This article is excerpted form the specification for concrete work from a high rise building. It is also applicable for similar construction job sites.

Concrete shall be transported and placed by approved methods that ensure segregation or loss of material will not occur.

Concrete drop during vertical placement shall not exceed 2.5m. For heights greater than 2.5m, the Contractor shall pour concrete through enclose chutes or access hatches, details of which shall be approved by the Engineer.

Concrete shall be transported as quickly as possibles from mixer to its final position, and in no case shall the time interval between the addition of water and placing exceed 30 minutes.

All placing and compacting shall be carried out by experienced workmen and under the the direct supervision of a competent staff.

Gangways for concrete transporter and foot traffic, shall not be permitted  to bear on the fixed reinforcement. They will be supported clear of the reinforcement on chairs or stools designed for the purpose.

Concrete shall remain in sufficiently plastic condition for adequate compaction when placed. Concrete shall be placed as near as possible to its final position, and shall be placed square against the forms. Concrete shall not be moved into position by means of vibrators.

In walls, the concrete shall be placed in approximately horizontal layers. The concrete shall be placed in one continuous operation, rising uniformly in the formwork at a rate not less tha 2.00m per hour. The concrete shall not be handled in any manner that may cause segregation.

A competent steel fixer shall be in continuous attendance during concreting to adjust and correct the position of any reinforcement which may be displaced.

Concreting operation must cease during rain and the Engineer will decide whether work can be done under light drizzle. The Contractor shall carry ut concreting in such sequence as to minimize the effects on the permanent works of temporary stoppage of concreting due to rain. The Contractor shall also provide adequate cover and protection from inclement weather for permanent works.

Epoxy Textured Coating is applied to be slip resistant coating for concrete and cement screeds. This flooring system can be subjected to normal up to medium heavy mechanical and chemical loading. It is designed for production areas, storage and assembly areas or exhibition areas etc.

Advantages of textured coating are slip resistant, good abrasion resistant, good chemical resistance, easy to clean etc.

This method statement is specified for the epoxy flooring system using Sikafloor 264 and other supporting products.

System build-up  for Sikafloor 264  textured coating

1. Primer (2 solutions, depend of the substrate porosity)

a. Less absorbent/dense substrate Primer 1 / 2 x Sikafloor 2420 + 25 % Thinner C  0.1 – 0.2 kg/m²

b. Normal substrate / Porous substrate Primer*   1 x Sikafloor 161  0.3 – 0.5 kg/m²

2.If needed, moisture barrier (if > 4% pbw moisture content into the substrate)

Epocem Primer ( Primer coat)  1 x Epocem Primer  Approximately 0.15 Kg/m²

Moisture barrier (Body coat)  1 x Sikafloor 81 Epocem (2 mm minimum):  2.1 kg/m²/mm

3.Roller and textured coat

1^st coat  Roller coating 1 X Sikafloor 264:  0.25 – 0.3 kg/m²

2^nd coat  Textured coating 1 X Sikafloor264 + Extender T (2%): 0.4 – 0.5 kg/m²  + 0.008-0.010 kg/m²

(Approx. system thickness from 0.45 to 0.5 mm, without moisture barrier)

Note: In cases of limited exposure and normal absorbent concrete substrates priming is not necessary.

Substrate preparation

The concrete substrate must be sound and of sufficient compressive strength (minimum 25 N/mm2) with a minimum pull off strength of 1.5 N/mm2

Prior to application, confirm substrate moisture content, relative humidity and dew point. Moisture content must  be  not  greater than 4%.

Test method:  Sika Tramex meter  or  Standard  Test method for indication of moisture in concrete by plastic sheet method according to ASTM D4263

Concrete  substrates  must  be  prepared  mechanically  using  abrasive  blast  cleaning  or  scarifying equipment to remove cement laitance and achieve an open textured surface.  Weak concrete must be  removed and  surface defects  such as blowholes and voids must be  fully exposed. All dust, loose and friable material must be completely removed from all surfaces before application of the product, preferably by brush and/or vacuum. If in doubt, apply a test area first.

Application of Epoxy Textured Coating  using Sikafloor 264 system:

Primer coat: Make sure that a continuous, pore free coat covers the substrate. If necessary, apply two priming coats.

Seal coat: Sikafloor 264 as coating can be applied by short-piled roller for the 1^st layer. The 2ndlayer is applied back-rolled (crosswise) with a textured roller.

Civil engineers design and supervise the construction of roads, buildings, airports, tunnels, dams, bridges, and water supply and sewage systems. They must consider many factors in the design process, from the construction costs and expected lifetime of a project to government regulations and potential environmental hazards such as earthquakes and hurricanes. Civil engineering, considered one of the oldest engineering disciplines, encompasses many specialties.

