Jan 02

Transform Old Concrete With Cement Stain

Boring concrete

Let’s be honest, while concrete is a great economical and lasting option, its look over time can turn a garage, a sun room, a basement, a porch or a patio into a plain eyesore! But do not despair, there are a number of options that can completely transform the look of old boring concrete at a fraction of the cost of replacing or pouring new concrete. One of this option consists in applying cement acid-stain, available in various colors, to give a brand new look and protective layer.

One of the advantages of using cement stain over paint, is that cement stain is permanent, won’t fade or peel. It creates marbled variations of color on cured concrete by chemical reaction with the minerals in the concrete. Concrete resurfacing results will vary greatly due to variations in the underlying concrete.

Concrete stain flooring

Concrete stain flooring

MATERIAL NEEDED:

Paint tray
Paint brush, spray bottle and/or pad
Paint roller
Tarp or plastic roll
Concrete stain (comes in solid and translucent colors)
Concrete sealer

PROCESS

STEP 1: CLEAN
As for all painting job, the first step is to clean the surface of oil, dirt, mud, dust and residues. Use coca cola to remove oil stain on garage floors. Use a broom, a brush for the areas that need the most work. You can also power wash the area but make sure that it has plenty of time to completely dry.  Skipping the drying process will prevent proper adhesion of the stain. This step is really important because stain is essentially translucent color that will not only show the underlying defects or colors variations but can also make them even more visible.

STEP 2: TEST STAIN
Always test the color you choose in a small area to make sure that the result is acceptable. Don’t just rely on the manufacturer’s color chart because stain reacts differently to different types of surfaces. This is especially important if you are working on an intricate pattern with various colors not just applying one color over the entire area.

STEP 3: APPLICATION TECHNIQUES
Apply too little and there won’t be enough color to etch the concrete and last. Spray too much and you will end up with a puddling problem and too dark effect. Practice makes perfect so either test a small area or hire a professional if you are going for a large area and complex design. This requires practice, proper timing.  Generally, you want to apply a first coat using one of the techniques below and finish with a light brush to soften the edges and  make sure the stain is evenly applied before moving to the next section. Some of the techniques are:

Paint with a brush: always start at the perimeter (edge of a wall or building)
Scrubbing: if you are using this technique make sure to maintain a n
atural stroke to avoid streaks
Spraying: this is great when creating flowing patterns that requires loose applications.
Rolling: Great for intricate geometrical patterns like diamond shapes.
Cut lines with a circular saw (1/8” deep) if you are making repeated patterns of different colors. Adding some blue tape in the grooves will help prevent stain of different colors from bleeding into other areas.
Use stencils to create beautiful forms
Use tape to create square tiles for a stone work look
Stamp concrete to create wood board patterns
Simulate bricks patterns and much more…

STEP 4: FINISHING
It is recommended to fully wet and neutralize the area to avoid accidental foot prints or marks. Let it dry fully then add a concrete sealant finish coat. This can be done either spraying, using a cross-hatch rolling, or even buffing if you are going for a wax finish look. Wait at least 4 hours before stepping or moving furniture back.

Artistic Concrete design

Artistic Concrete design

PRO TIPS:
If you have an area that can’t be cleaned, has some defect, you may have to be creative and turn defects or color variations into unique patterns and designs by applying more stain in these areas.

If you have rust stains or have filled cracks, the stain will appear darker in these areas, so plan accordingly.
The best time to apply stain is on a cloudy day. Avoid direct sun on a summer day. High heat will speed up the drying time and make it very difficult to smoothly blend one area into the next without creating color variations and streaks.

So if you have a concrete patio or a slab that is in need of some TLC, try out acid stain. Tackle it yourself or hire a professional and enjoy the results. Check out amazing diy projects and pictures on Pinterest to see how others have transformed their boring floors and patios into gorgeous creations!

Happy New Year!

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Dec 20

2015 CONSTRUCTION OUTLOOK

As we are approaching the end of the year, it is good to look back on the year and plan for the year to come. On the macro level, we see that the US economy is slowly and finally stabilizing. It continues to have its share of fits and starts that are being reflected in the construction industry which is expected to grow to $9.4 trillion in 2015, according to Construction Perspectives and Oxford Economics, and total construction employment reaching up to 5.85 million. This constitutes a record since 2009 but we are still at 50% pre-bubble levels and might have to wait until 2017 to have fully recovered! So while things are headed in the right direction but we are far from out of the tunnel!

Here is the good news, with higher income and more jobs (3 million new jobs in 2014), demand for housing keeps increasing. It is estimated that there is 1 more million potential home buyers on the market today (younger buyers). Record low interest rates combined with lower down payments from Fanny and Freddie mortgages, lesser restrictions on credit conditions, a stronger job market means greater home buying power for Americans. As of Dec. 11 2014, an average 30-year, fixed-ratmortgage was 3.93 percent, down from 4.53 percent from January 2013! Stronger rental market has also boosted multifamily constructions to normal levels.

