P. A. Muhammed Basheer

Resistance of concrete to chloride ingress: Testing and modelling

Chloride ingress in reinforced concrete induces corrosion and consequent spilling and structural weakness, and it occurs world-wide and imposes an enormous cost. Yet it can be resisted by using test methods and relevant models for service life prediction. Resistance of Concrete to Chloride Ingress sets out current understanding of chloride transport mechanisms, test methods and prediction models. It describes basic mechanisms and theories, and classifies the commonly used parameters and their units which expressing chloride and its transport properties in concrete. Laboratory test methods and in-field applicable test methods, including precision results from inter-laboratory comparison tests, are then outlined. Some of the fundamentals of models are explained, and the different types of models are then analyzed theoretically and critically. Analytical and probabilistic approaches are used to analyze the sensitivity of various models and the results from a benchmarking evaluation of different models are presented and discussed. Guidelines for the practical use of test methods and models are given, including tests for in-situ applications, and test methods validated by the precision results are detailed. The book draws to a large extent on the Chlortest project, which involved seventeen partners from ten European countries, and serves as an authoritative guide.

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.

Fibre optic chemical sensor systems for internal concrete condition monitoring

Methods for estimating the lifetime of reinforced concrete structures are being investigated with a fiber optic chemical sensor system, using a sol-gel as the matrix for the active material, for embedment in concrete for evaluation and testing. Results are presented on recent work.

Monitoring the cementitious materials subjected to sulfate attack with optical fiber excitation Raman spectroscopy

Abstract. Formation of ettringite and gypsum from sulfate attack together with carbonation and chloride ingress have been considered as the most serious deterioration mechanisms of concrete structures. Although electrical resistance sensors and fiber optic chemical sensors could be used to monitor the latter two mechanisms on site, currently there is no system for monitoring the deterioration mechanisms of sulfate attack. In this paper, a preliminary study was carried out to investigate the feasibility of monitoring sulfate attack with optical fiber excitation Raman spectroscopy through characterizing the ettringite and gypsum formed in deteriorated cementitious materials under an optical fiber excitation + objective collection configuration. Bench-mounted Raman spectroscopy analysis was also conducted to validate the spectrum obtained from the fiber-objective configuration. The results showed that the expected Raman bands of ettringite and gypsum in the sulfate-attacked cement paste can be clearly identified by the optical fiber excitation Raman spectrometer and are in good agreement with those identified from bench-mounted Raman spectrometer. Therefore, based on these preliminary results, it is considered that there is a good potential for developing an optical fiber-based Raman system to monitor the deterioration mechanisms of concrete subjected to sulfate attack in the future.

A durability performance-index for concrete: developments in a novel test method

Implementation of both design for durability and performance-basedstandards and specifications are limited by the lack of rapid, simple, sciencebasedtest methods for characterising the transport properties and deteriorationresistance of concrete. This paper presents developments in the application ofelectrical property measurements as a testing methodology to evaluate therelative performance of a range of concrete mixes. The technique lends itself toin-situ monitoring thereby allowing measurements to be obtained on theas-placed concrete. Conductivity measurements are presented for concreteswith and without supplementary cementitious materials (SCM’s) fromdemoulding up to 350 days. It is shown that electrical conductivitymeasurements display a continual decrease over the entire test period andattributed to pore structure refinement due to hydration and pozzolanicreaction. The term formation factor is introduced to rank concrete performancein terms of is resistance to chloride penetration.

Experimental research on concrete strength prediction by Limpet pull-off test in China

Using Limpet pull-off test for concrete strength prediction has now been accepted in standards of the UK, North America, Holland and some other countries. For its application in China, pull-off tests were carried out by using the Limpet in this study. Concrete specimens with four different mixtures and strength classes were cast, representing the normal and the high performance concretes commonly used in China. After different ages, the pull-off tensile strength was determined by using the Limpet and the compressive strength was obtained by carrying out cube crushing test using a WE-100 universal testing machine. To reflect the correlation between the pull-off tensile strength and the cube compressive strength, two types of curve were used for regression, y = axb and y = aebx respectively. The regression efficiency of the two curves was compared.

