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UNDERGROUND WATERPROOF STRUCTURES

By Attila FARSANG

1. INTRODUCTION

The designers and entrepreneurs working with underground waterproof structures unfortunatelyconsider this technology only as a cost reducing solution, which is a major misunderstanding.A waterproof structure realised according to the plans and specifications, with all itscomplementary elements including the price of the materials and the labour costs, is not cheaperthan the traditional solution that is the wall structure with waterproofing layers. Its advantage isfirst of all the rapid execution when one can do it with a routine but still paying extraordinaryattention to the execution. Secondly, because of the low number of required materials withwaterproof concrete fewer defects occur. Altogether, they might accelerate the execution andincrease the quality. Still, because of irresponsible execution and because the execution isconsidered a normal concrete casting work, a great number of faults appear, therefore thetechnology looses its greatest advantages.

2. THE LOCATION OF THE CONSIDERED STRUCTURES INSIDE THE BUILDING

Inside a building, waterproof concrete is used for protecting the structures against waterinfiltrations, the pressure of the ground water and the loads coming from the strata waters.Therefore it serves primarily the protection of underground structures such as vertical elements(load-bearing walls), tilted elements (staircases) and horizontal elements (ground-supportedslabs).

Waterproof concretes are cast as building foundations or as structures connected to those,therefore their faults can cause the damaging of the whole construction. For that reason theexecution has to be prepared and executed properly and with high responsibility.

3. CHARACTERISTIC FAULTS IN DESIGN, EXECUTION AND USE (OR WHAT ONECAN READ IN EXPERTISES)

Realising waterproof concrete implies first of all modern technology, consequently requires thelatest materials of our days, the most advanced tools and developed concrete technology. It asksalso for competent designers and last but not least a skilful team of craftsmen during the whole

process of execution.Many faults rests in the simplification of the problem, according which some designers considersufficient just to mark on the documentation drawings waterproof concrete. Therefore none ofthe cellar walls, or the ground-burned slabs, or the details of other structures are not really solved(detail drawings are never made and relevant data dont make part of the specification). It relatesto this problem that neither the designer feels any need for these drawings. In consequence faultsoccur primarily because of the lack of design and secondly because of missing concretetechnology and structural knowledge.One could state that the number of details to be prepared in the case of waterproof structures isnot less than for a structure built with a traditional technology.

For achieving the desired result, the joints of the walls and ground-supported slabs have to besolved, the detailed design of elevator shafts and other subsiding elements, the perforating points


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of the service system through the walls, the perforating points of the drainage system (drains andscuppers) through the ground-supported slab, the control and expansion joints, the execution oframps and staircases and the joints of the walls and slabs.When a water pipe brakes, the horizontal and vertical control joints that are not waterproofpermit a considerable water infiltration. Using concrete surfaces that are not of identical

waterproofing grade lead to the appearing of moisture in the interior spaces. A waterproofstructure that becomes thinner decreases the resistance to water infiltrations. A typical case iswhen the ground-supported slab becomes thinner under the inbuilt service pipes and scuppers.It is not enough to protect the waterproof structures against the infiltrating moisture and otherdamaging factors only from the exterior sides and from below. There are also interior factors thatweaken the structure; this way the structure becomes less resistant to exterior actions, in ourspecific case it diminishes its waterproof character. At this point one has to mention the lack ofregular concrete protection that permits the infiltration of water, oils, salts and acids (differentgases together with moisture) in the concrete damaging the quality of the material and itschemical resistance, decreasing the alkali level and increasing the corrosion.A specific case is when faults are caused by the improper behaviour of the users. The owners/

users dont respect the users instructions for the building (in some cases because they are notaware of them), and they exploit the building in the improper way. It may happen when thefunction of a construction is changed (e.g. a new owner arrives with brand new ideas for usingthe building in a certain way), or the inhabitants trust too much the structure of the building. Itis very typical for our days that cellar storages or garage spaces are converted into restaurants orfitness rooms that claim for different dryness and so for new insulations and service systems.The new function introduces new and higher loads that have to be overtaken by the structure, andit doesnt pay attention to exterior factors. As a result, the structures are decaying, the spacesbecome unsuitable and sometimes unhealthy, or even dangerous.

