High-performance concrete mix for an optimum protection in acidic conditions

High-performance concrete mixes, made with 10% silica fume and various percentages of pulvarized fly ash as an ordinary Portland cement replacement, were prepared and subjected to sulphuric and hydrochloric acid environments. This research was conducted in order to study the effect of various levels of replacement materials and to obtain the optimum mix possessing a maximum protection against acid attack. The parameter investigated was the time, in weeks, taken to cause 20% weight loss of fully-immersed concrete specimens in a 1% solution of sulphuric acid and the same amount of loss in a 1% solution of hydrochloric acid. The investigation indicated that the concrete consisting of 10% silica fume and a maximum of 60% pulvarized fly ash as an ordinary Portland cement replacement showed an optimum protection in the acidic environment.

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Résumé Des mélanges de béton de haute performance obtenus à partir de 10% de fumée de silice et de différents pourcentages de cendres volants (en substitution du ciment Portland ordinaire) ont été préparés et submergés dans des solutions contenant de l'acide sulfurique ou chlorhydrique. L'objet de ces recherches étaient d'étudier l'effet de différentes quantités de matériaux de substitution afin de déterminer le mélange optimal offrant la meilleure protection contre l'action de l'acide. Le paramètre étudié était le temps, exprimé en semaines, nécessaire pour occasionner 20% de perte en masse des échantillons de béton plongés dans une solution à 1% d'acide sulfurique ou à 1% d'acide chlorhydrique. L'étude a montré qu'un béton consitué de 10% de fumée de silice et de 60% de cendres volants au maximum (en substitution du ciment Portland ordinaire) offre une protection optimale dans un environnement acide.

     

A simple mix design method for structural lightweight aggregate concrete

Current design methods for structural lightweight aggregate concrete (SLWAC) are usually only valid for a limited range of concrete compositions that have previously been subjected to trial tests. The SLWAC mix design is more complex than that of normal weight concrete as more parameters need to be determined. Taking this into account, a simplified design method is proposed for SLWAC made with natural sand. The major advantages of the proposed method are that it is easy to apply and it can be generalized to any type of lightweight aggregate (LWA). For this, three additional design parameters are needed: the strength of LWA in concrete; the limit strength; the SLWAC potential strength. At most, two experimental mixtures are needed to determine these parameters. A biphasic model to estimate the strength of SLWAC is evaluated and high correlations are obtained. The good performance of the suggested method is demonstrated by examples of practical application and by the comparison with experimental results reported by the authors and other investigators.     

模拟退火算法设计阵元缺失基阵方向图的方法

基阵方向图设计是声纳设计中的核心和重要部分,由于声纳系统的使用环境比较复杂,为了快速、有效地在阵元缺失的情况下对基阵方向图进行设计,引入了模拟退火算法对这类问题进行处理。模拟退火算法是近年来出现的全局优化算法,易于编程、有良好的收敛性。计算机仿真结果表明,模拟退火算法可以很好地完成在阵元缺失情况下对基阵方向图的补偿设计。     

Concrete mix design for high strength self-compacting concrete using metakaolin

Metakaolin is a highly reactive pozzolanic admixture and has got significant potential for the development of concrete composites such as High Strength High Performance Concrete (HSHPC) and self compacting concrete (SCC), if appropriately designed. However, for obtaining the required performance in any of these concrete composites, metakaolin should be properly proportioned so that the resulting concrete would satisfy both the strength and performance criteria requirements of the structure. The present work is an effort towards obtaining a new mix methodology for the design of high strength self compacting metakaolin concretes based on the efficiency concept. The methodology has been successfully verified through a proper experimental investigation and the self compacting metakaolin concretes were evaluated for their self compactability and strength characteristics. The results indicate that the proposed method can be capable of producing high strength SCC of about 120 MPa.     

大体积混凝土配合比设计及裂缝控制研究

文章通过基础用大体积混凝土在设计施工中采取了一系列措施,保证该泵送混凝土多项性能达到了预期要求。     

New methods for accurate water dosage in concrete central mix plants

Online mixer measurements appear as being essential to the improvement of concrete manufacturing methods, as imposed by new economical and environmental demands. However, the lack of a well-established calibration procedure contributes to the poor reputation sometimes given to these measurements. The original in situ method developed and evaluated herein requires installing a sampler, yet only slightly disturbs the production process. By using this calibration method the mixing power becomes a reliable online indication of concrete water content (measurement standard deviation of 2.85 l/m³). A procedure for improving the regularity of water content in truck mixers has been presented to illustrate the benefit of well-calibrated online water content measurements in batch concrete in a central mix plant. The correction algorithms proposed herein have the potential to be automated and may improve up to 5 times the water content regularity in the truck mixers.     

