New York City Weather
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Special Concretes
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| Test Method | Description | ||
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ASTM C 1611 Test is performed similar to the conventional slump test (ASTM C 143) using the Abrams cone (use of inverted cone possible). However, instead of measuring the slumping distance vertically, the mean spread of the resulting concrete patty is measured horizontally. This number is recorded as the slump flow. Measured characteristic: Filling ability (deformability) & stability |
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ASTM C 1621 The J-Ring consists of a ring of reinforcing bar such that it will fit around the base of a standard slump cone. The slump flow with and without J-Ring is measured, and the difference calculated. Measured characteristic: Passing ability |
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ASTM C 1610 Test evaluates static stability of a concrete mixture by quantifying aggregate segregation. A column is filled with concrete and allowed to sit for awhile after placement. The column is then separated into three or four pieces. Each section is removed individually and the concrete from that section is washed over a No. 4 sieve and the retained aggregate weighed. A non-segregating mix will have a consistent aggregate mass distribution in each section. A segregating mix will have higher concentrations of aggregate in the lower sections. Measured characteristic: Stability |
Q:
What differences can I expect in the behavior and properties of recycled-aggregate
concrete compared to concrete made with natural aggregates?
A:Recycled aggregate will typically have higher absorption (see Figure) and lower specific gravity than natural aggregate and will produce concrete with higher drying shrinkage and creep. These differences become greater with increasing amounts of recycled fine aggregates. Too many recycled fines can also produce a harsh and unworkable mix.
Figure: Comparison of water absorption of three different recycled
aggregate particle sizes and one size of natural and lightweight
coarse aggregate.
Many transportation departments have found that using 100% coarse recycled aggregate but only about 10% to 20% recycled fines works well. The remaining percentage of fines is natural sand. The chloride content of recycled aggregates is of concern if the material will be used in reinforced concrete. However, the quantity of chloride typically found in old concrete pavement is usually below critical threshold values.
Concrete
countertops have been growing rapidly in popularity and have become
a prime focus for decorative concrete applications. There are many
fine articles in such magazines as Fine Homebuilding and
Concrete Construction, but perhaps the best one-volume
resource is A relatively new organization that offers comprehensive training
for contractors and others is The Concrete Countertop Institute,
www.concretecountertopinstitute.com.
The use of mineral oxide pigments in a shotcrete application is
probably not different from their use in a cast-in-place, mortar,
or thin specialty topping application. The typical recommendation
(ASTM C 979) is to use only the minimum color pigment required to
achieve the desired color (never more than 10% by mass of cement)
and to consider the use of white cement if the final color is to
be cleaner or brighter. Changing colors should not be a problem
as long as the expectation for the transition from one color to
the next is reasonable.
By allowing rain events to penetrate the pavement to the underlying soils, the first flush of the paved surface is contained on site. The natural infiltration of the area remains unchanged so the water can recharge the water table. This avoids surface runoff that must be held in detention ponds or added to the storm water surface runoff which must then be treated before it is returned to the local streams. In many cases the pavement may also be designed with a layer of coarse granular material below the pavement to increase the storage potential of the system. This has proven to be an effective tool to increase the area of usable pavement on a project as well as satisfy local water management regulations.