Experimental and Analytical Studies of Size Effects on Compressive Ductility Response of Ultra- High-Performance Fiber-Reinforced Concrete

Ultra-high-performance fiber-reinforced concrete (UHPFRC) has gained a great deal of increasing interest in structural engineering applications, particularly where high ductility, strength, and high impact resistance are of prime concern. This study focuses primarily on the size effects ductility characteristics of UHPFRC with varying fiber concentrations subjected to uniaxial compressive load. It shows how to process the data from compression cylinder tests to extract the size-dependent strain at peak stress to provide a generic size-dependent stress-strain analytical model. Furthermore, a numerical flexural segmental moment-rotation approach is applied to incorporate an analytical model to quantify apparently disparate UHPFRC member strength and ductility. Tests have shown that it is not the enhancement in the material concrete compressive strength but the phenomenal brittle ductility nature, observed as a result of increasing the slenderness of the specimen; in contrast, a substantial increase in ductility was achieved after crushing of concrete due to the addition of fibers. A size-dependent analytical approach has estimated good fit with the experimental and other published results. Finally, numerical simulation using a segmental approach at the ultimate limit state of rotation dealing with flexural ductility is significantly influenced by the increase in slenderness factor of the specimens and fiber concentrations

Flow and Strength Characteristics of Ultra-high Performance Fiber Reinforced Concrete: Influence of Fiber Type and Volume-fraction

Ultra-High Performance Fiber Reinforced Concrete (UHPFRC) has emerged all of the concrete in the construction industry because of its high strength, durability, serviceability and excellent ductility recently. Due to its high production cost, UHPFRC restricts its large-scale structural application. The conventional UHPFRC preparation consists of expensive materials such as specially graded sands which require complex mixing and curing process. The aim of this paper is to determine flow and strength properties of UHPFRC with the variation of fiber type and fiber volume-fraction. The UHPFRC composition was selected with four different fiber volume fractions (Vf = 0%, 1%, 2%, and 3%) of three different steel fibers at varying curing ages of 7, 28, 56 and 90 days within an identical mortar matrix. The paper provides an overview on the workability properties of UHPFRC followed by the presentation of compressive strength test results with different fibers and its volume-fraction with varying curing ages. The higher fiber volume-fraction resulted in a lower flow, and consequently an improvement of compressive strength observed up to 3% volume-fraction of fibers at 56 days curing. Finally, test results are compared and discussed with regard to the main variables: fiber volume-fraction, types of fiber; and curing ages of the specimens

A generic segmental analysis of all types of RC members.

This thesis contains a series of journal papers in which a new segmental moment-rotation (M/θ) approach is developed for both instantaneous and long term loading. The analysis technique is based on the starting position of moment-rotation rather than moment-curvature and the assumption that plane sections remain plane, but not on the often applied corollary of a linear strain profile. Using the well-established mechanics of partial-interaction theory, the M/θ approach simulates the formation and gradual widening of cracks as well as tension stiffening, as the reinforcement slips relative to the concrete which encases it, and, using the mechanics of shear-friction theory, the approach simulates the formation and failure of concrete softening wedges. Moreover, being mechanics based, the M/θ approach can in theory be applied to any type of member, that is any cross section, with any concrete properties, and any reinforcement type with any bond characteristic. Hence using partial-interaction and shear friction theories, the M/θ approach obviates the need for both empirically derived effective flexural rigidities and hinge lengths. This leads to the establishment of a new equivalent flexural rigidity that accounts for both concrete cracking and concrete softening and can be applied to both instantaneous and long term loading. Having established the equivalent flexural rigidity from segments of a member, it can then be used to predict the effective flexural rigidity of an entire member, and hence the load deflection behaviour through the application of a numerical segmental analysis procedure. It is further shown that with simplifying assumptions closed form solutions to describe the equivalent flexural rigidity of a segment can be obtained and member deflections described using standard analysis techniques. Having established that the M/θ technique can be applied using both numerical and closed form solutions, it is used to predict a broad range of reinforced concrete behaviours. These behaviours include: the instantaneous deflection of beams reinforced with both ductile steel and brittle fiber reinforced polymer bars and the instantaneous deflection of laterally and eccentrically loaded columns, including those in which second order effects are considerable and the long term deflection of simply supported beams. Through these broad applications, it is shown that the M/θ approach represents a mechanics based solution to reinforced concrete analysis, capable of accurately predicting both instantaneous and long term deflections from serviceability through to peak loading and collapse, where the only empirically derived requirements are material properties. Hence, the M/θ approach can be considered an extension of traditional analysis techniques in that it removes the need to empirically define effective flexural rigidities and hinge lengths to determine member behaviour.Thesis (Ph.D.) -- University of Adelaide, School of Civil, Environmental and Mining Engineering, 201

