Stability and instability of foamed concrete

Foamed concrete has proven to be an effective alternative to granular fills and is now widely used internationally. With increasing demand for lightweight materials for buildings in order to improve sustainability, foamed concrete has also developed as an ideal material for this purpose, and many countries utilise construction with precast foamed concrete blocks. However, at densities lower than current technology allows, typically &lt;500 kg/m3, foamed concretes are more prone to instability of the fresh mix. Furthermore at very low densities, ≤300 kg/m3, instability is almost inevitable, greatly limiting the potential of foamed concrete for applications where mass is critical (e.g. weak soils, backfilling damaged structure etc.). This paper aims to illustrate the mechanisms of stability and instability in foamed concretes and demonstrates how ultra-low density mixes (down to plastic density of 150 kg/m3) can be successfully produced. </jats:p

High-volume, ultra-low-density fly ash foamed concrete

Resource efficiency is a core criterion for the regulation of construction products and rightly promotes the most sustainable solution. This paper reports the development a low embodied carbon dioxide backfill material based on an ultra-low-density foamed concrete using a high volume of fly ash to replace Portland cement. This material builds on previously reported research on the underlying causes of instability in low-density foamed concrete mixes and demonstrates that, with the addition of a small amount of calcium sulfoaluminate cement, stable ultra-low-density foamed concretes with density as low as 150 kg/m3 can be produced. A high volume of fly ash up to 70% of cement phase has been used, which reduced the average bubble size of the foamed concrete and increased the thickness of the bubble walls. The observed microstructure of fly ash foamed concretes was improved over the long term. The use of fly ash significantly reduced the embodied carbon dioxide of these mixes, which potentially has significant benefits for large-scale backfill and similar applications. </jats:p

Predicting concrete durability from its absorption

This paper discusses the current approach for specifying the durability of concrete in structures. The shortcomings of the use of bulk parameters such as strength, water/binder ratio and binder content to specify durability are discussed. Studies carried out over the last 10 years at Dundee University, using simple permeation tests, which are sensitive to curing, cement type and grade of concrete, have shown close association between permeation properties and the durability of concrete. This paper deals with the measurement of concrete durability by the Dundeemodified Initial Surface Absorption Test (ISAT). A wide range of concrete mixes made with ordinary portland cement and blends with pulverized-fuel ash (PFA) and ground-granulated blastfurnace slag were designed. The duration of moist curing was varied from 0 to 28 days, and the maximum aggregate size from 5 to 40mm. All mixes were tested for absorptivity and aspects of durability including freeze/thaw resistance, carbonation, chloride ingress and mechanical wear. The results show that the absorptivity of concrete, measured with the ISAT, could be used as an accurate specification for concrete durability, irrespective of curing, grade or mix constituents. A tentative surface absorptivity classification for durability has been proposed

Influence of loading and cracks on carbonation of RC elements made of different concrete types

Accurate prediction of concrete carbonation is important for the correct assessment of both durability and environmental impact of reinforced concrete (RC) structures. Loading applied to a RC structure and concrete cracking caused by this loading may significantly affect the concrete carbonation process. However, so far these factors have received little attention of researchers, especially this concerns ‘green’ concretes, i.e. concretes in which Portland cement (PC) is partially replaced by supplementary cementitious materials such as fly ash (FA) and ground granulated blast-furnace slag (GGBS). Thus, the aim of the study presented in the paper was to experimentally investigate the influence of static loading and associated concrete cracking on carbonation of RC elements made of PC concretes and ‘green’ concretes containing significant amounts FA and GGBS. For this purpose, six concrete mixes with two water/binder (w/b) ratios (0.40 and 0.55) and different proportions of PC, FA and GGBS were prepared. The mixes were used to cast twelve RC beams (100 × 120 × 900-mm) and a larger number of 100-mm concrete cubes. The beam specimens were loaded in four-point bending to produce flexural cracks of maximum width of either 0.1 mm or 0.3 mm. The loaded beam specimens along with unloaded cube specimens were then placed into a carbonation chamber and subject to accelerated carbonation for 120 days. After that the carbonation depths in the beams and cubes were measured. Results of the tests show a significant effect of load induced stresses (both tensile and compressive) on the carbonation resistance of the concretes, especially of ‘green’ concretes. The influence of cracking on concrete carbonation was also observed and discussed in the paper.</p

