Curing Concrete in Construction

By Jerzy Z. Zemajtis, Ph.D., PE (WA)*

Curing plays an important role on strength development and durability of concrete. Curing takes place immediately after concrete placing and finishing, and involves maintenance of desired moisture and temperature conditions, both at depth and near the surface, for extended periods of time. Properly cured concrete has an adequate amount of moisture for continued hydration and development of strength, volume stability, resistance to freezing and thawing, and abrasion and scaling resistance.

The length of adequate curing time is dependent on the following factors:

• Type of cementitious materials used
• Mixture proportions
• Specified strength
• Size and shape of concrete member
• Ambient weather conditions
• Future exposure conditions

Slabs on ground (e.g. pavements, sidewalks, parking lots, driveways, floors, canal linings) and structural concrete (e.g. bridge decks, piers, columns, beams, slabs, small footings, cast-in-place walls, retaining walls) require a minimum curing period of seven days for ambient temperatures above 5°C (40°F)¹.
American Concrete Institute (ACI) Committee 301 recommends a minimum curing period corresponding to concrete attaining 70% of the specified compressive strength². The often specified 7-day curing commonly corresponds to approximately 70% of the specified compressive strengths. The 70% strength level can be reached sooner when concrete cures at higher temperatures or when certain cement/admixture combinations are used. Similarly, longer time may be needed for different material combinations and/or lower curing temperatures. For this reason, ACI Committee 308 recommends the following minimum curing periods³:

• ASTM C 150 Type I cement 7 days
• ASTM C 150 Type II cement 10 days
• ASTM C 150 Type III cement 3 days
• ASTM C 150 Type IV or V cement 14 days
• ASTM C 595, C 845, C 1157 cements variable

Effect of curing duration on compressive strength development is presented in Figure 1¹.

Figure 1. Moist Curing Time and Compressive Strength Gain

Higher curing temperatures promote an early strength gain in concrete but may decrease its 28-day strength. Effect of curing temperature on compressive strength development is presented in Figure 2¹.

Figure 2. Effect of Curing Temperature on Compressive Strength

There are three main functions of curing:

1) Maintaining mixing water in concrete during the early hardening process

a. Ponding and immersion
Ponding is typically used to cure flat surfaces on smaller jobs. Care should be taken to maintain curing water temperature at not more than 11°C (20°F) cooler than the concrete to prevent cracking due to thermal stresses.

Immersion is mainly used in the laboratory for curing concrete test specimens.

b. Spraying and fogging
Spraying and fogging are used when the ambient temperatures are well above freezing and the humidity is low. Fogging can minimize plastic shrinkage cracking until the concrete attains final set.

c . Saturated wet coverings
Wet coverings saturated with water should be used after concrete has hardened enough to prevent surface damage. They should be kept constantly wet.

d. Left in Place Forms
Left in place forms usually provide satisfactory protection against moisture loss for formed concrete surfaces. The forms are usually left in place as long as the construction schedule allows. If the forms are made of wood, they should be kept moist, especially during hot, dry weather.

2) Reducing the loss of mixing water from the surface of the concrete

a. Covering concrete with impervious paper or plastic sheets
Impervious paper and plastic sheets can be applied on thoroughly wetted concrete. The concrete surface should be hard enough to prevent surface damage from placement activities.

b. Applying membrane-forming curing compounds
Membrane-forming curing compounds are used to retard or reduce evaporation of moisture from concrete. They can be clear or translucent and white pigmented. White-pigmented compounds are recommended for hot and sunny weather conditions to reflect solar radiation. Curing compounds should be applied immediately after final finishing. Curing compound shall comply with ASTM C309⁴ or ASTM C1315⁵.

3) Accelerating strength gain using heat and additional moisture

a. Live steam
Live steam at atmospheric pressure and high-pressure steam in autoclaves are the two methods of steam curing. Steam temperature for live steam at atmospheric pressure should be kept at about 60°C (140°F) or less until the desired concrete strength is achieved.

b. Heating coils
Heating coils are usually used as embedded elements near the surface of concrete elements. Their purpose is to protect concrete from freezing during cold weather concreting.

c. Electrical heated forms or pads
Electrical heated forms or pads are primarily used by the precast concrete producers.

d. Concrete blankets
Concrete insulation blankets are used to cover and insulate concrete surfaces subjected to freezing temperatures during the curing period. The concrete should be hard enough to prevent surface damage when covering with concrete blankets.

Other forms of curing include internal moist curing with lightweight aggregates or absorbent polymer particles. For mass concrete elements (usually thicker than 3 ft.), a thermal control plan is usually developed to help control thermal stresses. Additional information can be found in ACI Committee 308 report Guide to Curing Concrete³. For specialty concretes, it is recommended to refer to other ACI reports as follows:

• Refractory concrete ACI 547.1R
• Insulating concrete ACI 523.1R
• Expansive cement concrete ACI 223
• Roller-compacted concrete ACI 207.5R
• Architectural concrete ACI 303R
• Shotcrete ACI 506.2
• Fiber-reinforced concrete ACI 544.3R
• Vertical slipform construction ACI 313

Curing in either cold or hot weather requires additional attention. In cold weather, some of the procedures include heated enclosures, evaporation reducers, curing compounds, and insulating blankets. The temperature of fresh concrete shall be above 10°C (50°F). The curing period for cold weather concrete is longer than the standard period due to reduced rate of strength gain. Compressive strength of concrete cured and maintained at 10°C (50°F) is expected to gain strength half as quickly as concrete cured at 23°C (73°F). In hot weather, curing and protection are critical due to rapid moisture loss from fresh concrete. The curing actually starts before concrete is placed by wetting substrate surfaces with water. Sunscreens, windscreens, fogging, and evaporation retardants can be used for hot weather concrete placements. Since concrete strength gain in hot weather is faster, curing period may be reduced. Additional information can be found in ACI 306.1, Standard Specification for Cold Weather Concreting, ACI 306R, Cold Weather Concreting, ACI 305.1, Specification for Hot Weather Concreting, and ACI 305R, Hot Weather Concreting.