BASIC PRINCIPLES, DEFINITIONS AND STRUCTURAL REQUIREMENTS

The concept of waterproofing is not clear to everybody and this provokes misunderstandings.For understanding its meaning one has to clarify the demands for dryness ininterior spaces.Absolute dryness is required for spaces used by human beings continuously (residential spaces,offices, working places, hospitals and schools), for spaces that serve for moisture-sensitivetechnologies, or for storing moisture-sensitive materials (paper, food, chemicals, microelectronicequipments). For protected spaces that claim absolute dryness the top value of relatively drynessis determinating factor.At relative dryness, some type of moisture can penetrate, but this may not influence the healthy

environment, or the characteristic airing factors which are needed for the function occupancy ofthe inner space, or the state of the building structures.The following definitions are given according to the directives for design and executionwaterproofing against ground water and moisture published by the Hungarian Union ofBuilding Insulaters, Roofers and Tinsmiths (MSZ).The codes and the required waterproofing performace of different concretes (classified by theHungarian Standard MSZ 4719 and analysed based on the MSZ 4715-3) are given below (theHungarian CSI Masterformat):Class vz2, vz4, vz6 and vz8, where there are grade marked out of them the water pressuremeasured in Bars that concrete resists to without infiltrations. Vz2 is a poor, vz4 is a medium,vz6 is a waterproof and vz8 is an exceptionally waterproof concrete. A reinforced concrete is

classified waterproof that on a surface of 1 m2

, during 1 day (24 hours) permits only 0.2 l of


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water to penetrate (to infiltrate in the inner space). In intensively ventilated spaces (or outdoorspaces) this amount of moisture evaporates, consequently no surface moisture ca be detected.It has to be mentioned that the MSZ 4719:1982 standard was annulled by the MSZ EN 206-1:2002 standard and its national applying documents, according to which in the future thewaterproofing value of the concretes has to be analysed is the MSZ EN 12390-8:2001 standard.

According to the draft of the national applying document a concrete is waterproof when thedepth of the water infiltration, measured under standard circumstances, doesnt exceed 60 mm inthe XV1(H) environmental class, or 40 mm in the XV2(H) environmental class, or 20 mm in theXV3(H) environmental class.During execution, the choice between the vz concrete categories could result millions ofFlorins differences for a medium-size building; therefore the correct selection of categoriesrequires serious preparatory works. In certain cases, for example for great interior spaces withhigh humidity it is recommended the use of an exceptionally waterproof concrete even when theinterior surfaces were treated with a waterproof coat (for diminishing the corrosion of thereinforcement).

On the cellar level one can usually find the car parks, where the relative dryness may besufficient (if there is no special demand for the space). Still, on this level and also on the higherones, small dependencies are connected to the main space with different function in constanthuman use a higher level of dryness. These can be spaces used by humans continuously,staircases, the rooms for electrical service connection, transformer rooms and storage spaces formoister-sensitive materials. For spaces requiring absolute dryness not even minuscule quantitiesof moisture are permitted, therefore the use of exceptionally waterproof concrete is compulsory.In conclusion, the waterproof structure has to be supplemented or combined with other insulatingsystems, so sole use is not tolerated.If the building, during its lifespan, suffers a change of function at the cellar level, this couldimply the necessity of further insulating systems, and competent designer should be involved.

During the design one has to be aware of the location of the characteristic ground water level(mBf) given by the soil dynamics expertise, from which the height of the water column thatloads the structure can be calculated. The result determines the factors that structures have to beprotected against. Data about the aggressiveness of ground water with other informations alsohave to be considered.Waterproof concrete structures have to be designed based on statics and insulation (buildingconstructure) details.The structure and the insulation against moisture of the cellar levels is composed of waterproofground-supported slab and wall structure, control and expansion joints filled with concreted

plastic sealants, expansive strips (filled joints), filled pipe penetrations, additional steel plateinsulation (shafts) and plastic strips for slabs and slab edges.When designing the insulation of a building against ground water one has to consider also thatthe prescribed structures providing the protection against moisture (insulations, sealants) have tofulfil security rules on long-term, even when deformations (sinking, cracking, change of groundwater level, vibrations etc.) occur.It is recommended to have the plans for the completion of waterproof concrete with its joints andsealants made by a competent specialist conductor in a competent way.

