Paste backfill of high-sulphide mill tailings using alkali-activated blast furnace slag: Effect of activator nature,concentration and slag properties

The effect of activator type, concentration and slag composition on the strength and stability properties of paste backfill (CPB) of high-sulphide tailings using alkali-activated slag (AAS) as binder (7 wt.%) were investigated in this study. Acidic and neutral (AS–NS) slags were activated with liquid sodium silicate (LSS) and sodium hydroxide (SH) at 6–10 wt.% concentrations. Ordinary Portland cement (OPC) results were used for comparison. The strength development was found to remarkably improve with increasing the concentration from 6 to 8 wt.%. Further increase in concentration did not enhance the strength. SH was determined to produce higher early-age strength whilst LSS produced higher long-term strengths as an indication of slag selectivity for activators. More extensive gypsum formation was observed at lower concentrations in SEM/EDS studies. An increase in Na₂O concentration raised the activator consumption. High concentrations also led to poorly crystallized C–S–H gel, loose structure and drying shrinkage cracks especially in NS–SH samples. A reduction in total porosity up to 20% was obtained in AAS samples compared to OPC. Amorphous structure, chemical modulus ratio and/or basicity index (BI) values were seen to control the pozzolanic reactivity, and therefore, the alkali-activation and hardening process.     

Combined size and shape optimization of structures with a new meta-heuristic algorithm

In this study, a new meta-heuristic algorithm called teaching-learning-based optimization (TLBO) is used for the size and shape optimization of structures. The TLBO algorithm is based on the effect of the influence of a teacher on the output of learners in a class. The cross-sectional areas of the bar element and the nodal coordinates of the structural system are the design variables for size and shape optimization, respectively. Displacement, allowable stress and the Euler buckling stress are taken as the constraint for the problem considered. Some truss structures are designed by using this new algorithm to show the efficiency of the TLBO algorithm. The results obtained from this study are compared with those reported in the literature. It is concluded that the TLBO algorithm presented in this study can be effectively used in combined size and shape optimization of the structures.     

Assessment of the effectiveness of steel fibre reinforcement for the punching resistance of flat slabs by experimental research and design approach

The present paper deals with the experimental assessment of the effectiveness of steel fibre reinforcement in terms of punching resistance of centrically loaded flat slabs, and to the development of an analytical model capable of predicting the punching behaviour of this type of structures. For this purpose, eight slabs of 2550 × 2550 × 150 mm³ dimensions were tested up to failure, by investigating the influence of the content of steel fibres (0, 60, 75 and 90 kg/m³) and concrete strength class (50 and 70 MPa). Two reference slabs without fibre reinforcement, one for each concrete strength class, and one slab for each fibre content and each strength class compose the experimental program. All slabs were flexurally reinforced with a grid of ribbed steel bars in a percentage to assure punching failure mode for the reference slabs. Hooked ends steel fibres provided the unique shear reinforcement. The results have revealed that steel fibres are very effective in converting brittle punching failure into ductile flexural failure, by increasing both the ultimate load and deflection, as long as adequate fibre reinforcement is assured. An analytical model was developed based on the most recent concepts proposed by the fib Mode Code 2010 for predicting the punching resistance of flat slabs and for the characterization of the behaviour of fibre reinforced concrete. The most refined version of this model was capable of predicting the punching resistance of the tested slabs with excellent accuracy and coefficient of variation of about 5%.     

Concrete–ice abrasion mechanics

The mechanisms of abrasion of concrete by ice are investigated by review of lab and field studies, wear theory, fracture-, contact- and poromechanics. Experience indicates that ice abrasion does not require freeze/thaw cycles. Three distinct mechanisms may contribute to abrasion damage of concrete: (1) asperities of ice sliding on concrete can create tensile stresses sufficient to initiate cracks (with fatigue from repeated contacts playing an important role); (2) debris released from the surface of the concrete can act as sharp abrasive particles that enhance the damage as the ice drags them along the surface; and (3) water forced into surface defects can create pressure that propagates cracks. Topics for further research and recommendations for minimizing abrasion are suggested.     

