Does vacuum saturation work for the higher-dimensional vacuum condensates in the QCD sum rules?

In the QCD sum rules for the tetraquark (molecular) states, the higher-dimensional vacuum condensates play an important role in extracting the tetraquark masses. We carry out the operator product expansion up to the vacuum condensates of dimension-10 and observe that the vacuum condensates of dimensions 6, 8 and 10 have the same expressions but opposite signs for the [Formula: see text]-type and [Formula: see text]-type four-quark currents, which make their influences distinguishable, and they are excellent channels to examine the vacuum saturation approximation. We introduce a parameter [Formula: see text] to parametrize the derivation from the vacuum saturation or factorization approximation, and choose two sets of parameters to examine the influences on the predicted tetraquark masses, which can be confronted to the experimental data in the future. In all the channels, smaller value of the [Formula: see text] leads to better convergent behavior in the operator product expansion, which favors the vacuum saturation approximation.

Basic physical and mechanical properties of cement composites after temperature exposure

Basic physical and mechanical properties of several cement composites are determined as functions of thermal load and the results are compared with reference materials. Bulk density, matrix density, and open porosity are measured using the water vacuum saturation method. Compressive and bending strengths are determined according to the European standard. High-temperature coefficient of thermal expansion is obtained using a comparative measurement. Experimental results show that composites based on Portland cement do not resist high temperatures well. Their applicability is limited to 400 °C, due to the damage caused by hydrates decomposition. On the other hand, composites based on calcium aluminate cement exhibit a better thermal stability and retain residual strength even after being exposed to 1000 °C.

Evolution Characteristics of the Cracks in the Completely Disintegrated Carbonaceous Mudstone Subjected to Cyclic Wetting and Drying

Completely disintegrated carbonaceous mudstone, a common embankment material, has significant swelling-shrinkage behavior under cyclic wetting and drying, which often causes the instability of embankments. In this paper, the evolution of the cracks in the completely disintegrated carbonaceous mudstone subjected to cyclic wetting and drying was studied by laboratory tests. The vacuum saturation method and the drying method based on heat lamps and a fan were employed to simulate the wetting and drying processes, respectively. The image processing technique was used to treat the images of the sample surface. Afterward, various geometric parameters of the cracks appeared on the sample surface were measured, and the evolution characteristics of the cracks were analyzed. The results show that with the increase in the number of wetting and drying cycles, the number of cracks on the sample surface gradually increases. After four wetting and drying cycles, the existing cracks produce a large number of small branches, which are connected to form irregular polygonal grids. The development of the cracks in the completely disintegrated carbonaceous mudstone sample can be divided into three stages, i.e., slow development, rapid development, and stable development. Both the surface density of crack and the crack rate first increase and then tend to be stable with the increasing number of wetting and drying cycles. New cracks are mainly generated on the basis of the existing cracks, and some cracks appear to heal under cyclic wetting and drying. The early cracks are mainly developed in the directions of 0°–90° and 300°–360°, and the development rate of the cracks in the directions of 30°, 90°, 140°–150°, and 180°–270° is significantly higher than that of the cracks in other directions.

Thermal and moisture properties of calcium silicate insulation boards

The purpose of this research was to determine thermal and moisture properties of calcium silicate insulation boards available on the Finnish market. Ruggedness testing and test arrangement development were done related to the pressure plate test, which was used to measure desorption isotherms in capillary range. Four calcium silicate and one calcium hydroxide board were examined. The determined material properties are water vapour permeability, water absorption coefficient, capillary saturation water content, moisture sorption isotherm in hygroscopic and capillary range, thermal conductivity and specific heat capacity. Ruggedness tests and development were done to the pressure plate measurement method. Capacitance needles were tested as a method to evaluate the state of equilibrium and different vacuum saturation methods were tested.