In 2015, new home sales are expected to increase 25 percent in the US, representing about 560,000 sales. This is still well below the 900,000 pre-bubble levels, but again, we are heading in the right direction. Housing starts should pick up 20% in 2015, for a total of 1.2 million, according to Kiplinger’s December economic outlook**

TOP HOUSING MARKETS FOR 2015
Here is Realtor.com top pick from their recently published 2015 Housing Forecast:

Dallas-Fort Worth-Arlington, Texas: ranked 1st in forecasted household growth over the next five years.
Houston-The Woodlands, Texas: ranked 3rd with 4% increase over the next five years.
Los Angeles-Long Beach, California: 4th place in potential household growth and a 4 percent increase over the next 5 years.
Washington, D.C.: ranks fifth. The sequester did deflate the housing market in 2013 and early 2014 but the situation is now corrected and a 10% increase in home sales is expected over the next 5 years.
Atlanta-Sandy Springs, Georgia: ranks seventh in forecasted household growth over the next five years with home sales are expected to rise by 11 percent.
Minneapolis-St.Paul-Bloomington, Minnesota is the second largest home-owning millenial households.
Denver-Aurora-Broomfield, Colorado is expected to see a 14% increase in home sales.
Des Moines-West Des Moines, Iowa
Phoenix-Mesa-Glendale, Arizona expects a 22 percent increase in new construction over the next 5 years.
San Jose-Sunnyvale-Santa Clara, California: Sustained employment and income growth makes this market outperform neighboring Bay area cities.

US Housing Starts

Courtesy of National Association of Home Builders

Top US states for Housing starts according to the National Association of Home Builders:

The South leads the pack with the following states:
Delaware, Maryland, District of Columbia, Virginia, West Virginia, North & South Carolina, Georgia, Florida, Kentucky.

Followed by West and the following states:
Montana, Idaho, Wyoming, Colorado, New Mexico, Arizona, Utah, Nevada, Washington, Oregon, California, Alaska, & Hawaii.

4 NEW TRENDS IN CONSTRUCTION :

  • Commercial lending on the increase:
    Following the financial crisis in 2008, banks proceeded with a complete lending freeze in 2009. A slight improvement was noticed in 2013 and 2014, leading to a jump in commercial lending and a record in construction starts*. This trend should continue and even increase in 2015.
  • Green from the get goEarth-Friendly-Icon
    What used to be seen as an expensive “nice to have” features for high end construction is now being incorporated at the design level, as part of the blueprint that includes sustainable building materials, renewable energy, optimized energy performance and cradle to cradle components (LEED v4) for new construction projects. Demand for green renovations in existing buildings will also continue to grow.
  • Mobile technology on the job
    Design firms, building contractors, project managers are ditching paper for tablets, laptops and smart phones on the job site to better plan, manage projects and overall productivity.
  • Demand for infrastructure repair
    Previously, demand for construction was mainly driven by the private sector, but recently, with more natural disasters and extreme weather conditions in our future, rebuilding and fixing existing infrastructure is taking a more prominent place in the US and around the world.

8 FASTEST GROWING CITIES IN THE US 

In addition to looking at housing starts, we also should take into consideration population growth provided by the U.S. Census Bureau population data (for July 1, 2012 through July 1, 2013) (measuring percentage population gain) and new construction for commercial and residential building. And the winners are:

Houston, TX (growing oil and gas industries) 2.6% gain
Austin, TX (fastest growing cities for the 4th year in a row) 2.5% gain
Phoenix, TX (construction industry jobs are up 5% year-over-year)
Raleigh, NC (Large tech companies, major universities, low unemployment rate) 2.2% gain.
Orlando, FL (booming tourism industry) 2% gain.
San Antonio, TX (oil industry) 1.9% gain.
Denver, CO (outdoor activities, growth in tourism, construction) 1.9% gain.
Nashville, TN (Music industry, healthcare companies, affordable cost of living) 1.8% gain.
Charlotte, NC (2nd largest banking center in the US after New York) 1.8% gain.
Oklahoma, OK (job growth in the oil industry) 1.7% gain.
Phoenix, AZ (growth in renewable energy, biomedical and aerospace) 1.6% gain.
Salt lake, UT (low 4% unemployment rate, growth in residential and commercial real estate, construction).

WHAT ABOUT EUROPE? 
With its aging population and low birth rate (1%), weaker economies (Spain, Greece, Portugal etc.) Europe isn’t a great prospect for construction and new housing in the coming years. There is one exception: Istanbul, Turkey, the frontier between Europe and Asia, is showing signs of both and economic growth.

TOP 10 FASTEST GROWING CITIES IN THE WORLD (Next decade growth)
NOTE: The data below is based on population projections from the United Nations and immediate need for rapid housing construction and infrastructure development. They do not cover megacities that have known massive expansion in the past 20 years (like Mumbai, Mexico City, Dhaka, Bangladesh). As in all cases of explosive urban growth, the road is paved with many obstacles such as government instability, natural disasters, poverty level etc.