SUGGESTED TRADITIONAL AND MODERN SOLUTIONS


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The presented example is a building with cellar level, where a car park was placed with a rampaccess and the additional spaces: the room with the main electric switch board, the staircase andsmaller storage spaces.Moisture protection is provided for a concrete slab set on a base course dimensioned accordingto the specific water pressure (at least 40 cm thickness) permitting limited cracks, with a certain

waterproofing value and by waterproof walls dimensioned for the same circumstances (at least30 cm thickness), with the same waterproofing value as the slab. The exact parameters and thewaterproofing values are given even in the structural engineering. Under the base course a 15-20cm thick compacted fill was set composed of gravel and sand.The garage function permits a relative dryness. On the cellar level, the waterproof slab usuallysatisfies the prescribed structure conditions.The other spaces of the cellar level, such as staircases, corridors and technical rooms need forabsolute dryness. To meet this requirement the horizontal concrete surfaces are coated with a topinsulation (set under the pavements or made in a passable quality) that protects the structure alsofrom vertical loads.

At the connection line of the slab with the walls requested control joints are formed that are aconsequence of the concrete shrinkage and are necessary for the execution. Through these joints,under the pressure of ground water, moisture can penetrate. Plastic strips sealants (e.g. a SIKAV-20 element) that are placed on the center line of the wall surface are used to stop thepenetration (the pressure of the penetrating water is reduced by the meandering form of theplastic profile). This meandering profile of the sealant becomes effective by lengthening thecourse of the penetrating moisture. Structural engineers dont prefer this solution, because thelocation of reinforcements becomes more difficult. They rather recommend the use of insulationstrips on the exterior surface, but these are less efective and are more exposed to injuriesprovoked by mechanical or other actions.The most important rules for placing interior profiled plastic sealants along the control jointsbetween ground-bourne slabs and walls and along the joints of the elevator shafts are thefollowing:

They have to be placed on the central zone of the structure, but the exactdistance and placement is given by the structure project (as part of thereinforcement drawings);

The longitudinal connection has to be executed and butt-joints with meltedwedges, eventually secured with sealants;

they have to be executed in the same time as the reinforcement; During execution they need propping and protection (with separate

formwork and reinforcement), a straight positioning on equal distances

assured by pegs placed at 25 cm distance from each other that clip the stripto the steel (profiles should not deviate from the prescribed plane); The median line has to coincide with the line of the control joint; The radius of the corners it has to be about 20 cm.

The ground-supported horizontal slabs and the continuous vertical side slabs of the elevatorshafts, technical shafts and other subsiding elements are also connected with control joints.Because of the increased water pressure, beside the plastic strips it is recommended the use ofexpanding strips (e.g. SIKA Hydrotite). These getting in contact with the infiltrated moistureexpands and presses itself to the surrounding concrete forcing the moisture to follow a longerpath, decreasing its pressure, this way protecting the spaces behind.


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Some expanding sealants can be ulterior by injected (if one choose such type). There is no needfor demolition or drilling; the sealant material can be introduced in the structure throughimbedded pipes in order to fill the control joints.The rules for placing the expanding sealant and its functioning principles (referring to theexample):

In our example the profiles are of 25 x 7 mm (with quadrangle section), have 3 cells thatexpand on water contact, have a neoprene core and are treated with expansion-retardersubstances (to make possible the execution and avoid the placing under reduced moisturequantity);

They have to be set on the external/ central zone of the vertical slabs, but according to thestructural plan (as part of the reinforcement set out);

The distance from the exterior surface of the slab has to be at least of 6 cm (10 cm arerecommended), otherwise the moisture can come round and also may crack the edge ofthe concrete slab;

For higher water pressure the given structures would not work properly with a singleprofile; for lengthening the path of the moisture more profiles are recommended;

At the longitudinal being connected they have to overlap at least on 15 cm (no butt-jointsare permitted!!!);

To avoid their displacing during casting, expanding sealants should be nailed or stuck atleast at 20 cm distances;

They have to be set simultaneously with the reinforcement; During the execution they have to be temporarily protected (with wooden boards), the

straight position (fixed distance) and the protection against moisture have to be assured(to avoid activating the expanding material of the strip).

