David Cleland

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.

Serviceability of bridge deck slabs with arching action

Although it is commonly known that bridge deck slabs have inherent enhanced strength due to the presence of arching or compressive membrane action, only recently has there been some acceptance of a rational treatment of this phenomenon for design and assessment purposes. To show the benefits of arching action, this paper presents the results of tests carried out on a reinforced-concrete beam and slab bridge in Northern Ireland that incorporated novel reinforcement type and position. The research was aimed at extending previous laboratory tests on 1/3-scale bridge deck edge panels. The measured crack widths and deflections were compared with the current code requirements. The full-scale bridge tests corroborated existing findings from scale model tests. The deflections in the tests panels, under a service wheel load of 25.3 kips (112.5kN), were independent of the amount of tensile reinforcement in the test panel. All of the test panels were uncracked under this service wheel load and all the test panels had much narrower crack widths than those predicted using current standards. The deck slabs with center reinforcement had strengths far in excess of the design ultimate loads and behaved in a similar manner to those with top and bottom reinforcement up to an applied load of 51 kips (225kN). This finding indicates that substantial economies in the amount of reinforcement could be made. By using the benefits of arching action on the strength of laterally restrained slabs, very low percentages of reinforcement are possible, which should decrease the likelihood of deterioration due to reinforcement corrosion.

Fiber-Optic Strain Sensor System With Temperature Compensation for Arch Bridge Condition Monitoring

This paper presents an innovative sensor system, created specifically for new civil engineering structural monitoring applications, allowing specially packaged fiber grating-based sensors to be used in harsh, in-the-field measurement conditions for accurate strain measurement with full temperature compensation. The sensor consists of two fiber Bragg gratings that are protected within a polypropylene package, with one of the fiber gratings isolated from the influence of strain and thus responding only to temperature variations, while the other is sensitive to both strain and temperature. To achieve this, the temperature-monitoring fiber grating is slightly bent and enclosed in a metal envelope to isolate it effectively from the strain. Through an appropriate calibration process, both the strain and temperature coefficients of each individual grating component when incorporated in the sensor system can be thus obtained. By using these calibrated coefficients in the operation of the sensor, both strain and temperature can be accurately determined. The specific application for which these sensors have been designed is seen when installed on an innovative small-scale flexi-arch bridge where they are used for real-time strain measurements during the critical installation stage (lifting) and loading. These sensors have demonstrated enhanced resilience when embedded in or surface-mounted on such concrete structures, providing accurate and consistent strain measurements not only during installation but subsequently during use. This offers an inexpensive and highly effective monitoring system tailored for the new, rapid method of the installation of small-scale bridges for a variety of civil engineering applications.

Investigation of Ultimate Strength of Deck Slabs in Steel-Concrete Bridges

Many bridges are composite structures with reinforced concrete decks supported by longitudinal steel beams. The presence of the longitudinal steel beams and the unloaded area of concrete slab cause the loaded deck slabs to be restrained against lateral expansion. This creates a compressive membrane (or arching) action. This study uses experimental tests to investigate the effects of structural variables on the load capacity of the deck slabs of the composite bridges. A practical design approach is presented to assess the restraint stiffness that exists in the composite bridge deck and thereby the strength enhancement due to arching action. A series of one-third scale steel-concrete composite bridge models were built with several varying structural parameters, including concrete compressive strength, reinforcement percentage, and the size of steel supporting beams. After comparing the results of different models, the influence of these structural parameters on the amount of compressive membrane action in the deck slab was evaluated. Experimental results showed that compressive membrane action is influenced by concrete compressive strength and lateral restraint stiffness. The proposed method provided accurate, consistent but slightly conservative predictions for the strength of a wide range of deck slabs.

