Precast construction is related to efficient manufacturing of precast concrete components and short construction periods. Therefore, also the connection of the elements among each other has to be realized quickly and easily, as to avoid any delay in the construction progress. For this reason, connection systems with cable loops have established themselves both in constructive as well as in approved fields. The time-saving installation and simple assembly meet very well the more and more important requirements in respect of time management, cost saving and efficiency.
In the so far known approvals for such kind of connection systems a grouting mortar has been integrated, which was filled in the joints after the erection of formwork. Although this free-flowing and high-strength grouting mortar is eminently suitable for filling in the narrow joints, it requires, however, a very careful sealing of the joint by means of appropriate sealing materials and subsequent concrete repair measures.
Due to the continuous advances in the development of the products in close collaboration with the customers, for the first time Philipp now has succeeded in achieving a decisive time and cost advantage in the field of grouting, too. Right now, the time-consuming erection of formwork on the grouting joint is a thing of the past. The approval of the Philipp Power Duo System was amended by a new thixotrope mortar (Philipp Thixo Mortar). This mortar was developed together with P&T Technische Mörtel GmbH & Co. KG in a long-drawn-out testing process. The respective tests were carried out at the RWTH Aachen in cooperation with the engineering office Hegger & Partner.
Components of the system
The Power Duo System consists of a flat galvanized rail section of 20 mm having a depth of 70 mm with built-in loops, which are folded in the respective storage box during shuttering. To prevent concrete penetrating into the storage boxes, which serve as permanent formwork, the rails are sealed with adhesive tapes on the front sides and are closed up in the front with a plastic cover.
The closed storage boxes are either nailed or glued flush to the formwork. After concreting when the side formwork is dismantled, the cover is removed and the loops are folded out of the retainer. Then the precast concrete component may be transported to the construction site for assembly. After assembly the adjacent cable loops bend back automatically because of their flexibility, overlap each other and are secured in their position by means of constructional steel. Any existing joint is subsequently filled with mortar.
Joint mortar – grouting mortar or thixotrope mortar
Filling of the joints is an important aspect, because in case of a wall and column connection and/or a wall and wall connection every meter of the joint has to be filled in an efficient and reliable way. Within the scope of the German national technical approval (No. Z-21.8-1867) it was possible to fill in the joint with grouting mortar. Although this mortar generates a force-locked and form-fit connection, it requires, however, quite extensive formwork because of its liquid consistency.
Using the new Thixo Mortar, it is not necessary to have any formwork at all. At first, the mortar is applied at the section of joints and edges in such a way that the joint between the connection chamber and the exterior of the precast component is completely sealed serving as one side, permanent formwork. Filling is made automatically with the aid of a spiral pump (e.g. the mortar machine Putzmeister Spray Boy S5, PFT G4/5), applying the mortar by means of a mortar hose having a special filler tube for squeezing the mortar out from the bottom up in the entire grouting joint. Afterwards the joint is smoothed out.
When processed appropriately, the consistency of the Thixo Mortar is that liquid that it fills out all hollow spaces completely and is that rigid as to be self-standing in the joint. Load-bearing capacities are as well in a range that fulfills the requirements in practice. In this way, the product covers the span between a reliable processability and a load-bearing capacity being suitable for everyday use. The advantages of this new system are perfectly obvious:
» Formwork and sealing are no longer necessary
» The joint can be leveled immediately (even before hardening of the mortar), thus the joint is also suitable for fair-faced concrete.
» High joints need not be filled in layers, but can continuously be filled in sideways.
A connection of precast concrete components with built-in Philipp Power Duo System is in the position to absorb, on the one hand, shear forces parallel to the joint and, on the other hand, shear forces perpendicular to the joint. A linear interaction of both forces is also possible. The load-bearing model for the shear force parallel to the joint consists of two components: the cable loops absorb the tensile force, whereas the grouting mortar is forming the strut. The recess formers filled with concrete transfer in combination with the friction of the perforated rail the forces from the grouting joint to the precast concrete component. Any shear forces occurring perpendicular to the joint will be transferred from one concrete edge to the opposite concrete edge. For this purpose, the wall thickness and the concrete strength of the precast component are the significant factors.
Thus, the load-bearing capacity of the shear force parallel to the joint essentially depends on loop and mortar. As the loop forms the tensile force and the mortar the strut, the load-bearing system depends on the tensile force of the cable loop and the compressive strength of the mortar.
The amendment of the national technical approval by the Thixo Mortar results in different load-bearing capacities of the system depending on the respective mortar. Whereas the Philipp Power Duo System used with Philipp Grouting Mortar is approved for a load-bearing capacity of shear forces parallel to the joint of vRd,II = 80 kN/m and of shear forces perpendicular to the joint of vRd, = 9.7–37.5 kN/m (depending on the concrete class and the wall thickness), using Philipp Thixo Mortar achieves a shear force parallel to the joint of 50 kN/m and a shear force perpendicular to the joint of vRd, = 9.7–28.1 kN/m (depending on the concrete class and the wall thickness).
The application of different mortars provides the planner and/or the user a wide range of different applications in practice. If a great number of joints has to be filled, which are however not that much subject to load, Thixo Mortar is excellently suitable. Philipp Grouting Mortar is recommended for applications requiring high load-bearing capacities.
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