Behaviour of reinforced self-consolidating concrete frames

Multi-storey reinforced concrete (RC) structural frames represent some of the most congested structural elements. Placing and consolidating concrete in such structural frames imposes substantial challenges. This offers a unique area of application for self-consolidating concrete (SCC) because of its inherent ability to flow under its own weight and fill congested sections, complicated formwork and hard-to-reach areas. Research is, however, needed to demonstrate the ability of SCC structural frames adequately to resist vertical and lateral loads. In the present study, full-scale 3 m high beam-column joints reinforced as per the Canadian Standards CSA A23·3-94 and ACI-352R-02 were made with normal concrete (NC) and SCC. They were tested under reversed cyclic loading applied at the beam tip and at a constant axial load applied on the column. The beam–column joint specimens were instrumented with linear variable displacement transducers and strain gauges to determine load–displacement traces, cumulative dissipated energy and secant stiffness. The current paper compares the performance of reinforced NC and SCC structural frames and discusses the potential use of SCC in such structural elements. Results indicate that reducing the coarse aggregate content in SCC mixtures can reduce the contribution of the aggregate interlock mechanism to total shear resistance, which leads to more rapid deterioration under cyclic loading. Further research is needed to ensure the safety of using low coarse aggregate content in SCC in highly seismic areas and assess the safety of already existing buildings cast using SCC

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

Unbiased in vitro selection reveals the unique character of the self-cleaving antigenomic HDV RNA sequence

In order to revisit the architecture of the catalytic center of the antigenomic hepatitis delta virus (HDV) ribozyme we developed an unbiased in vitro selection procedure that efficiently selected novel variants from a relatively small set of sequences. Using this procedure we examined all possible variants from a pool of HDV ribozymes that had been randomized at 25 positions (4(25)). The isolated set of sequences shows more variability than do the natural variants. Nucleotide variations were found at all randomized positions, even at positions when the general belief was that the specific base was absolutely required for catalytic activity. Covariation analysis supports the presence of several base pairs, although it failed to propose any new tertiary contacts. HDV ribozyme appears to possess a greater number of constraints, in terms of sequences capable of supporting the catalysed cleavage, than do other catalytic RNAs. This supports the idea that the appearance of this catalytic RNA structure has a low probability (i.e. is a rare event), which may explain why to date it has been found in nature only in the HDV. These contrasts with the hammerhead self-cleaving motif that is proposed to have multiple origins, and that is widespread among different organisms. Thus, just because a self-cleaving RNA motif is small does not imply that it occurs easily

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

Nonlinear Model for Reinforced Concrete under Cyclic Loading

Most of the available shear models for reinforced concrete rely on empirical formulations. In this study, a rational shear stress function is used to define the shear stress–strain envelope for reinforced concrete. Cyclic rules are proposed to define the loading, unloading and reloading relationships for reinforced concrete under shear stress reversals. A normal stress function describing the cyclic relationship of concrete under axial stress is also introduced. The proposed functions are verified using experimental data of reinforced concrete panels tested under monotonic and cyclic loading. Subsequently, the normal and shear stress functions along with their cyclic rules are integrated in a non-linear finite element analysis code. The resulting model accounts for tension stiffening, crack opening and closing, compression hardening and softening, degradation of concrete strength and stiffness in the direction parallel to the crack, compression unloading and reloading, as well as non-linear steel behaviour (strain hardening and Bauschinger effect). The finite element model is then used to analyse two Portland Cement Association shear walls with different geometries tested under cyclic loading. The results show a good agreement between analytical and experimental data. The model showed an excellent capacity of predicting shear deformations of reinforced concrete elements under cyclic loading with minimal computational efforts

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

Influence of astaxanthin, emulsifier and organic phase concentration on physicochemical properties of astaxanthin nanodispersions

BACKGROUND: The emulsification-evaporation method was used to prepare astaxanthin nanodispersions using a three-component emulsifier system composed of Tween 20, sodium caseinate and gum Arabic. Using Response-surface methodology (RSM), we studied the main and interaction effects of the major emulsion components, namely, astaxanthin concentration (0.02–0.38 wt %, x(1)), emulsifier concentration (0.2–3.8 wt %, x(2)) and organic phase (dichloromethane) concentration (2–38 wt %, x(3)) on nanodispersion characteristics. The physicochemical properties considered as response variables were: average particle size (Y(1)), PDI (Y(2)) and astaxanthin loss (Y(3)). RESULTS: The results indicated that the response-surface models were significantly (p < 0.05) fitted for all studied response variables. The fitted polynomial regression models for the prediction of variations in the response variables showed high coefficients of determination (R(2) > 0.930) for all responses. The overall optimum region resulted in a desirable astaxanthin nanodispersions obtained with the concentrations of 0.08 wt % astaxanthin, 2.5 wt % emulsifier and 11.5 wt % organic phase. CONCLUSION: No significant differences were found between the experimental and predicted values, thus certifying the adequacy of the Response-surface models developed for describing the changes in physicochemical properties as a function of main emulsion component concentrations

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