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BR1105 Construction Technology 2

National University of SingaporeSchool of Design & EnvironmentBachelor of Real Estate (Part-Time)

BR1105

CONSTRUCTION TECHNOLOGY 2

Report on

BASEMENT WATERPROOFING

CASE STUDY:HDB HUB TOA PAYOH

REACTIVE PODHHGFHTDJLYMERS

By : Phang Siew Boon Eric U028644U

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CONTENT PAGE

PAGE NOCHAPTER 1: INTRODUCTION 3

CHAPTER 2: DIFFERENT TYPES OF BASEMENT 4 WATERPROOFING SYSTEMS

2.1 INTERGRAL WATERPROOFING 42.2 MEMBRANE / TANKING SYSTEM 52.3 CAVITY / DRAINAGE SYSTEM 62.4 CHEMICAL GROUTING SYSTEM 92.5 CEMENTITUOUS/CRYSTALIZATION METHOD 10

CHAPTER 3: CASE STUDY: HDB HUB (TOA PAYOH) PART ONE – DIAPHRAGM WALLS &

ITS SUPPORT13

3.1 Introduction 133.2 Construction of Diaphragm walls 143.3 Support system for diaphragm wall –

Ground Anchors & Struttings 16

CHAPTER 4: CASE STUDY: HDB HUB (TOA PAYOH) PART TWO – BASEMENT WATERPROOFING 20

4.1 Introduction 204.2 Waterproofing of basement walls 214.3 Waterproofing of basement slab 26

CHAPTER 5: CASE STUDY: HDB HUB (TOA PAYOH) PART THREE – Defects & Xypex, the

waterproofing material 29

5.1 Defects after construction 295.2 Xypex, the waterproofing material 31

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CHAPTER 6: Conclusion 34

CHAPTER 1: INTRODUCTION

Basements can provide space for most commercial activities, storage or carparking. It is the inhabited storeys of a building constructed wholly or partially below ground level, exposed to soil, water and water vapour pressure.

Watertightness in a basement is the major consideration in basement construction. Another area of doubt is the performance of the system. Poor or non-performance will lead to additional financial burden to the parties involved. Upon completion and if there is leaking occurs, it is expensive problem to solve. Beside the cost of repair, it is impossible to carry out the repairs from outside, on the face where infiltration occurs. Hence, the importance of an effective waterproofing system for the basement is therefore important.

An effective waterproofing system of a basement is also necessary to ensure that all the commercial activities in the basement could smoothly carry out without interruption. There is also a need to keep basement watertight to prevent corrosion of the reinforcement in the concrete structure, preserving the integrity of the concrete structure. This can take place if oxygen, which water can seep through the concrete by capillary action. If basement is not properly waterproofed and as the result of corrosion, reinforcement steel will expand and the concrete structure will crack. The need to exclude chloride is another reason as it can attack and weaken the concrete. However, this is only limited to sea front structures.

For a basement to function and operate for its intended use without hiccups and also its long –term structural integrity, it is paramount that water is evidently absent.

This report will an overview of the different types of basement waterproofing. In particular, it will focus on a case study on the newly constructed HDB Toa Payoh HUB, which uses the method of crystalline waterproofing for the basement construction.

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CHAPTER 2: DIFFERENT TYPES OF BASEMENT WATERPROOFING SYSTEMS

2.1 INTERGRAL WATERPROOFING

This waterproofing system started in the mid sixties where Cementaids introduced their Caltite admixture, which were added into the concrete mix. It provides protection against water penetration based on the use of admixtures with waterproofing properties in the concrete mix to form concrete with surfaces that are repellent to water, and to fill the capillary pores hence reduces the permeability of the concrete.

Watertightness depends solely on the constituents of the concrete structure. The constituents, known as admixtures are mixed with the concrete during batching. This process integrates the admixtures into the concrete. An integral waterproofer is a material (in the form of powder, liquid or suspension/paste) that must able to reduce the hydraulic permeability of the cured concrete structure and/or have water repelling or excluding properties transferred to the set concrete. Common admixtures used are the reactive hydrophobic pre-blocking ingredients and silica fumes.

