Assessing the quality of concrete – reinforcement interface in Self Compacting Concrete

© 2019 Elsevier Ltd. This manuscript is made available under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International licence (CC BY-NC-ND 4.0). For further details please see: https://creativecommons.org/licenses/by-nc-nd/4.0/Research has shown that even self-compacting concrete (SCC) mixtures can exhibit the so-called “top-bar effect” which impacts bond and anchorage. Several instances of conflicting results have nevertheless been published regarding interfacial bond between self-compacting concrete and steel reinforcement. The scope of this paper is to present an experimental methodology for assessing the quality of the interface between self-compacting concrete and ribbed reinforcement. For this purpose, seven different self-compacting and four normally vibrated concrete (NVC) mixtures with diverse rheological characteristics were examined. Digital Image Analysis of cut sections containing reinforcing bars at different cast-heights was used as a diagnostic tool. The study illustrates that the quality of the interface is strongly affected by the viscosity of the SCC mixtures and by the slump values in NVC. Self-compacting concrete mixtures show greater inherent robustness and cohesion at the steel–concrete interface compared to conventionally vibrated concretes.Peer reviewe

Static response of UHPFRCC slab specimens

The aim of this study is to present the results of an extended work on the development of an Ultra High Performance Fibre Reinforced Cementitious Composite (UHPFRC) and the experimental determination of the mechanical properties of the produced material. Furthermore, the paper will present preliminary experimental results on the static response of Reinforced Concrete and UHPFRCC slab specimens

In-situ relative humidity sensing for ultra-high-performance concrete using polymer fiber Bragg gratings

We report on measuring, for the first time, the relative humidity in ultra-high-performance concrete mixtures using a Bragg grating in few-mode CYTOP polymer fiber (3 principal modes), inscribed in the fiber using a femtosecond laser technique. The sensor was characterized for temperature, strain and relative humidity noting improved sensitivity coefficients compared to other similar sensors. The polymer optical sensing elements successfully monitored the relative humidity for a period of eight days. We show that fiber optic sensing methods in concrete structures offer the ability to overcome deficiencies with existing electronic solutions such as scalability, reduction of single point monitoring sensing sites, and electromagnetic interference, while enabling ready installation within critical sections of the buildings

A Mechanical Treatment Method for Recycled Aggregates and Its Effect on Recycled Aggregate-Based Concrete

Recycle concrete aggregates (RCA) consist of natural aggregates and remnant mortar adhered to their surface. The amount, size, and morphology of the adherent remainder paste influences quality aspects of RCA, such as their bonding potential with new cement matrix in an RCA-based concrete, as well as the concrete’s overall rheological and performance characteristics. The objective of this research was to study the effect of reducing the adhered mortar in RCA, by means of a mechanical treatment method, on the performance of concrete containing RCA at different percentages. The treatment process was conducted within a concrete mixer truck drum at specific time intervals, the effect of which was determined by means of image analysis, mass loss recordings, and circularity determinations. The effect of size of treated and field RCA, as well as replacement percentages on mechanical performance and durability of high and normal strength concrete mixes, were also investigated. It was concluded that the optimal treatment duration where no further significant removal of adhered paste occurred thereon was 3 h, and concrete mixes containing 3 h treated RCA exhibited comparable performance characteristics to those of the reference concrete mix

Development of a new Ultra High Performance Fibre Reinforced Cementitious Composite (UHPFRCC) for impact and blast protection of structures

Ultra High Performance Fibre Reinforced Cementitious Composites (UHPFRCCs) represent a class of cement composites which have superior characteristics in terms of material properties. Their mechanical and fracture behaviour is substantially enhanced compared to other types of concrete. The aim of the specific paper is to present the results of an extended work focused on the development of the first UHPFRCC with the use of constituent materials available in Cyprus. The paper presents results on a broad variety of mechanical properties and the effect of several parameters on the strength development and the rheological characteristics of the produced material. Furthermore, the developed material should have certain properties and specifications, so as to have a sufficient response against blast and impact loading conditions. The optimum mixture has a water-binder ratio equal to 0.16 and volume fraction of steel fibres equal to 6%. The average compressive strength and specific fracture energy obtained for this mixture were around 175 MPa and 26000 N/m, respectively.Peer reviewe

A durable, screen-printed sensor for in-situ and real-time monitoring of concrete's electrical resistivity suitable for smart buildings cities and IoT

