THE DETERMINATION OF A CRACK IN STEEL FIBRE REINFORCED LIME-SAND CONCRETE

This paper studies the determination of a crack in steel fibre reinforced lime-sand concrete and its precision by acoustic emission(AE).The main AE paramters which influencethe precision of the determination of a crack are introduced,The properties of the lime-sand concretecan be increasted greatly with the steel fibre,The result in this paper can be used in the study of fi-bre re inforced cement concrete.     

THE RELATIONS BETWEEN THE HYDRATES AND PROPERTIES OF LIME-SAND MATERIALS

This paper summarized the previous research results of the physical-mechanical properties of the hydrated calcium silicate crystals and the relations between the hydrates and mechanical properties and durability of lime-sand materials. The key topicals of the relations between the hydrates and properties of lime-sand materials are discussed.     

ADVANCES IN PRACTICAL APPLICATION OF HIGH STRENGTH AND SUPER-HICH STRENGTH CONCRETE

Practical signicance of deceloping high strength and superhigh strength concrete was described in this paper. Development of high strength and super-high strength concrete in other countries was reviewed by authors, A new type of high strength and snper-high strength concrete, alkali-slag concrete, studied by authors, was introduced. This new concrete has more excellent properies than normal one, it can be used as either medium strength concrete or special concrete, high strength ahd super-high strehgth cohcrete.     

Anti sliding pile performance under acid stress coupling

Anti sliding piles are an important engineering structure used extensively in landslide prevention. Their durability influences their work lives. In a laboratory model experiment of a cantilevered anti sliding pile under acid stress coupling, the pile body displacement variation is monitored continuously, and both concrete strength and neutralization depth are tested. The results indicate that the concrete strength decreases gradually under acid stress coupling, while the displacement increases continuously. The neutralization depth of the concrete in the anti sliding pile is linear to the square of duration in acid stress coupling.     

Computational Model and Influencing Factor Analysis of Reinforced Concrete Walls under Fire

The finite element software ABAQUS is used to calculate the deformation of reinforced concrete walls under fire. The calculated results agree well with previous experimental results. Based on the finite element model, the influences of such parameters as axial load level, lateral load level, height-to-thickness ratio, wall thickness, concrete compressive strength, steel reinforcement yield strength, steel reinforcement ratio and concrete protection thickness on deformation and fire resistance of walls are analyzed systematically. It is found that, under the conditions of big axial load level or wall thickness without lateral load and small height-to-thickness ratio, the reverse deflection of reinforced concrete walls in fire is apt to occur. Within the work range of parameters in common use, the fire resistance of walls decreases with the increase of axial load level, lateral load level, height-to-thickness ratio, steel reinforcement yield strength or steel reinforcement ratio, and increases with the increase of wall thickness or concrete compressive strength.     

The Use of UEA Concrete in the Construction of the World Trade Centre in Chongqing

The reasons of cracking of large mass concrete construction in the early age are analysed and the technical thinking and ways of prevention of cracking are presented in this paper.UEA micro_expanding agent was used in the construction of the World Trade Centre of chongqing.The early contraction of corcrete is changed into limited expansion.the practical engineering experience is obtained in efficiently perventing the early cracking of concrete and ensuring the strength of concrete.     

Experimental Study on Shear Strength of High Strength Concrete Columns

On basis of the experiment on sixteen high strength concrete columns, their shear behaviors are analysed. The effects of shear-span ratio and axial compression ratio on failure behavior, cracking shear and shear strength are analysed. The authors have discussed the suitability of the design equations for shear strength in the code. This experimental study on shear strength of high strength concrete frame columns is the first one in this field at home and the results can be served as reference for the code of high strength concrete design.     

Experimental Analysis of Time-dependent Shear Behavior on Stud Connectors

With regard to the long span continuous composite beams, the early composite shear stud strength at the joint surface between the steel girder and concrete slab at different concrete ages should be considered while the concrete slabs are casted by phases in construction stage. In this study, the push-out test of stud shear connectors were conduced at different concrete ages. Meanwhile, the change law of the ultimate shear strength, ultimate slip deformation, design shear strength, and shear stiffness of the stud shear connectors with concrete ages were analyzed, and the corresponding time-dependent calculation equations were presented. The results include that the main failure modes of stud shear connectors are the concrete slab splitting failure before 3-days concrete age. The load-slip laws of stud shear connectors at different concrete ages are basically the same, however, the shear strength and stiffness all increase with the concrete ages prolonging, and the increase degree is faster at early ages, but slower at later ages, which indicates that the early composite shear stud strength at the joint surface of composite beams should not be neglected.     

