Verifi Concrete Quality Blog

Posts Tagged ‘concrete’

Load of the Week | Waiting to Pour Concrete

by Verifi

Today’s Load of the Week arrived on site 25 minutes after batching.  The contractor initially discharged a small amount of concrete upon arrival.  After a 30-minute delay, the contractor began to pour the remaining concrete.

Verifi continued to manage the load during this delay by automatically adding water so that when it was time to pour concrete, the slump was on target.  The driver followed prompts from Verifi to mix at high speed after water additions, per specification.  In addition, Verifi accounted for the the smaller volume in the mixing drum after the initial discharge.  This was important in both accurately measuring slump and in recording the amount of water added in gallons per cubic yard.

Concrete Load of the Week

© Verifi LLC

[LP = leave plant, AS = arrive site, BP = begin pour, LS = leave site, RP = return plant]

Nominate a future Load of the Week by emailing the ticket number and ready mix concrete supplier name to feedback@verificoncrete.com.

Eight Sources of Water in Concrete

by Verifi
Concrete batch tickets typically have the water added in the plant neatly printed on the ticket. What may surprise you is that there are actually multiple sources of water. For the total water content in the concrete to be correct, the concrete producer must carefully control and document each source. Here are eight potential sources of water:
  1. Water from cleaning the drum after the prior load 

    Some batch software programs let users input the amount of water in the drum prior to batching. However, measuring this water accurately is a challenge. So, in most cases, the driver should reverse the drum after washing and before loading to empty out the remaining water.

  2. Aggregate free moisture

    Aggregate free moisture can account for 10 to 40% of total water. That’s why aggregate moisture measurement is crucial.

  3. Batch water

    This water is measured by volume or weight. It may be heated or chilled. Given all the other water sources, it accounts for only 60 to 90% of total water.

  4. Admixtures

    Most admixtures contain water in addition to their active ingredients. Given typical volumes of admixture, this water content is very small, but easily and accurately accounted.

  5. Ice

    One pound of ice = one pound of water.

  6. Wash down water 

    After batching, the driver needs to clean any material that got on the hopper and the top of the drum during batching. This prevents material from building up and hardening on the truck. The driver simply “washes down” this material into the drum. Usually only a few gallons of water are needed.

  7. Driver water

    If the slump after batching or at the site is less than target, the driver may add water. This water can be measured with an electronic meter, or more commonly with the sight tube on the truck water tank. However, don’t assume that the sight tube shows all water added. Some water may be used for other purposes—such as washing the truck. Any water added before the tank is filled will be missed on the sight tube. Water can also be added from a fixed hose at the plant used to wash the truck.

  8. Contractor water

    The contractor may request a higher slump than ordered. When this happens, it’s actually not uncommon for the contractor to walk over to the truck and open the water valve leading to the drum, sometimes without the driver or inspector even seeing.

Verifi helps concrete producers control each of these sources of water and provide documentation to inspectors, engineers, and owners. Learn more at VerifiConcrete.com.

Do You Know Slump?

by Verifi

Can you tell the slump just by looking?  Without Verifi, slump is more often than not estimated visually. See how well you do with this short quiz.

joe truck

Click here to start.

ASTM C94 Allows Water Addition in Transit

by Verifi

ASTM C94 / C94M (Standard Specification for Ready-Mixed Concrete) was revised in 2013 to allow water additions during transit for trucks equipped with automated slump monitoring and water measurement systems. Verifi meets these standards.

Why is this change being made?

Previously, ASTM C94 / 94M limited water additions to the job site so that an inspector or other qualified person could oversee any additions of water to ensure the maximum water content was not exceeded, the amount of water added was recorded, and the concrete was properly mixed. Truck-mounted equipment is now available to automatically add water in transit, measure and record all slump modifications. The ASTM C94 / C94M revision enables concrete suppliers, contractors, and engineers to take advantage of this technology.

What are the benefits of this change?

The addition of water in transit allows concrete to arrive at the job site at the correct slump and water content, ready to complete mixing and start discharging. This results in consistent quality concrete and faster construction.

What does the standard require?

The standard allows water addition in transit under the following conditions:

  • Water addition in transit must be permitted by the purchaser.
  • The truck must have automated equipment to monitor and report slump or slump flow based on pre-established correlations.
  • The truck must have a water meter with accuracy of +/-3%. At the request of the purchaser, the ready mix producer must provide calibration data for the water meter no older than 6 months.
  • The water added cannot exceed the maximum water content for the mix.
  • The concrete must be mixed 30 revolutions at mixing speed after the last addition of water and before the start of discharge. It is not necessary to mix concrete at mixing speed before the truck arrives at the job site, even if multiple water additions are made in transit.
  • The water added to the truck mixing drum must be provided on the batch ticket.

Download the Standard:

astm.org/Standards/C94.htm

Read the full article here (requires subscription):

concreteinternational.com/pages/featured_article.asp?ID=51685804