The most important component of the nascent field of Biological Materials Science is the development of bioinspired materials and structures and understanding of the structure–property relationships across various length scales, from the macro-down to the molecular level. The most successful efforts at developing bioinspired materials that attempt to duplicate some of the outstanding properties are presented.