BOHS: ‘Legacy Asbestos Cement Spacers in reinforced concrete’

Who & why you should read this article.

Asbestos surveyors, persons with a Duty to Manage asbestos (CAR 2012 Reg 4), everyone who undertakes full or partial demolition or structural refurbishment as this article provides information on potential legacy asbestos containing materials (ACMs) spacers used predominantly in reinforced concrete (RC) from the 1960’s through to the 1980’s and even potentially into the 1990’s. It is essential before undertaking demolition or structural refurbishment/remodelling of buildings containing insitu reinforced concrete from this period to be aware of the potential of these asbestos cement spacers being present. Asbestos surveyors etc should look out for the indicators (see photos) of these often ‘butterfly shaped’ spacers that became loose, sank often making them visible on the exposed soffits, these spacers must be sampled and analysed to confirm if they contain asbestos or not.

The asbestos surveying, asbestos removal and demolition industry is familiar with asbestos cement sheets containing 10% to 15% Chrysotile (white) asbestos used as permanent formwork in concrete, mastic expansion joints, bituminous floor sealing compounds, floor ducts, pipes and contaminated screeds etc.

I wish to highlight these applications where ACM spacers may have been used as for in-situ reinforced concrete in floor slabs, beams, columns and panels etc during the 1960’s to the 1980’s and possibly in the 1990’s period in the absence of definitive manufacturing information.

Discovery and identification of Asbestos Cement Spacers (insitu RC).

In 2017 I was the appointed the client’s Consulting Demolition Engineer on a major development project, the work included the complete demolition of a 1960’s in-situ reinforced concrete multi-storey building. As part of my role, I advised the client to undertake various enabling works including an Asbestos (Refurbishment & Demolition) Survey in accordance with HSG 264 by an accredited1 surveying company.

The asbestos survey was undertaken in two phases to give a final report as part of the PCI² in compliance with The Construction (Design & Management) Regs 2015 i.e.

Phase 1 – When the building became vacant after a desktop study and planning.

Phase 2 – After disconnection of services and limited soft-strip exposing the structure.

After Phase 2, Whilst inspecting the building condition, construction type, connections, and load paths etc I noticed these ‘butterfly shaped’ impressions with a small centre hole and spread sporadically across the exposed soffit. When I asked what these were I was told they were cement spacer blocks used to support the steel reinforcing, being curious I requested these spacers must be sampled in various locations and aggregated into 1 sample double bagged per floor for analysis.

The following day the asbestos surveyor telephoned me and asked if I really wanted to know the answer, I replied you’ve just told me, however, I wanted to know what type(s) of asbestos was identified and approx concentration3. I was told they contained chrysotile (white) asbestos similar concentration to typical asbestos cement, however the material was very hard and difficult to sample.

I asked for a count of these exposed spacers per floor, there were in excess of 100 per floor spread randomly across the soffits.

Enquiries and history into these asbestos cement spacers

Having come across these surprising and totally unexpected, asbestos cement spacers manufactured for use in reinforced concrete I decided to undertake some research into these products. The spacers are shaped in such way to be installed perpendicular to the steel reinforcing cage and orientated to give different distances from the formwork it supported off to give the desired coverage of concrete to prevent corrosion and spalling etc.

As part of my research, I found manufacturers of these concrete products (now using alternative non-asbestos materials for reinforcing) and related trade groups unhelpful and cagey about providing me with any information on these old asbestos reinforced cement spacer products claiming they had no records from this period!

I was fortunate to that a person who must have seen my email or overheard a telephone conversation contacted me by telephone, they were nervous. wishing to remain anonymous but was at the time working for one of these manufacturers for almost 40 years, they provided me with a useful insight into the manufacturing process of extruded asbestos spacers, sources of asbestos, quantum, usage and where these manufactured products were shipped across the world.

