Tailor Made Concrete Structures Walraven & Stoelhorst (eds) 2008 Taylor & Francis Group, London, ISBN 978-0-415-47535-8

Subsequent sealing of buildings made of textile reinforced concrete

R. Mott & W. BrameshuberInstitute of Building Materials Research (ibac) of RWTHAachen University, Aachen, Germany

ABSTRACT: Many regions in Germany show a rising groundwater level. Hence the load case of buildingsconcerned changes from non-pressing to pressing water. Residential buildings not designed for the load case ofpressing water have to be refitted. Conventional sealing methods are often associated with high complexity andhigh costs as well as the loss of living space. Furthermore in many cases they do not consider the additionalstatic load of pressing water at all. This paper presents a newly developed subsequently applied sealing againstpressing water. It is made of textile reinforced concrete. Using this composite material it is possible to producea sealing system with a wall thickness of about 30 to 35 mm. During the production of an exhibit wall it becameapparent that the spraying technique is an adequate and practicable method to produce a subsequent sealing oftextile reinforced concrete.

1 INTRODUCTION

Many regions in Germany show a rising groundwa-ter level caused by different reasons. On the one handit may happen as a result of the climate changes ingeneral. On the other hand the shut-down of open-cast pits in some regions and the involved cut-off ofthe appendant water drainage can also be a reason forthe changing groundwater level. The rising level ofgroundwater has a direct effect on residential buildingsnot designed for this load case. The load case of build-ings concerned changes from non-pressing water topressing water.The buildings consist of base plates andmasonry walls which are not completely waterproof.This leads to the problem that water penetrates thewalls of the conventionally built basements.The build-ings concerned have to be refitted with a subsequentsealing.

Presently there are several subsequent sealing meth-ods to redevelop basements. It is possible to apply thesealing onto the walls from outside as well as frominside of the residential building. However, in mostcases the subsequent sealings only seal the buildingsagainst penetrating water. The changed load case andhence the additional static load are mostly not consid-ered at all. Furthermore, conventional sealing methodsoften involve high complexity and high costs. In addi-tion, sealing systems applied onto the inner walls aremostly associated with the loss of living space.

To minimize the mentioned problems this paperpresents the use of textile reinforced concrete as a sub-sequently applied waterproof structure. With this com-posite material it is possible to produce thin-walled

concrete building members with a dense structure andhigh compressive as well as tensile strength.

2 CONVENTIONAL SEALING METHODS

In case of a rising groundwater level the load case ofresidential buildings changes from non-pressing waterto pressing water. To redevelop the affected basementsit is possible to apply a sealing system from insideor from outside. It must be observed that the appliedsystem not only fulfills the requirements placed inthe sealings but also takes into account the additionalforces arising by the hydrostatic pressure.

Sealing methods that are applied to the outer wallsare generally associated with high complexity fromthe technical point of view and high costs. For thesereasons these methods are not explained here. A sub-sequent sealing from inside entails better workingconditions. In this chapter two conventional sealingmethods from inside are presented.

The first sealing system consists of waterproof con-crete which is installed on the inside of the basementwalls and on the base plate (Fig. 1).

The second method uses e.g. a bituminous sheetingor coating to subsequently seal the basement. Here,the base plate and the masonry walls are covered withthis dense layer. A layer of normal concrete is appliedadditionally to protect the sheeting against mechanicaldamage (Fig. 2).

The subsequent layers of concrete have to besteel-reinforced. As a consequence the wall thickness

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Figure 1. Sealing method from inside (waterproof concrete)in case of pressing water.

Figure 2. Sealing method from inside (bituminous sheetingor coating) in case of pressing water.

increases to avoid corrosion. This leads to an appar-ent loss of living space. In both cases horizontal waterbarriers in the masonry walls have to be arranged toavoid ascending water by capillary suction.

Applying the first sealing method (waterproof con-crete) it is possible to reduce the loss of living spacebecause this sealing system has to be applied onlyonto the inside of the outer walls. However, to avoidascending water in the inner masonry walls, anotherhorizontal water barrier has to be inserted at the bot-tom of all inner walls (Fig. 3). The disadvantage ofthis version is the high complexity and sensitivity inexecution (Hinzen et al. 2006).

3 TEXTILE REINFORCED CONCRETE

Textile reinforced concrete consists of fine grainedconcrete and technical fabrics as reinforcement. Thefabrics are mainly made of alkali-resistant (AR-) glassor carbon. Compared to steel-reinforced concrete theconcrete cover can be reduced to a minimum as thereis no corrosion risk with (AR)-glass or carbon fabrics.

Figure 3. Another version using water-impermeable con-crete as a sealing method from inside.

Thus building members made of textile reinforced con-crete are thin-walled. So if this composite material isused as a subsequent sealing from inside it will reducethe loss of living space.

Within a research project concerning the develop-ment of small sewage plants made of textile reinforcedconcrete (Hegger et al. 2003) it was found out thatthe functional efficiency of this construction is basedon the fact that the composite material is resistant tochemical attack as well as water-impermeable. Fur-thermore the wall thicknesses of the small sewageplants could be minimized. The density of the textilereinforced concrete and the minor wall thicknesses ledto the idea to develop a subsequent sealing of textilereinforced concrete.