10. Chittagong, Bangladesh with projected 80% growth from 2006 to 2020 (second largest city and commercial capital of Bangladesh with a booming commercial real estate industry and construction)
9. Dar Es Salaam, Tanzania with 82% growth from 2006 to 2020 (is the third fastest growing city in Africa after Bamako and Lagos and ninth in the world). Had major construction boom in the past few years.
8. Faridabad, India with 83% growth (residential growth, end-user driven market)
7. Lagos, Nigeria with 84% growth (following a building collapse from 2000 to 2010, rebuilding infrastructure, improving safety)
6. Bamako, Mali with 84% growth (improve Mali’s urban infrastructure, drainage projects, flood protection)
5. Kabul, Afghanistan with 91% growth (military and political instability are major factors affecting the rebuilding of the country)
4. Surat, India with 98% growth (Gujarat’s second-largest city, eighth largest city and ninth largest metropolitan area of India, first smart IT city in India)
3. Sana’a, Yemen with 98% growth (largest city in Yemen, massive rural immigration is forcing investment in underdeveloped infrastructure and municipal services)
2. Ghaziabad, India with 103% growth (infrastructure development, residential market growth offers affordable housing and mid- segment)
1. Beihai, China with 309% growth (higher demand in biggest cities continues to climb while demand in smaller cities continues to fall).

In addition to the above, there a few emerging powerhouse cities that act as strategic platforms for China and India with the rest of the world that should be mentioned. They are:

Chongqing, China: This city serves as connector for top interior cities like Shanghai, Hong Kong, Shenzen and Guangzhou. It is in the process of building a large transportation infrastructure (new plane, roads, rail connections…)

In India, Bangalore, Ahmedabad (100.000 new jobs this year) and Chenmai (highest per capital income in India) are becoming world centers for auto manufacturing, software and entertainment. New housing construction is on the rise as a result of a fast growing middle class, investments  from foreign companies, centers for higher education.

So whether in the US or abroad, the construction industry and new housing will continue to grow in the cities and regions mentioned above providing plenty of work and opportunities for this recovering industry.

Sources:

Commercial Construction Industry Outlook and Trends
*United States Construction Outlook
**Kiplinger’s Economic Outlook
New building permits from the US Census bureau

Dec 03

Hot Weather Concreting

Hot weather concreteWith rising world temperatures due to global warming, the job of concrete operators in hot, arid and tropical climates just got more challenging. Concrete placement in hot summer months or in regions of the world with constant high temperatures like Central & South America, the Middle East, Africa, South East Asia and Australia requires comprehensive planning, precise rapid execution and close monitoring during the finishing and curing phases.

High Temperature

High Temperature

What temperature range can be considered hot for fresh concrete pouring? Whenever the temperature reaches above 77 or 90 degrees Fahrenheit, a plan and specific measures should be put in place to remedy the damaging effect of such temperature. Consider that an increase of 20 degrees Fahrenheit can shrink the setting time to about 50 percent!

Placing fresh concrete in high temperatures impacts just about every step of the process, from concrete handling, the placing, setting and curing time. In addition, the high temperature also affect the cement mixture itself, the concrete equipment used to batch and transport the concrete. All of the above factors must be considered and addressed when designing a plan for the job.

Some of the main risks are accelerated cement hydration (which can cause plastic shrinkage and cracking), higher water-cement ratio that could cause reduce strength and slump loss.

Below are some measures that can be taken to reduce risks of plastic cracking and lower strength:

PLANNING PHASE

  • Hire a crew experienced in rapid concrete placing in these hot conditions.
  • Check forecast temperatures (day highs and night lows) and plan the job on the best days.
  • Make sure you have adequate water availability on the site.
  • Order or rent sunshades from the sun prior to pouring to reduce the surface temperature.
  • Schedule wind screens in areas prone to high winds conditions.
  • Rent misting or fogging equipment.
  • Schedule your crew and pouring at the coolest times of the day (early morning and night time).
  • Select the proper cool concrete mixture and set retarders for the job.
  • In temperatures above 90° F the use of liquid nitrogen on the batching truck.

PLACEMENT

  • Mist cool water on subgrade forms and steel reinforcement prior to placing.
  • Have chilled water on hand to adjust the slump when needed.
  • Check the rate of evaporation, the relative humidity and the concrete temperature with the help of a Nomogram. This is optional when operating in temperatures below 80° F but a must for temperatures above 90° F.
  • Poor softer concrete so that it can be placed more rapidly but don’t add too much water to the mix.
  • Choose proper curing methods (set retarders and water reducers) and apply when the concrete finishing is done.

