Base and Drainage Construction
1. The sub-base will have a slope of 0.5%.
2. The base aggregate shall consist of a minimum of four inches (4”), free-draining stone, depending on site location. Finish slope of porous aggregate should be 0.05% from the centerline of the field to the sidelines, and the grade should not vary more than a half an inch (1/2”) in ten feet (10’). The sieve analysis of the open grade stone shall show a gradation as follows:
% of Passing Sieve Size
100 1.25”
70-100 3/4”
30-50 3/8”
8-40 #4
0-12 #16
0-5 #200
The Stone shall be installed maintaining a finished grade slope of 0.5%. The owner and Synthetic Turf System Manufacturer must approve variations of this finished slope. The depth of the aggregate will increase at the edges of the field, as determined by the sub-base slope, as the elevations are maintained throughout. The washed stone aggregate material must be free draining, consistent with the vertical draining requirements of the Synthetic Turf System Manufacturer and owner.
3. The finished grade of the aggregate base shall not vary more than a quarter of an inch (1/4”) in ten feet (10’). A laser grader is to be employed.
4. Cut and fill of sub-base soils should be conducted as necessary to establish proper grade of sub-base to a tolerance of one-half inch (1/2”) in ten feet (10’). Sub-base shall be sloped of 0.5% from center of field toward sidelines.
5. The sub-base compacted using a ten (10) ton vibrating roller, to approximately 95% Proctor density.
6. Vendor will supply and install a porous non-woven polypropylene stabilization fabric (Amoco 4545 or equal) over the entire surface before the installation of the stone depending on geographic location.
7. Install a one inch by six inch (1” x 6”) prefabricated Multi-Flow (or equal) under drain system in a “V” deign as shown on drawing with lines approximately twenty feet (20’) on center and connect to a perimeter linear drain.
8. The Contractor shall supply water proof tape and all necessary connectors, per subsurface drainage system manufacturer’s recommendation, and is responsible for a proper and secure connection between all new and existing drainage lines.
9. Install up to a two-inch (2”) layer of one eighth to a quarter of an inch (1/8” – 1/4”) porous stone over the base, maintaining slope and grade, depending on the geographic location. Finish grade to tolerance of a quarter of an inch (1/4”) in ten feet (10’) and compact with four to six ton (4 – 6) motorized roller to approximately 90% Proctor. The sieve analysis of the fine grade stone shall show a gradation as follows:
% of Passing Sieve Size
100 1/4”
60-100 1/8”
5-10 #100
0-5 #200
10. The Synthetic Turf System Manufacturer and architect will accept the aggregate base in writing prior to the installation of the Synthetic Turf System.
Related Article: Artificial grass sub base
Wednesday, November 10, 2010
Wednesday, October 27, 2010
Tool Test: Airless Paint Sprayers - Technology
Pumped Up: Small-scale sprayers for pro painting results
Photo: dotfordot.com
Specs and Tester's Comments
Anatomy of a Winner
Detailed Tool Features
By Michael Springer
Photos by dotfordot.com
To keep busy during these hard economic times, many builders, framing contractors, and other tradesmen are turning to remodeling work. Homeowners are staying in their houses longer and choosing to make improvements instead of upsizing to a new address, and those who have to sell are often desperate to spruce up their homes so they'll stand out in a dismal real estate market. As a result, remodeling projects are a lot easier to come by than jobs at new-housing developments.
But switching focus from building to remodeling is no easy feat. Remodelers tend to be jacks-of-all-trades. They rely less on subs than large-scale builders do, and handle much more of the work in-house. This is especially true now. Guys who used to spend their time running from bid to bid are concentrating on their hands-on skills to keep the work flowing. They're hanging rock, setting tile, and doing their own painting – even more than they were before, during boom times.
Faced with this kind of sink-or-swim adaptation, contractors need tools that can add to their professional versatility (and, ultimately, to their bottom line). That's why we chose airless paint sprayers for this issue's tool test. These tools (which painters simply call "pumps") are great for putting down a lot of paint efficiently, indoors and out. Even if you're backrolling to even out the sheen on an interior wall, applying the paint with a sprayer instead of constantly dipping a roller keeps you moving – which keeps you competitive. For the three-dimensional surfaces (and sheer square footage) of exterior siding and trim, spray application is a necessity. And for fine trim and paneled doors, careful spray work can give you the finish you want – a smooth, evenly applied coat without brushmarks – fast. It takes practice to get really good at using these pumps, but the learning curve is forgiving and the work is actually pretty fun. The first time you paint an entire finished basement in just a few hours will likely put a satisfied smile on your face. It sure did for me.