Curing Concrete Test Specimens

Curing of concrete test specimens is usually different from concrete placed during construction. American Society for Testing and Materials (ASTM) has developed two standards for making and curing concrete specimens. ASTM C192 ⁶ is intended for laboratory samples while ASTM C31⁷ is intended for field samples. Both documents provide standardized requirements for making, curing, protecting, and transporting concrete test specimens under field or laboratory conditions, respectively.

ASTM C192 provides procedures for evaluation of different mixtures in laboratory conditions. It is usually used in the initial stage of the project, or for research purposes.

ASTM C31 is used for acceptance testing and can also be used as a decision tool for form or shoring removal. Depending on its intended purpose, the standard defines two curing regimes: standard curing for acceptance testing and field curing for form/shoring removal. Variation in standard curing of test specimens can dramatically affect measured concrete properties. According to the National Ready Mix Concrete Association ⁸ (NRMCA), strength for concrete air cured for one day followed by 27 days moist cured will be approximately 8% lower than for concrete moist cured for the entire period. The strength reduction is 11% and 18% for concrete specimens initially cured in air for 3 days and 7 days, respectively. For the same air/moist curing combinations, but 38°C (100°F) air curing temperature, the 28-day strength will be approximately 11%, 22%, and 26% lower, respectively.

* Jerzy Z. Zemajtis, Ph.D., PE (WA)
Senior Engineer, CTLGroup, Skokie, IL
begin_of_the_skype_highlighting              (847) 832-0260      end_of_the_skype_highlighting, jzemajtis@ctlgroup.com
(847) 832-0260 References:
¹S. Kosmatka et al, Design and Control of Concrete Mixtures, 14th Edition, PCA Engineering Bulletin EB 001, Portland Cement Association , Skokie, IL 2002

² Specifications for Structural Concrete, ACI 301 (www.concrete.org)

³ Guide to Curing Concrete, ACI 308R-01 (www.concrete.org)

⁴ ASTM C309, Standard Specification for Liquid Membrane-Forming Compounds for Curing Concrete (www.astm.org)

⁵ ASTM C1315, Standard Specification for Liquid Membrane-Forming Compounds Having Special Properties for Curing and Sealing Concrete (www.astm.org)

⁶ ASTM C192 / C192M, Standard Practice for Making and Curing Concrete Test Specimens in the Laboratory (www.astm.org)

⁷ ASTM C31 / C31M, Standard Practice for Making and Curing Concrete Test Specimens in the Fieldwww.astm.org) (
⁸ David N. Richardson, Review of Variables that Influence Measured Concrete Compressive Strength, NRMCA Publication 179, NRMCA, Silver Spring, MD, 1991.


The Link Between Concrete Sustainability and Curing

Sustainability, according to the Bruntland Report and adopted by many experts, is development that meets the needs of the present without compromising the ability of future generations to meet their own needs. This can be accomplished in one of two ways: either by using recyclable, reusable, or so little resources that future generations have the same access to them; or by producing development that meets our needs as well as the needs of future generations. We can use proper curing of concrete to advance towards the reduction of resource use.

A concrete element is expected to last a certain number of years. In order to meet this expected service life, it must be able to withstand structural loading, fatigue, weathering, abrasion, and chemical attack. The duration and type of curing plays a big role in determining the required materials necessary to achieve the high level of quality.

Curing is the process in which the concrete is protected from loss of moisture and kept within a reasonable temperature range. The result of this process is increased strength and decreased permeability. Curing is also a key player in mitigating cracks in the concrete, which severely impacts durability. Cracks allow open access for harmful materials to bypass the low permeability concrete near the surface. Good curing can help mitigate the appearance of unplanned cracking.

When smart, suitable, and practical curing is used, the amount of cement required to achieve a given strength and durability can be reduced by either omission or replacement with supplementary cementitious materials. Since the cement is the most expensive and energy intensive portion of a concrete mixture, this leads to a reduction in the cost as well as the absolute carbon footprint of the concrete mixture. Additionally, being practical with curing methods can enhance sustainability by reducing the need for resource intensive conditioning treatments, should the curing method be incompatible with the intended service environment.

Curing Pavements and Bridge Decks

While curing of concrete is an important issue with all concrete applications concrete pavements and bridge decks require careful consideration and have significantly different needs with regard to curing of the concrete of these structures. Both categories have basic requirements for the durability of the structures including strength, abrasion resistance, freezing and thawing and deicer resistance, and, in the case of bridges, low permeability for corrosion protection of the reinforcement of the structure.

Typical recommendations for curing of pavements allow the use of sheet curing, moist curing, or application of a film forming curing compound. Due to the large surface areas typical of concrete paving the application of curing compound to all exposed surfaces is the most common curing method. Moist curing and sheet curing of large surface areas may become cost prohibitive due to the large quantity of materials required to cover the full surface of concrete placed in any single day. In addition moist curing and sheet curing require maintenance to assure the curing method is properly completed for the full time duration chosen for paving (typically 7 days). Moist coverings require rewetting and sheet goods are prone to being disturbed by wind, either of which would reduce the effectiveness of the curing method.

Curing compounds should be applied to pavements as soon as possible after bleed water has left the surface of the concrete at a rate of 5 m ²/L (200 ft²/gal) for standard mixtures and application, 3.75 m²/L (150 ft²/gal) for fast track paving, and 2 1/2 m²/L (100 ft²/gal) for slabs thinner than 125 mm (5.0 in.)

In contrast concrete bridges require a higher standard of curing to achieve the low permeability required for protection of steel reinforcement. Standard recommendations for curing bridge decks is moist curing for a minimum of 7 days for concrete mixtures containing only portland cement and as long as 14 days when supplementary cementing materials are included in the concrete mixture. Some states also require the application of curing compound upon removal of the moist curing methods.

