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Frictional properties of longitudinally diamond ground concrete on the A12 Chelmsford bypass

Publication Details

Authors:  Sanders, P D Viner, H
Document Reference: 510596
Publication Date:  23 February 2011 15:15
Assessment Level: Addition to evidence pool

Exec­u­tive Summary

Fric­tional prop­er­ties of lon­gi­tu­di­nally dia­mond ground con­crete on the A12 Chelms­ford bypass

By: Sanders P D and Viner, H

Ref: 510596


The High­ways Agency is inves­ti­gat­ing the poten­tial of a lon­gi­tu­di­nal dia­mond grind­ing process, sim­i­lar to that com­monly used in Amer­ica, to pro­vide a cost-effective method of restor­ing the sur­face fric­tion char­ac­ter­is­tics of worn, but struc­turally sound con­crete pave­ments.  In March 2009, a 500m length of the A12 Chelms­ford bypass at Bore­ham was treated with a lon­gi­tu­di­nal dia­mond grind­ing tech­nique.  As part of the assess­ment of this trial sec­tion, TRL was com­mis­sioned to carry out mea­sure­ments of sur­face fric­tion using the Pave­ment Fric­tion Tester (PFT), a spe­cial­ist fric­tion mea­sure­ment device.
The grind­ing process involves pass­ing a rotat­ing pro­filed drum over the pave­ment sur­face.  The drum is con­structed of a num­ber of dia­mond blades of dif­fer­ent diam­e­ters ordered in such a fash­ion to cre­ate the desired pro­file.  The drum is rapidly spun over the pave­ment sur­face with pres­sure applied by a ver­ti­cal force and while being pulled along the sur­face in the direc­tion of traf­fic at a con­stant speed.  The result­ing sur­face tex­ture con­sists of lon­gi­tu­di­nal grooves approx­i­mately 2-3mm wide and 3-4mm apart.
In addi­tion to the PFT mea­sure­ments, SCRIM and GripTester data have been analysed as part of this study.  The data show that, seven months after treat­ment the dia­mond ground sur­face is pro­vid­ing a sig­nif­i­cant improve­ment in low-speed skid resis­tance (as mea­sured by SCRIM) and peak fric­tion com­pared with the untreated con­crete sur­face.  The level of locked wheel fric­tion reached has improved, but not to the same extent as would be expected by apply­ing a typ­i­cal asphalt over­lay; the level reached is just above the lower end of the range observed on HRA sur­faces.
Results gath­ered from GripTester show a rel­a­tively small loss of skid resis­tance fol­low­ing treat­ment, as expected, as the new sur­face is pol­ished by traf­fic.  It will be essen­tial to con­tinue mon­i­tor­ing the trial sec­tion to deter­mine whether this trend has reached equi­lib­rium or whether a fur­ther loss is expe­ri­enced.  In addi­tion, loss of tex­ture depth with time could reduce both peak and locked wheel fric­tion val­ues at higher speeds.
If the cur­rent per­for­mance is main­tained over time, the dia­mond grind­ing process could rep­re­sent a cost-effective treat­ment solu­tion to worn con­crete pave­ments.  How­ever, the loss of micro­tex­ture and tex­ture depth could result in the treated sur­face revert­ing to a sim­i­lar or lower fric­tion per­for­mance than the untreated sec­tion.  As it is not pos­si­ble to accu­rately quan­tify this risk, it is rec­om­mended that future trial treat­ments are con­fined to areas where the exist­ing fric­tion per­for­mance is poor.
It is rec­om­mended that the fric­tional prop­er­ties of both the treated and untreated sec­tions of the A12 trial con­tinue to be mon­i­tored over time, as planned, using GripTester, SCRIM and the PFT to assess the length of time for which the improve­ment in fric­tion con­tin­ues.  Other trial sec­tions should, sim­i­larly, be mon­i­tored closely until the per­for­mance is bet­ter under­stood.
Should the dia­mond grind­ing tech­nique become widely adopted, it will be nec­es­sary to review the approach to mea­sur­ing tex­ture depth in rou­tine TRACS sur­veys, since the lon­gi­tu­di­nal mea­sure­ments cur­rently used may not ade­quately char­ac­terise the lon­gi­tu­di­nally tex­ture surface.