This requirement for reinforcement is excerpted from the specification for concrete work.

Materials

Reinforcement bars shall conform to the requirements from the following specifications:

1. ASTM A 615M: Specification for deformed and plain billet steel bars for concrete reinforcement.
2. ASTM A 706M: Specification for low-alloy steel deformed and plain bars for concrete reinforcement.
3. ASTM A 996M: Specification for rail- steel and axle-steel deformed and plain bars for concrete reinforcement.

Types of reinforcement bars will be identified on the contract drawings as a prefix to the bar diameter. The prefixes have the following meaning:

• Rail-steel reinforcement bars marked with letter R for this type of steel.
• Deformed bars are marked with the letters S and W for type of bars. They are having yield strength not exceeding 410 MPa (4100kg/sq.cm)

The source of supply for all materials shall be approved by the Engineer before these materials are delivered o the site.

Reinforcement shall be stored clear of working areas and supported above the surface of the ground, and shall be protected from damage and from deterioration due to exposure.

Reinforcement hooks and bends shall comply with the relevant requirement of American Code. The Contractor shall prepare bar bending schedules, copies of which will be made available to the Quantity Surveyor for his assistance during any re-measurement of reinforcement.

Reinforcement not readily identifiable as to the required quality will be liable to rejection.

Test Certificates

The Contractor shall supply the Engineer with a test certificate fro the steel manufacturer showing compliance with specification requirements.

One tension test ad one bed test shall be made for each incremental lot of 50 tonnes (bar size distinction not necessary) supplied for the works, or as frequently as required by the Engineer. In addition, one re-bend test shall be conducted for each incremental lot of 100 tonnes delivered to site.

Here after is the Method Statement for the Application of Sarnafil F 610-12 Felt PVC Waterproofing Membrane.

Existing Roof Built-up

1. Cast in-situ concrete panels

2. Vapour control layer

3. Thermal insulation board

4. Existing waterproofing system (liquid/ bitumen or PVC membrane)

5. Leveling/ Concrete screed

6. Reinforced concrete slab

Sarnafil F 610-12 Felt mechanically fastened using Sarnafast System

7. Unroll Sarnafil F 610-12 Felt, homogenous PVC waterproofing membrane, loosely lay over the cast in-situ concrete panels and mechanically fastened the overlap with Sarnafil fastening components (membrane washers and fasteners).

8. Install IF/IG-C washers (for hard surface) and fasteners BD, centered along the 30mm line traced on the membrane. Fastener spacing is to be in accordance to the project specific calculations made by Sarnafil.

9. The fastener length must penetrate the concrete deck by a minimum embedment of 32mm. The fixation pattern must always be symmetrical (i.e. every 200mm, or every 400mm, etc.)

10. Install adjacent sheets along the lap lines marked on the membrane (120mm from the sheet edge).

Hot-air Welding Procedures

11. When hot air welding of Sarnafil membrane, the overlap area must be clean and dry. For straight seam welding (overlap is 120mm), Sarnamatic automated welding machine must always be use.

12. For hand welding, use the Leister Triac hand welder, 40mm wide nozzle for straight weld and 20mm wide nozzle for corners and detail work. The three stages are:

• Spot weld the overlap.
• Pre-weld: Weld the rear overlap area so that a 35mm opening remains for the finishing weld.
• Final weld: Sarnafil PVC hand roller should be guided at a distance of 30mm parallel to the air outlet of the welding nozzle. Always roll the hand roller fully across the seam.

13. Testing of welded seams:

• Visual seam check: Shiny surface and even quality of welding beads.
• Mechanical seam check: Use a screwdriver to slide along the welded seams to check for voids and any welding defect.
• Peeling test: At the overlapped cut the membrane into 50mm width strip and firmly peel it. Tearing point should be located beyond the effective welding seam.

14. For perimeter fixation around the roof edge or near the parapet wall, Sarnafil F 610-12 Felt membrane must be secured with Sarnafil U bars and PVC welding cord against tearing and peeling off by wind uplift.