For the elevator shafts further complementary measures can be needed, because the fixtures ofthe elevator rails penetrate the insulation. I this case the structure need additional coatings orinjection, or the project should specify that fixtures should avoid the insulating zone.

It is important to emphasize that in most of the cases spontaneous (not specified) control jointsmight be necessary (because of the rapid change of the weather, the concrete did not arrive intime etc.). It is indicated for the designers to have a plan for these kinds of situations, too. Theremight be a need for expanding profiles posed on already executed concrete surfaces. Asadditional measure it might be necessary the exterior sealing of the joints with a flexible strip(min. 20 cm width, e.g. SIKA COMBIFLEX) that is stuck only on the sides.

For larger vents fissures holes or surface irregularity one has to use a flexible joint sealingmaterial (e.g. SIKAFLEX PRO-2HP).

The pipes penetrating the walls have to be of tube-in-tube system (with an interior tubefunktional in use and a protecting one) that has to be sealed against moisture and protected fromground water pressure. For high ground water pressure an expanding profile is needed on theexterior side, at the bottom of the centrally placed steel flange (see the execution conditionsabove).

Because of the aggressive factors (CO, CO2, SO2, NO2, gases, rainfall, UV-radiation, windforces) that affect the concrete structure surfaces have to be treated with a protecting coating(e.g. ELASTOCOLOR W) that can be dyed and applied in multiple layers. Protecting coatingsfor interior and exterior surfaces have to be different. The exterior ones are more exposed to

rainfall, UV-radiation, wind forces and other exterior damaging factors.


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Referring to those above mentioned:

For spaces that dont require additional insulation (general layers): A levelling topping that protects the concrete, assures the slope, supports paints or

thinsets and is slip-resistant;

Waterproof ground-supported concrete slab; Concrete supporting layer; Gravel and sand base.

For spaces that require additional insulation (general layers): Ceramic tile floor; Adhesive layer (compatible with the isolution); Additional interior insulating membrane; Waterproof ground-supported slab; Concrete supporting layer; Gravel and sand base.

I some cases the concrete supporting layer is replaced with a plastic decking. The system permitsa quicker execution, an immediate set of the next layer, is cheaper, it doesnt crack (it needs noexpansion joints), it doesnt depend on weather conditions or the quality of the concrete set onthe top, it is less sensitive to the aggressive factors of the soil, the drying period is much shorter(it is also a more economic procedure), its execution doesnt request specific tools, it doesntneed ulterior surface protection (and time for that), and finally the system works as an insulatinglayer (sufficient for protecting against ground moisture). Its disadvantages are the reducedweight (wind forces can move it), the requested technology is not a traditional one, surfaces arenot perfectly smooth and it cannot overtake concentrated loads on small surfaces (machines cantbe moved on it). Being aware of these, one can decide for one system or the other, and whichadvantaged are worthy to be paid for.

Scuppers are set in the ground-supported slab in order the lead the rainfall or infiltrating waterfrom the garage surface. (If scuppers are sunken in the floor, the slab has to be thickened in thatarea below). The water collected by the scuppers gets to the main drain through proportionedpipes. The service pipes are placed in the ground-supported slab with a slope (0,5%), fixed to thereinforcement. Galvanised steel pipes are connected with waterproof fittings, plastic pipes withwaterproof welding. Slabs are thickened under the pipes in order to assure proper and continuousmoisture insulation.

