RSTA Case Studies

UK trials for ‘wet steel’ shot-blasting concept machine developed by pavement retexturing specialist, Klaruw

A prototype machine for ‘wet application’ shot blasting, designed to improve the macro-texture and micro-texture of highway, airport and racetrack pavements to safe levels, has just been trialled on UK roads.

Developed by the Dutch retexturing specialist, bv Klaruw Tilburg, the fully computer-controlled Macrotex (MAT) shot-blasting plant offers advantages in process control, treatment flexibility and rate of coverage over conventional shot-blasting machines. Most significantly, it innovates the use of ‘wet’ steel shot, allowing retexturing to be carried out in wet weather, even in heavy rain, unlike traditional ‘dry’ shot-blasting methods.

The MAT process has been developed to improve the macro-texture – the texture depth that allows surface water to escape to prevent aqua-planing - of most natural aggregate surfaces. Although it primarily works on macro-texture, improvement in micro-texture – the surface friction which provides wet weather skid resistance – is a secondary benefit of the process.

Trials

Klaruw’s MAT prototype machine arrived in the UK recently for evaluation in two separate night-time trials.

Area 10 Managing Agent Contractor, A-one+, has just undertaken trials on sections of concrete, HRA (hot rolled asphalt) and thin surfacing on the M56 near Chester. North Wales Trunk Road Agency (NWRTA) is also looking at results from HRA (hot rolled asphalt) and thin surfacing after trials on the A55 North Wales Coast Road.

A-one+ and NWTRA already use Klaruw’s bush hammering process, Klaruwtex190 (K190), as part of procedures for maintaining road surface skid-resistance on trunk roads and motorways in the region.

Hefin Lloyd Jones, A55 Route Manager for NWTRA, said: “The MAT shot blasting process has provided a rapid, single pass and non-weather dependent process for the improvement of the macro-texture of surface courses which require rejuvenation to return to an acceptable, serviceable condition. The process achieves this with minimal disruption to the road network and thereby being more acceptable to the road user.”

Phil Reynolds, Roads Renewals Manager with A-one+, said: “Improving the macro-texture of surfacing via shot-blasting has many potential benefits to the road user with regard to reducing levels of spray and the risk of aquaplaning. This trial has shown that the process both delivers the benefits and mitigates the risk of the weather impacting on scheduled work. With the current economic climate and the demands of maintaining the road network to provide safe roads, reliable journeys and reduce the amount of disruption to the user, this machine is a welcome development to the market for any organisation involved in pavement maintenance.”

Gains

Both agencies are currently assessing the results of tests to evaluate the macro-texture and micro-texture gains made on the surface types treated. The early indications are that both trials saw promising improvements in both.

Klaruw is confident that results will back up the findings of trials in Holland where significant improvements in macro-texture have been observed on asphaltic concrete (marshall asphalt) runways.

The MAT shot-blasting process has also been proven effective for removing bitumen residues left on newly laid porous asphalt to prevent so-called ‘bitu-planing’, and for cleaning the cementitious film off new concrete.

The machine will be undergoing further intensive trialling on HRA, a surfacing system more prevalent in the UK than on the continent.

Sustainable

Klaruw believes that macro-texture rejuvenation using the MAT machine is set to provide a versatile, cost-effective and highly sustainable solution for addressing aqua-planing and wet skid issues. By reworking existing surfaces, it extends service life of structurally sound roads by several years before more costly, disruptive overlay or inlay is needed.

The MAT machine shot blasts and cleans the road surface as one integral unit in one pass, simplifying traffic management and leaving treated sections ready for use immediately. The technique requires no after-treatment or curing time, and leaves no residual deposits.

MAT retexturing also has significant environmental benefits. It applies no new material to the road, produces minimal waste, and recycles water and shot used in the process, reducing reliance on virgin material and landfill. This leaves a lower carbon footprint than alternative methods of restoring macro-texture, such as surface dressing or material overlay. MAT therefore offers a highly sustainable solution to maintaining the safety of road surfaces for local authorities tasked with reducing their carbon footprint under the Climate Change Act 2008 and in reporting to National Indicator 185 (NI 185) ‘Percentage CO2 reduction from LA operations’.

Introduced in 2008, the Climate Change Act set a target for the UK to cut greenhouse gas emissions by 80% by 2050. NI 185 is one of three climate change indicators introduced by DEFRA in the same year as part of the local government performance framework.

NI 185 and NI 186 (Percentage reduction of the per capita CO2 emissions in the Local Authority Area) are associated with the management of carbon emissions. LAs are responsible for measuring NI 185 while the Department of Energy and Climate Change (DECC) publishes data for NI 186. LAs are also responsible for monitoring a third indicator, NI 188 ‘Planning to adapt to climate change.’

Direct contracting

Klaruw intends to offer the MAT process alongside the K190 process through direct contracting by its UK subsidiaries, Klaruw RMS and Briser Road Safety, which also specialises in airport applications.

Used successfully on UK roads since the late 80s, K190 provides controlled mechanical retexturing principally to restore surface micro-texture and improve wet weather skid resistance to above investigatory levels.

The new MAT unit can treat widths ranging from 24cm to a maximum 190cm. Working speed is also variable, ranging from 3 metres per minute for heavy duty, deep retexturing, up to 100 metres per minute for light cleaning.

Depending on pavement type and condition, and application requirements, the machine will generally treat around 1300 to 3000 sq/m of pavement per hour (between 3 to 7 lane kilometres a day).

Klaruw believes that the launch of MAT is well timed as UK road authorities face cuts in maintenance budgets while road safety performance targets for 2020 remain tough.