Liam J. Butler

Towards the classification of recycled concrete aggregates: influence of fundamental aggregate properties on recycled concrete performance

This study provides an in-depth evaluation of how fundamental aggregate properties affect mechanical properties of structural concretes produced using 100% coarse Recycled concrete aggregate (RCA) and constant mixture proportions. The key findings presented within this study will assist in developing a framework for classifying RCA sources for use in specific concrete applications. Fourteen mixture proportions were developed using three RCA types with compressive strengths of 30, 40, 50, and 60 MPa. Contrary to other studies, one RCA concrete type had compressive strengths up to 22% greater than the natural aggregate concrete. These results were confirmed by repeated batching and measured to be statistically significant. An analysis of the failure modes of RCA concrete and linking particular aggregate properties to the observed concrete failure mode were used to explain the results. Based on measured correlations, the modulus of elasticity of RCA concrete can be estimated based on the compressive strength and aggregate unit weight.

Bond of Reinforcement in Concrete Incorporating Recycled Concrete Aggregates

Using recycled concrete aggregates (RCAs) as coarse aggregate in concrete has the potential to supplement current natural aggregate reserves, divert construction and demolition debris from landfills, and promote the adoption of sustainable civil infrastructure. As many of the design equations used to calculate structural concrete properties are based on empirical data for natural aggregate concrete, using these equations for RCA concrete may not be applicable. This study examined the bond of reinforcement in concrete produced using RCA as coarse aggregate. One natural aggregate (NA) and three RCA sources were evaluated and used as coarse aggregate in 14 separate concrete mixtures with four compressive strength levels. Various concrete mechanical properties, including compressive strength, splitting tensile strength, modulus of rupture, and fracture energy, were tested, and correlations between these properties and reinforcement bond were studied. The reinforcement bond was measured using 48 beam-end specimens incorporating several bonded lengths. The results showed that bond strength of RCA concrete was reduced by up to 21% in comparison to NA concrete, and that there was a strong correlation between bond strength and coarse aggregate crushing strength. A regression model was developed to relate bond strength to coarse aggregate strength, concrete compressive strength, and the bonded length. Using this model, experimentally predicted development lengths were calculated to be up to 9% greater for RCA concrete members in comparison to NA concrete members. Overall, this study was directed at providing guidance on the evaluation of multiple RCA sources and their respective impact on the bond of reinforcement in structural concrete.

Effect of Recycled Concrete Aggregate Properties on Mixture Proportions of Structural Concrete

This study focuses on characterizing several recycled concrete aggregate (RCA) sources, developing concrete mixture proportions that incorporate RCA as coarse aggregate, and investigating the effect of coarse aggregate properties on the main mixture proportion parameters [i.e., cement content, water demand, and water–cement (w/c) ratio]. Four aggregate types were investigated: one control virgin aggregate source and three RCAs produced from the crushing of hardened concrete. Numerous aggregate tests, including density, absorption, abrasion resistance, adhered mortar content, and crushing value, were performed. Fourteen mixture proportions were developed with the use of three mixture proportion scenarios (control, direct replacement, and strength based) and two compressive strength levels (40 and 60 MPa). The effect of RCA on compressive strength and workability was evaluated by replacement of natural coarse aggregate with RCA. Contrary to numerous studies, one of the RCA concretes (RCA-1) had compressive strengths up to 12% higher than the equivalent control mixture. Mixture proportions (water, cement, and w/c ratio) were later adjusted to ensure that the RCA concretes had compressive strength and slump values similar to the control concretes. Variations in water demand, cement content, and w/c ratio could then be directly attributed to the properties of the RCA source. RCA-1 concrete required less cement (and a higher w/c ratio) to achieve strengths and slumps similar to the control concrete. The findings and recommendations of this research will assist concrete producers, engineers, and field technicians involved in the selection of RCA sources in developing mixture proportions for structural-grade RCA concrete.

Management of structural monitoring data of bridges using BIM

Engineering and Physical Sciences Research Council, Innovate UK (CSIC Innovation and Knowledge Centre (Grant ID: EP/L010917/1))

Guidelines for Selection and Use of Coarse Recycled-Concrete Aggregates in Structural Concrete

This paper presents guidelines for using recycled-concrete aggregate (RCA) as a full or partial replacement for natural coarse aggregate in new concrete (RCA concrete). Several international standards and guidelines for the use of RCA in concrete are reviewed and contrasted to identify areas in which further development is required. The main results of an extensive experimental research program by the authors are summarized here to provide a basis for the development of a framework for using RCA in structural concrete. Several RCA performance classes are proposed, each with a specific set of requirements and suitable applications. The proposed performance classes define further requirements and guidance for the use of RCA beyond the requirements of Canadian Standards Association A23.1 and ASTM C33. The authors propose a detailed decision tree to allow engineers, concrete producers, aggregate suppliers, and contractors to assess whether a particular RCA source is suitable for use in reinforced concrete or plain concrete or as fill material.

