Lulu Basheer

Assessment of the durability of concrete from its permeation properties: A Review

Abstract Concrete is a versatile and most popular construction material. Its long-term performance depends on the interactions with the service environment, in which the penetration of deleterious substances is highly significant. The latter can be considered solely controlled by permeation properties of the near surface concrete. This paper reviews first the various transport mechanisms which govern the ingress of deleterious substances into concrete and lists tests which could be used to determine these mechanisms. This is followed by a discussion on various mechanisms of deterioration of concrete in an attempt to highlight the transport mechanisms, which are relevant to each mechanism of deterioration. Finally, from the documented information the usefulness of permeation tests to assess the durability of concrete is discussed by presenting inter-relationships between the two obtained in laboratory studies.

Surface treatments for concrete: assessmentmethods and reported performance

Abstract Several products for surface treatment are available on the market to enhance durability characteristicsof concrete. For each of these materials a certain level of protection is claimed. However, there is no commonly accepted procedure to assess the effectiveness of these treatments. The inherent generic properties may be of use to the manufacturers and those responsible for specifications, however, practising engineers are interested in knowing how they improve the performance of their structures. Thus in this review an attempt is made to assess the engineering aspects of the various surface treatments so that a procedure for their selection can be proposed.

Full-Scale Marine Exposure Tests on Treated and Untreated Concretes Initial 7-Year Results

An extensive chloride profiling program was undertaken on concrete pier stems erected in the vicinity of the Dornoch Bridge located at the Dornoch Firth in Northeast Scotland. The pier stems were 2 m (6.562ft) high and octagonal in plan with 0.66 m (2.165ft) wide faces. The piers were constructed in sets of three with the lowest of each set in the tidal zone and the highest in the atmospheric zone. The pier stems were placed in such a way that they would represent the exposure conditions of the actual bridge piers of the Dornoch Bridge. In all, six of the pier stems were made using plain ordinary portland cement (OPC) concrete (with three of these having the surface treated with silane); the remaining three pier stems had a concrete containing caltite as an additive. Three exposure zones were studied: the tidal zone, the splash zone, and the atmospheric zone. The tidal zone was further subdivided into two levels defined as low-level and high-level. Chloride profiles were obtained from the different regimes over a period of 7 years for all nine pier stems. This paper describes the nature of chloride ingress and the usefulness of diffusion parameters in classifying each exposure regimes. Furthermore, the effectiveness of silane and caltite in protecting concrete from chloride ingress in different exposure zones was studied.

Developments in monitoring techniques for durability assessment of cover-zone concrete

This paper outlines developments in the use of an embedded multi-electrode sensor to study the response of the cover-zone (surface 50mm) to the changing ambient environment. The sensor enables the measurement of the spatial and temporal distribution of the electrical properties of concrete and temperature within the cover-zone thereby allowing an integrated assessment of cover-zone concrete performance. Both laboratory and field results are presented to highlight the information that can be obtained from embedded sensors. When exposed to the natural environment, the temperature dependence of the electrical response is highlighted and standardization protocols are developed to account for this effect. The monitoring system detailed also allows remote interrogation thereby providing (if required) a continuous output of real-time data and developments in this area are presented.

The influence of different European cements on the transport and early-age properties of concrete in the cover-zone

Abstract The use of in situ tests for performance based specification would require demonstration of their suitability to distinguish the quality of concrete. With the introduction of new European Standards for cements, this would mean concretes produced with these new cements should be classified for their quality using the performance tests. It is generally believed that transport properties of concrete are related to their durability and hence the measurement of these properties can form the basis of performance based specifications. This paper reports data indicating that transport properties measured at 28-days for concretes manufactured with different European cements and water-binder ratios can form the basis of classifying concrete for their durability. The results also demonstrated how the different cements specified in European Standards influence the transport properties and other early-age properties. Keywords: EN 206, concrete, cover-zone, transport properties, non-destructive testing, durability

Advances in the In-situ assessment of Construction Materials

The deterioration of concrete in structures is a major problem throughout the world. This has prompted research on methods of predicting the service life of both existing and new structures. Current prediction methods are still very basic and, before they can be used with confidence more reliable information on the properties of the concrete in these structures is needed. In this paper a range of test methods for determining the strength and transport properties of concrete are discussed from the perspective of research at Queen’s University Belfast on advances made over the past thirty years. The initial focus was on in-situ strength testing and this led to the pull-off test and the development of the LIMPET. However when it became apparent that durability was a matter of much greater concern to practising engineers, measurement of permeation properties became a priority. This led to the development of the AUTOCLAM which was found to give extremely useful correlation in the laboratory and on site between the air and water permeability and durability. Subsequently problems associated with the ingress of chlorides into concrete have been recognised and in response the PERMIT has been developed which allows the diffusion characteristics of the “covercrete” to be determined. Using a combination of such approaches simple durability based criteria can be developed for concrete and the remaining life of existing structures estimated.