Changes to Section 37: Bituminous Seals

Section 37: Bituminous Seals has been greatly revamped and expanded in Caltrans' 2010 Standard Specifications.  All of the previously existing information seems to have remained the same (albeit in different format) but the biggest change of which is the addition of specifications for Polymer Modified Asphaltic Emulsion Seal Coat.  Much of this addition does not affect aggregate suppliers but one thing to notice is that the aggregate screenings are a different gradation and cleanliness value for the Polymer Modified Emulsion Seal Coat than the standard Asphaltic Emulsion Seal Coat.

If you're in the seal coating business I greatly recommend reading over the new version of Section 37.  The Caltrans 2010 standard specifications can be found in pdf form at http://www.dot.ca.gov/hq/esc/oe/standards.php and are now for sale in book form on the Caltrans website here.

Hamburg Wheel Test Overview

There have been varying opinions of the Tensile Strength Ratio (TSR) test and how well it really reflects moisture sensitivity.  Because of these concerns, Caltrans is currently moving towards the replacement of the TSR test with the Hamburg Wheel Tracking Test which originated in Germany in the mid 1970s.  The test examines the susceptibility of the HMA to rutting and moisture damage.

Hamburg Wheel Tracking Device (HWTD) from (Stuart and Youtcheff, 2002).

The Hamburg Wheel Tracking Test uses a steel wheel with weight that rolls over the sample in a heated water bath.  A designated number of passes are performed on the sample.  I'm not sure what number Caltrans will settle on but in the United States, 20,000 passes seems to be used very commonly.  The rut depth is measured by the machine periodically, usually every 20, 50, 100 or 200 passes.  20,000 passes can take around 6.5 hours whereas the entire test can take around 3 days.  As you know, this is not much better than the TSR test so it doesn't look like we'll be shortening our mix design turn around time in the near future.

Several analytics are examined with the Hamburg Wheel Tracking Test including post-compaction consolidation, creep slope, stripping inflection point, and stripping slope.  The chart below illustrates these pretty well:

APA Samples showing rutting after 8,000 load cycles.
*This chart's data is for the Asphalt Pavement Analyzer, not the Hamburg Device but illustrates the  terminology well.

This type of information can tell us not only at what point in a roads' life it will become moisture sensitive but also how much the moisture will affect the road once it hits that point.  Studies have found that there is good correlation between the Hamburg test and field performance but it has also been determined that the test can fail to differentiate between some mixtures.  If you are interested in some of the more nitty gritty details there is a great writeup about the test by the Federal Highway Administration here and an evaluation of the Hamburg test for Caltrans by UC Davis here.

The Future of Concrete?

I know that this is primarily a asphalt and aggregate resource but I couldn't help being fascinated by this article that talks about the new innovations involving concrete.  Some of the new uses involve concrete printing, modified admixtures using less cement, and  CNC-generated concrete form work.  It's a short article but well worth the read.


http://www.smartplanet.com/blog/astute-architect/concrete-thinking-new-ideas-for-age-old-material/219

Changes to Section 26-Aggregate Bases in Caltrans 2010 Standard Specifications

In the new 2010 standard specifications there has been a change to Section 26-Aggregate Bases.  The most exciting of which is that there is no longer a provision that only 50% of the aggregate base can be made from recycled materials.  It is now allowed to have any combination of broken stone, crushed gravel, natural rough surfaced gravel, sand, and/or processed reclaimed asphalt concrete, PCC, LCB, or CTB.

The other big change is that the Class 3 Aggregate Base is no longer specified in the special provisions on a job by job basis.  The specification is now present in the Standard Specifications.  It reads as follows:


26-1.02C  Class 3 Aggregate Base

When tested under California Test 202, aggregate must comply with the grading requirements for the sieve sizes shown in the following table:

Aggregate Grading
Sieve sizes	Percentage passing
	1-1/2 inch maximum		3/4 inch maximum
	Operating range	Contract compliance	Operating range	Contract compliance
2"	100	100	--	--
1-1/2"	90–100	87–100	--	--
1"	--	--	100	100
3/4"	50–90	45–95	90–100	87–100
No. 4	25–60	20–65	40–70	35–75
No. 30	10–35	6–39	12–40	7–45
No. 200	3–15	0–19	3–15	0–19

Aggregate must comply with the quality requirements shown in the following table:

Aggregate Quality
Property	California Test	Operating range	Contract compliance
Resistance (R-value) (min)	301	--	50
Sand equivalent (min)	217	21	18

The Caltrans 2010 standard specifications can be found in pdf form at http://www.dot.ca.gov/hq/esc/oe/standards.php and are now for sale in book form on the Caltrans website here.


*Sorry about the tables looking weird...the platform I'm using doesn't seem to like them and gives me some funky formats... 

Class 3 Permeable Base

The 2010 version of the Caltrans Standard Specifications now includes a Class 3 Permeable Base.  This product has been showing up in special provisions for a while but is now incorporated in the standards.  The product can be found in section 68-2.02F(4) and states the following:

"The percentage composition by weight of Class 3 permeable material in place must comply with the grading requirements shown in the following table:

Sieve sizes	Percentage passing
1-1/2"	100
1"	88–100
3/4"	52–85
3/8"	15–38
No. 4	0–16
No. 8	0–6

At least 90 percent by weight of Class 3 permeable material must be crushed particles as determined by California Test 205."

The 2010 standard specifications can be found in pdf form at http://www.dot.ca.gov/hq/esc/oe/standards.php and are now for sale in book form on the Caltrans website here.