High performance concrete (HPC) has been defined as concrete that possesses high workability, high strength and high durability.  ACI (American Concrete Institute) has defined HPC  as a concrete in which certain characteristics are developed for a particular application and  environment. Under the ACI definition durability is optional and this has led to a number of HPC structures, which should theoretically have had very long services lives, exhibiting durability associated distress early in their lives. ACI also defines a high-strength concrete as concrete that has a specified compressive strength for design of 6,000 psi (41 MPa) or greater.

High Performance Concrete (HPC) is a concrete made with appropriate materials combined according to a selected mix design; properly mixed, transported, placed, consolidated and cured so that the resulting concrete will give excellent performance in the structure in which it is placed, in the environment to which it is exposed and with the loads to which it will be subject for its design life. Mix proportions for high-performance concrete (HPC) are influenced by many factors, including specified performance properties, locally available materials, local experience, personal preferences, and cost. With today’s technology, there are many products available for use in concrete to enhance its properties.

The primary application for HPC have been structures requiring long service lives such as oil drilling platform, long span bridges and parking structures. HPC still requires good construction practice and good curing to deliver high performance.

]]> http://civilengineersite.com/hpc-high-performance-concrete/feed/ 0 http://civilengineersite.com/civil-engineering-degree/ http://civilengineersite.com/civil-engineering-degree/#comments Sat, 24 Jul 2010 04:00:25 +0000 admin http://civilengineersite.com/?p=3

A civil engineer specializes in city building. This includes bridges, water distribution, infrastructure, and roads. In order to get a civil engineering degree, you will need to complete four requirements: find a school, meet admission requirements, pay tuition fees, and complete the coursework. All of these items are required to obtain a civil engineering degree.

Civil engineers typically work in teams with other professionals. They are responsible for taking designs, plans, and schematics and converting them into actual structures. This type of engineering job often requires travel for extended periods of time. Many key projects are located in other cities or countries.

A civil engineering degree can be obtained from both online or traditional universities. It is important to explore the different programs available in the engineering faculty to find the right discipline for you. Avoid schools that offer only one or two different types of engineering. The greater the breadth of courses available to you, the more enriched your education will be.

The admission requirements for a civil engineering degree vary, but typically require high school credits in calculus, algebra, physics, English, and technology.These programs are very competitive, requiring high marks to gain admission to the best programs. People who enjoy building structures and design are most likely to enjoy civil engineering.

Engineering is a professional program, and so the fees are sometimes significantly higher than a Bachelor of Arts and Sciences degree. It pays to explore scholarships and grants available to students based on marks or other requirements. Student jobs available on campus often pay significantly more than market rates. These jobs are considered part of the overall student aid package.

The first year of an engineering program is usually the same for all students, regardless of discipline. The courses are typically English, calculus, physics, structure, design, math, and technology. In the second year, more specialization in course offering becomes available, and the students begin to separate.

In the third and fourth years, the courses are focused on details of each field. Engineering programs have very heavy course loads, with a significant time commitment required. Many schools counsel students not to accept part time jobs or have outside commitments, as they will not have the time to follow through.

Upon successful completion, students apply for a professional engineering designation or P. Eng. The Professional Engineer Association of America manages this designation. They are responsible for evaluating courses, offering specific programs and running the examination and certification process.

Concrete materials and concrete applications have changed and improved in the last 100 years.  Whilst concrete admixtures have been around for many years, there has been an extensive amount of development of new admixtures in recent years. It is probable that almost all concrete used around the world today contains some types of admixtures.  Admixtures added to the concrete can modify its properties on both the fresh and hardened stages, but are used primarily to modify the properties of fresh or plastic concrete.

Admixture s can be employed to entrain air for free-thaw resistance, to accelerate or retard setting time, to control  strength development, to achieve shrinkage compensation and to improve workability. Most of unwanted effects of early admixtures have been overcome (such as the retarding effect of early plasticizers) so that modern admixture do not pacl “unexpected surprises”.

The most dramatic development have been in the area of superplasticizers or high range water reducers. These products now allow high level of water reduction without a loss in workability. Whilst early superplasticizers had a limited time over which they were effective, modern superplasticisers allow sufficient control for the setting in, for example, a large pour, until all the concrete has been placed.

