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Lean lessons

I was surprised to read the article 'Hidden danger threatens old roads' (NCE 17 September) stating that lean mix has now failed through 'slabbing'. My own experiences with the production and laying of the material, both as a contractor and as a resident engineer, were that the material naturally cracked soon after laying and often before the overlaying of subsequent surfacing materials.

Working in Yorkshire in the 1960s I was responsible for the site batching of lean mix concrete to an 18:1 ratio. We found it impossible, even using a pan mixer, to obtain full distribution of the cement in the matrix and when walking the laid material could predict the position of transverse cracking which occurred independent of any construction/day joints. There appeared to be no failure to comply with the current specification.

In the 1970s I was a resident engineer supervising laying of estate roads incorporating lean mix concrete and again experienced the transverse problems. At that time I discussed the matter with C&CA engineers and was told that research was being undertaken that showed that the introduction of 'silt' into the mix improved the quality of the product, probably by the improved dispersion of the cement. My own proposals then were to apply limited controlled rolling within about two days of laying to induce microcracking and the development of a 'flexible' mat before the high strengths in the material developed. It appeared that the strength of the material allowed shrinkage stresses to develop until failure occurred, such stresses developed high strains and subsequent cracking at large transverse centres; an inevitable consequence. The alternative being considered at that time was to develop 'wet lean concrete' as opposed to the current 'dry lean concrete'. The theory was that by increasing the water/cement ratio the paste would be better dispersed (with improvements in consistency) and natural microcracking would occur whilst retaining the macro interlocking structure desired in the semi-flexible matrix.

I further understood at the time that research had shown that an overlay of at least 175mm was required to avoid reflective cracking; analysis showed that at that depth alternative materials would be viable and thus the use of lean mix declined. It is thus surprising that at this juncture the problem is treated with surprise. These factors should be known and incorporated into appraisal methods such as CHART along with the added factors such as the inevitable weakening induced by any excavations or beaks in consistency caused by trenching for services or drainage.

We should not, however, overlook the fact that at that time there was a strong desire to reduce dependence upon oil- based products, for economic and political reasons.

Brian H Lintern, BLintern@aol.com

Linkspan report

Following your article on the Harwich ramp failure (NCE 3 September), readers will be pleased to know that guidance on the procurement, operation and maintenance of ship to shore linkspans is in course of preparation. It is being undertaken by CIRIA and funded by, among others, the Ports Safety Organisation, HSE and DETR. This means that a part of what ICE is seeking will be available long before a BS could be published, but there will still be a whole range of detailed design issues to be addressed for which ICE's initiative deserves support. We plan to publish our report at the end of this year.

Keith Montague, development director, CIRIA, 6 Storey's Gate, London SW1P 3AU.

Honest living

Your editorial 'Cruel to be kind' (NCE 10 September) referring to the current scramble by rival media companies to snap up listed football clubs said nothing surprising nor for which regret is necessary.

BSykB is locked in a deadly battle with its cable TV rivals for market domination in a huge growth area (digital TV) where rich pickings will go to the ultimate winner. It needs to secure a controlling influence over its prime time broadcasting (premier league football) and is clearly happy to pay a king's ransom to do so, at the same time driving its borrowings to breathtaking heights.

On the other hand, construction companies, along with their manufacturing cousins, operate in mature markets which are at the same time highly competitive. Their finances are often solid, but their growth prospects unexciting, and are therefore considered dull by investors.

If a loaf of bread can be bought for 50p, who would pay 60p? The same logic applies to construction industry's clients, who are by the same token getting outstanding value for money from the contracts they procure.

Comparisons, as they say, are odious. The construction industry has nothing to be ashamed of in making an honest, if not spectacular, living from its endeavours.

And if that does not attract speculative interest from Mr Murdoch, then that is something about which it should not in the least be concerned.

Vaughan Snook, (M), 26 Clere Gardens, Basingstoke, Hampshire RG24 8LZ.

Graduate payback

As a graduate engineer with one years experience, I write to express my frustration at the pay we can expect to receive as compared to fellow graduates.

I graduated in 1997 having already attained employment with a top civil engineering contractor. After nine months on site I had a company car and a financial package worth pounds16,500. What I did not have was a life outside of work. For a 22 year old, this was very hard. Regular hours of 07:30-19:00 plus weekends, with no overtime pay, meant that I often went weeks without seeing my friends. The nomadic lifestyle did not help either.

I decided I wanted a change and that I would move into consultancy. I moved to become a water network modeller at a fair sized consultancy. This was my choice and I dropped to a salary of pounds13,750.

It is frustrating for me, having spent three years at university attending 15 to 20 lectures per week, to now be in the situation where I take home pounds850 per month. I know secretaries who earn more! Comparing myself to other graduates from my year, I rate somewhere towards the bottom of the pay scale.

I really want to become a chartered engineer, this is what drives me, and I appreciate that once I achieve this status my situation should change but in the same time scale one can only expect other graduates to become likewise qualified. It is frustrating to see that the route to chartership rarely takes the three to four years sold to us at university, often taking double this projected timescale. I have seen this both in contracting and in consulting.

I am relatively happy to be working towards my goal of chartership. However, how can this industry expect to attract graduates when there are so many other graduate positions willing to pay in excess of pounds18,000 as a starting rate? If I left this industry today I would be confident that I could walk into another job and achieve a significant pay increase.

Graduates need to be encouraged to join this industry and we can only do this by paying competitive rates and ensuring that training promised is delivered on our route to chartership. I see myself as somebody who works well towards achieving my goals. There are plenty of others like me but we need to see that we are being supported in our careers.

Neil Colquhoun, 17 Charterhouse Road, Woolton, Liverpool L25 8ST.

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