Sreejith Nanukuttan

Developments in Performance Monitoring of Concrete Exposed to Extreme Environments

AbstractThe performance of the surface zone of concrete is acknowledged as a major factor governing the rate of deterioration of reinforced concrete structures because it provides the only barrier to the ingress of water containing dissolved ionic species such as chlorides, which ultimately initiate corrosion of the reinforcement. In situ monitoring of cover-zone concrete is therefore critical in attempting to make realistic predictions as to the in-service performance of the structure. To this end, this paper presents developments in a remote interrogation system to allow for continuous, real-time monitoring of the cover-zone concrete from an office setting. Use is made of a multi electrode array embedded within cover-zone concrete to acquire discretized electrical resistivity and temperature measurements, with both parameters monitored spatially and temporally. On-site instrumentation, which allows for the remote interrogation of concrete samples placed at a marine exposure site, is detailed together wi...

Optical Fiber Refractive Index Sensor for Chloride Ion Monitoring

The development of a reflective, gold-coated long-period grating-based sensor for the measurement of chloride ions in solution is discussed. The sensor scheme is based around a long-period fiber grating (LPG)-based Michelson interferometer where the sensor was calibrated and evaluated in the laboratory using sodium chloride solutions, over a wide range of concentrations, from 0.01 to 4.00 M. The grating response creates shifts in the spectral characteristic of the interferometer, formed using the LPG and a reflective surface on the distal end of the fiber, due to the change of refracting index of the solution surrounding it. It was found that the sensitivity of the device could be enhanced over that obtained from a bare fiber by coating the LPG-based interferometer with gold nanoparticles and the results of a cross-comparison of performance were obtained and details discussed. The approach will be explored as a basis to create a portable, low-power device, developed with the potential for installation in concrete structures to determine the ingress of chloride ions, operating through monitoring the refractive index change.

Transport Properties of Self-Consolidating Concrete

This study reports the findings from an investigation carried out to study the effect of the mixture variations on the durability of medium- and high-strength self-consolidating concrete (SCC). The mixture variations studied include the type of mineral admixtures, such as limestone powder (LSP) and pulverized fuel ash (PFA), and viscosity-modifying admixtures (VMA) for both medium- and high-strength SCC. Air permeability, water permeability, capillary absorption, and chloride diffusivity were used to assess the durability of SCC mixtures in comparison with normal, vibrated concretes. The results showed that SCC mixtures, for medium- and high-strength grades using PFA followed by LSP give lower permeability, properties compared with normal concretes. SCC made with VMA had a higher sorptivity, air permeability, and water permeability compared with other SCC mixtures, which can be attributed to higher water-cement ratio (w/c) and lack of pore filling effect. An in-place migration coefficient was obtained using the in-place ion migration test. This was used to compare the potential diffusivity of different concretes. The results indicated that SCC, for both grades of strength, made with PFA showed much lower diffusivity values in comparison with other mixtures, whereas the SCC mixtures with VMA showed higher diffusivity.

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.

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.

Retrofit versus new-build house using life-cycle assessment

This paper reports the findings of research on the environmental performance of two case-study houses, a retrofit and new build. The retrofit was completed to a Passivhaus standard while the new build was completed to current Irish building regulations. Environmental performance of the retrofit and new build was measured using life-cycle assessments, examining the assembly, operational and end-of-life stage over life spans of 50 and 80 years. Using primary information, life-cycle assessment software and life-cycle assessment databases the environmental impacts of each stage were modelled. The operational stage of both case studies was found to be the source of the most significant environmental damage, followed by the assembly and the end-of-life stage respectively. The relative importance of the assembly and end-of-life stage decreased as the life span increased. It was found that the retrofit house studied outperformed the new build in the assembly and operational stage, whereas the new build performed ...

Test methods for concrete durability indicators

Durability of concrete structures is primarily dependent on the environmental influences, i.e. the penetration of aggressive substances in the structural element from the environment. Penetrability is an important durability indicator of concrete and by specifying different classes of penetrability of concrete it should be possible to design a structure with the required resistance to environmental loads. This chapter covers descriptions of the available and commonly applied in situ and laboratory, non-invasive and semi-invasive test methods for evaluating concrete penetrability properties.

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.

Progress of Carbonation in Chloride Contaminated Concretes

Concretes used in marine environment are generally under the cyclic effect of CO 2 and chloride ions (Cl - ). To date, the influence of carbonation on ingress of chloride ions in concretes has been widely studied; in comparison, study on the influence of Cl - on the progress of carbonation is limited. During the study, concretes were exposed to independent and combined mechanisms of carbonation and chloride ingress regimes. Profiles of apparent pH and chloride concentration were used to indicate the progress of carbonation and ingress of Cl - in concretes. From the apparent pH profile, a carbonation front and a carbonation boundary were characterized according to profile of consumed hydroxyl ions (OH - ). Results show that carbonation was significantly slowed down due to the existence of Cl - , viz. the depth of carbonation boundary was decreased; the profile of consumed OH - became modest; the carbonation front for different mixes presented slightly different trends. For the sound concretes, carbonation generated microcracks on concrete surface and increased permeation properties; for the chloride contaminated concretes, due to the limited extent of carbonation, permeation properties did not present obvious difference.

Application Examples of Performance-Based Specification and Quality Control

This chapter presents an overview on several performance-based approaches for concrete durability specification and conformity assessment of the as-built structure.