Like other power tools, airless paint sprayers can be dangerous if used unsafely. If you spray your skin in close proximity to the spray tip, you can fall victim to a horrendous injection injury that could lead to amputation. Our tester shared horror stories of guys he knew in the trade who lost fingers, hands, and even a section of abdomen to such injuries. On the other hand, tool-rental shops will send these tools home with just about anybody, with no requirement for training. So our advice is treat the business end of the sprayer like a loaded gun and be very careful.
For our test, we gathered nine pumps, ranging from midlevel budget models to a few suited for everyday use on smaller jobs – they just had to be able to handle the pros' requisite .019-inch tip. Our painter of 25 years used them with interior and exterior latex paints to determine their worth from a full-time painting contractor's point of view.
These pumps are on the small side compared with the models a pro paint crew usually uses; pro rigs are typically capable of powering extra-long hoses with multiple spray guns running off one machine. Nevertheless, the single-gun units we tested generally impressed our painter – all were capable of putting out a suitable coat of quality latex paint. The least of the tools had too many compromises to be worth using, in his opinion, but to his surprise he found the winner proficient enough to take the place of one of his larger units for daily use on residential sites.
Winners
The performance results of our test support the old adage "You get what you pay for," as the units basically ranked right down the price line, with components and features commensurate with cost. The Airlessco LP 500 took top honors with output that seemed effortless and a commercial design built for hard work and tough conditions. The Graco Ultra 395 came in second with pro performance and advanced control features shared by only the top two pumps. Third place went to the Titan Impact 440 and fourth to the Graco 390. These four in the top tier are considered suitable for pro-level use on a consistent basis.
The midtier starts with the Graco 190 just edging out the Titan Advantage 400. Beneath these (in order) are the occasional-use tools, the Titan XT 420, Wagner Twin Stroke 9175, and Milwaukee M4910-20. If you're in the market for a pump you'll use only a handful of times per year, these lower-end units will put out the paint well enough, but they lack the convenience and durability of pricier models and don't quite make the cut for a solid job-site airless sprayer when compared with the other choices.
Dave Archuleta of Dave's Painting in Denver contributed to this test
Photo: dotfordot.com
Specs and Tester's Comments
Anatomy of a Winner
Detailed Tool Features
By Michael Springer
Photos by dotfordot.com
To keep busy during these hard economic times, many builders, framing contractors, and other tradesmen are turning to remodeling work. Homeowners are staying in their houses longer and choosing to make improvements instead of upsizing to a new address, and those who have to sell are often desperate to spruce up their homes so they'll stand out in a dismal real estate market. As a result, remodeling projects are a lot easier to come by than jobs at new-housing developments.
But switching focus from building to remodeling is no easy feat. Remodelers tend to be jacks-of-all-trades. They rely less on subs than large-scale builders do, and handle much more of the work in-house. This is especially true now. Guys who used to spend their time running from bid to bid are concentrating on their hands-on skills to keep the work flowing. They're hanging rock, setting tile, and doing their own painting – even more than they were before, during boom times.
Faced with this kind of sink-or-swim adaptation, contractors need tools that can add to their professional versatility (and, ultimately, to their bottom line). That's why we chose airless paint sprayers for this issue's tool test. These tools (which painters simply call "pumps") are great for putting down a lot of paint efficiently, indoors and out. Even if you're backrolling to even out the sheen on an interior wall, applying the paint with a sprayer instead of constantly dipping a roller keeps you moving – which keeps you competitive. For the three-dimensional surfaces (and sheer square footage) of exterior siding and trim, spray application is a necessity. And for fine trim and paneled doors, careful spray work can give you the finish you want – a smooth, evenly applied coat without brushmarks – fast. It takes practice to get really good at using these pumps, but the learning curve is forgiving and the work is actually pretty fun. The first time you paint an entire finished basement in just a few hours will likely put a satisfied smile on your face. It sure did for me.
Like other power tools, airless paint sprayers can be dangerous if used unsafely. If you spray your skin in close proximity to the spray tip, you can fall victim to a horrendous injection injury that could lead to amputation. Our tester shared horror stories of guys he knew in the trade who lost fingers, hands, and even a section of abdomen to such injuries. On the other hand, tool-rental shops will send these tools home with just about anybody, with no requirement for training. So our advice is treat the business end of the sprayer like a loaded gun and be very careful.