Hygric properties of hydrophobized building materials

Moisture loads due to wind-driven rain can lead to accelerated decay of exposed building facades. Hydrophobic impregnation reduces water absorption of facade materials and is thus presumed to decrease moisture related damages. Hydrophobic impregnation however also lowers the drying speed of the exposed facade, leaving mainly water vapour transfer to take place. This study examines the open porosity and capillary absorption coefficient of impregnated brick samples as well as the effect of hydrophobic impregnation on the vapour permeability of brick and mortar samples. The open porosity was measured with vacuum saturation test, the absorption coefficient was determined by water uptake tests, both done after one month of curing of the impregnated brick samples. The vapour permeability was `derived from cup tests and from drying tests. The resulting open porosity from brick samples indicates that the changes in the overall pore structure are minimal after impregnation. In addition, the absorption coefficient of brick was found to be fairly close to zero, even with low concentrations of active ingredient, and regardless the percentage of silane/siloxane. Our findings support the claim that the hydrophobic impregnation does not influence significantly the water vapour permeability of brick and mortar.

A round robin campaign on the hygric properties of porous building materials

The reliable determination of the hygric properties of porous building materials is important. In earlier round robin campaigns large discrepancies of measured hygric properties were found among different labs. Later studies indicated that differences in lab conditions and more importantly, personnel’s operation procedures and data processing methods, might have the greatest impact. To gain further insight, a new round robin campaign has been launched by KU Leuven (Belgium), to which another eight institutes contributed. A relatively stable and homogeneous ceramic brick is tested, and 3 standard tests are performed: the vacuum saturation test, the capillary absorption test and the cup test. During the campaign, two rounds of measurements are performed. In the 1st round, tests are performed according to participants’ respective experimental protocols. Next, a strict and detailed common protocol is prescribed. This paper reports on the results obtained in the 1st round of measurements. Results show that not much progress has been made since the EC HAMSTAD project: the vacuum saturation test leads to the most consistent results, while the cup test produces the largest discrepancies, most probably originating from sample sealing and humidity control.

Effectiveness of two field methods of saturating near surface concrete on the water permeability of in situ concrete

Determining the water permeability of concrete in structures remains a challenge because of difficulties in removing the influence of its moisture content. Saturating concrete with water could be one option, but this is not easy to achieve on site. This paper reports a testing programme carried out to assess the reliability and effectiveness of two field saturation methods, viz. vacuum saturation and ponding. The water permeability test results after applying the vacuum saturation and ponding were compared with that obtained after incremental immersion. It was found that ponding was unable to remove the influence of moisture, whilst vacuum saturation was effective for wet concretes. The results obtained from the electrical resistance measurements after incremental immersion suggested that the water permeability of concretes can be accurately determined by carrying out in situ permeability tests if the near surface region up to a depth of 25 mm is fully saturated.

Basic Physical and Mechanical Properties of Composites Based on Three Different Cements

This article is focused on cement based composites. Two cements differing in mineralogical composition are utilised as main binder in composites mixtures. Results of measured physical parameters of studied materials are presented. For the sake of comparison, a reference material with Portland cement was also prepared. Basic physical properties (measured by water vacuum saturation method and by helium pycnometry), characterizations of pore system (determined by mercury porosimetry) and mechanical properties are the matter of this study. Composites show various open porosity; the results of open porosity of materials containing special cements show higher values, in comparison with composite based on Portland cement. This fact of course influences other material characteristics - mainly mechanical properties.

Pore System and Hydric Properties of Two Different Lime Plasters with Finely Crushed Brick

Two different lime plasters with finely crushed brick are studied in this article. In the first plaster the pozzolan mixture was used as silica sand while in the second it was dosed as replacement of the lime substitute and silica sand (the substitution levels being 20% and 50%). Classic lime plaster was used as a reference material. Studied parameters were basic physical properties (measured by water vacuum saturation and by helium pycnometry), characterization of pore system (by mercury porosimetry) and transport of liquid water.