Influence of size-classified and slightly soluble mineral additives on hydration of tricalcium silicate

Early-age hydration of cement is enhanced by slightly soluble mineral additives (ie, fillers, such as quartz and limestone). However, few studies have attempted to systematically compare the effects of different fillers on cementitious hydration rates, and none have quantified such effects using fillers with comparable, size-classified particle size distributions (PSDs). This study examines the influence of size-classified fillers [ie, limestone (CaCO₃), quartz (SiO₂), corundum (Al₂O₃), and rutile (TiO₂)] on early-age hydration kinetics of tricalcium silicate (C₃S) using a combination of experimental methods, while also employing a modified phase boundary and nucleation and growth model. In prior studies, wherein fillers with broad PSDs were used, it has been reported that between quartz and limestone, the latter is a superior filler due to its ability to partake in anion-exchange reactions with C-S-H. Contrary to prior investigations, this study shows that when size-classified and area matched fillers are used—which, essentially, eliminate degrees of freedom associated with surface area and agglomeration of filler particulates—the filler effect of quartz is broadly similar to that of limestone as well as rutile. Results also show that unlike quartz, limestone, and rutile—which enhance C₃S hydration kinetics—corundum suppresses hydration of C₃S during the first several hours after mixing. Such deceleration in C₃S hydration kinetics is attributed to the adsorption of aluminate anions—released from corundum's dissolution—onto anhydrous particulates’ surfaces, which impedes both the dissolution of C₃S and heterogeneous nucleation of C-S-H.     

Strength of brittle materials in moderately corrosive environments

The strengths of four brittle materials―cordierite glass ceramic, fused silica, silicon, and polycrystalline alumina were measured after exposure to weakly corrosive water and moderately corrosive buffered HF (BHF) solution. Exposure to water did not alter the strengths in subsequent inert strength tests and decreased the strengths in reactive strength tests. Exposure to BHF increased the strengths in both tests, but only after an incubation exposure time. Prior to the incubation time, the BHF had the same effect as water, suggesting that the bond rupture kinetics were unaffected. Examination of strength‐controlling indentation flaws after the incubation time showed clear corrosive effects on the flaw geometry indicative of reductions in the indentation residual stress fields. The implication is that moderately corrosive environments increase the strength or lifetime of a brittle component by reducing the crack driving force via flaw alteration and do not, as perhaps expected, decrease the strength or lifetime through enhanced chemical reactivity.     

Extracting dust from soil: a simple solution to a tricky task

Air quality is commonly assessed by the ambient concentration of airborne particles sized smaller than 10 microm (PM10). However, in addition to concentration, particle shape as well as the type and bioaccessibility of elements adsorbed to this particulate fraction are likely to be related to subsequent respiratory health effects. In order to investigate this relationship, a relatively large mass of the relevant size fraction is needed since sample preparation is necessary prior to analysis. Most existing methods for sampling dust have been developed for analysing the dust directly, without prior handling or digestion. In order to provide sufficient material to be used for subsequent bioaccessibility analysis, these methods require repetitive and time consuming sampling as well as special equipment and procedures which are high in both cost and maintenance. This paper describes an inexpensive and relatively simple procedure for extracting the PM10 fraction from soil to be used for lung bioaccessibility studies. The method described involves dry and wet sieving in order to exclude larger size fractions as far as possible. Vacuum filtering of the wet-sieved soil solution through a 10 microm mesh was then employed to extract the required fraction. In order to avoid frequent blocking of the mesh, Stokes's law was applied in the construction of a tube which enables separation of the solution holding the smallest fraction.     

