It’s that time of year again when everyone starts building up for Christmas and the chaos it brings. For most of us that involves saving as much money as we can and making quite frankly ridiculous amounts of lists – Christmas presents, cards, food supplies… drink supplies for getting over the stress of making sure the other three lists are complete. There’s nothing worse than someone coming over to visit you, present in hand only for you to realise that you forgot to add them to one of your lists.

(Hence the ’emergency’ gifts everyone keeps stashed in over Christmas in the hope that no one visits so that they get to eat those chocolates themselves!)

For all of us at Taylor Tuxford Associates, the build up to the festive season marks one of our busiest times as we gear up for our Christmas fundraising sessions alongside our usual workload.

For those that might not know, we are part of a fundraising group known as Blu Crew. The group was founded initially with the primary aim of raising money for Bluebell Wood Children’s Hospice, but has now branched out to help other local charities and fundraising groups. During December, Blu Crew’s primary fundraising efforts involve multiple sessions at various shopping areas around South Yorkshire singing carols and other Christmas songs.

We started our fundraising efforts last weekend by singing on Saturday at the Wickersley Christmas lights switch on and on Sunday at the Alhambra shopping centre, Barnsley.

(You’ll notice that Michelle managed to avoid being in the photo by claiming responsibility as photographer!)

We’ll be in action every weekend between now and the 16th December, so you can come and see some or even all of us at the following locations – you’ll know it’s us when you see Anne bopping along to the music!

Saturday 1st December:     Crystal Peaks – indoor market area (10am – 4pm)

Sunday 2nd December:      Ikea Sheffield (11am – 4pm)

Sunday 9th December:       Crystal Peaks – Sainsburys (11am – 4pm)

Friday 14th December:       Greenhill Lights switch on (5pm onwards)

Saturday 15th December:  Crystal Peaks – indoor market area (10am – 4pm)

Sunday 16th December:     The Alhambra, Barnsley (11am – 4pm)

Start/finish times are approximate, but we’ll be at those locations between those times, so come along and say hello… and be prepared for the folks with the collecting buckets!

As some people might know, but most probably don’t, my main PhD project centered around an emergence of pyrite-related damage in Ireland. More to the point, the project looked at the damage caused by the expansion of pyritic mudrocks used as fill below domestic floor slabs.

Pyrite (chemical formula FeS2) is formed in low-oxygen environments such as those found in deep sea conditions, where organic-rich, fine grained sediments such as mudstone form. Many minerals that form in such environments are not stable under normal atmospheric conditions and so, when these minerals are exposed to air and water, they change to a more stable form. In the case of pyrite, it oxidises.

This exposure to air and water occurs naturally at the rock face in outcrops, although it is limited to the outer surface of the rock material. However, when the material is, for example, quarried and processed and compacted at optimum moisture content into the foundations of a domestic property, the outer surface of each individual fragment of rock is exposed to both air and moisture.

Exposure to the air and water has minimal direct effect on the mudstone, what it does is begin the process of oxidising and breaking down the pyrite crystals. One of the products of the oxidation is sulphuric acid, which means that the moisture in the fill also becomes acidic.

For many engineers, the problem stops there; or rather it starts there. Acidic groundwater is a key factor in sulphate attack on concrete, indeed, pyritic rock has itself been known to contribute to sulphate attack on concrete. Sulphate attack happens when ions from the acidic groundwater migrate from into the concrete causing reactions within the concrete matrix.

 

Degradation of concrete caused by sulphate (thaumasite) attack. (Source)

 

This migration of ions causes expansion of the concrete as secondary minerals such as gypsum, ettringite and thaumasite start to form within the matrix. This causes cracking and breakdown of the surface of the concrete, as the expansion overcomes the concrete’s tensile strength, and reduces the overall strength of the concrete in those areas. In severe cases, it can reduce the strength of the matrix to such an extent that the material can be broken apart by hand.