Agent-based monitoring service for management of disruptive events in supply chains

Schedules of supply chains are generated with buffers to absorb the effect of disruptive events that could occur during their execution. Schedules can be systematically repaired through specific modifications within buffers by using appropriate decision models that consider the distributed nature of a supply chain. To this aim, information of disruptive events at occurrence or in advance allows decision models to make better decisions. To detect and predict disruptive events along a schedule execution, a service-oriented monitoring subsystem that uses a reference model for defining monitoring models was proposed. This subsystem offers services for collecting execution data of a schedule and environment data, and assessing them to detect/anticipate disruptive events. Because of the distributed nature and the complexity of these services functionalities, this paper presents an agent-based approach for their implementation. This technology allows dealing with supply chain monitoring by structuring monitoring subsystem functionalities as a set of autonomous entities. These entities are able to perform tailored plans created at execution time to concurrently monitor different schedules. A case study is described to try out the implemented prototype system.     

Role of cement content on the properties of self-flowing Al2O3 refractory castables

In this work, Al₂O₃ self-flowing castables (SFCs) were produced based on various cement contents. The SFCs were sintered at 1273 K, 1573 K and 1773 K and the exhibited properties were experimentally determined. Among the properties determined in this work are bulk density (BD), apparent porosity (AP), water absorption (WA), cold crushing strength (CCS), modulus of rupture (MOR) and fracture toughness (K_IC). It is found that additions of 5% cement lead to SFCs with maximum MOR and K_IC values after firing at 1773 K. Firing at 1573 K leads to a reduction in both, MOR and K_IC. In SFC containing 3% cement, maximum K_IC values of 3.53 MPa m^1/2 were achieved after firing at 1573 K. In the low cement SFCs (1 wt%) after firing at 1773 K the exhibited K_IC values were below those obtained in either the SFC-3 or SFC-5, but they were significantly high (3.43 MPa m^1/2).     

对“考虑桩土接触特性的复合地基承载机理的数值分析研究”讨论的答复

丁春勇等同志对本人在《岩土工程学报》2006年第4期是发表的“考虑桩土接触特性的复合地基承载机理的数值分析研究”一文提出的一些问题及质疑,使我受益非浅,深表感谢,现在就一些问题进行解答,并提出个人的看法,不妥之处,请批评指正。(1)复合地基在我国的应用越来越广,然而复合地基理论中的一个根本问题--群桩、承台、土相互作用机理却一直没有得到令人满意的研究成果。针对这一问题,原文以复合地基为对象,将复合地基视为桩体、土体、垫层和承台所组成的一个体系,通过考虑桩土界面接触摩擦作用、土体的非线性特性及系统各个部分的主要作用及其相互影响,利用自编的三维复合地基有限元数值模拟分析软件,研究复合地基的承载机理     

一类新复合形法及其在临界滑动面搜索中的应用

针对广泛采用的基本复合形法存在着搜索不完全、映射系数取值不灵活、复形多样性保持差等缺陷,提出了相应的改进措施,如动态全域映射收缩算子以及最大冗余点映射准则,形成了一类新型的复合形法。在确定冗余点时综合考虑了距离空间和目标函数值两方面的信息。通过对某复杂土坡的最危险滑动面的搜索表明,新型复合形法的寻优成功率比基本复合形法大大提高。     

半空间饱和土中的圆形孔洞对稳态剪切波的散射

采用复变函数和多级坐标的方法并借助在非耗散情况下的Biot波动理论,对半无限饱和土中稳态剪切SV波在一个圆形孔洞周围的散射和动应力集中的问题提出了一种近似求解分析方法。其中利用一个半径很大的圆弧来逼近半空间的直边界,将半空间直边界问题转化为曲面边界问题。首先将饱和土中的Biot波动方程解耦成Helmhotz势方程并预先写出问题波函数的一般形式解,再利用边界条件并借助复数傅立叶级数展开把问题化为求解波函数中未知系数的无穷线性代数方程组,通过变换不同的条件组合,得出半空间的圆形孔洞周围的动应力集中系数的数值解的分布和变化情况。由具体算例及分析可知:本文方法对研究与稳态剪切波有关的散射问题是可行的,并对工程实践有一定的指导作用。     

路基沉陷预计及其安全性评估

1 INTRODUCTION The underground-excavated rooms are formed after constructing underground projects，mining me-tallic and non-metallic ore and taking out excessively groundwater. The ground subsidence is caused as a result of underground excavation. A roadbed sub-sidence (including stations，bridges，tunnels，road-bed，upper buildings，signal system and so on) is caused by the ground subsidence. The security of railway transportation is greatly threatened due to ground subsidence caused by…