Gents, some info on this topic from a friend very knowledgeable on the interface between Scottish railways and industry:
With reference to Lossiemouth and freight traffic, the harbour also saw deliveries of fuel oil onto the quayside and the post-WWII redevelopment of the military bases at Kinloss and Lossiemouth required huge volumes of cement to be delivered to a reliable timetable. Across Scotland, cement was transported to site either pre-bagged or in bulk (powder) loads. Transport was by a mix of ships (coasters into ports such as Grangemouth from Kent), road vehicles (flatbeds and bulk tankers) and by rail (vans and bulk tanks such as Presflo's). Blue Circle had two sites in Scotland that saw a lot of deliveries using Presflo rail wagons - Cambuslang and Irvine. It appears that many construction sites received their loads using a mixed journey of shipping, road and rail - depending on site location, volume of cement required and the supplier. After WWII, there were some colossal infrastructure projects in the Highlands driven by public-sector investment, with cement companies such as Blue Circle and Tunnel competing with each other.
For those with an interest in period road vehicles to complement their railway interests, the cement companies were using Commer trucks fitted with a 2-stroke diesel engine and complete with a supercharger. Other period trucks on this traffic were Foden S21, Scammels, Leyland Super Comet, Leyland Comet and Leyland Bison. The earlier trucks would each take 8 tonnes of cement and by the 1960's the loads had increased to 15 tonnes - worth thinking about if the rail siding was full of Presflos and departure time was imminent!
During the 1950's and 1960's there was still a lot of manual labour involved, with 'hand-balling' 50kg paper sacks of cement out of 12T Box vans onto Flatbed lorries - from the nearest railhead to the construction site. Alternatively, a trainload of bulk rail tankers (e.g. 'Presflo's) could be used - but only if a supply of compressed air was available to 'blow' the cement out of the rail wagons and into a road tanker for the final stage of the journey. Blue Circle appeared to have an advantage over some other cement producers at remote railheads, in that their road tankers were fitted with an integrated 'Roots' type blower - allowing them to discharge (blow) from the rail tanker straight into the road tanker and drive the 'final mile' to site. At site, the truck driver could then simply 'blow' his cement into a storage silo - ready to be used as required. Even today you will see 'blowers' fitted to bulk grain and cement lorries - attached to chassis rails with a drive-shaft off the gearbox. Pressure wise, the earlier cement conveying systems were operating at low pressure 1 to 1.5 barg (15 - 22 psig), then it evolved to 2 to 2.3 barg (29 - 33 psig) The same type of blower technology was also fitted to vintage Bentley cars as a form of supercharging to boost their racetrack performance - often seen located beneath the front headlights, being driven off the engine crankshaft.
At railheads with permanent cement handling infrastructure (silo, weighing facilities etc) - a large blower with drive motor would be located in an adjacent shed, with pipework from the siding to the silo. Discharge from the silo to the road tanker was usually by gravity. There were also blower units mounted onto four wheel trailers - these were more commonly used by the military for starting what are now classic jet aircraft.
Usually the pneumatic conveying of cement is referred to as 'blowing' - you are talking about high volumes of air at low pressure to 'fluidise' the material - not using high pressure compressors.