Typical moist curing for bridge decks requires the application of adequate quality water saturated burlap or other approved absorptive material covered with minimum 6 mil plastic covering. The temperature of the saturated materials should be within 11°C (20°F) of the temperature of the in-place concrete. In most cases plastic will be specified to be white in color to reflect solar radiation, reducing the temperature rise beneath the plastic, while cold temperatures (less than 10°C (50°F)) may allow the use of black plastic to add heat to the system. Proper moist curing will also require uncovering and rewetting the absorptive material to assure that there is a constant supply of water available to satisfy the evaporation rate at the project site.
References

Design and Control of Concrete Mixtures, 14th Edition, EB001

Construction Specification Guidelines for Concrete Streets and Local Roads, IS119

HPC Bridge Views, Issue No. 45, Fall 2006

Concrete Curing Compound

Concrete Curing Compound in practice

Curing is one of the last and perhaps the most neglected step in the manufacture of precast concrete products. The need for rapid production is of great importance in this industry. Balance between production rates and quality can be achieved through continuous improvement in product design, raw materials, manufacturing processes and employee education. Concrete Curing Compound is just one of the tools employed to facilitate the concrete curing process.
What Is Curing?
Simply stated, proper curing creates the optimum environment to promote the hardening or hydration of freshly cast concrete. Hydration is the chemical process that ultimately binds cement particles and aggregates into hardened concrete. Creating the optimum environment involves:

• Monitoring and controlling the humidity to prevent moisture loss from the fresh concrete. The primary object of curing is to prevent or replenish the loss of necessary moisture during the early, relatively rapid stage of hydration.
• Monitoring and controlling the temperature of the concrete and gradients (i.e., providing a favorable temperature (50-90°F) under conventional curing conditions and up to 150°F under low-pressure steam curing).

Curing practices that promote prolonged hydration of the cement results in gel development which reduces the size of the concrete’s internal voids and thereby greatly increases the water tightness of the concrete. For this reason, prolonged hydration through curing is a significant factor in attaining impermeable, watertight concrete. Concrete Curing Compound creates a barrier between the concrete and the elements.
Prevention of the loss of water from the concrete is of importance not only for the loss of strength, but it also leads to increased permeability, plastic shrinkage and other undesirable factors.
Conventional curing and low-pressure steam curing are two of the more common methods of curing precast concrete products.
Other Concerns During Curing
During curing, concrete products should also be protected from impact, loading, vibration, and other mechanical disturbances.
Why Cure Concrete?
Concrete gets hard as a result of the chemical reaction of the mix water and the cement, a reaction that starts at the instant the two materials first come in contact with each other, and can continue for many years. Concrete that “dries” out will not reach its design strength or meet specifications. The longer the cure, the better the concrete.
In general, all specifications will include details regarding curing of concrete products.
Curing Methods
Physical barriers to prevent evaporation

• Leaving forms in place
• Polyethylene sheets/tarps
• Curing papers
• Saturated burlap

Water Spray/Immersion

• Ponding
• Fog Spray

Membrane Curing Compounds

• Synthetic resin (plastic) base
• Wax base
• Wax and synthetic resin base
• Acrylic polymers in water base

Advantages of Concrete Curing Compound

• Easy to apply
• Cost effective
• No need for continuous monitoring or application as would be required for fog-spray systems or wetting burlap
• Minimal equipment requirements and costs
• No debris or tarps to reuse and store

Essential Properties of a Concrete Curing Compound

• Forms an impervious film on concrete
• Free of pinholes
• Strongly adheres to surface of concrete
• Prevents the concrete mixing water from evaporating

Percent Solids, What’s it All About?
In general, high-solids Concrete Curing Compound (about 30% solids) greatly reduce moisture loss. Better polymers in newer formulations can also be extremely effective, even with lower solids content. ASTM C-309 requires curing compounds to have a maximum moisture loss rate of 0.55 kilograms per square meter of surface in 72 hours. This standard requires a coverage rate of 200 square feet per gallon. Moisture loss when using a high solids curing compound at a coverage rate of 300 square feet per gallon will generally allow a lower maximum moisture loss of about 0.30 kilograms per square meter.
Products that cure and seal concrete tend to have higher solid content. Application of high-solids products is easier because they are unlikely to be applied too thin. These compounds leave a gloss on the concrete surface, so it is easy to see when coverage is complete.

Questions to Ask Your Concrete Curing Compound Supplier

• Compliant with ASTM C-390, Liquid Membrane – Forming Compounds for Curing Concrete
• Non-hazardous. Read the MSDS (Material Safety Data Sheet) before ordering
• VOC (Volatile Organic Compound) Compliant
• Compatible with form release agent
• Will not adversely affect subsequent use of sealers, coatings, and paint applied to the cured concrete
• Cost per square applied: ______________
• Mixing requirements, one part component
• Ease of applying to recommended thickness
• Application equipment concerns:
  • Ease of use
  • Maintenance and Cleanup
  • Initial cost
• Presence of fugitive dye or pigment (will show during application, but fades in a few days)
• Staining of finished product
• Percent/Solids: ______________
• Storage requirements

