MAT-714: CONDITION ASSESSMENT AND DETERIORATION PREDICTION TOOLS FOR CONCRETE BRIDGES: A NEW LOOK

Structural problems created by corrosion, ageing, aggressive environments, material defects and unforeseen mechanical or seismic loads can compromise the serviceability and safety of bridges. The importance of an effective bridge-management system (BMS) cannot be overstated, especially in light of the recent collapse of bridges in North America and elsewhere. Several technologies are available for assessing the condition of concrete bridges and a number of deterioration models are used to predict future bridge conditions and estimate associated funding requirements. This paper critically reviews the different available condition assessment and deterioration prediction approaches for concrete bridges. The potential applications of condition assessment technologies with particular focus on their advantages and limitations are presented. The various types of deterioration models are discussed and compared. The findings indicate that: (i) non-destructive testing (NDT) methods and structural health monitoring (SHM) systems can play a major role in effectively evaluating the conditions of concrete bridges; (ii) mechanistic models for deterioration prediction embrace a reliability-based approach that can provide bridge owners and maintenance personnel with an improved tool to assess bridge conditions and to make decisions regarding their maintenance; and (iii) automated data collection and interpretation analysis is needed for improved BMS. The challenges associated with the different technologies and models are outlined. Furthermore, to empower bridge asset managers in making more informed decisions, recommendations are made on the selection of appropriate evaluation and prediction models that meet desired service goals

MAT-713: EVALUATION OF NDT TECHNIQUES FOR CONCRETE BRIDGE DECKS USING FUZZY ANALYTICAL HIERARCHY PROCESS

Considering the colossal backlog of deteriorating bridges, transportation agencies need to systematically evaluate bridge deck conditions in order to optimize the timing, scope, and approach of preventive maintenance, repair, and replacement. Over the last few years, there have been growing interest among bridge infrastructure stakeholders in using non-destructive methodologies for bridge inspection, evaluation, and maintenance. Nondestructive testing (NDT) techniques can provide needed information about the “under-the-surface” deteriorated condition of bridge decks. This paper examines the most common NDT technologies for assessing bridge decks. Each technology was rated based on five performance measures: capability to detect subsurface defects, speed of data collection, simplicity of analysis and interpretation, accuracy of results, and cost of measurement. The study has particular emphasis on reinforcement corrosion, delamination, and internal cracking. The information sought to identify the significance of the factors affecting the analysis process was collected through a survey questionnaire. In order to incorporate the imprecise information and vagueness of human judgment in the decision-making, the fuzzy analytical hierarchy process (FAHP) is employed, as per the fuzzy preference programming method. Results demonstrate the capabilities of each technology and its ability to address bridge challenges. In order to assist bridge engineers and decision makers, recommendations were made with respect to the selection of the most appropriate technologies to identify specific deterioration mechanisms

MAT-720: EFFECT OF PORE STRUCTURE ON CONCRETE DETERIORATION BY PHYSICAL SULPHATE ATTACK

Repeated crystallisation of salt minerals has been considered as the driving force for surface scaling of concrete exposed to physical sulphate attack. This damage is initiated when stresses induced by the internal pressure created via repeated salt crystallisation exceed the tensile strength of the concrete. The degree of such damage will depend mainly on the structure and connectivity of pores, which control the penetration of sulphates into the concrete. Several factors affect the pore structure including the concrete constituents, mixture proportions and the curing process. Therefore, in this paper, the effect of the pore structure on concrete deterioration by physical sulphate attack was investigated. Results show that the durability of concrete against physical sulphate attack can be controlled by tailoring the pore structure of the concrete surface

MAT-721: ALKALI-SILICA REACTIVITY IN SOUTHWESTERN ONTARIO AGGREGATES

Alkali-silica reaction (ASR) occurs between alkalis in concrete and reactive silica in aggregates. This reaction results in the formation of alkali-silica gel, which fills the pore space in the cementitious matrix, leading to expansion and damage. Reactive aggregates that can cause this type of damage were identified in different locations in Southwestern Ontario. X-Ray diffraction and petrographic analysis were used to investigate the type of reactive minerals in such aggregates. In addition, the effect of using different types of cement replacement-materials, including crushed limestone powder, fly ash, silica fume, and nano-silica on ASR were investigated in cement mortars incorporating the reactive aggregates. Results indicate that the expansion of mortar bars due to alkali-silica reaction can be controlled using an adequate type and substitution level of cement replacement materials

MAT-717: MECHANICAL PERFORMANCE OF HYBRID FIBRE-REINFORCED ENGINEERED CEMENTITIOUS COMPOSITE INCORPORATING NITISMA SHORT FIBRES

A new high-strength, high-tensile ductility hybrid fibre-reinforced engineered cementitious composite (HECCSMAF) incorporating randomly dispersed nickel-titanium shape memory alloy short fibres (NiTi-SMA) has been pioneered in this study. The mechanical properties of the HECC-SMAF produced with a combination of 2% polyvinyl-alcohol (PVA) and 0.5%, 1%, and 1.5% NiTi-SMA fibres by volume fraction have been explored. The experimental results indicate that utilizing a combination of those fibres can enhance the tensile capacity of ECC by up to 39% with a slight to no increase in compressive strength. An overall reduction in workability was observed compared to that of ECC made with only 2% PVA by volume fraction, which is typical of metallic fibre-reinforced cementitious systems. Among the tested ECC mixtures, HECC-SMAF made with 2% PVA and 1% NiTi-SMA presents the best mechanical performance