For our test, we gathered nine pumps, ranging from midlevel budget models to a few suited for everyday use on smaller jobs – they just had to be able to handle the pros' requisite .019-inch tip. Our painter of 25 years used them with interior and exterior latex paints to determine their worth from a full-time painting contractor's point of view.
These pumps are on the small side compared with the models a pro paint crew usually uses; pro rigs are typically capable of powering extra-long hoses with multiple spray guns running off one machine. Nevertheless, the single-gun units we tested generally impressed our painter – all were capable of putting out a suitable coat of quality latex paint. The least of the tools had too many compromises to be worth using, in his opinion, but to his surprise he found the winner proficient enough to take the place of one of his larger units for daily use on residential sites.
Winners
The performance results of our test support the old adage "You get what you pay for," as the units basically ranked right down the price line, with components and features commensurate with cost. The Airlessco LP 500 took top honors with output that seemed effortless and a commercial design built for hard work and tough conditions. The Graco Ultra 395 came in second with pro performance and advanced control features shared by only the top two pumps. Third place went to the Titan Impact 440 and fourth to the Graco 390. These four in the top tier are considered suitable for pro-level use on a consistent basis.
The midtier starts with the Graco 190 just edging out the Titan Advantage 400. Beneath these (in order) are the occasional-use tools, the Titan XT 420, Wagner Twin Stroke 9175, and Milwaukee M4910-20. If you're in the market for a pump you'll use only a handful of times per year, these lower-end units will put out the paint well enough, but they lack the convenience and durability of pricier models and don't quite make the cut for a solid job-site airless sprayer when compared with the other choices.
Dave Archuleta of Dave's Painting in Denver contributed to this test
Concrete Technology
Article written by: Martin Dawson
There have been a number of advances in new concrete technology in the past ten years. There have been advancements made in almost all areas of concrete production including materials, recycling, mixture proportioning, durability, and environmental quality. However, many of these innovations have not been adopted by the concrete industry or concrete users / buyers. There is always some resistance to change and it is usually based on cost considerations and lack of familiarity with the new technology.
The latest new concrete technology is beginning to gain acceptance in the industry. Some of the more interesting new concretes are called high performance concrete (HPC), ultra high performance concrete, and geopolymer concrete. They have significant advantages and little or no disadvantages when compared to standard concrete in use today.
High performance concrete usually contains recycled materials and thereby reduces the need to dispose of these materials. Some of these materials include fly ash (waste by-product from coal burning), ground granulated blast furnace slag, and silica fume. But perhaps the biggest benefit of using some of these other materials is the reduction in the need to use cement, also commonly referred to as Portland cement. The reduction in the production and use of cement will have many beneficial effects. These benefits will include a reduction in the creation of carbon dioxide emissions and a reduction in energy consumption, both of which will improve the global warming situation. It is estimated that the production of cement worldwide contributes five to eight percent of global carbon dioxide emissions. In addition, the use of fly ash and furnace slag is usually cheaper than cement and they have properties that improve the quality of the final concrete.
Today’s new concrete technology has produced new types of concrete that have live spans measured in the hundreds of years rather than decades. The use of fly ash and other by-product materials will save many hundreds of thousands of acres of land that would have been used for disposal purposes. Fly ash and other by-products from burning coal, are some of the most abundant industrial waste by-products on the planet. The elimination of burial sites for these waste by-products will translate into less risk of contamination of surface and underground water supplies. When compared to standard concrete the new concretes have better corrosion resistance, equal or higher compressive and tensile strengths, higher fire resistance, and rapid curing and strength gain. In addition, the production and life cycle of these new concretes will reduce greenhouse gas emissions by as much as 90%.
BSI is a new concrete technology that has a much higher tensile and flexural (bending) strength than standard concrete. It is a fiber-reinforced concrete that is combined with premixed dry components. It is much denser than standard concrete and structures built with it will need far less new concrete, perhaps as much as 80% less. The high density gives BSI concrete other properties such as extremely high resistance to corrosion from chemicals. The higher strength of BSI eliminates the need for placement of steel rebar in structural designs. BSI, or some variation with metallic fibers and/or superplasticizers, will be used to build some structural elements less than an inch thick. Overall, structures built with BSI will have much greater life spans and will require far less maintenance.
