再生混凝土（RAC）的特性试验研究

论文摘要

再生骨料被用来作为替换已知的天然骨料已经数年,使用再生骨料的潜在利益再怎么强调都是不过分的。为使这些的利益切实可行,必须对再生混凝土工程特性进行研究。因此,本研究是试图评估再生骨料混凝土广泛的工程特点。为减少每个试验所需的样本数量,在本次研究中,采用了Taguchi正交优化技术方法。在此方法中,只用选择含控制因素的少量组合,并用与之相关的理论来设计整个试验并对试验结果进行统计学分析,该理论是基于正交矩阵的使用,方差分析（ANOVA）和F分布的显著性分析。另外,在分析中用到了信噪比值,信噪比分析的目的是根据不同因素影响的结果来确定最佳的控制条件。所有试验均符合中国规范和美国材料与试验协会（ASTM）的要求。试验分两个阶段进行:在第一阶段,在回收骨料含量和粉煤灰含量变化的条件下,研究再生混凝土的物理性能。这些性能包括抗压强度,断裂模数（抗折强度）,劈裂抗拉强度和弹性模量。选择三因素四水平正交表来确定配合比。主要因素有水灰比,回收骨料替代率和粉煤灰取代率。水平代表替代率,如下所示:（i）水灰比（W/C）=0.45,0.50,0.55,0.58（ii）再生骨料替代率%=0,30,60,100（iii）粉煤灰替代率%=0,20,30,40（iv）此外每平方混凝土1.5%的钢纤维以便知道对28天强度的影响。配合比28天设计强度为30Mpa,四个基本强度分别在7天,28天,90天测得,钢纤维再生混凝土只需测试28天强度。对不同强度值及强度之间的数量关系进行了回归分析,得到了最佳回归式（基于正交试验结果基础之上）。结果表明,随着水灰比和再生骨料替代率的增加,无论龄期,再生混凝土的抗压强度,抗折强度,劈裂抗拉强度均减小,但对每个水灰比而言,既含有天然骨料,也含有回收骨料的混凝土强度值差别不大,当再生骨料替代率没有到达60%时,相差在0.5-20%范围之内。粉煤灰对混凝土强度影响不大,仅减少了用水量和提高其工作性能。对于掺入钢纤维的混凝土,抗压强度和劈裂抗拉强度分别提高10-30%和27-41%。研究的第二部分,测试再生混凝土在冻融循环下的工作性能,采用四水平三因素的正交表来设计配合比,主要因素包括:水灰比,再生骨料替代率,粉煤灰替代率和空气含量,通过添加引气剂使混凝土中形成小的,不连续的所谓夹带空气的气泡。上述水平仍然代表替代率,如下所示:（ⅰ）水灰比（W/C）=0.45,0.50,0.55。（ⅱ）再生骨料替代率%=0,50,100（ⅲ）粉煤灰替代率%=0,20,30（ⅳ）空气掺入量%=2.5,3.5,4.5配合比28天设计强度为30Mpa。部分试件（100mm立方体和100×100×400mm棱柱）用来测试抗压和抗折强度,其余的样本（100×100×400mm棱柱）被安置在冻融机中,确定影响其耐久性的抗冻性能。结果表明,对饱和再生混凝土,再生骨料对其工作性能有负面影响。对于暴露于剧烈天气情况下的建筑,不建议采用回收混凝土。但采用矿物和化学外加剂,特别是引气剂和粉煤灰,再生混凝土可表现一定的耐久性。对不同强度值及强度之间的数量关系进行了回归分析,得到了最佳回归式（基于正交试验结果基础之上）。总而言之,从强度的角度来看,可以得出,在再生骨料替代率不超过60%的前提下,再生混凝土可应用于不同的工程实际。然而,从抗冻性能来看,仍需对再生混凝土在冻融循环下如何提高耐久性进行更多的研究。