SETTING, FINISHING & CURING

  • Use retardant admixtures during the setting time.
  • Make sure finishing is complete (when the surface sheen has disappeared) before starting the curing process (minimum 3 days).
  • Never add water to concrete during the 3 days of finishing!
  • Install sunshades, wind screen, misters or foggers to protect the concrete during the curing process.

United Equipment SalesFollowing the above recommendations, with proper planning and careful execution, placing concrete in hot weather conditions can be successfully achieved. Have any questions on concrete mix or equipment? Give us a call at: (503)283-2105

FURTHER READING

Hot weather concrete construction
Hot weather concrete tipsHot Weather Concreting

Nov 13

Fly Ash Concrete

Fly ash in concrete

FROM GREY TO GREENISH …

If you consider yourself a green person, you may think using fly ash, a by-product of burning coal, in your concrete mix rather sacro-saint! After all, coal plants are some of the biggest polluters and CO2 emitters.  In recent decades, in an attempt to minimize its environmental impact, the EPA forced coal-powered plants to trap particulate matter before it is released in the smokestacks, to properly capture and dispose coal ash, a.k.a. as fly ash, the residue found after smokestacks are cleaned. Disposal of fly ash is usually done by mixing it with water and placing it into open impoundments (that could be damaged by storms), storage ponds or buried in landfills that have been known to occasionally breach or leak as in the case of the December 2008 collapse at the Tennessee Valley Authority’s Kingston Fossil Plant, releasing 5.4 million cubic yards of coal fly ash into the Emory River! So how much are we reusing? Approximately 43-45% of all fly ash is being recycled today.

Electrical PoleWith 50% of all electricity in the US being generated by coal plants, one couldn’t begin to imagine the huge amount of fly ash produced by coal-powered plants daily. Capturing it and reusing it in a safe way would in fact prevent the inevitable spread of some of the heavy metals  it contains (depending on the coal bed makeup: arsenic, lead, chromium, mercury, dioxins etc.) in the atmosphere we breathe, the water we drink… So when the first attempts at substituting fly ash to Portland cement resulted in a concrete with greater strength and durability, what was once a worrisome problem looked like it could be turned into a solution for the environment and the construction industry. Recycling fly ash into concrete would not only reduce CO2 emissions but also neutralize the harmful effects of the known carcinogens it contains and the need to mine for new raw materials. Also called geopolymer concrete, this “green” concrete is cheaper to produce and is being widely adopted for all types of concrete applications.

2 TYPES OF FLY ASH
There are 2 classes and both can be used as a replacement for Portland cement or hydrated lime. They act as a filler providing contact points between larger aggregate particles in asphalt concrete mixes.

Class F: is made from burning anthracite and/or bituminous coal
Class C: is made from lignite or subbituminous coal

BENEFITS OF USING FLY ASH IN CONCRETE

Earth-Friendly-IconECO FRIENDLY?
The process of making cement is quite energy-intensive and could account for 5-8% of greenhouse gas emissions around the world. Factor in steady population growth and the number will continue to increase unless a massive adoption of greener alternatives happens. Fly ash concrete is one of them because of its abundant availability, cheap cost and the fact that it could reduce as much as 90% of CO2 emissions when considering the end to end process.

Green builders can gain points towards their LEED goals (Leadership in Energy and Environmental Design) if they can replace at least 40% of Portland cement with it. Bricks that are made with fly ash can even store CO2 from the atmosphere.

ALL AROUND BETTER CONCRETE
Fly ash is known to improve concrete’s workability, pumpability, chemical resistance, finish, strength, and durability. Fly ash particles are similar in size with Portland cement and as a result requires less water during the mixing stage. This means better surface finish, sharper edges in precast concrete. Its fine particles reduce bleeding and segregation and improve overall workability. This is especially helpful in extending working time in hot weather.

DECREASED PERMEABILITY:
Fly ash produces a concrete that is less porous than Portland cement. The pozzolanic effect of fly ash creates a denser product due to smaller pore sizes. It also reduces bleed channels and permeability in concrete.

Widely used in road projects, fly ash increases the stiffness of the asphalt, improving rutting resistance and mix durability.

EXAMPLES OF FLY ASH REUSE

In addition to replacing Portland cement, fly ash is being used in the following areas and the list keeps expanding:

  • Road construction: ideal self-compacting backfill material (as a replacement for compacted earth) for backfill, embankments, road sub base construction, mineral filler in asphaltic concrete, as a loose application on roads for ice control, in highway sound barriers…
  • Agriculture: fertilizer, soil amendment and stabilization.
  • Aggregate material substitute: for brick production replacing clay.
  • Dam construction: in roller compacted concrete dams.
  • Waste management: waste solidification and stabilization, conversion of sewage sludge into organic fertilizer or bio fuel.
  • Roofing material: tiles, granules.
  • Marine: pilings, artificial reefs
  • Binding agent: paints, undercoating.
    And much more

IN CONCLUSION

Only time will tell whether or not small amounts of heavy metals could leak from the concrete over time and if this new found durability is truly long lasting. Recent spills have prompted environmental groups to call for tougher regulations, so whether or not the EPA decide to classify it as hazardous  material remains to be seen. But until then and until coal powered plants are being phased out for greener alternatives, and the huge reserves of fly ash remains an environmental issue, the safe use of fly ash in concrete makes sense and should continue. 