The main advantage of the intergral system is the working space. This system does not need extra working space to operate and it can be simultaneously with the batching and casting of concrete. The construction time is shorter due to the virtue that it is being carried out together with the construction of the diaphragm wall. Intergral waterproofer can prove more reliable and be quicker to apply than membranes. By allowing their use in the tender documents the designer will force the contractor to consider external and intergral waterproofing in preparing the tender. Client will obtain the full benefit of cost and programme saving.

The use of this system will impose certain burden as well. The contractor has to ensure a higher quality of work. There is a need that the admixtures and the concrete mix is homogeneously mixed and the mix is free from lump. Failure to do so will mean imperfection of the system. The use of the intergral waterproofers is economical for wall thickness of between 300 and 400mm. The amount of admixture to be used is proportional to the volume of concrete; and volume of concrete depends on the structural size. In walls, the deciding dimension is the thickness. The use of this system for thicker walls of about 500mm would be uneconomical.

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Intergral waterproofers may enhance or limit concrete strength development. The low strength development associated with water repellents can be overcome by decreasing water cement ratio. If it is achieved by high cement ratio, heat generation must be considered. By contrast silica fume waterproofer will enhance strength development.

2.2 MEMBRANE / TANKING SYSTEM

Membrane system provides a physical barrier forming a tanking system using either sheet membranes or liquid membranes or both to the flow of water. This tanking principle of wrapping the whole basement is technically logical and has the advantage of ease of application. This system provides a continuous barrier system, which excludes water, and/or water and may exclude gases. It can be installed on the exterior face of the walls and floor (external), onto some external source of support (reversed), within the construction (sandwiched) or on the interior face of the walls (internal). See Fig 2a. Generally there are two types of membrane available, sheet and liquid membrane.

Membrane sheet is a lining that is attached to the external face of the basement walls through nailing or adhesion. Materials can range from the traditional rubber, bitumen sheeting to bentonite panels, unvulcanised polyvinyl chloride and polyurethnes. The latest system in tanking is the HDPE membrane with special profiles. Sheet membranes are preformed, factory-made in rolls, which are bonded or cast against the substrate to form a continuous membrane by lapping. Side laps of 100mm and end laps of 150mm are common. Lapping may be achieved by torching/ flaming, use of bonding compound or self-adhesive membranes. As a barrier between soil and the concrete itself, membrane must have properties to counter the undesired effect the soil has on the concrete. It must be strong enough to ensure that movement of the soil will not cause any damage or puncture that may cause water seepage. The basic problem of any sheet system is always the lap areas and extra care should always be observed.

Liquid membranes brought by companies like Tremco in the early 80s, come in either one or two-component in liquid or gel form. They are applied either by brush, rollers or spray. Liquid membranes give the flexibility for works on uneven surface and complicated details. This system also has limitation when problems of uniformed thickness, pinholes and dampness need to be overcome.

All membrane systems require protection to avoid problems of puncture, either on the horizontal along construction or on the wall

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during bankfilling. Tanking system also requires tedious workmanship where there are excessive ground beams, piles caps details or where raft foundation are designed. A major point for the use of membrane system is its attribute to maintained watertightness despite shrinkage and thermal cracks occurring in the concrete mass. However, this system is very susceptible to damages during construction that waterproofing cannot be ascertained until the structure shows no problem after a period of time. Extra construction time is required for surface preparation before contributed to the additional construction time.

Fig 2a - Tanked Protection. The structure itself does not prevent water ingress. Protection

is dependent on a total water or water an vapour barrier system applied internally or externally.

2.3 CAVITY / DRAINAGE SYSTEM

A cavity/ drainage system allows water to enter the structure, contain and direct it to sumps from where it is removed by draining or pumping. A cavity wall with a mass concrete outer leaf and a reinforced inner leaf is constructed. The cavity channel works as a drainage channel. Water flows out of the cavity through weepholes and internal drainage will steer the water towards a sump and mechanical pump. This technique envisages the basement to the likeness of the hull of a ship. The rational this technique is that as it is practically impossible to keep the basement free from water

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infiltration, thus it may be preferable to exclude waterproofing the basement and rely solely on the internal drainage system. This manner of keeping the basement waterfree in a waterlogged area may be unviable. The viability of using such a system will depend on the purpose of the basement. One possible use is for basement carkpark.

