Late Victorian Building Construction
The time was one of innovation and experimentation.
The late 19th Century had seen the culmination of the replacement of stone with brickwork as a primary unit of masonry construction and was most dramatic in the development of Portland cement and its use, particularly, in concrete and reinforced slabs, suspended between steelwork, also in its infancy.
Portland Cement was available from a number of developing suppliers, the most reliable company of the time was J B White and Brothers of Swanscombe, Kent. Portland Cement was invented in 1811 by Joseph Aspdin of Leeds, and met with considerable distrust until the late 19th century, when it was then considered to have resistive qualities in its use in forming reinforced concrete. Cement was not as finely ground as was later recognised as being necessary to give a finer spread of cement to the surfaces of the aggregate. There was also the likelihood that cements were over-limed. Portland Cement consists of lime, silica and alumina ( ie a calcareous and argillaceous mixture ) a mix of chalk/limestone and clay/shale/marl. Mixing and testing in these early days was rudimentary. Aeration of the mix on site was considered essential; it is now considered that this “air-slaking” was injurious to the final strength.
Aggregate primarily used was clinker and pulverised clinker dust mixed with mica based stone particles. Cement was often so poorly set that moisture penetration in subsequent years washed it out of the construction. This clinker is more properly called “breeze”, as it contains material which is not fully burnt. The unburnt portions include sulphur compounds, largely iron sulphates and iron sulphides, more commonly known as pyrites, the agent instrumental in mundic activity and decay of concrete and concrete blocks. The pyrites themselves do not present an immediate problem, but when the concrete becomes wet. the action is encouraged and continues until the whole of the wet/moist concrete has decayed to a gravel, caused by the sulpho-aluminates of lime. The distortion and de-lamination of the concrete is a primary indicator. Although the use of lightweight aggregate reduces the weight, it also reduces the strength and it is more fragile, more porous. It is therefore essential that buildings of this age are protected fully against the penetration of water/moisture into the fabric, and this includes prevention internally against pipe bursts, etc.,. There is also a higher likelihood of the partially burnt material being more susceptible to the effects of fire, and therefore greater reliance should be placed upon fire protection systems and construction.
Steel beams and reinforcement
Steel at the end of the 19th century would have been produced by the regenerative process of Pierre Martin, though it is more likely that they were solely made in the Bessemer/Siemens processes. This steel would have been placed ( unprotected and uncoated ) in the concrete ( this combination slab technique was widespread ). The use of steel as reinforcement ( instead of iron, which proved to be disastrous ) was not proposed until 1870, before which time it was thought that the use of Portland Cement would inhibit the formation of rust in iron.
Steelwork of this time is prone to de-lamination and expansion when exposed to water/moisture, lifting concrete, breaking down the concrete where it abuts the steel, introducing stresses and fractures in the concrete slabs. Very little of this is noticeable as Victorian floors were finished with a floating timber floor, and the ceilings were often battened-off and plastered on lath. A keen eye and vigilance is necessary.
If we are to preserve the inheritance of these buildings, we need to be aware of the construction and its susceptibilities and remedies.
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