Performance-based Testing Methodology for Concrete Durability

This report presents an overview of performance based testing methodology for concrete durability and work currently underway jointly at Queens University Belfast and Heriot Watt University, Edinburgh, to undertake this research under a EPSRC funded project (EP/G02152X/1). EN206-1 superseded BS 5328 on 1st December 2003 and allows designers and producers to use a wide range of cements and aggregate types for a variety of exposure conditions. In this new standard, the durability of concrete is specified in terms of the constituent materials of concrete, properties of fresh and hardened concrete, limitations for concrete composition, specification of concrete, delivery of fresh concrete, production control procedures, conformity criteria and evaluation of conformity and verification of these properties. Within this, six basic forms of exposure is also specified, namely XO (no risk of corrosion), XC (Corrosion induced by carbonation), XF (Freeze / thaw attack), XS (Corrosion induced by chlorides from seawater), XD (Corrosion induced by chlorides other than from seawater) and XA (Chemical attack). According to EN206-1, the performance method adopted should be based on satisfactory experience with local practices in local environments from data obtained from an established performance test method for the relevant mechanism, or using appropriate proven predictive models. Therefore, the methods that may be used include those methods based on:- · long-term experience of local materials and practices and on detailed knowledge of the local environment. · approved and proven tests that are representative of actual conditions and have approved performance criteria. · analytical models that have been calibrated against test data representative of actual conditions in practice. The concrete composition and the constituent materials should be closely defined to enable the level of performance to be maintained. In order to determine the best methods for assessing concrete durability for performance, it is important to review those methods which have been developed and used in Queens University Belfast and Heriot Watt University to test for permeability, diffusion and absorption as well as electrical methods used to assess if the performance criteria have been achieved in structures using non-destructive testing methods. Prior to specifying durability performance testing methods, a review of previous projects where limits on permeability, diffusion, electrical resistivity etc, are presented along with the various durability tests used to assess these limits. The examples given are from a number of projects in the UK, Ireland and Europe of varying complexity and size. Due to the relatively small number of such examples in the UK and Ireland, the need for the research presented here is further justified. The proposed experimental work for the EPSRC project is presented which includes a breakdown of the concrete samples, tests and details of a new marine exposure site on the Northwest coast of Ireland. Based on the findings of this experimental work and the numerical calibration using the ClinConc model, development of a methodology for testing the concrete durability to assess the performance limits set will be determined. Through this work, the performance methods adopted will satisfy the EN206-1 guidelines above

Influence of Environmental Parameters on the Distribution and Diversity of Molluscan Composition in Pondicherry Mangroves, Southeast Coast of India

Seasonal variation in the distribution of mollusks in relation to environmental parameters was studied at four mangrove stations on the Pondicherry coast during September 2008-August 2009. A total of 37 species of molluscs were recorded, among them 16 species of bivalves belonging to 7 families and 12 Genera, and 21 species of gastropods belonging to 14 families and 19 Genera, with the Cereithedia cingulata being the dominant group. An increase of species density and diversity in the Post monsoon season was observed, with the highest values for both indexes at stations 1 and 2, and the lowest at stations 3 and 4 fine where the sand assemblage was dominated by a few gastropods. Pollution indicator species Cassidula nucleus, Melampus ceylonicus, Sphaerassiminea minuta were found only in highly polluted regions near stations 3 and 4; they were totally absent in moderately polluted areas near stations 1 and 2. From a stepwise multivariate analysis of the different environmental parameters regarding molluscan density, it was found that in all 10 parameters govern the density variation of benthic mollusks in Pondicherry mangroves and that the organic matter of sediment and sulphide, DO, and salinity were the highly significant ones

Influence of Exposure Environments on the Durability of Slag-Blended Cements

Both chlorides and sulphates combine in seawater to affect the durability of reinforced concrete structures located in marine environments. This paper presents the results of an experimental study on slag blended cement systems, cured for 7 days, before exposure to a combined solution of sodium chloride (30 g/L) and sodium sulphate (3 g/L). Two slags of different chemical compositions, designated as slags 1 and 2 were respectively blended with Portland cement CEM I 52.5R at 30 and 70 wt.% replacement levels. Mechanical tests on mortar samples were complemented by microstructural examination and chemical characterisation on paste samples, all using a constant w/b ratio of 0.5, to investigate the influence of exposure environment. The exposure environments include water and ponding in combined chloride-sulphate solution at 20 °C and 38 °C (to reflect temperate and tropical climates). The results show that temperature has a significant effect on the durability of slag blends. Reduced sorptivity at higher temperature led to reduced chloride penetration at early age. This effect is less so at later age. Compressive strength generally improved with increase in chloride penetration. SEM-EDX elemental analysis provided a good basis for following chloride penetration profile. XRD analysis showed the conversion of monosulphate to ettringite, Friedel’s salt and Kuzel’s salt upon exposure to salt solution, which possibly led to improved sorptivity and mechanical properties

Acute pancreatitis: a study of urine trypsinogen-2 measurement as a screening test

