Durability performance of self-compacting concrete

Although self compacting concrete (SCC) is currently used in many countries, there is a fundamental lack of the intrinsic durability of the material itself. This article presents the outcomes from a research program on principal indicators that define the durability of SCC (sorptivity, porosity and chloride ion permeability) and compares these indicators with the corresponding parameters of conventional concrete. The results show, for the first time, that there is a correlation between the various durability indicators for the specific filler additives used in the mix designs incorporated in this paper. Such a correlation may be used to assess the durability of SCC without the need to rely on time consuming artificial weathering experimental procedures. © 2012 Elsevier Ltd. All rights reserved.

Performance of joints in reinforced concrete slabs for two-way spanning action

A series of tests on filigree slab joints was performed with the aim of assessing whether such joints can be reliably used in the construction of two-way spanning reinforced concrete slabs. The test results were compared with code requirements. Adequate joint performance is shown to be achievable when the joints are appropriately detailed. Further research is recommended for the formulation of a more generic understanding when the design parameters are varied from those studied in this work.

Determination of the rheological parameters of self-compacting concrete matrix using slump flow test

The classification of a concrete mixture as self-compacting (SCC) is performed by a series of empirical characterization tests that have been designed to assess not only the flowability of the mixture but also its segregation resistance and filling ability. The objective of the present work is to correlate the rheological parameters of SCC matrix, yield stress and plastic viscosity, to slump flow measurements. The focus of the slump flow test investigation was centered on the fully yielded flow regime and an empirical model relating the yield stress to material and flow parameters is proposed. Our experimental data revealed that the time for a spread of 500 mm which is used in engineering practice as reference for measurement parameters, is an arbitrary choice. Our findings indicate that the non-dimensional final spread is linearly related to the non-dimensional yield-stress. Finally, there are strong indications that the non-dimensional viscosity of the mixture is associated with the non-dimensional final spread as well as the stopping time of the slump flow; this experimental data set suggests an exponential decay of the final spread and stopping time with viscosity. © Appl. Rheol.

MgO expansive cement and concrete in China: Past, present and future

Uniquely, China employs MgO already contained in cement clinker or as an expansive additive to compensate for the thermal shrinkage of mass concrete, particularly dam concrete, with almost 40 years' experience in both research activities and industrial applications. Compensating shrinkage with expansion produced by MgO has been proved to effectively prevent thermal cracking of mass concrete, and reduce the cost of temperature control measures and speed up the construction process. Moreover, the expansion properties of MgO could be designed flexibly, through adjusting its microstructure by changing the calcination conditions (calcining temperature and residence time). The collective knowledge and experience of MgO expansive cement and concrete is worthy of sharing with relevant engineers and researchers globally but dissemination has been hindered as most of the relevant literature is published in Chinese. This paper reviews the history, state-of-the-art progress and future research needs in the field of MgO expansive cement and concrete. © 2013 Elsevier Ltd.

Achievements and challenges in machine vision-based inspection of large concrete structures

Large concrete structures need to be inspected in order to assess their current physical and functional state, to predict future conditions, to support investment planning and decision making, and to allocate limited maintenance and rehabilitation resources. Current procedures in condition and safety assessment of large concrete structures are performed manually leading to subjective and unreliable results, costly and time-consuming data collection, and safety issues. To address these limitations, automated machine vision-based inspection procedures have increasingly been proposed by the research community. This paper presents current achievements and open challenges in vision-based inspection of large concrete structures. First, the general concept of Building Information Modeling is introduced. Then, vision-based 3D reconstruction and as-built spatial modeling of concrete civil infrastructure are presented. Following that, the focus is set on structural member recognition as well as on concrete damage detection and assessment exemplified for concrete columns. Although some challenges are still under investigation, it can be concluded that vision-based inspection methods have significantly improved over the last 10 years, and now, as-built spatial modeling as well as damage detection and assessment of large concrete structures have the potential to be fully automated.