1 As strongly recommended in HSG 264 – UKAS accreditation to ISO 17020 (Inspection)

2 PCI = Pre-construction information being the client’s duty under CDM

3 The concentration would be a guesstimate opinion and outside of UKAS

 

From the 1960’s through to the late 1980’s where legacy asbestos cement spacers had been manufactured and installed and buried within the matrix of the material, these manufactured asbestos cement spacer blocks for insitu reinforced concrete. One such manufacturer was Creteco Limited who were founded in 1974, in a 1977 trade journal they advertised with the following headline, viz ‘Frank Asbestos Cement Bar Spacers and Distance Tubes – Bond naturally with concrete – stronger than the concrete itself – and fireproof’.

I was fortunate to speak with a retired Concrete Manager who worked in the industry in from the 1950’s, they described how cement spacer blocks used to be crudely manufactured on site until these work practices changed. The process used a strong mix of sand and cement in large, prefabricated moulds set at a depth ranging from circa 15mm to 75mm to provide the required coverage of the steel reinforcing bars/cage, allowed to set, scored to the desired size, and then broken the following day into rough square sections. It wasn’t until the industry (clients) insisted on consistent quality controls that contractors started to purchase manufactured extruded spacer blocks in 50kg sacks and use often a dog-bone shape (circa 40mm to 50mm square), these were made using asbestos, see some examples of these asbestos cement spacer blocks containing circa 10% Chrysotile (white) asbestos. The spacers were installed at approximately 1m centres and wired onto the metal cages, however, the majority would be dropped, became loose from walking on the cages, fall off and sink down onto the formwork below leaving a visible indicator impression shaped like a dog-bone or butterfly with a small hole in the centre for wiring them in-situ.

Estimated Asbestos concentrations, future solutions & collaboration

I have estimated there are a minimum of 4 spacer blocks installed per square or lineal metre of reinforced concrete floors, beams, and columns and invariably you can see the evidence on exposed soffits or beams, its often difficult to see these in columns for obvious reasons.

The concentration of ACMs in the concrete is well below the accepted hazardous waste threshold of 0.1% w/w, however, if you are demolishing or part demolishing the structure you have a duty of care to manage the process, for the health and safety of persons undertaking the works and anyone affected e.g. to prevent exposure and spread of asbestos. Without wishing to design the work as circumstances can vary in the any given situation, laws that apply vary in different countries, however, by adopting good industry practice using appropriate methodologies and dust control measures e.g. reducing airborne respirable crystalline silica (RCS) by wetting etc you would also reduce the asbestos risk.

Subject to the law and regulations that apply in your country and the regulators position you may be able to avoid expensive landfill of all the arisings. This could potentially involve some pre-treatment to allow limited re-use of the arisings in low-risk applications on site e.g. under floor slabs or car parks as sub-base aggregate where future disturbance is unlikely, irrespective of what you do records must be kept for the future.

Following a paper I presented in Vienna at the World Demolition Summit in 2022 a German Engineering company, Wessling contacted me requesting my paper which I sent to them, they have now identified these ACMs in some of their autobahn bridges that need replacing. We are now collaborating and recently delivered a joint paper at the European Asbestos Forum in Brussels last month.

Not all concrete spacers are asbestos.

Although 1000’s of tonnes of these products were manufactured with asbestos, some contained other reinforcing materials e.g granulated blast furnace slag (GBFS), therefore don’t despair even if your structure is within the critical age range your RC may not necessarily contain asbestos, however, the only way to be certain is to take representative samples and have these tested using polarised light microscopy at modest cost.

Managing or removing these asbestos cement spacers & further information

Asbestos is only a risk when it’s disturbed so where these are found in structures to remain in use it’s simply a case of identifying these, recording the findings, and provide this information to anyone liable to disturb them for maintenance, repair of refurbishment etc. It may be necessary to protect exposed spacers that have been damaged or in poor condition using a proprietary encapsulating material (thixotropic paint) and label if appropriate.

Where it becomes tricky is when you need to demolish or remove sections of concrete containing these asbestos cement spacers.

If you’d like a copy of my latest work and presentation, drop me an email request, all I ask is that you acknowledge me as the author.

Wayne is gathering empirical data for his research so if anybody comes across these spaces positive or negative, perhaps they could email him mwb@waynebagnall.com with some photos, and he could suitably anonymise the results to protect the innocent. 

 

Wayne Bagnall MBE MSc CFIOSH Hon-FIDE MCMI

January 2025