Ductal is another new concrete technology that is denser than BSI. Ductal uses steel or organic fibers to create a concrete that is stronger than BSI. Interestingly, the ancient Romans used horse hair in their concrete to improve its strength. Ductal is being tested for use in earthquake resistant structures, bridges, tunnels, and nuclear containment structures. Although it is more expensive than traditional concrete there are a number of cost savings that will make it price competitive. Among these cost savings are no steel rebar is needed, less material is needed with less related labor and equipment costs, and structures are thinner with less weight and require smaller foundations. In addition, both BSI and Ductal have low maintenance costs because of their very low porosity and are very resistant to penetration by water or chemicals. They are both resistant to salt water which is very corrosive and damaging to today’s bridges and roadways.
There have been a number of advances in new concrete technology in the past ten years. There have been advancements made in almost all areas of concrete production including materials, recycling, mixture proportioning, durability, and environmental quality. However, many of these innovations have not been adopted by the concrete industry or concrete users / buyers. There is always some resistance to change and it is usually based on cost considerations and lack of familiarity with the new technology.
The latest new concrete technology is beginning to gain acceptance in the industry. Some of the more interesting new concretes are called high performance concrete (HPC), ultra high performance concrete, and geopolymer concrete. They have significant advantages and little or no disadvantages when compared to standard concrete in use today.
High performance concrete usually contains recycled materials and thereby reduces the need to dispose of these materials. Some of these materials include fly ash (waste by-product from coal burning), ground granulated blast furnace slag, and silica fume. But perhaps the biggest benefit of using some of these other materials is the reduction in the need to use cement, also commonly referred to as Portland cement. The reduction in the production and use of cement will have many beneficial effects. These benefits will include a reduction in the creation of carbon dioxide emissions and a reduction in energy consumption, both of which will improve the global warming situation. It is estimated that the production of cement worldwide contributes five to eight percent of global carbon dioxide emissions. In addition, the use of fly ash and furnace slag is usually cheaper than cement and they have properties that improve the quality of the final concrete.
Today’s new concrete technology has produced new types of concrete that have live spans measured in the hundreds of years rather than decades. The use of fly ash and other by-product materials will save many hundreds of thousands of acres of land that would have been used for disposal purposes. Fly ash and other by-products from burning coal, are some of the most abundant industrial waste by-products on the planet. The elimination of burial sites for these waste by-products will translate into less risk of contamination of surface and underground water supplies. When compared to standard concrete the new concretes have better corrosion resistance, equal or higher compressive and tensile strengths, higher fire resistance, and rapid curing and strength gain. In addition, the production and life cycle of these new concretes will reduce greenhouse gas emissions by as much as 90%.
BSI is a new concrete technology that has a much higher tensile and flexural (bending) strength than standard concrete. It is a fiber-reinforced concrete that is combined with premixed dry components. It is much denser than standard concrete and structures built with it will need far less new concrete, perhaps as much as 80% less. The high density gives BSI concrete other properties such as extremely high resistance to corrosion from chemicals. The higher strength of BSI eliminates the need for placement of steel rebar in structural designs. BSI, or some variation with metallic fibers and/or superplasticizers, will be used to build some structural elements less than an inch thick. Overall, structures built with BSI will have much greater life spans and will require far less maintenance.
Ductal is another new concrete technology that is denser than BSI. Ductal uses steel or organic fibers to create a concrete that is stronger than BSI. Interestingly, the ancient Romans used horse hair in their concrete to improve its strength. Ductal is being tested for use in earthquake resistant structures, bridges, tunnels, and nuclear containment structures. Although it is more expensive than traditional concrete there are a number of cost savings that will make it price competitive. Among these cost savings are no steel rebar is needed, less material is needed with less related labor and equipment costs, and structures are thinner with less weight and require smaller foundations. In addition, both BSI and Ductal have low maintenance costs because of their very low porosity and are very resistant to penetration by water or chemicals. They are both resistant to salt water which is very corrosive and damaging to today’s bridges and roadways.