It will, if left long enough, result in the surface of the concrete, potentially to tens of millimetres depth, turning to what can be referred to as “mush”. This is an “accurate technical term”, more or less, and is wonderfully descriptive for what the material looks like after sulphate attack has been at work.

Sulphate attack on concrete was discovered when investigating the partial collapse of Carsington Dam in 1984. In this case, pyritic mudstone had been used to form the outer shoulders of the dam and, in order to prevent standing water, limestone drainage layers were added into that mudstone.

Unfortunately these drainage layers allowed for increased movement of water through the material, which meant that the acidic groundwater had easy access to buried concrete structures that subsequently suffered sulphate attack. Other problems linked to the pyrite at this site included blockage of drains due to precipitation of minerals, such as gypsum, and acid water runoff that required treatment before it could enter the local water system.

 

Partial collapse of Carsington Dam in 1984. (Source)

 

However, sulphate attack on concrete is only rarely seen in the Irish pyrite cases. Indeed, there was only one case that I looked at as part of my research where sulphate attack was confirmed to have occurred. In that case both ettringite and thaumasite were found in the upper few millimetres of the concrete ground beams.

However, in the cases that were the focus of the research, there were no confirmed cases of sulphate attack on concrete.

The problem with these properties instead leads back to the mention above about the mudstone material being organic-rich. The majority of the organic matter in the mudstone comes from decomposed micro-organisms that are primarily made of calcium carbonate (CaCO3). Calcium carbonate reacts in the presence of acids to release carbon dioxide gas and calcium ions into solution. The calcium ions in turn react with the sulphate from the acid to form gypsum (CaSO4.2H2O).

The pyrite crystals found in the mudstone are generally on the scale of tens of microns in size. By contrast, the gypsum crystals can be around 100 times larger at a few millimetres in size. This means that the very process of replacing the pyrite with gypsum causes expansion of the material.

This expansion is increased by the way in which the gypsum preferentially precipitates along layers in the mudstone. This forces open these pre-existing lines, making the material expand and also allowing better access for air and moisture through the material, which furthers the reaction process.

 

Comparison of pyrite crystals (left) and gypsum crystals (right). (Source: Dr A. J. Taylor, PhD Thesis)

 

As the mudstone is confined by the floor slab and the foundation walls, the expansion eventually reaches a point at which it exerts pressure on the underside of the floor slab and inside of the foundations. This in turn leads to upwards movement of the slab and, in some instances, outward movement of the foundation walls themselves.

The movement of the floor slab causes damage to the slab itself, as well as causing movement of and damage to structures sat on the floor slab. This includes movement of internal partition walls, and causes secondary effects such as doors not opening properly due to the uneven floor.

The amount of uplift often changes in amount across the floor slab in any given room, with humps often occurring towards the centre or one side of a given open space. Likewise, stellate cracking of the slab is common, although not always visible below fixed floor coverings such as tiles, although they may themselves show signs of cracking.

 

Pyrite damage seen to domestic properties. Clockwise from top left: cracking of a floor slab; uplift of a floor slab where it meets the external wall; separation and cracking of plasterboard over a door; shearing fractures where part of the wall is moving relative to the rest. (Source: Dr A. J. Taylor, PhD Thesis)

 

Shearing features are common where walls meet, especially where an internal stud partition (that has moved) meets an external wall (that has not moved). Cracks are also common around doors and in ceilings, occurring first along plasterboard seams and also at angles connecting seams with other features.

Much of this might sound familiar to an experienced engineer, several of the “features” of pyritic expansion are similar to those seen when settlement occurs at a property. Indeed, in several of the early pyrite cases the damage was assumed to be caused by foundation settlement and treated accordingly. It was only when damage reoccurred after repairs that other options were investigated.

 

Comparison of damage seen as caused by settlement (left) and pyritic heave (right). (Source: Dr A.J. Taylor, PhD Thesis)

 

Cases of pyritic heave damage in the UK are rare, however, they are not completely unheard of. There were a series of domestic properties in the Teesside area found to be affected in the 1970’s and a couple of isolated cases in Glamorgan in the 1980’s. The two cases in Glamorgan were related to pyritic bedrock rather than fill and so can be considered a little differently.

