Introduction
Pavements are usually subjected to alternate temperatures, experiencing high temperatures in the day and low temperatures in the night especially in the tropics. Thus, during high temperatures, the pavement which is more a polymeric substance experiences significant changes in dimensions, unequal shrinkage (warpage), and internal stresses.
It is necessary to determine coefficient of linear expansion (CLTE) for pavements because it helps to characterize the ability of a plastic or polymeric substance to expand when the temperature increases and also helps to estimate the dimensional stability of a developed part when temperature rises. The CLTE test is carried out using hardened specimen and it is expected that values obtained for pavement comprising of hydraulically bound macadam (HBM) should be within the normal range of temperature for pavement layers.
Apparatus for Test
The following apparatus shall be used:
(i) A water bath with sufficient capacity to accommodate three test specimens and capable of maintaining predetermined temperatures between 15ºC and 60ºC.
(ii) A device capable of measuring linear dimensions of not less than 275 mm to an accuracy of ± 0.002 mm, with a known temperature correction factor.
(iii) Vibrating hammer compaction apparatus capable of producing 150 mm diameter cylindrical test specimens, in accordance with BS EN 13286-51. The apparatus to be suitably modified to manufacture 300 mm long test specimens.
Procedure for Test
(i) Compact three 150 mm diameter test specimens, 300 mm in length, in accordance with BS EN 13286-51 but using six layers, each with a nominal depth of 50 mm.
(ii) Mark each specimen with 3 pairs of permanent reference points, aligned longitudinally. One of each pair to be at opposite ends of the specimen. Each pair to be located at 120º around the circumference of the specimens, aligned parallel to the axis, and not more than 30 mm from each end of the specimen.
(iii) Cure the specimens between temperatures of 20oC to 40oC depending on the type of mixture and curing policy and at 28 days.
(iv) Saturate the test specimens, either at atmospheric pressure or under vacuum, until the increase in the surface dried mass of each specimen, determined using two readings taken at least 24 hours apart, is less than 1%.
(v) Immerse the specimens in the water bath at a constant temperature (T1), maintained to an accuracy of ± 2ºC, for 24 ± 2 hours. Then measure the length (L1) of each test specimen at the locations defined by the three pairs of reference points. Repeat the measurement of length every 24 hours, until the change in length between successive measurements is less than 0.004 mm.
(vi) Raise the temperature of the water bath by at least 30ºC and record the temperature (T2). T2 should not to exceed 55ºC. Maintain the temperature at T2 ± 2ºC for 24 ± 2 hours and measure the length (L2) using the procedure in (v).
(vii) Lower the temperature of the water bath by at least 30ºC and record the temperature (T3). Maintain the temperature at T3 ± 2ºC for 24 ± 2 hours and measure the final length (L3) using the procedure in (v).
Calculations
The Coefficient of Linear Thermal Expansion (CLTE) shall be calculated as follows:
(1) For each pair of reference points for the heating sequence calculate: CLTEa = (L2 – L1) / (T2 – T1), giving 9 results in total.
(2) Reject the highest and lowest results and record the mean value of CLTEa for the remaining 7 results.
(3) For each pair of reference points for the cooling sequence calculate: CLTEb = (L2 – L3) / (T2 – T3), giving 9 results in total.
(4) Reject the highest and lowest results and record the mean value of CLTEb for the remaining 7 results.
(5) Calculate: CLTE = 0.5 ((Mean value of CLTEa) + (Mean value of CLTEb)).
(6) Check that the mean values of CLTEa and CLTEb lie in the range 0.95CLTE to 1.05CLTE. If the mean values lie outside this range, repeat the procedures (i) to (vi) for the tests again.
Reporting of Results
The value of CLTE is reported using units of m.10-6/ºC, expressed to the nearest whole number.
Source
Series 800: Road Pavements — Unbound, Cement and other Hydraulically Bound Mixture. Manual of Contract Documents for Highway Works, Volume 1 Specification for Highway Works.
