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Having recognised the need for large volumes of concrete for massive projects including dam building, the Americans had experimented with batching plants as early as 1913 and by 1926 were manufacturing purpose-built "transit mixer trucks".
While a lightweight chassis/cab may be considered desirable, if not essential, from the point of view of maximum payload, operational factors such as the requirement for both on and off-road capability mean that an acceptable compromise is usually sought. Mixer work is tough on equipment, the chassis having to cope with stresses imposed by the rotating drum, while the driveline is subject to high levels of wear and tear resulting from short journeys in largely urban areas. Add to this the extra weight and cost of multi-axle drive plus the need to strike a balance between good ground clearance and a low centre of gravity and one begins to glimpse the underlying complexity of the truck mixer.
From the driverís point of view the priorities are often very different, the man behind the wheel - while acknowledging the need for good traction and ground clearance - not necessarily appreciating a small, under-powered engine, utilitarian cab and long climb into the seat. As with most trucks, mixers are often a bit of a compromise, it being almost impossible to produce one that would be perfect for the job and still driver-friendly enough to attract drivers and safe enough to fall on the right side of existing legislation.
The physical appearance of mixers has always varied considerably, the inevitable result of operating conditions, differing approaches in terms of engineering and, inevitably, local legislation.
Similarly while some countries have stayed with the traditional layout which discharges to the rear of the vehicle, front-discharge mixers are now hugely popular, particularly the United States. There chassis manufacturers are accustomed to building vehicles tailored to specific demands resulting from complex axle-weight laws, so building low-volume chassis for the mixer market is considered cost-effective.
At first glance, the front-discharge mixer would appear to offer the best possible solution to the challenge of carrying, mixing and discharging concrete. The direction in which the drum faces means that the bulk of the weight is carried over the rear of the vehicle when on the road, resulting in optimum load distribution, traction and stability. Meanwhile the chutes can be positioned more easily by the driver on arrival at the discharge site. In fact, the ability to position the truck exactly where required, together with improved visibility while unloading (invariably from a centrally-mounted cab) are significant benefits in terms of operational efficiency and safety.
The drawback is that front discharge mixer drums are necessarily mounted on specialist chassis, so cost is a major consideration. The installation of a standard rear-discharge drum requires little modification to an otherwise standard vehicle meaning that the drum and driving mechanism may be transferred from one conventional chassis to another. Conversely, most front-discharge mixer chassis produced today are designed and built to accept a specific drum. And more importantly most of these chassis feature rear-mounted engines, and centrally mounted, driver-only cabs, rendering them completely unsuitable for every other type of bodywork.
During the past twenty-five years or so there have been several attempts to determine the ideal configuration for a mixer chassis and in the mid 1970s, the use of "booster" axles on conventional chassis layouts gained wide acceptance in some regions of the world permitting high gross weights. Boosters are lifting rear axles tagged on to the back end of large rigid trucks which, as their name suggests, boosts the overall capacity while in the lowered position. In Canada and the USA booster axles are still frequently seen at the rear end of four axle mixers, increasing overall capacity from weights of around 80,000-lbs gross (36.36 tonnes) to 100,000-lbs (45.45 tonnes). The axles are raised and lowered hydraulically and it is hydraulic pressure that ensures the appropriate load is transferred from the rear driving axles to the tag axle booster. Indeed, as the axle is lowered to the ground it is possible to watch the rear end of the chassis rising as weight is re-distributed.
When it comes to vehicles custom-built for the job of hauling large amounts of concrete, few were more impressive than the imposing 12 x 10 Oshkosh rigids used extensively throughout Michigan State during the 1960s and Ď70s. Capable of grossing nearly 55-tonnes and achieving 55-miles-per-hour, the big trucks also benefited from a safe twin-steer front axle set-up and unequalled off-road performance. These vehicles were among the very biggest rigids ever produced and a few were still to be seen delivering their massive loads of concrete into the mid 1990s.
Meanwhile in Holland where legislation also allows the operation of 50-tonne multi-axle rigids, domestic manufacturers Terberg and Ginaf have offered their own versions of high mobility mixers for almost 20 years. Despite the fact that both of these Dutch truck builders established their businesses by converting and modifying US trucks left in Europe after WW11, their modern mixers differ from the American Oshkosh units in several respects. Most obvious is the fact that the Dutch trucks feature forward control cabs (from Volvo and DAF) whereas the Oshkosh units were normal control or conventionals. The big Ginaf and Terberg outfits offer 10 x 8 drive, and tyres are often "super singles" in the interests of traction and floatation in the sandy, reclaimed areas of the Netherlands. Where the big trucks are alike is in the power department, the Oshkosh vehicles generally featuring a big Caterpillar or Detroit Diesel rated at around 350-hp and the more modern Europeans having Volvo or DAF engines in the 400-hp bracket.