This article shows initial experimental results on the utilization of a durable, low-cost, screen-printed resistivity sensor in concrete for real-time measurements, with the aim of correlating concrete's electrical resistivity with moisture content. The sensor was tested in two different concrete mixtures, i. e., one with highly-absorptive aggregates (5.1) and one with low-absorptive aggregates (1.0), in order to investigate two dissimilar drying rates. Initial experimental results show a significant correlation of the sensor's response and the electrical resistivity of concrete, with the sensor being capable of distinguishing between different concrete types by their different drying rates. The sensor recorded very similar resistivity rates as those found in the literature for low-absorptive and highly-absorptive aggregate concrete mixtures, respectively. This sensor features superior lifetime due to the impressive wear resistance of the alumina substrate. The sensor has the ability to be easily integrated in a structure management system employed within smart buildings and smart cities. Existing correlations of concrete resistivity with water content can provide vital information regarding key properties of concrete whose monitoring may contribute to more durable structures by the implementation of preventative maintenance rather than reactive maintenance

Light Transmitting Concrete: A Review

Recently, research attention has been drawn to the application of novel, unique, and innovative types of construction materials to fulfil diverse objectives associated with the ground-breaking concept of “Greener Architecture”, in order to improve the overall economic value and quality of construction. Among these revolutionary structural building materials is light-transmitting concrete, also referred to as translucent or transparent concrete. This material is based on the concept of nano-optics, which allows exterior light to transmit through internal spaces in which light elements, namely optical fibres, are incorporated during the material’s manufacture. The current review assesses earlier studies of translucent concrete, focusing on its applications, and the appropriate ratio and arrangement pattern of optical fibres. This study also investigated the light-transmitting, mechanical, thermal, and energy-saving properties of translucent concrete by analysing research conducted during the past decade. However, numerous material restrictions and research gaps were found in the earlier literature on this concrete. The principal restrictions relate to the material’s low material strength and the identification of the optimum ratio of fibres. The main gaps identified among the reviewed research investigations relate to tests aiming to identify the influence of dissimilar ratios of optical fibres on the material’s strength and energy-saving properties. In the current review, we also identify and recommend future areas of research, and provide suggestions to address the existing research gaps. Finally, we review the types of translucent materials, their properties, and their advantages and disadvantages, and provide illustrations and value-added applications. The aim is to promote translucent concrete as an attractive, promising, and innovative building material for the construction industry

Effect of Mechanically Treated Recycled Aggregates on the Long Term Mechanical Properties and Durability of Concrete

The objective of this research was to study the effect of an optimal mechanical treatment method to reduce the mortar adhered on recycled aggregates (RCA) on the long-term mechanical properties and durability of concretes containing RCA at different replacement levels. It was found that concretes incorporating treated RCA exhibited sharper and more significant increase on 90- and 365-day compressive strengths than any other investigated mixture. The same mixtures also benefitted from a ‘shrinkage-controlling’ effect, where strains and mass losses were reduced by almost 15% and 10%, respectively, compared to the reference concrete. While sulfate resistance and carbonation resistance are predominantly defined by the hydration products available within the cement paste and not to a large extent by the aggregate type and quality, the incorporation of either treated or untreated RCA in concrete did not appear to expose RACs to significant durability threats

Static response and modelling of impact resistance of UHPFRCC slab specimens

The demand for improved properties of the construction materials increase with time and the related design and construction codes are adapted in an analogous manner. UHPFRCCs represent a class of cement composites which have superior characteristics in terms of material properties. Their mechanical and fracture behaviour is substantially enhanced compared to other types of concrete. These materials have, however, a significant increase in cost over and above that of conventional and even High Performance Concrete and it is therefore appropriate to identify applications which will fully utilize their mechanical properties and performance characteristics. The aim of this study is to present the results on the development of an UHPFRCC, the experimental investigation of the quality and the behaviour of this material in a highly demanding application, such as the impact resistance of structures and finally the development of a Finite Element Analysis program which will form a basis for analysis of future field tests

Geopolymerization of Recycled Glass Waste: A Sustainable Solution for a Lightweight and Fire-Resistant Material

Glass is considered a sustainable material with achievable recovery rates within the EU. However, there are limited data available for construction glass waste management. Furthermore, glass is a heavy material, and considering the geographical limitations of Cyprus, the transportation trading cost within the EU is extremely high. Therefore, another method for utilizing this by-product should be developed. The aim of this research is to investigate the production of a low-cost, lightweight and fireproof material able to retain its structural integrity, using the geopolymerization method with the incorporation of randomly collected construction glass waste. The glass waste was initially processed in a Los Angeles abrasion machine and then through a Micro-Deval apparatus in order to be converted to a fine powder. Mechanical (compressive and flexural strength), physical (setting time and water absorption) and thermal properties (thermal conductivity) were investigated. The fire-resistant materials presented densities averaging 450 kg/m3 with a range of compressive strengths of 0.5 to 3 MPa. Additionally, a techno-economic analysis was conducted to evaluate the viability of the adopted material. Based on the results, the final geopolymer product has the potential to be utilized as a fire resistance material, preventing yielding or spalling