Selection and characterisation of geological materials for use as geopolymer precursors

Geopolymer binders are generally formed by reacting powdered aluminosilicate precursors with alkali silicate activators. Most research to date has concentrated on using either pulverised fuel ash or high purity dehydroxylated kaolin (metakaolin) in association with ground granulated blast furnace slag as the main precursor material. However, recently, attention has turned to alternative calcined clays that are abundant throughout the globe and have lower kaolinite contents than commercially available metakaolins. Due to the lack of clear and simple screening protocols enabling assessment of such geological resources for use as precursors in geopolymer systems, the present paper presents results from experimental work that was carried out to develop a functional binder using materials containing kaolinite taken from the Interbasaltic Formation of Northern Ireland. The influence of mineralogy has been examined, and a screening process, using three Interbasaltic materials as examples, that will assist in the rapid selection of suitable geopolymeric precursors from such materials is outlined.

A novel method of embedding distributed optical fiber sensors for structural health monitoring

A distributed optical fiber sensor based on Brillouin scattering (BOTDR or BOTDA) can measure and monitor strain and temperature generated along optical fiber. Because it can measure in real-time with high precision and stability, it is quite suitable for health monitoring of large-scale civil infrastructures. However, the main challenge of applying it to structural health monitoring is to ensure it is robust and can be repaired by adopting a suitable embedding method. In this paper, a novel method based on air-blowing and vacuum grouting techniques for embedding long-distance optical fiber sensors was developed. This method had no interference with normal concrete construction during its installation, and it could easily replace the long-distance embedded optical fiber sensor (LEOFS). Two stages of static loading tests were applied to investigate the performance of the LEOFS. The precision and the repeatability of the LEOFS were studied through an overloading test. The durability and the stability of the LEOFS were confirmed by a corrosion test. The strains of the LEOFS were used to evaluate the reinforcing effect of carbon fiber reinforced polymer and thereby the health state of the beams.

Corrosion of reinforcement in concrete repair

Abstract For a satisfactory patch repair to a concrete structural element the prevention of reinforcement against further corrosion is an important consideration. Therefore, the performance of a repair mortar and reinforcement coating in protecting the reinforcement against further corrosion may need to be considered in the selection of a repair system. An experimental investigation was designed to provide comparative data on the performance of five repair materials in preventing corrosion of both coated and uncoated reinforcing bars. A normal outdoor environment in the British Isles and an environment exposed to de-icing salt were considered. Corrosion was assessed by the half-cell potential method and visual examination. The paper discusses how the repair material influence the resistance to corrosion of reinforcement at the interface between the repair material and the surrounding concrete is affected by shrinkage, adhesion and compaction of the repair material. Conclusions and recommendations for corrosion protection are made. These can be used in assessing the suitability of repair materials for any given application.

State-of-the-Art Applications of the Pull-off Test in Civil Engineering

In 1974, the concept of using pull-off test as a means of predicting the compressive strength of concrete was patented in the UK by Professor Long at Queens University Belfast. Initially, the pull-off test was developed primarily aiming at unplanned in-situ strength determination. It was found later also particularly suited for assessment of bond strength of repairs. This test has now been accepted in British Standards, BS 1881-207:1992 for assessing the in-situ concrete strength in structures and BS EN 1542:1999 for assessing the bond strength between overlays and substrate concrete in patch repairs. In addition, BS 1881-201:1986 recommends it for quality control and long-term monitoring of hardened concretes. It has also been accepted in North America (ASTM C1583-04), Holland and some other countries for similar applications. This paper reviews its development history, principle, factors affecting the test results as well as its current applications in civil engineering fields.

Improved Equivalent Frame Analysis Method for Flat Plate Structures in Vicinity of Edge Columns

This paper proposes a modification to the ACI 318-02 equivalent frame method of analysis of reinforced concrete flat plate exterior panels. Two existing code methods were examined: ACI 318 and BS 8110. The derivation of the torsional stiffness of the edge strip as proposed by ACI 318 is examined and a more accurate estimate of this value is proposed, based on both theoretical analysis and experimental results. A series of 1/3-scale models of flat plate exterior panels have been tested. Unique experimental results were obtained by measuring strains in reinforcing bars at approximately 200 selected locations in the plate panel throughout the entire loading history. The measured strains were used to calculate curvature and, hence, bending moments; these were used along with moments in the columns to assess the accuracy of the equivalent frame methods. The proposed method leads to a more accurate prediction of the moments in the plate at the column front face, at the panel midspan, and in the edge column.