The inner wall is generally non-load bearing and may need to be designed to be free standing to prevent moisture paths occurring across ties. Vapour transmission through the fabric of the inner wall may be reduced by providing a vapour-resistant membrane, adequate ventilation of the cavity or by using a profiled cavity drainage former, which provides an integral vapour barrier. The later method cannot be used with wall ties.

Cavities under floor may be formed from no-fines concrete or proprietary systems such as profiled drainage sheets or purpose-made tiles. Wider cavities may be formed using pre-cast concrete planks to give a raised floor, which may be useful where access is required for maintenance of drainage channels or for servicing pumps.

Cavity/ drainage system is suitable for cases where tanking system, i.e. physically stopping the water could result in higher water table and/ or unacceptable stresses behind the structure.

See below Fig 2b, 2c and 2d for the construction details of cavity system.

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Fig 2b

Fig 2c

Fig 2d

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2.4 CHEMICAL GROUTING SYSTEM

Chemical grout membrane system has been used in Singapore and Malaysia for more than 15 years. This system is one of the well-proven and effective method for basement waterproofing especially for basements with high water table. The flexibility of the method and freedom from vandalism has been made the system cost effective.

Since it is a grouting system, it does not require a dry concrete surface for installation. For deep basement, especially those areas with high water table, it is almost impossible to have a total dry surface area whereas it is the prime requirement when sheet membrane system is being used. It is a tanking slab system. Unlike the sheet membrane where the membrane might be teared or damaged during the ground settlement, the grouted layer will act as a solid slab to resist any shear or tension forces.

This is flexible method that is particularly suitable for basement with a lot of ground beams or pile caps where sheet membrane systems have the continuous problems. Since it is a tanking slab, it does not need to worry about the damage by others like the sheet membrane systems does. There is freedom from vandalism. The system is particularly popular for a thick floor slab as it is cheaper than the admixture method in such circumstances.

A layer of aggregates were laid completed with grouting points prior to casting the reinforcement concrete slab on top. Thereafter a grout comprising cement and additives like AM-9 were injected. Mix designs of the grout and the additives used may have changed over the years, but these grouting systems are still widely used by companies. This system can be also used for basement walls. However, an appropriate formwork system would be necessary to set up before the grouting. For the walls, the sheet piles were left in place, joints welded and the reinforced concrete wall cast against it. In addition, grouting on the cold joints of the vertical construction joints were done and water stops was also incorporated in all joints. Water stops are available with hydrophilic compound incorporated, which will then expand when in contact with water and ensure a tighter fit. However the general worry of whether the position of the

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water stop inside the concrete wall after casting, it as design, has and always is debated. See Fig 2e

The chemical grout membrane system requires highly skilful and well-trained workers for all the grouting processes particularly the sequence of grouting and the installation of grout formers techniques. The process of laying and grouting the floor slab demands good cooperation between the main contractor and the waterproofing sub-contractor.

2.5 CEMENTITUOUS/CRYSTALIZATION METHOD

Hitchens introduced the Vandex system applied on the inside of walls and floors for waterproofing of basement in the mid to late 70’s. Since Xypex was introduced in the waterproofing market and the case study, waterproofing of HDB Toa Payoh HUB basement was using Xypex.

Xypex is a non-toxic, chemical treatment for the waterproofing and protection of concrete. Xypex's primary and most distinguishing performance feature is its unique ability to generate a non-soluble crystalline formation deep within the pores and capillary tracts of the concrete -- a crystalline structure that permanently seals the

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concrete against the penetration of water and other liquids from any direction.

To create its crystalline waterproofing effect, Xypex must become an integral part of the concrete mass. This is based on two simple reactions, one chemical and the other physical. Concrete is both porous (capillary tract system) and chemical in nature. By means of diffusion, the reactive chemicals in Xypex use water as a migratingmedium to enter and travel through the capillary tracts in the concrete. This process precipitates a chemical reaction between Xypex, moisture and the natural chemical by-products of cement hydration (calcium hydroxide, mineral salts, mineral oxides and unhydrated and partially hydrated cement particles). The result is crystallization and, ultimately, a non-soluble crystalline structure that plugs the pores and capillary tracts of the concrete. This will continue to migrate through the concrete and the crystalline growth will form behind this advancing front of chemicals. This process will reactivate whenever water is present, thus making the concrete totally sealed against the penetration of water (or other liquids) from any direction. Unlike most other system, A Xypex application is permanent. The fibrous crystalline growth, due to its unique composition, will not deteriorate under normal conditions.