Care should be taken when designing concrete mixes containing admixtures to assess sensitivity to changes of properties with changes in other ingredients and mix designs should be done on the specific materials that will be used.

Indeed in order to specify the proper repair solution we must know if we are in front of mechanical, chemical, physical damage or even carbonation damage. Proper assessment survey and diagnosis of damage must be extended before concrete repairing.

Basically, in this field Sika is proposing either additive promoter for mortar, like the well know Sika Latex, or ready to use pre-dosed mortar. Mortar could be cementitious or epoxy based.
For instance for mechanical damage the Sika MonoTop range – one component polymer modified cementitious mortar offers all variety of products covering from bonding agent to thick repair mortar.

• Chemical damage (like Alkali aggregate reaction) could be fixed with the Sikadur epoxy range mortar.

• Structural repair (crack) will be injected with Sikadur 752 – 2 component epoxy resin low viscosity.
• SikaGrout range – cementitious pumpable grout could be used for surface repair (honeycomb) for instance.

Products range summary for repair

Underground construction includes two types:

• Conventional: Means drilling and blasting
• Mechnical: TBM  (tunnel-Boring-Machine), Roadheader, excavator: Special Excavation methods in soft ground, in presence of water.

The TBM (Tunnel Drilling Machine) consists of the following elements: cutterhead with shield tubbing segment erector, backup trailer with hydraulic units and filtration plant, allow backup trailer with the monorail device to allow the unhindered construction of the temporary according road. The backup trailer consists of the flush ventilator, the rock bunkers and the tubbing and material yard. Finally is the back-up trailer with airduct magazine and cablebobine.

The advancement is split into 3 phases:

Phase 1: The shield will be pressed by means of hydraulic cylinders to the cutterhead. The cutterhead is equipped with concentric disks, to allow to split rock.

Phase 2: After the incremental advance the pressure ring will be removed towards cutterhead to have free space in the area of the shield to install the tubbing ring.

Phase 3: Secured by the shield the tubbing ring ring will be placed by means of an erection.

Possible erection phases:

1. Erection of the right bottom element
2. Erection of the left bottom element
3. Erection of the right sidewall element and support with roller.
4. Erection of the left sidewall element and support with roller,
5. Erection of te vault element and support with erector.
6. Spreading of the bottom elements with hydraulic cylinders and insertion of the key element.

Initial Curing

Immediately after finishing, shotcrete in tunnel areas shall be kept continuously moist for at least 3 days. In non tunnel application shotcrete shall be cured using any method as described below. One of the following materials or methods shall be used:

• Ponding or continuous sprinkling.
• Absorptive mat or fabric, sand, or other covering kept continuously wet.
• Curing compound. A coverage application requirement of 2.5 square meters per liter (100 square feet per gallon) or twice the manufacturer’s requirement, whichever is less. Curing compound shall not be used on any surface against which additional shotcrete or other cementitious finishing materials are to be bonded unless positive measure, such as sand blasting, are taken to completely remove curing compound prior to the application of such additional materials.

Final curing

Additional curing shall be provided immediately following the initial curing and before the shotcrete has dried. One of the following materials or methods shall be used:

• Continue the method used in initial curing
• Application of impervious sheet material that conforms to ASTM C171

Formed Surface

If form are to be removed during curing period, one of the curing materials or metheds listed in paragraph initial curing shall be used immediately. Such curing shall be continued for the remainder of the curing period.

Duration of curing

Curing shall be continued for the first 7 days after shotcreting or untill the specified compressive strength of the in-place shotcrete as determined by specimens obtained and tested in accordance with ASTM C42 is achieved.

Waver and/or modification of curing requirements

Within the interior of a tunnel, curing procedures and requirements may be waved or modified if the tunnel interior environment induces a moist curing condition. The contractor shall be responsible for evaluating conditions and proposing any modifications or waver for the consideration of the engineer. Approval of curing modifications and/or waver of curing requirements be the engineer, shall not relieve the contractor or his responsibility for  the proper curing of shotcrete.