Technology of Mixing High Property Concrete with Large Dosage Fly Ash

Being the largest mass of man-maded material, concrete demands much to resource and energy as well as affects much to environment. Whether concrete can be the dominating constructive material, the key is whether it can become green material and protect the environment at the same time. The important approach of developing is using industrial castoff largely in concrete. The tests note, that high performance concrete used of large mass of fly ash is doable. By grinding fly ash and adding high-efficient water reducer, when the dosage of cement clinker is only 25% and the dosage of fly ash is 70%, concrete with a good workability that 3 day and 28 day strength are bigger than 20 MPa and 50 MPa respectively can be achieved, which later strength develop very well. The large mass of fly ash concrete can utilize fly ash largely and reduce the dosage of clinker, that is very advantageous to protect environmental.     

Determination Analysis of Content of Aggregate Micro Fines of Middle and Low Compressive Strength Manufactured Fine Aggregate Concrete

There are some controversies on influences of stone powder on performances of concrete, and its content determination is one of the hot issues of manufactured fine aggregate (MFA) concrete. Slump and compressive strength of limestone MFA concrete were analyzed on contents of stone powder for middle-low strength and different flowability concrete. The experiment results show that there are different optimums percent of stone powder of MFA, such as 5, 10, and 20 for different types of concrete, but the water-powder ratio for them is 0.4. It is concluded that optimum percent of stone powder may be predicted by water-powder 0.4 for middle and low strength MFA concrete.     

Experimental Research on Concrete Strength under Freeze-thaw Recycle Action with Ultra-low Temperature

The concrete structure has been used in low and ultra-low temperature environment. But few researches are experienced on its properties under freeze-thaw recycles with ultra-low temperature. Based on the standard for test methods of long-term performance and durability of ordinary concrete, considering the influence of the times and minimum temperature of recycles, water-cement ratio and the external environment humidity, compressive and tensile strength of cubic concrete and scanning electron microscopy on the residual sample are experimented to explore the impact of freezing and thawing cycles under ultra-low temperature on its strength and microstructure. The results show that the role of cryogenic temperature for freeze-thaw cycles has a greater effect on concrete performance. With the temperature decreasing and water-cement ratio increasing, the damage tends to grow up. Consistent with the results of the strength tests, electron microscopy tests show that the pore size of mortar increases and the material becomes looser.     

Influence of Fine Recycled Aggregate on Physical and Mechanical Properties of Concrete

Based on a series of recycle process, waste concrete can be made into fine recycled aggregate which can be used completely or partly to compound concrete as a substitute for natural sand. But the special properties of fine recycled aggregate make the performance of concrete with fine recycled aggregate different from normal concrete. Characteristics of fine recycled aggregate and its influence on physical and mechanical properties of concrete are studied. On this basis, the influence of fine recycled aggregate on gas permeation properties, chloride permeability, and carbonation resistance of concrete are also studied. It is found that fine recycled aggregate produces a lot of defects in crushing preparation. And the compressive strength, the chloride permeability and the carbonation resistance of the concrete with fine recycled aggregate as substitution show difference from that of normal concrete.     

Experimental Research on High-strength Inorganic Anchoring Material

A new type of inorganic anchoring material is developed as a substitution for anchoring adhesive to overcome some imperfections in the process of planting reinforcing steel bar.The mix proportion of the anchoring material is determined by experiments.The compressive strength,adhesive force to concrete,volume stability and anchoring force with steel bar are studied.The early strength of the anchoring inorganic material is quite high: for 1d up to 38.5MPa and 3d up to 60MPa.It is a good adhesive to concrete and the adhesive strength of 28d is about 2MPa.The anchoring material will have tiny volume expansion with the age,which is beneficial to enhancing the anchoring force.The essential component of the inorganic anchoring material is cement-based material,so some defects of the organic macromolecular material can be avoided,such as poor stability and requirement for vigorous construction conditions.Its characteristics in early strength,adhesive force to concrete and volume expansion can satisfy the requirement of the construction to the planting reinforcing steel bar and the loading force,thus it can be used as a substituting material for anchoring adhesive.     

大跨度PC连续刚构桥徐变预测模型

为了能准确预测混凝土收缩徐变,提出了一系列徐变预测模型,但传统的徐变理论研究主要是针对普通混凝土进行的,所提出的徐变模型并不能完全适用于高强混凝土。对各徐变预测模型进行分析比较,最终参考了日本混凝土示方书建议模型,并在高强混凝土徐变试验的基础上,提出了一个适用于高强混凝土的徐变预测模型。基于Abaqus平台,使用Python语言进行二次开发,定义了修正模型的徐变规律,并采用修正后的模型计算牛角坪大桥的徐变应变。结果表明,修正模型的精度,能很好的满足工程需求。     