Cure and Seal
Some concrete curing compound can also be used as a sealer, hardener, and dust reducer. These products may have an acrylic polymer, sodium silicate, or chlorinated rubber base. Some cure and seal products can interfere with the bonding of coatings, coverings, or tile to the finished precast surface. Check with your supplier for use in these applications.
Application
“Prepare surfaces and apply concrete curing compound in accordance with manufacturer’s recommendations.”
Read the Directions
After the concrete has received its final finish (1-3 hours after concrete placement) and the water sheen has disappeared from the surface. Pinholes in the curing compound film will occur if applied when there is still standing water on concrete surface. Using pigmented curing compounds helps achieve complete application coverage. If the concrete appears to be dry, wet the surface before applying the concrete curing compound.
Concrete Curing Compound should be sprayed on uniform surfaces as soon as the water sheen disappears but while the surface is still moist to ensure adequate performance (i.e., 1-3 hours after concrete placement). Curing compounds should be stirred or agitated as needed prior to use.
Apply the curing compound in two applications, at right angles, to form a continuous film coating all surfaces of the precast product. Application of the coats in two directions (i.e., vertically and horizontally) while help to ensure full coverage.
Don’t thin or alter curing compounds
When possible, keep steel forms on new precast concrete products as long as possible. This is an excellent first step in protecting against loss of moisture.
Other concerns during curing
During curing, concrete products should also be protected from impact, loading, vibration, and other mechanical disturbances.
All beneficial properties of precast concrete including strength, durability and watertightness are enhanced through proper curing techniques.
Don’t Forget to CURE Curing, particularly within the first few hours after concrete placement, is one of the most important factors in manufacturing top quality precast concrete products. Properly cured precast concrete products have superior early and long term strength. Well cured precast concrete products are less permeable, more durable, and have greater surface hardness.
Proper use of quality Concrete Curing Compound is an excellent method to facilitate the production of top notch precast products. But don’t forget to maintain proper temperatures during curing and to protect your products from impact and vibration during this period or no matter how much Concrete Curing Compound you use it will not matter .

Dubai rental slide slows down in Q2

Residential lease rates in Dubai during the second quarter of this year showed short-term stability compared to the previous quarter, according to the CB Richard Ellis (CBRE) Dubai MarketView Q2 2010. However, the year on year figures registered an overall drop of 33 per cent.

• By Binesh Panicker, sub-editor, Freehold Monthly
• Published: 00:00 August 15, 2010
• 

• Rents continued to decline in Q2 but at a slower pace, according to CBRE
• Image Credit: Supplied

The significant new supply of smaller units coupled with the overall improvement in affordability has given the tenants an opportunity to rent larger properties at lower rates, states the report.
Matthew Green, head of research and consultancy UAE, CB Richard Ellis Middle East, says while there is an increasing degree of stability in the leasing market, the general trend is still downward.
"Areas that are seeing significant supply from multiple new projects continue to be most impacted as heightened competition and a greater level of choice is resulting in further rate reductions as landlords scrabble to secure tenancies in fear of growing rental voids. Obviously the rate of decline has slowed considerably and we are hopeful that this prolonged period of constancy will in time begin to build some more positive sentiment in the market."
Jumeirah Lakes Towers (JLT) and The Greens have been the most affected developments and Green attributes this to huge volumes of new supply that have come on stream in a very limited period.
While JLT has been adversely affected by infrastructure issues in terms of road networks and the lake, it is the traffic congestion in and around The Greens and the emergence of new properties such as Dubai Marina at competitive rates that has resulted in rising vacancy rates and reduced leasing potential in the development, explains Green.
He expects Q3 to be subdued with the usual summer slowdown and Ramadan. "With a large portion of the resident population choosing to take vacations to avoid the summer heat, the quarter is likely to see reduced activity across the board which could have a further impact on leasing rates," says Green.
bpanicker@alnisrmedia.com
Original news

