Assessing the influence of crack width on the durability potential of cracked concrete using the durability index approach

Durability is a major concern for reinforced concrete (RC) structures. RC structures both in service and new, are subject to cracking. Irrespective of the cause of the cracking, cracks can increase the rate of penetration of aggressive species into concrete and modify the transport properties. Consequently, the service life of corrosionaffected RC structures may be drastically reduced in the presence of cracks. However, no modifications are made for the influence of cracking on the penetration of aggressive species into concrete when analysing durability test results or making service life predictions, even through concrete is very often in a cracked state. This study focused on the influence of cracks on the ingress of aggressive species (carbon dioxide and chlorides) into cracked concrete in comparison to uncracked concrete. The aim was to establish any correlations between the transport properties in uncracked and cracked concrete. Furthermore, in a broader context, the aim was to assess to what extent the modified cracked concrete parameters used in service life predictions affect the service life outputs, when compared with service life outputs obtained using the uncracked concrete parameters. Six concretes mixes were investigated comprising two water/binder (w/b) ratios (0.40 and 0.55) and three binder types (100% CEM I 52.5N (PC), 70/30 PC/FA and 50/50 PC/GGBS). 100 x 100 x 500 mm beams were cast and cracks were induced after seven days in the mid-span of each beam using three-point loading. Two crack width ranges were investigated; 0.1-0.4 mm (wcr1) and 0.5-0.8 mm (wcr2). The central section of the beam that contained the crack was sawn from the rest of the beam and used for either accelerated carbonation or bulk chloride diffusion testing. Cores were drilled from the outer sections of the beam and used as specimens for the Durability Index tests. The cracked specimens were monitored for carbonation (accelerated carbonation) and chloride ingress (bulk diffusion), while the uncracked ones were monitored for durability parameters (OPI, WSI & CCI) after 8 and 16 weeks of exposure. Firstly, it can be concluded that the presence of cracks modifies the transport properties of concrete by promoting rapid increase of ingress of aggressive species (CO₂ & Cl-) into the concrete matrix. It was found that the degree to which the transport properties were modified increased as the crack width increased. This was primarily attributed to the increase in surface area created by the crack, which allowed increased amounts of species (CO₂ & Cl-) to penetrate into the concrete matrix. In the case of carbon dioxide ingress, the presence of cracks significantly increased the rate of carbonation (up to 50 %) in the concrete specimens that contained blended cements PC/FA and PC/GGBS when compared to the PC concrete specimens. However, in the case of chloride ingress the effects of cracks in the PC mix resulted in the highest presence of chlorides (up to 78 %) in the concrete specimens in comparison to the chlorides present in the PC/FA and PC/GGBS concrete specimens. Secondly, when the sound (DI) and cracked durability parameters (carbonation and diffusion coefficient) where used in carbonation and chloride ingress service predictions, it was found that the DI service life prediction outputs were more conservative in relation to service life outputs from the durability parameters obtained from cracked concrete specimens. These results highlighted the degree of influence which the presence of cracks had on modifying transport properties in concrete. Furthermore, it also highlights the impact of the presence of cracks on the service life of RC structures and the prediction of long-term carbonation- and chloride- induced corrosion. Due to the significant influence that cracks have on modifying the transport properties of concrete, the results show that some reduction factors need to be applied to the results from the DI approach to reflect a more realistic durability potential of the concrete. Further research into understanding how other crack parameters (crack depth, frequency etc.) modify transport properties in concrete will lead to a more accurate insight into dealing with and accounting for the presence of cracks in RC structures

A standards-based approach for reporting assessment results in South Africa

This article proposes the use of a standards-based approach to reporting results from large-scale assessment surveys in South Africa. The use of this approach is intended to address the key shortcomings observed in the current reporting framework prescribed in the national curriculum documents. Using the Angoff method and data from the Annual National Assessments, the article highlights how standard setting procedures should be conducted to develop meaningful reports that provide users with relevant information that can be effectively used to identify and develop appropriate interventions to address learning gaps. The findings of the study produced policy definitions and performance level descriptors that are proposed for use in enhancing the reporting of results for grade six English and mathematics. Moreover, the findings also indicate that the reporting of the Annual National Assessments using the national curriculum reporting categories overestimates the percentage of learners classified at the lowest performance levels and underestimates those in the next category. This finding has serious implications for the implementation of targeted interventions aimed at improving learning for all. The paper concludes by noting areas of further research for enhancing the use of results of large-scale assessment surveys and for supporting schools and teachers in addressing specific learning needs of all learners, especially the poor and marginalised