The crystallization process that Xypex causes within the pores and capillary tracts of The process by which Xypex waterproofs concrete is unique in that Xypex is a CATALYST. This crystalline growth is highly resistant to extreme water pressure from either side of the concrete and also to most aggressive chemicals. Since the process is catalytic, the crystalline structure can reactivate many years after the original application, to seal or re-seal many defects, which might occur in the concrete at a later time.

Xypex introduces a reactive, dynamic densification process, which continues throughout the life of the concrete. Being a permanent enhancement, Xypex will extend the service life of the concrete. Unlike barrier methods, XYPEX penetrates and waterproofs the concrete itself -- not just the surface. While other products degrade over time, Xypex continues on.

Concrete is illustrated below in electron microscope photos taken by an independent research team.

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1. CONCRETE (UNTREATED)

A control sample of concrete was sheared through at 50mm below the top surface. The sheared face shows some of the by-products of cement hydration with which Xypex reacts. Precipitated calcium hydroxides together with cubic and rhombic particles are visible.

2. XYPEX CRYSTALLIZATION (INITIATION)

Taken at 50mm within a Xypex-treated concrete sample, This photograph shows the initiation of the Xypex crystalline reaction after Xypex Concentrate was applied to the surface.

3. XYPEX CRYSTALLIZATION (MATURE)

This photo was taken 26 days after the application of Xypex Concentrate at a depth of 50mm into the concrete sample. A dense, fully developed crystalline structure has formed within the capillary tracts of the concrete to completely block the flow of water.

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The above steps depict the process by which Xypex penetrates and blocks the flow of water and other liquids.

The benefits of Xypex are listed as below:1. Xypex is less expensive than other methods such as membranes

with protective boards. 2. Xypex is construction-schedule friendly, and it can be applied

immediately after the forms are stripped. 3. Xypex cannot puncture, tear, or fall apart at the seams -- and it

needs no special sealing, lapping, or seam finishing. 4. Xypex needs no protective layers for backfill, and it leave no ugly

tar line to interfere with landscaping. 5. Xypex is breathable. It blocks water in liquid form, but allows water

vapor to escape, so the concrete can dry completely. 6. Xypex is self-healing. New cracks in the concrete (up to 1/64") will

mend with new crystalline growth. 7. Xypex is environmentally friendly - approved by the E.P.A. and the

NSF. 8. Xypex protects concrete. Crystalline waterproofing stops

transportation of water and rust-accelerating electrolytes to the reinforcing steel.

CHAPTER 3: CASE STUDY: HDB HUB (TOA PAYOH) PART ONE – DIAPHRAGM WALLS & ITS SUPPORT

3.1 Introduction

At the site of the HDB HUB, the soil condition is made up of Kallang Formation where organic clay, marine clay, silty clay and silty sand can be found residing at this formation. This formation goes go up to 30-35m below ground level and thereafter it is comprises mainly of sandstone, mudstone and siltstone, practical all weathered stones.

The construction of the HDB HUB by the main contractor, Shimizu Corporation used the semi top down basement method. This new

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and advanced technology is partially similar to the convention top down method. Semi top down casts the first storey slab before excavation works start on the basements. Which after, all necessary excavation work will be carry out together until the deepest level. This method provides a better and cleaner construction site, which enhance the site safety. In addition, this method ensures that simultaneous construction works above the ground level for the tower blocks while the basement construction is in progress.

This section will not be covering the entire semi top down construction. However, it will be touching on the construction of the diaphragm walls as well as its support system. Diaphragm walls will form part of the basement structure and also part of the cavity system in the role of basement waterproofing. In the part two of this case study, it will focus on the waterproofing systems of the HDB Hub’s basement.