Impact of particle packing mix design method on fracture properties of natural and recycled aggregate concrete

The fracture properties of four types of concrete prepared using natural coarse aggregate and recycled coarse aggregate and conventional and particle packing method (PPM) of mix design approaches are studied. The three‐point bending (TPB) test is performed using three different sizes of single edge notched beam. The fracture energy is calculated from the load‐CMOD curve obtained in the TPB test, and in this process the load‐CMOD curve is curtailed at 2% of the depth of the beam. Based on CTOD_c and w₁ relationship, appropriate softening function is used to estimate the double‐K fracture parameters. The fracture energy and fracture toughness parameters of recycled aggregate concrete (RAC) is inferior to the natural aggregate concrete (NAC). The PPM mix design improves the fracture properties of concrete in comparison to the conventional mix design approach. The fracture properties of PPM mix designed RAC are comparable to that of NAC prepared using conventional method.     

Effect of the mix design on the robustness of fresh self-compacting concrete

Self-compacting concrete (SCC) has many advantages compared to vibrated concrete. A disadvantage is the lower robustness of fresh SCC. SCC is more sensitive to small changes in the mix design, material properties, and the applied production methods. In an experimental program, the influence of important mix design parameters on the robustness of SCC was studied. First, the influence of the paste volume and the water-to-powder volumetric ratio was investigated. Depending on the mechanisms providing stability in the mixture, different levels of impact were observed. When the yield stress is the main factor providing stability in the mixture, a change in the water content will mainly affect the yield stress, making the stability of the yield stress the most important factor determining the robustness of the mixture and can be improved by lowering the paste volume. Analogue, the sensitivity of the plastic viscosity is determining the robustness of mixtures in which mainly the plastic viscosity is providing stability. The robustness of such a mixture can be improved by increasing the water-to-powder volumetric ratio. The influence of two types of viscosity modifying agents (VMA's) on the robustness of fresh SCC was examined in a second stage. The two used VMA's (diutan gum and attapulgite clay) were especially effective in SCC mixtures having a high yield stress and a low plastic viscosity. In mixtures having a low yield stress and a high plastic viscosity, the inclusion of a VMA in the mix design resulted in a decrease of the robustness.     

An optimized mix for the manufacture of sustainable aerated concrete blocks using waste rubber powder

Clean Technologies and Environmental Policy - Aerated concrete is a type of lightweight concrete in which air bubbles are incorporated into concrete using aluminium powder to make it light in...     

正交试验在多因素混凝土配合比设计中的运用

文章通过云南某水电站工程的混凝土配合比设计实例,介绍了正交试验结合多元回归分析的运用。实践证明,采用该法设计的混凝土配合比不仅具有较高的精度和使用时有一定的选择余地,而且还减少了混凝土的试验工作量。     

An experimental study on optimum usage of GGBS for the compressive strength of concrete

This paper presents a laboratory investigation on optimum level of ground granulated blast-furnace slag (GGBS) on the compressive strength of concrete. GGBS was added according to the partial replacement method in all mixtures. A total of 32 mixtures were prepared in four groups according to their binder content. Eight mixes were prepared as control mixtures with 175, 210, 245 and 280 kg/m³ cement content in order to calculate the Bolomey and Féret coefficients (K_B, K_F). For each group 175, 210, 245 and 280 kg/m³ dosages were determined as initial dosages, which were obtained by removing 30 percent of the cement content of control concretes with 250, 300, 350, and 400 kg/m³ dosages. Test concretes were obtained by adding GGBS to concretes in an amount equivalent to approximately 0%, 15%, 30%, 50%, 70%, 90% and 110% of cement contents of control concretes with 250, 300, 350 and 400 kg/m³ dosages. All specimens were moist cured for 7, 14, 28, 63, 119, 180 and 365 days before compressive strength testing.The test results proved that the compressive strength of concrete mixtures containing GGBS increases as the amount of GGBS increase. After an optimum point, at around 55% of the total binder content, the addition of GGBS does not improve the compressive strength. This can be explained by the presence of unreacted GGBS, acting as a filler material in the paste.     