United Equipment Sales

Sources:
Marc Boyer: How fly ash concrete works
Fly Ash on Wikipedia
Fly ash products
Fly ash suppliers

 

Oct 30

Avoid Common Mistakes When Pouring Concrete

Concrete PouringHandling concrete is both an art and a science! In this article we will focus more on the science part and the required steps that should be followed no matter what your budget or time frame is. In other words, don’t mess with the basic recipe or your cake will suffer!

PREPARATION: before any concrete is poured, you must make sure a few things are in place:

1)      Know if the base is ready
Starting with a solid base that has been properly drained is essential. Skipping this important step could cause soft areas to later produce cracks over time and under the pressure of heavy vehicles. The best way to do this is pour between 2-4 inches of sand or small gravel and pack it down. This is especially important if the area is known to not have good drainage.

2)      Use reinforcement
Once the forms are built, you should reinforce the concrete with rebars (3/8 or ½ inch). Avoid steel mesh or even plastic fibers because they do not provide additional strength. They are helpful in reducing cracking.

3)      Know how much water to add
While it may be tempting to add more water to the mix to ease its flow down the chute and speed the pouring process into forms, this will also result in a weaker concrete.
So resist the temptation and instead keep the cement mix as dry as possible. It may be a little more work to push it into the form, in the corners and the edges but this will pay in the short, medium and long-term.

There are a few things to keep in mind after the concrete has been poured:

Smoothing concrete1)      Know when to begin smoothing the surface
This step requires precise timing, having everyone ready and all the required tools nearby. What happens if you start trowelling too soon? You risk bringing the cement paste to the surface and weakening it. One easy way to know when it is time to start troweling is when the water starts to disappear from the surface. This signals the perfect time to start smoothing quickly as concrete is known to harden fast. Depending on the job you are doing, you may need a rebar cutter, a plate compactor, a bull float (for large slabs), a square-edge shovel, one or more finishing trowels. For the finishing details, you will need as a minimum, a groover, an edger and a stiff square broom.

2)      Cutting down control joints
Once the concrete has been poured, it is necessary to cut the control joints down to 25% of the depth of the slab. So if you poured a 4” slab, your joints should be 1” deep. This is done to accommodate for the shrinkage and cracking that occur during the curing process (about 1/8″ per 10 feet of length). The cutting can be done while the cement is still fresh using grooving tools or with an early-entry dry-cut lightweight saw (1” to 3” deep). On hot days, you may need to cut joints within 6-12 hours or risk cracks. The important thing, if you decide to wait and use a saw blade, is that the edges of concrete won’t chip during the cut.  So proceed carefully.

3)      Slow down the curing process
Good curing means evaporation should be prevented or reduced. Slowing down the drying process is the key to strong concrete. The strength is the direct result of the lime hydrating during the curing process. One simple way to do this is to cover the slab with wet burlap, wet blankets or a plastic sheet for a week or more. In hot conditions, above 80 degrees, watering the slab frequently with a garden hose or a light sprinkler is necessary to keep it moist and let it reach it maximum strength. Concrete will reach approximately 80% of its strength in 7 days and almost 100% after 28 days. Using curing compounds (retarders, air entraining agents, plasticizers etc.) will also help sealing the moisture. Find out more about ad mixers in this article http://excavatorheavyequipment.com/blog/2013/07/01/why-use-concrete-ad-mixers/

4)      Test concrete
As a minimum, you should conduct a slump test. Depending on your situation, you could also do a flow table test, or a ball penetration test.

5.      Wait to build
Concrete reaches a high percentage of its final strength after 28 days, so construction should wait for at least 5 days to start.

By following these important steps you will avoid some of the most common mistakes that are learned the hard way. They will save you time, money, reputation and give you more time to focus on the art of concrete and its many forms.

More questions? Call us at (503)283-2105 or visit our Youtube channel. We always like to hear from our readers.

Oct 09

The Schwing SP1000 – The Workhorse of the Concrete Industry

We are featuring this pump because it is one of the toughest, most reliable fuel efficient trailer concrete pump on the market. It is without any doubt one of the best built pump. This shouldn’t come as a surprise from Schwing, the company who invented the first concrete pump and as a result revolutionized the entire industry*.

So what makes this machine so great? It can pump 70 cubic yard per hour, it produces 1100 psi maximum pressure and uses a maximum aggregate size of 1.5 inch.

