There are two camps on how the Rice (or Maximum Specific Gravity) test needs to be done in order to be correct. One is team Autorice, who love that the unit performs the entire test automatically, and the Other is team “This is the way we’ve always done it”.
"The way we’ve always done it" is a mantra that many of us in the industry (including ourselves) have said for years. It has guided our operations and, for the most part, has given us profitable results. But what if that mantra is also holding us back?
Today we’re going to discuss and compare the Instrotek Autorice to the established methods and how it could impact your lab, your jobs, and the fate of roads in America.
What is the Old Way?
The maximum bulk specific gravity test (more commonly referred to as the Rice Test) conforms to the specifications outlined in AASHTO T209. It is a test that determines what your sample would weigh if it were possible to compact it down to 0% air voids and is mostly theoretical.
In fact, I'm pretty sure that if you built a machine that could do it, you would end up just creating lava but what do I know?
In order to perform the test, your lab needs to be equipped with the following:
- A vessel (pycnometer) to hold your sample, water, and also be able to contain everything under a vacuum
- You’ll also need to pay attention to your State’s specification as many states differ in what they want
- A vacuum pump capable of pulling your pycnometer down to 27.5 ± 0.5 mmHg
- We recommend the RiceVac
- Tubing that can connect to your pycnometer and can also handle the vacuum pressure without collapsing
- Some sort of desiccant or device inline to stop water from entering your pump
- We also recommend elevating your vacuum pump to let gravity do some of the work
- A vibrating table to shake your pycnometer
- It should also secure your pycnometer so that it doesn’t go flying or spinning
- A device (Manometer) to monitor your vacuum pressure
- An analog or digital timer to record testing time
- Needs to at least be 15 minutes
Starting with your vacuum pump, you’ll need to connect some tubing from the pump to your desiccant or Pumpsaver (Make sure that whatever you choose is below your vacuum pump).
Next you’ll run another bit of tube and connect it to your pycnometer. You also need to have a tube connecting your pycnometer to your manometer so that you can monitor your pressure.
If you’re in Florida your setup will be slightly different and you’ll use pycnometer flasks.
Once you have all your tubes connected you need to set up your vibrating table so that its flat and on a sturdy level surface
After all of that, place your pycnometer in your vibrating table and you are ready to start the test.
To run a rice test successfully your sample must be vibrated while under a vacuum pressure of 27.5 mmHg and submerged in water for 15 minutes. This means that when you run your test you have to make sure that your pump stays in that range for the entire 15 minutes.
If it goes outside of that range you need to stop your timer and adjust your manometer so that it's back in range and then begin the timer again.
Most vacuum pumps take anywhere from one to six minutes to pull down into that range once you press start (unless you have one of our RiceVacs). You have to wait until the pump levels the pressure out before you can start fine tuning your adjustments. Each one of those adjustments also takes a few seconds before you can see if its correct. Rinse wash and repeat until you get to the correct range.
Ideally once you set it the first time you shouldn’t have to make any more adjustments for that day. Of course I would be lying to you if I said that this is always the case, so make sure that you are allocating more than just the 15 minutes to do each test.
On a good day each of your tests should take approximately 20 minutes.
How the AutoRice does it for you
The AutoRice adjusts the vacuum pressure to be in range, controls the test timer, and stops that timer if for some reason your pressure moves outside of that range. It will then automatically pick right back up and continue trucking along when the conditions are correct.
How it works
Inside of every AutoRice unit there is a timer, a vacuum adjustment valve, a manometer, three power receptacles, and a digital display screen.
Each of the power receptacles are controlled by the AutoRice and will automatically turn on whatever’s plugged into them. This means that you can connect your vacuum pump, vibrating table, and pump saver (optional) to the unit and have them all controlled automatically when a test is run.
From power-up, the AutoRice will control the vacuum adjustment valve until the correct pressure range is established and will automatically adjust and compensate for changes to the pressure. This is especially handy if your vacuum pump jumps around a lot during a test.
The AutoRice has an internal timer that will run the test and automatically stop if the test somehow goes outside of the range. The timer will automatically start again when the pressure is in range again.
Data from your test will automatically be saved and is accessible via a usb port. You can use the data from the reports to make sure that your testing parameters are correct.
The only thing that you have to do is actually put your sample in your pycnometer and press the start button.
How much does each method cost?
The old way is considerably cheaper in terms of cost alone. In fact all of the components for the "way its always been done" can be grabbed for as much as an AutoRice unit costs.
However, in terms of time the low price is often offset by the sheer amount of time you have to give to each rice test. Granted some of the time can be shortened if you have a really good vacuum pump, but even if that’s the case you are still looking at roughly 20 minutes per test.
Keep in mind that you have to monitor that test for the full 20 minutes to make sure it stays in range.
Compare that to the AutoRice. Each test can still take 20 or so minutes to run depending on your vacuum pump, but you only have to dedicate 1-2 minutes of your time per test and can do something else while it's running. That’s only 6 minutes of your time to run 3 rice tests instead of 60.
Over the course of a week running 4 tests daily that equates to 6.7 hours of rice tests using "the way its always been done" and only 1 hour of in person time with the AutoRice™.
What's our opinion?
We understand that not every lab will benefit from the AutoRice. There are smaller operations where the extra time running a Rice Test isn't going to be wasted and the cost of the unit in those circumstances can be prohibitive.
For the vast majority of labs though, the unit should be seriously considered.
From a calibration standpoint, it is the only unit we sell that doesn't need a correction factor. The unit can be calibrated directly which means that it will always show the correct reading, you won’t have to reference a chart to determine what your pressure is.
The wall mount makes keeping the AutoRice out of the way easy. It can be elevated above your desiccant or water removing device. It can stay off of your counter which is extremely helpful in smaller labs.
In essence, the AutoRice is a manometer that automatically controls a Rice Test.
It’s not often that we see a piece of equipment in this industry that makes life easy and makes testing more accurate and efficient. This unit really does have it all. That’s why we at Gordon Technical recommend this to each and every one of our customers.