A popular use of Mobile Concrete Mixers is to produce high specification concretes used to overlay bridge decks. Bridge decks, being a structural component, contain a very high amount of reinforcing steel.  In northern climes bridge decks go through more freeze/thaw cycles than most concretes. That is because they are exposed to the weather on the top surface as well as the underside.  The motoring public expects highways (which include bridge surfaces) to be clear of snow and ice shortly after a storm subsides.  This has led to highway departments using salt based de-icing materials on the surface.  Cracks in the concrete would allow deicing salts to reach the reinforcement steel causing it to rust.  Rust (an iron oxide) occupies more volume than just iron.  This expansion caused the deck to deteriorate. Highway engineers were looking for a material that could repair the damage, be long lasting and prevent de-icing salts from reaching the reinforcement steel.

In the 1960's Dow Chemical developed an overlay concrete material that useds a latex modifier which iwas added to the concrete when mixing replacing most of the water. While laboratory studies showed great promise for the resulting concrete, actual field trials using conventional concrete delivery systems provided lackluster results.  Someone at Dow then decided to try the newly patented and manufactured mobile concrete mixer called the "Concrete Mobile." This mixer gave the engineers jobsite control of their concrete production.  The material now reached the potential shown in the laboratory studies.  All specifications from that period forward require the use of an on-site mobile mixer to produce a latex overlay.

Another method of overlay is known as the "Hi-Density" or "Iowa Low Slump" overlay. As the name suggests it was developed in Iowa (in the 1970's). The mix is a high cement content mix (824 lbs. cement per cu. yd.) with a low water/cement ratio. Maximum W/C ratio is 0.32 and slump is specified as ¾" plus or minus ¼".This high cement content,

low slump mix was not even tried in conventional delivery equipment as it would set up in the mixer without the adding additional water.  Special finishersing equipment consolidate and level this mix to produce an overlay that competes with the latex overlay in performance.  Producing this mix requires the use of a mobile mixer at the jobsite.  Again, job site control of the mixing allowed the engineers to achieve actual field performance that matches the performance observed in the laboratory.

A popular use of Mobile Concrete Mixers is to produce high specification concretes used to overlay bridge decks. Bridge decks, being a structural component, contain a very high amount of reinforcing steel. In northern climes bridge decks go through more freeze/thaw cycles than most concretes. That is because they are exposed to the weather on the top surface as well as the underside. The motoring public expects highways (which include bridge surfaces) to be clear of snow and ice shortly after a storm subsides.  This has led to highway departments using a lot of salt based de-icing materials on the surface.  Cracks in the concrete would allow deicing salts to reach the reinforcement steel causing it to rust. Rust (an iron oxide) occupies more volume than just iron. This expansion caused the deck to deteriorate. Highway engineers were looking for a material that could repair the damage, be long lasting and prevent de-icing salts from reaching the reinforcement steel.

Both of these mixes are highly engineered. A mobile mixer at the jobsite eliminates the factors of age of concrete, tempering water, revolutions of the drum, etc. associated with conventional concrete delivery systems. With the job site produced concrete engineers were able to reproduce the results they observed in their laboratory tests.