The siteof HDB HUB -Toa Payoh

3.2 Construction of Diaphragm walls

The construction of diaphragm walls is to be carried out concurrently with the construction of bored piles and king posts. This is due to time factor and the availability of construction equipment. When one side was done, the construction of diaphragm and bored piles will shift over.(i.e., the piling work will carry out on the diaphragm wall side and vice versa.

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1st storey structural slab as construction stage

Bored PileDiaphragm Wall

King Post


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The 2 pictures as shown above give a view of the reinforcement of the king posts

Diaphragm wall is used when the supporting system will be integrated as part of the permanent structure. By means of constructing cast in place reinforced concrete to form a continuous structure around the perimeter of the area of excavation, it offers support and watertightness to the excavation. The technique of diaphragm walling creates a concrete wall before any other excavation takes place. Excavation takes place the width of the wall and to the required depth by means of hydraulic grabs or special rotary cutters.

3.3 Support system for diaphragm wall – Ground Anchors & Struttings

Unlike the top down technique where each slab will be casted directly on the ground and the concrete floors were used as bracings, semi top down construction needs temporary supports in some parts of the area as full excavation work is done after the ground floor slab is casted. The lateral support from ground slab alone is insufficient

Ground anchors are used and served as temporary bracing during excavation. The basement slabs will provide the final support, and the ground anchors will eventually distressed. The use of the ground anchors allows the absence of interior obstructions and

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hence, allows mechanical earth moving. This improves the construction conditions of temporary supports and basement floors.

As ground anchor is a prestressing tendon embedded and anchored into the soil to provide resistance to structural movement of a member by acting on a tying-back technique, a through soil and site investigation is essential so as to ensure the chosen drilling technique will not result in loss of ground beneath the existing buildings and grouting will not cause heave of existing buildings or caused pressures to the back of the diaphragm wall being supported. It is also desirable to keep the wall away from the pile driving, blasting and freezing.

The use of ground anchors is highly suitable for this congested site at Toa Payoh. However, it cannot be installed where there are major obstructions such as utility lines and underground structures. Hence in this project, it cannot be used to support diaphragm walls along the MRT tunnel.

With this restriction, heavy lateral struttings are used for supporting diaphragm walls. However, the working space for the site will hence restricted.

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Diagram & picture showing the ground anchors system

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Pictures showing the strutting work of the new HUB

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Pictures showing the strutting work of the new HUB

CHAPTER 4: CASE STUDY: HDB HUB (TOA PAYOH) PART TWO – BASEMENT WATERPROOFING

4.1 Introduction

In the new HDB HUB basement, there are a total of 3 level basements. The 1st level is used as the function of carpark and a foodcourt. The last two levels are used as carpark. In this section, the report will cover the waterproofing of wall as well as the slab of the basement carpark.

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Basically, HDB basement carpark used the cavity and crystalline system of waterproofing. Xypex is the main material used for crystalline waterproofing. In the earlier section 2, Xypex was briefly introduced and in this section, the report will deeply covers how Xypex performed its roles for waterproofing the basement.

From construction tofinished basement

4.2 Waterproofing of basement walls

Earlier in section 3, the report covers the construction of the diaphragm walls. These diaphragm walls excavated below ground level together with the slabs will form an enclosure structure of the basement as shown in below, Fig 4a

Basement Slab

1st level

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Ground Level

Diaphragm walls

Fig 4a

This enclosure structure will make the task of waterproofing the basement earlier as there is no need of waterproofing the top 2 basement slabs. Waterproofing is done on the last slab of basement 3, which has a direct contact with the ground. In waterproofing the basement walls, cavity system was used in construction.

The cavity system that discussed in section 2 allows water to enter the structure, contain and direct it to sumps from where it is removed by draining. A cavity wall with a mass concrete dry wall on the outer leaf and a inner diaphragm wall is constructed. The cavity channel works as a drainage channel. Water flows out of the cavity through weepholes and internal drainage will steer the water towards a sump and mechanical pump. Aluminum angle supports were fixed at a downward inclined angle from the aluminum and dry wall to the diaphragm wall. The rational behind this was to allow water to flow downward toward the diaphragm wall. There are no way that the water could flow to the dry wall which affect the outlook of the wall of the basement and causing maintenance problem to the external wall of the basement.