The major ones are structural, water resources, construction, environmental, transportation, and geotechnical engineering. Many civil engineers hold supervisory or administrative positions, from supervisor of a construction site to city engineer. Others may work in design, construction, research, and teaching (Occupational statement fromUS Department of Labor)

A civil engineer is a person who practices civil engineering, one of the many engineering professions. Originally a civil worked on public works projects and was contrasted with the engineer military engineer, who worked on armaments and defenses. Over time, various branches of engineering have become recognized as distinct from civil engineering, including chemical engineering, mechanical engineering, and electrical engineering, while much of military engineering has been absorbed by civil engineering (Wikipedia)

Civil engineers design things. These might be roads, buildings, airports, tunnels, dams, bridges, or water supply and sewage systems. They must consider many factors in their designs, from the costs to making sure the structure will stay intact during bad weather. This is one of the oldest types of engineering.

Many civil engineers manage people and projects. A civil engineer may oversee a construction site or be a city engineer. Others may work in design, construction, research, and teaching. There are many specialties within civil engineering, such as structural, construction, environment, and transportation.

Civil engineers usually work in areas that are industry and business centers. Often they work at construction sites. Sometimes they work in places that are far away from cities. Most engineers work a 40-hour week. Some are required to travel.

]]> http://civilengineerlink.com/what-is-a-civil-engineer/feed/ 4 http://civilengineerlink.com/concrete-coating-hydro-power-plants/ http://civilengineerlink.com/concrete-coating-hydro-power-plants/#comments Thu, 01 Jul 2010 07:12:46 +0000 Civil Engineer http://civilengineerlink.com/?p=525

In the various and complex building structures composing a hydro power plant project, it is not unusual that concrete (or steel) must be coated.

Concrete must be coated in order to be waterproof or to provide high abrasive surface resistance. In certain case coating must be decorative coating.

For instance, Inertol Poxitar F – 2 components epoxy/coal tar base, will be used to protect either steel or concrete against abrasion flow (e.g. penstock lining).

Concrete or steel that need a protective coating suitable for contact with drinking water should be coated with SikaTop Seal 107 – 2 components flexible waterproofing slurry will be used as an internal or external waterproofing coating.

Powerhouse facilities as building will require a decorative and efficient flooring system.
Owing to its Sikafloor range, Sika is offering suitable flooring system for the following requirement for instance :

• Abrasion resistance (low – medium – high)
• Chemical resistance (low – medium – high)
• Impact resistance
• Antistatic flooring

Products range for protective coating and flooring coating:

Selection and Design of the Industrial Flooring

What causes the deterioration must be taken into account:

• Mechanical: Abrasion/ Erosion/ Impact/ Vibration
• Physical: Temperature/Humidity/ Water/Frost
• Chemical and Biological: Acids/ Oil/  Grease/ Gas/ Micro-organisms

and its intended used:

• Design: Assessment/ Standards/ Calculation/ Measurement/ Details
• Materials: Composition/ Properties/ Quality/ Durability/ Maintenance
• Labour: Experience/ Care/ Quality Control/ Concern

Factors to take into account for the design and construction of industrial floorings

• Ground conditions: strength, water table, type of soil, sub grade
• Type of slab: ground supported or pile supported or suspended slab
• Traffic and other loading requirements: frequency, duty and free or define traffic
• Method of construction: in stages/bays, in strips or in large pour
• Concrete mix design (especially critical w/c ratio):
  • The concrete deliveries must be of consistent quality. Otherwise negative impact on wetting/dry-shake workability/final finish performance (abrasion) and appearance.
  • A concrete slump in the range 75 to 110mm will normally give best results. This will depend on the placing method (manual/mechanical)
  • Do not use concrete where cement has partly been replaced with fly ash. This makes the mix is too sticky for proper dry-shake placing and workability, and will cause blisters during power-floating. Blisters are also caused by too early floatng or with inadequate tools (steel instead of wood or magnesium)
• Slab thickness and reinforcement requirements: steel fibers or re-bars, other fiber types and combination
• Jointless slabs or join spacing and positioning: Pinwheel contraction joint to separate columns. Design of joints according to traffic requirements. Less joints mean less cost (need for slab connectors) and less chance of damage and wear.
• Surface smoothness and flatness: TR34, ACI 117, DIN 15185, ASTM E 1155
• Durability and special operational conditions
• Lighting: Use of lighter colour dryshakes helps reduce cost.