Introduction to Industrial Construction

Industrial buildings consist of many different structures with their own specific function and specification. This in return will demand different requirements and of course specific system for each of the structures.

Warehouse for example, is exposed to heavy traffic such as forklift and this will demand a high abrasion resistance floor. While food and beverage production area may need a hygienic and easy-to-clean floor system.

Sika with its knowledge and experience is in best possible position to provide a total project based solution to its customers.

Below its some examples of Sika’s products involvement in industrial building projects.

1. Concrete works

Base on concrete requirements (workability, strength) a wide range of admixture (mainly Sikament and Sika Viscocrete range) is available for producing high quality and durable concrete. Use of silicafume based material, Sikacrete PP1 is also common to reduce concrete permeability, increase strength and resistance to aggressive environment (chlorides, sulfates). Following good concrete practice and use of reliable formwork release agent (Separol) and curing compound (Antisol) shall give the best possible concrete work quality.

2. Industrial Floor

Floor of a factory & warehouse has a key factor in ensuring the convenience of the production process. Bad condition floor will cause the disruption in productivity rate and furthermore, in some cases this will adversely affect the quality of goods produced.

Heavy traffic floor such as in warehouse or parking lot will require a high abrasion and mechanical resistance floor and this is best achieved by using Sikafloor Chapdur, non-metallic floor hardener, finished by power-float. For high abrasion requirement, Sikafloor 2 Syntop, dry shake floor hardener is a reliable solution. Pharmaceutical and food production area demand a seamless, easy-to-clean flooring system and sometimes require certain degree of chemical resistance.

Epoxy resin based flooring system has been used widely for this purpose where the type and thickness of epoxy layer are very dependant on the mechanical/chemical exposure and also the design life of the floor.

Sikafloor 2530-W New, coloured, 2-part epoxy dispersion, has been widely used in numerous projects in Vietnam. This epoxy coating produces a smooth, tough finish appearance and very suitable for use in food industry and light industry factory. If anti-skid appearance is required like in wet area such as kitchen, toilet and liquid contaminated floor then Sikafloor 7530 or Sikafloor 261 textured / screed system can be applied.

Besides these two products, Sika also provides various others flooring systems for other flooring requirements such as anti-static, high chemical and mechanical resistance floor.

3. Machine and Column Base Plate Grouting

To reach maximum effective bearing area, column base plate shall be grouted using non-shrink flowable grout such as SikaGrout 214-11. For heavy machine base plate, usually it is required to use high vibration resistant and high ultimate strength grout, Sikadur 42 MP, a 3-component castable epoxy grout, is suitable for this purpose.

Either the wet-mix process or the dry-mix process may be used to produce shotcrete.

Dry mix process

Batching and Mixing

Aggregate and cementitious materials shall be batched by mass. Equipment for batching by mass shall be capable of the accuracy specified in ASTM C94. The mixing equipment shall be capable of thoroughly mixing materials in sufficient quantity to maintain placing continuity and be capable of discharging all mixed material without any carryover from one batch to the next.

Delivery Equipment

The equipment shall be  capable of discharge the aggregate-cement mixture into the delivery hose and delivering a continuous smooth stream of uniformly mixed material to the discharge nozzle. The discharge nozzle shall be equipped with a manually operated water injection system (water ring) for directing an even distribution of water through the aggregate-cement mixture. The water valve shall be capable of ready adjustment to vary the quantity of water and shall be convenient to the nozzleman.  The water pressure at the discharge nozzle shall be sufficiently greater than the operation air pressure to ensure that the water is completely mixed with the other materials. If the line water is inadequate, a water pump shall be introduced into the line. The water pressure shall be steady (non-pulsating). The delivery equipment shall be thoroughly cleaned at the end of each shift. Equipment parts, especially the nozzle liner and water ring shall be regularly inspected and replaced  as required.

Wet mix process

Batching and mixing

Batching and mixing shall be accomplished in accordance with the applicable provisions of ASTM C94. The mixing equipment shall be  capable of thoroughly mixing the specified materials in sufficient quantity to maintain continouous placing. Ready-mix shotcrete complying with ASTM C94 may be used.