See Fig 4b for a detail section

Diaphragm wall

Alum Angle Support

Alum

Dry wall

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Channel

Fig 4b

The figure below shows the area that covers the construction area of the diaphragm walls and cavity walls, shown in However, at the entrance of the basement, there is no enclosed structure to waterproof the carpark entrance and the1st level basement retaining walls, shown in Hence retaining walls were waterproofed by Xypex concentrate slurry.

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Xypex Concentrate is applied as a cementitious slurry coating on retaining walls surfaces at the entrances to the basement carpark. Although applied as a coating, Xypex Concentrate is a unique chemical treatment for the waterproofing and protection of concrete. It is manufactured in the form of a dry powder compound. Xypex consists of Portland cement, very fine treated silica sand and various active proprietary chemicals. Xypex concentrate slurry prevents the penetration of water and other liquids from any direction by causing a catalytic reaction that produces a non-soluble crystalline formation within the pores and capillary tracts of concrete and cement-based materials.

When applying the Xypex treatment to the retaining wall, it must not be applied under rainy conditions or when ambient temperature is below 40°F (4°C). It is due to the fact that Xypex requires moisture to initiate the crystalline waterproofing process, all concrete, whether fresh or old, must be saturated with water. The concrete surface must be a minimum of 20 hours old before application of the Xypex coating treatment. For normal surface conditions, the coverage rate for each Xypex coat is 1.25 - 1.5 lb./sq. yd. (0.65 - 0.8 kg/m2).

The concrete surface to be treated must be clean and free of laitance, dirt, film, paint, coatings or other foreign matter. The surface must also have an open capillary system to provide "tooth and suction" for the Xypex treatment. If surface is too smooth (e.g. where steel forms are used) or if surface is covered with excess form oil or other foreign matter, the concrete should be lightly sandblasted, waterblasted, or etched with muriatic (HCL) acid. Surfaces to be etched with muriatic acid should be dampened with water before application of the acid. After acid etching, flush concrete thoroughly with clean water.

Xypex requires a saturated substrate and a damp surface. Therefore, the retaining walls surfaces must be thoroughly saturated with clean water prior to the application so as to aid the proper curing of the treatment and to ensure the growth of the crystalline formation deep within the pores of the concrete. Excess surface water must be removed before the application. If concrete surface dries out before application, it must be re-wetted.

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HDB HUB had used the Xypex Concentrate slurry in waterproofing the retaining walls due to the following advantages:

Xypex Concentrate Slurry has the abilities to:

Resists extreme hydrostatic pressure Becomes an integral part of the substrate Can seal hairline cracks up to 0.4 mm Allows concrete to breathe Highly resistant to aggressive chemicals Is non-toxic Does not require dry weather or a dry

surface Cannot puncture, tear or come apart at

the seams No costly surface priming or leveling

prior to application Does not require sealing, lapping and finishing of seams at

corners, edges or between membranes Can be applied to the positive or the negative side of the

concrete surface Does not require protection during backfilling or during

placement of steel, wire mesh or other materials Less costly to apply than most other methods Not subject to deterioration Permanent

4.3 Waterproofing of basement floor

Refer to Fig 4a, the earlier section had mentioned that waterproofing of basement floor slab is only be carried out to the 3 rd

level basement which is directly in contact with the ground level. The rest of the two basement floor slabs are enclosed in the structure without any moisture contact.

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These pictures above shows the view of basement 3

In constructing the basement 3 slab, Silica Fume concrete is used. The slab thickness is about 700 to 1200 and the grade G40 concrete is used. Xypex Concentrate DS2 is added on surface prior to power floating providing waterproofing and abrasion resistance.

DS-2 is a special dry shake formulations of Xypex Concentrate designed specifically for horizontal concrete surfaces such as parking decks and floor slabs. It is either applied by hand or by mechanical spreader. DS-2 is trowelled into fresh concrete prior to finishing and it is used for concrete structures where increased abrasion resistance is required.

