Mix proportioning of underground cemented tailings backfill

The usage of cemented tailings backfill (cemented paste backfill) in the underground by mining industry is becoming increasingly important. However, until now, the mix proportioning of CTB has been mainly based on the realization of extensive laboratory tests on a large number of CTB mixes. Therefore, this paper presents a design method for mix proportioning of CTB to minimize the number of trial mixes and provide an appropriate mix proportion. This method is based on the pairing of the response surface method (RSM) and the desirability approach. First, the RSM was used to develop predictive models for the performance properties of CTB. The predicted properties in question are the uniaxial compression strength (UCS), the slump, the solid concentration (solid percent, %Solid) and the cost (based on cement cost) of the CTB. The predictive models that were developed were able to accurately represent the relationships between the physical and chemical characteristics of the CTB components (tailings, binder, water) and the above properties. The results of the modeling phase were then used as input data in the optimization phase (based on desirability approach) to develop optimal recipes for the studied CTBs. This study has demonstrated that the combination of the RSM and desirability approach represents an effective tool for CTB mix proportioning. It has also shown that the mix parameters (cement content, water-to-cement ratio, tailings fineness and density) affect the performance properties of CTB. The results of this research provide a more comprehensive engineering approach to CTB mix proportioning. The developed design method can be useful in reducing the laboratory test protocol needed for the determination of the optimal mix composition.     

Hybrid random aggregation model and Bayesian optimization-based convolutional neural network for estimating the concrete compressive strength

Numerous experimental studies have shown the type and gradation of coarse aggregates effect on the mechanical properties of concrete. The type and gradation of coarse aggregates have not been taken into account in the available machine learning prediction models. In this study, a two-dimensional concrete microscopic image was generated by using a random aggregate model (RAM), and the coarse aggregate and other concrete ingredients were represented innovatively using polygons and trichromatic chromaticity values in the RAM images. The RAM image set was created by applying this method to represent 1110 sets of different concrete mixes. Then based on the Bayesian optimization algorithm and the image set, a compressive strength prediction model considering the effect of coarse aggregate types and gradations was developed utilizing a convolutional neural network (CNN) model. Meanwhile, an artificial neural network (ANN) compressive strength prediction model was developed using 1110 sets of mix ratio data. The results show that the proposed RAM image generation method has the capability to represent different concrete mix ratios collected in this study. The prediction performance of the CNN compressive strength model considering aggregate types and gradations is better than that of the ANN model. The method can provide a new perspective for predicting other concrete mechanical properties and technically support performance-based intelligent concrete mix design.     

影响道路混凝土强度的相关因素探讨

抗弯拉强度是道路水泥混凝土的控制技术指标。文章通过对道路混凝土所用材料水泥、石子、砂的品质,以及水泥用量、水灰比、单位用水量和砂率配合比设计参数确定对混凝土弯拉强度的影响情况的分析,可以看出合理选用原材料,慎重确定配合比参数,科学设计配合比,是改善道路混凝土性能、提高其抗弯拉强度的重要因素。     

A Fuzzy Adaptive Resonance Theory‐Based Model for Mix Proportion Estimation of High‐Performance Concrete

A new approach that adopts the use of fuzzy adaptive resonance theory (ART) neural network in estimating high‐performance concrete (HPC) mix proportion from experimental data is devised. The proposed model receives a set of desired concrete performances, searches for a set of mix proportions that is near to the desired concrete performances, classifies the mix proportions into clusters, measures the similarity between performances of deduced clusters with desired performances, and deduces a mix proportion. The proposed model was used to estimate the mix proportions of five batches of concrete based on the performance criteria of 7th and 28th day compressive strengths. The generated mix proportions were used in an experimental work and the errors were within 13% for 7th compressive strength; and 7% for the 28th day compressive strength, signifying the reliability of the fuzzy ART‐based model in estimating the mix proportion of HPC. This article contributes to an alternative method of mix proportion estimation of HPC by avoiding the use of complicated function approximation techniques.     