Robust fibre optic sensor arrays for monitoring early-age performance of mass-produced concrete sleepers

This study investigates integrating fibre optic sensing technology into the production process of concrete railway sleepers. Robust fibre Bragg grating strain and temperature sensor arrays were developed specifically for this application and were designed for long-term monitoring of sleeper performance. The sensors were used to monitor sleeper production and to help gain a deeper understanding of their early-age behaviour which can highly influence long-term performance. In total, 12 sleepers were instrumented and strain data were collected during the entire manufacturing process including concrete casting and curing, prestressing strand detensioning and qualification testing. Following the production process, sleepers were stored temporarily and monitored for 4 months until being placed in service. The monitoring results highlight the intrinsic variability in strain development among identical sleepers, despite high levels of production quality control. Using prestress loss as a quality control indicator, the integrated sensing system demonstrated that sleepers were performing within Eurocode-based design limits prior to being placed in service. A three-dimensional nonlinear finite element model was developed to provide additional insight into the sleepers’ early-age behaviour. Based on the fibre Bragg grating–calibrated finite element model, more realistic estimates for the creep coefficient were provided and found to be 48% of the Eurocode-predicted values.

Real-time statistical modelling of data generated from self-sensing bridges

Instrumentation of infrastructure is changing the way engineers design, construct, monitor and maintain structures such as roads, bridges and underground structures. Data gathered from these instru...

Monitoring, Modeling, and Assessment of a Self-Sensing Railway Bridge during Construction

© 2018 American Society of Civil Engineers. This study shows how integrating fiber optic sensor (FOS) networks into bridges during the construction stage can be used to quantify preservice performance. Details of the installation of a large FOS network on a new steel-concrete composite railway bridge in the United Kingdom are presented. An overview of the FOS technology, installation techniques, and monitoring program is also presented, and the monitoring results from several construction stages are discussed. A finite-element (FE) model was developed and a phased analysis was carried out to simulate strain development in the bridge during consecutive construction stages. The response of the self-sensing bridge to the time-dependent properties of the concrete deck was evaluated by comparing FOS measurements to predicted results according to several model code formulations implemented in the FE model. The preservice strain distribution due to dead loading is typically assumed to act uniformly along the bridge length; however, the monitoring results revealed that the distribution was highly variable as a result of the complex interactions between gravity loading, bridge geometry, time-dependent concrete properties, and temperature effects. Moment utilization of the main girders and composite beams, during preservice conditions, was assessed and found to be between 19.3 and 24.9% of the respective design cross-section capacities. Quantifying preservice performance via integrated sensing also provided a critical baseline for the bridge, which enables future data-driven condition assessments.

Research data supporting “Evaluating the Early-Age Behaviour of Full-Scale Prestressed Concrete Beams using Distributed and Discrete Fibre Optic Sensors”

Strain data collected during the casting, curing, detensioning and storage of 4 prestressed concrete bridge beams manufactured at EXPLORE Industrial Park, Worksop, UK. The data was collected/generated for the ME01 project being carried out in the Department of Engineering at the University of Cambridge. The ME01 project is a fibre optic instrumentation and dynamic monitoring programme at Norton Bridge, UK, part of the Stafford Area Improvements Programme. The strain data was collected using fibre optic monitoring technologies based on Brillioun Optical Time Domain Reflectometry (BOTDR) and fibre Bragg gratings (FBG).

Research data supporting “Development of Self-Sensing Concrete Sleepers for Next-Generation Rail Infrastructure”

Strain data collected during the casting, curing, and detensioning of prestressed concrete sleepers manufactured by CEMEX UK in Birmingham. The data was collected for the ME01 project being carried out in the Department of Engineering at the University of Cambridge. The ME01 project is a fibre optic instrumentation and dynamic monitoring programme at Norton Bridge, UK, part of the Stafford Area Improvements Programme. The strain data was collected using fibre optic monitoring technologies based on fibre Bragg gratings.