It is powered by a 139 horse power diesel engine, 35 pump stroke per minute max. This all-hydraulic concrete pump provides optimal fuel efficiency. Its lack of electronics makes it ideal for projects for humid regions and cold locations like Alaska, British Columbia. The hydraulic system is open loop, produces 4350 psi. It comes with a 70 gallon hydraulic tank, a standard hopper agitator and a 11 cubic feet hopper. The trailer unit also comes with a remote control and a 100 foot cable that  convenient to the operator and weighs 7580 pounds.

The Long Rock Valve™ provides better filling efficiency for the material cylinders. It can handle harsh mixes, shotcrete and grout and allows for a fast clean out with less water.

What is this pump designed for? Bridge work, apartment building, high rise work. Remember, it can pump over 1000 ft and over 400 ft straight up!

Dick Hibbard

Learn more about this amazing pump in this short video: Discover the Schwing SP1000X.
Call Dick Hibbard at (503)283-2105 if you were thinking of buying one or just to find out about our best deals on new and used concrete pumps.

 

Aug 05

Architectural & Decorative Concrete

The concrete industry has come a long way and keeps reinventing itself to answer the needs of builders, architects and even decorators. With more and more home owners attracted to a greener and more sustainable lifestyle, we have seen, in more recent years, a new use of concrete, blending innovation and artistry to create truly unique surfaces for interior floors, patios and kitchen counters. Here are some of the coolest new possibilities:

Concrete Countertops in the kitchen:

Granite Counter top

When you think kitchen countertop, a few options usually come up. Depending on your budget, you can get high end and more expensive products like: polished granite, marble, quartz, soapstone, stainless steel and glass.  On the cheaper end and ideal for DIY afficionados, you have tile, wood and laminate. Other options that are becoming more popular are concrete and recycled concrete. The later one being one of the most eco-friendly choice that allows you to combine post-consumer products like glass, paper, composite and plastic with concrete for a truly unique finished product.

Plain concrete can be used in countertops, landscaping and customized with various textures and finishes (stain color). A really nice feature of concrete is its ability to be energy efficient. Whenever the temperature rises, the concrete traps the heat and releases it when the temperature cools down.

White Portland cement
To transform what may be viewed as boring cold grey concrete into bright, elegant aesthetic surfaces requires a combination of special ingredients, forms and finishing technique. The magical ingredient in this case is white Portland cement.  It comes plain or pigmented and is available in wide array of colors, from pastel to saturated colors. It can be used indoor or outdoor and has the same durability properties as grey cement but contains more metal oxides like iron and manganese, giving it its whiteness. White cement concrete is used in exposed architectural concrete, landscaping, building accents and more. It provides greater energy efficiency and safety because of its light color.

Some design ideas

Stone finishing

Concrete can be transformed to look like natural stone. To create this effect, you will need to cast the concrete in an integral color then apply multiple layers of acid stain to the surface until the desired result is obtained. TIP: Use the veins produced by the marbelizing effect to hide seams on your countertop.

Wood grained concrete texture

 

Create a wood-grained finish to any surface by applying a technique called “board forming”. To create this unique texture, you will need to cast the concrete in forms that have been previously lined with unfinished wood that will imprint the wood texture into the concrete surface. You can also create board lines by cutting straight lines with a saw after it is cast. Next is creating a realistic color using both integral color with topical stains.

To create a smooth and elegant look to your surface, you can polish or sand your concrete. It is recommended that the counter top be poured in one piece and not show any seam. To create the look of marble, you will need to use a titanium-white concrete mix that contains white silica sand. You can also hand sand the surface lightly for a less shiny and more natural look.

Exposed Aggregate Finish
This is where the use of post-consumer products like glass, stones, bricks, even shells can be recycled and added to concrete to make truly unique finished surface. There are 3-4 steps to create this type of finish: first you pour the concrete, then you insert pieces of material of your choice (broken glass, decorative stone, shells etc.) Once the concrete has set  you grind the surface to expose the aggregate. Finish with a high gloss sealer to protect your newly created surface.
TIP: for spectacular results it is best to select pieces that will create the most contrast with the concrete color.

If you are looking for a good deal on a concrete pump or want to make sure you have the right pump for the job, give us a call at: (503)283-2105 or visit us at: www.Unitedequipmentsales.com

Related reading
Milestones in the history of concrete construction
Photos of concrete counter tops
Applications for architectural concrete

Aug 02

How to Minimize Dust Exposure in Shotcrete Placement

Dust generation may seem to be part and parcel of any construction job and nothing to worry about but long-time exposure and inhalation of dust can lead to damaging health effects especially when working in tunnels and mining jobs.

Let’s first look into factors that cause excess dust and how we can avoid or reduce them. Take for instance, the process of building tunnels. It requires going through a series of steps that generate huge amounts of dust: drilling, namely: blasting, crushing, extracting and shotcrete. While the first four processes have to control the dust generated and remove it from the atmosphere through special ventilation, water sprays and dust collectors, shotcrete placement doesn’t.  However, hiring a shotcrete crew that is experienced in working underground will minimize dust generation because they will know how to control it at the source.