Upstands, Flashings & Roof Details

15. Followed by the upturn membrane, Sarnafil F 610-12, hot-air welded overlap 40mm with Sarnafil F 610-12 Felt, covering Sarnafil U bars and fully adhered to the parapet wall with Sarnafil approved adhesive.

16. It can be terminated with metal strip fastened through the membrane and sealed with an approved sealant at a height at least 150mm. Or alternatively, make a groove line by saw cutting on the required height and tucked in with Sarnametal sheet (PVC coated) where the upturn membrane Sarnafil F 610-12 can be welded on it.

17. For corners, vent pipes, drains and other roof details, please refer to Sarnafil installation handbook procedures.

Water Ponding Test

18. Carry out flood test 48 hours minimum after completion of the waterproofing works. Restrict water run-off from membrane area by plugging drains and creating dams or dikes. Flood restricted area to depth of about 100 mm and maintain at this depth for 48 hours. Any punctured or defective areas shall be made good by an approved method and retested.

19. The membrane shall be cleaned and inspected before proceeding with the remaining built-up protection measure.

Keep reading: Application of Sarnafil PVC Waterproofing Membrane

When all the preliminaries are completed and the owner has decided to proceed with the work, tenders are invited. Legally this is an attempt to check if there would be interested contractors to carry out the work within the estimated limit of time and finance. The invitation to Tender is not binding to the owner to proceed with the work and does not cause any liability for any expenses to which contractors would spend in preparing and submitting their construction bids.

Information to be given in a Call for Bids Notice

The notice must be as short as possible, but conveying an adequate idea of the nature and scope of the proposed work and all essential details.

The text of a good advertisement should at least include the following information:
Mode of submitted bids: Bidders should be asked to submit bids in sealed covers, in order to maintain secrecy of quotations.
Form of Bid: It is advisable to get all offers in the same form to facilitate scrutiny, and comparison
Name of the inviting authority: This helps the bidder know the persons he will have to deal with and the co-operation he may receive, if his bid is accepted, and such may also affect his quotation.
Nature of the work and its location: If the nature and location of work is within his operating area, the prospective contractor will want to learn more about the job; else he may not waste time in reading further details
Estimated cost of the work: This most briefly indicates the magnitude of the work and enables him o see whether it is too small to interest him or perhaps too large for him to handle.
Time Limit: The time limit within which the work is to be completed should be mentioned. This will be of great help to the bidder to work out a realistic price of the work.. The time limit may influence the type and number of construction equipments and workers to be employed, and will vitally affect the contractor’s bid.
The availability of Data and forms:
where, from whom, at what cost and up to which date blank bid forms and specifications may be obtained and whether a refund will be made upon their return in satisfactory conditions.
Earnest money required with the bid: The amount and form of security; whether the amount will be accepted i the form of cash, bank guarantee, check or others. Also the number of days within which the amount will be refunded to the unsuccessful bidder.
Performance security: The amount, form, and procedure of recovering.
Information regarding drawings: where and when drawings can be examined by bidders.
Last date, place and time of receipt of sealed bid.
The date, time and place and procedure of opening bids.
Reservation to reject bids.

Tips for consideration in preparing construction bids

Careful study of the contract documents: The contract documents issued to the contractor or supplied for his inspection include general contract conditions, drawings, specifications, bills of quantities etc. These documents are to be studied carefully to check if any unusual conditions, specifications, or any feature of the work would demand special attention during pricing.
Sub-contractor’s work: Make relative inquiries about prices with sub-contractors and material suppliers for their respective portions of the job.
Site visit: This is important to ascertain the conditions under which the work has to be carried out and their impact on pricing.

* Difficulty to access the site
* Limited space on the site for vehicle movements
* Type of soil and depth of water table
* Availability of space for storing materials on site
* Availability of materials, their sources and prevailing market prices
* Local availability of skilled and unskilled labor, prevailing wages for workmen
* Source and cost of water needed for construction
* Power and lighting source, and the cost of erecting, marinating and dismantling power connection to the site

Time for completion: The bidder then estimates the length of time the work will take and the number and category of permanent staff suggested by the nature of the work for construction management . This helps to calculate the establishment charges.
Temporary works: The value of any temporary works needed to commence the construction and to clear away on completion, such as temporary office required for construction management purpose, store sheds for building materials, access road, water supply, depreciation of construction equipments, insurances, taxes, etc.