Landscape structure indices for assessing urban ecological networks

Analysis and planning of ecological networks is a relatively new phenomenon and is a response to fragmentation and deterioration of quality of natural systems. In urban areas, the problems of land use intransigence, political and jurisdictional issues create a difficult environment for implementing ecological networks. The specific questions addressed in this research program revolve around the viability of planning an ecological network in an urban landscape. The development and articulation of an ecological network plan was undertaken previously and in this paper, a series of assays of landscape structure are used to examine the viability of an ecological network in the Phoenix, Arizona urban area. Three principal analyses were utilized: (1) patch content analysis, (2) corridor content analysis, and (3) network structure analysis. Patch and corridor content analyses examined the internal characteristic and immediate context for each of the 89 ecological network elements. The network structure analysis incorporates a process for aggregating results of patch and corridor analyses and incorporates indicators that describe interrelationships between landscape elements. For each of these analyses the existing condition was compared to the optimal plan to demonstrate the level of change that can be expected. The results and conclusions of this research are that an ecological network plan provides modest but important improvement in ecological systems in the Phoenix urban area.     

Urban landscape networks: an ecological planning framework

This paper presents a framework for the planning of urban landscape networks in an attempt to have nature areas integrated into traditional urban land-use planning. The biophysical and socio-economic benefits of such a network are discussed to provide justification for this incorporation. A framework is described, building upon ecological planning processes and incorporating theory and methodology from landscape ecology. The framework includes an assessment of natural and cultural resources, formulating the spatial structure of the network and examination of network components. Implementation strategies are discussed within the context of traditional urban land-use planning practice.     

Modelling instream nitrogen variability in the Dee catchment, NE Scotland

The Integrated Nitrogen in CAtchments model (INCA) was applied to the River Dee, Aberdeenshire, NE Scotland. To a first approximation the model was able to simulate the annual mean streamwater NO3-N concentrations observed along the length of the main channel. This provided the basis for using INCA to subsequently explore the effects of N deposition and land use management on streamwater NO3-N concentrations and loads. On an annual timescale, the model predictions suggest that NO3-N concentrations will decrease by 5% following a 20% reduction in fertiliser application. Furthermore, model results also suggest that a 50% increase in N deposition will cause a 15% increase in the streamwater NO3-N concentrations. The utility of INCA as a tool for catchment management is discussed, current limitations are highlighted and possible improvements are suggested.     

Evaluation of buffer zone effectiveness in mitigating the risks associated with agricultural runoff in Prince Edward Island

To minimize the risk posed by runoff from row crops, Prince Edward Island introduced buffer legislation in 2000. The legislation mandates 10-m and 20-m buffers, respectively, for moderate sloped (i.e. < 5%) and steep sloped (i.e. > 5%) agricultural fields that border streams. Since 2001, Environment Canada has been evaluating the effectiveness of various buffer widths on operational farms in reducing toxicity and contaminant concentrations in runoff. Sample collectors, placed in 44 fields at the field edge (0 m), 10 m and at distances out to 30 m, collected overland flow following rainfall-induced runoff events. Samples were collected within 24 hours of an event and analysed for seven pesticides (endosulfan, chlorothalonil, carbofuran, linuron, metribuzin, metalaxyl, mancozeb), water quality parameters and Daphnia magna toxicity. The 10-m buffer required for moderate sloped fields was effective at reducing contaminant concentrations but not always to less than lethal concentrations to Daphnia magna. Limited data beyond 10 m for fields of both slope types precluded making recommendations on a suitable buffer width for shallow sloped fields and evaluating the effectiveness of 20-m buffers for steep sloped fields. When paired data were combined and statistically tested for all fields, the studied pesticides underwent a 52-98% and 68-100% reduction in aqueous and particulate concentrations within 10 m and 30 m, respectively. In addition, by 10 m, soluble phosphorus, nitrate-nitrogen and total suspended solids were reduced by 34%, 38% and 64%, respectively. Results suggest buffer zones on operational farms are capable of achieving contaminant reductions comparable to those reported for controlled experiments. Inconsistent siting of sample collectors beyond 10 m limited the evaluation of the effects of field slope and buffer width on buffer effectiveness on working farms. Future studies on buffer efficiency on operational farms should focus on building the data set beyond 10 m and evaluating load reductions.