Delivery Equipment

The equipment shall be capable of delivering the premixed materials accurately, uniformly and continuously through the delivery hose. Recommendations of the equipment manufacturer shall be followed on the type and size of nozzle to be used and on cleaning, inspection, and maintenance of the equipment.

Scope of work:
Injection of dead cracks with low viscosity 2 components epoxy resin in order to repair the concrete structures.

PREPARATION FOR INJECTION WORK

• 14mm holes must be drilled along the crack path between 200 – 300 mm centres. The holes must be deep enough to receive the ‘metal pipe sleeves’ (approx. 20mm)

• Insert Sika ‘metal pipe sleeves’ into all the holes and epoxy into position using Sikadur 731

• Clean the concrete surface adjacent to the crack with a wire brush or sandpaper.

• Wipe down the concrete with a clean rag to remove any dust and loosely adhering particles.

• The cleaned surface is then sealed using Sikadur 731 applied by a spatula or trowel.

CRACK INJECTION

• Following the curing of the Sikadur 731 (minimum of 12 hours at 30oC) the epoxy injection can commence.

• Starting from one side or the lowest point of the crack a Sika ‘nipple’ is screwed into the first pipe sleeve and Sikadur 752 injected into the crack until the epoxy is seen to ooze from the adjacent pipe sleeve, this pipe sleeve is then sealed with a nipple, continue to inject the current port until refusal (epoxy resin can not be injected more) and then start the injection of the adjacent port and so on. This procedure is continued in the sequence indicated until all have been completed.

• Beginning at the first nipple filled, the nipple is removed and checked for incomplete filling. If any of the pipe sleeves are found to be incompletely filled, the injection of Sikadur 752 must recommence from the previous pipe sleeve to the one found incomplete until full and the nipple replaced. This checking process is continued (without interruption) along the crack until all have been checked.

• After a curing time of 12 hours the sleeve and nipples are trimmed off with an angle grinder or other suitable equipment.

1. Introduction to light weight concrete

Lightweight concrete is mainly used as back-filling material. When talking about lightweight concrete, we refer to a concrete of which its specific gravity (density) is much more lower than normal concrete.

Basically normal concrete: 2.35 – 2.42 ton/m3 while lightweight concrete 0.80-1.40 t/m3.

Therefore final strength is not issue. Expected final strength would be usually lower 5 MPa at 28 dasy as such concrete contained of lot of air entrained.

The strength would be affected by type of lightweight aggregate to used.

2. Production Principle

Basically there are 2 ways to produce light weight concrete.

a. Cement/ Water/Sand/lightweight aggregate/ chemical additives (admixtures)

b. Cement/ Water/ Sand/ Chemical additives

By lightweight aggregate we can consider polystyrene balls, expanded clay for instance.  Chemical additives, we mainly means special air entrained agent such as Sika Lightcrete 1-500VP. This admixture ca entrained safely up to 30% of air entrained into the mix.

As per the use of the special air entrained, usually, the mix is batched for a designed volume the air entrained is measured in order to determine final volume of the concrete batched. Indeed in term of concrete production it is important to know about about which volume we are talking, we are referring to:

For instance: Expected air entrained 30%

Volume of fresh batch 1000 liters -> initial ar development 30% –> final hard volume ~1.3 m3

]]> http://civilengineersite.com/lightweight-concrete-production/feed/ 0 http://civilengineersite.com/concrete-work-marine-structure-projects/ http://civilengineersite.com/concrete-work-marine-structure-projects/#comments Sat, 15 May 2010 09:37:14 +0000 Civil Engineer http://civilengineersite.com/?p=567

1. Introduction to marine projects:

Marine structures are those structure built on sea or near it, properly designed to withstand internal, external loads and aggressive environmental exposures both physical and chemical in order to prolong service-life.

Reinforced concrete structures as part of marine structure are exposed to severe physical and chemical exposure such as wave impact, sulphate and chloride exposure. In tropical climates, the combination of above deleterious effects may cause severe defects in concrete structure only in very few years.