Preliminary Development and Evaluation of Fiber-Optic Chemical Sensors

Conventional methods of measuring carbonation and chloride ingress exist, but they are either inaccurate, expensive, or involve destructive testing. In seeking new solutions to this problem, the potential to use novel fiber-optic chemical sensors developed specifically for this application and designed to monitor chemical changes in cementitious materials, in situ and nondestructively, was explored in this study. Three types of fiber-optic sensors were thus constructed, tested, and evaluated, viz a temperature sensor, a pH sensor, and chloride sensors. The temperature sensor was based on the fluorescence decay of temperature-dependent materials, whereas the pH and chloride sensors were based on sol-gel technology, with pH and chloride sensitive indicators impregnated in the sol-gels. All the sensors were tested in situ, and subsequently, the temperature and the pH sensors were embedded in mortar and tested. It was found that both the temperature sensor and the pH sensor could function correctly for over 18 months after placement, but there was an issue with alignment of the sensor each time it was reconnected to the hardware. However, the laboratory tests showed that the chloride sensor was not reversible, and therefore further refinement was considered to be necessary before it could be used in situ in environments where the chloride content was known, from other measurements, to decrease. Research is ongoing to refine the sensor performance and expands the in situ testing program. The sensors themselves are inexpensive to fabricate, but the sensing hardware used in this work is costly because of its high versatility.

Benchmarking segmentation results using a Markov model and a Bayes information criterion

Features are derived from wavelet transforms of images containing a mixture of textures. In each case, the texture mixture is segmented, based on a 10-dimensional feature vector associated with every pixel. We show that the quality of the resulting segmentations can be characterized using the Potts or Ising spatial homogeneity parameter. This measure is defined from the segmentation labels. In order to have a better measure which takes into account both the segmentation labels and the input data, we determine the likelihood of the observed data given the model, which in turn is directly related to the Bayes information criterion, BIC. Finally we discuss how BIC is used as an approximation in model assessment using a Bayes factor.

Machine vision methods for the grading of crushed aggregate

We address the problems of (1) segmenting coarse from fine granularity materials, and (2) discriminating between materials of different granularities. For the former we use wavelet features, and an enhanced version of the widely used EM algorithm. A weighted Gaussian mixture model is used, with a second order spatial neighborhood. For granularity discrimination we investigate the use of multiresolution entropy. We illustrate the good results obtained with a number of practical cases.

Preliminary research on monitoring the durability of concrete subjected to sulfate attack with optical fibre Raman spectroscopy

Formation of ettringite and gypsum from sulfate attack together with carbonation and chloride ingress have been considered as the most serious deterioration mechanisms of concrete structures. Although Electrical Resistance Sensors and Fibre Optic Chemical Sensors could be used to monitoring the latter two mechanisms in situ, currently there is no system for monitoring the deterioration mechanisms of sulfate attack and hence still needs to be developed. In this paper, a preliminary study was carried out to investigate the feasibility of monitoring the sulfate attack with optical fibre Raman spectroscopy through characterizing the ettringite and gypsum formed in deteriorated cementitious materials under an ‘optical fibre excitation + spectroscopy objective collection’ configuration. Bench-mounted Raman spectroscopy analysis was also used to validate the spectrum obtained from the fibre-objective configuration. The results showed that the expected Raman bands of ettringite and gypsum in the sulfate attacked cement paste have been clearly identified by the optical fibre Raman spectroscopy and are in good agreement with those identified from bench-mounted Raman spectroscopy. Therefore, based on these preliminary results, there is a good potential of developing an optical fibre Raman spectroscopy-based system for monitoring the deterioration mechanisms of concrete subjected to the sulfate attack in the future.