Concrete features a high compressive strength. Thecomposite material of fine grained concrete and fab-rics gains additional tensile strength and a ductilebehavior (Brameshuber 2003).

Within this research project two kinds of short fibers(AR-glass and PVA) were investigated to verify theireffectiveness concerning the increase of the strengthand the improvement of the crack distribution. Fig-ure 4 shows the crack distribution of two slabs afterbeing tested in a 4-point-bending test. The one inFigure 4 a is reinforced with 4 layers of fabrics (AR-glass, 40.7 mm2/m) and 1.5Vol.-% AR-glass fibers, inFigure 4b with 4 layers of fabrics (AR-glass,40.7 mm2/m) and 1.5 Vol.-% PVA fibers. The slabswere wetted to visualize the cracks.

It becomes apparent that a reinforcement consistingof a combination of fabrics and AR-glass fibers leadsto an obvious improvement of the crack distribution.

For the use of textile reinforced concrete as asubsequent sealing the addition of AR-glass fibersbecomes important. It improves the crack distributionand decreases the crack widths and crack spacings.Concerning the water-impermeability of the textilereinforced concrete these issues are very important toimprove the properties of the composite material.

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Figure 4. Crack pattern in parts of slabs tested in4-point-bending tests, reinforced with 4 layers of fabrics(AR-glass, 40.7 mm2/m) and 1,5 Vol.-% AR-glass fibers (a)or 1,5 Vol.-% PVA fibers (b), after failure.

Similar results concerning the increase of thestrength and the improvement of the crack distribu-tion by adding short fibers have been investigatedby Brameshuber et al. 2002; Hinzen and Brameshu-ber 2006; Naaman et al. 2007. A good survey on theapplications, properties and durability aspects of tex-tile reinforced concrete is given in RILEM TechnicalCommittee 201-TRC 2006.

4 SUBSEQUENT SEALING USING TEXTILEREINFORCED CONCRETE

4.1 Principle of the subsequent sealing

Figure 5 shows a principle of a subsequent sealingmade of textile reinforced concrete. In a first stepthe base plate and the masonry walls of the residen-tial building are prepared with a system of specialanchors. Afterwards fine grained concrete and fab-rics are applied in layers with a defined position ofthe fabrics inside the concrete. The goal is to yield awall thickness of 20 mm as depicted in the detail of

Figure 5. Principle of the subsequent sealing using textilereinforced concrete.

Fig. 5. At the moment a wall thickness of 3035 mmis practicable.

4.2 Production technology

The requirements on the production technology arecomplex. To redevelop residential buildings it must bepossible to apply the textile reinforced concrete to thewalls as well as to the base plate. This means to insertthe textile reinforced concrete in a horizontal as wellas in a vertical alignment. The fine grained concretemust be adhesive to the walls during the productionprocess. Hence the fine grained concrete has to bewater-impermeable, resistant to chemical attacks ofthe groundwater, fulfill the requirements on the loadbearing capacity as well as on the practicability andfinally it has to be adjusted to the chosen productiontechnology.

As a result of the requirements on the fine grainedconcrete and the construction of the subsequent sealingthe spraying technique is the best production techniqueto apply the textile reinforced concrete to the base plateand masonry walls of residential buildings.

The spraying technique is very similar to laminat-ing. It means to insert fine grained concrete and fabricsin layers. The fine grained concrete is sprayed to thewalls and base plate with a pressure of 2 to 3 bar (Fig.6). This process is based on a low pressure system asit is used to spray plaster to the inside or outside wallsof a building. To ensure a good penetration and bondbehavior, the fabrics are rolled into the applied finegrained concrete with a steel roll.

Using the spraying method it is possible to pro-duce building members with a defined position of thefabrics inside the concrete. Furthermore it is also pos-sible to produce building members in a horizontal aswell as in a vertical alignment with a high amount ofreinforcement. Concerning the production of a sub-sequent sealing made of textile reinforced concrete

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Figure 6. Spraying technique.

Table 1. Fine grained concrete.

Materials Unit Content

CEM I 42.5 R HS (c) kg/m3 520Fly ash (f) kg/m3 250Silica fume (s) kg/m3 50Limestone sand 0-0.8mm kg/m3 1049Superplasticizer % by mass

of binder 0.79AR-glass fibers % by vol. 1.5Methyl cellulose % by mass

of solids 0.044w/c 0.60w/b* 0.49

* w/b = w/(c + 0.4 f + s)

the spraying technique is a practicable method toredevelop residential buildings (Mott & Brameshuber2007).

To fulfill the requirements on the fine grainedconcrete a new mix was developed (Table 1).