Using legume-based mixtures to enhance the nitrogen use efficiency and economic viability of cropping systems - Final report (LK09106/HGCA3447)

As costs for mineral fertilisers rise, legume-based leys are recognised as a potential alternative nitrogen source for crops. Here we demonstrate that including species-rich legume-based leys in rotations helps to maximise synergies between agricultural productivity and other ecosystem services. By using functionally diverse plant species mixtures, these services can be optimised and fine-tuned to regional and farm-specific needs. Replicated field experiments were conducted over three years at multiple locations, testing the performance of 12 legume species and 4 grass species sown in monocultures, as well as in a mixture of 10 of the legumes and all 4 grasses (called the All Species Mix, ASM). In addition, we compared this complex mixture to farmer-chosen ley mixtures on 34 sites across the UK. The trials showed that there is a large degree of functional complementarity among the legume species. No single species scored high on all evaluation criteria. In particular, the currently most frequently used species, white clover, is outscored by other legume species on a number of parameters such as early development and resistance to decomposition. Further complementarity emerged from the different responses of legume species to environmental variables, with soil pH and grazing or cutting regime being among the more important factors. For example, while large birdsfoot trefoil showed better performance on more acidic soils, the opposite was true for sainfoin, lucerne and black medic. In comparison with the monocultures, the ASM showed increased ground cover, increased above-ground biomass and reduced weed biomass. Benefits of mixing species with regard to productivity increased over time. In addition, the stability of biomass production across sites was greater in the ASM than in the legume monocultures. Within the on-farm trials, we further found that on soils low in organic matter the biomass advantage of the ASM over the Control ley was more marked than on the soils with higher organic matter content. Ecological modelling revealed that the three best multifunctional mixtures all contained black medic, lucerne and red clover. Within the long term New Farming Systems (NFS) rotational study, the use of a clover bi-crop showed improvement to soil characteristics compared to current practice (e.g. bulk density and water infiltration rate). Improvements in wheat yield were also noted with respect to the inclusion of a clover bi-crop in 2010, but there was evidence of a decline in response as the N dose was increased. Cumulatively, over both the wheat crop and the spring oilseed rape crop, the clover bi-crop improved margin over N. The highest average yield response (~9%) was associated with the ASM legume species mix cover cropping approach

‘I found out the hard way’: Micro-political workings in professional football

This paper examines the micro-political experiences of Adam (a pseudonym), a newly appointed fitness coach at a Football Association Premier League Club, in his search for acceptance by senior colleagues. Data were collected through a series of in-depth, semi-structured interviews, before being subject to a process of inductive analysis. Goffman’s (1959, 1963) writings on impression management and stigma, Ball’s (1987) micro-political perspective, and Garfinkel’s (1967) notion of status degradation are primarily utilised to make sense of Adam’s perceptions and actions. The findings point to the value of developing coaches’ micro-political understandings, and of including their formal facilitation within given professional preparation programmes. Doing so, it is argued, would better equip coaches for the problematic realities of their practice

The Reproducibility of Lists of Differentially Expressed Genes in Microarray Studies

Reproducibility is a fundamental requirement in scientific experiments and clinical contexts. Recent publications raise concerns about the reliability of microarray technology because of the apparent lack of agreement between lists of differentially expressed genes (DEGs). In this study we demonstrate that (1) such discordance may stem from ranking and selecting DEGs solely by statistical significance (P) derived from widely used simple t-tests; (2) when fold change (FC) is used as the ranking criterion, the lists become much more reproducible, especially when fewer genes are selected; and (3) the instability of short DEG lists based on P cutoffs is an expected mathematical consequence of the high variability of the t-values. We recommend the use of FC ranking plus a non-stringent P cutoff as a baseline practice in order to generate more reproducible DEG lists. The FC criterion enhances reproducibility while the P criterion balances sensitivity and specificity