论文目录

• ABSTRACT
• 摘要
• TABLE OF CONTENTS
• CHAPTER ONE:INTRODUCTION
• 1.1 BACKGROUND OF STUDY
• 1.2 OBJECTIVES
• 1.2.1 Part 1
• 1.2.2 Part 2
• 1.3 STRUCTURE OF THE THESIS
• CHAPTER TWO:LITERATURE REVIEWS
• 2.1 INTRODUCTION
• 2.2 AGGREGATES OBTAINED FROM RECYCLED CONCRETE
• 2.2.1 Grading of Recycled Aggregates
• 2.2.2 Properties of Recycled（Coarse）Aggregates
• 2.2.3 Recommendations of RILEM（1989）on Recycled Aggregates
• 2.3 FRESH PROPERTIES OF RECYCLED AGGREGATE CONCRETE
• 2.3.1 Water Demand and Workability
• 2.3.2 Water/Cement Ratio
• 2.3.3 Quantity of Cement
• 2.3.4 Density and Air Content
• 2.4 MECHANICAL PROPERTIES OF RAC
• 2.4.1 Rate of Strength Development and Compressive Strength
• 2.4.2 Modulus of Elasticity and Damping Capacity
• 2.4.3 Tensile and flexural strength
• 2.4.4 Durability of RAC
• 2.5 FIBER REINFORCED CONCRETE
• 2.5.1 Toughening Mechanisms of Fiber Reinforced Concrete
• 2.5.2 Steel Fiber Reinforced Concrete（SFRC）
• 2.5.3 Mix Design of SFRC
• 2.5.4 Technology for Producing SFRC
• 2.5.5 Mechanical Properties of SFRC
• 2.6 FREEZING AND THAWING MECHANISM
• 2.6.1 Background
• 2.6.2 Microstructure of Concrete
• 2.6.3 Air Voids in Concrete
• 2.6.4 Air-Entraining Admixture（AEA）
• 2.6.5 Mechanisms of Freeze-Thaw Damage
• 2.6.5.1 Hydraulic Pressure Theory
• 2.6.5.2 Ice Accretion and Osmotic Pressure Theory
• 2.6.6 Freezing and Thawing Resistance of Recycled Aggregates
• 2.7 ECONOMIC ASPECT OF CONCRETE RECYCLING
• CHAPTER THREE:MATERIALS SELECTION AND MAKING OF SPECIMENS
• 3.1 CONCRETE MATERIALS
• 3.1.1 Concrete with Natural Aggregate
• 3.1.2 Recycled Aggregate Concrete
• 3.2 DESIGN OF EXPERIMENTS AND MAKING OF SPECIMENS
• 3.2.1 Introduction to Taguchi Orthogonal Arrays
• 3.2.2 Design of Experiments
• 3.2.3 Mixing of Concrete
• 3.2.4 Casting of Concrete Specimens
• 3.2.5 Curing of Concrete Specimens
• CHAPTER FOUR:LABORATORY TESTING PROCEDURES
• 4.1 TEST PROGRAM
• 4.2 TESTING OF FRESH CONCRETE
• 4.3 FREEZE-THAW TEST
• 4.4 COMPRESSIVE STRENGTH TEST
• 4.5 MODULUS OF RUPTURE（FLEXURAL STRENGTH）TEST
• 4.6 SPLITTING TENSILE STRENGTH TEST
• 4.7 MODULUS OF ELASTICITY TEST
• CHAPTER FIVE:ANALYSIS OF RESULTS AND DISCUSSION
• 5.1 PROPERTIES OF RECYCLED AND NATURAL AGGREGATES
• 5.1.1 Grading
• 5.1.2 Shape and Texture
• 5.1.3 Water Absorption
• 5.1.4 Density
• 5.1.5 Crush Value Index of Coarse Aggregates
• 5.2 FRESH CONCRETE PROPERTIES
• 5.2.1 Workability
• 5.2.1.1 Analysis of slump
• 5.2.2 Air content
• 5.3 PART 1:HARDENED CONCRETE PROPERTIES
• 5.3.1 Compressive Strength
• 5.3.2 Modulus of Rupture（Flexural Strength）
• 5.3.3 Splitting Tensile Strength
• 5.3.4 Modulus of Elasticity
• 5.3.5 Steel Fiber Reinforced Concrete（SFRC）
• 5.4 EMPIRICAL MODELS PREDICTIONS FOR THE HARDENEDCONCRETE PROPERTIES
• 5.5 MODEL PREDICTION FOR THE RELATIONSHIPS BETWEEN THE HARDENED CONCRETE PROPERTIES
• 5.5.1 Introduction
• 5.5.2 Model Prediction the for Relationship between Splitting Tensile Strength and Compressive Strength
• 5.5.3 Prediction of Model for Relationship between Flexural Strength and Compressive Strength
• 5.5.4 Prediction of Model for Relationship between Modulus of Elasticity and Compressive Strength
• 5.5.5 Prediction of Model for Relationship between Splitting Tensile Strength and Flexural Strength
• 5.6 PART TWO:FREEZE-THAW RESISTANCE
• 5.6.1 Hardened Properties of Air-Entrained Concrete
• 5.6.2 Non-Destructive Evaluation of Dynamic Modulus of Elasticity
• CHAPTER SIX:CONCLUSIONS AND RECOMMENDATIONS
• 6.1 CONCLUSIONS
• 6.2 RECOMMENDATIONS
• REFERENCES
• APPENDIX A
• APPENDIX B
• ACKNOWLEDGMENTS