The effect of drying on early-age morphology of C–S–H as observed in environmental SEM

The morphology of early-age C–S–H, often referred to as outer product or low-density C–S–H, is generally accepted to be fibrillar and forms mainly during the early stages of hydration. This paper reports the effect of drying on the microstructure in young tricalcium silicate paste, which provides insight into the mechanism that leads to the fibrillar morphology. During the first few days after C₃S is mixed with water, the morphology of C–S–H is more affected by drying rate than by relative humidity. This sensitivity is most apparent at partial pressures greater than 85%. During this time, the fibrillar C–S–H product can be suppressed by drying C₃S paste samples very slowly prior to imaging. This approach is interpreted as evidence that this fibrillar morphology, which naturally form over time, grow as tiny colloidal particles that rearrange during the early stages of hydration, leading to well-established larger scale morphologies.     

Frequency measurement of the solitary ethyl alcohol laser line

We measured the frequency, the relative polarization and the pump frequency offset of the single FIR laser line obtained by optically pumping ethyl alcohol C₂H₅OH with a cw CO₂ laser.     

Thermal behaviour of partially neutralised ethylene-maleic acid copolymer

As part of continuing studies on the cure of candidate polymers for waterborne coatings, the thermal behaviour of partially neutralised ethylene-maleic acid copolymer, EMA, has been examined. Films of EMA neutralised with a variety of bases were heated at 250°C. For this copolymer, as for poly(acrylic acid) at the same temperature, reflectance infrared spectroscopy has shown that heating led initially to anhydride formation. In the unneutralised state, or with the divalent ions calcium, magnesium, cobalt or zinc, further heating led to little or no further reaction. By contrast, the presence of univalent metal ions lithium, sodium and potassium caused a second reaction to occur, namely decarboxylation to yield keto crosslinks. This second reaction, however, did not occur to the extent that it does with poly(acrylic acid) under identical conditions. Possible reasons for this are discussed. Unlike poly(acrylic acid), EMA when partially neutralised was found not to form continuous films on the tin-plate substrate.     

Case for Undergraduate Study of Disasters

Literature on disasters provides the focus for student-based learning exercises in civil and architectural engineering at Queen's University, Belfast, which have been ongoing since 1994. Incorporating these studies in the early part of the curriculum helps students to reorientate from their previous mainly science-based study by gaining some knowledge of the roles, responsibilities, priorities, and work practices of engineers in a way that would not be possible through lectures. In view of the influence of disasters on engineering thinking and work practice, they should have a much larger influence than they currently do on curriculum development.     

Thomas C. O’Connor (1931–2012)

Copyright 2013 American Association for Aerosol Research     

CONTROL OF FUGITIVE DUST BY WINDBREAKS

Fugitive dust generated by industrial haul roads can be reduced by windbreaks placed upwind or downwind of the road. For an elementary wind profile downwind of a windbreak, the fractional efficiency has been predicted as a function of downwind distance, wind speed and windbreak height and porosity. An analytical model and computer algorithm are proposed to enable engineers to predict the fractional efficiency for any source and wind profile of their choosing.