The mix contains short ARglass fibers to increasethe flexural strength and to improve the crack distri-bution as mentioned in chapter 3. Further on, methylcellulose is added to the mix to improve the thixotropyand tack. Both, fibers and methyl cellulose, stronglyinfluence the thixotropy of the spraying mix. Reasonsare the water-absorbing behavior of the fibers and thewater-retraining property of the methyl cellulose. Allthis reduces the workability but up to a certain amountit increases the ability to be pumpable, sprayable andespecially to adhere to vertical surfaces.

The fresh concrete properties density and spreadwere determined according to the German StandardDIN 18555-2:1982-09 as well as after the sprayingprocess. Table 2 shows the fresh fine grained concreteproperties.

Table 2. Fresh fine grained concrete properties.

Value

Sprayed Compacted with usualProperties Unit compacting equipment

Density kg/m3 2129 1987Spread mm 155

Table 3. Mechanical properties of fine grained concrete ata testing age of 28 days.

Mechanical properties Unit Value

Compressive strength fc N/mm2 88.0Flexural strength fct,fl N/mm2 7.8Dynamic Youngs modulus Ec N/mm2 31,500Density kg/m3 2164

A noticeable point is that the production techniquehas got a high influence on the compacting of theconcrete. The structure of the sprayed concrete obtainsits density from the spraying process. The concreteis pumped and leaves of the nozzle accelerated byair pressure. Accordingly, the fine grained concretegets strongly compacted by the air pressure in com-bination with hitting the surface. Hence the densityis higher in comparison with the one compacted withusual compacting equipment.

The hardened concrete properties compressive andflexural strength as well as the dynamic Youngs mod-ulus were determined at a testing age of 28 days. Firstthe dynamic Youngs modulus was tested by using theresonance frequency method according to a Germanguideline (Bunke 1991). To take the production pro-cess into account the specimens were sprayed. Theirdimensions were 30 30 160 mm3. The same prismswere used to determine the flexural strength in a three-point bending test with a span of 100 mm. The testingmachine was displacement controlled. As there are noguidelines concerning the loading rate, a reasonablevalue of 0.2 mm/min was chosen. The compressivestrength was determined according to the GermanStandard DIN 18555-3:1982-09 by using the abovementioned prisms again. The mechanical propertiesas well as the density are shown in Table 3.

Due to the higher content of cement paste and theaddition of methyl cellulose the dynamicYoungs mod-ulus of the spraying mix shows a comparatively lowvalue of about 31,500 N/mm2. The methyl celluloseapparently influences and decreases the value of thecompressive strength, too. The reason for this behav-ior and the effectiveness of the methyl cellulose hasnot been clarified completely until now.

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Figure 7. Front and side view of the exhibit wall subjectedto hydrostatic pressure.

5 EXHIBIT WALL

To check the functional efficiency of the developedsubsequent sealing an exhibit wall that can be sub-jected to hydrostatic pressure was produced.

Therefore a masonry wall consisting of calcium-silicate units with a wall thickness of 115 mm wasbuilt and prepared with special anchors.Afterwards thesubsequent sealing made of textile reinforced concretewas sprayed onto the masonry. The thickness of thetextile reinforced concrete wall was 30 mm.The wall isframed with a steel construction with acrylic walls likean aquarium. This allows the wall construction to besubjected to hydrostatic pressure. Hence it is possibleto test the tightness of the sealing method in a long-term test. The front and side view of the exhibit wallcan be seen in Figure 7.

It could be determined that the spraying technique isan adequate and practicable method to produce a sub-sequent sealing made of textile reinforced concrete.Initial observations of the wall subjected to hydro-static pressure reveal the application potential of thisconstruction. Long-term tests have been conducted formore than one year so far.

6 CONCLUSION

A new method for a subsequent sealing made of textilereinforced concrete for basements in case of pressinggroundwater is presented in this paper. Conventionalmethods to redevelop residential buildings are oftenassociated with high complexity and high costs aswell as the loss of living space. Using textile rein-forced concrete the wall thickness of the subsequentsealing can be minimized. Furthermore the densestructure of the fine grained concrete leads to a water-impermeability and a high chemical resistance. Thewater-impermeability is also ensured by small crack

widths and crack spacings as a result of the addedshort ARglass fibers.

The tightness of the construction was investigated ina long-term test by an exhibit wall. This set-up allowssubjecting the wall construction to hydrostatic pres-sure. Thus the functional efficiency and the design ofsuch a subsequent sealing could be demonstrated. Itwas shown that the spraying technique is an adequateand practicable method to produce a subsequent seal-ing of textile reinforced concrete. With this productiontechnique it is possible to produce building membersin a vertical as well as in a horizontal alignment. Alsoa defined position of the fabrics inside the concretecan be ensured.

Accordingly it is possible to produce a subsequentsealing made of textile reinforced concrete. The con-struction can fulfill two functions. It can seal thebasements of residential buildings and bear the addi-tional load due to pressing groundwater up to a waterpressure of about 0.2 bar. This is equivalent to a watercolumn of 2 meters. The required wall thickness ofthe textile reinforced concrete amounts to only 30 to35 mm. Hence the subsequent sealing of textile rein-forced concrete may offer a cost-effective method toredevelop residential buildings in case of pressinggroundwater with a minimized loss of living space.

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