Conclusion:

Again, never blame the product first. Failure can be due to the product, but are minimal and are mostly detected at QC:

• Malfunctions in equipment: Adding too much or too little particular raw material
• Human error

A proper design ensure the success of industrial flooring. Keep reading the  instruction on cleaning of Industrial floor.

Shotcrete Acceptance Criteria

Final acceptance of shotcrete will be based on compressive strength  results obtained from cores of test panels and shotcrete placement. In addition, all accepted shotcrete shall conform to the Execution and Material requirements set forth in this and other applicable sections, and initial and final set requirements.

Compressive strength acceptance of shotcrete

The average compressive strength of cores taken from the structure and test panels, representing a shift or ot more than 50 cubic meters of shotcrete (tested at 8 hours, 24 hours, 3 days, 7 days and 28 days) shall equal or exceed  the minimum strength specified, with no individual core less than 85 percent of the required minimum compressive strength.

Test panel cores

For every shift or every 50 cubic meters of shotcrete placement, at lest one sample panel fabricated in accordance with ASTM C1140 shall be made. From each set of panels core specimens shall be taken as follows:

• Three core fore testing at 8 hours
• Three core fore testing at 24 hours
• Three core fore testing at 3 days
• Three core fore testing at 7 days
• Three core fore testing at 28 days

Core testing shall be made in accordance with ASTM C42, core samples shall be taken perpendicular to test panels in accordance with requirements of ASTM C1140.

Shotcrete structure cores

For every shift or every 50 cubic meters of shotcrete placement, at lest one sample panel fabricated in accordance with ASTM C1140 shall be made. From each set of panels core specimens shall be taken as follows:

• Three core fore testing at 8 hours
• Three core fore testing at 24 hours
• Three core fore testing at 3 days
• Three core fore testing at 7 days
• Three core fore testing at 28 days

Core testing shall be made in accordance with ASTM C42

Initial and Final Setting

During the course of the work the Engineer may at any time direct the Contractor to test materials for initial and final set for conformance with requirements. Such testing shall be in accordance with the specified testing method.

Further information on Shotcrete Curing and Protection

Basically concrete mixture is composed of cement, aggregates, admixtures and water. This article will discuss on cement in concrete.

Portland cement is the most common type of cement in general use. It is basic ingredient of concrete, mortar and plaster. English engineer Joseph Aspdin patented Portland cement in 1824.

It is made by heating limestone (calcium) with clay until all water molecules are gone (calcination) and finely grinding it. This product (called clinker) is mixed with a source of sulfate (most commonly gypsum) which regulates setting. The strength of cement is related to its fineness or specific surface. Cement is a mixture of oxides of calcium, silicon and aluminium.

When portland cement and similar materials are mixed with water, the resulting powder will become a hydrated solid over time.

The water molecules react with the cement, creating crystalline structures, which grow out from the cement molecules and bond the other components  together, eventually creating a stone-like material.

The basic of the chemistry of cement are mostly understood, but the variations in the raw materials make 100% control of industrial process nearly impossible.

For these reasons, frequent controls are required for the production of concrete and admixture have to be adjusted to the  varying raw materials used in the concrete, depending on the source.

The most common types of portland cement are:

Type I: Portland Cement – General use

Type II: Composite Cement (>65% portland) – Moderate resistance to sulphates

Type III: Blast furnace cement – High early strength

Type IV: Pozzolan cement -Low hydration heat

Type V: Composite cement- High resistance to sulfates.

Again, concrete is a construction material that consists of cement (commonly portland cement), aggregate (generally gravel and sand), water and admixture. Concrete solidifies and hardens after mixing and placement due to a chemical process known as hydration.

]]> http://civilengineerlink.com/cement-concrete/feed/ 0 http://civilengineerlink.com/history-solar-energy/ http://civilengineerlink.com/history-solar-energy/#comments Wed, 26 May 2010 08:17:42 +0000 Civil Engineer http://civilengineerlink.com/?p=495

Humans have harnessed the power of the sun for millennia. In the fifth century B.C., the Greeks took advantage of passive solar energy by designing their homes to capture the sun’s heat during the winter. Later, the Romans improved on solar architecture by covering south-facing windows with clear materials such as mica or glass, preventing the escape of solar heat captured during the day.

In the 1760s, Horace de Saussure built an insulated rectangular box with a glass cover that became the prototype for solar collectors used to heat water. The first commercial solar water heaters were sold in the U.S. in the late 1890s, and such devices continue to be used for pool and other water heating.