Asphalt Paving Operation

by Stephanie Paul, Linda Puspa-Dewi, Kamolwan Lueprasert & Heinko Dona Madon

INDEX: Introduction Process Description MicroCYCLONE Model Discussion Conclusions References Introduction The subject of this term project was an asphalt paving process utilizing a paving machine and 20 tons capacity tri-axle trucks. The location of the process was at the corner of Main and Madison in Greenwood ( South of Indianapolis ). The project is being run by the Reith-Riley Construction Company. - Indianapolis. The overall process involved : Hot-mix batch plant cycle Tri-axle truck cycle Roller cycle Spreader cycle Crew cycle Because of the complexity of the overall construction process, we chose to observe, report on, analyze and model the paving process on the base layer of the 15' lane road. At that time, the other lane of the road was not paved yet. The road has slightly increasing grade and curve along the process. The preliminary process of gathering the data used in this project, the efficiency of the operation, a model and MicroCYCLONE simulation of the process, and illustrations will be discussed and presented. Asphalt has been used by man for its adhesive and waterproofing properties. Asphalt was used in 3800 B.C. in the Euphrates and 2500 B.C. in Egypt. The Sumerians used asphalt in 6000 B.C. for its shipbuilding industry. Today, asphalt is applied to roofing, sealants, caulking, brake linings, paints, enamels, and most widely used in the paving industry (Asphalt - Science and Technology, 1968). Process Description Batch Plant Production First, aggregate travels through the cold feed bins, where initial proportioning of the aggregate takes place. The quantity of material leaving each bin is regulated by the size of the gate opening, or the speed of a belt, or a combination of the two. The aggregate is sent to a drier. Here the moisture is removed and is heated to provide the proper mixing temperature in the pugmill. The aggregate continues to the hot elevator by screens to the hot bins. The screens provide the final separation of the aggregate. The different sizes of aggregate are released into the weight hopper one bin at a time. The aggregate is dropped into the pugmill for mixing with the asphalt. The mixture is then dropped into a waiting truck or moved to a storage silo. Samples are taken from each hot bin for testing. A sieve analysis is conducted as well as gradation test. From the gradation information, the weight of the aggregate must be equal to the design gradation. A trial run should be performed and the weights adjusted until the desired mix is produced. (U.S. Department of Transportation, December 1984) Placing Asphalt Pavement Placing the Coat Before the paving operation starts, an asphalt distributor is used to spray asphalt on the unpaved surface. This film of asphalt serves as the prime and tact coats. The coats are then allowed to cure before the actual paving resume. The purpose of having these coats is to prevent any slippage between the surface and overlay during or after the compaction. (The Asphalt Institute) Placing the Asphalt Mix To start the paving operation, the paver is positioned properly onto the road. The screed of the paver is lowered onto block of the same depth of the loose asphalt mat that is going to be laid on the road. (The screed is responsible for the setting the depth of the asphalt mix.) After that, the block can be removed and paving can start. As soon as the haul truck arrives at the job site, the paving inspector must check that the asphalt delivered must be in a satisfactory condition. The paving inspector usually check for these criteria listed below: blue smoke - blue smoke indicate that the mix is too hot. stiff appearance mix slumped in truck. lean, dull appearance - this indicates that the mix has insufficient asphalt. rising steam - too much moisture. segregation. contamination. If there is any of the signs above is observed, the mix will be sent back to the batch plant to be reprocessed. After all conditions are satisfied, the haul truck can load the mix into the receiving hopper of the paver. When loading the mix into the receiving hopper, the haul truck is placed carefully in front of the paver. The rear wheels of the truck should be in contact with the truck roller of the paver to avoid any misalignment with the paver. The paver will push the truck forwards as it paves the road. If skewness happens, the whole process will be delayed because they have to reposition the truck in front of the paver. Most paver used are self-propelled paver. Each of them consists of two main units: tractor unit. -it includes the receiving hopper, slot conveyor, flow control gates, spreading crew, power plant, transmission, operator control for use on either side, and operator's seat. This unit will move the whole system forward. screed unit. -it is attached to the tractor unit by long screed arms on both sides of the machine. It consists of screed plate, vibrators or tamper bars, thickness control, crown control, and screed heater. As soon as the the first load of asphalt mix has been spread, the uniformity of the asphalt texture should be checked. Operators will adjust the the appropriate adjustment points to correct any nonuniformity. Any segregation of materials also should not be allowed. Operation should be stopped immediately if any segregation is detected. The operators should also be aware of is the crown control. Pavement with crown has to be redone all over again. In addition to that, operators should continuously loosen the mix that clings to the sides of the hopper and push it back into the active mix. If the asphalt mix grow cold, it cannot be properly compacted and thus, looses its strength. The last process of paving is compaction. This process is highly influenced by major mix proportion; (1) asphalt content: aggregate size, shape texture and distribution gradation; (2) filler content, and; (3) mix temperature. Appropriate rollers and rolling methods should be used in accordance with these proportion. There are several roller combinations used for maximum results: steel-tired static and pneumatic-tired rollers, vibratory and steel-tired static rollers, or vibratory rollers used in vibrating and static modes. These combinations are highly recommended by the asphalt institute. Rollers should be moved in a slow but uniform speed to achieve the best result. (See table) These rollers should also be in good conditions. Any irregularities in the rollers' performances will result in poor compaction of the asphalt; thus, the pavement will not last long. The rollers should not reverse suddenly while compacting because this action can displace the mix. If displacement happens, the whole mat should be loosened with lutes or rakes and restored to the original grade before rolling can restart. A pattern that is economical and provides the maximum compaction result should be established. (The Asphalt Institute) Testing Method Why Evaluate Density of Hot Asphalt Concrete As we know, lacking of density during construction of asphalt concrete causes many problems. It is necessary to obtain high density to insure that the asphalt concrete will provide the necessary stability and durability for performance. For instance, low density generally causes long-term deterioration when the asphalt begins cracking. Therefore various methods have been used to measure the density in the asphalt concrete. Procedures Used to Obtain Density Proper aggregate gradation and asphalt content are important parameters to ensure that the density of asphalt concrete meets the requirement. Generally, poor gradation results in a reduction of voids in the mixture; thus, reduces the asphalt content which serves as the lubricant for aggregates in the mix. The stiff mix is more difficult to compact. Both the aggregate gradation and the asphalt content are interrelated and equally important. Paving asphalt is really difficult in cold climate. The hot mix cools down faster and harder to compact. To overcome this, contractors usually increase the temperature of the mix. Unfortunately excessively increasing the temperature of asphalt mixture may cause problems during compaction and increase oxidation of the asphalt cement. This may result in a hard and brittle pavement. The mix temperature should be selected so that the mixture would be able to support the roller immediately behind the paver. Since