Sunday, September 5, 2010
Sri lanka Highway Construction
Project type
Express Highway Project
Completion
2010
Sponsors
Japanese Bank for International Corporation, Asian Development Bank and Government of Sri Lanka
Lead contractors
Kumagai Gumi, China Harbor Engineering Company, Taisei Corporation
| The Southern highway project in Sri Lanka is a 126km-long express highway running from Colombo to Matara on the south coast. The project is a major part of the 130.9km Southern Transport development project. The Southern Highway project was divided into two sections for financing purposes. The first section consists of the expressway from Kottawa (a suburb in Colombo) to Kurundugahahetekma. The second section consists of the long expressway from Kurundugahahetekma to Matara.  "Construction was started in 2003 and the project is anticipated to be completed by 2010." The southern region of Sri Lanka will become easily accessible once the project is completed. The project will increase road safety and the travel time between Colombo and Matara will be greatly reduced. The project was initially estimated to cost $348.75m, but escalated to $741.1m. Construction was started in 2003 and the project is anticipated to be completed by 2010. Planning and design The expressway between Kottawa and Kurundugahahetekma is 66.5km long. The section is divided into two parts: package I and package II. Package I comprises the road from Kottawa to Dodangoda (35km) and package II is from Dodangoda to Kurundugahahetekma (31.5km). The road in package I was originally planned to be a four-lane road and package II a two-lane road. However, while implementing the project, a decision was taken that the entire expressway should be a four-lane road structure, with phase II expanded from the planned two lanes. The project's second section involves construction of a 59.5km-long four lane road between Kurundugahahetekma and Matara. The speed limint of the express highway is 120km/hr. Once the project is finished, the travel time between Colombo and Matara will be reduced from four hours to 1.5 hours. Financing The project is being financed by Japan Bank for International Corporation (JBIC), the Asian Development Bank (ADB) and the Government of Sri Lanka (GOSL). JBIC provided a loan of $2.05bn, while ADB and GOSL provided $1.03bn and $1.26bn, respectively. JBIC's loan is availed for the 66.5km-long first section expressway from Kottawa to Kurundugahahetekma while ADB is funding the 59.5km-long second section expressway from Kurundugahahetekma to Matara. Construction Construction commenced on the ADB-funded section in April 2003. Package I in the other section commenced construction in September 2005 whereas package II commenced in March 2006. The Ministry of Highways of Sri Lanka is the executing agency of the project whereas the Road Development Authority is the implementing agency. "The project was initially estimated to cost $348.75m, but escalated to $741.1m." The intersections on the Colombo-Matara expressway include Kottawa, Baddegama, Kahatuduwa, Pinnaduwa, Gelanigama, Deegoda, Dodangoda, Kokmaduwa, Welipanna, Godagama and Kurundugahetekma. The majority of the construction work of the ADB-funded section of the project such as construction of bridges, tunnels and earth fillings has been finished as of September 2009. Other works including carpeting and fencing remain to be completed. Bridge construction A total of 22 bridges are being constructed along the expressway. As of 2009, three bridges have opened: the Kalu Ganga bridge, the Welipenna Bridge and the Benthara Ganga bridge. These bridges were opened in part to mitigate flooding in their respective areas. Contractors The ADB-funded section or the road from Kurundugahahetekma to Matara Godagama was contracted to Kumagai Gumi of Japan. The contractor was selected by the Road Development Authority of Sri Lanka in December 2002. Under the contract, Kumagai has to build a 29km-long express highway, a 5km access road and 16 bridges. The supervision consultants in the section are Halcrow Group with Roughton International and Engineering Consultant. Package I of the section was contracted to China Harbor Engineering Company while package II was contracted to Taisei Corporation of Japan. The civil works contractor pre-qualification was completed in March 2003. In March 2004, bid documents were issued to the prequalified contractors and the bids were closed in June 2004. The supervision consultants are Pacific Consultant International with Resources Development Consultant. | 
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The Southern highway project in Sri Lanka is a 126km-long express highway running from Colombo to Matara on the south coast. |
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Southern districts of Sri Lanka. | |
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The project was initially estimated to cost $348.75m, but escalated to $741.1m. |
Bridge seals
A basic requirement for the functional efficiency of many structures, including bridges, is a durable seal. The reliability of the type of seal is crucial for the safety, functional performance, value in use and service life of a bridge. Reinforced concrete has a tendency to crack under high thermal and mechanical loads. Through constant movement, the cracks become bigger over the course of time, rainwater and aggressive substances from the environment penetrate into the cracks, destroy the concrete and attack the steel. The structural safety of the building may even be at risk. Reinforced concrete structures subjected to this kind of environmental stress should therefore be treated at the earliest possible stage with a permanently elastic, crack-bridging seal capable of long-term resistance to all manner of loads. Due to its high flexibility and high elongation at break, building structures can be safely and durably sealed with Baytec® Spray Systems.
Wednesday, August 25, 2010
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
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
Figure 1. Moist Curing Time and Compressive Strength Gain
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 sheets3) Accelerating strength gain using heat and additional moisture
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.
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).
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
- Ponding
- Fog Spray
- 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
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
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 .
Thursday, August 19, 2010
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
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
Tuesday, August 17, 2010
Asphalt Paving Operation
by Stephanie Paul, Linda Puspa-Dewi, Kamolwan Lueprasert & Heinko Dona Madon
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