In the late 19th century, inventors and entrepreneurs in Europe and the U.S. developed solar energy technology that would form the basis of modern designs. Among the best known of these inventors are August Mouchet and William Adams. Mouchet constructed the first solar-powered steam engine. William Adams used mirrors and the sun to power a steam engine, a technology now used in solarpower towers. He also discovered that the element selenium produces electricity when exposed to light.

In 1954, three scientists at Bell Labs developed the first commercial photovoltaic (PV) cells, panels of which were capable of converting sunlight into enough energy to power electrical equipment. PV cells powered satellites and space capsules in the 1960s, and continue to be used for space projects.

In the 1970s, advances in solar cell design brought prices down and led to their use in domestic and industrial applications. PV cells began to power lighthouses, railroad crossings and off shore gas and oil rigs. In 1977, solar energy received another boost when the U.S. Department of Energy created the Solar Energy Research Institute. It was subsequently renamed as the National Renewable Energy Laboratory (NREL), and its scope expanded to include research on other renewable energy sources. NREL continues to research and develop solar energy technology.

In the last 20 years, solar energy has made further in roads and now is used extensively in off -grid and remote power applications such as data monitoring and communications, well pumping and rural power supply, and in small-scale applications such as calculators and wristwatches. But solar power has not yet achieved its potential to become a major contributor to world electrical grids.

Private and government research and development in solar energy technologies have led to continuing innovation over the last 30 years. The conversion efficiency of PV cells — that is, the percentage of sunlight hitting the surface of the cell that is converted to electricity — continues to improve.

Commercially available cells now on the market have efficiencies approaching 20 percent.

Cell efficiencies achieved in research laboratories recent surpassed 40 percent. The worldwide PV market has grown by an average of 30 percent annually for the past 15 years, an increase that has improved economies of scale for manufacturers.

As a result, the cost of electricity generated from PV modules has fallen significantly, from more than 45 cents per kilowatt hour (kWh) in 1990 to about 23 cents per kWh in 2006.

In 2006 and 2007, a shortage of silicon (a primary component of crystalline silicon PV systems) temporarily increased PV module costs, but prices are expected to decline once again between 2008 and 2011, when silicon plants currently under construction are completed.

Scope of work

Application of curing compound onto fresh concrete surface

General purpose of curing compounds for fresh concrete

• To form a film covering the surface of concrete to prevent premature water loss due to evaporation

• Allow the concrete to cure with complete hydration of cement and achieve maximum properties.

Materials available for concrete curing

ANTISOL E

• Emulsified paraffin based curing compound.
• Ready to use
• Very effective particularly on horizontal surfaces even subject to windy and sunny conditions
• Shall be removed prior application of subsequent surface treatment

ANTISOL S

• Aqueous concrete curing silicate solution
• Ready to use
• Particularly used for the treatment of vertical concrete surface
• Does not impair adhesion of subsequent treatments to concrete surface (when applied within recommended dosage rates)

Compound  Application procedure

Please consult our product technical data sheets for full application recommendations.

• Applicable by spray.
• Typical Consumption rate: 0.2 to 0.25 litre of Antisol E or Antisol S per m2.
• Protect fresh coat from rain

I. TYPE OF DEFECTS
Type of defects: Non-structural and movable cracks.

II. SURFACE PREPARATION

• The cracks and adjacent substrate must be clean, sound and free of contaminated material. Remove dust, laitance, grease, curing compounds and other bond inhibiting materials from surface by mechanical means.

• “V” notch the surface of crack with mechanical router or hand chipping to maximum width of 8 mm and to minimum depth of 8 mm.

III. SEALING

• Material: Sikaflex Construction (J)

• To ensure the cleanliness of the substrate, use high pressure air compressor to clean the substrate from any dust and loose particle.

• In case there is possibility of the sealant adheres to the bottom of the joints then a backer rod with diameter min. 20 % bigger than the width of joint shall be applied.

• The application of Sika Primer 3 is recommended

• Gun Sikaflex Construction (J) into prepared crack to a minimum depth of 8 mm.

• Allow sealant to cure for at least 24 hours before the application of elastic water dispersed paint.

The number of “green building”, as the ecologically designed building are called in the USA, is increasing significantly worldwide. These buildings conform to very high ecological standards, save energy and preserve the environment. Environmentally-friendly, sustainable building starts with the planning. It means a resource-preserving, healthy and energy-saving way of building. Professional building implementation as well as carefully of building products and building systems is gaining in important.