there is less time to roll the mixture before it cools, more rollers or larger rollers are required for the compaction process. After the mixture is transported to the site, the next step is to ensure proper density while laying down the asphalt with a spreader. A continuos availability of the asphalt mix for the paver is crucial. The spreader cannot afford to start and stop while waiting for the materials. It important to have material that has the same texture and appearance. Evaluation of In-Place Density An evaluation of the in-place material is necessary to ensure that a satisfactory density is obtained. Most of the time, a nuclear gage is used to estimate the density. However, the results obtained using this equipment are not accurate. It has to be calibrated by taking a number of measurements from different location as soon as the project starts. After calibrations, a series of readings are taken and then, the readings are compared to the density obtained from the laboratory. The laboratory results are the density of core samples taken from the same location. (Placement and Compaction of Asphalt Mixtures, 1982) Laboratory and Field Pavement Stability Tests The American Association of State Highway Officials (AASHO) and the American Society for Testing and Materials (ASTM) are two agencies which set forth methods and test procedures the paving industry must follow. Five test methods readily used in the field and laboratory are: The Hubbard Field Stability Test (ASTM-D-1138-52 or AASHO Test 169) - tests the resistance to plastic flow of fine aggregate mixtures. The Unconfined Compression Test (ASTM-D-1074-52-T) - measures the cohesion of paving binder and performance of the internal friction of the aggregate. The Marshall Test (ASTM-Method-D-1559) - measures the flow value or flow index by distorting the specimen until fracture. The Hveem Test (ASTM-Method-1560) - uses stabilometer and cohesiometer apparatus. The stabilometer determines the maximum amount of asphalt which will obtain the greatest stability by measuring the internal fiction of the mineral aggregate. The cohesiometer determines the cohesion properties and the strength of asphalt films by bending and breaking a specimen. The Triaxial Compression Test - is useful in determining the cohesion of the mix and asphalt contents and the angle of internal friction of the entire mixture by applying lateral pressures. Theses are the most widely used although a variety of other methods exist. It must be stated that different local, state, and federal organizations will require certain tests to be performed and may accept a different range of values. MicroCYCLONE Model Note: Clicking this button will open a new window Resources Description Material: Aggregates Hot mix asphalt material Equipment: Trucks Spreader Roller Batch plant (hot mix) Laborer : 4 laborer 1 roller operator 1 paver operator 1 superintendent 1 truck operators 1 foreman Discussion Discussion Preliminary Procedure to Obtain Data Initially contacting the company and project engineers involved was necessary before we could obtain access to the site and accumulate data and information about the operation. Dan Patrick, the superintendent of Reith-Riley Construction, provided general information regarding this operation. This included cost ( by providing us with the Company's Job Calculation Sheet ), specific details concerning the operation described and modeled in this paper and details of the crew sizes, equipment, materials, efficiency and variables of the operation. The site was visited often to observe and obtain the details of the operation. Pictures were taken, and individual questioning of the crews and inspector involved in the plant and job site were employed to get an accurate idea and necessary data. Mr. Patrick couldn't provide a pool data regarding production times. We were given an estimate of schedule of the job calculation sheet which were used to compare with the observed/actual production. Data Collection The general description of the project, the process involved, and the equipment used was obtained from Dan Patrick, the superintendent of Reith-Riley Construction. The actual project site and time duration for each activities were obtained from field observation on October 9th, 1991. A digital watch was used to time every activities involved in the process. The data collected were averaged for the ease of calculation. The data include the average for : loading at batch plant travelling to the job site dumping the asphalt to spreader back-cycle of the truck spreading the asphalt compacting the asphalt checking the level All the data obtained were approved by the superintendent as standard time for this particular paving operation. This information is listed in table 1. The high and low data in table 2.1 and 2.2. were given by the superintendent. Therefore, the average values of the deterministic input were used as the mode values for the Triangular and Beta distribution. The Beta 'a' and Beta 'b' values were calculated by the Vibes program. Note: Clicking this button will open a new window Note: Clicking this button will open a new window Note: Clicking this button will open a new window Material Handling and Processing System Loading hot mix asphalt to the truck Hauling asphalt to job site Dumping the asphalt to the spreader Spreader paving the asphalt Roller breaking down the asphalt Roller finishing the surface Productivity Comparison The productivity level can be measured in three different ways Deterministic time Triangle distribution Beta Distribution The values for all three methods were closely related (table 3.). Generally the deterministic values were higher while Beta values were lower. Triangle values were located somewhere in between the aforementioned. The range of differences between the distribution is 0.0289 to 0.4278. These difference were not significant; therefore, any distribution could be used in an actual situation. The production values from Beta distribution were used for determining the theoretical productivity because they were more conservative. From the company's Job Calculation Sheet, they estimated the capacity of the truck to be 20 tons and working 30 cycles per day. The company's estimated productivity is 600 tons per day which was equal to 3.75 truck-loads per hour. Refer to table 3 for comparison of productivity. The productivities of the simulated result of the MicroCYCLONE model were found to be a little bit lower. The percentage differences as given in table 3 were as followed : Note: Clicking this button will open a new window compared with deterministic time : 4.67 % compared with Triangle distribution time : 10.78 % compared with Beta distribution time : 12.87 % Improvement of Productivity Using sensitivity analysis, the productivity of the whole asphalt paving operation could be increased by adding one more roller. With only one roller, the deterministic productivity at cycle 30 was 3.575 truck-loads per hour. By adding the second roller, the productivity was increased to 6.4632 truck-loads per hour. The productivity was increased by about 81 %. ( look at appendix for the output files ). Also the sensitivity analysis showed that increasing truck did not increase the productivity at all. Conclusion The rate of the operation was determined by the rate of the roller. This was because the roller took 15 minutes to compact the surface of the asphalt. Thus, to improve the productivity, more roller should be added into the operation. Nevertheless, the company chose to use only one roller. Perhaps, the decision to only have one roller was determined by cost factor. The productivity obtained from the MicroCYCLONE model was within the expected productivity by the company. References Barth, Edwin J., "Asphalt-Science and Technology," Gordon and Breach, New York, New York, 1986. Wagner, F.T., "Placement and Compaction of Asphalt Mixture," ASTM Publication, Philadelphia, PA 19103. The Asphalt Institute, "Asphalt Paving Manual," Manual Series No. 8, Third Edition, April 1978. U.S. Department of Transportation, Federal Highway Administration, "Hot-Mix Bituminous Paving Manual," December 1984. Personal interview with Reith Riley Construction Company Indianapolis, Job Superintendent: Mr. Dan Patrick, October 2nd, 1991. Job Calculation Sheet of Greenwood Man and Madison, Bid date: September 30, 1991, Courtesy of Reith Riley Construction Company.

