A Summary of Concrete-road Experience
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TBE technical committee, appointed to advise the Minister of Transport on experimental work, expressed the opinion, some time ago, that if details of the design, construction, maintenance and behaviour of concrete roads already laid in Great Britain could be collected and examined, it might be-possible to draw.COnclusions which would prove, helpfai for. the. future, Accord iugly, a questionnaire was issuedhighway authorities asking for inorMotion on such points as road conditions (Width, gradient, sub-soil, traffic, etc.), the thickness, reinforcement and consistency of _the concrete, the methods employed, the cost of the work, the re-'
sults obtained, etc.
It has• been difficult to draw definite conclusions from the answers, owing to the comparatively small number of replies received and to the relatively large number of variable conditions involved. Some of the most interesting variations in practice indicated by the 132 replies were as follow :—(a) 102 roads were laid as two-course and 30 as single-course concrete; (b) 90 per cent. of the roads were from 6 ins. to 8 ins. thick, whilst one road was 101 ins. thick and the thinnest road (laid on existing macadam surface carrying light traffic) was only 5 ins. thick ; (c) 16 roads were unreinforced concrete, three were reinforced at the top, 82 at the bottom and 31 both top and bottom ;
(d.) the period of curing veiled from two days to more than four, weeks, damp earth or sand being by far the most usual mailed employed ; silicate of soda was employed for curing six roads; (e) the cost of 82 per bent, of the roads worked out at between is, and Is. 9d. per sq. yd. per in. of thickness.
Conclusions from Information.
It was not found possible to determine from the replies the influence of any one detail of construction, or to separate the effect of One detail from another in such a way as to justify any particular conclusion.
The information supplied, however,
tends to suggest :—(a) transverse cracking was reduced by the use of transverse joints, but where reinforcement was continued across transverse joints, the value of the joints in reducing transverse cracks was considerably less. This statement does not apply to dowelled butt joints ; (b) roads in which no attempt was made to prevent evaporation of water during curing were more liable to crack than those in which such precautions had been taken; (c) two-course roads did not withstand cracking so well as single-course roads ; (d) roads laid on a wet sub-course cracked less than those laid on a dry sub-course ; (e) the six roads which were cured with silicate of soda were reported to be in very good condition.
A review of the data emphasizes the need for highway engineers to keep records, so that the results obtained in different parts of the country may ba correlated for the benefit of all concerned. Further investigations are being made into certain of the roads which present factors of special interest.