Yeonho Park

Time-Dependent Behavior of Synthetic Fiber-Reinforced Concrete Pipes Under Long-Term Sustained Loading

This study presents the long-term behavior of synthetic fiber–reinforced concrete pipe (SYNFRCP) in actual field conditions. Conventional reinforced concrete pipe (RCP) was tested for comparison purposes. The research program was twofold. First, the short-term relationships between the applied loads and the deflections of SYNFRCP were obtained on the basis of the ASTM C497 three-edge bearing test. Second, the changes in the deformations of the buried RCPs and SYNFRCPs under sustained loading were monitored for up to 4,200 h. Two fiber dosages of 8 lb/yd3 (4.8 kg/m3) and 12 lb/yd3 (7.0 kg/m3) were used during the pipe production. Two 24-in. (600-mm) and two 36-in. (900-mm) pipes were buried in trenches with a sustained load of 1,350 lb/ft/ft (65 kN/m/m). The pipes were initially backfilled with native soil up to 2 ft (600 mm) and 4 ft (1,200 mm) over the top of the pipe and then backfilled with 14 ft of pea gravel above this to simulate the maximum fill height sustained by a Class 3 Wall B precast concrete pipe on the basis of ASTM C76. Two displacement transducers were installed from the crown to the invert at two sections along the length of each pipe. All buried pipes were precracked until the first visible crack was observed. The precracking was done to evaluate the long-term performance of SYNFRCP in which fibers are engaged after cracking. The strength, the crack width, and the change in the vertical deformation of the buried SYNFRCP and RCP are compared and presented in this paper.

Flexural Characteristic of Rubberized Hybrid Concrete Reinforced With Steel and Synthetic Fibers

To enhance the low strain capacity and brittleness of concrete, several researchers have already reported on the mechanical properties of rubberized concrete, which lead to reduced environmental concerns, direct cost reduction, low unit weight, high toughness, and improved absorption of impact. However, to overcome the drawbacks of low flexural strength and the low stiffness of rubberized concrete and to improve the crack resistance, steel, or synthetic (polypropylene) fibers, or both, were added into the rubberized concrete in this study. Based on the flexural performance test according to ASTM C1018 and ASTM C1609, this study investigates the combination of crumb rubber, steel or synthetic fibers, or both, in zero-slump concrete mixtures used in the dry-cast production method for concrete pipes. A series of concrete mixes were examined with the variation of the fiber volume fraction (Vf) (steel: 0.17 % and 0.33 %/synthetic-polypropylene: 0.17 %, 0.33 %, and 0.52 %), and crumb rubber with different replacement ratios of 3 % to 20 % (by volume) for sand (fine aggregate) in the concrete mixture. Seventeen rubberized mixtures were developed by incorporating different dosages of steel and polypropylene fibers and their combinations. The influence of fiber type, dosages of fibers, and rubber are analyzed on the basis of experimental results. Results indicate that the effect of hybrid reinforcement using both steel and polypropylene fiber in rubberized concrete is considerable in terms of increase in both peak load and toughness. The specimen of hybrid fiber-reinforced rubberized concrete (HYFRC) with 44 lb/yd3 (0.33 %: Vf) of steel fiber, 8 lb/yd3 (0.33 %: Vf) of polypropylene fiber and 3 % of crumb rubber (replacement with fine aggregates) showed higher peak load, modulus of rupture, and toughness than other mixtures. However, excessive replacement of rubber into the specimens had a negative effect on the flexural properties (strength and toughness).

