Decrease In Expansion Rate Research Articles

Increase in volume stability of RO phases in steel slag by combined treatment of alkali and dry carbonation

RO phases account for 8.5–16.9 wt% of steel slags and exhibit delayed hydration activity, which may result in poor volume stability of steel slags (SS). Treatment of alkali activator (sodium silicate) followed by dry carbonation technology (ADC) was conducted on synthetic RO phases with various molar ratios of FeO, MgO, and MnO to promote its early hydration activity. Results show that 28 d compressive strength of mortar added by ADC_SS is 19.67% higher than that of added untreated SS and 26% decrease in expansion rate. Hydration degree of RO phases increases obviously during alkali treatment from 10.6% to 21.7% (RO-6), and is further stimulated by subsequently carbonation (reaching 44.1%), both resulting in much consumption of expansive component (i.e., MgO) in RO phases. The early hydration activity of cement promoted by adding ADC_RO phase/SS, which mainly attributes to the nucleation effect of hydration and carbonation products (i.e., Mg(OH)2, pyoaurite, and MgCO3·3H2O). The alkali excitation reaction of silica gels produced during carbonation as well as the formation of monocarboaluminate further contribute to the strength gain. ADC_SS used as admixture for cement makes pastes have advantage of higher strength, higher hydration rate, lower heat release, and less expansion rate compared to the system contained untreated SS. ADC may be a potential method to treat SS and makes SS to be used as admixture for Portland cement.

Recycling of industrial waste and performance of steel slag green concrete

Workability and mechanical properties of steel slag green concrete with different types of steel slag and different dosages of admixtures were investigated. The effectiveness of steel slag powder on suppressing alkali aggregate reaction (AAR) expansion was assessed using the method of ASTM C441 and accelerated test method. Experimental results show that mechanical properties can be improved further due to the synergistic effect and mutual activation when compound mineral admixtures with steel slag powder and blast-furnace slag powder are mixed into concrete. In addition, about 50% decrease in expansion rate of mortar bars with mineral admixtures can be achieved in AAR tests. Mineral admixtures with steel slag powder as partial replacement for Portland cement in concrete is an effective means for controlling expansion due to AAR.

Effectiveness of Steel Slag Powder on Suppressing Alkali Aggregate Reaction of Concrete

Concrete properties can be greatly improved with the advanced mineral admixtures such as steel slag powder. Used in combination with Super-plasticizer admixture, steel slag powder can lead to economical high performance concrete with enhanced durability and reduced cement content. The effectiveness of steel slag powder on suppressing Alkali Aggregate Reaction is analyzed. The effectiveness of steel slag powder on suppressing AAR expansion was assessed using the method of ASTM C441 and accelerated test method. Results show that mineral admixtures with steel slag powder as partial replacement for Portland cement in concrete is an effective means for controlling expansion due to AAR. At most a 50% decrease in expansion rate of mortar bars can be found.

Coalescence of Protein-Stabilized Bubbles Undergoing Expansion at a Simultaneously Expanding Planar Air−Water Interface

A novel design of apparatus is described that allows observation of the coalescence stability of bubbles at a planar interface when the planar interface and the bubble surface both expand. Bubbles are introduced beneath the planar air-water interface contained within a square barrier made of perfluorocarbon rubber. The bubbles are then expanded by reducing the air pressure above the interface, while at the same time the rubber barrier is mechanically expanded, maintaining its square shape, to give the same rate and extent of expansion of the planar interface. The area can typically be increased by a factor of three over time scales as short as 0.2 s. This arrangement has been designed to mimic the behavior of aerated products when they exit from a pressurized aeration unit or product dispenser. Compared to results obtained via a previous technique, where it was only possible to expand the bubbles but not the planar interface, the bubbles are less stable. The apparatus has been used to compare the stabilizing effects of ovalbumin, beta-lactoglobulin, whey protein isolate, and sodium caseinate, in a model aqueous food system thickened with 40% invert sugar. Stability improved with increasing concentration of all the proteins and with a decrease in expansion rate, but considerable instability remained even at protein concentrations as high as 4 to 6 wt % and also at very low expansion rates, though the systems were stable in the absence of expansion. However, the stability was greatly improved by the replacement of the above proteins by the hydrocolloids gelatine or polypropylene glycol alginate. Detailed analysis revealed that the coalescence of individual bubbles in clusters of bubbles were not strongly correlated in distance or time, but larger bubbles and bubbles toward the outside of a cluster were found to be, on average, less stable than smaller bubbles and bubbles located more toward the interior of a cluster. The different degrees of stability are discussed in terms of local deformation, fracture behavior, and time-dependent composition of the adsorbed layers.

Collimation of the radio jets in 3C 31

Observations of the radio jets in 3C 31 using the VLA show that the rates of expansion of these jets transverse to their length decrease with increasing distance from the radio core. A rapid decrease in expansion rate in the northern jet occurs where its magnetic field appears dominated by an organized circumferential component. We use the supersonic beam model of Chan and Henriksen to show that the energy of this circumferential field need only be approx.1% of the flow kinetic energy to produce the observed changes in expansion rate by an incipient magnetic pinch. If the beams in 3C 31 are described by the Chan-Henriksen model, their circumferential field strengths cannot significantly exceed their equipartition values, or pinches much stronger than those observed would result.