Applicability of two standard setting methods for enhancing the reporting of assessment results within the South African education context

The study reported on here contributes to the growing body of knowledge on the use of standard setting methods for improving the reporting and utility value of assessment results in South Africa as well as for addressing the conceptual shortcomings of the Curriculum and Assessment Policy Statement (CAPS) reporting framework. Using data from the “verification” version of the Annual National Assessments (ANAs), we explored relevant technical and conceptual factors to consider for the application of standard setting methods. Two sets of panellists were trained to generate cut scores for Grade 6 mathematics and English First Additional Language (FAL), one using the Angoff method and the other the Objective Standard Setting (OSS) method. The findings indicate that the 2 methods generated different sets of cut scores across the performance levels for both subjects. While these cut scores had significant implications for the percentage of learners classified at each performance level, they were consistent with findings from other studies. We also identified 4 key factors to address when undertaking standard setting exercises: engagement with test content, resource requirements, requisite expertise and software, and collective accountability. We conclude that standard setting approaches should be the preferred option to the CAPS reporting framework when reporting assessment results in South Africa. More importantly, the decision on the most appropriate method for the South African context depends largely on the extent to which the 4 key factors identified can be addressed

Vision-based adaptive cruise control using pattern matching

Adaptive Cruise Control (ACC) is a relatively new system designed to assist automobile drivers in maintaining a safe following distance. This paper proposes and validates a vision-based ACC system which uses a single camera to obtain the clearance distance between the preceding vehicle and the ACC vehicle. Pattern matching, with the aid of lane detection, is used for vehicle detection. The vehicle and range detection algorithms are validated using real-world data, and then the resulting system performance is shown to be sufficient using a simulation of a basic vehicle model

Tinder or flint: igniting grade 2 teachers’ understanding of learning, teaching and assessment

This article reports on a study conducted to determine Grade 2 teachers’ knowledge and understanding of learning, teaching and assessment for use in the planning and implementation of a large-scale professional development programme on Assessment for Learning. A baseline survey was used to collect data from teachers in 86 schools, randomly selected across fee paying and no-fee schools in two Gauteng districts. Teacher responses across both school types indicate a predominant emphasis on teacher-centred approaches, despite acknowledging the importance of effective learner engagement in their lessons. An overwhelming majority displayed limited knowledge of formative assessment, often conflating formative with formal assessment. More concerning however, was the absence of a deeper understanding regarding the use of assessment for enhancing learner participation and for identifying specific learning needs of learners. The implications of these findings for supporting teachers to develop and implement formative assessment approaches are explored further. The paper concludes by noting areas for further research to determine whether professional development programmes, implemented within the context of learning and teaching in South African schools, can succeed in enhancing teachers’ knowledge and skills for the effective use of formative assessment approaches to improve learning for all

Entrenching performativity or enhancing pedagogy: Addressing the challenge of assessment policy and practice

The focus of the South African Education Research Association’s Assessment and Testing Special Interest Group (SIG) is to contribute to current initiatives and debates pertaining to the development and implementation of assessment systems for improving learning and teaching. In particular, the SIG’s members aim to address dominant performativity discourses impacting schools and universities by (1) providing a common understanding of the purpose and use of assessment, (2) locating the different assessment applications across the broader system within which learning and teaching occurs, and (3) highlighting recent initiatives impacting on assessment policy and practices. We think it essential to highlight critical policy and practice questions, while simultaneously acknowledging ongoing challenges for implementing enabling assessment systems that support the specific pedagogical needs of learners, teachers, students, and lecturers. Notwithstanding the complexities ofeffecting change, increasing discourse on, as well as relevant critique of, policies and practices that fail to improve learning and teaching, enhances possibilities for implementing enabling assessment policy and practice that seek to address the elusive challenge of equity and quality within the education system.&nbsp