There are significant developments in concrete technology for a number of different and unique applications. Shrinkage compensating concrete is a concrete made with an expansive cement which, when properly restrained by reinforcement or other means, will expand by an amount equal to or slightly greater than the anticipated drying shrinkage.

Ideally a residual compression will remain in the concrete reducing the risk of shrinkage cracking. In the USA and Russia, expansive cements are produced as an enity, whereas in Japan they are produced by adding expansive admixtures to ordinary porland cement (OPC). A number of types of expansive cements have been used in USA namely Types K, M and S but type K is most prevalent. These cements which either contain or are blended with combinations of calcium sulphate,  calcium aluminates and calcium aluminate sulphates. In Japan another type of expansive cement. not based on sulphate and owing it s expansive properties to hydration of free lime, is used.

Care must be taken to ensure that continuous wet curing is provided for at least 7 days after placing to ensure that the expansion develops. Care also needs to be taken to prevent plastic shrinkage cracking. Expansive cements have been used to produce both shrinkage compensating concrete and self-stressing concrete for use in slabs, pavements, prestressed beams and roofs.

]]> http://constructionenglish.net/shrinkage-compensating-concrete/feed/ 0 http://constructionenglish.net/sika-shotcrete-technology/ http://constructionenglish.net/sika-shotcrete-technology/#comments Thu, 01 Jul 2010 06:49:03 +0000 Construction English http://constructionenglish.net/?p=684

Sika accelerator range groups Sigunit D54 AF – powder accelerator intended for dry process and Sigunit L – liquid accelerator. Sika as innovative company has been the first one to introduce Alkali free accelerator like Sigunit 54AF, Sigunit 53MY range. Sikacrete products ranges based on Silicafume technology are sprayable shotcrete repair products.

During rock excavation it is sometimes necessary to stabilize rock massif. As injection aid, Intraplast Z  will allow producing high quality rock bolt grout.

When shotcrete as preliminary rock support, concrete lining will take place. Because water flowing through those concrete structures may contain sediment or flowing with high speed, it is necessary to produce high quality concrete.

Products range summary in excavation and shotcrete practice

If the flooring gets failed, never blame the product first. The majority of flooring failures are due to application mistakes or carelessness.

Failures can have root causes:

• Prior to flooring application
• During flooring application
• After application, prior to service
• During service

Failure factors prior to flooring application

• Design failures: two weak substrate, poor reinforcement.
• Wrong flooring product selection: unsuitable for actual working conditions.
• Incompatible products
• Age of material: Shelf life exceeded
• Improper storage conditions:  temperature/humidity/leaks…
• Wrong mixing proportion: not all component added or even improper weight or packaging)
• Bad or no substrate evaluation:
  • Streng: Compression, Cohesion or pull-out
  • Moisture content
  • Dew point
• Wrong mixing tools/equipment
• Inadequate surface preparation
  • Substrate too old (primers which are not sticky)
  • No scabbing, grinding, shot or sand blasting when required
  • No priming/ inadequate priming/no dampening/saturation
  • No broadcasting, no blinding when required
  • Inadequate QS type
  • Superficial condensation (not checking ambient conditions and dew point)
• Excessive surface humidity – H2O reacts with isocyanides resulting of CO2
• Insufficient mixing time (leaving lumps in mortars, color streak in resin resins, etc.
• Only one of a two component system applied (no hardener in Epoxy system)
• Not pouring epoxy into another container (may leave unmixed material in the bottom edges)
• Supervision of application required: improperly trained applicators
• Inadequate applications:
  • two low temperature -> no reaction (cementitious or epoxy)
  • high ambient humidity -> bad film formation of water based resins
• liquid applied membranes: delayed film formation causes blistering
• single layer facade mortar: carbonation
• No homogenisation of components prior to mixing. Setting of pigment or aggregate, causes not homogeneous results or performance.
• Water or solvent addition to increase yield: make application easier but ruins product.
• Wrong or inadequate application tools
• Improper application thickness: too thin may not have enough material to achieve full properties or too thick may cause setting, cracking…
• Contamination of surface in between layers/coats by foreign materials: dust, chemical incompatible products (silicones), welding particles, etc,
• Pot life not controlled: end of pot life not visible
• Contamination from release agents on the pin-rollers used.
• Sabotage: addition of foreign substrate to the mix.
• Weakening of the concrete substrate due to sulfate contamination in high water table.