Articulated mixers are still used in some areas of Europe, but as the result of generous weight legislation, today these are most commonly found in Holland where 6x4 tractors coupled to tri-axle semi trailers can legally operate at up to 55-tonnes gross provided individual axle loadings are not exceeded. In North America, this concept is fully exploited by the use of extendable semi trailers which are "stretched" when the mixer drum is fully loaded in order that axle weights conform to state laws or Federal Bridge Formulae. These complex trailers may then be shortened or "snugged up" again when returning empty to the batching plant for the next load.
|The first example of a Challenge-Cook mixer installation aboard an 8x6 Mack DMM686SX seen in Toronto in the mid 1970s.||Vancouver-based Freightliner 8x4 plus hydraulic booster axle at the rear.||Business end of Surrey-based Volvo-Autocar detailing lift axle and discharge chute.|
|Mack tractor with semi-trailer mixer loading at batching plant in B.C.||Cabover Freightliner mixer is an impressive piece of machinery.||Articulated-frame Rubber Railway Company 8x6 in the colours of Custom Concrete during the mid 1970s.|
|Freightliner cabover prepares to leave discharge site in Vancouver.||Western Star 8x4 mixer posing against a clear Vancouver skies.||Articulated-frame RRC in the colours of Armbro demonstrates its manoeuvrability.|
|Stunning Peterbilt tractor and extendable trailer seen in south Seattle.||Rear view of front-discharge Oshkosh 10x6 from Michigan shows power plant.||The advantages of front discharge are clearly demonstrated by this Oshkosh.|
|This impressive 10x6 Oshkosh from Michigan is washed and ready to roll.||In the 1970s, these 12x10 R-series Oshkosh capable of grossing around 50,000-kgs. (110,000-lbs) were considered King of the Road in Michigan.|
|This 10x10 FWD looks like it has hauled its last load.||Crane Carrier Corporation (CCC) half-cabs were always popular as transit mixers featuring low tare weight and good all-round vision.||In the center or off to one side? It looks like you can put the cab where you want on a mixer unit.|
|Front discharge, rear engine Advance mixer at work in Ohio.||International S-Line chassis in Las Vegas, Nevada.||They donít come much wierder than this 14x6 front-discharge rig with three driven axles, three lift axles and a steering tag! Where else but Vegas!|
|Early example of a front-discharge unit -- possibly built by Advance -- at work in Ohio.||Dial Mixed Concrete of Toronto, Ontario, operated these Mack six wheel trucks equipped with REX mixers in the late 1940s.||Owner-drivers take the appearance of the trucks very seriously as evidenced By this stunning Swedish Scania 8x4 sleeper-cab mixer with extra lights, chassis side fairing and an eye-catching paint job.|
|There aren't many of these left anymore. This B61 Mack was caught on the streets of Antwerp, Belgium in 1971. Inter-Beton is one of the largest concrete companies in Belgium. These Mack B61 trucks have been replaced by Mack DM trucks. Now Inter-Beton does drive Mercedes and Iveco. (Beton means concrete in Dutch).||Impressive Autocar in the colours of Sogetra from Bruxelles, Belgium seen at work in 1971.||Samsung is a name more usually associated with electrical goods than with heavy trucks but this 6x4 mixer with short sleeper cab was seen working in Istanbul, Turkey in 1999.|
|The driver of this Swedish Volvo NH 12 with high-rise Globetrotter cab presumably works away from home during the week and lives in the cab.||DAF 95-Series 6x4 cabover with tri-axle mixer trailer can operate at 50-tonnes gross weight in Holland.||Iveco 8x4 seen working in Eilat, Israel. In the background is a mountain range in neighbouring Jordan.|
|Sisu 8x4 mixer working in Finland.||Sisu cabover 8x4 loading at a batching plant near Turku in southern Finland.|
|1970s Henschel 6x4 tractor with mixer trailer.||Heavy-duty British-built Scammell S-24 mixer working on the Mediterranean island of Malta. This vehicle is one of several used by civilian contractors to build a new airport and military installations in the Falkland Islands during the period 1983 to 1986 and subsequently returned to the U.K. for re-sale."||Italian-built half-cab Astra mixer seen in the mountains of Carrara.|
|Ashdod-built Mack mixer seen crossing the bleak Negev desert in Israel.||Scania 8x4 mixer at work in sunny Switzerland.||Swiss-built Saurers were renowned for their comfort and build quality.|
|It would be interesting to know how this little Jugoslavian-built FAP mixer ended up in Zimbabwe in southern Africa.||In Spain, four-axle trucks such as this 8x4 Renault-Barreiros can operate at 38-tonnes gross weight.||This British-built ERF four-axle mixer is equipped with an Austrian-built Steyr cab in order to save weight.|
|Truck mixers are always busy in Holland where land reclamation projects never seem to stop. This Terberg 10x6 with three steering axles and a Volvo driveline can operate at 50-tonnes gross weight.||This Ginaf 8x8 working in Holland uses a DAF cab and driveline.||FTF trucks, once built in Holland, are no longer produced. When they were in business they used a British cab, Detroit Diesel engines and Allison transmission.|
|Terberg 10x4 en route to pour.||This compact Terberg 10x4 mixer employs the Volvo FL lowline cab.||Unusual MAN with rear-steer axle.|
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