Still, materials containing pyrite can be common in the UK, from red ash colliery spoil which was used as fill, to mudrocks and shales formed as part of the Coal Measures.

Tests for sulphates can be carried out by most testing laboratories and samples can be obtained from simple trial pit or borehole methods. I know everyone expects the geotechnical engineer to say this, but proper site investigation is important; even a desk study looking at the geology and history of an area can highlight potential issues.

Any instance where these materials are exposed to air and water could result in the production of acidic groundwater, at which point the possibility of sulphate attack and gypsum production is a viable issue that should be considered in the design process.

 

Amy Taylor
March 2018

 

CABE regional AGM

Michelle recently organised the Annual General Meeting for the Yorkshire and Humber Region on Thursday 25th January 2018. The meeting was held at The Clifton Park Museum in Rotherham.

It was confrmed at the meeting, which was attended by over 20 delegates, that Michelle and Tony Riley were to continue as regional Secreatry and Treasurer respectively. Basil Parylo, the region’s Chairman handed over the role to John Loom. Basil will remain on the Committee as an active CPD Co-ordinator.

 

Immediately after the formal AGM Sarah Siyver from CABE HQ gave a presentation by the Association’s President David Taylor who unfortunately was unable to attend in person.

The delegates were then provided with a CPD session presented by Simon Leeming of the Coal Authority, this gave an insight into who the Coal Authority are and the services which they provide. He disussed how they have arrived at where they are today and a range of examples of the work that they carry out across the UK. The presentation then looked forward at the new types of work they are undertaking and the opportunities that they see for the future.

 

More about the Museum

The Clifton Park Museum is an exciting modern museum that takes you through Rotherham’s rich history. The Museum highlights the history of the borough in a way that appeals to all ages and helps to bring both our lives, and those of our ancestors, into sharp focus.

Clifton House was built for Joshua and Susannah Walker in 1783 and has housed Rotherham Museum since 1893. It was designed by the Yorkshire architect John Carr, with additional work added at a later date by Rotherham architect John Platt. It is listed Grade II* due to the many original features still intact.

The Walker family lived here until 1861, when Henry Walker died. After his death the house was bought by William Owen who died 1881. In 1883 the house and grounds were put up for auction for redevelopment but failed to meet the reserve. In 1891 the house was sold to Rotherham Corporation for £23,000 for use as a Municipal Park. The park was opened by the Prince of Wales (Edward VIII) in 1891 with grand celebrations, with the Museum opening in 1893. Many of the early collections were made up of items donated and lent by local people. A significant number were also provided by local societies, such as finds from the Roman excavations of Templeborough in 1877 by Rotherham Literary and Scientific Society. The first Museum Curator was also the President of the Rotherham Naturalists Society.

Why not visit http://cliftonpark.org.uk/ for more details on the exhibitions and collections held at the Museum, and entry is completely free.

Michelle Tuxford

January 2018

Are Unisex Disabled toilets really genderless?

We happened across an interesting article recently on Scope’s website where they were discussing whether loo designers see the users of the disabled facilities as genderless.

Source: Scope Community

A guest writer on their Blog, Milo, presented a thought-provoking post about disabled toilets but from a very different perspective: the provision, or lack thereof, of multi-sex facilities within these toilets. More specifically, the general lack of vending machines for tampons, condoms etc.

Designed for People or Compliance?

It’s fair to say that most designers will follow the guidance set down in approved Document M for disabled toilet layouts and consider that they have successfully achieved compliance with the Building Regulations, job done.

Milo’s perspective shows us that as Designers we must remember that the building must be suitable for everyone, that we are designing spaces for Humans with all kinds of needs, and make sure that we’re not just complying with legislation and guidance. Oh, and we need to provide more mirrors.