Case studies of material properties of late nineteenth-century unreinforced masonry buildings in unreinforced masonry buildings in Adelaide

An experimental programme was developed to improve our understanding of the actual in situ strength of non-structural components in typical South Australian unreinforced masonry (URM) construction. The focus was on testing URM walls and chimneys in out-of-plane direction, and in the course of this study 132 as-built URM material specimens were collected. The specimens were tested either in situ or in laboratory. In total, four URM houses located in Darlington, a southern suburb of Adelaide, South Australia, were studied. Three of the buildings were built in the 1960s and the fourth was built in the 1980s. A comparison between the buildings material strength and the default values recommended in the Australian Masonry Standards, AS3700, suggests that the code specified default lower 5% characteristic values were often greater than the measured characteristic strength. The collected data are presented for documentation and some comparison between this and other studies are also made

A comprehensive data driven study of mechanical properties of concrete with waste-based aggregates: Plastic, rubber, slag, glass and concrete

In an attempt to reduce the consumption of natural resources, much research has focused on the development of mix designs with waste aggregates. While this research has demonstrated feasibility, investigations into the broader mechanical properties of concrete with various types of waste aggregates have been limited. To this end, this paper studies a wide variety of concrete properties with plastic, rubber, slag, glass and recycled concrete aggregates by analysing a large database of 5321 concrete mixes. The effects of waste aggregate type and replacement ratio on mechanical properties, workability and durability are investigated and relationships between the mechanical properties of concrete with various types of waste aggregates are quantified and compared to the existing design codes. The findings from this study can be used to assist in identifying optimum waste aggregate type and replacement ratio based on intended use and the databases compiled will assist in future data-driven modelling approaches

A pilot study of laser-welding cast basalt blocks for lunar construction

Using sintered or melted regolith to produce masonry units is a promising option for constructing lunar base civil infrastructure. However, the ingredients needed to produce cementitious mortar are not easily available on the moon and using water-based mortars in the lunar vacuum could be problematic. This pilot study reports experimental trials using specimens cut from cast basalt tiles to investigate laser welding as an alternative method of bonding lunar masonry. In a bead-on-block study to identify the optimal laser parameters it was found that weld penetration was limited to 1.5 mm and that without preheating and annealing, cracking was unavoidable. Pairs of blocks were also butt-welded together autogenously and tested for flexural strength. With preheating and annealing in a furnace, it was possible to produce welds with tensile strengths of up to 16.5 N/mm (≈ 12.7 MPa). Even without preheating and annealing, a weld strength of 0.9 N/mm (≈ 0.6 MPa) was achieved. This might be sufficient to support masonry unit self-weight during construction to avoid the need for falsework. The pilot study demonstrated that although preventing cracking when welding cast regolith materials is challenging and weld penetration depth places an absolute limit on scalability, the technology shows sufficient promise to justify further trials. Improved results might be achieved in a vacuum with a controllable laser and if the porosity of the sintered or cast regolith parent material was optimised for weldability

Experimental and Analytical Studies of Size Effects on Compressive Ductility Response of Ultra-High-Performance Fiber-Reinforced Concrete

Ultra-high-performance fiber-reinforced concrete (UHPFRC) has gained a great deal of increasing interest in structural engineering applications, particularly where high ductility, strength, and high impact resistance are of prime concern. This study focuses primarily on the size effects ductility characteristics of UHPFRC with varying fiber concentrations subjected to uniaxial compressive load. It shows how to process the data from compression cylinder tests to extract the size-dependent strain at peak stress to provide a generic size- dependent stress-strain analytical model. Furthermore, a numerical flexural segmental moment-rotation approach is applied to incorporate an analytical model to quantify apparently disparate UHPFRC member strength and ductility. Tests have shown that it is not the enhancement in the material concrete compressive strength but the phenomenal brittle ductility nature, observed as a result of increasing the slenderness of the specimen; in contrast, a substantial increase in ductility was achieved after crushing of concrete due to the addition of fibers. A size-dependent analytical approach has estimated good fit with the experimental and other published results. Finally, numerical simulation using a segmental approach at the ultimate limit state of rotation dealing with flexural ductility is significantly influenced by the increase in slenderness factor of the specimens and fiber concentrations