Doka’s Formwork System

Doka’s Formwork System Achieves Pristine Architectural Concrete Finish on University of Pennsylvania Campus

As more and more building owners begin to embrace the architectural possibilities of concrete, achieving a high-end concrete finish has become a top priority on many job sites. Such is the case on a mixed-use student housing project currently under construction on the University of Pennsylvania campus, where the exposed concrete on the 14-story structure demanded an impeccable finishing job. Although “architectural concrete” or “fair-faced concrete” have been coined as the accepted verbiage to describe such a pristine finish, there is still some discussion about the best way to achieve it. In general, most concur that success is tied to three main variables: a proper formwork system, the right concrete formula and the care that is taken when pouring the concrete and stripping the forms.

With the first of these concerns in mind, B. Pietrini & Sons, the concrete contractor for the 350,000-square-foot Walnut Street 14-story housing project, turned to Doka USA to provide a variety of formwork solutions. Before the project began, planning efforts focused heavily on form design and layout to make sure the architectural details of the structure could be constructed without a hitch. Because the concrete exterior will be left exposed once the project is complete, it was paramount to select formwork that would aid in this quality of finish. All of Doka’s formwork systems allow the contractor to specify any type of form facing and tie-hole pattern, meaning that B. Pietrini & Sons was free to choose the option that would give the best finish.

“Because of the design intent, the quality of the finished concrete really matters in this project. That is why we chose Doka to supply the formwork for this project because we needed extensive engineered drawings, good quality equipment and on-time deliveries,” stated Mike Vail, Project Manager, B. Pietrini & Sons.

The architectural concrete motif also can be found on the building’s interior as the architect designed 36-foot diagonal beams constructed using exposed concrete as a main feature. The main floor of the project, which is 36 feet in height, will be used for commercial and retail space. However, not all of the building’s levels were the same height—four of the 14 floors varied in height up to 36 feet. Framax Xlife was used to form all of the columns on these floors.

The special pattern of holes makes Doka’s Framax Xlife panels ideal for the economical forming of outside corners, wall connections, bulkheads and columns. According to John Podkrajac, Doka Account Manager, Framax Xlife provides an exceptional finish and the strong clamping system was well suited on this project for the 39-foot-plus pours. The columns for the remaining 10-foot floors were formed using the lightweight Frami system, while the shear and core walls were all formed using Top 50 large-area formwork, along with MF-240 climbing platforms, which were mounted on all of the exterior walls to ensure safe working conditions. The main entrance of the building is set off by two V-shaped columns, which were also formed using the Top 50 system. The Top 50 modular gang form system is constructed out of standard parts that can be assembled in any configuration for a wide range of applications. Shape, size, tie pattern, and plywood can be adapted to suit your jobsite requirements.

Work began on the project in February 2007, and the use of the Doka formwork has helped accommodate the relatively tight construction schedule—the Top 50 forms were pre-assembled and delivered to the site, and the ease of erection for the Framax and Frami formwork (both of which can be assembled using just a hammer and two lightweight clamps) helped produce quick cycling results for the columns. When it is completed in 2008, the building will house ground-level retail space, a mixed-use mezzanine level and 11 floors of student apartments for Penn students.

About DOKA
With nearly 50 years experience in formwork engineering, DOKA serves customers in more than 35 countries and has participated in construction of some of the world’s best known structures including the world’s tallest skyscraper (Burj Dubai), the Hoover Dam Bypass bridge, along with many other projects of all sizes. From wall and slab formwork systems to automatic climbing technology and superior safety solutions, Doka can deliver any type of formwork needed for residential, industrial, commercial, transportation, infrastructure as well as stadium and sports arena projects. For more information, please visit www.dokausa.com

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Circuit expands into the UAE with multi-million dollar projects

Circuit expands into the UAE with multi-million dollar projects

Specialised commercial and residential automation consultancy opens new office in Dubai to capitalise on business potential in UAE and wider Gulf region
Circuit Gulf, an extra low voltage (ELV) automation systems consultancy, has inaugurated an office in Dubai Silicon Oasis, to consolidate its growing residential and corporate business throughout the UAE.

The Egyptian company offers full consultancy and installation services, spanning all residential and commercial properties. Circuit also provides full technology management systems, such as smart video analysis, touch screens and surfaces, as well as integrated controls and state of the art biometric solutions, to name but a few.

Nathan Williams, Circuit Gulf General Manager, clarifies that despite the tough economic climate of late, the company has continued to thrive over the past 12 months. It has completed multi-million dollar projects in the UAE, including contracts for the royal family in both Abu Dhabi and Al Ain and various residential and commercial projects on Palm Jumeirah and Emirates Hills, cementing its enviable market reputation.
Williams added: “As the commercial hub of the GCC countries, Dubai is an ideal location to service our existing clients as well as compete for potential new business not only in the UAE, but throughout the Gulf economies.”

Circuit will also be showcasing a number of innovative products at this month’s Professional Audio, Light, Entertainment, Music and AV Exhibition (PALME), the region’s leading AV trade show, taking place at Dubai International Exhibitions Centre from April 18 to 20. Circuit is featuring the very latest in-home technology including AMX touch panels, Sony video conferencing, and video walls in a fully integrated home set up.

Circuit also has a specialist consulting team of engineers to assist clients from conceptualisation through to completion bringing with them experience of many top international automation brands. As well as being KNX certified (the worldwide standard for home and building control), the company has recently become the first Egyptian company and one of very few in the GCC region to be accredited by the Custom Electronic Design and Installation Association (CEDIA).
With such a broad range of expertise, Circuit is able to provide a full service offering from consultation to the latest bespoke fit-out, adapting to the requirements of all customers and catering to all budgets.

Williams said: “Implementing the latest technology has many long-term economic and environmental benefits, including reducing power consumption and manpower requirements for corporations by centralising equipment control and administration.”
A subsidiary of Circuit Holding, Circuit Gulf aims to add value to its customers’ projects and developments through the application of a wide variety of effective and efficient system integration techniques, solutions and products for ease of operation.

For more information, please visit www.circuit-holding.com

About Circuit Gulf: Circuit Gulf is a subsidiary of Egypt-based Circuit Holding, a company specialised in integrating extra low voltage (ELV) systems for residential and commercial projects. There are three companies under the Circuit Holding umbrella, servicing clients in Egypt, the Gulf and Europe. Circuit Gulf is the Engineering Service Provider that will enable MEP, real estate developers, consultancy offices, light current system integrators, and the hospitality industry achieve better and more cost efficient results when implementing comprehensive ELV solutions.

feather details : -m4ritek0@gmail.com

4D BIM Modeling - BIM Construction Modeling

BIM 4D Services is a Engineering Services Outsourcing firm offering BIM Services for a new building and construction planning at 60% off on US rate.

