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UHPC curing regimes
Curing regime plays an important role on the properties of concrete especially on the compressive strength of UHPC. The most commonly implemented curing regime for UHPC is heat treatment which involves subjecting the specimen to 90°C under very moist conditions. As UHPC mostly contains cement extenders, there is a belief that high temperatures accelerate the pozzolanic reaction in concrete (Yazıcı et al., 2010; Zheng et al., 2012; Abid et al., 2017; Peng et al., 2018). Actually, the microstructure of the concrete is improved by the heat treatment accelerating the pozzolanic reaction of silica fume and cement modifying the structure of the hydrate. However, heat treatment is not required for all application of UHPC. Without any heat treatment, the concrete can still have superior strength and ductility characteristics compared to any previously manufactured concrete.
Various investigations have been published referring to various curing regimes with different procedures in order to reach to the highest possible compressive strength (Ay, 2004; Schachinger et al., 2008; Ahlborn et al., 2008; Yang et al., 2009; Askar et al., 2017; Peng et al., 2018). These different curing regimes include hot air curing, steam curing, water curing and autoclaving at different temperatures and durations.
Richard and Cheyrezy (1995) suggested heat treatment as one of the basic principles used to increase the compressive strength of RPC. In their study the compressive strength of concretes were enhanced from 170 MPa to 230 MPa by heating samples from 20°C to 90°C, respectively. De Larrard and Sedran (1994) observed that the 7-day compressive strength improved from 120.6 MPa to 235.8 MPa. This improvement was achieved by changing the curing regime from normal water curing to thermal curing at 90°C for 48 hours. Heat treatment is considered as curing regime in most of the UHPC studies (Voo et al., 2006; Yang et al., 2010; Hassan et al., 2012; Yoo, 2013; Kang et al., 2017; Li et al., 2017).
Graybeal and Davis (2008) studied the compressive strength of UHPC with different size of cubes (51, 70.7 and 100 mm) and cylinders (51, 76 and 102 mm) with the aim of checking the reliability of compressive strength results obtained from other cube and cylinder sizes rather than the standard sizes. In their research, they also applied different curing regimes. Some of the specimens were kept in a laboratory environment, some were kept in 95% humidity at different temperatures (95°C, 90°C, 80°C, 60°C, 40°C and 22°C) mostly for 2 days. The results showed that by decreasing the temperature from 95°C to 22°C the average 28-day compressive strength of 100 mm cubes decrease from 198.1 MPa to 139.0 MPa. An average compressive strength of 141.5 MPa was obtained from the specimens kept in a laboratory environment for 28 days. The results revealed that the 70.7 and 51 mm cubes, as well as the 102 and 76 mm cylinders tend to show similar strengths.
In the study done by Yang et al. (2009) two types of curing were considered, 20°C and 90°C water. Some of the specimens were kept in 90°C water for 6 days (followed by storing in air at room temperature until testing) and the rest were cured in 20°C water until testing. Results revealed that at 28 days specimens cured at 90°C had 20% higher compressive strength, 10% higher flexural strength and 15% higher fracture energy than specimens cured at 20°C.
CHAPTER 1 INTRODUCTION
1.1 BACKGROUND
1.2 PROBLEM STATEMENT
1.3 OBJECTIVE
1.4 METHODOLOGY
1.5 SCOPE OF RESEARCH
1.6 ORGANIZATION OF THE THESIS
CHAPTER 2 LITERATURE STUDY
2.1 INTRODUCTION .
2.2 DESIGN CONSIDERATION IN PRESTRESSED CONCRETE .
2.3 ULTRA HIGH PERFORMANCE CONCRETE (UHPC) .
2.4 UHPC MIX DESIGN AND CURING
2.5 EFFECT OF FIBRE ON MECHANICAL PROPERTIES OF CONCRETE
2.6 PRESTRESS LOSS
2.7 BOND BEHAVIOUR IN PRESTRESSED BEAMS
2.8 FAILURE OF REINFORCED CONCRETE BEAMS .
2.9 CONCLUSION AND STUDY MOTIVATION
CHAPTER 3 PRELIMINARY INVESTIGATION ON THE DEVELOPMENT OF A LOCAL MIX DESIGN AND CURING REGIME
3.1 INTRODUCTION
3.2 MATERIALS
3.3 MECHANICAL PROPERTIES TESTING METHOD .
3.4 THE PROCEDURE TO DETERMINE THE MIX COMPOSITION
3.5 MATERIAL COST OF THE MIX DESIGNS
3.6 COMPREHENSIVE STUDY ON THE EFFECT OF DIFFERENT TYPES OF FIBRE AND CURING REGIME ON THE MECHANICAL PROPERTIES OF UHPC
3.7 CURING REGIME: THE EFFECT OF HEAT GRADIENT ON THE COMPRESSIVE STRENGTH OF UHPC
CHAPTER 4 EXPERIMENTAL SETUP TO DETERMINE LOSSES AND BOND BEHAVIOUR
4.1 INTRODUCTION
4.2 DRYING SHRINKAGE
4.3 CREEP .
4.4 PRESTRESSING STEEL WIRE PROPERTIES
4.5 PULL-OUT TESTING PLAN .
4.6 BOND STRESS CALCULATION
CHAPTER 5 EXPERIMENTAL RESULTS OF DRYING SHRINKAGE, CREEP AND BOND PERFORMANCE
5.1 INTRODUCTION
5.2 DRYING SHRINKAGE RESULTS
5.3 CREEP RESULTS
5.4 EVALUATION OF DEVELOPMENT LENGTH
5.5 EFFECT OF CONCRETE COVER ON BOND STRENGTH
5.6 CONCLUSION
CHAPTER 6 PRELIMINARY STUDY ON PRESTRESSED BEAMS
CHAPTER 7 PREPARATION OF LARGE-SCALE UHPFRC PRESTRESSED BEAMS
CHAPTER 8 RESULTS AND ANALYSIS OF LARGE-SCALE UHPFRC PRESTRESSED BEAMS
CHAPTER 9 CONCLUSIONS AND RECOMMENDATIONS
CHAPTER 10 REFERENCES