MAT-715: SUSTAINABLE HIGH-VOLUME FLY ASH GROUTS FOR TWO-STAGE CONCRETE

Two-stage concrete (TSC) is a special type of concrete in which coarse aggregates are pre-placed in the formwork and subsequently injected with a grout. Beneficiating fly ash in TSC grouts increases TSC sustainability through the ecological use of large quantities of fly ash, reduced carbon-dioxide emissions associated with cement production, and enhancement of resource productivity of the concrete industry. Limited research has explored the effects of using high volume of fly ash as partial replacement for cement in TSC grout mixtures. Therefore, the flowability of grout mixtures incorporating various fly ash addition rates (i.e. 0%, 30%, 50% and 70%) was evaluated using the flow cone method and spread flow test. Correlations between the efflux time and spread flow for the grout mixtures were developed. Results show that increasing the fly ash addition reduced the grouts efflux time while increasing its spread flow. The optimum high-volume fly ash dosage for achieving high flowability and acceptable TSC compressive strength was identified

MAT-719: INVESTIGATION OF GROUTED PRECAST CONCRETE WALL CONNECTIONS AT SUBFREEZING CONDITIONS

The effect of exposing grouted precast wall connections to subfreezing curing temperatures at early-age was explored in this study. In cold weather construction, heating of the surrounding environment of grouted precast wall connections is usually conducted for short periods of time. Hence, subfreezing conditions can affect the strength of the grout and the bond strength of the connection, which can ultimately compromise the integrity of the structure. In this study, grout specimens typical of that used in precast wall construction were cured at ambient conditions for one day, and then placed in an environmental chamber at subfreezing temperatures (-10°C and -20°C). The compressive strength development of the grout was monitored, and the bond strength of grouted connections cured at cold temperature were quantified and compared to that of specimens cured at ambient temperature. The bond was investigated on 25M deformed steel bars, which is the typical size used in precast concrete wall grouted connections. Test results indicate a reduction in grout strength and the need for a longer embedment length when early-age curing is conducted at subfreezing conditions

Seismic Performance of RC Beam-Column Edge Joints Reinforced with Austenite Stainless Steel

Using stainless steel (SS) reinforcement can mitigate colossal corrosion damage inflicted to reinforced concrete (RC) structures worldwide. However, there is still dearth of studies on the seismic behavior of SS-RC structures. Hence, quasi-static tests were carried out in this study to explore the seismic performance of three RC frame edge joint specimens reinforced with SS having strength grade of 500 and one control RC specimen made with grade 400 normal steel. RC edge frame joints reinforced with ordinary steel and SS exhibited similar bending-shear failure patterns at the beam root. The load bearing capacity of the SS-RC edge fame joint specimens was greater than that of the control ordinary steel specimen. SS-RC specimens BJD-1, BJD-2 and BJD-3 had 66.7%, 33.3% and 25% higher cracking load capacity than that of the control specimen BDJ-4, respectively. The yield load increased by 54.5%, 42.3% and 50.4%; while the ultimate load increased by 22.3%, 35.2% and 16.8%, respectively. The yield and ultimate displacements of the specimens were both larger, while the displacement ductility coefficient was smaller, than that of the control specimen. In addition, the energy dissipation and equivalent viscous damping coefficients of the SS reinforced specimens BJD-1, BJD-2 and BJD-3 in both the cracking and yield stages were all greater than that of the control specimen BDJ-4 but were slightly lower in the limit stage. Generally, SS-RC specimens met design code ductility requirements under earthquake loading, with adequate plastic deformation. A constitutive relationship for SS rebar was proposed in this study and used to conduct finite element simulations of the tested specimens. Good correlation between simulation and experimental results was observed. Thus, a parametric study was conducted to numerically investigate the influence of the axial compression, longitudinal and hoop reinforcement ratios on the seismic behavior of SS-RC joints. The findings could provide insight and guidance for future design provisions of concrete structures reinforced with stainless steel

MAT-723: BOND BEHAVIOUR OF GROUTED CONNECTIONS UNDER MONOTONIC TENSILE LOADS

Grouted bar-in-conduit connections are versatile connections widely used in the precast concrete construction. In precast load bearing wall structures, two vertical wall panels are connected by a reinforcing bar, which is projected from one panel and grouted into a sleeve placed in the other. The main function of the ties is to resist tension induced by in-plane and out-of-plane straining actions and to provide ductility to the wall assembly through the yielding of the reinforcement. Limited information is currently available on the behaviour of such connections. This paper presents the findings of an investigation conducted to investigate the behaviour of grouted reinforcing bar connections and their failure mechanisms. The bond strength was evaluated using a pull-out test on a bar extended from a grouted sleeve specimen. The test parameters of the study were the bar surface condition (deformed and smooth) and the embedded length (6, 12 and 36 diameter-of-bar (db)). A total of eight specimens were tested to failure under direct tensile loads and the slip of the bars was recorded. Results indicate that an embedment length of 6db allowed the bar to yield, but bond failure dominated in the strain hardening zone. It was also observed that an embedment length of 12db was sufficient to mobilize the tensile capacity of the bar, after which an increase in the grouted sleeve length resulted in no additional capacity

MAT-741: IMPACT BEHAVIOUR OF SHAPE MEMORY ALLOY HYBRID FIBRE-REINFORCED ENGINEERED CEMENTITIOUS COMPOSITE

An experimental study was conducted to evaluate the impact behaviour of an innovative hybrid-fibre engineered cementitious composite (ECC) incorporating randomly dispersed short shape memory alloy fibres (SMA). A modified drop weight test was conducted on specimens from various ECC mixtures with and without SMA fibres. The impact behaviour was evaluated and compared based on the ability to dissipate energy and sustain impact load without damage. Results show that the addition of SMA to ECC mixtures significantly enhanced their performance under impact loading. The amount of dissipated energy by ECC increased by about 51% as a result of SMA fibre addition. This highlights the potential benefits of incorporating SMA in composite materials exposed to impact loads, paving the way for a wider implementation in the field of fortified structures