Proper training or simply reading the Product Data Sheet and Method Statement with prevent most of above factors.

Failure factors after application and before service of flooring

• Other trades present, working on the floor without properly protecting it.
• Welding
• Scratching by pulling loads over the surface

Failure factors during service of flooring

• Inadequate service temperature
• Unsuitable chemical environment
• Unsuitable floor cleaning methods
• Unexpected or modified working condition over the service time of application.

These can be traced back to bad product selection, or lack of information when specifying a product or system. And another thing should be consider is the design of industrial floor. A good design helps to avoid flooring failures.

]]> http://constructionenglish.net/factors-influence-flooring-failures/feed/ 0 http://constructionenglish.net/waterproofing-protective-coating-concrete-water-tank/ http://constructionenglish.net/waterproofing-protective-coating-concrete-water-tank/#comments Sat, 05 Jun 2010 13:06:41 +0000 Construction English http://constructionenglish.net/?p=662

Basically, internal surface coating in potable water tank shall be smooth, easy-to-clean and has high mechanical resistance to accommodate the erosion of movement of water. Most important thing is that this coating shall not adversely influence the quality of water.

Sika has been supplying SikaTop Seal 107 or Icosit TW 450 to large numbers of water projects. This product has been tested in local and international laboratory and meets the requirement for waterproofing and protective coating in contact with potable water.

In waste water treatment, besides providing waterproofing properties, internal surface coating shall be able to protect the reinforced concrete structure from aggressive chemicals attack. The degree of chemical attacks then depends on type of chemical involved, time of exposure as well as service temperature itself.

To give the right solution, it is necessary to know all these information before hand. As reference, herewith is some Sika products that have been applied for waste water treatment internal coating: Inertol Poxitar F, 2-part protective coating on epoxy coal tar pitch base and Sikagard 63 N, high build, chemical resistant epoxy resin coating.

In providing waterproofing system to concrete water tank, a good surface coating does not by itself makes a water tank waterproofed. Area of weaknesses are often found at the openings, pipe entry and construction joint or expansion joint system and for these areas waterstops and joint sealant have become an integral part of the whole waterproofing system.

Various types of waterstops are available from Sika, ranging from Sika Waterbars- flexible PVC waterbar to Sika Hydrotite – water swellable profiles. Sikaflex PRO-2HP is one of joint sealant available from Sika. This polyurethane based joint sealant is also has test certificate in compliance with potable water. Sikaflex Pro-3WF is usually used to seal gap & opening of joints when chemical resistance is required especially in waste water treatment plants. Sikadur Combiflex a highly chemical resistant PVC is also available to seal large or wide gaps and openings.

After obtaining approval of his accelerator, other admixtures, cement, and aggregate from the Engineer, the contractor shall  submit his proposed shotcrete mix designs to the Engineer for initial evaluation and comment. Such designs shall include both regular shotcrete as well as a mix design for use as a finishing layer in areas receiving a waterproofing membrane. No sooner than 14 days after mix design submittal, the Contractor shall (afer giving the Engineer at least 48 hours prior notice) prepare test panels his proposed. Shotcrete mix design in the presence of the Engineer.

Selection Criteria for shotcrete mix designs

Mixture proportions (mix designs) for shotcrete shall be selected and approved on the basis of compressive strength tests of cores obtained from test panels fabricated in accordance with ASTM C1140 and the initial and final set properties of the mix as determined in accordance with ASTM  C403.

