Screed

Abstract: area (loading about 0.4 m 2 /m 3 ) with about 100 g/m 2 (primer), 1000 g/m 2 /mm (screed) and 300-600 g/m 2 (adhesive) making them an important possible source for VOC/SVOC-emissions, additionally to those from the floor covering. Within the research project ''Environmental and health quality of composite building products'' which Abstract Emissions of volatile organic compounds (VOC) and semivolatile organic compounds (SVOC) from materials for flooring installation (primer, screed, adhesive, floor covering) were measured by means of emission test chambers and cells over a time period of at least 28 days at 23 � C, 50% relative humidity and an area specific air flow rate of q ¼ 1.25 m 3 /m 2 h. Single com- ponents were tested in comparison to three complete structures (same concrete, primer, screed, adhesive) with different types of floor covering (PVC, carpet, linoleum). Sorption into concrete/screed and different permeability of flooring materials affected the emissions from the complete structures. The complete structures with linoleum and PVC showed the same types of emission and emission rates as the individual floor coverings themselves. Emissions from the carpet-covered structure resulted also from the lower layers. In all cases emis- sions from the complete structures were lower than the sum of emissions from the single components. For two adhesives the formation of secondary emissions (aldehydes and organic acids) was observed starting after the standard testing time of 28 days.

Abstract: An asphalt paver includes a microprocessor controlled integrated control system to control both the operation of a tractor unit of the paver and the positioning of the screed during a paving operation. A paver operator may operate the paver and monitor the screed position with respect to a grade reference. The correction of grade or transverse slope errors is accomplished by monitoring the linear advance of the paver and then measuring a any deviation of the screed with respect to a grade reference. The amount of vertical deviation and the linear advance since a most recent correct reading allows a rate of deviation per unit advance of the paver to be determined. A correction is applied as a change in the angle of attack of the screed, the change being equal and opposite to the determined rate of deviation. A transverse slope change is also measured directly at the screed. A measured transverse angular deviation is translated into a vertical deviation which is then translated into a rate of deviation per unit advance of the paver with a corrective twist being applied to the screen to offset the deviation. Advantageously dual grade sensors and dual slope sensors are contemplated to provide an automated microprocessor controlled grade and slope control in accordance herewith.

Abstract: The results of a study undertaken to evaluate premixed polymer concrete overlays (PMPCO) over a 3-year period are presented. The PMPCO evaluated were constructed with polyester amide para resin and silica sand 1;. polyester styrene resin 1 and silica sand 2; polyester styrene resin 2, basalt aggregate and coke breeze (for conductivity); polyester styrene resin 2, silica sand 3 and coke breeze; and vinyl ester styrene resin, silica sand 2, and coke breeze. The mixing of the ingredients was done with either portable concrete mixers, mortar mixers, or a continuous batching mobile concrete mixer. The overlays were struck off and consolidated with a vibrating screed or a slip form paver. The report indicates that a nonconductive PMPCO with high bond strength, low permeability, and high skid resistance can be successfully installed by a contractor and opened to traffic after only three hours of curing. The report indicates that a conductive PMPCO with high bond strength and skid resistance can be successfully installed as a secondary anode for a cathodic protection system. Also, it is shown that the special provision for a PMPCO should require the installation of test patches or test sections of overlay prior to placing the final overlay to assure that the surface preparation is adequate and the mixing, installation equipment, procedures, and materials will provide a satisfactory overlay.

Abstract: The disclosure relates to a floating screed type asphalt paver provided with extendable, retractable auxiliary screed units which, in their retracted positions, are mounted in front of the main screed and carry edger plates. By mounting the screed extensions in front of the main screed units, it is possible to retract the extension units without interrupting paving operations. A strike-off plate may be positioned in front of the extension units to limit the presence of paving material between them and/or the extension units may be provided with bevelled inner edges for displacing such material during retraction. Novel arrangements are provided for mounting and adjusting the screed extensions.

Abstract: An apparatus and method are disclosed for pivoting a screed assembly during screeding of placed and/or poured, uncured concrete or like loose, spreadable materials to maintain proper screeding contact by the screeding assembly with the concrete or like material by counteracting the force of concrete or other like material acting against the screed assembly as it is moved along the concrete The apparatus includes a support, preferably of the self-propelled type, a boom and boom mount, and a pivot between the boom and the screed assembly The axis of the pivot extends generally perpendicularly to the screeding direction in which the screed sassmblyis moved A power source, such as a pair of fluid cylinders, rotates the screed about the pivot axis, preferably in response to an electro-hydraulic leveling sensor mounted on the screed The lateral incline of the screed perpendicular to the screeding direction may be controlled about additional pivot axes orthogonal to the first A power operated elevation control is preferably responsive to a fixed laser beam reference plane positioned externally of the screed assembly The boom is telescoping and has multiple sections for extending and retracting the screeding assembly with respect to the support The screed preferably includes a vibration assembly vibrationally isolated from the remainder of the screed for smoothing the concrete