Background: Usefulness of urine trypsinogen-2 as screening test for acute pancreatitis in Indian population.Methods:We prospectively compared the urinary trypsinogen-2 dipstick test and serum amylase assays in 100 consecutive patients with acute abdominal pain at the emergency department. Urine samples were obtained on admission and tested for the dipstick. The diagnosis of acute pancreatitis was made on the basis of a typical clinical picture and serum amylase at least more than threefold the upper reference limit (300 IU) and/or radiological evidence (Abdominal X ray/ultrasonography/contrast enhanced CT).Results: 1. Urine trypsinogen-2 dipstick test was having 100% sensitivity and 85.71% specificity in diagnosing acute pancreatitis in Indian population. 2. Serum amylase was having 61.36% sensitivity and 78.57% specificity in diagnosing acute pancreatitis. 3. Sensitivity and specificity of urine trypsinogen-2 dipstick test is more than that of serum amylase in diagnosing acute pancreatitis which is statistically proved to be significant (P <0.05).Conclusion:Detection of trypsinogen-2 in urine is a simple office test in diagnosing acute pancreatitis in emergency department. As the sensitivity and specificity are high, detection of urine trypsinogen-2 in urine can be used as a screening test, which will definitely help in early diagnosis and prompt treatment of acute pancreatitis.

Effect of screentime in college students during the COVID-19 online classes on their neck posture and postural control: an observational study

Background: Corona virus which is the source of severe acute pulmonary syndrome causes an airway tract contamination (COVID 19). Prolonged sitting for online classes in the college students leads to the enlarged postural deviation, increased low back pain. Prolonged static contraction of skeletal muscles of the cervical region, lower back leads to impaired flow of blood to the muscle groups together with edema and accumulation of waste metabolites will trigger the muscle spasm. Methods: Total 30 college students aged between 18-25 years who attended the online classes during COVID-19 were included in this study by using a questionnaire. The outcome measures used were the measurement of CV angle, SEBT and BBS. The postural control was estimated by using star excursion balance test and Berg balance scale. Results: Using Karl Pearson’s correlation coefficient, a positive correlation was observed between CV angle and BBS (r = 0.82). Between BMI and CV angle there exists a statistically significant negative correlation (r = -0.564). Conclusions: This study proved that there exists a forward neck posture in the students who attended the online classes during the COVID-19 pandemic and that also affected their postural control

Effects of Temperature and Curing Duration on the Stability of Slag Cements in Combined Chloride-Sulphate Environments

This experimental study investigates the effects of temperature and curing duration on the stability of slag blended cement systems exposed at 20 °C and 38 °C to combined sodium chloride (30 g/L) – sodium sulphate (3 g/L) solutions. Two slags, designated as slag 1 and 2, having CaO/SiO2 ratios of 1.05 and 0.94, were respectively blended with Portland cement CEM I 52.5R at 30 wt.% replacement level. Mortar prisms and cubes with w/b ratio of 0.5 and binder/aggregate ratio of 1:3 were then prepared for length and mass changes. The samples were cured in lime water for either 7 or 28 days before ponding for a total exposure period of 544 days. Analogous paste samples were also prepared to follow changes in the hydration products using x-ray diffraction (XRD). The results showed that curing at 38°C resulted in less expansion and prolonged curing generally reduced expansion except for slag 1 blend at 20 °C. Also, mass-change was minimal at 38 °C compared to 20 °C, and curing up to 28 days further improved mass stability. There was a positive correlation between mass change and length change for the period of investigation

Engineering Performance of a New Siloxane-Based Corrosion Inhibitor

This paper presents an evaluation of a new non-toxic corrosion inhibitor on selected engineering properties of concrete mixes with different cementitious materials following a corrosion and durability study on concrete samples. Corrosion inhibitors consist of powders or solutions which are added to concrete when mixed to prevent or delay corrosion of steel by their reaction with ferrous ions to form a stable and passive ferric oxide film on the steel surface. The new inhibitor functions slightly differently and its corrosion inhibition effect is due to the formation of a siloxane coating on the steel surface. Therefore, the performance of the new inhibitor in concrete mixes manufactured with CEM I, PFA and GGBS cements was compared against a well known and established corrosion inhibitor on the market, namely calcium nitrite in terms of their effect on workability (measured in terms of slump), compressive strength, freeze–thaw durability and macro-cell corrosion. The results from this experimental programme have demonstrated that the new inhibitor is effective in reducing or slowing down corrosion. In addition, it was found that CEM I concrete containing the new inhibitor was less penetrable to chlorides than that without. A similar set of results was obtained for the freeze– thaw resistance, but the compressive strength was found to decrease with the addition of the new inhibitor. In the case of concretes containing PFA and GGBS, the new inhibitor was found to be less effective. Further, long-term investigations are recommended to assess the effectiveness over time

Methods of assessing the durability and service life of concrete structures

Characterisation of cover concrete is often the most viable means for assessing the durability and has become increasingly evident over the past 20 years. A variety of field methods and laboratory techniques exist, which provide a number of properties, such as air permeability index, water absorption rate, water permeability index, chloride diffusivity, electrical resistivity, moisture content and porosity gradient. Most techniques are economical and appropriate for assessing the durability of structures subjected to a single mechanism of deterioration. In reality, structures may face multiple deterioration mechanisms, stress/strains due to both environmental and structural loading and related acceleration of deterioration. Developing an understanding of such multimode deterioration may help in addressing the performance gap between laboratory and field. In this paper, a brief review of some of the ways by which a performance testing strategy could be developed is given so that service life prediction could be more realistic