Compressive strength and microstructural properties of fly ash-based geopolymer concrete

AbstractThis study examines the role of alkali hydroxide and its concentration on the microstructure and compression strength of fly ash–based geopolymer concrete. Geopolymer is an innovative ceramic material, composed of long chains and networks of inorganic molecules, that is used as an alternative to conventional portland cement for civil infrastructure applications. Some of the advantages of geopolymer concrete are its fast setting time, rapid strength development, and its significantly reduced carbon footprint. In this study, aluminosilicate geopolymers with different alkaline solutions [NaOH, KOH, Ba (OH)2, and LiOH] were prepared by mixing Class C (9.42% CaO) and Class F-fly ash (1.29% CaO). The samples were cured under different experimental conditions and then tested for compressive strength. X-ray diffraction (XRD) and scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS) have been used to identify the new phases formed in the geopolymeric matrix. The results revealed that micros...

Probabilistic Shear Capacity Models for Concrete Members with Internal Composite Reinforcement

AbstractThis paper presents probabilistic models for estimating shear capacity of concrete members reinforced internally with fiber-reinforced polymer (FRP). The application of FRP in concrete structures has steadily gained popularity since the late 1980s; however, the wide range of mechanical properties and various manufacturing processes have made it challenging to unify the design formulation for engineers and code developers. Consequently, the conservative approach has been used to predict structural performance, particularly shear capacity, which has limited its application and resulted in excessive use of materials. In this paper, a robust prediction model is proposed to capture the variety of characteristics of FRPs based on an available database. The database includes various FRPs used as flexural reinforcement for beam members. The model was formulated using the Bayesian parameter estimation method, which takes into account the uncertainties of the parameters that are considered the potential pre...

Staged construction modeling of steel pipes buried in controlled low-strength material using 3D nonlinear finite-element analysis

AbstractSeveral complexities are inherent in numerical simulation of staged construction modeling of large-diameter steel pressure pipes. A comprehensive robust three-dimensional (3D) nonlinear finite-element analysis model was developed and verified using three experimental field tests conducted at the Rolling Hills Booster Pump Station, Fort Worth, Texas, to simulate the behavior of buried steel pipes during staged construction installation. Controlled low-strength material (CLSM) was used as the embedment material, and the depth of the CLSM embedment and the trench width varied. The developed numerical model includes three possible nonlinearities, including geometric, material, and contact nonlinear algorithms. A large deformation algorithm was considered in the finite-element model and its associated analysis using a total Lagrangian formulation. The contact between each soil layer, soil-to-trench wall, and soil to pipe was carefully implemented. The lateral effect of compaction was identified in prev...

Meridian Stresses in Thin-Walled Steel Pipes as Reason for Cross-Sectional Ovalization

AbstractThis work was motivated by the need for providing designers with more effective rehabilitation procedures. The initial step taken was to assess the ovality of the cross sections of thin-wal...

Field Deflection-Measurement Techniques and Finite-Element Simulation for Large-Diameter Steel Pipes with Controlled Low-Strength Material

AbstractDeflection measurements and finite-element simulation were conducted for buried steel pipes that had been installed using a staged construction technique. The pipes were mortar lined, with ...

Acoustic Emission Performances of Stressed-GFRP Bars Embedded in Concrete under Accelerated Aging Conditions

This research presents test results of an experimental study to investigate tensile strength degradation of stressed-GFRP bars embedded in concrete after accelerated aging. The experimental program included twelve tensile specimens with two different types of GFRP bars [Wrapped surface (herein, Type-A) and Sand-coated surface (herein, Type-B)]. Specimens were placed in a weathering chamber [46°C (115°F) and RH: 80%] with a sustained load. In addition, acoustic emission as a nondestructive evaluation was performed to investigate the degradation of GFRP bars. Results revealed that the residual tensile strengths were about 85.5 and 82.5% (reduction by 14.5 and 17.5%) after 300 days of exposure, respectively, for Type-A and Type-B bars. This paper devotes attention to the acoustic emission performance on the aged GFRP tensile curves. Test results indicated that changes in AE parameters due to aging could be identified as strength/stiffness degradation. AE parameters also showed a good correlation with the mechanical responses of test specimens after accelerated aging. Author keywords: Accelerated aging, Acoustic emission, Durability, Glass fiber reinforced polymer (GFRP), Tensile strength