Physical deterioration of sedimentary rocks subjected to experimental freeze-thaw weathering

Ten types of sedimentary rock were subjected to repeated cycles of freezing and thawing. In addition to monitoring sample weight loss throughout testing, a detailed graphic record was made of deterioration mode and its relationship to pre-existing rock flaws. Results suggest that the presence or absence of rock flaws alone does not control deterioration mode, but rather that it is the coupled relationship between these flaws, and rock strength and textural properties which exerts greatest influence. While some pre-existing flaws such as syndepositional deformation structures do not appear to influence breakdown, others such as incipient fractures, cavities and minor lithological boundaries frequently coincide with concentrations of deterioration. A characteristic mode of deterioration which is independent pre-existing flaws tends to develop in sandstones, indicating the influence, in this case, of rock texture. Particularly strong rocks such as crystalline limestone and metasediment tend to fracture preferentially along distinct linear weaknesses such as mineral veins, stylolites and incipient fractures. Particularly weak rocks, such as low-density chalk, break down in a random fashion without regard to pre-existing flaws. In addition to providing some insight into the role of pre-existing flaws in rock deterioration, this work also has practical implications for (i) the study of landform development due to weathering, and (ii) the selection of representative rock samples in durability testing for building stone. Copyright (C) 2000 John Wiley and Sons, Ltd

Frequent rapid feedback, feed-forward, and peer learning, for enhancing student engagement in online portfolio assessment (Webinar)

This paper presents outcomes from a 3-year initiative to enhance student engagement through weekly summative and formative feedback. The research concerns a first year undergraduate, tutorials-supported, academic skills module, with an assessed online portfolio. In phases 1 and 2, half the student cohort submitted a printed portfolio, while half completed an online portfolio. In the final phase, all students completed an online portfolio (c.190 students). The research design has enabled a robust comparison of the influence of assignment mode on the efficacy of marking and feedback, attainment, student engagement, and tutorial management

Computer-aided assessment as a holistic learning tool in geoscience

A common perception exists that computer-assisted assessment (CAA) is synonymous with summative multiple choice testing. This perception may be partly responsible for a lack of enthusiasm encountered among some academic staff to incorporate CAA into teaching programmes. This has been the experience in attempts to promote the use of communications and information technology in the curriculum in the Earth and Environment Faculty at the University of Leeds. Nevertheless a wide range of CAA applications is in use in the faculty. In this paper, examples of the imaginative employment of CAA in geosciences are used to illustrate that CAA can, in fact, be a major player in a holistic, high order learning environment. In the Earth and Environment Faculty, objective, multiple choice question (MCQ) tests are used for summative assessment, self assessment and as a revision tool. There are also examples of the use of MCQ's primarily as a teaching, rather than an assessment tool, and for the management of student learning. Interactive computer-based learning (CBL) and web-based resources incorporate smart assessment systems with revision loops, where poor scores on a test prevent further progression until a revision area with alternate questions has successfully been visited. A growing number and variety of Virtual Field Resources (VFR's) are being developed by geoscience staff, containing elements of formalised CAA and self assessment. Further developments in CAA are being encouraged at LU using the in-house managed learning environment (MLE) 'Bodington Common'. This facility enables on-line tutor marking of short answer questions and electronic submission of coursework. The latter is of particular interest because it presents opportunities for introducing management tools such as plagiarism detection. Currently, there is no faculty-wide strategy for the implementation of CAA. The challenges for the future are (i) to raise the profile and encourage the use of CAA; (ii) to demonstrate the potential of CAA for learning and teaching at higher cognitive levels; and (iii) to co-ordinate the implementation of different CAA methods within a programme in order that students experience a balanced learning environment

Quantification and description of rock breakdown for experimental weathering studies

Determination of the severity of rock breakdown due to experimental weathering is strongly influenced by the properties quantified. Traditionally, percentage weight loss has been used to quantify breakdown but this method does not reflect in situ breakdown, nor hidden, internal breakdown which may occur at the microscale. In this paper, results of some experimental rock weathering studies are presented to illustrate the relative merits associated with a range of different methods for quantifying rock breakdown. A range of sedimentary rocks were subjected to accelerated freezing and thawing, salt weathering and wetting and drying tests. The amount of deterioration was measured using techniques selected to provide insight into different facets of rock breakdown. For instance, percentage weight loss was measured to indicate the extent of material detachment; change in fracture density was measured to indicate visible, in situ weakening and fracturing; and fracture porosity (based on change in ultrasonic velocity) was calculated to indicate change in void space induced by weathering. Percentage change in Young's dynamic modulus was also recorded to indicate changes in elastic and mechanical properties. The results show that in some cases there is good agreement between different methods, in terms of the relative magnitude of breakdown and temporal trends, while in other cases there is little or no agreement. For cases in which there is good agreement between methods, it can be inferred that a range of breakdown processes are operating and that the quantification of breakdown is therefore independent of the method used. However, the converse is true for rocks where there is poor agreement between methods. For these, it can be inferred that a much narrower range of breakdown processes are operating and that the results of quantification of breakdown are therefore dependent on the method used. This may bring into question the validity of breakdown assessments for some rocks where the results are based on a single measurement method. The paper includes a description of the theoretical basis of the measurement methods listed. Selected results from experimental weathering are used to illustrate their relative merits. It is concluded that rock weathering studies would benefit from a more holistic approach to the quantification of breakdown which utilises several complementary indicators

