Das Kapitel befasst sich mit der Anwendung von Polypropylenfaserverstärkung - latexmodifiziertem Mörtel (PFR-LMM) für die Verlegung von Granitpflastersteinen auf verschiedenen Straßenabschnitten, einschließlich Kreisverkehren und städtischen Straßen. Es werden Fallstudien aus Krško und Šoštanj in Slowenien vorgestellt, die die Leistungsfähigkeit des Materials unter schweren Verkehrslasten und seine Fähigkeit zur Verbindung mit Stahlfaserbetonplatten und GPBs hervorheben. Laboruntersuchungen zeigen die hervorragenden Druck- und Biegefestigkeiten von PFR-LMM, zusammen mit seiner minimalen Volumenänderung und seinen guten Haftungseigenschaften. Das Kapitel schließt mit Beobachtungen zur Haltbarkeit und Sicherheit der Straßenabschnitte über mehrere Jahre und unterstreicht die praktischen Vorteile der Verwendung von PFR-LMM in solchen Anwendungen.
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Abstract
The paper discusses the use of Polypropylene Fiber Reinforced - Latex Modified Mortar (PFR-LMM) for installation of granite paving blocks (GPBs) on various road sections in Slovenia. The following four examples are considered: two inner rings of roundabouts on both sides of the bridge over the Sava River on the bypass near Krško, a roundabout in front of the entrance to the Šoštanj thermal power plant and one part of a street in Ljubljana. GPBs were installed on a slab made with Steel Fiber Reinforced Concrete (SFRC). The workability of the fresh PFR-LMM had to be such that it filled the joints between the GPBs. Hardened PFR-LMM, however, must provide a good bond between the GPBs to ensure resistance to traffic loads and resistance to constantly changing weather and temperature influences. The age of the subject applications is between 5 and 11 years.
1 Introduction
Larger granite paving blocks (GPBs) are generally used on roadway sections where higher traffic loads are expected and where the visual appearance of the surface needs to be improved. Examples of such use have been considered for the projects presented in this paper. In all these projects, the GPBs were placed on top of a steel fiber reinforced concrete (SFRC) slab using Polypropylene Fiber Reinforced - Latex Modified Mortar (PFR-LMM). The thickness of the PFR-LMM layer between the GPBs and the SFRC slab was 3 cm. The width of the joints between the GPBs was 2 cm. The subgrade of SFRC slab was constructed as elastic, isotropic and homogeneous body with modulus of deformation Ev2 ≥ 120 MPa.
2 Brief Description of Applications on Different Road Sections
2.1 Two Inner Rings of Roundabouts on Both Sides of the Bridge Over the Sava River on the Bypass Near Krško
The roundabout on the left bank of the river was built in 2012 and the one on the right bank a little later (see Fig. 1a and b).
Fig. 1.
(a) Location of roundabouts on both sides of the bridge over the Sava River
This bypass passes the Krško Nuclear Power Plant. Due to the occasional heavy traffic for the Krško NPP, it was required that the inner ring of both roundabouts should also be able to withstand the heavy traffic loads. The 20 × 20 × 20 cm GPBs were installed on a 24 cm thick SFRC slab.
PFR-LMM was used for the installation of the GPBs with the following mix-proportion: Portland cement CEM I 52,5 R (480 kg/m3), silica fume (7,5 w. % to cement content), styrene-butadiene copolymer latex (solid particles 3,5 w. % to cement content), effective water-binder ratio (w/b)eff = 0,33, high-range superplasticizer (0,6 w. % to cement content), admixture for expansion (0,5 w. % to cement content), polypropylene fibers with length of 10 mm and with diameter of 30 to 40 m (1,0 kg/m3), crushed gravel aggregate with Dmax = 4 mm.
The mix-proportion of the SFRC was as follows: Portland cement CEM I 52,5 R (420 kg/m3), silica fume (2,5 w. % to cement content), effective water-binder ratio (w/b)eff = 0,37, high-range superplasticizer (0,75 w. % to cement content), hooked steel fibers with a length of 16 mm and a diameter of 0,5 mm (0,38 vol. %) and wavy steel fibers with a length of 39 mm and a diameter of 1,25 mm (0,64 vol. %), natural gravel and crushed aggregate with Dmax = 32 mm.
2.2 Roundabout in Front of the Entrance to the Šoštanj Thermal Power Plant
This roundabout was built during the construction of Šoštanj TPP Block 6 in 2012. It is in front of the entrance to the TPP, next to the cooling tower of Block 4 (see Fig. 2).
Fig. 2.