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Xypex Concentrate is a unique chemical treatment for the waterproofing and protection of concrete as mentioned earlier. XYPEX CONCENTRATE DS-2 is a special formulation designed specifically for a dry-shake application on horizontal concrete surfaces where greater resistance to impact and abrasion is required. It is packaged in the form of a dry powder compound, Concentrate DS-2 consists of Portland cement, various active proprietary chemicals, and a synthetic aggregate hardener, which has been crushed and graded to particle sizes suitable for concrete floors. DS-2 later becomes an integral part of the concrete surface thereby eliminating problems normally associated with coatings (e.g. scaling, dusting, flaking and delamination). The active chemicals react with the moisture of the fresh concrete causing a catalytic reaction, which generates a non-soluble crystalline formation within the pores and capillary tracts of the concrete.

The application of the DS2 dry shake started when the fresh concrete is placed, consolidated and levelled. There is a waiting period until the concrete can be walked on leaving an indentation of 1/4 in. - 3/8 in. (6.5 mm - 9.5 mm). The concrete should be free of bleed water and be able to support the weight of a power trowel. The surface is then float opened. Immediately after floating open the surface, one half of the dry shake material is applied and spread evenly by hand or mechanical spreader. As soon as the dry shake material has absorbed moisture from the base slab, it should be power floated into the surface. Immediately after power floating, the remaining dry shake material at right angles is applied to the first application, allowing the remaining dry shake material to absorb moisture from the base slab and then power float the material into the surface. When the concrete had harden sufficiently, the power trowel surface to the required finish.

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The picture above shows Xypex DS2 being applied to the basement 3 slab

HDB HUB had used the Xypex Concentrate DS2 dry pack in waterproofing the basement 3 floor slab due to the following advantages:

Xypex Concentrate DS2 has the abilities to:

Resists extreme hydrostatic pressure from either positive or negative surface of the concrete slab

Becomes an integral part of the substrate

Highly resistant to aggressive chemicals Seal hairline cracks up to 0.4 mm Allows concrete to breathe Non-toxic Less costly to apply than most other

methods Permanent Increases flexibility in the construction

schedule

CHAPTER 5: CASE STUDY: HDB HUB (TOA PAYOH) PART THREE – DEFECTS & XYPEX,THE MATERIAL

FOR CRYSTALLINE WATERPROOFING

5.1 DEFECTS AFTER THE CONSTRUCTION

Unlike the membrane system, crystalline system does not have the ability to cover the cracks immediately. The crystalline effect does not take place immediately. Hence, prior to the construction, there were unsightly cracks found on the basement 3 slab.

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There was an immediate need to seal off the cracks to prevent the seepage of water through cracks causing maintenance problem. However as the basement 3 slab was waterproofed with Xypex Concentrate DS2, the material that used to seal the crack is Xypex Patch’n Plug. In sealing the cracks, a similar product needs to be used to prevent unsuitability of material so that there won’t be no unnecessary problems.

Xypex Patch'n Plug is formulated as a crystalline, fast-setting, non-shrink, high-bond-strength, hydraulic cement compound for concrete patching and repairs. It stops flowing water in seconds and is used to seal cracks, fill tie-holes and other defects in concrete. It has the ability to stop an active flow of water through cracks and repair the concrete substrates before the application of Xypex coating materials.

The crack sealing process started by routing out the crack by chiseling or chipping to a minimum depth of one inch (25 mm). There is a need to form a square or dovetail shaped space, not using "V" cut and flush away all loose materials and dirt from the cavity with water and a stiff brush. 1 part water to 3.5 parts Patch'n Plug by volume is added and mixed to the consistency of stiff putty enough for the use in 3 minutes. For best results, water temperature should be approximately 60°F - 70°F (15°C - 20°C). Later, the plug is formed with gloved hand and it is plug into cavity pressing firmly until it is hard. The sealing of cracks begins at the highest point and work down from that point. When there is a high volume of water flow due to extreme hydrostatic pressure, a bleeder hose may be necessary to relieve the water pressure while sealing the repair area.