模糊综合评估方法在高性能混凝土质量控制中的适用性分析

采用模糊综合评估方法用于高性能混凝土质量控制有如下优点：可改进以往混凝土质量判定结果因采用互斥性评语所导致的不客观性；可综合考虑耐久性，力学性能等重要的性能指标对HPC质量的影响；可解决存在于HPC质量体系中通常的数学思想所不能客观解决的具有模糊性不确定性的问题。     

Properties of sustainable concrete containing fly ash,slag and recycled concrete aggregate

The suitability of using more “sustainable” concrete for wind turbine foundations and other applications involving large quantities of concrete was investigated. The approach taken was to make material substitutions so that the environmental, energy and CO₂-impact of concrete could be reduced. This was accomplished by partial replacement of cement with large volumes of fly ash or blast furnace slag and by using recycled concrete aggregate.Five basic concrete mixes were considered. These were: (1) conventional mix with no material substitutions, (2) 50% replacement of cement with fly ash, (3) 50% replacement of cement with blast furnace slag, (4) 70% replacement of cement with blast furnace slag and (5) 25% replacement of cement with fly ash and 25% replacement with blast furnace slag. Recycled concrete aggregate was investigated in conventional and slag-modified concretes. Properties investigated included compressive and tensile strengths, elastic modulus, coefficient of permeability and durability in chloride and sulphate solutions. It was determined that the mixes containing 50% slag gave the best overall performance. Slag was particularly beneficial for concrete with recycled aggregate and could reduce strength losses. Durability tests indicated slight increases in coefficient of permeability and chloride diffusion coefficient when using recycled concrete aggregate. However, values remained acceptable for durable concrete and the chloride diffusion coefficient was improved by incorporation of slag in the mix. Concrete with 50% fly ash had relatively poor performance for the materials and mix proportions used in this study and it is recommended that such mixes be thoroughly tested before use in construction projects.     

免振高性能混凝土力学性能及耐久性研究

采用超细磨粉煤灰和复合高效减水剂双掺技术研制出了Ｃ６０～Ｃ８０免振高性能混凝土,在优选了免振高性能混凝土配合比主要设计参数的基础上,对免振与振捣成型的高性能混凝土的抗压强度、劈裂抗拉强度、抗折强度、弹性模量、抗冻性能、干综性能等进行了对比试验研究。结果表明：免振高性能混缔造人有优异的物理力学性能及耐久性。     

索塔锚固区泵送高性能钢纤维混凝土的研制

普通纤维混凝土因可泵送性差很少用于索塔锚固区。采用多重复合技术,优选纤维混凝土配合比,并研究了各配合比的泵送性能;模拟干热环境,对优选的高性能混凝土(HPC)和钢锚箱锚固区专用高性能钢纤维混凝土(HPSFRC)进行了塑性收缩试验;研究了纤维掺量和减缩剂对塑性收缩和干燥收缩性能的影响,并对其机理进行了探讨。研究表明,经优化的高性能钢纤维混凝土2h内泵送性能优良。随着纤维掺量的增加,塑性收缩的开裂总面积下降,混凝土的抗裂等级提高。当钢纤维的体积掺量为0.8%时,高性能钢纤维混凝土自由干燥90d的收缩值同高性能混凝土相比下降了50%;有约束的干燥收缩66d试验环未见开裂,从而减少混凝土开裂的风湿,提高混凝土结构的耐久性。与同强度等级的高性能混凝土相比,钢纤维的加入也改善了混凝土的力学性能,高性能钢纤维混凝土的抗弯强度和劈拉强度提高了近30%。试验结果还表明,纤维体积率为0.6%的钢纤维与减缩剂复合后,对抑制塑性收缩和干燥收缩效果显著。     

Bulk engineering and durability properties of washed glass sand concrete

The paper reports the results of an experimental programme aimed at examining the performance of Portland-cement concrete produced with washed glass sand (WGS), as natural sand substitute- by mass. The effects of up to 50% WGS on fresh, engineering and durability related properties have been established and its suitability for use in a range of normal-grade concrete production assessed. WGS characteristics results showed that the post-container glass waste can be crushed to provide WGS of physical properties that satisfy the current requirements set in appropriate standards for natural sand for concrete. The density and water absorption of WGS was found to be lower than natural sand. The results for fresh concrete showed a reduction in workability of concrete with increase WGS proportion beyond 20% in the mix, although slump measurements remained within the allowable margin of ±25 mm. The mixes with high proportions of WGS were found to be less cohesive. Studies of hardened concrete properties, comprising bulk engineering properties (compressive cube and cylinder strength, flexural strength, modulus of elasticity, drying shrinkage) and durability (near surface absorption, alkali silica reaction) showed similar performance for concrete produced with natural aggregates and up to 15% WGS.     