In order to delay these detrimental effects, high durability, chloride and sulphate resistant concrete become a necessity in constructing marine structure. The use of silica fume  with a high water reducing admixture with retarding effect then become increasingly popular to produce a low permeability concrete and high sulphate resistant concrete.

2. Concrete Work in In Marine Structures

a) Objective:
High strength concrete and durable concrete

b) Design Criteria:
• Sulphate and chloride resistance
• Low W/C ratio (splash & atmospheric zone < 0.40, submerged < 0.45) target 0.3 – 0.38 W/C
• High strength
• Abrasion resistance
• Low permeability
• Durability (High Performance Concrete = HPC)

c) Concrete Production:
• Objectives: Produce high strength concrete (HSC) & durable concrete (HPC)
• Targets: Maximization of concrete density
• Actions: Adherence to good construction practices

d) Concrete Mix Design:
• Performance for both fresh & hardened
• Maintenance – free during design life
• Re-orientation in the usual mixture design concepts and techniques
• Proper selection of material
• High cementing materials
• Use SilicaFume
• Use superplasticizer

e) Concrete Curing:
• For HSC and other concrete structures, proper curing is essential. In order to maintain a satisfactory moisture content and temperature in concrete during its early stages so that desired properties may develop. The strength and durability of concrete will be fully developed only if it is cured.
• Failure to prevent such excessive evaporation, frequently causes plastic shrinkage and loss of strength in the material near the concrete surface.

From Singapore to Chicago or Berlin to Santiago, city planners, architects and civil engineers over the world are turning to green roof systems to curb air pollution, decrease energy expense and reduce storm runoff.

High above Chicago’s busy finance district, a rooftop island of greenery stands out among its neighbor buildings. Covered with grasses and plants, the Chicago City Hall is a heaven, especially on a hot day when the temperatures on the black asphalt of neighbors roofs soar.

“You can feel the difference in summer” said Kevin Laberge of the City of Chicago’s Department of Environment. “One roof is big, empty and unused while the other is providing a habitat for wildlife, reducing temperatures and retaining storm water”. Chicago’s City Hall has a green roof, a planted rooftop with system of waterproofing, insulation, and a layer of grow medium used to conserve energy and to contribute to a more healthy environment.

More city planners, architects and civil engineers around the world are turning to green roof technology because it makes environmental and economic sense. Most notably, in Chicago, it saves the city almost $10,000 annually in energy costs. During summer and winter months, the roof exhibits superior insulation properties, requiring as much as 30% less from City Hall’s heating and air-conditioning systems over the last four years.

Additionally, the green roof reduce storm water runoff by absorbing as much as 75% of the rainwater that fall on it, lightening the load of Chicago’s sewer system. Improved air quality and a reduction in noise pollution by as much as 40 decibels as compared to a traditional flat roof are also typical to green roofs like the City Hall’s.

Finally, planted roofs extend their own life by moderation temperture swings that can lead to additional wear and tear on an exposed roof in  climate like Chicago’s. Where the average life expectancy of an exposed roof may be 20 years, green roofs can be expected to las considerably longer.

]]> http://civilengineersite.com/green-roof-systems/feed/ 0 http://civilengineersite.com/rcc-roller-compacted-concrete/ http://civilengineersite.com/rcc-roller-compacted-concrete/#comments Mon, 22 Mar 2010 10:33:57 +0000 Civil Engineer http://civilengineersite.com/?p=553

What is RCC?

RCC Definition: ACI 116 defines Roller Compacted Concrete as “concrete compacted by roller compaction”; concrete that, in its unhardened state, will support a (vibratory) roller while being compacted.
RCC is usually mixed using high-capacity continuous mixing or batching equipment, delivered with trucks or conveyors, and spread with one or more bulldozers in layers (also called lifts) prior to compaction.

RCC is used mainly for:
Dam / Mass concrete (described in ACI 207.5R) and
Pavements (described in ACI 325.10R)
Advantages & Disadvantages of RCC in Dam Structure
The main advantages of RCC are most generally:
Reduced cost and time for construction.
The RCC technology can be implemented rapidly.
RCC may not be appropriate when:
Aggregate material is not reasonably available, the foundation rock is of poor quality or not close to the surface, or where foundation conditions can lead to excessive differential settlement.