Enhancing student engagement through online portfolio assessment

This paper reports on an existing undergraduate academic skills module with a printed portfolio assessment that has been modified to an online portfolio. Qualitative feedback reveals that students most valued the provision of rapid and regular feedback on work, and had a raised awareness of employability goals. Tutors most valued the ability to track students' progress and provide rapid feedback on work. Some also valued the ease of the marking process and the positive impact on tutorials. However, portfolio organisation had an adverse impact on the marking process for some, while others struggled with the effect of the online approach on face-to-face meetings, highlighting the need for further guidance on tutorial management. Quantitative analysis of student grades tentatively indicates higher attainment levels for online portfolios compared with printed equivalents. The findings suggest that personalised progress tracking and prompt, regular feedback on small tasks can promote student engagement in classroom activities, and has implications for the efficacy of student engagement monitoring

Pore properties as indicators of breakdown mechanisms in experimentally weathered limestones

The results are reported of four experimental weathering tests - freeze - thaw, wetting and drying, slake durability and salt weathering - on five different types of limestone. Effective porosity, mercury intrusion porosimetry and scanning electron microscopy were used to evaluate changes in pore properties, while weight loss and fracture density were used to assess deterioration severity. A primary aim was to observe modifications in porosity due to weathering and to draw inferences about the internal rock deterioration mechanisms taking place. It is concluded that the five limestones not only show a wide range of resistance to weathering in general but considerable difference in resistance to particular weathering processes. Consequently, when assessing durability it is essential to consider rock properties in the context of the weathering process to which the rock is subject. The type of deterioration indicator used is also important in interpretation of durability. A variety of pore modification mechanisms operate, including changes in pore connectivity, pore infilling, and the introduction of additional void space. There are indications that changes to the internal pore structure of rocks due to weathering may be a precursor to more substantial macrodeterioration. Copyright © 2001 John Wiley and Sons, Ltd

Manchester Metropolitan University promotes the major benefits of an inclusive curriculum

Manchester Metropolitan University (MMU) is a long-term member of Business Disability Forum (BDF). As a Disability-smart organisation, the university has developed an inclusive curriculum, which is designed and delivered in a way that is accessible to all students, regardless of the student’s educational, dispositional, circumstantial, or cultural background

Embedding Research in a Field-based Module through Peer Review and Assessment for Learning

A case study is presented of embedding research in a final year undergraduate, field-based, physical geography module. The approach is holistic, whereby research-based learning activities simulate the full life cycle of research from inception through to peer review and publication. The learning, teaching and assessment strategy emphasizes the progressive nature of knowledge and skills acquisition, facilitated through multiple opportunities for progressive, formative feedback. Students value the challenging yet rewarding nature of the module and engage with formative activities and peer review. The model presented demonstrates the value of peer review, fieldwork and research-based learning to facilitate progressive skills development and learner autonomy. © 2011 Copyright Taylor and Francis Group, LLC

Rock control on microweathering of bedrock surfaces in a periglacial environment

Microweathering of ice-smoothed bedrock surfaces was investigated in the Røldal area of Hardanger Plateau (60°), southern Norway. Postglacial rates of weathering were determined from surface lowering using quartz veins as reference surfaces. Weathering processes are inferred from assessment of weathering rind formation, surface hardness, and the preservation of small-scale glacial erosional features. Surface lowering rates for a range of metamorphic rocks vary from 0.05 to 2.20 mm ka - 1 and are broadly comparable with those obtained from crystalline rocks in other periglacial environments. The mean rate of surface lowering at 0.55 mm ka - 1 is low and demonstrates the relatively small impact of microweathering on postglacial landscape evolution. Variations in bedrock microweathering can be explained by lithological variation. Amphibolite and mica-rich bedrock surfaces experience greater denudation and weakening, least weathering rind formation, and abundant preservation of glacial striae, despite greater surface lowering. Conversely, quartz-rich bedrock surfaces are most resistant to denudation and weakening, but have greater weathering rind formation and fewer preserved striae. Postglacial microweathering is achieved primarily through granular disintegration involving detachment and removal of mineral grains and weakening from increased porosity. Granular decomposition is manifest in the formation of weathering rinds. Analysis of interactions between weathering indices indicates that rind accumulation is limited by microerosion. A conceptual model is proposed that illustrates the temporal interrelationships between in situ and erosional facets of microweathering in two contrasting mineral assemblages. The model proposes that cyclic processes of in situ disintegration, decomposition, and erosion are at work. The relative balance between these processes varies with lithology so that in more resistant quartz-rich rocks the net effect is minimal surface lowering and accumulation of weathering rind. In weaker, amphibolitic and micaceous rocks, the net effect is greater surface lowering and minimal accumulation of weathering rind. The results of the research demonstrate the important influence of rock properties, notably mineral composition, in postglacial microweathering of crystalline bedrock in a periglacial environment. © 2008 Elsevier B.V. All rights reserved