按耐久性设计高性能混凝土的原则和方法

高性能混凝土不是一个混凝土的品种,而是表明混凝土的“性能（performance）或者 质量、状态、水平的一种称谓,是按照具体工程要求和所处环境条件,满足特殊组合的性能而均匀、致密的高质量混凝土。高性能混凝土的耐久性设计步及原材料选择与控制、配合比设计、制备工艺和施工质量控制的全过程。按工程要求的耐久性选定原材料后,从“NEL法的氯离了扩散系数－渗透性关系”中初选水胶比,用绝对体积法计算配合比,进行试配和强度样核。     

大型渡槽高性能混凝土的配制与性能研究

基于大型渡槽预应力槽身混凝土的抗裂、防渗与抗冻等耐久性的较高要求,采用聚羧酸系高效减水剂,通过试验研究了水胶比、粉煤灰掺量、粉煤灰单掺与粉煤灰、矿渣粉复掺等配合比设计参数对混凝土性能的影响,优化出2个C50高性能混凝土配合比,并系统研究了优化的C50高性能混凝土的工作性、力学性能、收缩变形及抗渗、抗碳化和抗冻等耐久性能.     

人工砂及矿物掺和料配制高性能混凝土的研究

通过对北京市现有混凝土配制技术的调研,分析了现有配制技术存在的问题.在此基础上对混凝土配制技术进行了改进,研究了人工砂、矿物掺和料配制的混凝土的强度和耐久性,提出了配制高性能混凝土的技术参数.     

高性能混凝土配合比设计的正交试验研究

高性能混凝土配合比设计的研究对实际工程应用有着重要的意义 ,是高性能混凝土研究领域的主要方面之一。采用四因素、三水平的正交试验设计方法对高性能混凝土的配合比进行了试验 ,研究了水泥、硅灰、粉煤灰和外加剂等不同试验因素对高性能混凝土强度的影响 ,分析了每个因素水平对高性能混凝土配合比的作用及各个水平之间的差异。结果表明 ,对混凝土强度的影响因素依次为外加剂、硅灰、水灰比和粉煤灰。并用正交试验结果进行了线性回归 ,给出了预测模型     

基于灰关联熵法的高性能混凝土强度影响因素分析

对于多种掺合料的高性能混凝土,找出诸多影响性能因素中的关键因素对配合比设计具有现实意义.通过强度试验,运用灰关联熵的系统分析方法,分析了胶水比、水泥强度、水泥掺量、磨细矿渣粉掺量、硅灰及膨胀剂掺量等因素对高性能混凝土28 d抗压强度性能影响的主次关系和影响程度.分析表明:对于高性能混凝土,胶水比始终是一个非常重要的参数,同时水泥的强度及其在胶凝材料中的掺量也是混凝土强度的重要保证;外加剂及矿物掺合料对混凝土强度的贡献则取决于外掺料本身的性能.结果证明:在高性能混凝土多因素的分析中,灰关联熵法是一种简单实用且结果比较准确的方法,研究结果可为高性能混凝土配合比设计参数提供有效的计算依据.     

高强度混凝土配合比设计要点

高强混凝土强度等级高,密实性能好,一般运用于高层建筑、大跨度桥梁等结构中,如果混凝土的配合比设计不合理,会影响到混凝土的强度,缩短混凝土构件的使用寿命。文章论述了高强度混凝土在原材料选择及配合比设计时应注意的一些要点。     

Influence of physical and geometrical properties of granite and limestone aggregates on the durability of a C20/25 strength class concrete

This paper presents an experimental study to evaluate the influence of physical and geometrical properties of granite and limestone aggregates on the durability of a C20/25 strength class concrete. Different granite and limestone aggregates were collected from seven quarries. Physical, geometrical and mechanical properties of aggregates as well as the rock weathering state were quantify by several tests such as, abrasion, surface hardness, uniaxial compressive strength, ultrasonic pulse velocity, water absorption by capillarity, vacuum water absorption and oxygen permeability.