Location of the roundabout in front of the TPP entrance, next to the cooling tower of Block 4
During the construction of Block 6, very large and heavy steel structural elements and components of the TPP, such as the turbine (200 t) and the transformer (60 t), were transported. Therefore, most of the central part, as well as the inner ring of the roundabout, was built in the same composition as that used for the two roundabouts on both sides of the bridge over the Sava River - the 20 × 20 × 20 cm GPBs were installed on a 24 cm thick SFRC slab (see Sect. 2.1). In this way, large and heavy vehicles were able to drive through the roundabout to the entrance of the TPP (see Fig. 3).
Fig. 3.
The inner ring and most of the central part of the roundabout are lined with GPBs with dimensions 20 × 20 × 20 cm
The mix-proportions of the PFR-LMM and SFRC was also like that of the roundabouts discussed above (see Sect. 2.1).
2.3 Part of a Street in Ljubljana
During the renovation of Gosposvetska Street in Ljubljana in 2018, the architect (Medprostor - architectural atelier) designed one part of the street in front of the church to be made of decorative GPBs (see Fig. 4 a and b). The dimensions of the granite paving block are length 30 cm, width 20 cm and thickness 10 cm. The floor layout also included the insertion of smaller parts from the basic module of granite paving block (see Fig. 4 b).
The thicknesses of the upper pavement bearing layers are (from top to bottom): GPBs 10 cm, PFR-LMM binder 3 cm, SFRC slab 21 to 24 cm, subbase asphalt 6 cm and tampon 20 cm.
The mix-proportion of the PFR-LMM used for the installation of the granite paving blocks on the SFRC slab was slightly modified from the mix-proportion of the PFR-LMM in Sect. 2.1 and was: Portland cement CEM I 42,5 R (480 kg/m3), silica fume (7,5 w. % to cement content), styrene-butadiene copolymer latex (solid particles 3,5 w. % to cement content), effective water-binder ratio (w/b)eff = 0,39, high-range superplasticizer (1,4 w. % to binder content), admixture for shrinkage reduction (1,6 w. % to binder content), polypropylene fibers with length of 10 mm and with diameter of 30 to 40 m (1,5 kg/m3), crushed gravel aggregate with Dmax = 4 mm.
The mix-proportion of the SFRC was approximately the same as that used in the construction of the roundabouts described in Sects. 2.1 and 2.2. The required compressive strength class of the SFRC was C35/45 in accordance with SIST EN 206:2013 + A1:2016 [1].
Fig. 4.
(a) The part of Gosposvetska Street in front of the church is lined with decorative GPBs
This chapter discusses the properties of PFR-LMM based on the results obtained from laboratory investigation prior to the construction of a part of Gosposvetska Street in Ljubljana, which was carried out as part of the reconstruction of this street. The mix-proportion of the PFR-LMM given in Sect. 2.3 is like the PFR-LMMs used for the construction of the roundabouts discussed in Sects. 2.1 and 2.2. Therefore, the performance of all PFR-LMMs is similar, as shown by the results of the permanent controls carried out during the construction of all the road sections discussed in Sect. 2.
3.1 Fresh PFR-LMM
The consistency of the fresh PFR-LMM, measured by the slump - flow test method given in the SIST EN 12350-8:2019 [2], was SF = 500 ± 100 mm. This means that PFR-LMM was a self-compacting mortar that was able to fill the joints between the GPBs without additional compaction (see Fig. 5).
Fig. 5.
PFR-LMM completely fills the joints between GPBs without additional compaction.
×
The volume change of the PFR-LMM was measured according to the method given in SIST EN 445:2008 [3]. After 24 h, a volume change of + 0,1% was obtained. So PRF-LMM expanded very little, with no inhomogeneity and no water bleeding detected. In addition, the effect of polypropylene fibers on the reduction of autogenous as well as total shrinkage of concrete is well known [4, 5].
3.2 Hardened PFR-LMM
3.2.1 Compressive Strength
Compressive strength tests were carried out on the halves of the prisms with dimensions 40 × 40 × 160 mm in accordance with SIST EN 13892 – 2:2003 [6]. The age of the PFR-LMM was 20 days.
The results obtained are: average compressive strength Rc,aver. = 66,3 MPa; minimum compressive strength Rc,min. = 57,3 MPa; standard deviation sc = 4,5 MPa; n = 12.