The expansion joint of the ramp slab and the ground-supported slab (and the ones between theramp and the cellar walls): Both the ground-supported slab and the ramp slab claim for a min. 40 cm thick

waterproof reinforced concrete structure; A subsiding of these elements is expected; its degree has to be estimated by the

structural engineer; The expansion joint has to be filled with glass fibre or rock wool insulation both for slabs

and walls; The expansion joint of the slabs has to be sealed from the top with a waterproof steel

fixture (e.g. MIGUA) that can overtake loads (e.g. D400) and is properly fixed to bothslabs;

The expansion steel fixture can be driven up to the wall surface until a height of 20 cm;


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The vertical sealing of the expansion joint is realised with durable elastic putty (e.g.SIKAFLEX PRO-2 HP); it can be masked with a metal fixture, if necessary;

On the water pressure side, ribbed and profiled plastic sealant is recommended (beneathe.g. SIKA O-35) that has to be fixed to the structure at about 15-15 cm and it can be alsodriven into the gaps of the side walls and the reinforced concrete cellar walls (bent with a

20 cm radius) until the ground level (or the top of the walls).Units are separated by thermal insulation made of fibrous materials (!). The use of stiff, plasticfoams in the expansion joints are strictly prohibited.The placement rules of ribbed, plastic expansion strips are similar to those placed in the medianplane of the wall.

For the superior part of the monolith, reinforced concrete cellar walls, on the exterior side, onehas to use ribbed plastic (surface) strips (e.g. SIKA AR-26) in order to assure the insulation ofthe cellar ceiling against rainwater. As the joint of the waterproof concrete structure with theinsulating strip cannot be directly solved, the insulation strip driven out from the ceiling slaband through the control joint of the wall overlap and assure the insulation.

Surface strips are used also when sidewalls are insulated with membranes (mule-structures). Inthese cases strips ribbed on one side are set in the concrete at the bottom part of the ground-supported slab edges, much lower from the control joint, and the insulating membranes of thewalls are driven to and overlapping it. They can be set simultaneously with the formwork and thereinforcement. Their placement has to be exact, according to the project, and it has to be checkedbefore casting.

When the building is exposed to strata waters (in case of sloping terrains), one has to realise adrainage system that can help to relieve any build-up of hydrostatic pressure against the cellarwall (this also improves the protection of waterproof systems against moisture infiltration).

Few words have to me mentioned about the importance of the used concrete technology forwaterproof concrete structures. Waterproof structures can be realised only according to thespecific construction prescriptions for the very building. One of the determinative factors is thewater/cement ratio (w/c). For a 0.4 w/c, no capillary pores remain in the structure (that couldcause water infiltration); therefore moisture cannot go through the structure. Therefore it isindicated to keep the 0.4-0.45 w/c ratio, which with a long ulterior treatment offers a reliablesolution. The placement of the concrete in forms becomes easier with the use of plasticizers.

CONCLUSIONS

The above-mentioned facts can drive to the conclusion that the design of waterproof structures isnot an easy task; it demands concentration and skill. Unfortunately, more and more expertisesare required, and are followed by rehabilitation works. The characteristic causes of the faultswere presented and their occurrence places. Perhaps soon we will reach the stage when thedesign of buildings with faulted or damaged structures that make difficult its use will bepunished. It is difficult to rehabilitate faulted structures, and they are not equivalent (they donthave the same lifespan anymore) to the well-designed and properly executed ones. Besides, arenovation work raises the original price. Being aware of the number of the faulted structures, Iam afraid that a misunderstanding will be created, according to which technologies related to thewaterproof concrete production couldnt be operated successfully. One might think that these

structures dont work properly; water penetrates and damages them. It could happen that eventhe most competent firms will refuse to produce these structures.


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REFERENCES

Hungarian standard MSZ 4719: 1982;

Hungarian standard MSZ 4715-3;MSZ (Hungarian Union of Building Insulators, Roofers and Tinsmiths): Design and executiondirectives for waterproofing against ground water and moisture (2001);

Hungarian standard MSZ EN 206-1:2002;Hungarian standard MSZ EN 12390-8:2001;SIKA Hungaria Ltd.: Concrete pocket-book.

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