Patent Application
20080019773
Mortar prisms were produced in order to investigate the introduction by scattering and watering of joints under conditions which are as clearly defined as possible. From this it was possible to subsequently determine physical values such as the tensile strength in bending and the compressive strength.
A paving joint dry mortar was prepared by mixing homogenously in an agitator 5% by weight of Portland cement CEM I 42.5 N, 87% by weight of quartz sand with a sieve line of 0.063 to 1.5 mm, 3% by weight of a calcium carbonate (Durcal 10) and 5% by weight of a polymer powder redispersible in water. A comparative example was carried out using in place of the polymer powder a partially saponified polyvinyl alcohol with a degree of hydrolysis of 88 mole % and a viscosity of 4 mPas (according to Höppler as 4% aqueous solution, measured according to DIN 53015 at 20° C.) (in the following tables referred to as “PVOH”). Another comparative example was carried out entirely without polymer powder, the omitted polymer quantity being replaced by quartz sand.
500 g of the dry mortar produced were then scattered into a 4 cm×4 cm×16 cm metal prism mould, the inside wall of the prism mould having been painted with mould oil as release agent using a painter's brush. The dry formulation was compacted by manually shaking and tapping for 10 seconds. The surface of the dry mortar scattered in was smoothed off with a trowel.
A spray bottle typically used for spraying plants was used for watering. The water cone formed during spraying was adjusted so that the water was sprayed selectively onto the mortar surface from a distance of 10 cm. The spray duration was 5 to 10 minutes, depending on how well the surface was wetted and the water was able to penetrate inside. The necessary quantity of water was determined by way of a separate test wherein the surface was damaged periodically using a fine spatula and the depth of water penetration assessed optically until the water had reached the lowermost layer of the paving jointing mortar.
During watering the following assessments were carried out: (a) wetting of the surface (i.e., how well the water is absorbed by the joint during the entire watering process), (b) water saturation (i.e., how much water can be sprayed continually onto the prism until water floats on the surface), (c) bubble formation (i.e., whether bubbles rise to the surface during or immediately after spraying on of the water, which may have a negative influence of the surface properties), and (d) cleaning after contamination (i.e., how simply the prism mould could be cleaned after releasing the prisms). These assessments provide a good indication regarding the behavior of the watered paving joint mortar on the surface of the paving stones.
18 hours after completion of the introduction of water, the prisms were released and stored at 23° C. and a relative atmospheric humidity of 50% (standard climate).
a)The polymer powders re-dispersible in water EVA-1, EVA-2 and St/Ac consist of different spray-dried dispersions stabilised with polyvinyl alcohol based on ethylene-vinyl acetate (EVA-1 and EVA-2) copolymers and styrene-acrylate copolymers (St/Ac).
b)“Excellent” means that cleaning caused no problems whatsoever and the residues were easily removed by washing. “Smeared” means that the residual layer could be removed only after intensive cleaning.
c)PVOH represents partially hydrolysed polyvinyl alcohol.
d)P.P. represents “polymer powder”.
d)Indicated in % by weight.
e)The surface hardness was assessed by scratching with a pointed metal rod.
f)To assess the surface hydrophobicity, 1 ml of water was placed drop-wise onto the surface using a pipette and the time was measured by which all the water had been absorbed by the subgrade.
Tables 1 and 2 show, among other things, that paving joint mortar with partially hydrolysed polyvinyl alcohol exhibits the greatest water requirement. In contrast to paving jointing mortars prepared without polymer powder or with polymer powders redispersible in water (EVA-1, EVA-2 and St/Ac), the paving joint mortar with PVOH absorbs a relatively large amount of water at its surface, preventing the water from reaching the underlying layers. Thus, the mineral binder does not set and the organic binder does not form a film, resulting in a lack of strength of these layers.
Even if wetting of the dry mortar is excellent, the unset paving jointing mortar may exhibit a moderate hydrophobicity as shown by the example of EVA-1. This contributes to less dirt penetrating into the joints and being washed away, particularly in the case of an inclination and/or fairly strong rain.
g)No values available.
Tensile strength and compressive strength are excellent measures for assessing cohesion of the watered paving jointing mortar. The values given in Tables 3 and 4 clearly show the additional cohesion achieved by adding polymer powder redispersible in water versus those containing only mineral binder (indicated by “without polymer powder”). These high values are highly surprising since the dry mortar was merely watered without mixing the mortar. Mixing enhances the redispersion of the polymer powder redispersible in water, guaranteeing good distribution of the redispersion achieved. The cohesion achieved is sufficient to prevent damage, for example, in the case of impact or expert cleaning with sweeping machines or high pressure cleaners. The corresponding early strength values additionally provide the paving jointing mortar applied with sufficient protection against driving rain and hail. The polymer powder redispersible in water used provides the paving joint mortar also with a good flank adhesion such that the joint does not detach itself from the paving stone. The low proportion of mineral binder guarantees the required flexibility needed to survive deformations of the subgrade without cracking. As a result of the controlled optimisation of the types and quantities of hydraulically binding binder used and of the polymer powder redispersible in water, it is, moreover, possible to correspondingly optimize flexibility, tensile strength and compressive strength, as well as tensile bond strength in line with users' requirements without having to change processing.
The paving joint dry mortar produced according to Example 1 is stirred with water for one minute using a propeller stirrer at 900 rpm, the amount of water adjusted for consistency. During this process, care was taken in mixing that the resulting mortar was not too thin but also not too highly viscous, and could be introduced into a prism box as described in Example 1 by simply using a trowel. Prior to addition to the box, the mixed paving joint mortar was allowed to mature for 3 minutes and was then stirred once more for 15 seconds. Following the introduction of the mortar, the surface of the mortar was smoothed off with a trowel. The storage conditions were handled in a manner analogous to Example 1.
Quantities of water used for adjusting the consistency of the different samples of EVA-1, St/Ac and the comparative sample without polymer powder and tensile strength in bending and compressive strengths after different storage periods, in N/mm2, in line with EN13892-2 are illustrated in Table 5 below.
Table 5 illustrates that by mixing the paving joint dry mortar with water prior to introduction into the joints, the physical values obtained are slightly higher than by introduction of water over the surface according to Example 1. Consequently, by using paving joint dry mortar according to the present invention, the user has the choice of choosing either an extremely simple and convenient type of application involving dry introduction with subsequent surface watering, or by externally mixing the paving joint dry mortar with water and subsequent introduction to obtain even higher physical strength values.
Although the present invention has been described and illustrated in detail, it is to be understood that the same is by way of illustration and example only, and is not to be taken as a limitation. The spirit and scope of the present invention are to be limited only by the terms of any claims presented hereafter.
| Number | Date | Country | Kind |
|---|---|---|---|
| 06015384.8 | Jul 2006 | EP | regional |