RCC in Dam Structure (principle)
The edges of the dam are formed first, by making low concrete walls on the upstream and downstream faces of the dam.

Concrete is then transported by dump trucks to the area between the walls, and spread in layer/lift (typically 300 mm thick) using bulldozers.

Rollers are then driven over the concrete to compact it down.

Mix Design of RCC
RCC is composed of:Cementitious Materials + Coarse Aggregates + Fines Aggregates + Water + Admixtures
But… mix proportioning differs from conventional concrete.
The aggregates grading and paste content are critical parts of mixture.
The paste volume must fill (or nearly fill) aggregates voids.
Design of RCC is extensively guided in ACI 207.5R.

Mix design proportioning methods:
ACI 207.5R (chapter 2.4) and ACI 211.3R extensively described the mix design proportioning methods for no slump concrete applicable for RCC

Because the construction bid evaluation is limited to price and other price-related factors only, the decision procedure of bidder evaluation criteria is much more simpler than other competitive procurement measures relating  more complicated evaluating factors.

Bid Evaluation Procedure  is carried out in 2 steps. After the bid has been determined responsive, the bidder must be determined responsible as follows.

7 bidder evaluation criteria

In order to be determined responsible, a bidder must be successfully evaluated against the 7 following criteria:

1. Performance Schedule.

The bidder must be able to comply with the performance schedule, required or proposed delivery, taking into consideration all existing commercial and governmental business commitments.

2. Financial Resources.

The bidder must have adequate financial resources to perform the contract, or the ability to obtain them.

3. Performance Record.

The bidder must have have a satisfactory performance history, if any. Nevertheless, a prospective contractor shall not be determined responsible or non-responsible solely because of a lack of relevant performance history, except when specified in a standard for special acquisitions.

4. Integrity and Ethics.

The bidder must have a satisfactory record of integrity and business ethics including satisfactory compliance with laws related to taxes, labor and employment, environment, antitrust, and consumer protection.

5. Construction Machinery .

The bidder must have the necessary technical equipment and facilities for production or construction, or ability to obtain them.

6. Organization and Skills.

The bidder must have the necessary organization and skills, experience, accounting and operational controls, and technical skills, or the ability to obtain them.

7. Other Qualification.

The bidder must be otherwise qualified and eligible to receive an award under applicable laws and regulations.

Bidder evaluation criteria is also known as: bidder Responsibility Determination, contractor responsibility determination, vendor responsibility determination, bidder evaluation worksheet.

Construction is an industry method that consists of assembling or building infrastructure. It has many types such as heavy or civil construction, building construction and industrial construction. Construction works are managed by a project managers and supervised by a construction engineers, construction managers, project architects or design engineers.

What is heavy Construction

Heavy or civil construction is a procedure of adding infrastructure to the environment of a building. The builders are usually government agencies both at the local or national level. These also have legal and financial considerations. This project primarily serves the public interest. They are undertaken and supervised by some large private corporations such as power companies, golf courses and whoever oversees the construction of access dams, roads and railroads.

What is Industrial Construction

Industrial construction requires highly specialized skill in construction, planning and design. Holders of this project are normally industrial, for profit or large corporations. This corporation can be found in industries such as chemical, medicine, power generation and petroleum manufacturing.

What is building Construction

Building construction is a process of adding small or big structures to land or real property. Most of the building construction jobs are small reconstructions like adding bathroom or reconstruction of a room. Often times, the titleholder of the property acts as a designer, paymaster and laborer for the entire job. However, all the building construction jobs include several elements in legal consideration, financial and usual design.

Building constructions are procured publicly or privately using different delivery methodologies such as management contracting, hard bid, construction management at risk, design & build bridging, and negotiated price.

Residential construction technologies, resources and practices should conform to the codes of practice and local building authority regulations. The materials used are widely accessible in the market. The common materials used are timber, stone and brick. The cost of construction is on a “per square foot” basis. This is since homes can vary significantly on local site considerations, conditions, and economies of scale.