In order to achieve higher , more constant thermal insulation capacity of facade panels of buildings, the Thermomass building system was developed in the USA. Thermomass is a powerful, long-life construction system for thermally insulated concrete sandwich elements. The system is distinguished by two main components: connectors made from a glass-fiber reinforced synthetic resin, which connect the inner ad outer concrete layers, and between them a layer of thermal insulation made of XPS or EPS hard foam panels. Together with the outstanding performance of the thermally insulating panels, the Thermomass connectors are extremely efficient in preventing thermal bridges in the sandwich elements.

A new further development of the Thermomass connector also enables the manufacture of precast walls with integrated thermal insulation and the subsequent addition of in-situ concrete. This new system is called Megablock. The special feature of this system is that the integrated insulation is only punctured by the glass fibre reinforced synthetic resin connectors. These connect the inner and outer wall shell to each other and, in a built condition, absorb the fresh concrete pressure of the additional in-situ concrete. For  the dissipation of building loads,  the added in-situ concrete interacts with the inner load bearing shell. In this system too, the Thermomass connectors prevent thermal bridges efficiently and permanently.

Together with other already well-known products ad materials, the Thermomass system supports sustainable green building. The high cold and warm insulation values of the sandwich elements with the Thermomass connecting system provide for significant energy savings and preserve natural resources. Due to the high degree of industrial prefabrication, the building  are quickly usable. The simple mounting of the sandwich elements on the building site provides for comparatively little environmental pollution. Green building is a trendsetting way  to build in Germany and throughout the world.

]]> http://civilengineerlink.com/ecological-construction-system/feed/ 0 http://civilengineerlink.com/scc-compacting-concrete/ http://civilengineerlink.com/scc-compacting-concrete/#comments Mon, 22 Mar 2010 13:30:01 +0000 Civil Engineer http://civilengineerlink.com/?p=466

SCC Definition:

Self Compacting Concrete is an innovative concrete that does not require vibration for placing and compaction. It is able to flow under its own weight, completely filling formwork and achieving full compaction, even in the presence of congested reinforcement.

The hardened concrete is dense, homogeneous and has the same engineering properties and durability as traditional vibrated concrete.

SCC Potentials beyond conventional concrete:

• Improved efficiency
• Use with close meshed reinforcement
• For complex geometric shapes
• For slender components
• Generally where compaction is difficult
• Fast installation rates
• Noise reduction
• Reduced damage to health

How is this performance achieved?

• This concrete is extremely soft and flowable.
• SCC remains homogeneous and cohesive without segregation, separation or bleeding
• With the application of polycarboxylate based superplasticizers an outstanding fluidity at lowest water/cement ratios could be achieved.
• Special mix design considerations due to its high content of fines (≤ 0,125mm) and adapted grading curve
• Special high performance superplasticizers are necessary to produce SCC, in order to ensure a fluid concrete with controlled workability, a very high water reduction and a stable and cohesive concrete.

SCC Placing:

• Same procedure as with normal concrete, but faster and with less manpower
• SCC would not be freely discharged from a great height
• Conventional formwork can be used
• Pressure of fresh concrete on formwork is slightly higher than with conventional concrete
• If the concrete surface has to satisfy high aesthetic demands, the SCC should be placed under pressure, i.e. via a filling socket from below or by pipes which reach beneath the concrete surface level

Scope of work:
Construction joint sealing with hydrophilic rubber profile bonded to concrete with water swelling polyurethane based adhesive

I. SIKA MATERIALS
Sika Hydrotite CJ type:
• Hydrophilic rubber sealing profile
• Made of high durable material which can not be washed out by water.
• Specific shape profile which allow optimal expansion
• Treated with delay coating to preserve it from early expansion when in contact with freshly poured concrete
• Easy to place Sika Swell S2
• Extrudible water swelling material
• Use for bonding Sika Hydrotite CJ Type to concrete surface.

II. CONCRETE SURFACE PREPARATION

• Concrete surface shall be sound and solid, free of laitance, oil, dust, loose and friable particles
• Concrete shall be dry prior application of Sika Swell S2 material.

III. APPLICATION PROCEDURE

• Use Sika Swell S2 applied in thin bed to glue Sika Hydrotite CJ type to concrete substrate (consumption of Sika Swell S2 shall be approx. 30-50 ml per meter of Sika Hydrotite  CJ type depending on concrete roughness)
• Apply Sika Hydrotite CJ type to the still freshly applied Sika Swell S2.

• In meeting point (edge), butt joint the Sika Hydrotite CJ type and covered with Sika Swell  S2
• It is recommended to wait for min. 4 hours until Sika Swell S2 has sufficiently cured before to pour the new concrete. Meanwhile, the concrete formwork can be placed.

The minimum thickness of concrete around Sika Hydrotite CJ type should be at least 100 mm on each side.

Please Consult technical data sheet for further information.