BIM 4D Services specializes in providing highly accurate BIM services as per the specifications and requirements at affordable rates. BIM 4D Services is a one stop solution for all your BIM Construction Planning requirements.

BIM 4D Modeling has new concept of building and construction planning design to the worldwide. BIM services is means building modeling of design, construction modeling, construction process, construction planning estimated cost and thus all CAD related information. We have been providing BIM services in all over world.

Our 4D Model encompasses all the details right to the last bolt or screw and is very effective tool for visualization of construction process before it commences.

Our expert team of engineers and cad operators is extremely competent and has rich experience in delivering quality and cost-effective BIM services for any type of construction planning. Over a decade the company has specialized in providing high quality Building Information Modeling (BIM) services and is catering to many Real Estate Developers, Consultant Engineers and Building Product Manufacturers across the globe.

We serve almost every industry including:

• Residential
• Commercial
• Corporate
• Educational
• Industrial
• Healthcare
• Hospitality

Building Information Modeling (BIM) services include:

• Creation and Visualization of Virtual Intelligent 3D Model
• 4th Dimension Incorporation
• Clash Detection and Risk Mitigation
• Creation of Libraries
• High Quality Construction Documents

BIM 4D Services employs well defined execution methodology to achieve highest standard of service and as a result it has become market leader in the BIM modeling and construction planning sector within a very short period of time. We have many satisfied offshore clients on ongoing basis from USA, UK, Australia, etc.

If you have any confusion or query about BIM Services, please feel free to visit our website at http://www.bim4dservices.com

Drop an Email at: info@bim4dservices.com

Diesel Pile Hammers

pile driving dragon

Aluminum Building Technology

Top 10 Tips on Managing People

1. Set clear direction: Might seem obvious that you need to have clear goals and yet almost 40% of employees in UK companies are not sure what their employer expects of them.

2. Link individual goals to the strategy of the company: As a manager you might know what your company is trying to achieve but the likelihood is that your people don't. Only 30% of UK employees understand how their job role impacts and contributes to their organisation reaching its strategic vision. It's your job to make this link clear and you can only do that by talking about it - all the time!

3. Know what your people have natural aptitude for: Your key function as a manager is to know your people well enough to understand what they do best. Where they have natural aptitude, they can excel. Practise doesn't make perfect unless you are practising in an area of natural talent.

4. Know your people's weaknesses: Where your people have no natural talent, they will not excel. Best case scenario, they can become average with practise and training but let go of the notion that they will ever become high performers in those areas.

5. Recruit, promote and performance manage according to the strengths needed and weaknesses that are acceptable for each role.

6. Create the right attitude: You can motivate your people by providing them with clear direction and playing to their strengths - but you also need to find out what makes them tick as individuals. What motivates you rarely motivates your people. Everyone is different and you would be wise to ask as opposed to making too many assumptions.

7. Give praise when praise is due: This is the most under utilised tool for motivating your people. Don't wait for perfection! Notice and praise situations and behaviours that went well, pointing out specifically what was good and the positive impact they had. 70% of UK employees report that they don't receive praise regularly. What an easy thing to do that makes a lot of difference.

8. Manage yourself: As a manager, you are a mini celebrity and your team watch your every move - including the inconsistencies between what you say and what you do. Don't expect your people to be something you are not.

9. Handle critical conversations: Learn how to tackle giving negative feedback and handling difficult situations (like behaviours and performance issues) with your people. It's a skill, usually something we either want to avoid or end up doing badly.

10. Deal with change: Dealing with a constantly changing environment is hard for many people. Especially when they don't see the benefits themselves. Every manager needs to be a change expert, not in theory but in practise. Delivering the message and getting buy in is one thing, where the real difference is made is by executing with consistency.

Read more: http://www.articlesbase.com/management-articles/top-10-tips-on-managing-people-612457.html#ixzz0wTkLClKi
Under Creative Commons License: Attribution

Effective Leadership, Managing People: 10 Timeless Principles

In my management and effective leadership skills seminars, I often ask participants, based on their years of experience, to list their top do's and don'ts for effectively managing people. After conducting workshops and keynotes all over the world for over 12 years, I've come up with ten timeless principles, or tips for managing people. Here are the top ten:

1. Set goals collaboratively with your employees. You're more likely to have employees who are accepting of the solution because they were involved in the process.

2. Follow through. Always do what you say you're going to do. Otherwise, your credibility is destroyed. As the saying goes, they remember your last act.

3. In managing people, be empathetic and compassionate when the situation calls for it. For example, when a good employee is experiencing personal problems. Remember, your employees are your most important asset. And, you are managing people.

4. Be honest, trustworthy, fair and respectful. In managing people, if you employees don't perceive you as trustworthy, you're less likely to have real influence over them.

5. Lead by example. Be a good role model. If you are honest, trustworthy, respectful, and hardworking, you're training them to be the same.

"Effective leadership in managing people = getting along with others."

6. Communicate clearly with your staff on a regular basis. The importance of good communication sounds so obvious, it's as if it shouldn't need to be mentioned! But over and over, I hear about managers who don't communicate effectively.

7. Take care of important issues. Don't procrastinate working on projects you don't want to do. And promptly address performance issues with a difficult employee. Otherwise, these problems only get worse.

8. Have goals and objectives clearly defined in writing for accountability. Include dates, deadlines, and numbers so it's very clear what's expected. For example, if someone is in customer service they are to, "Respond to all customer inquiries and complaints within 12 hours of receiving them.This way, the employee clearly understands what's expected of them and is less likely to say, "Well,that's just your perception. You're just picking on me."

9. In managing people, be available. Be approachable.

10. Empower and motivate the team not just in terms of completing tasks, but also in terms of good communication and managing conflict.

Effective leadership when managing people correlates to successfully managing conflict. Learn to get along with others. It's not just what you know, or who you know, but how well you get along with others.