Strength-permeability Model of Pervious Cement Concrete

High permeability is an important characteristic of pervious concrete. For the existing permeability testing devices of pervious concrete, the specimen sidewall leakage is serious due to the large numbers of open pores on the surface of specimens. To solve the problem, a new permeability testing method for pervious concrete was developed and a composite sidewall structure with waterproof daub, flexible rubber cushion and rigid sleeve sidewall was proposed. Meanwhile, the strength and permeability of pervious cement concrete are incompatible with a reciprocal relationship. However, limited research has been conducted on the relationship between them. Effects of water-cement ratio (W/C), aggregate-cement ratio and porosity on the properties of pervious concrete, including strength and permeability, were studied. Furthermore, strength-porosity model, permeability-porosity model and strength-permeability model were established. Tests reveal that: a) There is an optimum W/C of pervious concrete, at which strength reaches the maximum; b) The relationship between the strength and W/C shows a downward quadratic curve, and the permeability is proportional to porosity and aggregate-cement ratio; c) The relationship between strength and permeability of pervious cement concrete can be well fitted with the Lorentzian function, and the strength decreases when the permeability increases, but the rate of reduction decreases gradually. The optimum combination of strength and permeability should be determined based on the specific engineering requirements in design.     

Experimental study on the mechanical behavior of eccentrically loaded steel tubular columns filled with structural steel and concrete

Considered strength classes of concrete, ratio of structural steel to concrete, ratio of steel tube to concrete and eccentricity ratio of load, 6 test specimens of steel tubular columns filled with structural and concrete are designed. The damage phenomena of specimens are described in detail and the failure mechanism is analyzed. The results show the initial failure of the specimens are began from the yield of steel tube, the ultimate failure are ended from the buckling of steel tube caused by the expansion of core concrete. Due to the existence of structural steel, the ductility of specimens is superior to steel tubular columns. Before the yield of steel tube, the plane cross-section assumption of specimens can be put into use. The ultimate bearing capacity of specimens is increased with the increase of strength classes of concrete, ratio of structural steel to concrete and ratio of steel tube to concrete. But the ultimate bearing capacity and ductility are decreased with the increase of eccentricity ratio.     

Preparing Technique of Super High StrengthHigh Performance Concrete with Superfine Sand

With the understanding that there will be a great demand for superhigh performance concrete (SHPC) in the future construction engineering,while the resources of coarse and intermediate sand commony used for SHPC are scarce,so it is very important to replace coarse and intermediate sand by plentiful superfine one; First in China and abroad as well a superfine sand superhigh performance concrete with max. slump 255mm and max.28d compressive strength 126.8 MPa was prepared.It was compared with superhigh performance concrete with intermediate sand.     

Performance Comparison of High Strength Concrete Prepared with Metakoalin and Silica Fume

This paper makes a comparison of high strength concrete prepared with Metakoalin and that prepared with silica fume in terms of their workability, compressive strength , shrinkage and resistance to sulphate attack. The research results indicate that high strength concrete prepared with Metakoalin is better than that prepared with silica fume in terms of workability. When the water to binder ratio is high, concrete prepared with Metakoalin has a greater compressive strength than that prepared with silica fume. In contrast, when the ratio is low, it is the concrete prepared with silica fuma has a higher strenth. Concrete prepared with Metakoalin has a smaller auto -shrinkage and dry-shrinkage than that prepared with silica fume. And concrete prepared with Metakoalin will be just as good as concrete prepared with silica fume in terms of resistance to sulphate attack. It is indicated by the research that Metakoalin has same high activity as silica fume in the preparation of high strength concrete.     

THE EVALUATION OF SHEAR STRENGTH TAKING ACCOUNT OF SPAN-TO-HEIGHT RATIO OF SIMPLE BEAMS UNDER UNIFORM LOADS

By introducing the span-to-height ratio,this paper deduces wo evaluating equations of shear strength of simple reinforced concrete beamwith stirrups and under uniform loads.This makes the shear stressing concept consistent with the evaluating equations,thus improves the evaluating equationsof shear strength of the New Code.Two equations are provided with auto-regulating function on shear strength for a cross section of beam.They aresimple and convenient in evaluation.The working time used for design is not increased and 10% of stirrups is economized in frequent conditions of span-to-height ratio.     

The Relationship of Strength,Pore Structure andAutoclaving Schedule of Lime_Sand Concrete

The influences of autoclaving schedule on the compressive strength,bending strength,spliting strength and fracture energy are studied by testing the strengths,fracture energy,pore structure and BET surface of lime_sand concrete with 2 kinds of mix proportion and 8 autoclave schedules.The purpose of the work is to explain the changes of mechanical behaviors of lime_sand concrete by the data of pore structure and BET surface.