Quality control of concrete

Concrete, Mar 2005 by Rattue, Roger

Bureau Veritas UK and Ireland is a professional services company specialising in quality, health and safety, environmental management and social accountability. Operating through a network of regional offices, Bureau Veritas employs 1100 people in the UK and Ireland and provides services through four cross-industry divisions: Inspection, Laboratories, Certification (BVQI) and Consulting.

I have spent the majority of my professional years in concrete testing, starting at a time when collecting and testing cubes was an innovative service to the industry. Throughout this period I have remained convinced that British concrete is a product of very high standard at international level. The demand for quality from contractors, suppliers, engineers and other authorities has given additional layers of quality control within the construction industry and given independent testing a justifiable prominence, so that it has become a fundamental tool for fresh concrete control and structural quality. Contractors and engineers obtain fast and accurate solutions to immediate problems and gain confidence from transparent and indepth procedures. This is particularly relevant to modern fast-track construction projects.

The test cube

The humble site test cube has been a simple indicator of quality for many decades for both suppliers and contractors. Over the years, it has evolved into a high-quality assessment of acceptability. This supports and complements the suppliers' quality control systems. Modern day concretes have become complex, involving more efficient and varied cements/cement blends, cement replacements and admixture types and dosages, all exacerbated by the selection of aggregate combinations and choices. The rate of strength increase, for all of these variables, can be assessed through the cube test to enable early prediction of acceptance which gives confidence to strength prediction and progress planning.

In the past, test cubes were low-key systems, and sometimes given little value and easily criticised. Therefore, confidence in results was also low and occasionally treated with scepticism. Over recent years, the industry has applied higher levels of education and improved quality procedures to such an extent that on-site control using test cubes can now be treated confidently as a stand-alone control of the highest value and importance. Greater numbers of United Kingdom Accreditation Service (UKAS) accredited technicians are now routinely on site, monitoring and recording concrete quality. This is a clear indication of the higher investment in quality and transparency, which is now being implemented. Some contractors are now running training programmes for their site operatives. This is creating additional awareness and care by these relevant site operatives who, being at the 'sharp end', have the greatest influence on site quality control procedures.

New European Standards

With the introduction of the new European Standards on 1 December 2003, the greatest initial influence is the demand for producing equipment of improved quality to allow more accurate tolerance control of specimen measurement. Although implementation of the European Codes has been slow, we are now witnessing the higher value given to on-site control and assessment. This, together with the new quality production systems, has further enhanced the belief that we have the potential for the highest level of quality control for ready-mixed concrete supplied in the UK. These in-depth, on-site, fresh concrete quality control procedures for visual assessment and workability allow early identification of problem mixes on receipt, thereby reducing the risk of actually placing problem material. Early trend analysis of test cube results can also be an early indicator of a problem, and once identified, actions are swift and conclusive, causing minimal interference with the construction programme.

Quality control procedures

There is still room to give the industry an even greater consistency in quality control procedures. For example, freshly cast samples are susceptible to water loss and vibration and are influenced by ambient temperature ranges. Occasionally, unacceptable strength variations are identified during this initial period. It is extremely easy to create an additional layer of control to monitor and overcome this, as can be witnessed on most major projects. The new European Standard should be tightened in order to give a more defined sampling and manufacture method and to eliminate and control variations caused by misinterpretation. Early striking requirements for projects such as tunnel-forming are now widespread for most major projects with the test cube still being the only conclusive means of early strength indication. The additional levels of quality applied are giving even greater confidence for striking and construction progression

Concluding remarks

It is imperative that we all demand consistency in quality procedures throughout our industry from on-site contractors, suppliers and test houses, to allow this versatile product to maintain the high quality we all now expect, understand and generally receive. Test cubes under their new label of 'Identity Testing' remain an integral part of our onsite quality control, giving higher value to cooperation and partnering with all quality control systems. Only transparency will give us the confidence to meet the demands of our fast- track, high-quality industry from which we can all benefit and prosper.