Effect of mix design on restrained shrinkage of self-consolidating concrete

This paper presents test results carried out to evaluate the potential due to restrained shrinkage cracking of self-consolidating concrete (SCC). The mix design approach and binder type of the SCC are shown to have considerable influence on cracking potential. Mixtures made with 0.42 w/cm and incorporating viscosity-enhancing admixture (VEA) to ensure proper stability exhibited approximately 25–35% longer time before cracking than SCC prepared with 0.35 w/cm and no VEA. The former concrete design had lower elastic modulus at 3 days when the drying shrinkage was initiated and hence greater stress relaxation. This was reflected in greater tensile creep coefficient which reduces tensile stress due to restrained shrinkage. The SCC made with 0.42 w/cm exhibited slightly higher drying shrinkage after 56 days of drying compared to similar concrete prepared with 0.35 w/cm. In general, the tested SCC mixtures had higher cracking potential than the reference high-performance and conventional concretes. This may be due to the higher paste volume of SCC that resulted in greater drying shrinkage. Mixtures with 670 mm slump flow consistency and 180 mm slump values of the same mix design had similar elapsed times before cracking of 6.3 and 5.6 days, respectively.     

Numerical computation in the viscoelastoplastic continuum damage of hot mix asphalt concrete

The objective of this paper is to develop an accurate and advanced material characterization of hot mix asphalt concrete using an existing viscoelastoplastic constitutive model that accounts for rate of loading, temperature and stress state with growing damage. The modelling strategy of viscoelastoplastic continuum damage is based on modelling strain components separately and then combining the resulting models to obtain a final integrated viscoelastoplastic model. According to this model, the initial-boundary value problem is numerically solved using the constitutive relationship expressed in the convolution integral form. The model is successful in predicting responses up to localization when microcracks start to coalesce.     

浅谈铁路高性能混凝土配合比设计

通过对贵广高速铁路高性能混凝土配合比的设计和施工,铁路高性能混凝土配合比的设计也有自己的特点,现加以总结,为以后铁路混凝土配合比的设计提供有益的借鉴。     

Consequence of cement constituents, mix composition and curing conditions for self-desiccation in concrete

This article outlines an experimental and analytical expression study on the consequence of cement constituents, mix composition and curing conditions as regards self-desiccation in concrete. For this purpose nine concretes with three values of w/c (0.32, 0.38 and 0.50), based on two types of Portland Cement, were manufactured. Five per cent silica fume was used in one third of the concretes as calculated on the basis of the cement content. The measurements were done at 1 and 6 months' age. An analysis of the conditions of the measurements was performed. Parallel tests were performed on strength. The results indicated high influence of w/c, age and cement type on self-desiccation. The curing conditions only influenced internal relative humidity and strength. The study was performed at Lund Institute of Technology 1997–1998.     

A steepest gradient method for optimum structural design

This paper describes a search procedure for finding the unconstrained maximum or minimum of a function of many independent variables. If this function represents the volume, cost, stiffness, etc. of a structure and each of the independent variables is associated with a parameter governing the geometry of the structure then designs of optimum geometry may be made in certain cases with the assistance of this search procedure. The procedure consists of steepest gradient calculations used in conjunction with a reverse Fibonacci location process. A ridge-following technique is included to speed convergence in addition to localized exploration in the region of an optimum. The search procedure has been programmed for computer use and an outline of its structural design applications is presented together with an example of its efficiency in a specific case.     

A simple simulation method for designing fibrous insulation materials

Conductive heat in a fibrous material travels through both the air (interstitial fluid) and the fibers (solid phase). The numerical simulations reported in this paper are devised to study the effective thermal conductivity of fibrous media with different microstructural parameters. Simulations were conducted in 3-D fibrous geometries resembling the microstructure of a fibrous material. Assuming that the heat transfer through the interstitial fluid is independent of the geometrical parameters of the solid phase (for when the porosity is held constant), the energy equation was solved only for the solid structures, and the resulting values were used to predict the effective thermal conductivity of the whole media. This treatment allows us to drastically reduce the computational cost of such simulations. The results indicate that heat conduction through the solid fibrous structure increases by increasing the material’s solid volume fraction, fiber diameter, and fibers’ through-plane orientations. The in-plane orientation of the fibers, on the other hand, did not show any significant influence on the material’s conductivity. It was also shown that the microstructural parameters of fibrous insulations have negligible influence on the material’s performance if the conductivity of the solid phase is close to that of the interstitial fluid.