碳酸钙形态对卷烟纸透气性能和凝灰性能的影响

本研究比较了椭圆状、球状、纺锤体状和花瓣状轻质碳酸钙的差异,将不同形态轻质碳酸钙应用于卷烟纸生产过程。结果表明,椭圆状轻质碳酸钙制备的卷烟纸凝灰性能最好,球状次之,花瓣状最差;纺锤体状轻质碳酸钙制备的卷烟纸透气性能最好,花瓣状次之,椭圆状碳酸钙最差;椭圆状和球状轻质碳酸钙在卷烟纸中的留着率明显高于纺锤体状和花瓣状。

BOND PERFORMANCE EXPERIMENT FOR FLY ASH CONCRETE AND STEEL BAR

The impact of fly ash content on bond performance of steel bars and their surrounding concrete is studied by means of sticking strain gauges on steel bars. The average bond stress-slip curves, the steel strain-anchor location curves, and the bond stress-anchor position curves of the pullout specimens with various fly ash contents are obtained. Results indicate that the bond performance of concrete and steel bars can be improved and the distribution of steel strain along the anchorage length tends to be more uniform by adding fly ash in concrete specimens, and both ultimate bond stress and ultimate slip deformation increase the most when 20% of specimens′ content is fly ash.

Improving performance of recycled aggregate concrete with superfine pozzolanic powders

Phosphorous slag （PHS）, ground granulated blast-furnace slag （GGBS） and fly ash （FA） were used as replacements of Portland cement to modify the microstruc^xe of recycled aggregate concrete （RAC）. A new manufacturing method named ＂W3T4＂ was proposed to improve the performances of interracial transition zone （ITZ） between recycled aggregate and mortar. The mechanical properties and the durability of RAC were tested, which show that this new manufacturing method improves the properties of RAC, and the GGBS with finest size makes a great contribution to the performance of RAC due to its better filling effect and much earlier pozzolanic reaction. Combined with GGBS, the effects of PHS on the retardation of setting time can be alleviated and the synergistic effect helps to make a more compact RAC. For the RAC with 25% of the recycled aggregate （RA） replacement and 10% PHS ＋ 10% GGBS additives, the compressive strength increases by 25.4%, but the permeability decreases by 64.3% with respect to the reference concrete made with nature aggregates. The micro-mechanisms of these improvements were investigated by the scanning electron microscope （SEM）. The SEM images show that the new manufacturing method, adding superfine pozzolanic powders and super-plasticizer benefits, makes a much denser ITZ in RAC.

Research on the influence of the fly ash on the concrete carbonation

The influence of fly ash on the fresh properties, mechanical properties and carbonation properties were studied in this paper. The performance of a kind of curing agent which was applied to the hardened concrete surface was evaluated. Incorporating large volume of fly ash will risk the concrete carbonation. The curing agent could prevent the concrete carbonation, and the mechanism was explained.

Grinding Properties of Abandoned Concrete

The grinding properties of abandoned concrete, which consists primarily of hardened cement, limestone aggregate and river sand, are studied. Theoretical models of grinding are used to explain the experimental observation. The results show that 1) The principle disintegration mechanism of hardened cement and river sand is volumetric grinding, although at later stages grinding of cement becomes difficult because of its flaked structure; 2) The lime- stone grinding process can be divided into two steps. First, volumetric grinding, with an obvious component of surface grinding, followed by primarily surface grinding as the micro-particle content increases; 3) Initially, the principle mechanism of grinding limestone and river sand is volumetric grinding, albeit less efficient grinding than if these components were ground separately, and; 4) After 10 to 20 min of grinding the grinding bottleneck phenomenon ap- pears and after 20 min of grinding the content of micro-particles is large and surface grinding is the main mechanism while the particle size of the mixture is smaller than that of separately ground river sand and cement but bigger than that of separately ground limestone.