The Lighthouse that inspires the invention of a new cement!

This is the extraordinary story of a man that while he was trying to build the strongest lighthouse ever built; he lays the foundations of a new engineering type, invented a new lighthouse design, and discover a new cement!

Everything starts for the need of a light

This story starts for the need of a light in the middle of the sea in front of the south of the England; exactly in the Eddystone rocks.

The Eddystone Rocks are an extensive reef in front of Plymouth one of the most important naval harbors of England (specially in the XVI/XVII centuries). They are submerged at high spring tides and were so feared by mariners entering the English Channel. It was responsible for an awesome toll of shipwrecks...

The solution; place a Lighthouse!

Winstanley Lighthouse- The building of the first lighthouse started in 1697 and finished in 1698 by Henry Winstanley, after he lost one of his ships in that area. The structure was made of wood, 80 feet height and full of ornate. The strong weather conditions damaged the structure and Winstanley re-built it in 1699 with the tower now with 120 feet height. The tower survived until 1703 when a terrific storm completely destroyed the lighthouse and Winstanley, with his workforce, were lost with it.

Rudyard Lighthouse- The danger of the reef was still apparent with more ships than ever being lost. Following the destruction of the first lighthouse, Captain Lovett acquired the lease of the rock, and he was allowed to charge all passing ships a toll of 1 penny per ton. He commissioned John Rudyard (or Rudyerd) in 1706 to design the new lighthouse. His design was a smooth conical shape to reduce the resistance of the sea and at a height of approximately 100 feet. The structure was mainly of wood but set on a granite base with the door entry in the base.The lighthouse was completed and entered service in 1709, it survived until 1755 when it was destroyed by fire.

The Smeaton Lighthouse design

John Smeaton, an instrument maker from Yorkshire, was commissioned by the Royal Society to construct a new lighthouse.

He also realized that such a masonry structure, exposed to the ravages of temperature, wind, and sea, would require a far stronger and more sea water-resistant mortar than the ordinary masonry mortars of the day.

There was a constant spray of seawater over the foundations and footings, and the surface would never dry out properly. Smeaton’s aim was to make a cement that would equal the best Portland stone in solidity and durability.

The Cement knowledge in 1750

Up to this time varied proportions of lime and tarras were used in the preparation of mortars for engineering works in water. The practical masons of those days were of opinion that:

• the harder the stone from which the lime was made, the better would it set or harden.
• if the mortar was made with sea water it would never harden in so great a degree as that made from fresh water.

The Smeaton's experiments

He started an investigation of the various kinds of limestone he could obtain and the performance of the limes that they produced upon calcination.

He took made balls of 2 inch diameter with the materials to be tested. He wait until the ball were settled and covered with water and what happened to the ball in this state was the criterion to evaluate the materials.

2 parts lime and 1 tarras, set in water, although not so good. He found: the fallacy of the strongest lime being obtained from the hardest rock, and also that these proportions behaved equally well in salt water and fresh. This difficulty therefore was overcome. The Aberthaw lime, from Glamorganshire, with various proportions of tarras, excelled in a great degree any of the other mixtures, and its behavior under water was of the most satisfactory character, besides it continued to harden for months.

2 parts lime and 1 Puzzolana, he read in the literature that Puzzolana found in Italy, made a good water cement. Fortunately he found at Plymouth a considerable quantity of this material, which a merchant had imported for speculation (but finally he could not finished the business). His experiments proved it superior to tarras, and in the end he says:

"The balls made with Puzzolana even if were constantly kept under water, acquire hardness gradually, that I did not doubt but to make a cement that would equal the best Portland stone in solidity and durability"

The resemblance to the Portland stone, and hence the origin of the name of Portland cement, is clearly also due to Smeaton.

The secret of Aberthaw limestone

In order to better understand why the Aberthaw limestone proved to be such an admirable source of hydraulic lime, he made more experiments dissolving the lime with "aqua fortis" (nitric acid). By washing and decanting, a muddy residue was obtained from the Aberthaw limestone that resembled a blue clay and weighed about one-eighth of the original sample. When this material was formed into a ball and burned, it became reddish and hard as a brick (like clay). White chalk and Plymouth marble, on the other hand, dissolved completely in the acid.

Smeaton determined the fundamental relationship between clay content of argillaceous limestone and the hydraulic characteristics of a lime produced from it.

The Dovetail System and the Oak tree shape Innovations

He modelled the shape on an oak tree, the foundations and outside structure built of local Cornish granite, and lighter Portland limestone masonry used on the inside, it developed a technique of securing the blocks using dovetail joints and marble dowels. Smeaton’s new hydraulic cement sealed the 1,493 interlocked granite blocks which had been secured by 700 marble plugs.

The construction started in 1756 an finished in 1759, and it was stood for 123 years.

Douglas Lighthouse - In 1870 it was observed that the reef beneath the lighthouse was beginning to crumble. A new, similar lighthouse was then constructed on an adjacent site and completed in 1882. The Smeaton structure was dismantled stone by stone and then re-erected on Plymouth, where it stands until today.

The Penny Coin

Smeaton did not patent his cement but his lime-pozzolana mixture for a hydraulic cement was specified for Government contracts and for mortar up 1867, over 43 years after the invention of Portland cement.

What is the importance of the Smeaton Discovery?

Smeaton paved the road to the Portland Cement. Apparently unaware of Smeaton's work, the same principle was identified by Louis Vicat in the first decade of the nineteenth century. Vicat developed a method of combining chalk and clay into an intimate mixture, and, burning this, he made an "artificial cement" in 1817.

James Frost, working in Britain, produced what he called "British cement" in a similar manner around the same time, but did not obtain a patent until 1822. In 1824, Joseph Aspdin patented a similar material, which he called Portland cement, because its color is similar to the prestigious Portland stone (as Smeaton mentioned first!)

The cement discovered by Smeaton was the beginning of rapid hydraulic cement development and the modern cement industry

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