Silica

Where is silica found:
Silica is found in asphalt, brick, cement, concrete, drywall, grout, mortar, stone, sand, and tile. OSHA regulation 29 CFR 1926.55(a) requires that exposures must be below a Permissible Exposure Level (PEL) of 0.1 mg/m3. The National Institute for Occupational Safety and Health has a lower Recommended Exposure Level of 0.05 mg/m3.

Health risks from exposure to Silica:
Repeated exposure to cement dust will lead to irritation to eye, nose, throat and upper respiratory system. When skin is directly exposed to cement, further irritation can occur and skin cracking can result from chemical burns. Rinse eyes or skin with water and soap if it comes into contact with cement dust and if the burning continues consult a doctor.

Another serious risk for workers is lung injuries from Silica exposure. This can lead to chronic obstructive pulmonary disease (COPD), lung cancer, tuberculosis and Silicosis. There are about 3,600 to 7,300 new cases of silicosis every year. Note: This is a progressive illness that will continue to worsen even after exposure to silica has stopped. While it may take years for these diseases to show up, workers should be on the lookout for certain symptoms like a chronic dry cough and shortness of breath. These disabling, irreversible and at times fatal diseases occur when silica particles are inhaled by workers. As a result, nodules start growing and can become so large that they impede normal breathing.

concrete safety

Dust Control Checklist

How to protect your crew:
1. Prevent dust from being released in the air by using water or vacuums at the source.
2. When water and vacuums are not available use a respirator.
3. Replace sand with aluminum oxide for blasting.
4. Use a wet abrasive blaster that mixes water with media before leaving the nozzle.
5. Avoid eating, drinking and smoking in dusty area to reduce, wash face and hands first.
6. Use disposable clothing or wash work clothes at the work site.
7. Shower and change into clean clothes before leaving the job site to avoid contamination.
8. Do a periodic lung screening.

With over 40 years of experience in the industry, we know the importance of safety at work. We also know that using the right pump for the job means even greater safety, better results and more savings in the long run. So if you are looking for a great deal on concrete or plaster pumps, give us a call at (503)283-2105  or visit our website.

Additional reading:
Concrete Safety procedures
Maintenance Tips for gunite
Work Safely with Silica 

Jul 17

TESTING FRESH CONCRETE – PART 3: Ball Penetration Test

In our previous article, we looked into Flow test as another common test method to ensure that fresh poured concrete has the right consistency and workability. As in all testing methods, always keep in mind that some limitationsoften apply. Today we will focus on a third method called Ball Penetration Test (ASTM C360) and better understand main causes of segregation and bleeding in concrete.

Kelly Ball

THE BALL PENETRATION TEST (a.k.a Kelly Ball Test) can be conducted on site by measuring the indentation made by a Kelly Ball into plastic concrete. The device consists of a 6 inches steel cylinder (15cm) in diameter with a semi spherical shaped bottom and 4 5/8 inches in height. It also comes with a frame that guides a vertical handle marked in ¼” increments on one side and half inches on the other.

Advantages: this test can be conducted directly on the concrete in site (in a form, a hopper, wheelbarrow), there is no need for filling and rodding a container. This means that the test can be completed faster than with a slump test and will yield more precise results.

California Case Study:
The California Division of Highways used to perform a slump cone method but in 1953, they adopted the Kelly Ball Test. In addition to the ASTM and AASHO requirements, they looked for a minimum depth of 6 inches on concrete and a minimum clearance of 9 inches. If the test fails to show 1 inch of slump (1/2 inch of penetration), more reading must be taken until 3 successive readings within 1 inch are obtained. They average the first three valid penetration readings. ASTM and AASHO test methods are to the nearest ¼ inch while with the California method each inch of penetration.is read as 2 inches on the ball shaft.

WORKABILITY
DEGREE

SLUMP/PENETRATION (mm)

USES

Very low

0-25

Roads with power operated machines

Low

25-50

Road with hand operated machines

Medium

50-100

Flat slabs with crushed aggregates

High

100-175

For congested reinforcement (not for vibration)

Limitations:
There are several known sources of variances of the Kelly Ball Test, namely: sampling, testing, differences in moisture content, inadequate mixing of materials, variation in mixing time and types of aggregates.

To better master concrete workability, one must study and understand  what causes segregation and bleeding in fresh concrete. Below is some useful information that should help concrete operators on the job.

CONCRETE SEGREGATION
This phenomenon occurs when the elements of the cement paste separate creating an uneven distribution. It can happen when the concrete is mixed, transported, placed or compacted.

Types of segregation
When coarse particles are mixed with finer particles they can settle more because they are heavier. This is the first form of segregation also called coarse segregation.  The mix will have a low asphalt content, low density, lots of air voids. It is the main cause for segregation.
The second type of segregation can happen in wet mixes, when cement and water separate from the mix. It is called Fine segregation and produces cement with high asphalt content with low density, concrete deformation and more.