Test Panels

Test panels shall be at least 762mm by 762mm. Test panels shall be made  using equipment, water pressure, air pressure and nozzleman the Contractor proposes to use for the work. Four separated test panels shall be made, two shall be vertical placements (representing side placement of shotcrete) and two shall be overhead placements. From each panel, ten (10) cores shall be taken. Two (2) from each panel for testing at 8 hours after placement, two (2) from each panel for testing at 24 hours after placement, two (2) from each panel for testing at 3 days after placement, two (2) from each panel for testing at 7 days after placement and two (2) from each panel for testing at 3 days after placement. Cores shall be taken perpendicular to the test panel and cured in accordance with the requirements of ASTM C1140, until testing.

Mix design acceptance criteria

a. All cores shall meet or exceed the mix design strength requirements for 8 hours, 24 hours, 7 days and 28 days. The average compressive strength of all cores (for 8 hours, 24 hours, 7 days and 28 days) shall be 1.2 times the required minimum compressive strength specified.

b. Material from each sample panel shall meet or exceed the minimum initial and final set requirement.

Revision of approved mix design

Shotcrete mix designs, as approved by the Engineer, shall be based on the approvals for cement, admixtures and aggregates used with an approved mix. If the Contractor, for any reason, change his cement, any admixture and/or his aggregate source or gradation, the Contractor shall submit and obtain approval for any/all new mix constituents and provide a new mix design for approval by the Engineer.

Keep reading Shotcrete Specification for further instruction.

]]> http://constructionenglish.net/specification-shotcrete-mix-design/feed/ 0 http://constructionenglish.net/solar-energy/ http://constructionenglish.net/solar-energy/#comments Wed, 26 May 2010 07:19:23 +0000 Construction English http://constructionenglish.net/?p=651

Uses of Solar Energy

Solar energy has many uses. It can be used to provide heat, light or to generate electricity. Passive solar energy refers to the collection of heat and light; passive solar design, for instance, uses the sun’s energy to make homes and buildings more energy-efficient by eliminating the need for day-time lighting and reducing the amount of energy needed for heating and cooling. Active solar energy refers to storing and converting this energy for other uses, either as photovoltaic (PV) electricity or thermal energy.

The uses of solar power in some States of the US

Texas, due to its large size and abundant sunshine, has the largest solar energy resources among the states. Several other states, however, lead the nation in terms of using solar energy, mostly due to state policies and incentives that encourage the installation of solar energy systems.

California is the nation’s largest solar energy market by far, and has eff ective state initiatives promoting the industry. Other states with notable markets for solar energy include New Jersey, Arizona, Colorado and New York. Even so, in 2006 solar energy accounted for just 0.01 percent of all U.S. electricity, mainly because of its higher costs compared to other power options.

Solar energy plays an even smaller role in the Texas electricity market. Still, Texas has the sunshine, manufacturing base and research institutions needed to become a leader in the development of solar energy. The state is well positioned to compete with other states and countries in a global solar energy market worth $10.6 billion in 2006.

One study estimates that Texas could capture about 13 percent of all new jobs and investments related to solar photovoltaic technologies by 2015, primarily in manufacturing.

Regarding material viewpoint, concrete itself could be described as a mixture of sand, cement, aggregate, water, admixture and air. Practically speaking, concrete consists a lot of inter-depend task. The basic way to achieve this target is to produce concrete with low water cement ration (W/C).

The use of plasticizer or superplasticiser will allow producing concrete with low W/C by still maintaining suitable workability. Water reducers or high range water reducing and set retarding admixture have been used worldwide in this matter. Sometime due to very high solid content of the water flowing into the structure, it is requested to produce concrete that provide excellent abrasion resistance. In this case the use of silica fume will be recommended. Other benefits when using silica fume are production of watertight, durable, high strength concrete. High strength development will be achieved by using a ultra water reducer.

Seeing that high quality concrete is one of the main requirements from each designer, it will be necessary to keep this objective during all concrete production process. This concept will start by spraying mold release agent  on the formwork surface prior to pour concrete. When concrete has been produced using admixtures cited above, it will be necessary to cure it properly. Antisol range – curing compound – grouping different chemical base will allow protecting concrete from pre water lost and therefore limiting cracks.

More details on concrete production for hydro-power plants will be discussed on next post. More helpful information can be also found on Sika Products for Hydropower Plants

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