Using aggregates from each quarry, several C20/25 strength class concrete mixes have been produced, with the same workability and volume proportions. Concrete specimens have been cured under water for 90 days; after that time concrete durability parameters were obtained through tests such as, vacuum water absorption, capillarity water absorption, water permeability and oxygen permeability.

Relevant statistical correlations have been obtained between absorption and permeability test of rock material and rock deterioration state (weathering). Valid statistic correlation was also obtained between durability parameters as well as among aggregates geometrical properties and concrete durability parameters.     

Shear capacity evaluation of steel reinforced recycled concrete (RRC) beams

The applicability of some major concrete design standards and other pertinent methods to calculate the concrete contribution to the shear resistance of reinforced recycled concrete (RRC) beams without stirrups is investigated. Results of a relatively comprehensive experimental program are used to compare the actual shear strength of the tested beams with their corresponding predicted values. The concrete mixes for the RRC beams were proportioned by the so-called Equivalent Mortar Volume (EMV) method. The method is predicated on the fact that recycled concrete aggregate (RCA) is a composite material, comprising mortar and natural aggregate, and the volumetric content and properties of each phase must be quantitatively accounted for when proportioning concrete mixes containing RCA. The test variables included in the test program are shear-span/depth ratio, beam size, RCA source, and coarse aggregate type. The results show that the shear capacity of a RRC beam is comparable, or sometimes superior, to that of a companion beam made of conventional concrete. The analyses performed in the current investigation show, contrary to previous findings, that existing shear design methods, such as the ACI and CSA codes methods, are applicable to RRC beams, provided the EMV method of mix design is used.     

C80机制砂高强混凝土的研制及工程应用

通过原材料选择、配合比设计、混凝土耐久性能评价等途径,研制出了性能优良的C80机制砂高强混凝土,并成功应用于成都群光广场与成都茂业中心,取得了良好的实施效果.结果表明,该混凝土具有良好的工作性能、力学性能与耐久性能,完全满足结构设计要求.     

Release of air from unsaturated aggregate during setting of concrete

Eight concrete mixes, with various mix proportions and cement replacements, were assessed for strength development in a laboratory-based trial mix programme. All concretes had substantially lower strength than expected. The cause was the release of air from partially dry aggregate after placing, prior to setting, producing air voids, typically 100 μm in diameter, in the cement paste at the surface of aggregate particles. This paper presents the evidence, details the mechanisms involved and discusses the implications for concreting practice.     

Genetic programming based formulation for fresh and hardened properties of self-compacting concrete containing pulverised fuel ash

Self-compacting concrete (SCC) flows into place and around obstructions under its own weight to fill the formwork completely and self-compact without any segregation and blocking. Elimination of the need for compaction leads to better quality concrete and substantial improvement of working conditions. This investigation aimed to show possible applicability of genetic programming (GP) to model and formulate the fresh and hardened properties of self-compacting concrete (SCC) containing pulverised fuel ash (PFA) based on experimental data. Twenty-six mixes were made with 0.38 to 0.72 water-to-binder ratio (W/B), 183–317 kg/m³ of cement content, 29–261 kg/m³ of PFA, and 0 to 1% of superplasticizer, by mass of powder. Parameters of SCC mixes modelled by genetic programming were the slump flow, JRing combined to the Orimet, JRing combined to cone, and the compressive strength at 7, 28 and 90 days. GP is constructed of training and testing data using the experimental results obtained in this study. The results of genetic programming models are compared with experimental results and are found to be quite accurate. GP has showed a strong potential as a feasible tool for modelling the fresh properties and the compressive strength of SCC containing PFA and produced analytical prediction of these properties as a function as the mix ingredients. Results showed that the GP model thus developed is not only capable of accurately predicting the slump flow, JRing combined to the Orimet, JRing combined to cone, and the compressive strength used in the training process, but it can also effectively predict the above properties for new mixes designed within the practical range with the variation of mix ingredients.