3.2.2 Flexural Strength
The flexural test was not carried out according to SIST EN 13892–2:2003, which specifies a three-point bending, but a four-point bending configuration was used to determine the flexural strength of the PFR-LMM. ACI Committee 544 mentions that both methods can be used to determine the flexural strength [7]. Since a larger proportion of the total volume is loaded in the four-point bending configuration, the flexural strength is lower compared to the three-point bending configuration [8]. The flexural strength obtained with the three-point bending configuration test is about 22% higher than that obtained with the four-point bending configuration test [9]. A slightly smaller difference was obtained when high-performance SFRCs with very high fiber content were investigated [10].
The flexural strength of 20 day-old PFR-LMM was tested on prisms with dimensions 40 × 40 × 160 mm, applying a four-point bending configuration. The span length was 120 mm.
The results obtained are: average flexural strength Rf,aver. = 8,6 MPa; minimum flexural strength Rf,min. = 7,9 MPa; standard deviation sf = 0,5 MPa; n = 6.
3.3 Evaluation of the Bond Between SFRC and GPBs Made from PFR-LMM
The ability to bond the GPBs to the SFRC slab with PFR-LMM was evaluated based on the results of the flexural test. The test was carried out on prisms with dimensions 100 × 100 × 400 mm, applying a four-point bending configuration. The span length was 300 mm (see Fig. 6 a). The age of the PFR-LMM was 20 days.
Fig. 6.
(a) A prism made of three layers with dimensions 100 × 100 × 400 mm during a flexural test with a four-point bending configuration. (b) Progress of the vertical crack through all layers after the test.
×
The prisms were made of three layers: the lower layer with a thickness of 35 mm was made with SFRC, the middle layer with a thickness of 30 mm was made with PFR-LMM and the upper layer with a thickness of 35 mm was composed of two GPBs with a joint between them with a width of 20 mm made with PFR-LMM (see Fig. 6 a). In Fig. 6 a, a vertical crack can be seen running through the whole thickness of the lower SFRC layer, which has already extended into the second PFR-LMM layer and is oriented at the joint angle between the GPBs.
Figure 6 b shows the final progression of the vertical crack, which completely split the prism in two through all the layers. The steel fibers still bridge the crack in the bottom layer, while the polypropylene fibers bridge the crack in the middle layer. In the upper layer, there is a crack at the interface between the GPB and the PFR-LMM, which fills the joint between the two GPBs.
One very important finding is that all the prisms tested never developed horizontal cracks at the interfaces between the layers. This means that the PFR-PMM provided a good bond to the SFRC slab and the GPBs.
During the test, the deflections were measured continuously as a function of the load. A typical load - deflection diagram is given in Fig. 7.
Fig. 7.
Typical load - deflection diagram.
×
From the load-deflection diagram, the maximum flexural strength Rfmax and the toughness as measure of absorption energy G are calculated. The results of the test on the three prisms are given in Table 1. The absorbed energy, or toughness, is obtained by calculating the area up to a certain deflection.
Table 1.
Maximum flexural strength Rfmax and the toughness GI, GII and GIII.
At the end of the elastic zone, a crack is formed which propagates in the first layer of SFRC as the external load continues to be applied. At the point of maximum load, the stress concentration is highest and the relatively greatest reduction in absorbed energy occurs. Due to the presence of the steel fibers, the reduction in absorbed energy is moderated up to the point where the crack reaches the horizontal interface between the SFRC layer and the PFR-LMM layer. In the diagram in Fig. 7, this is the end point of zone I, when the crack passes into the second layer of the PFR-LMM. The reduction in absorbed energy is moderate because the crack propagation is restrained by the polypropylene fibers in the PFR-LMM and still by the steel fibers in the SFRC.
However, when the crack reaches the interface between the PFR-LMM layer and the GPB (this is the end point of zone II in the load - deflection diagram), the absorbed energy decreases rapidly, and a prism fracture occurs at the deflection of 4 mm. The crack runs along the vertical interface between the GPB and the PFR-LMM, which fills the joint between the two GPBs. The poorer adhesion between the PFR-LMM and the vertical face of the GPB was expected because this surface was sawn and therefore smooth. In practice, GPBs with rough side surfaces have been used, so their bonding to PFR-LMM is much better.
4 Conclusions
The findings of the permanent observation of the road sections in question, where polypropylene fiber reinforced - latex modified mortar (PFR-LMM) was used for the installation of granite paving blocks (GPBs), show that no changes affecting traffic safety and the durability of these sections have occurred during several years of use (between 5 and 11 years). During construction, it was found that fresh PFR-LMM was very easy to cast without additional compaction and despite this, good installation of the GPBs was ensured. Laboratory tests have shown that PFR-LMM provides good bond to steel fiber reinforced concrete (SFRC) base slab and GPBs.
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