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The pictures above show the sealing of basement 3 slab by Patch’n Plug

HDB HUB had used the Patch’n Plug in waterproofing the basement 3 floor slab due to the following advantages:

Patch’n Patch is:

Single component (simply add water) Fast setting: two to three minutes at

70°F (21°C) Excellent structural strength As durable as the masonry and

concrete to which it is applied Non-metallic (won't rust or deteriorate) Non-toxic

5.2 Xypex, the crystalline waterproofing material

As mentioned in section 2.5, Xypex introduced a reactive, dynamic densification process, which continued throughout the life of the concrete. Being a permanent enhancement, Xypex will extend the service life of the concrete. Unlike barrier methods, XYPEX penetrates and waterproofs the concrete itself not only t the surface.

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Since the beginning of time, erosion has been grinding the toughest building materials to dust. The building's foundation waged a constant battle to keep water out. Xypex, being a through-and-through concrete enhancement, resists these erosive processes by making the concrete stronger, more durable and dense. For a small fraction of the cost of new construction, a significant extension of structural service life can be expected. This is simply illustrated in the below figures.

Step 1 - The Battle Snow and ice, wet dirt, groundwater, foundations are exposed to many sources of water and moisture. Problems are often made worse by poor drainage, faulty gutters, and sprinklers.

Step 3 - Applying The Cure Applied from the inside or the outside, to new or old concrete, XYPEX reacts with concrete byproducts to cause integral waterproofing.

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Step 2 - The Water Leaks In Floor-wall cold joints, cracks, tie holes, capillaries, bleed paths, degrading tar coats, torn or delaminating membranes -- water finds many ways to get through concrete.


Step 4 - Crystallization Begins XYPEX causes quartz-like dendrites crystalline structure to form within the capillary system of the concrete. It becomes a part of the concrete, not just a sealer that's "stuck on the surface."

Step 5 - Water Leaks Are Stopped XYPEX crystals fill all water paths through concrete. The crystals continue to develop in the concrete over time, blocking new water paths that developed even years after application. The concrete heal itself.

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Step 6 - Dynamic--Integral--Permanent Over time the XYPEX-catalyzed crystal growth forms a waterproof layer over the entire surface of the foundation. Given enough time the crystals will penetrate the entire mass of concrete. And new cracks, should any form, will be sealed in an ongoing, dynamic process.

In comparison with other waterproofing system, the crystalline nature of the Xypex waterproofing system provides many application advantages as listed below:

1. It does not require a dry surface; in fact, a wet surface is necessary.

2. Can be applied at wet weather. 3. Do not require costly surface priming or leveling prior to

application. 4. It cannot puncture, tear or come apart at the seams. 5. Do not require protection during backfilling or during

placement of steel, wire mesh or other materials. 6. It can be applied on either side of the concrete surface, the

negative or the positive (water pressure) side. 7. Do not require sealing, lapping and finishing of seams at

comers, edges or between membranes. 8. Less costly compared to most other methods.9. It continues to perform its function while other system

degrades

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6. CONCLUSION

In addition to seepage that is visible, i.e. water entry under hydrostatic head, basements must combat transpiration. In transpiration, moisture, which may be present in the soil only as dampness not as ground water, is drawn through the concrete by the humidity gradient, i.e. the lower humidity inside the basement compared with the soil. Where the concrete surface is exposed and the ventilation is good transpiration can take place unnoticed as the moisture evaporates within the concrete.

If the water is carrying dissolved salts, these were deposited where the water evaporates leading the building of chloride, which later leads to reinforcing corrosion. If there is porous finishes, present more of a barrier to transportation than concrete, it the applied water will evaporate immediately behind them. This will lead to damp staining and formation of crystals at the bond interface leading to bond failure between the substrate and the applied layer.

Hence, a good waterproofing system is essential and utmost important for basement construction. With all the different systems introduced in Section 2, the waterproofing system may be used as an individual system or a combination of the systems. Commonly, a selection of a suitable waterproofing system for a particular project is dominated by economic factor and this is probably the major cause for non-performance of the waterproofing system.

To select and install a waterproofing system that has the lowest cost per unit can be detrimental. Consideration should be given to determine the cost of replacing, maintain and repairing of a waterproofing system failing prematurely before its intended life. Other cost associated to the failure like damage to expensive finishes and inconvenience caused should also consider.

A decision should be made whether to use a waterproofing system and its selection when the concrete structure is in its design stage, since site conditions, configuration of the structure, construction method and job sequence can affect the waterproofing installation.

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Date post:	25-Apr-2020
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