Factors causing segregation:

  • Too much coarse aggregate in the concrete mix (in coarse segregation)
  • Too much fine aggregate in the mix (in fine segregation)
  • Excessive vibration
  • Overworking and flowing of concrete along the form through a chute
  • Pouring concrete from considerable height
  • Sudden change of direction through a chute

CONCRETE BLEEDING

This happens when the solid elements of the mix do not properly hold to the water when they are poured and some of the water rises to the surface of the fresh concrete. This being said, most freshly placed concrete will result in some level of bleeding. The amount of bleeding is proportional to the depth of concrete poured. Bleeding can create pores or “wormhole channels” in the interior and weaken the concrete. Do not attempt to remix the bleeding water during the finishing steps as this will result in a weak surface, non-durable concrete vulnerable to freezing and thawing and rebar corrosion.

What can cause bleeding
Too much water in the mix. Whatever time you thing you may have saved during placement will be lost waiting for the water to evaporate! Excessive compaction can also push up water to the surface of the fresh concrete.

Solution:

  • Wait for the bleeding water to evaporate before completing the finishing of the top surface.
  • Never trowel concrete while bleedwater is still on the surface!
  • Use more finely ground cement.
  • Add calcium chloride to cement and increase the fineness of cement.
  • Add fly ash, pozzolans or aluminium powder in the concrete.
  • Select a proper finishing method to protect the slab surface.
  • For air-entrained concrete, use an air-entraining agent to lower the amount of water needed to achieve the desired slump.

Having the right concrete pump for the job is also important to minimize risks of segregation or bleeding. Not sure about which pump to buy? Why guess when you can just give us a call us at (503)281-2105? We always love a challenge and are ready to help you save money on your next job.

SUGGESTED FURTHER READING

Testing Fresh Concrete Part 1: Slump Test
Testing Fresh Concrete Part 2: Flow Test
Report from the California Division of Highways
More info on Concrete workability

 

Jun 30

TESTING FRESH CONCRETE – PART 2

In our previous article, we investigated slump testing as one of the most commonly used test method by site engineers to ensure that fresh poured concrete has the right consistency and workability. We also learned that this method is not optimal for all forms of concrete. There are 2 other methods for testing consistency, they are Flow test (using vibration) and Ball penetration test.

Fresh Concrete Testing with a Flow Table

Flow test:
Also known as Flow Table Test is often performed when fresh, unhardened self-consolidating concrete arrives on site and the operator needs to monitor its consistency before pouring can start. It is simple, inexpensive and can be easily reproduced and conducted on any site.

How does it works:  Viscosity is what determines the rate of spread.
1. Make sure the flow table is perfectly flat on the ground.
2. Clean the surface of the flow table.
3. Place the cone in the center of the flow table in between your feet and proceed as you would for a standard slump test (fill it with fresh concrete applying 2 equal layers.that each have been tamped down a dozen times). Level the top of the mold removing any excess. Clean up the table of any extra concrete.
4.Wait 30 seconds, then lift the cone.
5. Raise up the tabletop 40 mm and drop it 15 times forcing the concrete to flow.
6. You can now measure the diameter with a rule in both directions to the nearest 10 mm. Watch a video of a flow table test being conducted.

Tools for performing a flow test

Best applications:
This testing methods works best for high concrete workability using coarse aggregates no larger than 25 mm (1 in.) and with a slump of more than 175 mm.The reason why is that anything larger will not produce flowable and nonsegregating self-consolidating concrete.

Limitations: 
Flow test results can be difficult to interpret, so they are used primarily as a qualitative index of workability. The good news is that there are several other tests relying on vibration such as compaction test (Waltz test), Vebe consistometer, Thaulow tester etc. that can also measure the rheological properties of cement mixtures.

Understanding the results:
If the concrete is too pasty, it which will cause cavities and corrosion of the rebar in the medium term and weaken the concrete’s ability to resist stress.
A mix that tends to segregate will produce a non-circular pool of concrete.
If a ring of clear water appears after a few minutes, the mix indicates a bleeding problem.
NOTE: concrete slump and final mortar spread correlate linearly when the concrete slump is greater than sever inches.

Diameter of flow (cm)-25
———————————— X 100 = FLOW %
               25

% of Flow

0-20%

20-60%

60-100%

100-120%

120%-150%

Consistency

Dry

Stiff

Plastic

Wet

Sloppy

Dick Hibbard

Combining a slump test with a flow table test will ensure that your mix has the right consistency and workability on the job. So don’t cut corners and do the right thing, it will save you money and time. And if you are looking for a great deal on a concrete pump, give us a call at: (503)283-2105. We would love to hear from you!
SUGGESTED FURTHER READING
ASTM Standards
Sampling & testing fresh concrete (UK)
Flow Test Evaluation (Georgia Department of Transportation)